Atara Biotherapeutics proposes up to $200M offering

Specific sale terms will appear in later prospectus supplements, while the $23,011,805 sales-agreement amount is included within the shelf ceiling.

Available on EDGAR 11/10/2026 - 04:59 PM EST Accepted by SEC EDGAR 11/10/2026 - 04:59 PM EST Learn about SEC filing dates

Rhea-AI Filing Summary

Atara Biotherapeutics, Inc. (ATRA) filed a replacement shelf registration covering up to $200,000,000 in aggregate securities, including up to $23,011,805 of common stock through an at-the-market sales agreement with TD Cowen. The ATM amount is included within, not additional to, the shelf ceiling. Sales under the preliminary prospectus may begin only after the registration statement becomes effective; later supplements will set the terms for any offering. The shelf lists common stock, preferred stock, debt securities, warrants, rights and units.

While its public float remains below $75.0 million, Atara says it will not sell securities under the cited public-float provision with a value exceeding one-third of its public float in any 12-month period. It states its current permitted amount under that provision is $23,011,805. Net proceeds, if any, are intended for working capital and general corporate purposes, including research and development and capital expenditures. Separately, Pierre Fabre resubmitted tab-cel’s U.S. biologics license application in September 2026; the FDA accepted it for Class 2 review in October, with a March 31, 2027 target action date.

Filing Explained

The new shelf is not effective yet: $23,011,805 of ATM capacity is not a sale, and prior-shelf sales may continue during the transition.

Atara filed a replacement Form S-3 shelf on November 10, 2026; the registration is preliminary and not yet effective. It covers up to $200,000,000 of securities, including up to $23,011,805 of common stock through the ATM, so these are offering capacities, not completed sales. However, sales under the existing Sales Agreement and prior registration may continue until the new registration becomes effective or 180 days after November 13, 2026, whichever comes first.

At September 30, 2026, Atara reported $9,917,000 in cash and investments, compared with the $23,011,805 maximum ATM amount: the first is existing liquidity, while the second is potential financing capacity, not funds already raised.

Key Figures

Aggregate shelf offering amount: Up to $200,000,000 Sales-agreement common stock offering: Up to $23,011,805 Aggregate market value of non-affiliate common stock: Approximately $69,035,417 +5 more

8 metrics

Aggregate shelf offering amount Up to $200,000,000 Base prospectus; aggregate amount across offerings.

Sales-agreement common stock offering Up to $23,011,805 Maximum aggregate offering price; included within the $200,000,000 shelf amount.

Aggregate market value of non-affiliate common stock Approximately $69,035,417 Public-float calculation based on the September 16, 2026 closing sale price.

Public-float threshold $75.0 million The stated public-float limit relevant to sales under the cited provision.

Outstanding common shares 10,188,438 shares Share count used in the public-float calculation.

Closing sale price $10.11 per share September 16, 2026; used in the public-float calculation.

Last reported sale price $8.18 per share November 9, 2026.

Tab-cel PDUFA target action date March 31, 2027 FDA accepted the BLA resubmission for a Class 2 review.

Key Terms

at-the-market equity offering program, public float, Class 2 review, biologics license application

4 terms

at-the-market equity offering program financial

"through an “at-the-market” equity offering program"

A program that lets a company sell newly issued shares directly into the open market at whatever the current trading price is, usually through a broker, and do so gradually over time instead of all at once. Investors care because it can dilute existing ownership and put steady selling pressure on the stock price, while giving the company a flexible, on-demand way to raise cash — like adding small amounts of water to a pool rather than dumping in a bucket.

public float financial

"one-third of our public float in any 12-month period"

Public float is the total number of a company's shares that are available for trading by the general public. It excludes shares held by company insiders or large stakeholders who are unlikely to sell them easily. This figure helps investors understand how much of the company's stock is actively available, which can influence its liquidity and how easily its price might change.

Class 2 review regulatory

"accepted the resubmission for a Class 2 review"

biologics license application regulatory

"resubmitted the biologics license application (BLA) for tab-cel"

A biologics license application is a formal request submitted to regulatory authorities seeking approval to market a new biological medicine, such as vaccines or treatments made from living organisms. It is a comprehensive review process that evaluates the safety, effectiveness, and manufacturing quality of the product. For investors, receiving approval signals that a biological therapy can be sold to the public, potentially leading to revenue growth and market success.

Offering Details

shelf · Up to $200,000,000 aggregate; includes up to $23,011,805 of common stock under the sales agreement prospectus

Offering

Offering Type shelf

Securities Offered Common stock, preferred stock, debt securities, warrants, rights and units

Offering Amount Up to $200,000,000 aggregate; includes up to $23,011,805 of common stock under the sales agreement prospectus

Use of Proceeds Net proceeds, if any, are intended for working capital and general corporate purposes, including research and development expenses and capital expenditures; pending use, proceeds are intended for temporary investment in short-term, interest-bearing instruments.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How much can Atara raise under the ATRA shelf registration?

The shelf covers up to $200,000,000 in aggregate securities. That amount includes, rather than adds to it, up to $23,011,805 of common stock under the sales agreement with TD Cowen.

How long can Atara use its prior registration statement?

Atara may issue and sell securities under the prior registration statement, including through the sales agreement prospectus, until the earlier of the new registration statement’s effective date or 180 days after November 13, 2026.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Table of Contents

As filed with the Securities and Exchange Commission on November 10, 2026

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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

​

FORM S-3

REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

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ATARA BIOTHERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)​

​

​	Delaware​	​	​	46-0920988​	​
​	(State or other jurisdiction of incorporation or organization)​	​	​	(I.R.S. Employer Identification Number)	​

1280 Rancho Conejo Boulevard
Thousand Oaks, California 91320
(805) 623-4211

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

​

AnhCo Thieu Nguyen
President and Chief Executive Officer
1280 Rancho Conejo Boulevard
Thousand Oaks, California 91320
(805) 623-4211

(Name, address, including zip code, and telephone number, including area code, of agent for service)

​

Copies to:

​ Kevin G. Sarney
Interim Chief Financial Officer
1280 Rancho Conejo Boulevard
Thousand Oaks, California 91320
(805) 623-4211 ​ ​ Carlton Fleming
Helen Theung
Sidley Austin LLP
101 California Street, Suite 3500
San Francisco, California 94111
(415) 772-1200 ​

​

Approximate date of commencement of proposed sale to the public: From time to time after the effective date of this Registration Statement.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box: ☐

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, as amended, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box: ☒

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering: ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. ☐

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. ☐

Indicate by check mark whether the Registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

​	Large accelerated filer ☐ ​	​	​	Accelerated filer ☐ ​	​
​	Non-accelerated filer ☒ ​	​	​	Smaller reporting company ☒ ​	​
​	​	​	​	Emerging growth company ☐ ​	​

If an emerging growth company, indicate by check mark if the Registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

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The Registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment that specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until this registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8 (a), may determine.

​

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EXPLANATORY NOTE

This Registration Statement is a replacement registration statement being filed pursuant to Rule 415(a)(6) under the Securities Act of 1933, as amended (Securities Act), with respect to securities which remain unsold under the Registration Statement on Form S-3 (File No. 333-275256) (Unsold Securities) filed on November 1, 2023, and declared effective on November 13, 2023, which is due to expire on November 13, 2026 (Prior Registration Statement). Pursuant to Rule 415(a)(5)(ii) under the Securities Act, by filing this Registration Statement, the Company may issue and sell securities under the Prior Registration Statement, including pursuant to the sales agreement prospectus included in the Prior Registration Statement, as supplemented, in connection with our existing Sales Agreement, dated November 1, 2023 (Sales Agreement), with Cowen and Company, LLC (Cowen), until the earlier of the effective date of this Registration Statement or 180 days after November 13, 2026. TD Securities (USA) LLC (TD Cowen) is now the sales agent under the Sales Agreement as successor to Cowen. In accordance with the terms of the Sales Agreement, we may offer and sell our common stock from time to time through TD Cowen, acting as our agent under an “at-the-market” equity offering program (ATM program). Pursuant to General Instruction I.B.6 of Form S-3, in no event will we sell securities registered on this registration statement in a public primary offering with a value exceeding one-third of our outstanding voting and nonvoting common equity held by non-affiliates (the “public float”) in any 12-month period so long as our public float remains below $75,000,000. As of the date of this registration statement, the amount we may sell pursuant to General Instruction I.B.6 is $23,011,805. Pursuant to Rule 415(a)(6) under the Securities Act, the offering of the Unsold Securities under the Prior Registration Statement will be deemed terminated as of the date of effectiveness of this registration statement.

This registration statement contains:

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a base prospectus, which covers the offering, issuance and sale by us of up to $200,000,000 in the aggregate of the securities identified above from time to time in one or more offerings; and

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a sales agreement prospectus, which covers the offering, issuance and sale by us of up to a maximum aggregate offering price of $23,011,805 of the registrant’s common stock that may be issued and sold from time to time under a sales agreement with TD Cowen.

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The base prospectus immediately follows this explanatory note. The specific terms of any other securities to be offered pursuant to the base prospectus will be specified in one or more prospectus supplements to the base prospectus.

The sales agreement prospectus immediately follows the base prospectus. The specific terms of the securities to be issued and sold under the sales agreement are specified in the sales agreement prospectus that immediately follows the base prospectus. The $23,011,805 of our common stock that may be offered, issued and sold under the sales agreement prospectus is included in the $200,000,000 of securities that may be offered, issued and sold by us under the base prospectus. Upon termination of the offering of our common stock under the sales agreement with TD Cowen and the sales agreement prospectus, any portion of the $23,011,805 included in the sales agreement prospectus that is not sold pursuant to the sales agreement will be available for sale in other offerings pursuant to the base prospectus and a corresponding prospectus supplement, and if no shares are sold under the sales agreement, the full $23,011,805 of securities not sold may be sold in other offerings pursuant to the base prospectus and a corresponding prospectus supplement.

Table of Contents

The information in this preliminary prospectus is not complete and may be changed. These securities may not be sold until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell nor does it seek an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED NOVEMBER 10, 2026

Prospectus

$200,000,000
Common Stock
Preferred Stock
Debt Securities
Warrants
Rights to Purchase Common Stock, Preferred Stock,
Debt Securities or Units
Units

​

From time to time, we may offer and sell up to $200,000,000 of any combination of the securities described in this prospectus, either individually or in combination with other securities. We may also offer common stock or preferred stock upon conversion of debt securities, common stock upon conversion of preferred stock, or common stock, preferred stock or debt securities upon the exercise of warrants.

Each time we sell securities pursuant to this prospectus, we will provide the specific terms of these offerings and securities in one or more supplements to this prospectus. We may also authorize one or more free writing prospectuses to be provided to you in connection with these offerings. The prospectus supplement and any related free writing prospectus may also add, update or change information contained in this prospectus. You should carefully read this prospectus, the applicable prospectus supplement and any related free writing prospectus, as well as the documents incorporated by reference, before buying any of the securities being offered.

The aggregate market value of our outstanding common stock held by non-affiliates pursuant to General Instruction I.B.6 of Form S-3 is approximately $69,035,417, based on 10,188,438 shares of outstanding common stock, of which 6,828,429 shares are held by non-affiliates, and a per share price of $10.11, the closing sale price of our common stock on the Nasdaq Global Select Market on September 16, 2026, which was the highest closing sale price within 60 days prior to the date of this prospectus. Pursuant to General Instruction I.B.6 of Form S-3, in no event will we sell securities pursuant to this prospectus with a value exceeding more than one-third of our public float in any 12-month period so long as our public float remains below $75.0 million. During the 12 calendar months prior to and including the date of this prospectus, we have not offered or sold any securities pursuant to General Instruction I.B.6 of Form S-3.

Our common stock is listed on the Nasdaq Global Select Market under the trading symbol “ATRA.” On November 9, 2026, the last reported sale price of our common stock was $8.18 per share. The applicable prospectus supplement will contain information, where applicable, as to other listings, if any, on the Nasdaq Global Select Market or other securities exchange of the securities covered by the applicable prospectus supplement.

Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading “Risk Factors” beginning on page 5 of this prospectus and contained in the applicable prospectus supplement and in any free writing prospectuses we have authorized for use in connection with a specific offering, and under similar headings in the documents that are incorporated by reference into this prospectus and any prospectus supplement from our filings with the Securities and Exchange Commission, before investing in any of our securities.

This prospectus may not be used to consummate a sale of securities unless accompanied by a prospectus supplement.

The securities may be sold directly by us to investors, through agents designated from time to time or to or through underwriters or dealers, on a continuous or delayed basis. For additional information on the methods of sale, you should refer to the section titled “Plan of Distribution” in this prospectus. If any agents, underwriters or dealers are involved in the sale of any securities with respect to which this prospectus is being delivered, the names of such agents, underwriters or dealers and any applicable fees, commissions, discounts and over-allotment options will be set forth in a prospectus supplement. The price to the public of such securities and the net proceeds we expect to receive from such sale will also be set forth in a prospectus supplement.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

​

The date of this prospectus is            , 202   .

Table of Contents​

TABLE OF CONTENTS

​	​	​	Page				​
ABOUT THIS PROSPECTUS	​	​	​	​	ii	​	​
PROSPECTUS SUMMARY	​	​	​	​	1	​	​
RISK FACTORS	​	​	​	​	5	​	​
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	​	​	​	​	6	​	​
USE OF PROCEEDS	​	​	​	​	8	​	​
DESCRIPTION OF CAPITAL STOCK	​	​	​	​	9	​	​
DESCRIPTION OF DEBT SECURITIES	​	​	​	​	13	​	​
DESCRIPTION OF WARRANTS	​	​	​	​	20	​	​
DESCRIPTION OF RIGHTS	​	​	​	​	22	​	​
DESCRIPTION OF UNITS	​	​	​	​	24	​	​
LEGAL OWNERSHIP OF SECURITIES	​	​	​	​	25	​	​
PLAN OF DISTRIBUTION	​	​	​	​	28	​	​
LEGAL MATTERS	​	​	​	​	30	​	​
EXPERTS	​	​	​	​	30	​	​
WHERE YOU CAN FIND MORE INFORMATION	​	​	​	​	30	​	​
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE	​	​	​	​	30	​	​

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Table of Contents​

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. Under this shelf registration process, we may offer and sell shares of our common stock and preferred stock, various series of debt securities, warrants to purchase any of such securities, rights to purchase common stock, preferred stock, debt securities or units, and/or units that include any of these securities, either individually or in combination with other securities, in one or more offerings for an aggregate offering amount of up to $200,000,000.

This prospectus provides you with a general description of the securities we may offer. Each time we offer securities under this prospectus, we will provide a prospectus supplement that will contain more specific information about the terms of that offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. The prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change any of the information contained in this prospectus or in the documents that we have incorporated by reference into this prospectus. We urge you to read carefully this prospectus, any applicable prospectus supplement and any free writing prospectuses we have authorized for use in connection with a specific offering, together with the information incorporated herein by reference as described under the heading “Incorporation of Certain Information by Reference,” before buying any of the securities being offered.

This prospectus may not be used to consummate a sale of securities unless it is accompanied by a prospectus supplement.

We have not authorized anyone to provide you any information other than that contained or incorporated by reference in this prospectus or in any prospectus supplement or free writing prospectus prepared by or on behalf of us or to which we have referred you. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. This prospectus is an offer to sell only the securities offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so.

The information appearing in this prospectus, any applicable prospectus supplement and any related free writing prospectus is accurate only as of the date on the front of the document and any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus, the applicable prospectus supplement or any related free writing prospectus, or any sale of a security. Our business, financial condition, results of operations and prospects may have changed since those dates.

This prospectus contains summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described below under the section titled “Where You Can Find More Information.”

Unless the context indicates otherwise, as used in this prospectus, the terms “Atara,” “Atara Biotherapeutics,” “Company,” “we,” “us” and “our” refer to Atara Biotherapeutics, Inc. and, where appropriate, its subsidiaries on a consolidated basis.

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PROSPECTUS SUMMARY

This summary highlights selected information contained elsewhere in this prospectus or incorporated by reference in this prospectus and does not contain all of the information that you need to consider in making your investment decision. You should carefully read the entire prospectus, the applicable prospectus supplement and any related free writing prospectus, including the risks of investing in our securities discussed under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus. You should also carefully read the information incorporated by reference into this prospectus, including our financial statements, and the exhibits to the registration statement of which this prospectus is a part.

Company Overview

Atara Biotherapeutics is a leader in T-cell immunotherapy, leveraging its novel allogeneic Epstein-Barr virus (EBV) T-cell platform to develop transformative therapies for patients with cancer and autoimmune disease. Tab-cel® (tabelecleucel) has received marketing authorization approval under the proprietary name Ebvallo™ by the European Commission (EC) for commercial sale and use in the European Economic Area (EEA), by the Medicines and Healthcare products Regulatory Agency (MHRA) for commercial sale and use in the United Kingdom (UK) and by Swissmedic for commercial sale and use in Switzerland. We partnered with Pierre Fabre Medicament (Pierre Fabre) for commercialization of tab-cel in Europe and potential commercialization, if approved, worldwide, including in the U.S. Tab-cel is currently in Phase 3 development in the U.S. for patients with EBV-associated post-transplant lymphoproliferative disease (EBV+ PTLD) who have failed rituximab or rituximab plus chemotherapy, as well as other EBV-driven diseases. In September 2026, Pierre Fabre resubmitted the biologics license application (BLA) for tab-cel to the U.S. Food and Drug Administration (FDA), and in October 2026, the FDA accepted the resubmission for a Class 2 review with a PDUFA target action date of March 31, 2027.

Summary Risk Factors

Investing in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should consider carefully the risks and uncertainties described under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and discussed under the sections titled “Risk Factors,” “Summary Risk Factors,” “Selected Risks Affecting Our Business,” or similar title contained in our most recent Annual Report on Form 10-K, as may be updated by our subsequent Quarterly Reports on Form 10-Q and other filings we make with the SEC, which are incorporated by reference into this prospectus in their entirety, together with other information in this prospectus, the documents incorporated by reference and any free writing prospectus that we may authorize for use in connection with a specific offering.

Corporate Information

We were incorporated in Delaware in August 2012. Our principal executive offices are located at 1280 Rancho Conejo Boulevard, Thousand Oaks, California 91320, and our telephone number is (805) 623-4211. Our website address is www.atarabio.com. Information contained on or accessible through our website is not a part of this prospectus.

“Atara,” “Atara Bio,” “Atara Biotherapeutics” and the Atara logo are the property of Atara Biotherapeutics, Inc. This prospectus contains references to our trademarks and to trademarks belonging to other entities. We do not intend our use or display of other companies’ trade names or trademarks to imply a relationship with, or endorsement or sponsorship of us by, any other companies.

Description of Securities

We may offer shares of our common stock and preferred stock, various series of debt securities, warrants to purchase any of such securities, rights to purchase common stock, preferred stock, debt securities or units, and/or units comprising one or more securities described in this prospectus in any combination, either individually or in combination with other securities, from time to time under this prospectus, together with the applicable prospectus supplement and any related free writing prospectus, at

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prices and on terms to be determined by market conditions at the time of any offering. We may also offer common stock, preferred stock and/or debt securities upon the exercise of warrants. This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities under this prospectus, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities, including, to the extent applicable:

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designation or classification;

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aggregate principal amount or aggregate offering price;

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maturity date, if applicable;

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original issue discount, if any;

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rates and times of payment of interest or dividends, if any;

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redemption, conversion, exercise, exchange or sinking fund terms, if any;

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ranking;

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restrictive covenants, if any;

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voting or other rights, if any;

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conversion or exchange prices or rates, if any, and, if applicable, any provisions for changes to or adjustments in the conversion or exchange prices or rates and in the securities or other property receivable upon conversion or exchange; and

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material or special U.S. federal income tax considerations, if any.

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The applicable prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change any of the information contained in this prospectus or in the documents we have incorporated by reference.

We may sell the securities directly to investors or to or through agents, underwriters or dealers. We, and our agents or underwriters, reserve the right to accept or reject all or part of any proposed purchase of securities. If we do offer securities to or through agents or underwriters, we will include in the applicable prospectus supplement:

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the names of those agents or underwriters;

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applicable fees, discounts and commissions to be paid to them;

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details regarding over-allotment or other options, if any; and

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•

the net proceeds to us, if any.

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Common Stock.   We may issue shares of our common stock from time to time. The holders of common stock are entitled to one vote per share on all matters to be voted on by the stockholders. Subject to the preferences that may be applicable to any outstanding shares of preferred stock, the holders of common stock are entitled to receive ratably any dividends our board of directors declares out of funds legally available for the payment of dividends. If we are liquidated, dissolved or wound up, the holders of common stock are entitled to share pro rata all assets remaining after payment of liabilities and liquidation preferences of any outstanding shares of preferred stock. Holders of common stock have no preemptive rights or rights to convert their common stock into any other securities. There are no redemption or sinking fund provisions applicable to the common stock. In this prospectus, we have summarized certain general features of the common stock under the heading “Description of Capital Stock — Common Stock.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to any common stock being offered.

Preferred Stock.   We may issue shares of our preferred stock from time to time, in one or more series. Our board of directors will determine the designations, voting powers, preferences and rights of the preferred stock, as well as the qualifications, limitations or restrictions thereof, including dividend rights, conversion rights, preemptive rights, terms of redemption or repurchase, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of any series. Convertible preferred stock

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will be convertible into our common stock or exchangeable for other securities. Conversion may be mandatory or at your option and would be at prescribed conversion rates.

If we sell any series of preferred stock under this prospectus as supplemented by a prospectus supplement and, if applicable, a free writing prospectus, we will fix the designations, voting powers, preferences and rights of the preferred stock of each such series, as well as the qualifications, limitations or restrictions thereof, in the certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that contains the terms of the series of preferred stock we are offering. In this prospectus, we have summarized certain general features of the preferred stock under “Description of Capital Stock — Preferred Stock.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to the series of preferred stock being offered, as well as the complete certificate of designation that contains the terms of the applicable series of preferred stock.

Debt Securities.   We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. The senior debt securities will rank equally with any other unsecured and unsubordinated debt. The subordinated debt securities will be subordinate and junior in right of payment, to the extent and in the manner described in the instrument governing the debt, to all of our senior indebtedness. Convertible or exchangeable debt securities will be convertible into or exchangeable for our common stock or our other securities. Conversion or exchange may be mandatory or optional (at our option or the holders’ option) and would be at prescribed conversion or exchange prices.

The debt securities will be issued under an indenture that we will enter into with a national banking association or other eligible party, as trustee. In this prospectus, we have summarized certain general features of such debt securities under the heading “Description of Debt Securities.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to the series of debt securities being offered, as well as the complete indenture and any supplemental indentures that contain the terms of the debt securities. We have filed the form of indenture as an exhibit to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

Warrants.   We may issue warrants for the purchase of common stock, preferred stock and/or debt securities in one or more series. We may issue warrants independently or in combination with common stock, preferred stock and/or debt securities offered by any prospectus supplement. In this prospectus, we have summarized certain general features of the warrants under the heading “Description of Warrants.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to the particular series of warrants being offered, as well as the form of warrant and/or the warrant agreement and warrant certificate, as applicable, that contain the terms of the warrants. We have filed the forms of the warrant agreements and forms of warrant certificates containing the terms of the warrants that we may offer as exhibits to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant and/or the warrant agreement and warrant certificate, as applicable, that contain the terms of the particular series of warrants we are offering, and any supplemental agreements, before the issuance of such warrants.

Warrants may be issued under a warrant agreement that we enter into with a warrant agent. We will indicate the name and address of the warrant agent, if any, in the applicable prospectus supplement relating to a particular series of warrants.

Rights.   We may issue rights to purchase common stock, preferred stock or units. Rights may be issued independently or together with other securities and may or may not be transferable by the person purchasing or receiving the rights. In this prospectus, we have summarized certain general features of the terms of the rights under the heading “Description of Rights.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to

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you) related to the particular rights being offered. In connection with any rights offering to our stockholders, we may enter into a standby underwriting, backstop or other arrangement with one or more underwriters or other persons pursuant to which such underwriters or other persons would purchase any offered securities remaining unsubscribed for after such rights offering. In connection with a rights offering to our stockholders, we would distribute certificates evidencing the rights and a prospectus supplement to our stockholders on or about the record date that we set for receiving rights in such rights offering.

Units.   We may issue units comprising one or more securities described in this prospectus in any combination. Each unit will be issued so that the holder of the unit also is the holder of each security included in the unit. Thus, the unit will have the rights and obligations of a holder of each included security. In this prospectus, we have summarized certain general features of the terms of the units under the heading “Description of Units.” We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to the particular units being offered. Units will be issued pursuant to the terms of a unit agreement, which may provide that the securities included in the unit may not be held or transferred separately at any time or at any time before a specified date. A copy of the forms of the unit agreement and the unit certificate relating to any particular issue of units will be filed with the SEC each time we issue units, and you should read those documents for provisions that may be important to you.

Use of Proceeds

Except as described in any applicable prospectus supplement or in any free writing prospectuses we have authorized for use in connection with a specific offering, we currently intend to use the net proceeds from the sale of the securities offered by us hereunder, if any, for working capital and general corporate purposes, including research and development expenses and capital expenditures. See “Use of Proceeds” in this prospectus.

Nasdaq Global Select Market Listing

Our common stock is listed on the Nasdaq Global Select Market under the symbol “ATRA.” The applicable prospectus supplement will contain information, where applicable, as to other listings, if any, on the Nasdaq Global Select Market or any other securities market or other exchange of the securities covered by the applicable prospectus supplement.

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RISK FACTORS

Investing in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should consider carefully the risks and uncertainties described under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and described under the section titled “Risk Factors” contained in our most recent annual report on Form 10-K and in our most recent Quarterly Report on Form 10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC which are incorporated by reference into this prospectus in their entirety, together with other information in this prospectus, the documents incorporated by reference and any free writing prospectus that we may authorize for use in connection with a specific offering. The risks described in these documents are not the only ones we face, but those that we consider to be material. There may be other unknown or unpredictable economic, business, competitive, regulatory or other factors that could have material adverse effects on our future results. Past financial performance may not be a reliable indicator of future performance, and historical trends should not be used to anticipate results or trends in future periods. If any of these risks actually occurs, our business, financial condition, results of operations or cash flow could be seriously harmed. This could cause the trading price of our securities to decline, resulting in a loss of all or part of your investment. Please also carefully read the section below titled “Special Note Regarding Forward-Looking Statements.”

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and any accompanying prospectus supplement, as well as the documents incorporated by reference in this prospectus or any accompanying prospectus supplement, contain “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act. These statements relate to future events or to our future operating or financial performance and involve known and unknown risks, uncertainties and other factors that may cause our actual results, performance or achievements to be materially different from any future results, performances or achievements expressed or implied by the forward-looking statements. Forward-looking statements may include, but are not limited to, statements about:

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our review of strategic alternatives;

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our expectations with regard to our programs, including clinical sites, the clinical studies, and reporting results of such studies;

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the likelihood and timing of regulatory submissions or related approvals for tab-cel, including the expectations about the timing of approvals for a biologics license application (BLA) for tab-cel® for patients with Epstein-Barr virus with post-transplant lymphoproliferative disease (EBV+ PTLD);

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the potential indications for tab-cel;

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commercialization of tab-cel (Ebvallo™ in the United Kingdom (UK), the European Economic Area (EEA) and Switzerland) worldwide and our amended and restated Commercialization Agreement with Pierre Fabre Medicament, as amended, including potential milestone and royalty payments under the agreement (Ebvallo in the UK, the EEA and Switzerland subject to the Purchase and Sale Agreement with HCR Molag Fund, L.P.);

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our Purchase and Sale Agreement, as amended, and related transactions with HCR Molag Fund, L.P.;

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our expectations regarding the potential commercial market opportunities, market size and the size of the patient populations for tab-cel;

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estimates of our expenses, capital requirements and need for additional financing;

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our expectation regarding the length of time that our existing capital resources will be sufficient to enable us to fund our planned operations, including our going concern assessment;

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the scope of protection we are able to obtain and maintain for the intellectual property rights covering tab-cel;

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our financial performance;

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our election to rely on reduced reporting and disclosure requirements available to smaller reporting companies;

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developments and projections relating to our competitors and our industry;

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our partner’s ability to have tab-cel manufactured for clinical studies or for commercial sale, including at commercially reasonable values;

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the impact of public health emergencies to our business and operations, as well as the businesses and operations of third parties on which we rely;

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the impact of our workforce reductions on our ability to attract, retain and motivate qualified personnel and on our business, operations, and financial condition;

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timing and costs related to the qualification of the manufacturing facilities of contract manufacturing organizations (CMO) for commercial production; and

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our intended use of the net proceeds from offerings of our securities under this prospectus.

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In some cases, you can identify forward-looking statements by words such as “believe,” “may,” “will,” “estimate,” “continue,” “anticipate,” “intend,” “could,” “would,” “project,” “predict,” “plan,” “expect” or

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the negative or plural of these words or similar expressions. These statements reflect our current views with respect to future events, are based on assumptions and are subject to risks and uncertainties. Given these risks and uncertainties, you should not place undue reliance on these forward-looking statements. We discuss in greater detail, and incorporate by reference into this prospectus in their entirety, many of these risks and uncertainties under the heading “Risk Factors” contained in the applicable prospectus supplement, in any free writing prospectus we may authorize for use in connection with a specific offering, and in our most recent annual report on Form 10-K, and in our most recent quarterly report on Form 10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC. Also, these forward-looking statements represent our estimates and assumptions only as of the date of the document containing the applicable statement. Unless required by law, we undertake no obligation to update or revise any forward-looking statements to reflect new information or future events or developments. Thus, you should not assume that our silence over time means that actual events are bearing out as expressed or implied in such forward-looking statements. You should read this prospectus, the applicable prospectus supplement, together with the documents we have filed with the SEC that are incorporated by reference and any free writing prospectus we have authorized for use in connection with a specific offering completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in the foregoing documents by these cautionary statements.

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USE OF PROCEEDS

Except as described in any applicable prospectus supplement or in any free writing prospectuses we have authorized for use in connection with a specific offering, we currently intend to use the net proceeds from the sale of the securities offered by us hereunder, if any, for working capital and general corporate purposes, including research and development expenses and capital expenditures.

The amounts and timing of our use of the net proceeds from this offering will depend on a number of factors, such as the timing and progress of our research and development efforts, the timing and progress of any partnering and commercialization efforts, technological advances and the competitive environment for our products. As of the date of this prospectus, we cannot specify with certainty all of the particular uses for the net proceeds to us from the sale of the securities offered by us hereunder. Accordingly, our management will have broad discretion in the timing and application of these proceeds. Pending application of the net proceeds as described above, we intend to temporarily invest the proceeds in short-term, interest-bearing instruments.

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DESCRIPTION OF CAPITAL STOCK

As of the date of this prospectus, our authorized capital stock consists of 500,000,000 shares of common stock, $0.0001 par value, and 20,000,000 shares of preferred stock, $0.0001 par value. A description of material terms and provisions of our amended and restated certificate of incorporation (Certificate of Incorporation) and third amended and restated bylaws (Bylaws) affecting the rights of holders of our capital stock is set forth below. The description is intended as a summary, and is qualified in its entirety by reference to the Certificate of Incorporation and Bylaws.

Common Stock

The holders of common stock are entitled to one vote per share on all matters to be voted on by the stockholders. Subject to the preferences of any outstanding shares of preferred stock, the holders of common stock are entitled to receive ratably any dividends our board of directors declares out of funds legally available for the payment of dividends. If we are liquidated, dissolved or wound up, the holders of common stock are entitled to share pro rata all assets remaining after payment of liabilities and liquidation preferences of any outstanding shares of preferred stock. Holders of common stock have no preemptive rights or rights to convert their common stock into any other securities. There are no redemption or sinking fund provisions applicable to the common stock. When we issue shares of common stock under this prospectus, the shares will be fully paid and nonassessable.

Additional shares of authorized common stock may be issued, as authorized by our board of directors from time to time, without stockholder approval, except as may be required by applicable stock exchange requirements.

Preferred Stock

Our board of directors is authorized, subject to limitations prescribed by Delaware law, to issue preferred stock in one or more series, to establish from time to time the number of shares to be included in each series and to fix the designation, powers, preferences and rights of the shares of each series and any of its qualifications, limitations or restrictions. Our board of directors can also increase or decrease the number of shares of any series, but not below the number of shares of that series then outstanding, without any further vote or action by our stockholders. Our board of directors may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of the common stock. The issuance of preferred stock, while providing flexibility in connection with financings, possible acquisitions and other corporate purposes, could, among other things, have the effect of delaying, deferring, discouraging or preventing a change in control of our company, may adversely affect the market price of our common stock and the voting and other rights of the holders of common stock, and may reduce the likelihood that common stockholders will receive dividend payments and payments upon liquidation.

We will fix the designations, voting powers, preferences and rights of the preferred stock of each series we issue under this prospectus, as well as the qualifications, limitations or restrictions thereof, in the certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that contains the terms of the series of preferred stock we are offering. We will describe in the applicable prospectus supplement the terms of the series of preferred stock being offered, including, to the extent applicable:

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the title and stated value;

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the number of shares we are offering;

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the liquidation preference per share;

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the purchase price per share;

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the dividend rate per share, dividend period and payment dates and method of calculation for dividends;

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whether dividends will be cumulative or non-cumulative and, if cumulative, the date from which dividends will accumulate;

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our right, if any, to defer payment of dividends and the maximum length of any such deferral period;

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the procedures for any auction and remarketing, if any;

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the provisions for a sinking fund, if any;

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the provisions for redemption or repurchase, if applicable, and any restrictions on our ability to exercise those redemption and repurchase rights;

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any listing of the preferred stock on any securities exchange or market;

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whether the preferred stock will be convertible into our common stock or other securities of ours, including warrants, and, if applicable, the conversion period, the conversion price, or how it will be calculated, and under what circumstances it may be adjusted;

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whether the preferred stock will be exchangeable for debt securities, and, if applicable, the exchange period, the exchange price, or how it will be calculated, and under what circumstances it may be adjusted;

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voting rights, if any, of the preferred stock;

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preemption rights, if any;

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restrictions on transfer, sale or other assignment, if any;

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a discussion of any material or special United States federal income tax considerations applicable to the preferred stock;

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the relative ranking and preferences of the preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs;

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any limitations on issuances of any class or series of preferred stock ranking senior to or on a parity with the series of preferred stock being issued as to dividend rights and rights if we liquidate, dissolve or wind up our affairs; and

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any other specific terms, rights, preferences, privileges, qualifications or restrictions of the preferred stock.

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When we issue shares of preferred stock under this prospectus, the shares will be fully paid and nonassessable.

Unless we specify otherwise in the applicable prospectus supplement, the preferred stock will rank, with respect to dividends and upon our liquidation, dissolution or winding up:

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senior to all classes or series of our common stock and to all of our equity securities ranking junior to the preferred stock;

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on a parity with all of our equity securities the terms of which specifically provide that the equity securities rank on a parity with the preferred stock; and

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junior to all of our equity securities the terms of which specifically provide that the equity securities rank senior to the preferred stock.

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The term “equity securities” does not include convertible debt securities.

The General Corporation Law of the State of Delaware, the state of our incorporation, provides that the holders of preferred stock will have the right to vote separately as a class on any proposal involving fundamental changes in the rights of holders of that preferred stock. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.

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Antitakeover Effects of Provisions of Charter Documents and Delaware Law

Amended and Restated Certificate of Incorporation and Third Amended and Restated Bylaws

Because our stockholders do not have cumulative voting rights, our stockholders holding a majority of the voting power of our shares of common stock outstanding will be able to elect all of our directors. Our Certificate of Incorporation and Bylaws provide that all stockholder actions must be effected at a duly called meeting of stockholders and not by written consent. A special meeting of stockholders may be called by the majority of the total number of authorized directors, our chief executive officer or the chair of our board of directors.

Our Certificate of Incorporation provides for our board of directors to be divided into three classes, with staggered three-year terms. As a result, only one class of directors will be elected at each annual meeting of stockholders, with the other classes continuing for the remainder of their respective three-year terms. Stockholders have no cumulative voting rights, and the stockholders representing a majority of the shares of common stock entitled to vote in any election of directors may elect all of the directors standing for election.

Our Certificate of Incorporation further provides that the affirmative vote of holders of at least sixty-six and two-thirds percent (66-2/3%) of the voting power of all of the then outstanding shares of voting stock entitled to vote generally in the election of directors, voting as a single class, will be required to amend certain provisions of our Certificate of Incorporation, including provisions relating to the size of the board, removal of directors, special meetings and actions by written consent. The affirmative vote of holders of at least sixty-six and two-thirds percent (66-2/3%) of the voting power of all of the then outstanding shares of voting stock entitled to vote generally in the election of directors, voting as a single class, will be required to amend or repeal our Bylaws, although our Bylaws may be amended by a simple majority vote of our board of directors.

The foregoing provisions will make it more difficult for our existing stockholders to replace our board of directors as well as for another party to obtain control of us by replacing our board of directors. Since our board of directors has the power to retain and discharge our officers, these provisions could also make it more difficult for existing stockholders or another party to effect a change in management. In addition, the authorization of undesignated preferred stock makes it possible for our board of directors to issue preferred stock with voting or other rights or preferences that could impede the success of any attempt to change our control.

These provisions are intended to enhance the likelihood of continued stability in the composition of our board of directors and its policies and to discourage certain types of transactions that may involve an actual or threatened acquisition of us. These provisions are also designed to reduce our vulnerability to an unsolicited acquisition proposal and to discourage certain tactics that may be used in proxy fights. However, such provisions could have the effect of discouraging others from making tender offers for our shares and may have the effect of deterring hostile takeovers or delaying changes in our control or management. As a consequence, these provisions also may inhibit fluctuations in the market price of our stock that could result from actual or rumored takeover attempts.

Section 203 of the Delaware General Corporation Law

We are subject to Section 203 of the Delaware General Corporation Law, or the DGCL, which prohibits a Delaware corporation from engaging in any business combination with any interested stockholder for a period of three years after the date that such stockholder became an interested stockholder, with the following exceptions:

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before such date, the board of directors of the corporation approved either the business combination or the transaction that resulted in the stockholder becoming an interested stockholder;

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upon closing of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction began, excluding for purposes of determining the voting stock outstanding (but not the outstanding voting stock owned by the interested stockholder) those shares owned by

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(1) persons who are directors and also officers and (2) employee stock plans in which employee participants do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer; or

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on or after such date, the business combination is approved by the board of directors and authorized at an annual or special meeting of the stockholders, and not by written consent, by the affirmative vote of at least 662∕3 % of the outstanding voting stock that is not owned by the interested stockholder.

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In general, Section 203 defines business combination to include the following:

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any merger or consolidation involving the corporation and the interested stockholder;

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any sale, transfer, pledge or other disposition of 10% or more of the assets of the corporation involving the interested stockholder;

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subject to certain exceptions, any transaction that results in the issuance or transfer by the corporation of any stock of the corporation to the interested stockholder;

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any transaction involving the corporation that has the effect of increasing the proportionate share of the stock or any class or series of the corporation beneficially owned by the interested stockholder; or

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the receipt by the interested stockholder of the benefit of any loans, advances, guarantees, pledges or other financial benefits by or through the corporation.

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In general, Section 203 defines an “interested stockholder” as an entity or person who, together with the person’s affiliates and associates, beneficially owns, or within three years prior to the time of determination of interested stockholder status did own, 15% or more of the outstanding voting stock of the corporation.

Choice of Forum

Our Bylaws provide that, unless a majority of our board of directors consents in writing to an alternative forum, the Court of Chancery of the State of Delaware shall be the exclusive forum for (i) any derivative action or proceeding brought on behalf of us under Delaware law, (ii) any action asserting a claim of breach of a fiduciary duty owed by any current or former director, officer, or other employee of the Company to us or our stockholders, (iii) any action asserting a claim against us or any of our directors, officers, or other employees arising pursuant to any provision of the DGCL or our Certificate of Incorporation or Bylaws (as either may be amended from time to time), (iv) any action asserting a claim against us or any director or officer or other employee of the Company governed by the internal affairs doctrine, or (v) any other action asserting an “internal corporate claim,” as defined under Section 115 of the DGCL. The foregoing provisions do not apply to any claims arising under the Securities Act and, unless we consent in writing to the selection of an alternative forum, the federal district courts of the United States will be the sole and exclusive forum for resolving any action asserting a claim arising under the Securities Act.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A. The transfer agent and registrar’s address is 250 Royall Street, Canton, Massachusetts 02021.

Listing on the Nasdaq Global Select Market

Our common stock is listed on the Nasdaq Global Select Market under the symbol “ATRA”. The applicable prospectus supplement will contain information, where applicable, as to any other listing, if any, on the Nasdaq Global Select Market or any securities market or other exchange of the preferred stock covered by such prospectus supplement.

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DESCRIPTION OF DEBT SECURITIES

We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. While the terms we have summarized below will apply generally to any debt securities that we may offer under this prospectus, we will describe the particular terms of any debt securities that we may offer in more detail in the applicable prospectus supplement. The terms of any debt securities offered under a prospectus supplement may differ from the terms described below, and the applicable prospectus supplement, to the extent inconsistent with any portion of the description of our debt securities contained in this prospectus, will supersede the applicable portion of the description contained in this prospectus. Unless the context requires otherwise, whenever we refer to the indenture, we also are referring to any supplemental indentures that specify the terms of a particular series of debt securities.

We will issue the debt securities under the indenture that we will enter into with the trustee named in the indenture. The indenture will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We have filed the form of indenture as an exhibit to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

The following summary of material provisions of the debt securities and the indenture is subject to, and qualified in its entirety by reference to, all of the provisions of the indenture applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplements and any related free writing prospectuses related to the debt securities that we may offer under this prospectus, as well as the complete indenture that contains the terms of the debt securities.

General

The indenture does not limit the amount of debt securities that we may issue. It provides that we may issue debt securities up to the principal amount that we may authorize and may be in any currency or currency unit that we may designate. Except for the limitations on consolidation, merger and sale of all or substantially all of our assets contained in the indenture, the terms of the indenture do not contain any covenants or other provisions designed to give holders of any debt securities protection against changes in our operations, financial condition or transactions involving us.

We may issue the debt securities issued under the indenture as “discount securities,” which means they may be sold at a discount below their stated principal amount. These debt securities, as well as other debt securities that are not issued at a discount, may be issued with “original issue discount,” or OID, for U.S. federal income tax purposes because of interest payment and other characteristics or terms of the debt securities. Material U.S. federal income tax considerations applicable to debt securities issued with OID will be described in more detail in the applicable prospectus supplement.

We will describe in the applicable prospectus supplement the terms of the series of debt securities being offered, including:

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the title of the series of debt securities;

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any limit upon the aggregate principal amount that may be issued;

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the maturity date or dates;

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the form of the debt securities of the series;

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the applicability of any guarantees;

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whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;

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whether the debt securities rank as senior debt, senior subordinated debt, subordinated debt or any combination thereof, and the terms of any subordination;

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if the price (expressed as a percentage of the aggregate principal amount thereof) at which such debt securities will be issued is a price other than the principal amount thereof, the portion of the principal amount thereof payable upon declaration of acceleration of the maturity thereof, or if

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applicable, the portion of the principal amount of such debt securities that is convertible into another security or the method by which any such portion shall be determined;

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the interest rate or rates, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;

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our right, if any, to defer payment of interest and the maximum length of any such deferral period;

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if applicable, the date or dates after which, or the period or periods during which, and the price or prices at which, we may, at our option, redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemption provisions;

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the date or dates, if any, on which, and the price or prices at which we are obligated, pursuant to any mandatory sinking fund or analogous fund provisions or otherwise, to redeem, or at the holder’s option to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;

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the denominations in which we will issue the series of debt securities, if other than denominations of $1,000 and any integral multiple thereof;

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any and all terms, if applicable, relating to any auction or remarketing of the debt securities of that series and any security for our obligations with respect to such debt securities and any other terms which may be advisable in connection with the marketing of debt securities of that series;

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whether the debt securities of the series shall be issued in whole or in part in the form of a global security or securities; the terms and conditions, if any, upon which such global security or securities may be exchanged in whole or in part for other individual securities; and the depositary for such global security or securities;

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if applicable, the provisions relating to conversion or exchange of any debt securities of the series and the terms and conditions upon which such debt securities will be so convertible or exchangeable, including the conversion or exchange price, as applicable, or how it will be calculated and may be adjusted, any mandatory or optional (at our option or the holders’ option) conversion or exchange features, the applicable conversion or exchange period and the manner of settlement for any conversion or exchange;

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if other than the full principal amount thereof, the portion of the principal amount of debt securities of the series which shall be payable upon declaration of acceleration of the maturity thereof;

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additions to or changes in the covenants applicable to the particular debt securities being issued, including, among others, the consolidation, merger or sale covenant;

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additions to or changes in the events of default with respect to the securities and any change in the right of the trustee or the holders to declare the principal, premium, if any, and interest, if any, with respect to such securities to be due and payable;

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additions to or changes in or deletions of the provisions relating to covenant defeasance and legal defeasance;

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additions to or changes in the provisions relating to satisfaction and discharge of the indenture;

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additions to or changes in the provisions relating to the modification of the indenture both with and without the consent of holders of debt securities issued under the indenture;

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the currency of payment of debt securities if other than U.S. dollars and the manner of determining the equivalent amount in U.S. dollars;

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whether interest will be payable in cash or additional debt securities at our or the holders’ option and the terms and conditions upon which the election may be made;

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the terms and conditions, if any, upon which we will pay amounts in addition to the stated interest, premium, if any, and principal amounts of the debt securities of the series to any holder that is not a “United States person” for federal tax purposes;

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any restrictions on transfer, sale or assignment of the debt securities of the series; and

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any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, any other additions or changes in the provisions of the indenture, and any terms that may be required by us or advisable under applicable laws or regulations.

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Conversion or Exchange Rights

We will set forth in the applicable prospectus supplement the terms on which a series of debt securities may be convertible into or exchangeable for our common stock or our other securities. We will include provisions as to settlement upon conversion or exchange and whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock or our other securities that the holders of the series of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the indenture will not contain any covenant that restricts our ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of our assets as an entirety or substantially as an entirety. However, any successor to or acquirer of such assets (other than a subsidiary of ours) must assume all of our obligations under the indenture or the debt securities, as appropriate.

Events of Default under the Indenture

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the following are events of default under the indenture with respect to any series of debt securities that we may issue:

•

if we fail to pay any installment of interest on any series of debt securities, as and when the same shall become due and payable, and such default continues for a period of 90 days; provided, however, that a valid extension of an interest payment period by us in accordance with the terms of any indenture supplemental thereto shall not constitute a default in the payment of interest for this purpose;

​

•

if we fail to pay the principal of, or premium, if any, on any series of debt securities as and when the same shall become due and payable whether at maturity, upon redemption, by declaration or otherwise, or in any payment required by any sinking or analogous fund established with respect to such series; provided, however, that a valid extension of the maturity of such debt securities in accordance with the terms of any indenture supplemental thereto shall not constitute a default in the payment of principal or premium, if any;

​

•

if we fail to observe or perform any other covenant or agreement contained in the debt securities or the indenture, other than a covenant specifically relating to another series of debt securities, and our failure continues for 90 days after we receive written notice of such failure, requiring the same to be remedied and stating that such is a notice of default thereunder, from the trustee or holders of at least 25% in aggregate principal amount of the outstanding debt securities of the applicable series; and

​

•

if specified events of bankruptcy, insolvency or reorganization occur.

​

If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the trustee or the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series, by notice to us in writing, and to the trustee if notice is given by such holders, may declare the unpaid principal of, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default specified in the last bullet point above occurs with respect to us, the principal amount of and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.

The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or

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events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any waiver shall cure the default or event of default.

Subject to the terms of the indenture, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series, provided that:

•

the direction so given by the holder is not in conflict with any law or the applicable indenture; and

​

•

subject to its duties under the Trust Indenture Act, the trustee need not take any action that might involve it in personal liability or might be unduly prejudicial to the holders not involved in the proceeding.

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A holder of the debt securities of any series will have the right to institute a proceeding under the indenture or to appoint a receiver or trustee, or to seek other remedies only if:

•

the holder has given written notice to the trustee of a continuing event of default with respect to that series;

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•

the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made written request, such holders have offered to the trustee indemnity satisfactory to it against the costs, expenses and liabilities to be incurred by the trustee in compliance with the request; and

​

•

the trustee does not institute the proceeding and does not receive from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series other conflicting directions within 90 days after the notice, request and offer.

​

These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities.

We will periodically file statements with the trustee regarding our compliance with specified covenants in the indenture.

Modification of Indenture; Waiver

We and the trustee may change an indenture without the consent of any holders with respect to specific matters:

•

to cure any ambiguity, defect or inconsistency in the indenture or in the debt securities of any series;

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•

to comply with the provisions described above under the heading “Description of Debt Securities — Consolidation, Merger or Sale;”

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•

to provide for uncertificated debt securities in addition to or in place of certificated debt securities;

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•

to add to our covenants, restrictions, conditions or provisions such new covenants, restrictions, conditions or provisions for the benefit of the holders of all or any series of debt securities, to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default or to surrender any right or power conferred upon us in the indenture;

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•

to add to, delete from or revise the conditions, limitations, and restrictions on the authorized amount, terms, or purposes of issue, authentication and delivery of debt securities, as set forth in the indenture;

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to make any change that does not adversely affect the interests of any holder of debt securities of any series in any material respect;

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•

to provide for the issuance of and establish the form and terms and conditions of the debt securities of any series as provided above under the heading “Description of Debt Securities — General” to establish the form of any certifications required to be furnished pursuant to the terms of the indenture or any series of debt securities, or to add to the rights of the holders of any series of debt securities;

​

•

to evidence and provide for the acceptance of appointment under any indenture by a successor trustee; or

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•

to comply with any requirements of the SEC in connection with the qualification of any indenture under the Trust Indenture Act.

​

In addition, under the indenture, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of at least a majority in aggregate principal amount of the outstanding debt securities of each series that is affected. However, unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, we and the trustee may make the following changes only with the consent of each holder of any outstanding debt securities affected:

•

extending the fixed maturity of any debt securities of any series;

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•

reducing the principal amount, reducing the rate of or extending the time of payment of interest, or reducing any premium payable upon the redemption of any series of any debt securities; or

​

•

reducing the percentage of debt securities, the holders of which are required to consent to any amendment, supplement, modification or waiver.

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Discharge

Each indenture provides that we can elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

•

provide for payment;

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•

register the transfer or exchange of debt securities of the series;

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•

replace stolen, lost or mutilated debt securities of the series;

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•

pay principal of and premium and interest on any debt securities of the series;

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•

maintain paying agencies;

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hold monies for payment in trust;

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•

recover excess money held by the trustee;

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compensate and indemnify the trustee; and

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•

appoint any successor trustee.

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In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of, any premium, if any, and interest on, the debt securities of the series on the dates payments are due.

Form, Exchange and Transfer

We will issue the debt securities of each series only in fully registered form without coupons and, unless we provide otherwise in the applicable prospectus supplement, in denominations of $1,000 and any integral multiple thereof. The indenture provides that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company, or DTC, or another depositary named by us and identified in the applicable prospectus supplement with respect to that series. To the extent the debt securities of a series are issued in global form and as book-entry, a description of terms relating to any book-entry securities will be set forth in the applicable prospectus supplement.

At the option of the holder, subject to the terms of the indenture and the limitations applicable to global securities described in the applicable prospectus supplement, the holder of the debt securities of any

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series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.

Subject to the terms of the indenture and the limitations applicable to global securities set forth in the applicable prospectus supplement, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will impose no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

We will name in the applicable prospectus supplement the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

If we elect to redeem the debt securities of any series, we will not be required to:

•

issue, register the transfer of, or exchange any debt securities of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption of any debt securities that may be selected for redemption and ending at the close of business on the day of the mailing; or

​

•

register the transfer of or exchange any debt securities so selected for redemption, in whole or in part, except the unredeemed portion of any debt securities we are redeeming in part.

​

Information Concerning the Trustee

The trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture. Upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs. Subject to this provision, the trustee is under no obligation to exercise any of the powers given it by the indenture at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur.

Payment and Paying Agents

Unless we otherwise indicate in the applicable prospectus supplement, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.

We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that, unless we otherwise indicate in the applicable prospectus supplement, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

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Governing Law

The indenture and the debt securities will be governed by and construed in accordance with the internal laws of the State of New York, except to the extent that the Trust Indenture Act is applicable.

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DESCRIPTION OF WARRANTS

The following description, together with the additional information we may include in any applicable prospectus supplement and free writing prospectus, summarizes the material terms and provisions of the warrants that we may offer under this prospectus, which may consist of warrants to purchase common stock, preferred stock or debt securities and may be issued in one or more series. Warrants may be offered independently or in combination with common stock, preferred stock or debt securities offered by any prospectus supplement. While the terms we have summarized below will apply generally to any warrants that we may offer under this prospectus, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement. The following description of warrants will apply to the warrants offered by this prospectus unless we provide otherwise in the applicable prospectus supplement. The applicable prospectus supplement for a particular series of warrants may specify different or additional terms.

We have filed forms of the warrant agreements and forms of warrant certificates containing the terms of the warrants that may be offered as exhibits to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant and/or the warrant agreement and warrant certificate, as applicable, that contain the terms of the particular series of warrants we are offering, and any supplemental agreements, before the issuance of such warrants. The following summaries of material terms and provisions of the warrants are subject to, and qualified in their entirety by reference to, all the provisions of the form of warrant and/or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements applicable to a particular series of warrants that we may offer under this prospectus. We urge you to read the applicable prospectus supplement related to the particular series of warrants that we may offer under this prospectus, as well as any related free writing prospectus, and the complete form of warrant and/or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements, that contain the terms of the warrants.

General

We will describe in the applicable prospectus supplement the terms of the series of warrants being offered, including:

•

the offering price and aggregate number of warrants offered;

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•

the currency for which the warrants may be purchased;

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•

if applicable, the designation and terms of the securities with which the warrants are issued and the number of warrants issued with each such security or each principal amount of such security;

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•

in the case of warrants to purchase debt securities, the principal amount of debt securities purchasable upon exercise of one warrant and the price at, and currency in which, this principal amount of debt securities may be purchased upon such exercise;

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•

in the case of warrants to purchase common stock or preferred stock, the number of shares of common stock or preferred stock, as the case may be, purchasable upon the exercise of one warrant and the price at which these shares may be purchased upon such exercise;

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•

the effect of any merger, consolidation, sale or other disposition of our business on the warrant agreements and the warrants;

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•

the terms of any rights to redeem or call the warrants;

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•

any provisions for changes to or adjustments in the exercise price or number of securities issuable upon exercise of the warrants;

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•

the dates on which the right to exercise the warrants will commence and expire;

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•

the manner in which the warrant agreements and warrants may be modified;

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•

a discussion of material or special U.S. federal income tax considerations, if any, of holding or exercising the warrants;

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•

the terms of the securities issuable upon exercise of the warrants; and

​

•

any other specific terms, preferences, rights or limitations of or restrictions on the warrants.

​

Before exercising their warrants, holders of warrants will not have any of the rights of holders of the securities purchasable upon such exercise, including:

•

in the case of warrants to purchase debt securities, the right to receive payments of principal of, or premium, if any, or interest on, the debt securities purchasable upon exercise or to enforce covenants in the applicable indenture; or

​

•

in the case of warrants to purchase common stock or preferred stock, the right to receive dividends, if any, or payments upon our liquidation, dissolution or winding up or to exercise voting rights, if any.

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Exercise of Warrants

Each warrant will entitle the holder to purchase the securities that we specify in the applicable prospectus supplement at the exercise price that we describe in the applicable prospectus supplement. The warrants may be exercised as set forth in the prospectus supplement relating to the warrants offered. Unless we otherwise specify in the applicable prospectus supplement, warrants may be exercised at any time up to the close of business on the expiration date set forth in the prospectus supplement relating to the warrants offered thereby. After the close of business on the expiration date, unexercised warrants will become void.

Upon receipt of payment and the warrant or warrant certificate, as applicable, properly completed and duly executed at the corporate trust office of the warrant agent, if any, or any other office, including ours, indicated in the prospectus supplement, we will, as soon as practicable, issue and deliver the securities purchasable upon such exercise. If less than all of the warrants (or the warrants represented by such warrant certificate) are exercised, a new warrant or a new warrant certificate, as applicable, will be issued for the remaining warrants.

Governing Law

Unless we otherwise specify in the applicable prospectus supplement, the warrants and any warrant agreements will be governed by and construed in accordance with the laws of the State of New York.

Enforceability of Rights by Holders of Warrants

Each warrant agent, if any, will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, its warrants.

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DESCRIPTION OF RIGHTS

The following is a general description of the terms of the rights we may issue from time to time unless we provide otherwise in the applicable prospectus supplement. Particular terms of any rights we offer will be described in the prospectus supplement relating to such rights.

General

We may issue rights to purchase common stock, preferred stock, debt securities or units. Rights may be issued independently or together with other securities and may or may not be transferable by the person purchasing or receiving the rights. In connection with any rights offering to our stockholders, we may enter into a standby underwriting, backstop or other arrangement with one or more underwriters or other persons pursuant to which such underwriters or other persons would purchase any offered securities remaining unsubscribed for after such rights offering. In connection with a rights offering to our stockholders, we would distribute certificates evidencing the rights and a prospectus supplement to our stockholders on or about the record date that we set for receiving rights in such rights offering.

The applicable prospectus supplement will describe the following terms of any rights we may issue, including some or all of the following:

•

the title and aggregate number of the rights;

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•

the subscription price or a formula for the determination of the subscription price for the rights and the currency or currencies in which the subscription price may be payable;

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•

if applicable, the designation and terms of the securities with which the rights are issued and the number of rights issued with each such security or each principal amount of such security;

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•

the number or a formula for the determination of the number of the rights issued to each stockholder;

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•

the extent to which the rights are transferable;

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•

in the case of rights to purchase debt securities, the principal amount of debt securities purchasable upon exercise of one right;

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•

in the case of rights to purchase common stock or preferred stock, the type of stock and number of shares of stock purchasable upon exercise of one right;

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•

the date on which the right to exercise the rights will commence, and the date on which the rights will expire (subject to any extension);

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•

if applicable, the minimum or maximum amount of the rights that may be exercised at any one time;

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•

the extent to which such rights include an over-subscription privilege with respect to unsubscribed securities;

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•

if applicable, the procedures for adjusting the subscription price and number of shares of common stock or preferred stock purchasable upon the exercise of each right upon the occurrence of certain events, including stock splits, reverse stock splits, combinations, subdivisions or reclassifications of common stock or preferred stock;

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•

the effect on the rights of any merger, consolidation, sale or other disposition of our business;

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•

the terms of any rights to redeem or call the rights;

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•

information with respect to book-entry procedures, if any;

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•

the terms of the securities issuable upon exercise of the rights;

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•

if applicable, the material terms of any standby underwriting, backstop or other purchase arrangement that we may enter into in connection with the rights offering;

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if applicable, a discussion of material U.S. Federal income tax considerations; and

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•

any other terms of the rights, including terms, procedures and limitations relating to the exchange and exercise of the rights.

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Exercise of Rights

Each right will entitle the holder to purchase for cash or other consideration such shares of stock or principal amount of securities at the subscription price as shall in each case be set forth in, or be determinable as set forth in, the prospectus supplement relating to the rights offered thereby. Rights may be exercised as set forth in the applicable prospectus supplement beginning on the date specified therein and continuing until the close of business on the expiration date set forth in the prospectus supplement relating to the rights offered thereby. After the close of business on the expiration date, unexercised rights will become void.

Upon receipt of payment and a subscription certificate properly completed and duly executed at the corporate trust office of the subscription agent or any other office indicated in the prospectus supplement, we will, as soon as practicable, forward the securities purchasable upon such exercise. If less than all of the rights represented by such subscription certificate are exercised, a new subscription certificate will be issued for the remaining rights. If we so indicate in the applicable prospectus supplement, holders of the rights may surrender securities as all or part of the exercise price for rights.

We may determine to offer any unsubscribed offered securities directly to stockholders, persons other than stockholders, to or through agents, underwriters or dealers or through a combination of such methods, including pursuant to standby underwriting, backstop or other arrangements, as set forth in the applicable prospectus supplement.

Prior to exercising their rights, holders of rights will not have any of the rights of holders of the securities purchasable upon subscription, including, in the case of rights to purchase common stock or preferred stock, the right to receive dividends, if any, or payments upon our liquidation, dissolution or winding up or to exercise any voting rights or, in the case of rights to purchase debt securities, the right to receive principal, premium, if any, or interest payments, on the debt securities purchasable upon exercise or to enforce covenants in the applicable indenture.

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DESCRIPTION OF UNITS

We may issue units comprising one or more securities described in this prospectus in any combination. The following description sets forth certain general terms and provisions of the units that we may offer pursuant to this prospectus. The particular terms of the units and the extent, if any, to which the general terms and provisions may apply to the units so offered will be described in the applicable prospectus supplement.

Each unit will be issued so that the holder of the unit also is the holder of each security included in the unit. Thus, the unit will have the rights and obligations of a holder of each included security. Units will be issued pursuant to the terms of a unit agreement, which may provide that the securities included in the unit may not be held or transferred separately at any time or at any time before a specified date. A copy of the forms of the unit agreement and the unit certificate relating to any particular issue of units will be filed with the SEC each time we issue units, and you should read those documents for provisions that may be important to you. For more information on how you can obtain copies of the forms of the unit agreement and the related unit certificate, see “Where You Can Find More Information.”

The prospectus supplement relating to any particular issuance of units will describe the terms of those units, including, to the extent applicable, the following:

•

the designation and terms of the units and the securities comprising the units, including whether and under what circumstances those securities may be held or transferred separately;

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any provision for the issuance, payment, settlement, transfer or exchange of the units or of the securities comprising the units; and

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whether the units will be issued in fully registered or global form.

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LEGAL OWNERSHIP OF SECURITIES

We may issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee, depositary or warrant agent maintain for this purpose as the “holders” of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names, as “indirect holders” of those securities. As we discuss below, indirect holders are not legal holders, and investors in securities issued in book-entry form or in street name will be indirect holders.

Book-Entry Holders

We may issue securities in book-entry form only, as we will specify in the applicable prospectus supplement. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary’s book-entry system. These participating institutions, which are referred to as participants, in turn, hold beneficial interests in the securities on behalf of themselves or their customers.

Only the person in whose name a security is registered is recognized as the holder of that security. Securities issued in global form will be registered in the name of the depositary or its participants. Consequently, for securities issued in global form, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.

As a result, investors in a book-entry security will not own securities directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary’s book-entry system or holds an interest through a participant. As long as the securities are issued in global form, investors will be indirect holders, and not holders, of the securities.

Street Name Holders

We may terminate a global security or issue securities in non-global form. In these cases, investors may choose to hold their securities in their own names or in “street name.” Securities held by an investor in street name would be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor would hold only a beneficial interest in those securities through an account he or she maintains at that institution.

For securities held in street name, we will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we will make all payments on those securities to them. These institutions pass along the payments they receive to their customers who are the beneficial owners, but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not holders, of those securities.

Legal Holders

Our obligations, as well as the obligations of any applicable trustee and of any third parties employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or has no choice because we are issuing the securities only in global form.

For example, once we make a payment or give a notice to the holder, we have no further responsibility for the payment or notice even if that holder is required, under agreements with depositary participants or customers or by law, to pass it along to the indirect holders but does not do so. Similarly, we may want to obtain the approval of the holders to amend an indenture, to relieve us of the consequences of a default or of our obligation to comply with a particular provision of the indenture or for other purposes. In such

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an event, we would seek approval only from the holders, and not the indirect holders, of the securities. Whether and how the holders contact the indirect holders is up to the holders.

Special Considerations for Indirect Holders

If you hold securities through a bank, broker or other financial institution, either in book-entry form or in street name, you should check with your own institution to find out:

•

the performance of third-party service providers;

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•

how it handles securities payments and notices;

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•

whether it imposes fees or charges;

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•

how it would handle a request for the holders’ consent, if ever required;

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•

whether and how you can instruct it to send you securities registered in your own name so you can be a holder, if that is permitted in the future;

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•

how it would exercise rights under the securities if there were a default or other event triggering the need for holders to act to protect their interests; and

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•

if the securities are in book-entry form, how the depositary’s rules and procedures will affect these matters.

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Global Securities

A global security is a security that represents one or any other number of individual securities held by a depositary. Generally, all securities represented by the same global securities will have the same terms.

Each security issued in book-entry form will be represented by a global security that we deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, DTC will be the depositary for all securities issued in book-entry form.

A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under the section titled “Special Situations When a Global Security Will Be Terminated” in this prospectus. As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and holder of all securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a holder of the security, but only an indirect holder of a beneficial interest in the global security.

If the prospectus supplement for a particular security indicates that the security will be issued in global form only, then the security will be represented by a global security at all times unless and until the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.

Special Considerations for Global Securities

The rights of an indirect holder relating to a global security will be governed by the account rules of the investor’s financial institution and of the depositary, as well as general laws relating to securities transfers. We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

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If securities are issued only in the form of a global security, an investor should be aware of the following:

•

an investor cannot cause the securities to be registered in his or her name, and cannot obtain non-global certificates for his or her interest in the securities, except in the special situations we describe below;

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•

an investor will be an indirect holder and must look to his or her own bank or broker for payments on the securities and protection of his or her legal rights relating to the securities, as we describe above;

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•

an investor may not be able to sell interests in the securities to some insurance companies and to other institutions that are required by law to own their securities in non-book-entry form;

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•

an investor may not be able to pledge his or her interest in a global security in circumstances where certificates representing the securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective;

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•

the depositary’s policies, which may change from time to time, will govern payments, transfers, exchanges and other matters relating to an investor’s interest in a global security;

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•

we and any applicable trustee have no responsibility for any aspect of the depositary’s actions or for its records of ownership interests in a global security, nor do we or any applicable trustee supervise the depositary in any way;

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•

the depositary may, and we understand that DTC will, require that those who purchase and sell interests in a global security within its book-entry system use immediately available funds, and your broker or bank may require you to do so as well; and

​

•

financial institutions that participate in the depositary’s book-entry system, and through which an investor holds its interest in a global security, may also have their own policies affecting payments, notices and other matters relating to the securities.

​

There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

Special Situations When a Global Security Will Be Terminated

In a few special situations described below, the global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks or brokers to find out how to have their interests in securities transferred to their own name, so that they will be direct holders. We have described the rights of holders and street name investors above.

Unless we provide otherwise in the applicable prospectus supplement, the global security will terminate when the following special situations occur:

•

if the depositary notifies us that it is unwilling, unable or no longer qualified to continue as depositary for that global security and we do not appoint another institution to act as depositary within 90 days;

​

•

if we notify any applicable trustee that we wish to terminate that global security; or

​

•

if an event of default has occurred with regard to securities represented by that global security and has not been cured or waived.

​

The applicable prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the applicable prospectus supplement. When a global security terminates, the depositary, and not we or any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

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PLAN OF DISTRIBUTION

We may sell the securities from time to time pursuant to underwritten public offerings, direct sales to the public, “at-the-market” offerings, negotiated transactions, block trades or a combination of these methods. We may sell the securities to or through one or more underwriters or dealers (acting as principal or agent), through agents, or directly to one or more purchasers. We may distribute securities from time to time in one or more transactions:

•

at a fixed price or prices, which may be changed;

​

•

at market prices prevailing at the time of sale;

​

•

at prices related to such prevailing market prices; or

​

•

at negotiated prices.

​

A prospectus supplement or supplements (and any related free writing prospectus that we may authorize to be provided to you) will describe the terms of the offering of the securities, including, to the extent applicable:

•

the name or names of the underwriters, dealers or agents, if any;

​

•

the purchase price of the securities or other consideration therefor, and the proceeds, if any, we will receive from the sale;

​

•

any over-allotment or other options under which underwriters may purchase additional securities from us;

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•

any agency fees or underwriting discounts and other items constituting agents’ or underwriters’ compensation;

​

•

any public offering price;

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•

any discounts or concessions allowed or reallowed or paid to dealers; and

​

•

any securities exchange or market on which the securities may be listed.

​

Only underwriters named in the prospectus supplement will be underwriters of the securities offered by the prospectus supplement. Dealers and agents participating in the distribution of the securities may be deemed to be underwriters, and compensation received by them on resale of the securities may be deemed to be underwriting discounts. If such dealers or agents were deemed to be underwriters, they may be subject to statutory liabilities under the Securities Act.

If underwriters are used in the sale, they will acquire the securities for their own account and may resell the securities from time to time in one or more transactions at a fixed public offering price or at varying prices determined at the time of sale. The obligations of the underwriters to purchase the securities will be subject to the conditions set forth in the applicable underwriting agreement. We may offer the securities to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate. Subject to certain conditions, the underwriters will be obligated to purchase all of the securities offered by the prospectus supplement, other than securities covered by any option to purchase additional shares or other option. If a dealer is used in the sale of securities, we or an underwriter will sell the securities to the dealer, as principal. The dealer may then resell the securities to the public at varying prices to be determined by the dealer at the time of resale. To the extent required, we will set forth in the prospectus supplement the name of the dealer and the terms of the transaction. Any public offering price and any discounts or concessions allowed or reallowed or paid to dealers may change from time to time.

We may use underwriters, dealers or agents with whom we have a material relationship. We will describe in the prospectus supplement, naming the underwriter, dealer or agent, the nature of any such relationship.

We may sell securities directly or through agents we designate from time to time. We will name any agent involved in the offering and sale of securities and we will describe any commissions payable to the agent in the prospectus supplement. Unless the prospectus supplement states otherwise, the agent will act on a best-efforts basis for the period of its appointment.

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We may provide agents, underwriters and dealers with indemnification against civil liabilities, including liabilities under the Securities Act, or contribution with respect to payments that the agents, underwriters or dealers may make with respect to these liabilities. Agents, underwriters and dealers, or their affiliates, may engage in transactions with, or perform services for, us in the ordinary course of business.

All securities we may offer, other than common stock, will be new issues of securities with no established trading market. Any underwriters may make a market in these securities, but will not be obligated to do so and may discontinue any market making at any time without notice. We cannot guarantee the liquidity of the trading markets for any securities.

Any underwriter may be granted an option to purchase additional shares and engage in stabilizing transactions, short-covering transactions and penalty bids in accordance with Regulation M under the Exchange Act. An underwriter’s option to purchase additional shares involves sales in excess of the offering size, which creates a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum price. Syndicate-covering or other short-covering transactions involve purchases of the securities, either through exercise of the option to purchase additional shares or in the open market after the distribution is completed, to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a stabilizing or covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of the activities at any time.

Any underwriters, dealers or agents that are qualified market makers on the Nasdaq Global Select Market may engage in passive market making transactions in the common stock on the Nasdaq Global Select Market in accordance with Regulation M under the Exchange Act, during the business day prior to the pricing of the offering, before the commencement of offers or sales of the common stock. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded. Passive market making may stabilize the market price of the securities at a level above that which might otherwise prevail in the open market and, if commenced, may be discontinued at any time.

In compliance with guidelines of the Financial Industry Regulatory Authority (FINRA) the maximum consideration or discount to be received by any FINRA member or independent broker dealer may not exceed 8% of the aggregate amount of the securities offered pursuant to this prospectus and the applicable prospectus supplement.

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LEGAL MATTERS

Unless otherwise indicated in the applicable prospectus supplement, the validity of the securities offered by this prospectus, and any supplement thereto, will be passed upon for us by Sidley Austin LLP.

EXPERTS

The consolidated financial statements of Atara Biotherapeutics, Inc. incorporated by reference in this Prospectus have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report. Such consolidated financial statements are incorporated by reference in reliance upon the report of such firm, given their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

This prospectus is part of the registration statement on Form S-3 we filed with the SEC under the Securities Act and does not contain all the information set forth or incorporated by reference in the registration statement. Whenever a reference is made in this prospectus to any of our contracts, agreements or other documents, the reference may not be complete and you should refer to the exhibits that are a part of the registration statement or the exhibits to the reports or other documents incorporated by reference into this prospectus for a copy of such contract, agreement or other document. Because we are subject to the information and reporting requirements of the Exchange Act, we file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC’s website at http://www.sec.gov.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information from other documents that we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus. Information in this prospectus supersedes information incorporated by reference that we filed with the SEC prior to the date of this prospectus, while information that we file later with the SEC will automatically update and supersede the information in this prospectus. We incorporate by reference into this prospectus and the registration statement of which this prospectus is a part the information or documents listed below that we have filed with the SEC (Commission File No. 001-36548):

•

our Annual Report on Form 10-K for the year ended December 31, 2025 filed with the SEC on March 16, 2026;

​

•

the information specifically incorporated by reference into our Annual Report on Form 10-K for the year ended December 31, 2025 from our Definitive Proxy Statement on Schedule 14A filed with the SEC on April 24, 2026;

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•

our Quarterly Report on Form 10-Q for the quarter ended March 31, 2026 filed with the SEC on May 12, 2026;

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•

our Quarterly Report on Form 10-Q for the quarter ended June 30, 2026 filed with the SEC on August 12, 2026;

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•

our Quarterly Report on Form 10-Q for the quarter ended September 30, 2026 filed with the SEC on November 10, 2026;

​

•

our Current Reports on Form 8-K filed with the SEC on January 2, 2026, January 12, 2026 (solely with respect to Items 8.01 and 9.01), February 23, 2026, March 3, 2026, March 12, 2026, May 1, 2026, May 7, 2026, June 12, 2026 and June 26, 2026; and

​

•

the description of our common stock contained in our registration statement on Form 8-A filed with the SEC on July 16, 2014, including any amendments or reports filed for the purposes of updating this description, including Exhibit 4.8 to our Annual Report on Form 10-K for the year ended December 31, 2025 filed with the SEC on March 16, 2026 and any further amendments or reports filed for the purpose of updating such description.

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We also incorporate by reference any future filings (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items unless such Form 8-K expressly provides to the contrary) made with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act until we file a post-effective amendment that indicates the termination of the offering of the securities made by this prospectus and will become a part of this prospectus from the date that such documents are filed with the SEC. Information in such future filings updates and supplements the information provided in this prospectus. Any statements in any such future filings will automatically be deemed to modify and supersede any information in any document we previously filed with the SEC that is incorporated or deemed to be incorporated herein by reference to the extent that statements in the later filed document modify or replace such earlier statements.

We will furnish without charge to each person, including any beneficial owner, to whom a prospectus is delivered, upon written or oral request, a copy of any or all of the documents incorporated by reference, including exhibits to these documents. Any such request may be made by writing or telephoning us at the following address or phone number:

Atara Biotherapeutics, Inc.
Attn: Investor Relations
1280 Rancho Conejo Boulevard
Thousand Oaks, California 91320
Telephone: (805) 623-4211

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The information in this preliminary prospectus is not complete and may be changed. These securities may not be sold until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell nor does it seek an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED NOVEMBER 10, 2026

PROSPECTUS

$23,011,805

Common Stock

​

Pursuant to this prospectus, we may offer and sell up to $23,011,805 of shares of our common stock. We previously entered into a sales agreement (Sales Agreement) with TD Securities (USA) LLC (as successor to Cowen and Company, LLC) (TD Cowen) dated November 1, 2023 relating to shares of our common stock. In accordance with the terms of the Sales Agreement, we may offer and sell shares of our common stock having an aggregate offering price of up to $100,000,000 from time to time through or to TD Cowen acting as our agent or principal. To date, we have sold an aggregate of 1,828,092 shares pursuant to the Sales Agreement under the Company’s registration statement on Form S-3 (File No. 333-275256) filed on November 1, 2023, and declared effective on November 13, 2023 for aggregate gross proceeds of approximately $21.7 million.

As of the date of this prospectus, the aggregate market value of our outstanding common stock held by non-affiliates pursuant to General Instruction I.B.6 of Form S-3 is approximately $69,035,417, based on 10,188,438 shares of outstanding common stock, of which 6,828,429 shares are held by non-affiliates, and a per share price of $10.11, the closing sale price of our common stock on the Nasdaq Global Select Market on September 16, 2026, which was the highest closing sale price within 60 days prior to the date of this prospectus. Pursuant to General Instruction I.B.6 of Form S-3, in no event will we sell securities pursuant to this prospectus with a value exceeding more than one-third of our public float in any 12-month period so long as our public float remains below $75.0 million. During the 12 calendar months prior to and including the date of this prospectus, we have not offered or sold any securities pursuant to General Instruction I.B.6 of Form S-3.

Our common stock is listed on the Nasdaq Global Select Market under the symbol “ATRA”. On November 9, 2026, the last reported sale price of our common stock was $8.18 per share.

Sales of our common stock, if any, under this prospectus will be made in sales deemed to be “at the market offerings” as defined in Rule 415 promulgated under the Securities Act of 1933, as amended, or the Securities Act. TD Cowen is not required to sell any specific amount of securities, but will act as our sales agent using commercially reasonable efforts consistent with its normal trading and sales practices, on mutually agreed terms between TD Cowen and us. There is no arrangement for funds to be received in any escrow, trust or similar arrangement.

Under the Sales Agreement, if authorized by us in writing, TD Cowen may purchase shares of our common stock as principal for its own account.

The compensation to TD Cowen for sales of common stock sold pursuant to the Sales Agreement will be an amount equal to 3.0% of the gross proceeds of any shares of common stock sold under the Sales Agreement. In connection with the sale of the common stock on our behalf, TD Cowen will be deemed to be an “underwriter” within the meaning of the Securities Act and the compensation of TD Cowen will be deemed to be underwriting commissions or discounts. We have also agreed to provide indemnification and contribution to TD Cowen with respect to certain liabilities, including liabilities under the Securities Act or the Exchange Act of 1934, as amended.

Our business and an investment in our common stock involve significant risks. These risks are described under the caption “Risk Factors” beginning on page SA-4 of this prospectus and in the documents incorporated by reference into this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

TD Cowen

           , 2026

Table of Contents​

TABLE OF CONTENTS

​	ABOUT THIS PROSPECTUS	​	​	​	​	SA-ii	​	​
​	PROSPECTUS SUMMARY	​	​	​	​	SA-1	​	​
​	THE OFFERING	​	​	​	​	SA-3	​	​
​	RISK FACTORS	​	​	​	​	SA-4	​	​
​	SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	​	​	​	​	SA-6	​	​
​	USE OF PROCEEDS	​	​	​	​	SA-8	​	​
​	DESCRIPTION OF CAPITAL STOCK	​	​	​	​	SA-9	​	​
​	DILUTION	​	​	​	​	SA-13	​	​
​	PLAN OF DISTRIBUTION	​	​	​	​	SA-15	​	​
​	LEGAL MATTERS	​	​	​	​	SA-17	​	​
​	EXPERTS	​	​	​	​	SA-18	​	​
​	WHERE YOU CAN FIND MORE INFORMATION	​	​	​	​	SA-19	​	​
​	INCORPORATION OF CERTAIN INFORMATION BY REFERENCE	​	​	​	​	SA-20	​	​

SA-i

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ABOUT THIS PROSPECTUS

This prospectus relates to the offering of our common stock. Before buying any of the common stock that we are offering, we urge you to carefully read this prospectus, together with the information incorporated by reference in this prospectus, and any free writing prospectus that we have authorized for use in connection with this offering when making your investment decision. You should also read and consider the information in the documents we have referred you to under the headings “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.” These documents contain important information that you should consider when making your investment decision.

This prospectus adds to and updates information contained in the documents incorporated by reference into this prospectus. To the extent there is a conflict between the information contained in this prospectus, on the one hand, and the information contained in any document incorporated by reference into this prospectus that was filed with the SEC before the date of this prospectus, on the other hand, you should rely on the information in this prospectus. If any statement in one of these documents is inconsistent with a statement in another document having a later date (for example, a document incorporated by reference into this prospectus) the statement in the document having the later date modifies or supersedes the earlier statement.

We have not, and the sales agent has not, authorized anyone to provide any information other than that contained or incorporated by reference in this prospectus and any free writing prospectus prepared by or on behalf of us or to which we have referred you. We and the sales agent take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We are not, and the sales agent is not, making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus, the documents incorporated by reference in this prospectus, and any free writing prospectus that we have authorized for use in connection with this offering, is accurate only as of the date of those respective documents. Our business, financial condition, results of operations and prospects may have changed since those dates.

SA-ii

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PROSPECTUS SUMMARY

This summary highlights certain information about us, this offering and selected information contained elsewhere in or incorporated by reference into this prospectus. This summary provides an overview of selected information and does not contain all of the information you should consider before deciding whether to invest in our common stock. Therefore, you should read the entire prospectus carefully (including the documents incorporated by reference herein and therein), especially the “Risk Factors” section beginning on page SA-4 of this prospectus and in the documents incorporated by reference and our consolidated financial statements (which we refer to as our “Financial Statements”) and the related notes incorporated by reference in this prospectus, before deciding to invest in our common stock. Unless the context otherwise requires, we use the terms “Atara,” “Atara Biotherapeutics,” “Atara Bio,” “Company,” “we,” “us” and “our” in this prospectus to refer to Atara Biotherapeutics, Inc. and, where appropriate, our consolidated subsidiaries.

Company Overview

Atara Biotherapeutics is a leader in T-cell immunotherapy, leveraging its novel allogeneic Epstein-Barr virus (EBV) T-cell platform to develop transformative therapies for patients with cancer and autoimmune disease. Tab-cel® (tabelecleucel) has received marketing authorization approval under the proprietary name Ebvallo™ by the European Commission (EC) for commercial sale and use in the European Economic Area (EEA), by the Medicines and Healthcare products Regulatory Agency (MHRA) for commercial sale and use in the United Kingdom (UK) and by Swissmedic for commercial sale and use in Switzerland. We partnered with Pierre Fabre Medicament (Pierre Fabre) for commercialization of tab-cel in Europe and potential commercialization, if approved, worldwide, including in the U.S. Tab-cel is currently in Phase 3 development in the U.S. for patients with EBV-associated post-transplant lymphoproliferative disease (EBV+ PTLD) who have failed rituximab or rituximab plus chemotherapy, as well as other EBV-driven diseases. In September 2026, Pierre Fabre resubmitted the biologics license application (BLA) for tab-cel to the U.S. Food and Drug Administration (FDA), and in October 2026, the FDA accepted the resubmission for a Class 2 review with a PDUFA target action date of March 31, 2027.

Summary Risk Factors

Our business is subject to numerous risks and uncertainties that may have a material adverse effect on our business, financial condition or results of operations. These risks are more fully described below. These risks include, among others:

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we have incurred substantial losses since our inception and anticipate that we will continue to incur substantial losses for the foreseeable future;

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we have earned limited commercialization revenues to date, and we may never achieve profitability;

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we have one approved product, Ebvallo, in the EEA, the UK, and Switzerland. If we or our collaborators are unable to successfully develop, manufacture and commercialize tab-cel or experience significant delays in doing so, our business may be materially harmed;

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we will require substantial near-term financing to continue operations, and a failure to obtain this necessary capital when needed could force us to delay, limit, reduce or terminate our product development or manufacturing efforts, impair our exploration of strategic alternatives, or require us to pursue a liquidation and dissolution or other wind down of our business;

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our future success depends on our ability to retain our executive officers and to attract, retain and motivate qualified personnel;

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the results of preclinical studies or earlier clinical studies are not necessarily predictive of future results, and tab-cel may not receive regulatory approval in the U.S.;

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clinical drug development involves a lengthy and expensive process with an uncertain outcome;

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tab-cel represents a new therapeutic approach that could result in heightened regulatory scrutiny, delays in clinical development or our inability to achieve regulatory approval, or our partner’s inability to achieve commercialization or secure payor coverage of tab-cel;

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SA-1

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•

there can be no assurance that we will achieve all of the anticipated benefits of our collaboration with Pierre Fabre, and we could face unanticipated challenges;

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the market opportunities for our product and product candidates may be limited to those patients who are ineligible for or have failed prior treatments and may be small;

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we may not be able to obtain or maintain orphan drug exclusivity for tab-cel;

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our activities to review and pursue strategic alternatives may not result in a strategic transaction, and even if we do consummate a strategic transaction, there is no assurance that it will deliver the benefits we expect or enhance stockholder value;

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if we are unable to obtain and maintain sufficient intellectual property protection for our product candidates, or if the scope of the intellectual property protection is not sufficiently broad, our ability to commercialize our product candidates successfully and to compete effectively may be adversely affected;

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•

our principal stockholders own a significant percentage of our stock and will be able to exert control or significant influence over matters subject to stockholder approval;

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our workforce reductions may not result in anticipated savings, could result in total costs and expenses that are greater than expected and could disrupt our business; and

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maintaining clinical and commercial timelines is dependent on our partner’s end-to-end supply chain network to support manufacturing; if they experience problems with their third party suppliers or CMOs, development and/or commercialization of tab-cel may be adversely affected.

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Corporate Information

We were incorporated in Delaware in August 2012. Our principal executive offices are located at 1280 Rancho Conejo Boulevard, Thousand Oaks, California 91320, and our telephone number is (805) 623-4211. Our website address is www.atarabio.com. Information contained on or accessible through our website is not a part of this prospectus.

“Atara,” “Atara Bio,” “Atara Biotherapeutics” and the Atara logo are the property of Atara Biotherapeutics, Inc. This prospectus contains references to our trademarks and to trademarks belonging to other entities. We do not intend our use or display of other companies’ trade names or trademarks to imply a relationship with, or endorsement or sponsorship of us by, any other companies.

SA-2

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THE OFFERING

Common Stock Offered by Us

Shares of our common stock having an aggregate offering price of up to $23,011,805.

Manner of Offering

“At the market” offering that may be made from time to time through our sales agent, TD Securities (USA) LLC, or TD Cowen. See “Plan of Distribution” on page SA-15 of this prospectus.

Use of Proceeds

We currently intend to use the net proceeds, if any, of this offering for working capital and other general corporate purposes, including research, development, manufacturing and commercialization of our product candidates.

See the section of this prospectus titled “Use of Proceeds” on page SA-8 for a more complete description of the intended use of proceeds from this offering.

Risk Factors

Investing in our common stock involves significant risk. See “Risk Factors” beginning on page SA-4 of this prospectus and other information included and incorporated by reference in this prospectus for a discussion of factors that you should carefully consider before deciding to invest in our common stock.

Nasdaq Global Select Market Symbol

“ATRA”

SA-3

Table of Contents​

RISK FACTORS

Investing in our common stock involves a high degree of risk. You should carefully consider the risk factors described below and the risk factors incorporated by reference to our Annual Report on Form 10-K for the fiscal year ended December 31, 2025 and in our most recent Quarterly Report on Form 10-Q, and all other information contained or incorporated by reference into this prospectus, including our financial statements and the related notes, as updated by our subsequent filings under the Securities Exchange Act of 1934, as amended, or the Exchange Act, and in any free writing prospectus that we have authorized for use in connection with this offering before acquiring any of our common stock. These risks could have a material and adverse impact on our business, results of operations, financial condition and growth prospects, which may cause the trading price of our common stock to decline and you could lose all or part of your investment.

Additional Risks Related to this Offering

We will have broad discretion in the use of the net proceeds from this offering and may not use them effectively.

Our management will have broad discretion in the application of the balance of the net proceeds from this offering and could spend the proceeds in ways that do not improve our business, financial condition or results of operations or enhance the value of our common stock. You may not agree with our decisions, and our use of the proceeds may not yield any return on your investment. We intend to use the proceeds from this offering for working capital and other general corporate purposes, including research, development and manufacturing of our product candidates.

Because of the number and variability of factors that will determine our use of the net proceeds from this offering, their ultimate use may vary substantially from their currently intended use. Our failure to apply the net proceeds of this offering effectively could compromise our ability to pursue our growth strategy and we might not be able to yield a significant return, if any, on our investment of these net proceeds. You will not have the opportunity to influence our decisions on how to use the net proceeds from this offering. The failure by our management to apply these funds effectively could result in financial losses that could harm our business, cause the price of our common stock to decline and delay the development of our product candidates. Pending their use, we may invest the net proceeds from this offering in a manner that does not produce income or that loses value.

You will experience immediate and substantial dilution.

The offering price per share in this offering may exceed the net tangible book value per share of our common stock outstanding prior to this offering. Assuming that an aggregate of 2,923,990 shares of our common stock are sold at a price of $7.87 per share, the last reported sale price of our common stock on the Nasdaq Global Select Market on November 6, 2026, for aggregate gross proceeds of $23,011,805, and after deducting commissions and estimated offering expenses payable by us, you would experience immediate dilution of $9.08 per share, representing the difference between our as adjusted net tangible book value per share as of September 30, 2026 after giving effect to this offering, on the one hand, and the assumed offering price, on the other. The exercise of outstanding stock options and pre-funded warrants will result in further dilution of your investment. See the section titled “Dilution” below for a more detailed illustration of the dilution you would incur if you participate in this offering.

The actual number of shares of common stock we will issue under the Sales Agreement, at any one time or in total, is uncertain.

Subject to certain limitations in the Sales Agreement and compliance with applicable law, we have the discretion to deliver a placement notice to TD Cowen at any time throughout the term of the Sales Agreement. The per share price of the shares of common stock that are sold by TD Cowen after delivering a placement notice will fluctuate based on the market price of our common stock during the sales period and limits we set with TD Cowen. Because the price per share of each share of common stock sold will fluctuate based on the market price of our common stock during the sales period, it is not possible at this stage to predict the number of shares of common stock that will be ultimately issued.

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The common stock offered hereby will be sold in “at the market offerings,” and investors who buy shares at different times will likely pay different prices.

Investors who purchase shares in this offering at different times will likely pay different prices, and so may experience different outcomes in their investment results. We will have discretion, subject to market demand, to vary the timing, prices and numbers of shares sold. In addition, subject to any restrictions in any applicable placement notice delivered to TD Cowen, there is no minimum or maximum sales price per share to be sold in this offering. Investors may experience a decline in the value of their shares as a result of share sales made at prices lower than the prices they paid.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and the documents incorporated by reference herein and therein, and any free writing prospectus that we have authorized for use in connection with this offering, contain forward-looking statements. The forward-looking statements include, but are not limited to, statements about:

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our review of strategic alternatives;

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our expectations with regard to our programs, including clinical sites, the clinical studies, and reporting results of such studies;

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•

the likelihood and timing of regulatory submissions or related approvals for tab-cel, including the expectations about the timing of approvals for a biologics license application (BLA) for tab-cel® for patients with Epstein-Barr virus with post-transplant lymphoproliferative disease (EBV+ PTLD);

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•

the potential indications for tab-cel;

​

•

commercialization of tab-cel (Ebvallo™ in the United Kingdom (UK), the European Economic Area (EEA) and Switzerland) worldwide and our amended and restated Commercialization Agreement with Pierre Fabre Medicament, as amended, including potential milestone and royalty payments under the agreement (Ebvallo in the UK, the EEA and Switzerland subject to the Purchase and Sale Agreement with HCR Molag Fund, L.P.);

​

•

our Purchase and Sale Agreement, as amended, and related transactions with HCR Molag Fund, L.P.;

​

•

our expectations regarding the potential commercial market opportunities, market size and the size of the patient populations for tab-cel;

​

•

estimates of our expenses, capital requirements and need for additional financing;

​

•

our expectation regarding the length of time that our existing capital resources will be sufficient to enable us to fund our planned operations, including our going concern assessment;

​

•

the scope of protection we are able to obtain and maintain for the intellectual property rights covering tab-cel;

​

•

our financial performance;

​

•

our election to rely on reduced reporting and disclosure requirements available to smaller reporting companies;

​

•

developments and projections relating to our competitors and our industry;

​

•

our partner’s ability to have tab-cel manufactured for clinical studies or for commercial sale, including at commercially reasonable values;

​

•

the impact of public health emergencies to our business and operations, as well as the businesses and operations of third parties on which we rely;

​

•

the impact of our workforce reductions on our ability to attract, retain and motivate qualified personnel and on our business, operations, and financial condition;

​

•

timing and costs related to the qualification of the manufacturing facilities of contract manufacturing organizations (CMO) for commercial production; and

​

•

our intended use of the net proceeds from this offering.

​

All statements other than statements of historical facts contained in this prospectus and the documents incorporated by reference herein are forward-looking statements. These statements involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements. This prospectus and the documents incorporated by reference herein also contain estimates and other statistical data made by independent parties and by us relating to market size and growth and other data about our industry.

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This data involves a number of assumptions and limitations, and you are cautioned not to give undue weight to such estimates. In addition, projections, assumptions and estimates of our future performance and the future performance of the markets in which we operate are necessarily subject to a high degree of uncertainty and risk.

In some cases, you can identify forward-looking statements by words such as “believe,” “may,” “will,” “estimate,” “continue,” “anticipate,” “intend,” “could,” “would,” “project,” “predict,” “plan,” “expect” or the negative or plural of these words or similar expressions. The forward-looking statements in this prospectus and the documents incorporated by reference herein are only predictions. We have based these forward-looking statements largely on our current expectations and projections about future events and financial trends that we believe may affect our business, financial condition and results of operations. These forward-looking statements speak only as of the date of this prospectus and are subject to a number of risks, uncertainties and assumptions, including those under the heading “Risk Factors” in this prospectus and in the documents incorporated by reference herein, and elsewhere in this prospectus. The events and circumstances reflected in our forward-looking statements may not be achieved or occur and actual results could differ materially from those projected in the forward-looking statements. Moreover, we operate in an evolving environment. New risk factors and uncertainties may emerge from time to time, and it is not possible for management to predict all risk factors and uncertainties. Except as required by applicable law, we do not plan to publicly update or revise any forward-looking statements contained in this prospectus or the documents incorporated by reference herein, whether as a result of any new information, future events, changed circumstances or otherwise.

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USE OF PROCEEDS

We may issue and sell shares of our common stock having aggregate sales proceeds of up to $23,011,805 from time to time. Because there is no minimum offering amount required as a condition to close this offering, the actual total public offering amount, commissions and proceeds to us, if any, are not determinable at this time. There can be no assurance that we will sell any additional shares under or fully utilize the Sales Agreement with TD Cowen as a source of financing.

We currently intend to use the net proceeds from this offering primarily for working capital and general corporate purposes, including research, development and manufacturing of our product candidates. Pending our use of our net proceeds from this offering, we intend to invest the net proceeds in a variety of capital preservation investments, including short-term, investment-grade, and interest-bearing debt securities.

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DESCRIPTION OF CAPITAL STOCK

As of the date of this prospectus, our authorized capital stock consists of 500,000,000 shares of common stock, $0.0001 par value, and 20,000,000 shares of preferred stock, $0.0001 par value. A description of material terms and provisions of our amended and restated certificate of incorporation (Certificate of Incorporation) and third amended and restated bylaws (Bylaws) affecting the rights of holders of our capital stock is set forth below. The description is intended as a summary, and is qualified in its entirety by reference to our Certificate of Incorporation and our Bylaws.

Common Stock

The holders of common stock are entitled to one vote per share on all matters to be voted on by the stockholders. Subject to the preferences of any outstanding shares of preferred stock, the holders of common stock are entitled to receive ratably any dividends our board of directors declares out of funds legally available for the payment of dividends. If we are liquidated, dissolved or wound up, the holders of common stock are entitled to share pro rata all assets remaining after payment of liabilities and liquidation preferences of any outstanding shares of preferred stock. Holders of common stock have no preemptive rights or rights to convert their common stock into any other securities. There are no redemption or sinking fund provisions applicable to the common stock. When we issue shares of common stock under this prospectus, the shares will be fully paid and nonassessable.

Additional shares of authorized common stock may be issued, as authorized by our board of directors from time to time, without stockholder approval, except as may be required by applicable stock exchange requirements.

Preferred Stock

Our board of directors is authorized, subject to limitations prescribed by Delaware law, to issue preferred stock in one or more series, to establish from time to time the number of shares to be included in each series and to fix the designation, powers, preferences and rights of the shares of each series and any of its qualifications, limitations or restrictions. Our board of directors can also increase or decrease the number of shares of any series, but not below the number of shares of that series then outstanding, without any further vote or action by our stockholders. Our board of directors may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of the common stock. The issuance of preferred stock, while providing flexibility in connection with financings, possible acquisitions and other corporate purposes, could, among other things, have the effect of delaying, deferring, discouraging or preventing a change in control of our company, may adversely affect the market price of our common stock and the voting and other rights of the holders of common stock, and may reduce the likelihood that common stockholders will receive dividend payments and payments upon liquidation.

We will fix the designations, voting powers, preferences and rights of the preferred stock of each series we issue under this prospectus, as well as the qualifications, limitations or restrictions thereof, in the certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that contains the terms of the series of preferred stock we are offering. We will describe in the applicable prospectus supplement the terms of the series of preferred stock being offered, including, to the extent applicable:

•

the title and stated value;

​

•

the number of shares we are offering;

​

•

the liquidation preference per share;

​

•

the purchase price per share;

​

•

the dividend rate per share, dividend period and payment dates and method of calculation for dividends;

​

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•

whether dividends will be cumulative or non-cumulative and, if cumulative, the date from which dividends will accumulate;

​

•

our right, if any, to defer payment of dividends and the maximum length of any such deferral period;

​

•

the procedures for any auction and remarketing, if any;

​

•

the provisions for a sinking fund, if any;

​

•

the provisions for redemption or repurchase, if applicable, and any restrictions on our ability to exercise those redemption and repurchase rights;

​

•

any listing of the preferred stock on any securities exchange or market;

​

•

whether the preferred stock will be convertible into our common stock or other securities of ours, including warrants, and, if applicable, the conversion period, the conversion price, or how it will be calculated, and under what circumstances it may be adjusted;

​

•

whether the preferred stock will be exchangeable for debt securities, and, if applicable, the exchange period, the exchange price, or how it will be calculated, and under what circumstances it may be adjusted;

​

•

voting rights, if any, of the preferred stock;

​

•

preemption rights, if any;

​

•

restrictions on transfer, sale or other assignment, if any;

​

•

a discussion of any material or special United States federal income tax considerations applicable to the preferred stock;

​

•

the relative ranking and preferences of the preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs;

​

•

any limitations on issuances of any class or series of preferred stock ranking senior to or on a parity with the series of preferred stock being issued as to dividend rights and rights if we liquidate, dissolve or wind up our affairs; and

​

•

any other specific terms, rights, preferences, privileges, qualifications or restrictions of the preferred stock.

​

When we issue shares of preferred stock under this prospectus, the shares will be fully paid and nonassessable.

Unless we specify otherwise in the applicable prospectus supplement, the preferred stock will rank, with respect to dividends and upon our liquidation, dissolution or winding up:

•

senior to all classes or series of our common stock and to all of our equity securities ranking junior to the preferred stock;

​

•

on a parity with all of our equity securities the terms of which specifically provide that the equity securities rank on a parity with the preferred stock; and

​

•

junior to all of our equity securities the terms of which specifically provide that the equity securities rank senior to the preferred stock.

​

The term “equity securities” does not include convertible debt securities.

The General Corporation Law of the State of Delaware, the state of our incorporation, provides that the holders of preferred stock will have the right to vote separately as a class on any proposal involving fundamental changes in the rights of holders of that preferred stock. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.

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Antitakeover Effects of Provisions of Charter Documents and Delaware Law

Amended and Restated Certificate of Incorporation and Third Amended and Restated Bylaws

Because our stockholders do not have cumulative voting rights, our stockholders holding a majority of the voting power of our shares of common stock outstanding will be able to elect all of our directors. Our Certificate of Incorporation and Bylaws provide that all stockholder actions must be effected at a duly called meeting of stockholders and not by written consent. A special meeting of stockholders may be called by the majority of our board of directors, our chief executive officer or the chair of our board of directors.

Our Certificate of Incorporation provides for our board of directors to be divided into three classes, with staggered three-year terms. As a result, only one class of directors will be elected at each annual meeting of stockholders, with the other classes continuing for the remainder of their respective three-year terms. Stockholders have no cumulative voting rights, and the stockholders representing a majority of the shares of common stock entitled to vote in any election of directors may elect all of the directors standing for election.

Our Certificate of Incorporation further provides that the affirmative vote of holders of at least sixty-six and two-thirds percent (66-2/3%) of the voting power of all of the then outstanding shares of voting stock entitled to vote generally in the election of directors, voting as a single class, will be required to amend certain provisions of our Certificate of Incorporation, including provisions relating to the size of the board, removal of directors, special meetings and actions by written consent. The affirmative vote of holders of at least sixty-six and two-thirds percent (66-2/3%) of the voting power of all of the then outstanding shares of voting stock entitled to vote generally in the election of directors, voting as a single class, will be required to amend or repeal our Bylaws, although our Bylaws may be amended by a simple majority vote of our board of directors.

The foregoing provisions will make it more difficult for our existing stockholders to replace our board of directors as well as for another party to obtain control of us by replacing our board of directors. Since our board of directors has the power to retain and discharge our officers, these provisions could also make it more difficult for existing stockholders or another party to effect a change in management. In addition, the authorization of undesignated preferred stock makes it possible for our board of directors to issue preferred stock with voting or other rights or preferences that could impede the success of any attempt to change our control.

These provisions are intended to enhance the likelihood of continued stability in the composition of our board of directors and its policies and to discourage certain types of transactions that may involve an actual or threatened acquisition of us. These provisions are also designed to reduce our vulnerability to an unsolicited acquisition proposal and to discourage certain tactics that may be used in proxy fights. However, such provisions could have the effect of discouraging others from making tender offers for our shares and may have the effect of deterring hostile takeovers or delaying changes in our control or management. As a consequence, these provisions also may inhibit fluctuations in the market price of our stock that could result from actual or rumored takeover attempts.

Section 203 of the Delaware General Corporation Law

We are subject to Section 203 of the Delaware General Corporation Law, or the DGCL, which prohibits a Delaware corporation from engaging in any business combination with any interested stockholder for a period of three years after the date that such stockholder became an interested stockholder, with the following exceptions:

•

before such date, the board of directors of the corporation approved either the business combination or the transaction that resulted in the stockholder becoming an interested stockholder;

​

•

upon closing of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction began, excluding for purposes of determining the voting stock outstanding (but not the outstanding voting stock owned by the interested stockholder) those shares owned by (1) persons who are directors and also officers and (2) employee stock plans in which employee

​

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participants do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer; or

•

on or after such date, the business combination is approved by the board of directors and authorized at an annual or special meeting of the stockholders, and not by written consent, by the affirmative vote of at least 662∕3% of the outstanding voting stock that is not owned by the interested stockholder.

​

In general, Section 203 defines business combination to include the following:

•

any merger or consolidation involving the corporation and the interested stockholder;

​

•

any sale, transfer, pledge or other disposition of 10% or more of the assets of the corporation involving the interested stockholder;

​

•

subject to certain exceptions, any transaction that results in the issuance or transfer by the corporation of any stock of the corporation to the interested stockholder;

​

•

any transaction involving the corporation that has the effect of increasing the proportionate share of the stock or any class or series of the corporation beneficially owned by the interested stockholder; or

​

•

the receipt by the interested stockholder of the benefit of any loans, advances, guarantees, pledges or other financial benefits by or through the corporation.

​

In general, Section 203 defines an “interested stockholder” as an entity or person who, together with the person’s affiliates and associates, beneficially owns, or within three years prior to the time of determination of interested stockholder status did own, 15% or more of the outstanding voting stock of the corporation.

Choice of Forum

Our Bylaws provide that, unless a majority of our board of directors consents in writing to an alternative forum, the Court of Chancery of the State of Delaware will be the exclusive forum for (i) any derivative action or proceeding brought on behalf of us under Delaware law, (ii) any action asserting a claim of breach of a fiduciary duty owed by any current or former director, officer, or other employee of the Company to us or our stockholders, (iii) any action asserting a claim against us or any of our directors, officers, or other employees arising pursuant to any provision of the DGCL or our Certificate of Incorporation or Bylaws (as either may be amended from time to time), (iv) any action asserting a claim against us or any director or officer or other employee of the Company governed by the internal affairs doctrine, or (v) any other action asserting an “internal corporate claim,” as defined under Section 115 of the DGCL. The foregoing provisions do not apply to any claims arising under the Securities Act and, unless we consent in writing to the selection of an alternative forum, the federal district courts of the United States will be the sole and exclusive forum for resolving any action asserting a claim arising under the Securities Act.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A. The transfer agent and registrar’s address is 250 Royall Street, Canton, Massachusetts 02021.

Listing on the Nasdaq Global Select Market

Our common stock is listed on the Nasdaq Global Select Market under the symbol “ATRA”.

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DILUTION

Dilution is the amount by which the price paid by the purchasers of the shares of common stock sold in the offering exceeds the net tangible book value per share of common stock after the offering. Net tangible book value per share is determined by subtracting our total liabilities from the total book value of our tangible assets and dividing the difference by the number of shares of common stock deemed to be outstanding at that date.

Our historical net tangible book value as of September 30, 2026 was $(37.9) million, or $(3.72) per share.

After giving effect to the sale of 2,923,990 shares of common stock in this offering at the assumed public offering price of $7.87 per share, which is the last reported sale price of our common stock on the Nasdaq Global Select Market on November 6, 2026, after deducting estimated offering commissions and offering expenses payable by us, our as adjusted net tangible book value as of September 30, 2026 would have been $(15.8) million, or $(1.21) per share. This represents an immediate increase in as adjusted net tangible book value of $2.51 per share to our existing stockholders and immediate dilution of $9.08 per share to new investors purchasing common stock in this offering.

The following table illustrates this dilution on a per share basis:

​

Assumed public offering price per share

​

​

​

​

​

​

​

​

​

$

7.87

​

​

​

Historical net tangible book value per share as of September 30, 2026

​

​

​

$

(3.72)

​

​

​

​

​

​

​

​

​

Increase per share attributable to new investors

​

​

​

​

2.51

​

​

​

​

​

​

​

​

​

As adjusted net tangible book value per share after giving effect to this offering

​

​

​

​

​

​

​

​

​

​

(1.21)

​

​

​

Dilution in adjusted net tangible book value per share to new investors

​

​

​

​

​

​

​

​

​

$

9.08

​

​

The outstanding share information in the table above is based on 35,601,398 shares of our common stock outstanding as of September 30, 2026 and excludes as of that date:

•

57,507 shares of common stock issuable upon the exercise of outstanding stock options with a weighted-average exercise price of $173,519 per share;

​

•

336,618 shares of common stock available for grant under our 2024 Equity Incentive Plan;

​

•

20,738 shares of common stock reserved for issuance under our 2014 Employee Stock Purchase Plan;

​

•

338,217 shares of common stock issuable upon the settlement of outstanding restricted stock units;

​

•

141,763 shares of common stock available for grant under our 2018 Inducement Plan; and

​

•

5,233,873 shares of common stock issuable upon the exercise of outstanding pre-funded warrants with exercise prices of $0.0001 or $0.0025 per share.

​

To the extent that options or pre-funded warrants are exercised, new options are issued under our equity incentive plans, or we issue additional shares of common stock in the future, there will be further dilution to investors participating in this offering.

The table and discussion above assume for illustrative purposes that an aggregate of 2,923,990 in shares of our common stock are sold under this prospectus at a price of $7.87 per share, the last reported sale price of our common stock on The Nasdaq Global Select Market on November 6, 2026, for aggregate gross proceeds of $23,011,805. The shares subject to the Sales Agreement with TD Cowen are being sold from time to time at various prices. An increase of $1.00 per share in the price at which the shares are sold from the assumed offering price of $7.87 per share shown in the table above, assuming all of our common stock in the aggregate amount of $23,011,805 under this prospectus is sold at that price, would increase our adjusted net tangible book value per share after the offering to $(1.24) per share and would increase the dilution in net tangible book value per share to new investors in this offering to $10.11 per share, after deducting commissions and estimated aggregate offering expenses payable by us. A decrease of $1.00 per share in the price at which the shares are sold from the assumed offering price of $7.87 per share shown in the

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table above, assuming all of our common stock in the aggregate amount of $23,011,805 under this prospectus is sold at that price, would decrease our adjusted net tangible book value per share after the offering to $(1.17) per share and would decrease the dilution in net tangible book value per share to new investors in this offering to $8.04 per share, after deducting commissions and estimated aggregate offering expenses payable by us. This information is supplied for illustrative purposes only.

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PLAN OF DISTRIBUTION

We have entered into the Sales Agreement with TD Cowen, under which we may issue and sell from time to time shares of our common stock under this prospectus through or to TD Cowen as our sales agent or principal. Pursuant to this prospectus and the accompanying base prospectus, we may offer and sell shares of our common stock having an aggregate offering price of up to $23,011,805. Sales of our common stock, if any, will be made by any method permitted by law, including, without limitation an “at the market offering” as defined in Rule 415 under the Securities Act, sales made by means of ordinary brokers’ transactions, or sales made to or through a market maker at market prices prevailing at the time of sale, at prices related to the prevailing market prices or at negotiated prices and subject to certain limitations in and compliance with the conditions of the Sales Agreement. In addition, our common stock may be offered and sold by such other methods, including privately negotiated transactions (including block trades and block sales) in compliance with the terms of the Sales Agreement. Sales pursuant to the Sales Agreement may be made through an affiliate of TD Cowen.

TD Cowen will offer our common stock subject to the terms and conditions of the Sales Agreement on a daily basis or as otherwise agreed upon by us and TD Cowen. We will designate the maximum amount of common stock to be sold through TD Cowen on a daily basis or otherwise determine such maximum amount together with TD Cowen. Subject to the terms and conditions of the Sales Agreement, TD Cowen will use its commercially reasonable efforts to sell on our behalf all of the shares of common stock requested to be sold by us. We may instruct TD Cowen not to sell common stock if the sales cannot be effected at or above the price designated by us in any such instruction. TD Cowen or we may suspend the offering of our common stock being made through TD Cowen under the Sales Agreement upon proper notice to the other party. TD Cowen and we each have the right, by giving written notice as specified in the Sales Agreement, to terminate the Sales Agreement in each party’s sole discretion at any time.

The aggregate compensation payable to TD Cowen as sales agent equals 3.0% of the gross sales price of the shares sold through it pursuant to the Sales Agreement. We have also agreed to reimburse TD Cowen up to $75,000 of the actual outside legal expenses incurred by TD Cowen. We estimate that the total expenses of the offering payable by us, excluding commissions payable to TD Cowen under the Sales Agreement, will be approximately $350,000.

The remaining sales proceeds, after deducting any expenses payable by us and any transaction fees imposed by any governmental, regulatory or self-regulatory organization in connection with the sales, will equal our net proceeds for the sale of such common stock.

TD Cowen will provide written confirmation to us following the close of trading on The Nasdaq Global Select Market on each day in which common stock is sold through it as sales agent under the Sales Agreement. Each confirmation will include the number of shares of common stock sold through it as sales agent on that day, the volume weighted average price of the shares sold, the percentage of the daily trading volume and the net proceeds to us.

We will report at least quarterly the number of shares of common stock sold through TD Cowen under the Sales Agreement, the net proceeds to us in connection with the sales of common stock.

Settlement for sales of common stock will occur, unless the parties agree otherwise, on the first business day that is also a trading day following the date on which any sales were made in return for payment of the net proceeds to us. There is no arrangement for funds to be received in an escrow, trust or similar arrangement.

In connection with the sales of our common stock on our behalf, TD Cowen may be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation paid to TD Cowen may be deemed to be underwriting commissions or discounts. We have agreed in the Sales Agreement to provide indemnification and contribution to TD Cowen against certain liabilities, including liabilities under the Securities Act. As sales agent, TD Cowen will not engage in any transactions that stabilize our common stock.

This summary of the material provisions of the Sales Agreement does not purport to be a complete statement of its terms and conditions. A copy of the Sales Agreement is filed as an exhibit to our Current Report on Form 8-K filed with the SEC on November 1, 2023 and incorporated by reference in this prospectus.

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Our common stock is listed on the Nasdaq Global Select Market and trades under the symbol “ATRA”. The transfer agent of our common stock is Computershare Trust Company, N.A. The transfer agent’s address is 250 Royall Street, Canton, Massachusetts 02021.

TD Cowen and/or its affiliates have provided, and may in the future provide, various investment banking, commercial banking and other financial services for us and our affiliates for which they have received, and may in the future receive customary fees. TD Cowen and certain of its affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing and brokerage activities. In the ordinary course of their various business activities, TD Cowen and certain its affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers, and such investment and securities activities may involve securities and/or instruments of the issuer or its affiliates. TD Cowen and certain of its affiliates may also communicate independent investment recommendations, market color or trading ideas and/or publish or express independent research views in respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

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LEGAL MATTERS

Sidley Austin LLP is serving as our counsel in this offering. Paul Hastings LLP is counsel for TD Cowen in connection with this offering.

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EXPERTS

The consolidated financial statements of Atara Biotherapeutics, Inc. incorporated by reference in this Prospectus have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report. Such consolidated financial statements are incorporated by reference in reliance upon the report of such firm, given their authority as experts in accounting and auditing.

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WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and other reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC’s website at http://www.sec.gov. The SEC website referenced above also contains reports, proxy statements, and other information about issuers, like us, that file electronically with the SEC.

Our Annual Report on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, including any amendments to those reports, and other information that we file with or furnish to the SEC pursuant to Section 13(a) or 15(d) of the Exchange Act can also be accessed free of charge on the Investor section of our website, which is located at investors.atarabio.com. These filings will be available as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC. The information contained in, or that can be accessed through, our website is not incorporated by reference into this prospectus.

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INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information from other documents that we file with it, which means that we can disclose important information to you by referring you to those documents instead of having to repeat the information in this prospectus. The information incorporated by reference is considered to be part of this prospectus, and later information that we file with the SEC will automatically update and supersede this information. We incorporate by reference the documents listed below and any future filings we will make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, after the date of the prospectus (other than information furnished under Item 2.02 or Item 7.01 of Form 8-K) and before the sale of all the securities covered by this prospectus:

•

our Annual Report on Form 10-K for the year ended December 31, 2025 filed with the SEC on March 16, 2026;

​

•

the information specifically incorporated by reference into our Annual Report on Form 10-K for the year ended December 31, 2025 from our Definitive Proxy Statement on Schedule 14A filed with the SEC on April 24, 2026;

​

•

our Quarterly Report on Form 10-Q for the quarter ended March 31, 2026 filed with the SEC on May 12, 2026;

​

•

our Quarterly Report on Form 10-Q for the quarter ended June 30, 2026 filed with the SEC on August 12, 2026;

​

•

our Quarterly Report on Form 10-Q for the quarter ended September 30, 2026 filed with the SEC on November 10, 2026;

​

•

our Current Reports on Form 8-K filed with the SEC on January 2, 2026, January 12, 2026 (solely with respect to Items 8.01 and 9.01), February 23, 2026, March 3, 2026, March 12, 2026, May 1, 2026, May 7, 2026, June 12, 2026 and June 26, 2026; and

​

•

the description of our common stock contained in our registration statement on Form 8-A filed with the SEC on July 16, 2014, including any amendments or reports filed for the purposes of updating this description, including Exhibit 4.8 to our Annual Report on Form 10-K for the year ended December 31, 2025 filed with the SEC on March 16, 2026 and any further amendments or reports filed for the purpose of updating such description.

​

We will provide to each person, including any beneficial owner, to whom a prospectus is delivered, without charge upon the written or oral request, a copy of any or all of the documents that are incorporated by reference into this prospectus but not delivered with the prospectus, including exhibits that are specifically incorporated by reference into such documents. Requests for such copies should be directed to us at the following address:

Atara Biotherapeutics, Inc.
Attn: Investor Relations
1280 Rancho Conejo Boulevard
Thousand Oaks, California 91320
Telephone: (805) 623-4211

Exhibits to the filings will not be sent, however, unless those exhibits have specifically been incorporated by reference in this prospectus.

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​

​

$23,011,805

Common Stock

​

PROSPECTUS

​

TD Securities (USA) LLC

​

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PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14.   Other Expenses of Issuance and Distribution

The following table sets forth an estimate of the fees and expenses, other than the underwriting discounts and commissions, payable by us in connection with the issuance and distribution of the securities being registered. All the amounts shown are estimates.

​	​	​	Amount				​
SEC registration fee	​	​	​	$	29,520(1)	​	​
FINRA filing fee	​	​	​	$	3,952	​	​
The Nasdaq Global Select Market listing fee	​	​	​	​	​ (2)	​	​
Accounting fees and expenses	​	​	​	​	​ (2)	​	​
Legal fees and expenses	​	​	​	​	​ (2)	​	​
Transfer agent and registrar fees and expenses	​	​	​	​	​ (2)	​	​
Trustee fees and expenses	​	​	​	​	​ (2)	​	​
Blue sky fees and expenses (including legal fees)	​	​	​	​	​ (2)	​	​
Printing and miscellaneous fees and expenses	​	​	​	​	​ (2)	​	​
Total	​	​	​	$	(2)	​	​

​

(1)

In accordance with Rule 415(a)(6), includes certain fees previously paid in respect of Unsold Securities previously registered under the registrant’s registration statement on Form S-3 (File No. 333-275256), as further described in the Filing Fee Table included as Exhibit 107 hereto.

​

(2)

The amount of securities and number of offerings are indeterminable and the expenses cannot be estimated at this time. An estimate of the aggregate expenses in connection with the sale and distribution of securities being offered will be included in the applicable prospectus supplement.

​

Item 15.   Indemnification of Directors and Officers

Section 145 of the Delaware General Corporation Law authorizes a court to award, or a corporation’s board of directors to grant, indemnity to directors and officers in terms sufficiently broad to permit such indemnification under certain circumstances for liabilities, including reimbursement for expenses incurred, arising under the Securities Act.

As permitted by the Delaware General Corporation Law, the Registrant’s Certificate of Incorporation provides that the liability of the directors for monetary damages shall be eliminated to the fullest extent under applicable law. If the Delaware General Corporation Law is amended to authorize corporate action further eliminating or limiting the personal liability of directors, then the liability of a director of the Registrant shall be eliminated to the fullest extent permitted by the Delaware General Corporation Law, as so amended. Under the Delaware General Corporation Law, no director will be personally liable to the Registrant or the Registrant’s stockholders for monetary damages for breach of fiduciary duty as a director, except for liability:

•

for any breach of the duty of loyalty to the Registrant or the Registrant’s stockholders;

​

•

for acts or omissions not in good faith or that involve intentional misconduct or a knowing violation of law;

​

•

for unlawful payment of dividends or unlawful stock repurchases or redemptions under Section 174 of the Delaware General Corporation Law; or

​

•

for any transaction from which the director derived an improper personal benefit.

​

As permitted by the Delaware General Corporation Law, the Registrant’s Bylaws provide that:

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•

the Registrant is required to indemnify the Registrant’s directors and executive officers to the fullest extent not prohibited by Delaware law, subject to limited exceptions;

​

•

the Registrant may indemnify the Registrant’s other officers, employees and agents as set forth in the Delaware General Corporation Law;

​

•

the Registrant is required to advance expenses to the Registrant’s directors and executive officers as incurred in connection with legal proceedings against them for which they may be indemnified, against an undertaking by the indemnified party to repay such advances if it is ultimately determined that the indemnified party is not entitled to indemnification; and

​

•

the rights conferred in the Bylaws are not exclusive.

​

The Registrant has entered into indemnification agreements with each of the Registrant’s directors and executive officers that require the Registrant to indemnify these persons against all direct and indirect costs of any type or nature whatsoever, including attorney’s fees, witness fees, and other out of pocket costs of whatever nature, incurred by the director or officer in any action or proceeding, whether actual, pending or threatened, subject to certain limitations, to which any of these people may be made a party by reason of the fact that he or she is or was a director or an executive officer of the Registrant or is or was serving or at any time serves at the request of the Registrant as a director, officer, employee or other agent of another corporation, partnership, joint venture, trust, employee benefit plan or other enterprise.

The Registrant has purchased insurance on behalf of any person who is or was a director or officer of the Registrant against any loss arising from any claim asserted against him or her and incurred by him or her in any such capacity, subject to certain exclusions.

The underwriting agreement that the Registrant may enter into (Exhibit 1.1) may provide for indemnification by any underwriters of the Registrant, its directors, its officers who sign the registration statement and the registrant’s controlling persons for some liabilities, including liabilities arising under the Securities Act.

Item 16.   Exhibits

​

​

​

​

​

​

​

Incorporation By Reference

​

​

Filed Herewith

​

​

Exhibit

​

​

Description

​

​

Form

​

​

SEC File No.

​

​

Exhibit

​

​

Filing Date

​

​

1.1*

​

​

Form of Underwriting Agreement

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

1.2

​

​

Sales Agreement, dated November 1, 2023, by and between Atara Biotherapeutics, Inc. and Cowen and Company, LLC

​

​

8-K

​

​

001-36548

​

​

1.1

​

​

11/1/2023

​

​

​

​

​

3.1

​

​

Amended and Restated Certificate of Incorporation

​

​

S-1

​

​

333-196936

​

​

3.2

​

​

6/20/2014

​

​

​

​

​

3.2

​

​

Certificate of Amendment of Amended and Restated Certificate of Incorporation of Atara Biotherapeutics, Inc.

​

​

8-K

​

​

001-36548

​

​

3.1

​

​

6/20/2024

​

​

​

​

​

3.3

​

​

Third Amended and Restated Bylaws

​

​

8-K

​

​

001-36548

​

​

3.1

​

​

12/23/2024

​

​

​

​

​

4.1

​

​

Form of Common Stock Certificate of the Registrant

​

​

S-1/A

​

​

333-196936

​

​

4.1

​

​

7/10/2014

​

​

​

​

​

4.2*

​

​

Specimen Preferred Stock Certificate and Form of Certificate of Designation of Preferred Stock

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

4.3

​

​

Form of Indenture

​

​

S-3

​

​

333-253731

​

​

4.3

​

​

3/1/2021

​

​

​

​

​

4.4*

​

​

Form of Debt Securities

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​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

4.5

​

​

Form of Common Stock Warrant Agreement and Warrant Certificate

​

​

S-3

​

​

333-253731

​

​

4.5

​

​

3/1/2021

​

​

​

​

​

4.6

​

​

Form of Preferred Stock Warrant Agreement and Warrant Certificate

​

​

S-3

​

​

333-253731

​

​

4.6

​

​

3/1/2021

​

​

​

​

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​

​

​

​

​

​

Incorporation By Reference

​

​

Filed Herewith

​

​

Exhibit

​

​

Description

​

​

Form

​

​

SEC File No.

​

​

Exhibit

​

​

Filing Date

​

​

4.7

​

​

Form of Debt Securities Warrant Agreement and Warrant Certificate

​

​

S-3

​

​

333-253731

​

​

4.7

​

​

3/1/2021

​

​

​

​

​

4.8*

​

​

Form(s) of Rights Agreement(s) (including form(s) of Rights)

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

5.1

​

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Opinion of Sidley Austin LLP

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​

​

​

​

​

​

​

​

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​

X

​

​

23.1

​

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Consent of Independent Registered Public Accounting Firm

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​

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​

​

​

​

​

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X

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​

23.2

​

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Consent of Sidley Austin LLP (See Exhibit 5.1)

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​

​

​

​

​

​

​

​

​

​

​

​

​

X

​

​

24.1

​

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Power of Attorney (see signature page hereto)

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​

​

​

​

​

​

​

​

​

​

​

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X

​

​

25.1**

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Statement of Eligibility of Trustee under the Debt Indenture

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​

​

107

​

​

Calculation of Filing Fee Table

​

​

​

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​

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​

​

​

​

​

​

​

​

X

​

​

*

To be filed by amendment or as an exhibit to a Current Report on Form 8-K and incorporated herein by reference, if applicable.

​

**

To be filed in accordance with the requirements of Section 305(b)(2) of the Trust Indenture Act of 1939, as amended, and the applicable rules thereunder, if applicable.

​

Item 17.   Undertakings

(a)   The undersigned registrant hereby undertakes:

(1)   To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

(i)   To include any prospectus required by Section 10(a)(3) of the Securities Act of 1933;

(ii)   To reflect in the prospectus any facts or events arising after the effective date of the registration statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the registration statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than 20% change in the maximum aggregate offering price set forth in the “Calculation of Filing Fee Tables” or “Calculation of Registration Fee” table, as applicable, in the effective registration statement;

(iii)   To include any material information with respect to the plan of distribution not previously disclosed in the registration statement or any material change to such information in the registration statement;

provided, however, that paragraphs (a)(1)(i), (ii), and (iii) do not apply if the registration statement is on Form S-3 and the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the Commission by the registrant pursuant to Section 13 or Section 15(d) of the Securities Exchange Act of 1934 that are incorporated by reference in the registration statement, or, as to a registration statement on Form S-3, is contained in a form of prospectus filed pursuant to Rule 424(b) of the Securities Act of 1933 that is part of the registration statement.

(2)   That, for the purpose of determining any liability under the Securities Act of 1933, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

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(3)   To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

(4)   That, for the purpose of determining liability under the Securities Act of 1933 to any purchaser:

(i)   Each prospectus filed by the registrant pursuant to Rule 424(b)(3) shall be deemed to be part of the registration statement as of the date the filed prospectus was deemed part of and included in the registration statement; and

(ii)   Each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5), or (b)(7) as part of a registration statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(1)(i), (vii), or (x) for the purpose of providing the information required by section 10(a) of the Securities Act of 1933 shall be deemed to be part of and included in the registration statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule 430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the registration statement relating to the securities in the registration statement to which that prospectus relates, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof. Provided, however, that no statement made in a registration statement or prospectus that is part of the registration statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such effective date, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such effective date.

(5)   That, for the purpose of determining liability of the registrant under the Securities Act of 1933 to any purchaser in the initial distribution of the securities, the undersigned registrant undertakes that in a primary offering of securities of the undersigned registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

(i)   Any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424;

(ii)   Any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant;

(iii)   The portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and

(iv)   Any other communication that is an offer in the offering made by the undersigned registrant to the purchaser.

(b)   The undersigned registrant hereby undertakes that, for purposes of determining any liability under the Securities Act of 1933, each filing of the registrant’s annual report pursuant to section 13(a) or section 15(d) of the Securities Exchange Act of 1934 (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to section 15(d) of the Securities Exchange Act of 1934) that is incorporated by reference in the registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(c)   Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that in the opinion of the Securities and Exchange Commission

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such indemnification is against public policy as expressed in the Securities Act of 1933 and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act of 1933 and will be governed by the final adjudication of such issue.

(d)   The undersigned registrant hereby undertakes to file an application for the purpose of determining the eligibility of the trustee to act under subsection (a) of section 310 of the Trust Indenture Act (Act) in accordance with the rules and regulations prescribed by the Commission under section 305(b)(2) of the Act.

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SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Thousand Oaks, State of California, on November 10, 2026.

​	​	​	​	ATARA BIOTHERAPEUTICS, INC.	​
​	Date: November 10, 2026	​	​	By: /s/ AnhCo Thieu Nguyen ​ ​ AnhCo Thieu Nguyen President and Chief Executive Officer	​

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints AnhCo Thieu Nguyen and Kevin G. Sarney and each of them, as his or her true and lawful attorneys-in-fact and agents, each with the full power of substitution, for him or her and in his or her name, place or stead, in any and all capacities, to sign any and all amendments to this Registration Statement (including post-effective amendments), and to sign any registration statement for the same offering covered by this Registration Statement that is to be effective upon filing pursuant to Rule 462(b) promulgated under the Securities Act, and all post-effective amendments thereto, and to file the same, with exhibits thereto and other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or their, his or her substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed below by the following persons in the capacities and on the dates indicated.

​	Signature	​	​	Title	​	​	Date	​
​	/s/ AnhCo Thieu Nguyen ​ AnhCo Thieu Nguyen	​	​	President, Chief Executive Officer and Director (principal executive officer)	​	​	November 10, 2026	​
​	/s/ Kevin G. Sarney ​ Kevin G. Sarney	​	​	Interim Chief Financial Officer (duly authorized officer and principal financial and accounting officer)	​	​	November 10, 2026	​
​	/s/ Gregory Ciongoli ​ Gregory Ciongoli	​	​	Director, Chair	​	​	November 10, 2026	​
​	/s/ Brian Cherry ​ Brian Cherry	​	​	Director	​	​	November 10, 2026	​
​	/s/ Matthew K. Fust ​ Matthew K. Fust	​	​	Director	​	​	November 10, 2026	​
​	/s/ William K. Heiden ​ William K. Heiden	​	​	Director	​	​	November 10, 2026	​

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​	Signature	​	​	Title	​	​	Date	​
​	/s/ James Huang ​ James Huang	​	​	Director	​	​	November 10, 2026	​
​	/s/ Nachi Subramanian ​ Nachi Subramanian	​	​	Director	​	​	November 10, 2026	​

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