Redmile reports 9.9% stake in Atara Biotherapeutics

Redmile Group and related entities updated their ownership disclosure for Atara Biotherapeutics.

Rhea-AI Filing Summary

Redmile Group and related entities updated their ownership disclosure for Atara Biotherapeutics. They report beneficial ownership of 950,994 shares of common stock, representing 9.9% of the class, including shares issuable from pre-funded warrants subject to a 9.99% Beneficial Ownership Limitation.

The filing explains that this increase in deemed beneficial ownership results from a higher number of Atara shares outstanding, which raised the maximum shares issuable upon warrant exercise. Redmile-managed funds directly hold 441,701 common shares and 3,412,843 pre-funded warrants, of which 509,293 shares are currently counted toward beneficial ownership under the limitation.

Key Figures

Beneficial ownership: 950,994 shares Ownership percentage: 9.9% RBI II holdings: 651,924 shares +5 more

8 metrics

Beneficial ownership 950,994 shares Shares of Atara common stock beneficially owned by each of Redmile and Jeremy C. Green

Ownership percentage 9.9% Percent of Atara common stock class represented by 950,994 shares

RBI II holdings 651,924 shares Atara shares beneficially owned by Redmile Biopharma Investments II, L.P. (6.9% of class)

Redmile Long Only holdings 576,148 shares Atara shares beneficially owned by Redmile Strategic Long Only Trading Sub, Ltd. (6.1% of class)

Direct common shares 441,701 shares Atara common stock held by Redmile Funds before considering warrants

Warrant shares counted 509,293 shares Atara shares issuable upon exercise of warrants currently included under Beneficial Ownership Limitation

Total pre-funded warrants 3,412,843 warrants Pre-funded warrants to purchase Atara common stock held by Redmile Funds

Shares outstanding baseline 9,010,172 shares Atara common stock outstanding as of May 8, 2026, used for ownership calculations

Key Terms

Beneficial Ownership Limitation, pre-funded warrants, shared voting power, Schedule 13D, +1 more

5 terms

Beneficial Ownership Limitation financial

"under the 9.99% beneficial ownership limitation (the "Beneficial Ownership Limitation")."

A beneficial ownership limitation is a rule that caps the percentage of a company’s shares an investor can be treated as owning or controlling for voting, regulatory or tax purposes. It matters to investors because it can restrict how many shares a person or group can buy or vote, affect takeover chances, and influence share liquidity and value — like a speed limit that prevents any single driver from taking over the whole road.

pre-funded warrants financial

"certain pre-funded warrants to purchase Common Stock (the "Warrants")"

Pre-funded warrants are financial instruments that give investors the right to purchase a company's stock at a set price, but with most or all of the purchase price paid upfront. They function like a coupon or gift card for stock, allowing investors to buy shares later at a fixed price, which can be beneficial if they want to avoid future price increases. This makes them important for investors seeking flexibility and certainty in their investment plans.

shared voting power financial

"Shared Voting Power 950,994.00"

Shared voting power occurs when two or more parties jointly have the right to vote or decide how a block of company shares is cast, like co-owners who must agree before moving a piece of furniture. Investors care because who controls voting rights affects board elections, major corporate decisions and takeover outcomes, and shared control can alter regulatory disclosures and the practical influence any holder has over a company’s direction and value.

Schedule 13D regulatory

"previously filed a statement on Schedule 13G to report the acquisition"

A Schedule 13D is a legal document that investors file with regulators when they buy a large enough stake in a company to potentially influence its management or decisions. It provides details about the investor’s intention, ownership stake, and plans, helping other investors understand who is gaining control and what their motives might be.

investment manager financial

"Redmile Group, LLC, investment manager of Redmile Strategic Long Only Trading Sub, Ltd."

FAQ

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

What ownership stake does Redmile report in Atara Biotherapeutics (ATRA)?

Redmile and related entities report beneficial ownership of 950,994 Atara Biotherapeutics shares, or 9.9% of the common stock. This total includes both currently held shares and shares issuable from pre-funded warrants subject to a 9.99% Beneficial Ownership Limitation.

Did Redmile trade Atara Biotherapeutics (ATRA) shares in this Schedule 13D/A?

The filing states the Reporting Persons have not engaged in any transactions in Atara securities since the prior Schedule 13D. The change in reported beneficial ownership arises from an increase in Atara’s outstanding common shares, which affects warrant-based calculations.

How many Atara (ATRA) shares and warrants do Redmile funds hold?

Redmile-managed funds hold 441,701 Atara common shares and 3,412,843 pre-funded warrants. Under the 9.99% Beneficial Ownership Limitation, 509,293 common shares are currently treated as issuable from these warrants for ownership reporting purposes.

What percentage of Atara (ATRA) does Redmile Biopharma Investments II, L.P. own?

Redmile Biopharma Investments II, L.P. reports 651,924 Atara shares beneficially owned, representing 6.9% of the common stock. This figure combines directly held shares and shares deemed beneficially owned through pre-funded warrants managed within the Redmile fund structure.

What is the Beneficial Ownership Limitation in the Atara (ATRA) warrants?

The pre-funded warrants held by Redmile funds include a 9.99% Beneficial Ownership Limitation. This cap restricts the number of common shares issuable upon exercise, so only 509,293 shares are counted in current beneficial ownership calculations despite a larger total warrant position.

How many Atara Biotherapeutics (ATRA) shares were used to calculate Redmile’s ownership?

Ownership percentages are based on 9,010,172 Atara shares outstanding as of May 8, 2026, plus 509,293 shares issuable upon warrant exercise. This combined figure is used to derive the 9.9% ownership reported by Redmile and related reporting persons.

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

See more from StockTitan in Google Search and AI answers. Adds StockTitan as a preferred source · opens Google

Add on Google Not now

Accepted by SEC EDGAR 05/14/2026 - 09:00 PM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 2)

Atara Biotherapeutics, Inc.

(Name of Issuer)

Common Stock, par value $0.0001 per share

(Title of Class of Securities)

046513206

(CUSIP Number)

Josh Garcia
Redmile Group, LLC, 900 Larkspur Landing Circle, Suite 270
Larkspur, CA, 94939
(415) 489-9980

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

05/12/2026

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

schemaVersion:

SCHEDULE 13D

CUSIP Number(s): 046513206

1

Name of reporting person

Redmile Group, LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 950,994.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 950,994.00

11

Aggregate amount beneficially owned by each reporting person

950,994.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.9 %

14

Type of Reporting Person (See Instructions)

IA, OO

Comment for Type of Reporting Person:

(1) The source of funds was working capital of certain private investment funds managed by Redmile Group, LLC (the "Redmile Funds"), including Redmile Biopharma Investments II, L.P. ("RBI II") and Redmile Strategic Long Only Trading Sub, Ltd. ("Redmile Long Only"). (2) The information in Item 5(a) relating to the shares of common stock, par value $0.0001 per share, of the Issuer (the "Common Stock") that are or may be deemed beneficially owned by Redmile Group, LLC ("Redmile") and the calculation of the percent of such class of securities are incorporated by reference herein.

SCHEDULE 13D

CUSIP Number(s): 046513206

1

Name of reporting person

Jeremy C. Green

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED KINGDOM

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 950,994.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 950,994.00

11

Aggregate amount beneficially owned by each reporting person

950,994.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

9.9 %

14

Type of Reporting Person (See Instructions)

IN, HC

Comment for Type of Reporting Person:

(1) The source of funds was working capital of the Redmile Funds, including RBI II and Redmile Long Only. (2) The information in Item 5(a) relating to the shares of Common Stock that are or may be deemed beneficially owned by Jeremy Green and the calculation of the percent of such class of securities are incorporated by reference herein.

SCHEDULE 13D

CUSIP Number(s): 046513206

1

Name of reporting person

Redmile Biopharma Investments II, L.P.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 651,924.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 651,924.00

11

Aggregate amount beneficially owned by each reporting person

651,924.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

6.9 %

14

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person:

(1) The information in Item 5(a) relating to the shares of Common Stock that are or may be deemed beneficially owned by RBI II and the calculation of the percent of such class of securities are incorporated by reference herein.

SCHEDULE 13D

CUSIP Number(s): 046513206

1

Name of reporting person

Redmile Strategic Long Only Trading Sub, Ltd.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 576,148.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 576,148.00

11

Aggregate amount beneficially owned by each reporting person

576,148.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

6.1 %

14

Type of Reporting Person (See Instructions)

CO

Comment for Type of Reporting Person:

(1) The information in Item 5(a) relating to the shares of Common Stock that are or may be deemed beneficially owned by Redmile Long Only and the calculation of the percent of such class of securities are incorporated by reference herein.

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, par value $0.0001 per share
(b)	Name of Issuer: Atara Biotherapeutics, Inc.
(c)	Address of Issuer's Principal Executive Offices: 1280 Rancho Conejo Blvd, Thousand Oaks, CALIFORNIA , 91320.
Item 2.	Identity and Background
(a)	This Amendment No. 2 to Schedule 13D (this "Amendment") amends and supplements the Schedule 13D filed with the SEC on May 23, 2025, which was previously amended and supplemented by that Amendment No. 1 to Schedule 13D filed with the SEC on November 14, 2025 (collectively, the "Prior Schedule 13D"). This Amendment reports an increase in the beneficial ownership of Redmile Group, LLC ("Redmile"), Jeremy C. Green, Redmile Biopharma Investments II, L.P. ("RBI II"), and Redmile Strategic Long Only Trading Sub, Ltd. ("Redmile Long Only", and, collectively with Redmile, Mr. Green and RBI II, the "Reporting Persons") due solely to the increase in the aggregate number of the Issuer's outstanding Common Stock, which increased the number of shares of Common Stock issuable to the Reporting Persons upon exercise of certain pre-funded warrants to purchase Common Stock (the "Warrants") under the Beneficial Ownership Limitation described in Item 5(a) below. The Reporting Persons have not engaged in any transactions in the Issuer's securities since the Prior Schedule 13D. Capitalized terms used but not defined in this Amendment shall have the meanings set forth in the Prior Schedule 13D. Except as specifically amended by this Amendment, the Prior Schedule 13D is unchanged.
(b)	Item 2(b) of the Prior Schedule 13D is hereby amended and restated in its entirety as follows: Redmile: 900 Larkspur Landing Circle, Suite 270 Larkspur, California 94939 Jeremy C. Green: c/o Redmile Group, LLC (NY Office) 45 W. 27th Street, Floor 11 New York, NY 10001 RBI II: c/o Redmile Group, LLC 900 Larkspur Landing Circle, Suite 270 Larkspur, California 94939 Redmile Long Only: c/o Redmile Group, LLC 900 Larkspur Landing Circle, Suite 270 Larkspur, California 94939
Item 5.	Interest in Securities of the Issuer
(a)	Item 5(a) of the Prior Schedule 13D is hereby amended and restated in its entirety as follows: The aggregate amount of shares of Common Stock that may be deemed beneficially owned by the Reporting Persons is comprised of (i) 441,701 shares of Common Stock held by the Redmile Funds, including the 142,631 shares of Common Stock directly held by RBI II and the 66,855 shares of Common Stock directly held by Redmile Long Only, and (ii) 509,293 shares of Common Stock issuable upon the exercise of the Warrants held by the Redmile Funds. The shares of Common Stock issuable upon the exercise of the Warrants represent the maximum number of shares of Common Stock that could be issued under the 9.99% beneficial ownership limitation (the "Beneficial Ownership Limitation"). Subject in each case to the Beneficial Ownership Limitation, the Redmile Funds directly hold 3,412,843 Warrants, including the 2,054,155 Warrants directly held by RBI II and the 827,581 Warrants directly held by Redmile Long Only. All of the reported securities are directly owned by certain investment vehicles for which Redmile is the investment manager (the "Redmile Funds"), including RBI II and Redmile Long Only. Redmile may be deemed to beneficially own these securities in its capacity as the investment manager with discretion to vote and dispose of the securities held by the Redmile Funds. Mr. Green also may be deemed to beneficially own these securities as the principal of Redmile. Redmile and Mr. Green each disclaim beneficial ownership of these securities, except to the extent of its or his pecuniary interest in such securities, if any. Percentage for each Reporting Person is based on the sum of: (i) 9,010,172 shares of Common Stock outstanding as of May 8, 2026, as reported by the Issuer in its Form 10-Q for the quarterly period ended March 31, 2026 filed with the Securities and Exchange Commission (the "SEC") on May 12, 2026, plus (ii) 509,293 shares of Common Stock issuable upon exercise of the Warrants directly held by the Redmile Funds, which due to the Beneficial Ownership Limitation is the maximum number of shares that could be issued upon exercise of those Warrants.
(b)	Item 5(b) of the Prior Schedule 13D is hereby amended and restated in its entirety as follows: Redmile: (1) Sole Voting Power: 0 (2) Shared Voting Power: 950,994 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 950,994 Jeremy C. Green: (1) Sole Voting Power: 0 (2) Shared Voting Power: 950,994 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 950,994 RBI II: (1) Sole Voting Power: 0 (2) Shared Voting Power: 651,924 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 651,924 Redmile Long Only: (1) Sole Voting Power: 0 (2) Shared Voting Power: 576,148 (3) Sole Dispositive Power: 0 (4) Shared Dispositive Power: 576,148

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Redmile Group, LLC

Signature:	/s/ Jeremy C. Green
Name/Title:	Managing Member
Date:	05/14/2026

Jeremy C. Green

Signature:	/s/ Jeremy C. Green
Name/Title:	Jeremy C. Green
Date:	05/14/2026

Redmile Biopharma Investments II, L.P.

Signature:	/s/ Jeremy C. Green
Name/Title:	Managing Member of Redmile Biopharma Investments II (GP), LLC, general partner of Redmile Biopharma Investments II, L.P.
Date:	05/14/2026

Redmile Strategic Long Only Trading Sub, Ltd.

Signature:	/s/ Jeremy C. Green
Name/Title:	Managing Member of Redmile Group, LLC, investment manager of Redmile Strategic Long Only Trading Sub, Ltd.
Date:	05/14/2026