Panacea funds cut Atara (ATRA) stake but remain 16.1% holder

Rhea-AI Filing Summary

Atara Biotherapeutics’ largest Panacea-affiliated holder updated its ownership report after a significant share sale. Panacea Venture Healthcare Fund II, L.P. and Panacea Opportunity Fund I, L.P. together now report beneficial ownership of 1,318,894 shares of Atara common stock, representing 16.1% of the company’s outstanding shares as of March 10, 2026.

On May 7, 2026, Panacea Venture Healthcare Fund II, L.P. sold 313,446 shares in open market transactions at a weighted average price of $10.0975 per share. James Huang, through Panacea Innovation Limited and related general partners, may be deemed to share beneficial ownership of these holdings but disclaims such beneficial ownership.

Insights

Equity ownership and governance analyst

Panacea reduced its Atara position but remains a major 16.1% holder.

Panacea-affiliated funds continue to hold a substantial stake in Atara Biotherapeutics, reporting beneficial ownership of 1,318,894 common shares, or 16.1% of shares outstanding as of March 10, 2026. This level of ownership keeps them an important shareholder.

On May 7, 2026, Panacea Venture Healthcare Fund II, L.P. sold 313,446 shares in open market transactions at a weighted average price of $10.0975 per share. The filing clarifies the control chain through Panacea Innovation Limited and general partner entities, with James Huang able to be deemed a beneficial owner yet formally disclaiming such ownership.

The filing is an amendment to an existing Schedule 13D, signaling an update rather than a new position. Future changes in reported share counts or percentages in subsequent beneficial ownership filings will further indicate how Panacea adjusts its exposure to Atara over time.

Key Figures

Beneficial ownership: 1,318,894 shares Ownership percentage: 16.1% Fund II holdings: 1,011,000 shares +4 more

7 metrics

Beneficial ownership 1,318,894 shares Panacea-affiliated entities; 16.1% of common stock as of March 10, 2026

Ownership percentage 16.1% Beneficial ownership of Atara common stock by Panacea-related holders

Fund II holdings 1,011,000 shares Panacea Venture Healthcare Fund II, L.P. record holdings; 12.4% of class

Opportunity Fund I holdings 307,899 shares Panacea Opportunity Fund I, L.P. record holdings; 3.8% of class

Shares outstanding 8,178,114 shares Atara common stock outstanding as of March 10, 2026

Shares sold 313,446 shares Sold by Panacea Venture Healthcare Fund II, L.P. on May 7, 2026

Sale price $10.0975 per share Weighted average price for May 7, 2026 open market sales

Key Terms

Schedule 13D, beneficial ownership, open market transactions, weighted average price, +2 more

6 terms

Schedule 13D regulatory

"This Amendment No. 3 to amends and supplements the statement on originally filed with the"

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.

beneficial ownership financial

"The ownership information presented herein represents beneficial ownership of Common Stock as of the date of this filing"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

open market transactions financial

"sold 313,446 shares of Common Stock in open market transactions at a weighted average price"

Open market transactions are the buying and selling of a company’s shares or other securities conducted on public exchanges or through the wider market rather than through private deals or negotiated placements. They matter to investors because these trades change supply and demand in real time—like shoppers affecting a store’s inventory—and so can move prices, signal management or investor sentiment, affect liquidity, and alter ownership stakes that influence future returns and risk.

weighted average price financial

"open market transactions at a weighted average price of $10.0975 per share"

Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.

shared voting power financial

"Number of Shares Beneficially Owned by Each Reporting Person With: | 7 | Sole Voting Power 0.00 8 | Shared Voting Power 1,318,894.00"

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.

shared dispositive power financial

"Number of Shares Beneficially Owned by Each Reporting Person With: | 9 | Sole Dispositive Power 0.00 10 | Shared Dispositive Power 1,318,894.00"

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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 3)

Atara Biotherapeutics, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

046513107

(CUSIP Number)

James Huang
Panacea Capital, 79 Science Park Drive, #04-05
Singapore, U0, 118264
(86-21) 6176-1101

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

05/07/2026

(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): 046513107

1

Name of reporting person

Panacea Innovation Limited

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

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 1,318,894.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 1,318,894.00

11

Aggregate amount beneficially owned by each reporting person

1,318,894.00

12

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

13

Percent of class represented by amount in Row (11)

16.1 %

14

Type of Reporting Person (See Instructions)

CO

SCHEDULE 13D

CUSIP Number(s): 046513107

1

Name of reporting person

Panacea Venture Healthcare Fund 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)

OO

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 1,011,000.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 1,011,000.00

11

Aggregate amount beneficially owned by each reporting person

1,011,000.00

12

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

13

Percent of class represented by amount in Row (11)

12.4 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

CUSIP Number(s): 046513107

1

Name of reporting person

Panacea Venture Healthcare Fund II GP Company, 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)

OO

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 1,011,000.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 1,011,000.00

11

Aggregate amount beneficially owned by each reporting person

1,011,000.00

12

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

13

Percent of class represented by amount in Row (11)

12.4 %

14

Type of Reporting Person (See Instructions)

CO

SCHEDULE 13D

CUSIP Number(s): 046513107

1

Name of reporting person

Panacea Opportunity Fund I, 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)

OO

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 307,899.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 307,899.00

11

Aggregate amount beneficially owned by each reporting person

307,899.00

12

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

13

Percent of class represented by amount in Row (11)

3.8 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

CUSIP Number(s): 046513107

1

Name of reporting person

Panacea Opportunity Fund I GP Company, 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)

OO

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 307,899.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 307,899.00

11

Aggregate amount beneficially owned by each reporting person

307,899.00

12

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

13

Percent of class represented by amount in Row (11)

3.8 %

14

Type of Reporting Person (See Instructions)

CO

SCHEDULE 13D

CUSIP Number(s): 046513107

1

Name of reporting person

James Huang

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

CHINA

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 1,318,894.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 1,318,894.00

11

Aggregate amount beneficially owned by each reporting person

1,318,894.00

12

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

13

Percent of class represented by amount in Row (11)

16.1 %

14

Type of Reporting Person (See Instructions)

IN

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock
(b)	Name of Issuer: Atara Biotherapeutics, Inc.
(c)	Address of Issuer's Principal Executive Offices: 1280 Rancho Conejo Blvd, Thousand Oaks, CALIFORNIA , 91320.
Item 1 Comment: This Amendment No. 3 to Schedule 13D amends and supplements the statement on Schedule 13D originally filed with the United States Securities and Exchange Commission on May 21, 2025 (as amended, the "Schedule 13D"), relating to the Common Stock. Capitalized terms used herein without definition shall have the meaning set forth in the Schedule 13D.
Item 5.	Interest in Securities of the Issuer
(a)	The information contained on the cover pages is incorporated by reference into this Item 5. Panacea Venture Healthcare Fund II, L.P. is the record holder of 1,011,000 shares of Common Stock, and Panacea Opportunity Fund I, L.P. is the record holder of 307,894 shares of Common Stock. The ownership information presented herein represents beneficial ownership of Common Stock as of the date of this filing, based upon 8,178,114 shares of Common Stock outstanding as of March 10, 2026 as disclosed in the Issuer's Definitive Proxy Statement filed with the Securities and Exchange Commission on April 24, 2026. James Huang is the sole owner of Panacea Innovation Limited, which is the sole owner of Panacea Venture Healthcare Fund II GP Company, Ltd. and Panacea Opportunity Fund I GP Company, Ltd., which are the general partners of Panacea Venture Healthcare Fund II, L.P. and Panacea Opportunity Fund I, L.P., respectively. As a result, Panacea Venture Healthcare Fund II GP Company, Ltd. and Panacea Opportunity Fund I GP Company, Ltd. may be deemed to share beneficial ownership of the securities held of record by Panacea Venture Healthcare Fund II, L.P. and Panacea Opportunity Fund I, L.P., respectively. Panacea Innovation Limited and Mr. Huang may be deemed to share beneficial ownership of the securities beneficially owned by the foregoing entities, but each disclaims such beneficial ownership.
(b)	The information contained on the cover pages is incorporated by reference into this Item 5.
(c)	On May 7, 2026, Panacea Venture Healthcare Fund II, L.P. sold 313,446 shares of Common Stock in open market transactions at a weighted average price of $10.0975 per share. The Reporting Persons undertake to provide, upon request by the staff of the Securities and Exchange Commission, the Issuer, or a security holder of the Issuer, full information regarding the number of shares sold at each separate price for this transaction.
(d)	None.
(e)	Not applicable

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.

Panacea Innovation Limited

Signature:	/s/ James Huang
Name/Title:	James Huang, Founding Managing Partner
Date:	05/11/2026

Panacea Venture Healthcare Fund II, L.P.

Signature:	By: Panacea Venture Healthcare Fund II GP Company, Ltd., its general partner By: Panacea Innovation Limited, its sole owner By: /s/ James Huang
Name/Title:	James Huang, Founding Managing Partner
Date:	05/11/2026

Panacea Venture Healthcare Fund II GP Company, Ltd.

Signature:	By: Panacea Innovation Limited, its sole owner By: /s/ James Huang
Name/Title:	James Huang, Founding Managing Partner
Date:	05/11/2026

Panacea Opportunity Fund I, L.P.

Signature:	By: Panacea Opportunity Fund I GP Company, Ltd., its general partner By: Panacea Innovation Limited, its sole owner By: /s/ James Huang
Name/Title:	James Huang, Founding Managing Partner
Date:	05/11/2026

Panacea Opportunity Fund I GP Company, Ltd.

Signature:	By: Panacea Innovation Limited, its sole owner By: /s/ James Huang
Name/Title:	James Huang, Founding Managing Partner
Date:	05/11/2026

James Huang

Signature:	/s/ James Huang
Name/Title:	James Huang
Date:	05/11/2026

FAQ

How many Atara Biotherapeutics (ATRA) shares do Panacea-affiliated funds currently report owning?

Panacea-affiliated entities report beneficial ownership of 1,318,894 Atara common shares, representing 16.1% of the company’s outstanding stock as of March 10, 2026, based on Atara’s Definitive Proxy Statement filed April 24, 2026.

What recent Atara Biotherapeutics (ATRA) share sale did Panacea report in this Schedule 13D/A?

The filing states that Panacea Venture Healthcare Fund II, L.P. sold 313,446 Atara shares on May 7, 2026, in open market transactions at a weighted average price of $10.0975 per share, and will provide detailed price breakdowns on request.

What percentage of Atara Biotherapeutics (ATRA) does Panacea Venture Healthcare Fund II, L.P. hold?

Panacea Venture Healthcare Fund II, L.P. is the record holder of 1,011,000 Atara shares, which the filing reports as 12.4% of the common stock, using 8,178,114 outstanding shares as of March 10, 2026 as the reference.

What stake in Atara Biotherapeutics (ATRA) is held by Panacea Opportunity Fund I, L.P.?

Panacea Opportunity Fund I, L.P. is the record holder of 307,899 Atara common shares, representing 3.8% of the company’s outstanding stock, based on the 8,178,114 shares outstanding disclosed in Atara’s March 10, 2026 share count.

How is James Huang related to the Panacea entities holding Atara (ATRA) shares?

The filing explains that James Huang is the sole owner of Panacea Innovation Limited, which owns the general partners of the Panacea funds. Through this structure he may be deemed to share beneficial ownership, though he disclaims such beneficial ownership.

What share count did Atara Biotherapeutics (ATRA) report as outstanding in this ownership filing?

The Schedule 13D/A states that the ownership percentages are based on 8,178,114 Atara common shares outstanding as of March 10, 2026, a figure taken from Atara’s Definitive Proxy Statement filed on April 24, 2026.