[SCHEDULE 13D/A] Atara Biotherapeutics, Inc SEC Filing

Rhea-AI Filing Summary

Amendment No. 1 to a Schedule 13D reports that a group of Panacea-related entities and James Huang together beneficially own 1,712,900 shares of Atara Biotherapeutics common stock, representing 20.0% of the 7,023,032 shares outstanding as of August 6, 2025. The position includes 307,900 warrants that are immediately exercisable but are subject to a contractual cap preventing exercise to the extent it would increase beneficial ownership above 19.99%, so the warrants cannot currently be exercised. Panacea Venture Healthcare Fund II, L.P. purchased 74,335 shares in open market transactions from July 17 through August 19, 2025 for approximately $857,000, including 19,335 shares at a weighted average $9.6391 and 55,000 shares at a weighted average $12.1895. The filing discloses the ownership chain: James Huang owns Panacea Innovation Limited, which controls the GP entities and the funds. No legal proceedings are reported.

Positive

• Detailed ownership disclosure showing aggregate beneficial ownership of 1,712,900 shares (20.0%).
• Recent open-market purchases of 74,335 shares totaling approximately $857,000, demonstrating accumulation.

Negative

• Warrants cannot currently be exercised due to a 19.99% beneficial ownership cap, limiting immediate dilution or increase in stake.
• High ownership concentration (20.0%) under a single affiliated group may raise governance or influence considerations for other shareholders.

Insights

Financial Analyst

TL;DR Panacea and affiliated entities hold a disclosed 20.0% stake in Atara, with recent open-market purchases totaling 74,335 shares for ~$857k.

The filing documents a material passive equity position representing one-fifth of Atara's outstanding shares. Recent buys were executed across July and August 2025 at weighted average prices of $9.6391 and $12.1895, indicating accumulation via open market purchases rather than a block trade. The position includes 307,900 warrants that are immediately exercisable but effectively restricted by a 19.99% beneficial ownership cap, meaning no warrant exercises are currently permitted. The ownership structure is centralized under James Huang through Cayman entities, which is important for understanding control and voting influence.

Corporate Governance Expert

TL;DR A single affiliate group reports shared voting/dispositive power over 1,712,900 Atara shares and discloses governance control links to James Huang.

The amendment clarifies beneficial ownership and the chain of control: James Huang is the sole owner of Panacea Innovation Limited, which controls the GP entities for the reporting funds. That centralized ownership and shared voting power over 20.0% of the class are governance-relevant facts for Atara boards and investors evaluating shareholder concentration. The filing includes standard disclaimers of beneficial ownership by affiliated entities but establishes the practical linkage for coordination and potential influence.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 1)

Atara Biotherapeutics, Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

046513107

(CUSIP Number)

James Huang
Panacea Venture, No. 5, Lane 1350, Fuxing Middle Road
Xuhui District, Shanghai, F4, 200031
(86-21) 6176-1101

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

08/15/2025

(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).

SCHEDULE 13D

CUSIP No. 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 1,712,900.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 1,712,900.00

11

Aggregate amount beneficially owned by each reporting person

1,712,900.00

12

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

13

Percent of class represented by amount in Row (11)

20.0 %

14

Type of Reporting Person (See Instructions)

CO

Comment for Type of Reporting Person:

Includes 307,900 warrants to purchase Common Stock. The warrants are immediately exercisable and do not expire. No portion of the warrants beneficially owned by the Reporting Persons may be exercised to the extent that, after giving effect to the attempted exercise, the Reporting Persons would beneficially own in excess of 19.99% of the outstanding Common Stock. Based on 7,023,032 shares of Common Stock outstanding as of August 6, 2025, the Reporting Persons may not exercise any warrants currently.

SCHEDULE 13D

CUSIP No. 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 1,405,000.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 1,405,000.00

11

Aggregate amount beneficially owned by each reporting person

1,405,000.00

12

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

13

Percent of class represented by amount in Row (11)

20.0 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

CUSIP No. 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 1,405,000.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 1,405,000.00

11

Aggregate amount beneficially owned by each reporting person

1,405,000.00

12

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

13

Percent of class represented by amount in Row (11)

20.0 %

14

Type of Reporting Person (See Instructions)

CO

SCHEDULE 13D

CUSIP No. 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 307,900.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 307,900.00

11

Aggregate amount beneficially owned by each reporting person

307,900.00

12

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

13

Percent of class represented by amount in Row (11)

4.2 %

14

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person:

Includes 307,900 warrants to purchase Common Stock. The warrants are immediately exercisable and do not expire. No portion of the warrants beneficially owned by the Reporting Persons may be exercised to the extent that, after giving effect to the attempted exercise, the Reporting Persons would beneficially own in excess of 19.99% of the outstanding Common Stock. Based on 7,023,032 shares of Common Stock outstanding as of August 6, 2025, the Reporting Persons may not exercise any warrants currently.

SCHEDULE 13D

CUSIP No. 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 307,900.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 307,900.00

11

Aggregate amount beneficially owned by each reporting person

307,900.00

12

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

13

Percent of class represented by amount in Row (11)

4.2 %

14

Type of Reporting Person (See Instructions)

CO

Comment for Type of Reporting Person:

Includes 307,900 warrants to purchase Common Stock. The warrants are immediately exercisable and do not expire. No portion of the warrants beneficially owned by the Reporting Persons may be exercised to the extent that, after giving effect to the attempted exercise, the Reporting Persons would beneficially own in excess of 19.99% of the outstanding Common Stock. Based on 7,023,032 shares of Common Stock outstanding as of August 6, 2025, the Reporting Persons may not exercise any warrants currently.

SCHEDULE 13D

CUSIP No. 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 1,712,900.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 1,712,900.00

11

Aggregate amount beneficially owned by each reporting person

1,712,900.00

12

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

13

Percent of class represented by amount in Row (11)

20.0 %

14

Type of Reporting Person (See Instructions)

IN

Comment for Type of Reporting Person:

Includes 307,900 warrants to purchase Common Stock. The warrants are immediately exercisable and do not expire. No portion of the warrants beneficially owned by the Reporting Persons may be exercised to the extent that, after giving effect to the attempted exercise, the Reporting Persons would beneficially own in excess of 19.99% of the outstanding Common Stock. Based on 7,023,032 shares of Common Stock outstanding as of August 6, 2025, the Reporting Persons may not exercise any warrants currently.

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. 1 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 3.	Source and Amount of Funds or Other Consideration
	From July 17, 2025 through August 19, 2025, Panacea Venture Healthcare Fund II, L.P. purchased 74,335 shares of Common Stock in a series of open market transactions for aggregate cash consideration of approximately $857,000. Panacea Venture Healthcare Fund II, L.P. obtained the funds used to purchase the Common Stock through capital contributions from their partners.
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 1,405,000 shares of Common Stock, and Panacea Opportunity Fund I, L.P. is the record holder of warrants to purchase 307,900 shares of Common Stock. The warrants are immediately exercisable and do not expire. No portion of the warrants beneficially owned by the Reporting Persons may be exercised to the extent that, after giving effect to the attempted exercise, the Reporting Persons would beneficially own in excess of 19.99% of the outstanding Common Stock. 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 July 17, 2025, Panacea Venture Healthcare Fund II, L.P. purchased 19,335 shares of Common Stock at a weighted average price of $9.6391 per share in a series of open market transactions. On August 15, 2025, Panacea Venture Healthcare Fund II, L.P. purchased 55,000 shares of Common Stock at a weighted average price of $12.1895 per share in a series of open market transactions. Except for the transactions disclosed in this Item 5(c), none of the Reporting Persons has effected any transactions in the Common Stock during the past sixty days.
(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:	08/19/2025

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:	08/19/2025

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:	08/19/2025

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:	08/19/2025

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:	08/19/2025

James Huang

Signature:	/s/ James Huang
Name/Title:	James Huang
Date:	08/19/2025

FAQ

What stake does Panacea report in Atara Biotherapeutics (ATRA)?

The reporting persons beneficially own 1,712,900 shares, equal to 20.0% of Atara's outstanding common stock based on 7,023,032 shares.

Did Panacea make recent purchases of ATRA shares and at what cost?

Yes. Panacea Venture Healthcare Fund II, L.P. bought 74,335 shares from July 17 through August 19, 2025 for about $857,000 in aggregate.

Are there warrants included in the reported position for ATRA?

Yes. The position includes 307,900 warrants that are immediately exercisable and do not expire, but they currently cannot be exercised because of a 19.99% beneficial ownership cap.

Who controls the Panacea reporting group for this ATRA filing?

James Huang is the sole owner of Panacea Innovation Limited, which controls the GP entities for the funds, establishing the ownership chain disclosed in the filing.

Were any legal proceedings disclosed in the Schedule 13D/A for ATRA?

No. The filing indicates no disclosure of legal proceedings pursuant to the applicable items.