13D Filings
Atara Biotherapeutics, Inc.
ATRA
Amendment
Ownership

19.99%

Total Shares

1,632,345

Issuer CIK

1604464

CUSIP

046513107

Event Date

Jan 11, 2026

Accepted

Jan 14, 2026, 09:20 PM

Reporting Persons (6)
Joint Filing

This is a joint filing. The reported shares may overlap between reporting persons and should not be summed.

NameType% of ClassAggregateSole VotingShared Voting
Panacea Innovation Limited
CO
19.99%1,632,34501,632,345
James Huang
Individual
19.99%1,632,34501,632,345
Panacea Venture Healthcare Fund II, L.P.
Partnership
18.20%1,324,44601,324,446
Panacea Venture Healthcare Fund II GP Company, Ltd.
CO
18.20%1,324,44601,324,446
Panacea Opportunity Fund I, L.P.
Partnership
4.10%307,8990307,899
Panacea Opportunity Fund I GP Company, Ltd.
CO
4.10%307,8990307,899
Disclosure Items (2)

Security Title

Common Stock

Issuer Name

Atara Biotherapeutics, Inc.

Issuer Address

1280 Rancho Conejo Blvd, Thousand Oaks, CA, 91320

Percentage of Class

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 1,324,446 shares of Common Stock, and Panacea Opportunity Fund I, L.P. is the record holder of 48,736 shares of Common Stock and warrants to purchase 259,163 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.

Number of Shares

The information contained on the cover pages is incorporated by reference into this Item 5.

Transactions

On November 28, 2025, Panacea Opportunity Fund I, L.P. exercised warrants to purchase an aggregate of 48,736 shares of Common Stock, after tax witholding. On January 12, 2026, Panacea Venture Healthcare Fund II, L.P. sold 80,554 shares of Common Stock in open market transactions at a weighted average price of $6.0707 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.

Shareholders

None.

Date of 5% Ownership

Not applicable