Panacea entities boost Atara (ATRA) stake via 259,163-share warrant exercise

Rhea-AI Filing Summary

Atara Biotherapeutics, Inc. reported an insider transaction in which entities associated with Panacea funds exercised warrants to acquire common stock indirectly. Panacea Opportunity Fund I, L.P. exercised 259,163 warrants at an exercise price of $0.0001 per share, converting them into the same number of Atara common shares.

In connection with this exercise, 5 common shares were withheld at a price of $5.23 per share to cover tax obligations, a non-market disposition. Following these transactions, indirect holdings reported for these affiliated entities totaled over one million Atara common shares, while the reporting persons formally disclaim beneficial ownership beyond what may be attributed through their roles.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Panacea Innovation Ltd

(Last) (First) (Middle)

C/O MAPLES CORPORATE SERVICES LIMITED,

UGLAND HOUSE

(Street)

GRAND CAYMAN KY1-1104

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Atara Biotherapeutics, Inc. [ ATRA ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
03/17/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

	Form filed by One Reporting Person
X	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	03/17/2026		M		259,163	A	$0.0001	307,899	I	See Footnotes(1)(2)
Common Stock	03/17/2026		F		5	D	$5.23	307,894	I	See Footnotes(1)(2)
Common Stock								1,324,446	I	See Footnotes(2)(3)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Warrants	$0.0001	03/17/2026		M			259,163	(4)	(4)	Common Stock	259,163	$6.6099	0	I	See Footnotes(1)(2)

1. Name and Address of Reporting Person^*

Panacea Innovation Ltd

(Last) (First) (Middle)

C/O MAPLES CORPORATE SERVICES LIMITED,

UGLAND HOUSE

(Street)

GRAND CAYMAN KY1-1104

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

Huang James

(Last) (First) (Middle)

C/O MAPLES CORPORATE SERVICES LIMITED,

UGLAND HOUSE

(Street)

GRAND CAYMAN KY1-1104

(City) (State) (Zip)

UNITED STATES

(Country)

Relationship of Reporting Person(s) to Issuer

X	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

Explanation of Responses:

1. Represents securities held by Panacea Opportunity Fund I, L.P.

2. James Huang is the sole owner of Panacea Innovation Limited, which is the sole owner of Panacea Venture Healthcare Fund II GP Company, Ltd. ("Fund II GP") and Panacea Opportunity Fund I GP Company, Ltd. ("Opportunity Fund GP"), which are the general partners of Panacea Venture Healthcare Fund II, L.P. and Panacea Opportunity Fund I, L.P. As a result, each of the Reporting Persons 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., but each disclaims such beneficial ownership.

3. Represents securities held by Panacea Venture Healthcare Fund II, L.P.

4. The warrants are immediately exercisable and do not expire. Pursuant to the terms of the warrants, no portion of the warrants held by a holder may be exercised to the extent that, after giving effect to the attempted exercise, such holder, together with such holder's affiliates and any other person whose beneficial ownership of the Issuer's common stock would be aggregated with such holder's for the purposes of Section 13(d) of the Exchange Act, would beneficially own in excess of 19.99% of the outstanding common stock.

	Panacea Innovation Limited By: /s/ James Huang, Founding Managing Partner	03/19/2026
	/s/ James Huang	03/19/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)

FAQ

What insider transaction did Panacea-related entities report in Atara Biotherapeutics (ATRA)?

Entities associated with Panacea funds exercised warrants to acquire 259,163 Atara common shares at a $0.0001 exercise price. The filing treats this as a derivative exercise, increasing indirect equity exposure rather than an open-market share purchase.

Who are the reporting persons in the Atara Biotherapeutics (ATRA) Form 4?

The Form 4 lists Panacea Innovation Ltd and James Huang as reporting persons and ten percent owners. Footnotes explain their control relationships over Panacea Opportunity Fund I, L.P. and Panacea Venture Healthcare Fund II, L.P., while also stating that each reporting person disclaims beneficial ownership.

How many Atara Biotherapeutics (ATRA) shares were acquired through warrant exercise?

Panacea Opportunity Fund I, L.P. reported exercising warrants into 259,163 Atara common shares at a $0.0001 per share exercise price. This derivative conversion shifts exposure from warrants into ordinary equity without involving an open-market stock purchase transaction.

Was there any sale of Atara Biotherapeutics (ATRA) stock in this Form 4?

The filing reports a disposition of 5 common shares at $5.23 per share, classified as a tax-withholding transaction. This reflects shares delivered to satisfy obligations related to the exercise, not an open-market sale expressing a view on Atara’s stock price.

What indirect Atara Biotherapeutics (ATRA) holdings are shown after these transactions?

After the reported exercise and tax withholding, one indirect line shows 307,894 Atara common shares, and another indirect holding line shows 1,324,446 shares. Together, these entries indicate substantial ongoing indirect ownership via Panacea-affiliated funds following the derivative exercise.

Do the Panacea-related reporting persons claim full beneficial ownership of ATRA shares?

Footnotes state that James Huang, through Panacea Innovation Limited, controls the general partners of the Panacea funds and may be deemed to share beneficial ownership, but each reporting person expressly disclaims beneficial ownership of securities held by the funds beyond any indirect economic interest.