# EDGAR Filing Document

**Accession Number:** 0001604464
**File Stem:** 0000905148-26-002919
**Filing Date:** 2026-6
**Character Count:** 10054
**Document Hash:** e7d69639eaf1c89e30459b696083efe0
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0000905148-26-002919.hdr.sgml**: 20260611

**ACCESSION NUMBER**: 0000905148-26-002919

**CONFORMED SUBMISSION TYPE**: 4

**PUBLIC DOCUMENT COUNT**: 2

**CONFORMED PERIOD OF REPORT**: 20260609

**FILED AS OF DATE**: 20260611

**DATE AS OF CHANGE**: 20260611

**REPORTING-OWNER**: 

**OWNER DATA:**
- **COMPANY CONFORMED NAME:** Ciongoli Gregory Austin
- **CENTRAL INDEX KEY:** 0002023732

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** 4
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-36548
- **FILM NUMBER:** 261083654

**MAIL ADDRESS:**
- **STREET 1:** 30 GREYLOCK ROAD
- **CITY:** WELLESLEY
- **STATE:** MA
- **ZIP:** 02481
**ISSUER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Atara Biotherapeutics, Inc.
- **CENTRAL INDEX KEY:** 0001604464
- **STANDARD INDUSTRIAL CLASSIFICATION:** BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 460920988
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**BUSINESS ADDRESS:**
- **STREET 1:** 1280 RANCHO CONEJO BLVD
- **CITY:** THOUSAND OAKS
- **STATE:** CA
- **ZIP:** 91320
- **BUSINESS PHONE:** 805-623-4211

**MAIL ADDRESS:**
- **STREET 1:** 1280 RANCHO CONEJO BLVD
- **CITY:** THOUSAND OAKS
- **STATE:** CA
- **ZIP:** 91320

## Ex-24

**POWER OF ATTORNEY**

Know all by these present, that the undersigned, as a Section 16 reporting person of Atara Biotherapeutics, Inc. (the "Company"), hereby constitutes and appoints each of Yanina Grant-Huerta, and John Chao, or either of them acting individually, and with full power of substitution, the undersigned's true and lawful attorneys-in-fact to:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;

1. Complete and execute Forms 3, 4 and 5, Forms 144, and other forms and all amendments thereto, as such attorneys-in-fact shall in their discretion determine to be required or advisable pursuant to Section 16 of the Securities Exchange Act of 1934 (as amended) and the rules and regulations promulgated thereunder, Rule 144 under the Securities Act of 1933 ("Rule 144"), or any successor laws and regulations, as a consequence of the undersigned's ownership, acquisition or disposition of securities of the Company; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;

2. Enroll the undersigned in the SEC's enhanced Electronic Data Gathering, Analysis, and Retrieval system ("EDGAR Next"), and serve as an Account Administrator for the undersigned's account in EDGAR Next; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;

3. Do and perform any and all acts on behalf of the undersigned which may be necessary or desirable to complete and execute any such Form 3, 4, or 5, or Form 144 with the Securities and Exchange Commission (the "SEC"), any securities exchange or national association, the Company and such other person or agency as the attorneys-in-fact shall deem appropriate.

The undersigned hereby ratifies and confirms all that said attorneys-in-fact and agents shall do or cause to be done by virtue hereof. The undersigned acknowledges that the foregoing attorneys-in-fact, in serving in such capacity at the request of the undersigned, are not assuming, nor is the Company assuming, any of the undersigned's responsibilities to comply with Section 16 of the Securities Exchange Act of 1934 (as amended) or Rule 144.

This Power of Attorney shall remain in full force and effect until the undersigned is no longer required to file Forms 3, 4 and 5, and Forms 144 with the SEC with respect to the undersigned's holdings of and transactions in securities issued by the Company, unless earlier revoked by the undersigned in a signed writing delivered to the Company and the foregoing attorneys-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be executed as of June 11, 2026.

---

| | |
|:---|:---|
| Signature:  | /s/ Gregory A. Ciongoli  |
|  | Gregory A. Ciongoli  |

---

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

## FORM 4

### STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

[ ] 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**<sup>*</sup><br>Ciongoli Gregory Austin<br><sub>(Last) (First) (Middle)</sub><br>C/O ATARA BIOTHERAPEUTICS, INC.<br>1280 RANCHO CONEJO BOULEVARD<br><sub>(Street)</sub><br>THOUSAND OAKS, CA 91320<br><sub>(City) (State) (Zip)</sub> | **3. Date of Earliest Transaction (Month/Day/Year)**<br>2026-06-09 | **5. Relationship of Reporting Person(s) to Issuer**<br>(Check all applicable)<br>[X] Director [X] 10% Owner<br>[ ] Officer (give title below) [X] Other (specify below)<br>_See Remarks_ |
| **2. Issuer Name and Ticker or Trading Symbol**<br>Atara Biotherapeutics, Inc. [ ATRA ] | **4. If Amendment, Date of Original Filed (Month/Day/Year)**<br>  | **6. Individual or Joint/Group Filing (Check Applicable Line)**<br>[X] Form filed by One Reporting Person<br>[ ] Form filed by More than One Reporting Person |

---

## Table I - Non-Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | 3. Transaction Code (V) | 3. Transaction Code (V) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | Code | V | Amount | (A) or (D) | Price | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
| Common Stock | 2026-06-09 |  | A |  | 12000<sup>(1)</sup> | A | $0 | 12000 | D |  |
| Common Stock |  |  |  |  |  |  |  | 1209395 | I | See Footnote<sup>(2)</sup> |

---

## Table II - Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | 4. Transaction Code (V) | 4. Transaction Code (V) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 6. Date Exercisable and Expiration Date | 6. Date Exercisable and Expiration Date | 7. Title and Amount of Underlying Securities | 7. Title and Amount of Underlying Securities | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | Code | V | (A) | (D) | Date Exercisable | Expiration Date | Title | Amount or Number of Shares | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

---

### Footnotes:

(1) These restricted stock units shall vest on the earlier of June 9, 2027 or the date of the next annual meeting of stockholders, subject to the Reporting Person's continuous service.

(2) The securities reported on this row are directly held by Adiumentum Capital Fund I LP, a limited partnership organized under the laws of Delaware ("Adiumentum"). Adiumentum Capital Fund I GP LLC, a limited liability company organized under the laws of Delaware ("Adiumentum GP"), is the general partner of Adiumentum. Gregory A. Ciongoli is the managing partner of Adiumentum and the managing member of Adiumentum GP. Each of Adiumentum, Adiumentum GP, and Mr. Ciongoli may be deemed to have the shared power to vote or direct the vote (and the shared power to dispose or direct the disposition of) the securities that are directly held by Adiumentum. Each of Adiumentum, Adiumentum GP, and Mr. Ciongoli may be deemed to have a pecuniary interest in the securities that are directly held by Adiumentum, but disclaims any beneficial ownership of such securities, except to the extent of any pecuniary interest therein.

**Remarks:**
Exhibit List: Exhibit 24 - Power of Attorney. Mr. Ciongoli serves as a director on the Board of Directors of the Issuer and, as a result, Adiumentum and Adiumentum GP are directors by deputization for purposes of Section 16 of the Securities Exchange Act of 1934, as amended. Neither Adiumentum nor Adiumentum GP have a pecuniary interest in the restricted stock units awarded to Mr. Ciongoli as reported in this Form 4, and therefore Adiumentum and Adiumentum GP have been excluded as reporting persons from this Form 4.

**Signature:** /s/ John Chao, Attorney-in-Fact for Gregory A. Ciongoli  
**Date:** 2026-06-11

### Remarks:

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).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.

**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.**