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Definitive Proxy Statement

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ATARA BIOTHERAPEUTICS, INC.

Meeting Information

Meeting Type:             Annual Meeting

For holders as of:        April 19, 2018

Date:   June 14, 2018   Time:   8:00 AM PDT

Location: 2430 Conejo Spectrum St.

Thousand Oaks, CA 91320

ATARA BIOTHERAPEUTICS, INC.

611 GATEWAY BLVD., SUITE 900

SOUTH SAN FRANCISCO, CA 94080

You are receiving this communication because you hold shares in the company named above.

This is not a ballot. You cannot use this notice to vote these shares. This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials online at www.proxyvote.com or easily request a paper copy (see reverse side).

We encourage you to access and review all of the important information contained in the proxy materials before voting.

See the reverse side of this notice to obtain proxy materials and voting instructions.

Proxy Materials Available to VIEW or RECEIVE:

1.Notice & Proxy Statement      2. Form 10-K

How to View Online:

Have the information that is printed in the box marked by the arrow (located on the following page) and visit: www.proxyvote.com.

How to Request and Receive a PAPER or E-MAIL Copy:

If you want to receive a paper or e-mail copy of these documents, you must request one. There is NO charge for requesting a copy. Please choose one of the following methods to make your request:

1) BY INTERNET:       www.proxyvote.com

2) BY TELEPHONE:   1-800-579-1639

3) BY E-MAIL*:           sendmaterial@proxyvote.com

* If requesting materials by e-mail, please send a blank e-mail with the information that is printed in the box marked by the arrow (located on the following page) in the subject line.

Requests, instructions and other inquiries sent to this e-mail address will NOT be forwarded to your investment advisor. Please make the request as instructed above on or before May 31, 2018 to facilitate timely delivery.

Vote In Person: Many stockholder meetings have attendance requirements including, but not limited to, the possession of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any special requirements for meeting attendance. At the meeting, you will need to request a ballot to vote these shares.

Vote By Internet: To vote now by Internet, go to www.proxyvote.com. Have the information that is printed in the box marked by the arrow available and follow the instructions.

Vote By Mail:  You can vote by mail by requesting a paper copy of the materials, which will include a proxy card.

Voting Items

The Board of Directors recommends you vote
FOR the following:

1.   Election of Directors

      Nominees:

01     Eric L. Dobmeier     02 William K. Heiden     03 Beth Seidenberg, M.D.

The Board of Directors recommends you vote FOR the following proposal:

2.   Ratification of the selection of Deloitte & Touche, LLP as the Company's independent registered public accounting firm for the fiscal year ending December 31, 2018.

NOTE: In their discretion, upon such other matters that may properly come before the meeting or any adjournment or adjournments thereof.