SCHEDULE 14A INFORMATION

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Atara Biotherapeutics, Inc.

(Name of Registrant as Specified In Its Charter)

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***Exercise Your Right to Vote*** Important Notice Regarding the Availability of Proxy Materials for the Stockholder Meeting to Be Held on June 23, 2016 ATARA BIOTHERAPEUTICS, INC. ATARA BIOTHERAPEUTICS, INC. 611 GATEWAY BLVD., SUITE 900 SOUTH SAN FRANCISCO, CA 94080 Investor Address Line 1 Investor Address Line 2 Investor Address Line 3 Investor Address Line 4 Investor Address Line 5 John Sample 1234 ANYWHERE STREET ANY CITY, ON A1A 1A1 1 OF 2 12 15 Meeting Information Meeting Type: Annual Meeting For holders as of: April 25, 2016 Date: June 23, 2016 Time: 9:00 AM PDT Location: 611 Gateway Blvd. Suite 900 S. San Francisco, CA 94080 You are receiving this communication because you hold shares in the above named company. This is not a ballot. You cannot use this notice to vote these shares. The 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. Broadridge Internal Use Only Job # Envelope # Sequence # # of # Sequence # BARCODE 0000291615_1 R1.0.1.25

— Before You Vote —How to Access the Proxy MaterialsProxy Materials Available to VIEW or RECEIVE1. Notice & Proxy Statement 2. Annual Report How to View Online:Have the information that is printed in the box marked by the arrow  xxxx xxxx xxxx xxxx (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:BY INTERNET:    www.proxyvote.comBY TELEPHONE: I-800-579-1639BY 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  xxxx xxxx xxxx xxxx (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 June 09, 2016 to facilitate timely delivery.— How To Vote —Please Choose One of the Following Voting MethodsVote In Person: Many stockholder meetings have acceptance 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 xxxx xxxx xxxx xxxx 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. 0000291615_2 R1.0.1.25

Voting Items The Board of Directors recommends you vote FOR the following: 1. Election of Directors Nominees 01 Matthew K. Fust02 Joel S. Marcus The Board of Directors recommends you vote FOR the following proposals: 2 Ratification of the appointment of Deloitte & Touche, LLP as the Company's independent registered public accounting firm for the fiscal year ending December 31, 2016. 3 To approve the Company's 2014 Equity Incentive Plan, as amended, to increase the aggregate number of shares of Common Stock authorized for issuance thereunder by 4,000,000 shares and to make certain other changes thereto as described in the proxy statement. NOTE: In their discretion, upon such other matters that may properly come before the meeting or any adjournment or adjournments thereof.0000291615_3 R1.0.1.25 0000 0000 0000 0000BARCODEBroadridge Internal Use Only xxxxxxxxxx xxxxxxxxxx Cusip Job # Envelope # Sequence # # of # Sequence #

Reserved for Broadridge Internal Control Information NAME THE COMPANY NAME INC. – COMMON THE COMPANY NAME INC. – CLASS A THE COMPANY NAME INC. – CLASS B THE COMPANY NAME INC. – CLASS C THE COMPANY NAME INC. – CLASS D THE COMPANY NAME INC. – CLASS E THE COMPANY NAME INC. – CLASS F THE COMPANY NAME INC. – 401 K 123,456,789,012.12345 123,456,789,012.12345 123,456,789,012.12345 123,456,789,012.12345 123,456,789,012.12345 123,456,789,012.12345 123,456,789,012.12345 123,456,789,012.12345 THIS SAPCE RESERVED FOR SIGNATURES IF APPLICABLE Broadridge Internal Use Only Job # Envelope # Sequence # # of # Sequence # 0000291615_4 R1.0.1.25