Exhibit 99.1

JOINT FILING AGREEMENT

THIS JOINT FILING AGREEMENT (this “Agreement”) is made and entered into as of this 17^th day of February 2015, by and among Carlos Slim Helú, Carlos Slim Domit, Marco Antonio Slim Domit, Patrick Slim Domit, María Soumaya Slim Domit, Vanessa Paola Slim Domit, Johanna Monique Slim Domit and Inmobiliaria Carso, S.A. de C.V.

The parties to this Agreement hereby agree to prepare jointly and file timely (and otherwise to deliver as appropriate) all filings on any Schedule 13D or 13G relating to their ownership (direct or otherwise) of any securities of Atara Biotherapeutics, Inc., a corporation organized under the laws of Delaware, and any and all amendments thereto and any other document relating thereto (collectively, the “Filings”) required to be filed by them pursuant to the Securities Exchange Act of 1934, as amended.  Each party to this Agreement further agrees and covenants to the other parties that it will fully cooperate with such other parties in the preparation and timely filing (and other delivery) of all such Filings.

IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of the date first set forth above.