Atara Biotherapeutics, Inc. (Nasdaq: ATRA), a pioneer in T-cell immunotherapy leveraging its novel allogeneic EBV T-cell platform to develop transformative therapies for patients with serious diseases including solid tumors, hematologic cancers and autoimmune diseases, today announced that it has commenced an underwritten public offering of $150,000,000 of shares of its common stock. In connection with the proposed offering, Atara Biotherapeutics expects to grant the underwriters a 30-day option to purchase up to an additional $22,500,000 of shares of its common stock at the public offering price, less the underwriting discounts and commissions. All of the shares in the proposed offering will be sold by Atara Biotherapeutics. The proposed offering is subject to market and other conditions, and there can be no assurances as to whether or when the proposed offering may be completed, or as to the actual size or terms of the proposed offering.

Citigroup, Evercore ISI and Mizuho Securities are acting as joint book-running managers for the proposed offering.