Led by Existing Top Institutional Investors With Participation From a New Strategic Investor

Well Positioned To Execute on Tab-cel^® U.S. BLA Approval and Advancement of ATA3219

Further Strengthens Balance Sheet With Cash Runway Into 2027 Enabling Key Pipeline Readouts

Atara Biotherapeutics, Inc. (Nasdaq: ATRA), a leader in T-cell immunotherapy, leveraging its novel allogeneic Epstein-Barr virus (EBV) T-cell platform to develop transformative therapies for patients with cancer and autoimmune diseases, today announced that it has entered into definitive agreements for the issuance and sale of 758,900 shares of its common stock at a purchase price of $8.25 per share and the issuance and sale of pre-funded warrants to purchase up to 3,604,780 shares of its common stock at a purchase price of $8.2499 per share in a registered direct offering, representing a premium of 15% to Atara’s 7-day volume-weighted average price, to entities affiliated with Redmile Group, EcoR1 Capital, and Adiumentum Capital Management, as well as a strategic investment from a large public biotechnology company. The pre-funded warrants will have an exercise price of $0.0001 per share and will be immediately exercisable upon issuance. The offering is expected to close on or about September 5, 2024, subject to the satisfaction of customary closing conditions.

In connection with the offering, Greg Ciongoli, founder and managing partner of Adiumentum Capital Management, will join Atara’s Board of Directors.

“Atara’s innovative cell therapies, like tab-cel and its differentiated allogeneic CAR-T portfolio, have the potential to transform the lives of cancer and autoimmune patients,” said Greg Ciongoli. “With the prospective U.S. approval for tab-cel and several anticipated CAR-T data readouts all approaching, this is an exciting time to join Atara’s Board and to partner with its strong leadership team.”

“We are very pleased to have Greg join our Board, and I look forward to collaborating with him as I transition to Chairman,” said Pascal Touchon, President and Chief Executive Officer. “He has over two decades of investing experience and deep industry knowledge, which will complement our Board of Directors well.”

The gross proceeds to Atara from the offering are expected to be $36 million, before deducting estimated offering expenses payable by Atara. Atara currently intends to use the net proceeds from the offering for working capital and general corporate purposes.

The securities described above are being offered by Atara pursuant to a shelf registration statement on Form S-3 (No. 333-275256), including a base prospectus, that was previously filed by Atara with the U.S. Securities and Exchange Commission (the “SEC”) and was declared effective on November 13, 2023. A prospectus supplement containing additional information relating to the offering will be filed with the SEC and will be available on the SEC’s website located at http://www.sec.gov.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy, nor shall there be any sale of these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to the registration or qualification under the securities laws of any such state or jurisdiction.

About Atara Biotherapeutics, Inc.

Atara is harnessing the natural power of the immune system to develop off-the-shelf cell therapies for difficult-to-treat cancers and autoimmune conditions that can be rapidly delivered to patients from inventory. With cutting-edge science and differentiated approach, Atara is the first company in the world to receive regulatory approval of an allogeneic T-cell immunotherapy. Atara’s advanced and versatile T-cell platform does not require T-cell receptor or HLA gene editing and forms the basis of a diverse portfolio of investigational therapies that target EBV, the root cause of certain diseases, in addition to next-generation AlloCAR-Ts designed for best-in-class opportunities across a broad range of hematological malignancies and B-cell driven autoimmune diseases. Atara is headquartered in Southern California.

Forward-Looking Statements

This press release contains or may imply “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. For example, forward-looking statements include statements regarding the completion, timing and size of the offering and the anticipated use of proceeds of the offering and Mr. Ciongoli’s service on the Company’s board of directors. Because such statements deal with future events and are based on Atara’s current expectations, they are subject to various risks and uncertainties and actual results, performance or achievements of Atara could differ materially from those described in or implied by the statements in this press release. These forward-looking statements are subject to risks and uncertainties, including without limitation risks and uncertainties related to market conditions and satisfaction of customary closing conditions related to the offering, as well as those discussed in Atara’s filings with the SEC, including in the “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” sections of the prospectus supplement and Atara’s most recently filed periodic reports on Form 10-K and Form 10-Q and subsequent filings and in the documents incorporated by reference therein. Except as otherwise required by law, Atara disclaims any intention or obligation to update or revise any forward-looking statements, which speak only as of the date hereof, whether as a result of new information, future events or circumstances or otherwise.

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