By Adriano Marchese

Atara Biotherapeutics shares fell Monday after the company said the U.S. health regulator didn't approve its therapy, backtracking on its previous guidance.

Shares fell 53% to $6.40.

The biotech company on Monday said the Food and Drug Administration issued a complete response letter that refused to approve Ebvallo in its current form, with the regulator saying a previous trial is no longer considered to provide adequate evidence of effectiveness for accelerated approval.

Ebvallo, also known as tabelecleucel, aims to treat Epstein-Barr virus positive post-transplant lymphoproliferative disease, which is a potentially fatal complication after transplantation.

Atara said the decision is a departure from the FDA's prior stance, which had identified only one deficiency regarding manufacturing issues that Atara has since resolved.

The company also said the FDA hadn't previously raised any new safety concerns, whereas the regulator now said the trial's design and analysis limit its interpretability.

Atara said its partner, Pierre Fabre Pharmaceuticals, intends to request a type A meeting with the FDA, and said it expects the request to be granted within 45 days. Pierre Fabre and Atara plan to interact with the FDA to find a path forward for the timely accelerated approval, Atara said.

Atara said it cut about 90% of its total headcount in 2025 in an effort to improve operational efficiencies. The Thousand Oaks, Calif., company also transitioned nearly all Ebvallo activities and associated costs to Pierre Fabre during the year. Atara had $8.5 million of cash or cash equivalent left on its balance sheet as of Dec. 31, it said.

Write to Adriano Marchese at adriano.marchese@wsj.com

(END) Dow Jones Newswires

January 12, 2026 10:24 ET (15:24 GMT)

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