The US Food and Drug Administration (FDA) has placed a clinical hold on two of Atara Biotherapeutics’ T-cell therapies, following the issuance of a complete response letter (CRL).

The California-based company noted that the clinical hold covers investigational new drug applications for Europe-approved Ebvallo (tabelecleucel), which Atara is developing in partnership with Pierre Fabre Laboratories, along with a pipeline candidate, ATA3219. The clinical hold directly follows a CRL issued by the US FDA to Atara, earlier this month.

As per the clinical hold, the company has paused screening and enrollment of new participants in both programs. Although the currently enrolled subjects “may continue to receive treatment in accordance with the ongoing study protocols”. Earlier in January, Atara noted that the CRL did not identify deficiencies related to clinical efficacy or safety data in the Biologics License Application (BLA), and the FDA did not request any new clinical studies to support approval

Atara was quick to point out that the “clinical hold for Ebvallo is directly linked to inadequately addressed GMP compliance issues identified during the pre-license inspection of the third-party manufacturing facility referenced in the CRL”. Adding that although the “ATA3219 drug product is manufactured at a separate, fully compliant GMP-certified facility, the starting materials used in its production are affected by the compliance issues at the same third-party facility referenced in the CRL”.

While Atara did not name the third-party manufacturer in question, it noted that it was not a FUJIFILM Diosynth Biotechnologies (FDB) facility in Thousand Oaks, California.

Following the news of CRL on 16 January, Atara’s share price cratered, falling by 47.5% at market open on 16 January compared to market close on the previous day. The company’s stock price has not recovered to its previous standing on 15 January.

Ebvallo is an off-the-shelf, allogeneic T-cell immunotherapy, which has been approved as monotherapy by the European Commission (EC) for treating patients ages two years and above with Epstein‑Barr virus-positive post‑transplant lymphoproliferative disease (EBV+ PTLD).

Pierre Fabre first acquired the marketing rights to the therapy in 2021 for Europe, the Middle East, Africa, and other select emerging markets. In 2023, the companies expanded their partnership to give Pierre Fabre marketing rights to Ebvallo in North America, Asia Pacific, and Latin America.

Atara exploring “strategic alternatives”

In January, Atara noted that it “remains eligible to receive a $60 million milestone payment from Pierre Fabre upon FDA approval of the Ebvallo”. Along with “significant double-digit” tiered royalties as a percentage of net sales.

The company is exploring strategic alternatives. Adding, if no resolution is reached to provide funding for its chimeric antigen receptor (CAR) T-cell therapies by the first quarter of 2025, Atara intends to “suspend all CAR-T activities, and significantly reduce company expenses and activities to only those that support the approval of Ebvallo”.

Atara has also entered into a non-binding term sheet with Redmile Group for up to $15 million in equity line of credit funding. The company noted that the financing is “sufficient” to fund the ongoing activities required to achieve BLA approval. Atara reported approximately $43 million in cash reserves at the end of 2024.