Atara Biotherapeutics, Inc. Securities Fraud Investigation

Peiffer Wolf is investigating Atara Biotherapeutics, Inc. (NASDAQ: ATRA) for potential violations of SEC Rule 10b-5 and related federal securities laws in connection with alleged material misrepresentations about the regulatory prospects of the company’s lead product candidate, tabelecleucel (“tab-cel”), and the manufacturing issues that ultimately led to two FDA Complete Response Letters (“CRL”).

Atara Biotherapeutics is a clinical-stage biopharmaceutical company that develops therapies for patients with solid tumors, hematologic cancers, and autoimmune diseases. A recent federal court Complaint claims the company violated SEC Rule 10b-5, which prohibits misleading or omitting crucial information in securities transactions.

If you invested in Atara Biotherapeutics securities between May 20, 2024, and January 9, 2026, (the “Class Period”) and suffered losses, Contact Us as soon as possible for a Free Case Evaluation.

Important: The deadline to seek lead plaintiff status in this lawsuit is May 22, 2026.

Atara Biotherapeutics Stock | What Happened

According to a Complaint, Atara and its executives allegedly made materially false and misleading statements to investors throughout the Class Period about the regulatory viability of its Biologics License Application (“BLA”) for tab-cell, a T-cell immunotherapy for Epstein-Barr virus positive post-transplant lymphoproliferative disease (EBV+ PTLD).

Specifically, the lawsuit alleges the following conduct:

• Concealed Manufacturing Issues — The complaint alleges that throughout the Class Period, Defendants failed to disclose that serious manufacturing deficiencies at a third-party contract manufacturing organization (CMO) made it unlikely the FDA would approve the tab-cel BLA. Further, despite being aware of contamination and manufacturing compliance failures at the CMO, Defendants continued to tout the BLA’s regulatory path as on track.
• Overstated Regulatory Prospects — The complaint alleges that throughout the Class Period, Defendants represented that tab-cel’s BLA was supported by a pivotal study demonstrating statistically significant efficacy. The complaint alleges Defendants failed to disclose inherent deficiencies in the study’s design, conduct, and analysis that made it unlikely to satisfy FDA requirements for accelerated approval.
• False SOX Certifications — The complaint alleges that Individual Defendants signed Sarbanes-Oxley Act certifications appended to multiple quarterly and annual SEC filings attesting that those reports did not contain materially false or misleading statements. Those certifications are alleged to be falsified due to the undisclosed manufacturing and clinical study deficiencies.
• Capital Raises During Inflated Prices — While allegedly maintaining artificially inflated stock prices by concealing the foregoing risks, Atara raised approximately $36 million in gross proceeds through a September 2024 registered direct offering and an additional $16 million through a May 2025 underwritten direct offering. The complaint identifies these capital raises as evidence of motive to maintain positive public statements about tab-cel’s regulatory prospects.

Stock Price Decline and Investor Harm

The complaint further alleges that when information regarding the manufacturing failures and study deficiencies began to emerge, investors suffered significant losses across multiple corrective disclosures:

• January 16, 2025: Atara announced receipt of a Complete Response Letter (CRL) from the FDA which cited negative observations from a pre-license inspection of Atara’s third-party CMO. Following this disclosure, Atara’s stock fell $5.33 per share, or 40.5%, to close at $7.83.
• January 21, 2025: Atara announced that the FDA had placed a clinical hold on certain active applications due to inadequately addressed compliance issues at the same third-party facility. Following this announcement, the stock fell an additional $0.52 per share, or 7.91%, to close at $6.05.
• January 12, 2026: After Atara resubmitted its BLA in July 2025, the FDA issued a second CRL finding that the single-arm study done for tab-cel “is no longer considered to be adequate to provide evidence of effectiveness for accelerated approval” and that “the trial’s interpretability is confounded due to trial study design, conduct, and analysis.” Following this disclosure, Atara’s stock fell $7.79 per share, or 56.99%, to close at $5.88.

Atara Biotherapeutics Lawsuit | Legal Claims

The complaint asserts that the defendants’ actions violate federal securities laws, specifically:

• Section 10(b) of the Securities Exchange Act of 1934 and SEC Rule 10b-5 — These provisions prohibit the use of any manipulative or deceptive device in connection with the purchase or sale of securities. The complaint alleges that Atara and its executives violated these provisions by making materially false and misleading statements and omitting material facts about their manufacturing deficiencies, the structural weaknesses of their study, and the true likelihood of FDA approval.
• Section 20(a) of the Securities Exchange Act of 1934 (Control Person Liability) — Section 20(a) provides that individuals who control a company can be held liable for the company’s securities law violations. The complaint alleges that Defendants AnhCo Thieu Nguyen (President and CEO), Pascal Touchon (former President and CEO), Eric Hyllengren (former CFO), and Yanina Grant-Huerta (Chief Accounting Officer) controlled the decision-making of the company and the content of its public statements and SEC filings.

FREE Consultation | 585-310-5140

Atara Biotherapeutics allegedly misled investors by representing that its tab-cel BLA was on a clear path to FDA approval while allegedly concealing critical manufacturing deficiencies and fundamental weaknesses in the pivotal clinical trial supporting the application. Following the FDA’s second CRL to Atara in January 2026, Atara’s stock price declined significantly and it is alleged that investors suffered devastating losses.

Peiffer Wolf is currently investigating potential Rule 10b-5 violations involving Atara Biotherapeutics securities sold to retail investors. If you purchased Atara securities during the Class Period and suffered losses, Contact Us for a Free Case Evaluation by filling out an online form or calling 585-310-5140.

Important: The deadline to seek lead plaintiff status in this lawsuit is May 22, 2026.