Class Action Lawsuits Filed Against Atara, Ultragenyx, Mereo, and Vistagen Over Alleged Misstatements
Class action lawsuits allege false statements about clinical trial results and regulatory prospects at Atara Biotherapeutics, Ultragenyx, Mereo BioPharma, and Vistagen Therapeutics. The complaints cite failed Phase 3 studies for setrusumab in Osteogenesis Imperfecta and fasedienol for social anxiety disorder, along with manufacturing issues affecting Atara's tabelecleucel application. Investors have deadlines ranging from April to May 2026 to seek lead plaintiff status.
A series of class action lawsuits have been filed against multiple biotechnology companies alleging false and misleading statements about clinical trial results and regulatory prospects. Investors have until various deadlines in 2026 to apply to courts to be appointed as lead plaintiffs in these cases.
A class action lawsuit has been filed against Atara Biotherapeutics, Inc. on behalf of investors who purchased securities between May 20, 2024 and January 9, 2026. The lawsuit alleges that defendants issued false and misleading statements and/or failed to disclose material adverse facts regarding Atara's business, operations, and prospects. Specifically, the complaint alleges that certain manufacturing issues, as well as deficiencies inherent in the ALLELE study, made it unlikely that the FDA would approve the tabelecleucel Biologics License Application, and that tabelecleucel's regulatory prospects were overstated. The lawsuit further alleges that the manufacturing issues also subjected Atara to a heightened risk of regulatory scrutiny and jeopardized its ongoing clinical trials. Investors have until May 22, 2026 to apply to the Court to be appointed as lead plaintiff.
Separate class actions have been commenced on behalf of stockholders of Ultragenyx Pharmaceutical Inc. and Mereo BioPharma Group plc. The Ultragenyx complaint alleges that during the class period from August 3, 2023 to December 26, 2025, defendants provided investors with material information concerning Ultragenyx's expected results for its Phase III Orbit and Cosmic Studies, which tested setrusumab (UX 143) in patients with Osteogenesis Imperfecta. The complaint alleges defendants provided positive statements while concealing material adverse facts concerning the true state of setrusumab's potential and the true risk inherent in the study protocols, notably that while setrusumab does increase material bone density, this increase does not correlate to a decrease in annualized fracture rates.
On December 29, 2025, Ultragenyx announced that both its Phase III Orbit and Cosmic Studies had not achieved statistical significance against the primary endpoints of reduction in annualized clinical fracture rate compared to placebo or bisphosphonates, respectively. The Company attributed the study failure to a low fracture rate in the placebo group of Orbit and a trend that fell shy of statistical significance in Cosmic. On this news, the price of Ultragenyx's stock fell from a closing market price of $34.19 per share on December 26, 2025, to $19.72 per share on December 29, 2025, a decline of about 42.32% in the span of just a single day. Stockholders have until April 6, 2026 to petition the court to serve as lead plaintiff.
The Mereo BioPharma complaint covers the class period from June 5, 2023 to December 26, 2025. The complaint alleges defendants provided investors with material information concerning their expected results for the Phase 3 ORBIT and COSMIC studies for setrusumab in Osteogenesis Imperfecta, while disseminating false and materially misleading statements and/or concealing material adverse facts concerning the true state of the Phase 3 ORBIT and COSMIC programs. On December 29, 2025, Mereo issued a press release announcing that neither the ORBIT nor the COSMIC Phase 3 studies met its primary endpoint of reduction in annualized clinical fracture rate compared to placebo or bisphosphonates, respectively, despite improved bone mineral density. On this news, the price of Mereo's ADS declined from $2.31 per share on December 26, 2025, to $0.29 per share on December 29, 2025, a decline of more than 87.7%. Stockholders have until April 6, 2026 to petition the court to serve as lead plaintiff.
Another class action has been commenced on behalf of stockholders of Vistagen Therapeutics, Inc. The complaint alleges defendants provided overwhelmingly positive statements to investors while disseminating materially false and misleading statements and/or concealing material adverse facts concerning its Phase 3 PALISADE-3 trial study of fasedienol, an investigational pherine candidate in development for the acute treatment of social anxiety disorder. On December 17, 2025, Vistagen issued a press release announcing that the PALISADE-3 Phase 3 study of intranasal fasedienol for the acute treatment of social anxiety disorder did not demonstrate a statistically significant improvement on the primary endpoint of change on the Subjective Units of Distress Scale. Following this news, the price of Vistagen's common stock declined dramatically from a closing market of $4.36 per share on December 16, 2025 to $0.86 per share on December 17, 2025, a decline of more than 80%.