Poseida shares plunge after death in solid tumor CAR-T trial, clinical hold

Poseida Therapeutics saw its shares plummet after-hours Monday when it revealed in a Securities and Exchange Commission (SEC) filing that its cancer drug has been slapped with a full clinical hold.

The hold has hit its phase 1 test for P-PSMA-101 in metastatic castration-resistant prostate cancer and comes after a patient died of liver failure in the study, the cause of which could “possibly related to P-PSMA-101 pending further investigation,” the biotech said in the SEC filing.

“Although the direct cause of the hepatic failure has not yet been confirmed, the patient developed symptoms consistent with macrophage activation syndrome (MAS),” Poseida explained. “MAS is a serious and potentially fatal overactivation of the immune system which has been associated with CAR-T therapies, but can have other causes such as infection and autoimmune disease.

“The patient also developed blurred vision which was diagnosed as uveitis. The clinical investigator has assessed the SAE as possibly related to P-PSMA-101 pending further investigation.” The patient died 17 days after receiving the therapy.

Shares in the biotech, which has been strongly backed by Novartis in its early funding rounds, fell 34% on the news.

It is now awaiting a formal response from the FDA and is “preparing recommendations designed to allow resumption of the clinical trial.”

The drug is its first solid tumor autologous CAR-T product candidate targeting prostate-specific membrane antigen, or PSMA. The most success with CAR-T has been across blood cancers, but, like a growing number of other biotechs, Poseida was hoping to unlock its potential in solid tumors.

Poseida had IPO’d this summer on the strength of its pipeline, which includes P-PSMA-101 and leading drug P-BCMA-101, an autologous CAR-T currently in a potentially registrational phase 2 trial for multiple myeloma.

Toxicity in cell therapy has long been an issue for this new cancer R&D area, and Poseida is not the first biotech to be hit by CAR-T trial deaths, with Juno Therapeutics (bought by Celgene, which was bought by Bristol Myers Squibb), seeing a group of deaths in mainly young people from its now ditched CAR-T JCAR015. Here, the deaths were caused by cerebral edema.

Poseida only got off its IPO last month, worth $224 million and valuing the biotech at a cool $1 billion. That second IPO attempt came a year after ditching its first in favor of a new funding round led by Novartis, which was worth a major $142 million.

And, in the middle of its second IPO attempt, it found time to raise a quick $110 million in private funding.