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FDA Lifts Hold on Poseida Therapeutics' CAR T-cell Trial in Advanced Prostate Cancer Patients

NEW YORK – Poseida Therapeutics on Monday announced that the US Food and Drug Administration has allowed the firm to resume a Phase I clinical trial evaluating its CAR T-cell therapy, P-PSMA-101, in metastatic castration-resistant prostate cancer patients.

The FDA had placed a clinical hold on the trial in mid-August after a patient died, effectively suspending the study from proceeding until the cause of death could be assessed and the trial amended, if need be. The primary aims of the previously halted Phase I trial include evaluating P-PSMA-101's safety, maximum tolerated dose, and patients' overall response rates.

P-PSMA-101 is Poseida's first therapeutic candidate intended to treat solid tumors rather than hematologic malignancies. It is an autologous CAR T-cell therapy, which involves harvesting mCRPC patients' immune cells, engineering them to target prostate-specific membrane antigen (PSMA), and reinfusing the engineered cells back into patients. Poseida developed the treatment using its piggyBac DNA Modification System, which produces cell-based therapeutic candidates with high percentages of stem cell memory T cells.

According to a letter that Poseida Founder Mark Gergen issued to shareholders on Aug. 17, the patient who died in the Phase I study received P-PSMA-101 in July after progressing on multiple lines of therapy. He died 19 days after receiving P-PSMA-101 due to hepatic failure, having experienced symptoms of macrophage activation syndrome, a potentially fatal immune system reaction that has been previously associated with CAR T-cell therapies. The patient also experienced blurred vision and eye inflammation. The patient's death could not be attributed directly to Poseida's cell therapy, but the FDA put in place the clinical hold to allow for further investigation and protocol amendments.

Now, following changes to the trial's protocol, including modified inclusion and exclusion criteria and safety and compliance measures, the agency has allowed the trial to proceed. Poseida has said it will immediately resume evaluating P-PSMA-101 in the Phase I trial.