The FDA has placed Poseida Therapeutics’ phase 1 trial of its experimental CAR-T therapy, P-PSMA-101, in metastatic castrate-resistant prostate cancer on hold following the death of a patient.

The California-based company said the patient had normal lab results through the first week of post-treatment, but developed symptoms days later that led to his death at day 19. The symptoms were consistent with macrophage activation syndrome, a serious and potentially fatal overactivation of the immune system.

Poseida is investigating the patient’s death and preparing recommendations that may enable the trial to resume if the FDA allows it.