Chimeric antigen receptor (CAR+) modified T cells targeting prostate specific membrane antigen (PSMA) in patients (pts) with castrate metastatic prostate cancer (CMPC).

TPS3115 Background: A phase I dose-escalating study to assess safety, dose and targeting efficiency of genetically modified autologous human T cells targeted to PSMA was initiated. Preclinical models demonstrated anti-tumor activity and accumulation, migration, and persistence of these cells to tumor. The autologous PSMA-targeted T cells utilizes the P28z second generation chimeric antigen receptor following iv cyclophosphamide (Cy). For safety, the herpes simplex virus-1 thymidine kinase (hsvtk) gene is co-expressed with the P28z receptor, rendering T cells sensitive to ganciclovir for immediate T cell elimination. The expression of hsvtk enables PET imaging using radiolabeled FIAU to localize these T cells Methods: Autologous T cells are activated from a leukapheresis product using anti-CD3/CD28 Dynabeads. Release criteria include mean vector copy number by Q-PCR and vector identity by Southern blot, absence of Replication Competent Retrovirus and residual Dynabeads. Pts were dosed from 10 7 to 3 x 10 7 CAR + T cells/kg.All 7 pts received 300mg/m 2 of Cy one day before infusion. Baseline and post treatment imaging included FDG, FDHT and 18 F-FIAU PET scans. Results: Three pts in cohort 1 received 1 x 10 7 CAR + T cells/kg safely. A fourth pt received the same dose with a modified vector with higher copy number. One pt had stable disease for > 6 months; a second pt has stable scans for > 20 months; the third and fourth patients progressed. Of 3 pts in cohort 2, one received 1.5 x 10 7 CAR + T cells/kg and 2 received 3 x 10 7 CAR + cell/kg. All 3 had intermittent fever spikes up to 39 o C associated with increased levels of IL-4, IL-8, IP-10, sIL-2ra and IL-6 suggesting T cell activation. CAR + cells persisted in the circulation for up to 2 weeks. Scans with 18 F-FIAU labeling suggests that imaging may be cell dose dependent. Conclusions: We have shown that pts can be safely treated with an ex vivo transduction, expansion and therapeutic protocol for the generation of PSMA targeted T cells. Cytokine production suggests in vivo activation and persistence of T cells in blood for up to 2 weeks. Ongoing imaging with 18 F may be suboptimal; a second cohort of pts will be studied with 124 I-FIAU. Clinical trial information: NCTO1140373.