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

Abstract

72 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 107 to 3 x 107 CAR+ T cells/kg. All 7 pts received 300mg/m2 of Cy one day before infusion. Baseline and post treatment imaging included FDG, FDHT and 18F-FIAU PET scans. Results: Three pts in cohort 1 received 1 x 107 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 > 16 months; the third and fourth patients progressed. Of 3 pts in cohort 2, one received 1.5 x 107 CAR+ T cells/kg and 2 received 3 x 107 CAR+ cell/kg. All 3 had intermittent fever spikes up to 39oC 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 18F-FIAU labeling suggests that imaging may be cell dose dependent. Conclusions: We have shown that pts can be safetly treated with an ex vivo transduction, expansion and therapeutic protocol for the generation of PSMA targeted T cells. Cytokine production suggests activation of these T cells with their persistence in blood for up to 2 weeks. If imaging with FIAU is suboptimal, a second cohort of pts will be studied with 124I- FIAU. Clinical trial information: NCT01140373.

Comparative Analysis of Human Nucleoside Kinase-Based Reporter Systems for PET Imaging

“…Generation of isogenic cell lines from parental U87 cells (here referred to as WT) bearing dCK, dCK-R104M/D133A (dCKDM) [9, 10], dCK-R104Q/D133N (dCKep16A) [11], dCK-A100V/R104M/D133A (dCK3M) [10, 11], TK2-N93D/L109F (TK2DM) [14], and HSVTK reporter genes fused to the green fluorescent protein (GFP) were described previously [15]. SFG-based helper-free retroviruses encoding each of the mutant genes were produced by transient transfection of H29 producer cells.…”

“…Most recently, HSVTK with the F-18 radiolabeled 9-[4-[ 18 F]fluoro-3-(hydroxymethyl)butyl]guanine ([ 18 F]FHBG) detected localization of adoptively transferred cytotoxic T lymphocytes in a glioma patient [8]. Ongoing clinical trials at Memorial Sloan Kettering Cancer Center and other institutes further support reporter gene imaging as a promising technology for monitoring gene and cell-based therapies [9]. …”

Immune Therapy for Prostate Cancer

“…Besides the aforementioned phase I trial in patients with castrate-resistant prostate cancer (NCT01140373), there is only 1 other trial in patients with advanced castrate resistant prostate cancer after non-myeloablative conditioning (NCT00664196) [63]. There is rationale for combining CAR T cell therapy with checkpoint blockade, AR-direceted therapy or cytotoxic chemotherapy in an effort to augment CAR T cell efficacy, decrease tumor burden or facilitate antigen spreading.…”

Making Better Chimeric Antigen Receptors for Adoptive T-cell Therapy

“…Several trials investigating CAR T-cell therapy in solid tumors have been initiated, but efficacy has been low. Best responses recently reported in trials using CAR T cells specific for the solid tumor antigens mesothelin, PSMA, or ERBB2 were stable disease in 24-67% of patients (42-44). The efficacy of CAR T-cell therapy in solid tumors may be reduced due to several factors.…”

“…Additionally, both PSCA and PSMA were targeted in a preclinical study that showed that CAR T cells can be engineered to recognize only tumors expressing both antigens, thereby increasing CAR T-cell specificity and reducing off-tumor effects (40). A phase 1 clinical trial (NCT01140373) using PSMA-specific CAR T cells in patients with metastatic prostate cancer resulted in stable disease in 2 of 4 patients treated (44). …”