Efficacy Against Human Prostate Cancer by Prostate-specific Membrane Antigen-specific, Transforming Growth Factor-β Insensitive Genetically Targeted CD8+ T-cells Derived from Patients with Metastatic Castrate-resistant Disease

Abstract

Current immunotherapy has limited efficacy on metastatic castrate-resistant prostate cancer (mCRPC). We therefore sought to improve the antitumor ability of mCRPC patient-derived CD8⁺ T-cells by the endowment of specificity to prostate-specific membrane antigen (PSMA) and insensitivity to immunosuppressant molecule transforming growth factor-β (TGF-ß) under the control of herpes simplex virus-1 thymidine kinase. CD8⁺ T-cells were collected by leukapheresis and cultured in a Food and Drug Administration-approved Cell Processing Work Station. We developed a chimeric antigen receptor retroviral construct using an anti-PSMA chimeric immunoglobulin-T-cell receptor(ζ) gene (PZ1) and dominant negative TGF-ß type II receptor (TßRIIDN), that could induce CD8⁺ T-cells to be PSMA reactive and insensitive to TGF-ß. Cr⁵¹ release assay was performed on PC-3 and PC-3-PSMA. The further antitumor functions of PSMA-specific, TGF-ß insensitive CD8⁺ T-cells was evaluated using an immunodeficient RAG-1^-/- mouse model. We found PSMA-specific, TGF-ß insensitive CD8⁺ T-cells from mCRPC were expanded with strong expression of PZ1 and thymidine kinase genes, and their growth was not suppressed by TGF-ß. The survival of these cells decreased sharply after treatment with ganciclovir. Treatment of PSMA-specific TGF-ß, insensitive CD8⁺ T-cells was associated with 61.58% specific lysis on PC-3-PSMA, and significantly suppressed PC3-PSMA tumor compared with the PC3 tumor. A large amount of tumor apoptosis and CD8⁺ T-cell infiltration were found only in the PC3-PSMA tumor. This study verified that PSMA-specific, TGF-ß insensitive CD8⁺ T-cells derived from mCRPC patients could be successfully expanded and used to overcome the immunosuppressive effects of the tumor microenvironment to control PSMA-expressing PC in vitro and in vivo. This may provide a promising approach for men with mCRPC who fail androgen deprivation therapy.

Patient summary: We investigated the role of a novel chimeric antigen receptor T-immunotherapy based on autologous metastatic castrate-resistant prostate cancer patient-derived prostate-specific membrane antigen (PSMA)-specific, transforming growth factor-ß insensitive CD8⁺ T-cells on PSMA-positive prostate cancer. We found that this chimeric antigen receptor T-cells could kill PSMA-positive prostate cancer specifically. The results suggest that this novel immunotherapy treatment is a potential new approach for men with metastatic castrate-resistant prostate cancer.

Keywords: CD8(+) T-cells; PSMA; Prostate cancer; TGF-β; mCRPC.