Exploring novel targets for CAR-T therapy for prostate cancer

Abstract

Background & Aim Prostate Cancer (PCa) affects one in six men. Treatment options for men with localized disease include radical prostatectomy or brachytherapy. Unfortunately, patients may also present with advanced PCa which invariably progresses to castration-resistant prostate cancer (CRPC), which is lethal due to treatment resistance. There is an unmet need in CRPC to develop new therapies that improve outcome. Harnessing the immune system offers great potential in this regard. In this study, we have identified novel antigens as targets for immunotherapy in men with prostate cancer. These include the carbohydrate antigen Lewis Y, and the stress response chaperone protein GRP-78. Lewis Y antigen is highly expressed in prostate cancer, particularly in higher grade primary tumours and in metastatic and hormone refractory disease. GRP78 is also expressed in prostate cancer in men with more aggressive disease. Methods, Results & Conclusion We generated a second-generation CAR targeting either Lewis Y or GRP-78 with a truncated CD34-tag for purification. Because the differentiation and phenotype of the CAR-T product may have a critical impact on the post-infusion antitumor effect and persistence of the cells, we also investigated the phenotype of CAR-T product with different γc cytokines, i.e. IL-2, IL-7 and IL-15, to generate early differentiation stage cells with less exhaustion phenotypes. In the optimized protocol, by using the retroviral transduction system, starting from 3 × 107 PBMC, we're now able to produce approximately 109 bulk CAR-T cells or 5 × 108 purified CAR-T cells with over 98% purity, within 7-10 days. Furthermore, most of these cells remained early naive or memory-like phenotype. These engineered T cells are capable to eradicate prostate cancer tumour cells in vitro and to secrete TNF-α and IFN-γ cytokines. The in vivo study also showed that the infused cells can reduce the tumour burden and persist post infusion. Our results demonstrate that the novel CAR-T cells exhibited specific and efficient tumoricidal effect against prostate cancer cells. Furthermore, by introducing the CD34-tag, with the optimized protocol, we're now able to produce CAR-T cells with high purity and more early differentiation stage in a relatively shorter time. This may further benefit the clinical application of CAR-T therapy, by reducing the total number of the infused cells and shortening the waiting period for CAR-T production.