Patients with neuroendocrine prostate cancer (NEPC) currently have few effective treatment options. We previously demonstrated that LeY is a promising target for CAR T cell therapy in prostate cancer and that preconditioning LeY-directed CAR T cells with carboplatin enhances tumour responses in metastatic castration-resistant prostate cancer (1). Using an autologous disease model, we aimed to assess if LeY can serve as a novel target for CAR T cell therapy in NEPC.
The expression of the Lewis Y antigen was assessed in our patient-derived xenograft collection using immunohistochemistry (IHC) and was detected in 81% (9/11) of NEPC samples. To assess the efficacy of LeY-CAR T cells, we used specimens from a patient (Patient 508) with de novo NEPC who had incurable metastatic disease and failed standard treatments. We generated CAR T cells from the patient’s peripheral blood mononuclear cells (PBMCs) to test their specificity and efficacy in vitro against LeY+ OVCAR3 and LeY− MDA-MB435 cell lines and autologous PDX-508M-derived organoids. We showed that LeY-CAR T cells can be effectively produced from patient PBMCs using retroviral transduction. We tested CAR T specificity in releasing proinflammatory cytokines using an immunobead assay, which showed significant cytokine production after a 4-hour co-culture with LeY+ OVCAR3 cells compared to control LeY− MDA-MB435 cells (p=0.0004). We further showed that patient CAR T cells can effectively kill LeY+ OVCAR3 but not control LeY− MDA-MB435 cells in a chromium release assay (p<0.0001). Finally, using a 24-hour co-culture assay and flow cytometric live cell count, we showed that PDX-508-derived organoids can be killed by LeY-CAR T cells.
Our preclinical data demonstrate that the LeY antigen is expressed in NE tumours and patient PBMCs can be used to generate efficacious CAR T cells, identifying a novel target for CAR T cell therapy in NE-prostate tumours.