Innovative immunotherapies for prostate cancer: understanding the synergies between checkpoint inhibition, CAR T-cell therapy, and next-generation therapeutic modalities

Immunotherapy has transformed oncology, yet has only been marginally effective in prostate cancer (PCa), which is a malignancy with a low mutational load and a highly immunosuppressive tumor microenvironment (TME). This critical review is a reflection on the changing position of the innovative immunotherapies in PCa that extends beyond the description stage to synthesize the synergies and constraints of immune checkpoint inhibitors (ICIs), chimeric antigen receptor (CAR) T-cell therapy, and next-generation modalities such as bispecific T-cell engagers (BiTEs). We assess the mechanistic reasoning of combination therapies, comprising androgen receptor signaling communicators, PARP communicators, and radioligand therapies, which seek to modulate the immunogenicity of the immune-cold PCa TME. Also, we combine new knowledge to novel resistance pathways, including the newly discovered thrombospondin-1-CD47 axis, in the process of T cell exhaustion through calcineurin-NFAT signaling. Although some preclinical data and initial clinical indicators in biomarker-selected subpopulations are promising, the vast majority of Phase III trials of ICIs in unselected populations with metastatic castration-resistant prostate cancer (mCRPC) have failed. This review reveals that the next generation of PCa immunotherapy would not be sequential monotherapies but rather rationally designed multimodal combinations guided by profound molecular and immune profiling to overcome inherent resistance mechanisms.