Development of immune checkpoint inhibitor in colorectal cancer.

Nowadays immune checkpoint inhibitors such as anti-CTLA-4, PD-1 and PD -L1 anti- bodies, are most striking among the clinical development of immunotherapy. These mono- clonal antibodies restore and augment the anti-tumor immune activities of cytotoxic T cells by mainly blocking immune checkpoint molecules on T cells or their ligands on antigen presenting and tumor cells. Based on preclinical data, many clinical trials have demonstrated the acceptable safety profiles and efficacies in a variety of cancers. Early phase clinical of mono therapies of immune checkpoint inhibitors had failed for colorectal cancer (CRC). How- ever, some pilot studies suggested anti -PD-1 antibody was very effective in CRC patients with microsatellite instability (MSI) -high. Now several clinical trials are investigating new agents, alone and in combination, for colorectal cancer patients with microsatellite stable (MSS). The current clinical development and TR research and future challenges in utilizing immune checkpoint inhibitors in CRC will be described.