CD4 and cancer: Given that MHC-II is mainly responsible for antigen presentation, the fact that MHC-II expressing in cancer cells may be involved in this process by functionally mimicking antigen presentation process and priming CD4 T cells, which directly bind to MHC-II to activate immune response, and this idea has been supported by the discovery of certain MHC-II specific neoantigens in tumor cells and their necessities in promoting successful anti-tumor response [49].