CD4 and neoplasm: From a mechanistical perspective, the treatment efficacy of immunotherapies predominantly relies on the mobilization of tumor-specific effector T cells, during which the naive CD4 and CD8 T cells are activated through interacting with the antigen-bound Class II and Class I major histocompatibility complex (MHC-II and MHC-I) expressed on antigen-presenting cells (APCs)4–6.