CD4 and neoplasm: Cytotoxic CD8+ T cells and their activated cytotoxic T cells have a functional impact on cellular immunity, efficiently eliminating malignant cells in tumor tissues and providing long-term protective immunity, whereas CD4+ T cells assist the activation and memory of cytotoxic CD8+ T cells, regulating antigen-presenting cells (APCs) to provide stronger antigenic signals to naive CD8+ T cells (Nakanishi et al., 2009; Ma et al., 2021; Pipkin, 2021).