CD4 and neoplasm: The main types of T cells include (i) effector T cells (CD8+ T cells), which induce apoptosis in tumor cells by recognizing tumor-specific antigens and releasing cytotoxic molecules such as perforin and granzyme; (ii) helper T cells (CD4+ T cells), which enhance the immune response by activating B cells, macrophages, and dendritic cells through the secretion of cytokines such as IL-2 and IFN-γ; and (iii) regulatory T cells, which play important roles in maintaining immune tolerance and suppressing excessive immune responses.