CD4 and neoplasm: Tumor‐derived extracellular vesicles can stimulate CD4+ T cells to release IL‐2, stimulate CD8+ T cells to release IFN‐γ, and finally activate helper T lymphocytes and cytotoxic T lymphocytes, increase the percentage of immune effector cells, induce anti‐tumor immunity, and reverse the tumor immunosuppressive microenvironment51, 52(Figure 3).