CD4 and neoplasm: Additionally, tumor cells exert suppressive effects on immune cells by secreting various chemokines and small molecules, leading to exhaustion of effector CD8+ T cells, differentiation of CD4+ T cells to regulator T cells (Tregs), and M2 polarization of macrophages, which, in general, renders the tumor microenvironment immune-suppressive or even cancer-promoting (Li et al. 2019).