CD4 and ovarian carcinoma: For example, fibroblast activation protein-α (FAP-α) + CAFs can increase the survival of CD4 + CD25 + T lymphocytes by secreting CXCL-12 and further induce these T cells differentiation into CD4 + CD25 + FOXP3 + Tregs and increase their ability to inhibit CD4 + effector T cell proliferation, thereby contributing to a tumor-promoting microenvironment in breast cancer and ovarian cancer [98].