CD4 and neoplasm: - Associated with increased intratumoral Treg infiltration and impaired cytotoxic T-cell function (23–30) - Conversion of CD4+CD25−Treg into CD4+CD25+ cells (31) - Prevents degranulation of CD8+ and γδ T-cells (32, 33) - Associated with MDSC infiltration (34) - Promotes proliferation of HUVEC cells (35) - Associated with metastasis (35–42) - Drives dormancy of tumor repopulating cells (11, 43) - Correlates with PD-1 and PD-L1 expression (29, 30, 44–46)