FOXP3 and neoplasm: Moreover, FAI administration decreased the proportion of Treg (FOXP3+CD25+/CD4+) cells among PBMCs and enhanced the ability of T cells derived from PBMCs to induce tumor cell apoptosis (Fig. 5D,E), indicating that FFA production from MFC-OE cells is essential for the survival and immunosuppressive functions of Treg cells.