FOXP3 and neoplasm: Compared to induced Treg development from CD4+ naïve T cells in the absence of tumor cells and the transwell-based co-culture system (Supplementary Figs. 1m,, n), the direct co-culture system demonstrated that C666 cells enhanced polarization from CD4+ naïve T cells to FOXP3+ Tregs and upregulated the vital eTreg marker, CTLA423 (Figs. 1j–l).