CD4 and neoplasm: Many tumors secrete TGF-β that may directly or indirectly induce naïve T cell conversion to Foxp3+ iTregs (19, 20, 23) Consistent with this, another group demonstrated that in a mouse prostate tumor model, tumor-derived TGF-β potentiated the conversion of CD4+CD25− T conventional cells into Foxp3-expressing, CD25+ iTreg cells (19).