TGFB1 and cancer: In order to address, the source of inactive TGF-β1 which accumulate in the TME of Foxp3ΔItgβ8 mice, we selectively ablated tgf-β1 in cancer cells regarded as high producer cells of TGF-β1 (TGF-β1KO) in the TME2,3 (Supplementary Fig. 3A).