TGFB1 and neoplasm: Hence, here we examined several tumour-derived factors that have been implicated either in MDSC expansion or Id1 upregulation1, 39, 40, 42 in addition to factors that we identified as predicted upstream regulators of Id1-induced gene changes, and we identified TGFβ as one of the main tumour-derived factors responsible for Id1 upregulation in MDSCs.