TGFB1 and cancer: When cancer-cell-derived exosomes are taken up by monocytes, the TGF-β and prostaglandin E2 contained in the exosomes induce the differentiation of monocytes into bone-marrow-derived immunosuppressive cells, which in turn release various immunosuppressive molecules, such as IL-10, thereby promoting the inactivation of immunocompetent cells and the induction of regulatory T cells to suppress anti-tumour immunity.