TGFB1 and neoplasm: The inability of NK cells to reach the lesion because of imperfect vascularization, the undersupply of expression of adhesion molecules, the elevated expression of MHC class I on tumor cells, resistance to Fas- or perforin-mediated apoptosis, and the release of immunosuppressive factors by tumors, such as IL-10 or TGF-β, are some of the other mechanisms that have been proposed (75).