TGFB1 and neoplasm: Since the presence of soluble factors such as TGF-β in the tumor microenvironment (TME) can significantly affect NK cell phenotype and function in response to target cell stimulation, we analyzed TGF-β1 content in the supernatant of tumor target cells incubated alone or co-cultured with NK cells but found no detectable levels of TGF-β1 secretion (S2 Fig) [19, 20].