IDO1 and melanoma: In contrast, pro-tumoral effects of IFNγ have been observed in colon carcinoma and melanoma, leading to a loss of IFNγ signaling sensitivity, reduced antigen expression (Beatty and Paterson, 2001), and induction of key immune suppressive molecules such as indoleamine-2,3-dioxygenase (IDO1) (Spranger et al., 2013) and immune checkpoint proteins (Benci et al., 2016).