IDO1 and melanoma: In addition, when we took advantage of the endogenous IFN-γ and injected IDO1-knockdown B16 cells into wild-type mice, we found that IDO1 knockdown significantly suppressed B16 melanoma growth and prolonged the survival of mice (Fig. 8b), which however was effectively blunted by IFN-γ neutralizing antibody (Fig. 8c), further confirming that an IDO inhibitor requires the combination of IFN-γ.