In combination anti-PD-1 and anti-CTLA-4 in B16 melanoma, reduced treatment efficacy was observed when MDSCs were recruited via IDO overexpression (B16-IDO) by the tumor [59, 60] and blocking MDSCs recruitment via CSF-1R blockade improved efficacy in B16-IDO but not in B16. The gene discussed is IDO1; the disease is neoplasm.