Then, we applied 11C-l-1MTrp to longitudinally monitor whole-body IDO1 variations in immunocompetent melanoma-bearing mice treated with 1-methyl-l-tryptophan plus either chemotherapeutic drugs or antibodies targeting programmedcell death 1 and cytotoxic T-lymphocyte-associated protein 4. This evidence concerns the gene IDO1 and melanoma.