IDO1 and neoplasm: Some differences based on gender have been highlighted in the neoantigen load, PD-L1 protein expression and tumor mutational burden (TMB), as well as in other immune checkpoints (e.g., LAG3 and IDO1) and the distribution of immune cell populations (active CD4/CD8 T cells, memory CD4/CD8 T cells and Treg cells) [135].