IDO1 and neoplasm: Another study documented the role of attenuated shIDO-ST (S. typhimurium delivering an shRNA plasmid targeting IDO) in inhibiting the expression of several inhibitory checkpoint proteins, including PD-L1, PD-1, and CTLA4, in different splenic immune cells [137] which highlights the capacity of Salmonella to restructure the immune component of the tumor microenvironment in favor of tumor inhibition.