Comprehensive evaluation of tumor-infiltrating immune cells revealed that SLC25A22 knockout consistently decreased infiltration of immunosuppressive MDSC in KRAS-mutant tumors in murine allografts, intestine-specific SL25A22 knockout mice, and in human CRC xenografts engrafted in PBMC humanized mice, whereas CD4+ and CD8+ T cells were increased. The gene discussed is KRAS; the disease is colorectal carcinoma.