We find this to be the case in our human CRC and mouse colon tumor samples, where reduced GPR15 levels (in human tumor samples and in tumors from the AOM-DSS Gpr15 KO experimental group) is associated with the enrichment of immune subsets with inflammatory and immune-suppressive phenotypes (e.g. IL17+ CD4+ and CD8+ T cells). Here, CD4 is linked to infectious otitis media.