Wang and Wang believed that GPR15 may be a tumor suppressor by regulating a serial of genes enriched in immune systems and increasing the infiltration of B cells (in neck squamous carcinoma, lung adenocarcinoma, and stomach adenocarcinoma), CD4+ T cells, and DCs (in neck squamous carcinoma and stomach adenocarcinoma) [30]. This evidence concerns the gene CD4 and gastric adenocarcinoma.