Under polarizing conditions to form induced regulatory T cells, the percentages of CD3+CD8+ T cells in PBMCs (Fig. 5A) significantly decreased, whereas the percentages of CD3+FOXP3+ cells in PBMCs (Fig. 5B) markedly increased after co-culturing of PBMCs with MDA-MB-231-GPR81-ncRNA cells in contrast with that after co-culturing with MDA-MB-231-GPR81-shRNA cells, suggesting an induced immunosuppression potentially medicated by GPR81 on BC cells. Here, HCAR1 is linked to breast cancer.