Similarly, HCAR1-mediated recruitment of the C-C motif chemokine receptor 2 positive (CCR2+) immunosuppressive polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) to the TME was observed in colorectal cancer cells, and reserpine inhibition of HCAR1 activation by lactate decreased CCR2+ PMN-MDSCs recruitment and enhanced antitumor immunity and cancer cell sensitivity to programmed cell death protein 1 (PD-1) antibody treatment [62]. Here, PDCD1 is linked to colorectal cancer.