CCL2 and hepatocellular carcinoma: This was in accordance with some previous studies, for example, Li et al. revealed that in retinoblastoma FAO in tumor cells facilitated secretion of CCL2 that globally attracted a series of the immunosuppressive population including MDSCs, TAMs, and Tregs.55 Interestingly, instead of observing a mast infiltration of MDSCs into PIWIL1-overexpressing HCC tumors, we found most of the immunosuppressive MDSCs harbored accumulatively at the hepatic tissues surrounding the tumors.