NOS2 and hepatocellular carcinoma: Treatment with all-trans retinoic acid (ATRA) supplements reduced splenic M-MDSCs and G-MDSCs in HCC-bearing mice, along with inhibiting iNOS, Arg1, S100A8 and S100A9 expression in G-MDSCs in tumours, resulting in increased CD8+ T cell infiltration consistent with enhanced anti-tumour immune activity [65].