HLA-C and neoplasm: Lu et al. (2011) demonstrated that MDSCs are a predominant origin of the free radical peroxynitrite (PNT) in lung, pancreatic, and breast cancer samples. PNT induces post-translational modifications of cell surface molecules while not affecting cell viability, inhibiting processed peptides presentation to tumor-associated MHC molecules. Thus, tumor cells escape from antigen-specific CTLs and acquire immunological resistance (Lu et al., 2011).