HLA-C and Ewing sarcoma: Borowski et al. examined the expression of polymorphic and non-polymorphic MHC antigens in Ewing tumor cells, and observed that the exceptionally constant expression of HLA-C or some other non-A and non-B antigens (reactive with defined monoclonal antibodies) has important consequences for the resistance of tumor cells against specific CTL and NK cell activity in vivo [95].