CD8A and melanoma: To be sure that resistance to melanoma was not caused by a failure to negatively select T cells specific for peptides derived from H2-Aa, leading to CD8 T cell recognition of non-mutated H2-Aa peptides presented by tumor cells, we knocked out H2-Aa in B16F10 melanoma cells and showed that H2-Aacit/cit mice rejected the KO cells as well as they rejected WT B16F10 (Fig. 1 I).