Genetic associations with both HLA-class I and class II risk alleles as well as clonal expansions of both CD4+ and CD8+ T cells in the inflammatory infiltrate of type I diabetes (11), however, complicate the decision as to which T-cell populations are ultimately pathogenetically critical and should be addressed to investigate T-cell epitopes, because they are likely to interact in the autoimmune process. The gene discussed is CD8A; the disease is type 1 diabetes mellitus.