In NOD mice, the following observations have been made: development of type 1 diabetes requires CD4+ and CD8+ T cells; autoreactive T cells differentiate into killers by engaging beta cell antigens on local antigen-presenting cells; initiating CD4+ T cells are insulin-reactive; and CD8+ T cells play a major role as beta cell killers [6, 7]. The gene discussed is CD8A; the disease is type 1 diabetes mellitus.