Diabetes does not occur in the absence of CD4+ cells, as shown by studies using anti-CD4 antibodies [9] as well as in mice that lack CD4+ T-cells [10], mice that are deficient in CD8+ cells, either by anti-CD8 antibody injection into young mice [11], or mice in which few CD8+ T-cells develop because of a genetic lack of Beta-2 microglobulin [12–14]. Here, CD8A is linked to diabetes mellitus.