CD4 and type 1 diabetes mellitus: However, there was a significant difference in type 1 diabetes development in recipients of CD226 KO CD4+ + CD226 KO CD8+ T cells versus those in which only CD8+ T cells were CD226 KO, suggesting that while CD226 expression on both CD4+ and CD8+ T cells may contribute toward diabetogenesis in the NOD mouse, the CD226 KO effect is primarily manifest in CD4+ T cells in this adoptive transfer setting with a fixed CD4+:CD8+ T cell ratio.