At the cellular level, T2DM is marked by expansion of CD8+ effector memory T cells (TEMRA), progressive depletion of naïve CD4+ and CD8+ T cells, increased frequencies of senescent CD28− T cells, and reductions in regulatory T- and B-cell populations—phenotypic hallmarks associated with immunosenescence [38,39]. The gene discussed is CD28; the disease is type 2 diabetes mellitus.