For lymphocyte subsets, CD8+ T cell and CD4+ CD8dim T cell count were identified with causal effect on T2D susceptibility (CD8+ T cell: OR = 1.09, 95% CI = 1.03–1.17, p = 0.0053; CD4+ CD8dim T cell: OR = 1.04, 95% CI = 1.01–1.08, p = 0.0070). The gene discussed is CD8A; the disease is type 2 diabetes mellitus.