Notably, IL-10, the traditional Th2 cytokine which usually exerts dual effects on T cells in terms of inhibiting Th1 cell production of IL-2, IFNs as well as TNF-α and enhancing the proliferation and cytolysis activity of NK and CD8+ T cells, elevated in infected CMs, which indicated the susceptibility to COVID-19. The gene discussed is CD8A; the disease is COVID-19.