Due to the significant side effects in the treatment of ICI-associated colitis with corticosteroids or immunosuppressive agents, a recent study provided novel evidence that modulation of the gut microbiome via fecal microbiota transplantation could abrogate ICI-associated colitis with a substantial reduction in CD8+ T-cell density (Wang Y. et al., 2018). The gene discussed is CD8A; the disease is colitis.