CD4 and inflammatory bowel disease: Recent studies have indicated the pathogenic role of CD8+ tissue-resident memory T (TRM) in immune-mediated inflammatory disorders, including psoriasis7, inflammatory bowel disease (IBD)8, and multiple sclerosis9, in which IL-17-producing CD8+ TRM (CD8+ TRM17) rather than traditionally emphasized IL-17-producing CD4+ TRM (CD4+ TRM17)10,11, drive disease progression and recurrence.