Single-cell technologies have unveiled distinct subsets, such as synovial CXCR6+ TRM cells in RA that fuel osteoclastogenesis and chronic synovitis via GM-CSF and the IL-23/IL-17 axis, and CCR10+ TRM cells in SLE skin that act as reservoirs for type I interferon production. The gene discussed is CSF2; the disease is rheumatoid arthritis.