JAK3 and rheumatoid arthritis: Ritlecitinib is a selective, covalent, irreversible inhibitor of Janus kinase 3 and the tyrosine kinase expressed in hepatocellular carcinoma family kinases (1) currently in development for the treatment of alopecia areata (AA) (2), rheumatoid arthritis (RA) (3), vitiligo, ulcerative colitis, and Crohn’s disease (4).