Human CD4+CCR6+CD161+ T cells from healthy donors or synovial cells from RA patients were cultured in Iscove’s modified Dulbecco’s medium with KnockOut Serum Replacement (both from Life Technologies) for 6 days in the presence of Human T Cell Activator CD3/CD28 Dynabeads (Life Technologies). IL-1β, IL-6, IL-23, and transforming growth factor–β (TGF-β1) (all at 10 ng/ml) were added on the first day of culture. On day 3, IL-2 (0.5 U/ml) and IL-23 were added. All cytokines were supplied by PeproTech, except IL-23, which was obtained from R&D Systems. Synovial tissue biopsies were obtained from RA patients undergoing joint replacement surgery after written informed consent was received.