HLA-DRB1 and rheumatoid arthritis: As a first step, in this first-in-human phase I study, we wished to explore feasibility, safety, and immunological and clinical effects of a single low, medium, or high dose of CII/calcitriol liposomes in MTX-treated HLA-DRB1*04:01/01:01+ RA patients, using a fit-for-purpose flow cytometric assay of antigen-specific T cells previously evaluated for reproducibility (25).