Li et al. investigated the immunological mechanisms by which arsenic trioxide (As2O3) can inhibit the differentiation of T helper 17 (Th17) cells by promoting the generation of regulatory T (Treg) cells by modulating the signal transducer and activator of transcription 3 (STAT3) in treatment-naïve RA patients. This evidence concerns the gene STAT3 and rheumatoid arthritis.