The JAK1/3 Inhibitor Tofacitinib Regulates Th Cell Profiles and Humoral Immune Responses in Myasthenia Gravis

ABSTRACT Introduction/Aims Tofacitinib, a first‐generation Janus kinase (JAK) 1/3 inhibitor, is commonly used for treating ulcerative colitis and rheumatoid arthritis. However, its role in myasthenia gravis (MG) remains unclear. This study aimed to evaluate the immunomodulatory effects of tofacitinib on experimental autoimmune myasthenia gravis (EAMG) and peripheral blood mononuclear cells (PBMCs) from patients with MG. Methods Flow cytometry, enzyme‐linked immunosorbent assay (ELISA), quantitative reverse transcription polymerase chain reaction (qRT‐PCR), and Western blot were used to evaluate the effects of tofacitinib on T helper (Th) cell profiles, humoral immune responses, and the JAK‐signal transducer and activator of transcription (STAT) pathway proteins. Results In vivo, tofacitinib significantly ameliorated EAMG severity in rats, reducing the proportions of Th1, Th17 and memory B cells, and anti‐acetylcholine receptor (AChR) antibodies levels, while increasing the proportions of regulatory T (Treg) cells. In vitro, tofacitinib administration resulted in a significant decrease in the proportions of Th1 and IgG‐secreting B cell, and a significant upregulation of Treg cells in mononuclear cells (MNCs) from EAMG rats, which was consistent with findings in PBMCs from MG patients. Further analysis revealed that tofacitinib inhibited CD4 + T cell differentiation into Th1 by decreasing phosphorylated STAT1 levels, while promoting Treg differentiation via increased phosphorylated STAT5 levels in MNCs from EAMG rats. Discussion Tofacitinib modulates Th cell profiles and humoral immune responses by targeting the JAK–STAT pathway, suggesting its potential as a therapeutic candidate for MG. Further clinical studies are warranted to evaluate the efficacy and safety of tofacitinib in MG patients.