This is a 6 month study that will evaluate the efficacy of 5mg tofacitinib tablet taken twice a day in patients with refractory myasthenia gravis. Twenty adult participants will receive a four month treatment of tofacitinib followed by elution for one month.

Inclusion Criteria:

• fluctuating muscle weakness and fatigability classified as the Myasthenia Gravis Foundation of America (MGFA) clinical classification Type IIa-IVa;
• more than 10% amplitude decrement in low frequency repetitive nerve stimulation, and less than 10% amplitude increment in high frequency repetitive nerve stimulation;
• understanding and assigning the informed consent form, and having a good compliance with treatment.

meet all of the criteria in above as well as at least one of the below:

• refractory: insufficient response to full dose- and course- steroids treatment (0.75-1mg per kg per day for at least 3-6 months), failure to respond adequately to tacrolimus (no less than 3mg per day) for 3 months;
• severe or intolerable adverse effects from conventional immunosuppressive therapy.

Exclusion Criteria:

• positive for muscle-specific kinase (MuSK) antibodies;
• a tumor history except for thymoma;
• a history of Type B and Type C hepatitis;
• a history of tuberculosis or T-SPOT.TB tset positivity;
• hepatic, renal and cardial insufficiency (baseline: ALT/AST>50U/L;BNP>200pg/ml）;
• severe allergy or infection, or chronic or recurrent infection;
• pregnancy;
• hyperlipidemia;
• participating other clinical trials

Individual participant data (IPD) are not available to other researchers.