Inclusion Criteria:  Willing to give written informed consent Patients diagnosed with musculoskeletal mGvHD based on 2014 NIH consensus criteria (with diagnosis confirmed by biopsy only if clinically required). Willing and able to comply with all study requirements, including treatment, and periodic assessments.  Exclusion Criteria:  Patients with known hypersensitivity to leflunomide especially previous Steven Johnson syndrome, toxic epidermal necrolysis after leflunomide. Pregnant females Patients with musculoskeletal manifestations explained by other potential causes ( (drugs, trauma, etc). Patients with calculated glomerular filtration rate (GFR) <30ml/min at the time of screening.