Ruxolitinib for Bronchiolitis Obliterans Syndrome (BOS) After Allogeneic Hematopoietic Cell Transplantation (HCT)

Inclusion Criteria: * Diagnosis of BOS after HCT defined when all of the following criteria are met (as defined by the 2014 NIH criteria): * FEV1/VC \< 0.7 or the 5th percentile of predicted. * FEV1 = Forced Expiratory Volume in 1 second. * VC = Vital Capacity (Forced Vital Capacity "FVC" or Slow Vital Capacity "SVC", whichever is greater) * The 5th percentile of predicted is the lower limit of the 90% confidence interval. * For elderly patients, use the lower limits of normal defined according to NHANESIII calculations. * FEV1 \<75% of predicted with ≥ 10% absolute decline over less than 2 years. FEV1 should not correct to \>75% of predicted with albuterol, and the absolute decline for the corrected values should still remain ≥ 10% over 2 years. The remote comparator would be an evaluation of PFTs done within 2 years of the PFTs assessment being evaluated to determine eligibility. * Absence of active infection in the respiratory tract, documented with investigations directed by clinical symptoms, such as chest radiographs or computed tomographic scans or microbiologic cultures (sinus aspiration, upper respiratory tract viral screen, sputum culture, bronchoalveolar lavage). * One of the two supporting features of BOS: * Evidence of air trapping by expiratory CT or small airway thickening or bronchiectasis by high-resolution chest CT OR * Evidence of air trapping by PFTs: RV (Residual Volume) \> 120% of predicted or RV/TLC elevated outside the 90% confide…