Ruxolitinib for Early Lung Dysfunction After Hematopoietic Stem Cell Transplant

Inclusion Criteria: Subjects ≥ 5 years and ≤ 60 years of age who have undergone allogeneic HCT AND exhibit early lung dysfunction as defined by any one of the following: * \>10% decrease in FEV1 from baseline or decrease of 25% of FEF 25-75 from baseline * active GVHD in another organ system + pulmonary symptoms (Tachypnea without wheezing, new oxygen requirement, cough) * Increased R5 by 50% by clinical oscillometry * Air trapping on CT, small airway thickening, or bronchiectasis AND - All age groups, including adults: Adequate renal function defined as estimated Creatinine Clearance (CrCl) ≥ 30 mL/min as calculated by the cystatin c GFR or nuclear GFR Adequate hepatic function as defined by: * ALT and AST ≤ 5 x ULN, unless the ALT / AST increase is due to cGVHD * Total bilirubin of ≤ 5 x ULN (unless of non-hepatic origin or due to Gilbert's Syndrome) or Total bilirubin of \< 10 x ULN if due to GVHD Adequate hematological function defined as: * Absolute neutrophil count ≥1.0 x 10\^9/L * Platelets ≥30 x 10\^9/L PT/INR \<2 x ULN and PTT (aPTT) \< 2 x ULN (unless abnormalities are unrelated to coagulopathy or bleeding disorder) Exclusion Criteria: * Known hypersensitivity to any constituent of the study medication. * Active uncontrolled pulmonary infection (preceding infectious evaluation including bronchoscopy as clinically indicated) * Subjects who are pregnant or breastfeeding or are at risk of pregnancy or fathering a baby and are unable to use acceptable highly effective method of birth control (e.g., implants, injectables, combined oral contraceptives, some intrauterine devices \[IUDs\], complete abstinence or sterilized partner) and a barrier method (e.g., condoms, cervical ring, sponge, etc.) during the period of therapy and for 90 days for both females and males after the last dose of study drug. * Subjects previously treated with investigational agent for GVHD within the 30 days prior to first dose of study treatment. Other non-GVHD additional investigational agents may be allowed on a case by case basis with review/approval by the study Lead PI.