Itacitinib for the Treatment of Bronchiolitis Obliterans Syndrome After Donor Hematopoietic Cell Transplant

Inclusion criteria: 1. BOS diagnosed within the past 6 months of enrollment, defined by 2015 National Institutes of Health (NIH) Consensus Criteria 126 2. Age 18-75 years 3. Undergone allogeneic SCT 4. ANC \>1,000/µL, hemoglobin \> 8 gm/dL (untransfused) and platelet count \>25,000/ µL (untransfused) 5. Karnofsky performance score \>60 6. The ability to understand and sign a written informed consent form 7. Contraception for women and men of child bearing potential. Permitted methods should be at least 99% effective in preventing pregnancy. 8. Male patients must be willing to refrain from donating sperm during their participation in the study and for at least 3 months after completing the study. Exclusion Criteria: 1. Prior treatment with any other JAK inhibitor (including Ruxolitinib) for BOS or any other indication within the past 6 months of enrolment. 2. Patients on mechanical ventilation or resting by pulse oximetry O2 saturation \<88% 3. FEV1 \<40% predicted 4. Relapsed primary malignancy for which SCT was performed 5. History of progressive multifocal leuko-encephalopathy (PML) 6. Active uncontrolled bacterial, fungal, parasitic, or viral infection 7. Known human immunodeficiency virus (HIV) infection or active hepatitis B or C infections. 8. History of tuberculosis anytime after SCT 9. Severe renal dysfunction defined by serum creatinine \> 2 mg/dL, creatinine clearance \<60 mL/minute or dialysis dependence 10. Serum transaminases \> 5 × upper limit of normal 11. inability to perform PFT reliably 12. Positive Beta HCG test in a woman with child bearing potential defined as not post-menopausal for 12 months or no previous surgical sterilization. 13. Lactating/nursing women 14. Life expectancy \< 6 months 15. Other severe organ dysfunction unrelated to underlying GVHD. For example, uncontrolled or significant cardiac disease, including any of the following: recent myocardial infarction (within last 6 months from randomization); New York Heart Association Class III or IV congestive heart failure; unstable angina (within last 6 months prior to randomization); clinically significant (symptomatic) cardiac arrhythmias (e.g., sustained ventricular; tachycardia, and clinically significant second or third degree AV block without a pacemaker); uncontrolled hypertension. Or any other concurrent severe and/or uncontrolled medical conditions which, in the opinion of the investigator, could compromise participation in the study, pose a significant risk to the subject, or interfere with study results.