This trial tests how well itacitinib works to treat bronchiolitis obliterans syndrome, a lung condition, after a donor hematopoietic cell transplant.
The primary treatment being studied is itacitinib, which is being used to treat the primary condition of Bronchiolitis Obliterans. This treatment has previously been approved by the FDA for a different condition. There is no charge for this treatment. All patients in this trial will receive the active treatment, and there will be no placebo group.