Targeted Therapy of Bronchiolitis Obliterans Syndrome

Inclusion Criteria:

   - Diagnosis of BOS after HCT within the 6 months before study enrollment; for this
   study, BOS is defined as:

      - Forced expiratory volume in 1 second (FEV1) < 75% of the predicted normal and
      FEV1 to slow or inspiratory vital capacity ratio (FEV1/SVC or FEV1/IVC) =< 0.7,
      both measured before and after administration of bronchodilator OR

      - Pathologic diagnosis of BOS demonstrated by lung biopsy

   - The baseline absolute FEV1 must be >= 10% lower than the pre-transplant absolute FEV1
   as defined by the pre-transplant FEV1 minus the baseline FEV1, both measured before
   administration of a bronchodilator

   - Participant (or parent/guardian) has the ability to understand and willingness to sign
   a written consent document

Exclusion Criteria:

   - Recurrent or progressive malignancy requiring anticancer treatment

   - Known history of allergy to or intolerance of montelukast, zafirlukast, azithromycin,
   erythromycin, or clarithromycin

   - Pregnancy or nursing; all females of childbearing potential must have a negative serum
   or urine pregnancy test < 7 days before study drug administration

   - Transaminases > 5 X upper limit of normal (ULN)

   - Total bilirubin > 3 X ULN

   - Chronic treatment with any inhaled steroid for > 1 month in the past three months

   - Treatment with montelukast or zafirlukast for > 1 month during the past three months

   - Treatment with prednisone at > 1.2 mg/kg/day (or equivalent steroid)

   - Treatment with rifampin or phenobarbital, aspirin at doses > 325 mg/day, or ibuprofen
   at doses > 1200 mg/day

   - Treatment with any Food and Drug Administration (FDA) non approved study medication
   within the past 4 weeks; off-label treatment with an FDA-approved medication is
   allowed

   - Chronic oxygen therapy

   - Evidence of any viral, bacterial or fungal infection involving the lung and not
   responding to appropriate treatment

   - Clinical asthma (variable and recurring symptoms of airflow obstruction and bronchial
   hyper-responsiveness)

   - Any condition that, in the opinion of the enrolling investigator, would interfere with
   the subject's ability to comply with the study requirements

   - Uncontrolled substance abuse or psychiatric disorder

   - Inability to perform pulmonary function tests (PFT) reliably, as determined by the
   enrolling investigator or PFT lab

   - Life expectancy < 6 months at the time of enrollment as judged by the enrolling
   investigator

   - Baseline post-bronchodilator FEV1 < 20% of predicted normal before or after albuterol