Macitentan in the Treatment of Organ Rejection After Lung Transplantation

Inclusion Criteria: * UCLA unilateral or bilateral lung transplant recipients, ages: 21-65 years. * Females of child bearing age who could become pregnant, must implement appropriate contraception per FDA requirement for "ERA medical treatment" with mandatory MONTHLY monitoring of urine or serum pregnancy tests. * No concurrent clinically significant chronic liver disease * Screening echocardiogram (performed as usual post-transplant standard of care) with LVEF\>40%, only "Grade I" or less for "LV diastolic dysfunction". * Non-intubated, fully ambulatory patients who can perform respiratory maneuvers for office Spirometry and DCO and 6MWD (no tracheostomy). * Total of 20 patients with BOS Stage I or II, randomized double-blind to 'standard of care + placebo" versus "standard of care + MACITENTAN" Groups. * Laboratory "safety studies" are already routinely monitored in the context of post-transplant patients' chronic immunosuppressive regimen and include: comprehensive metabolic panel, tacrolimus trough level, B-type natriuretic peptide (BNP), CBC + platelet count. * "Physiologic" outcomes for this study are already considered "standard of care" for lung transplant recipients that include: Office-based Spirometry pre- and post-bronchodilator, corrected DCO, six minute walk distances + BORG score assessments (6MWD) at intervals of 1-3 months during routine Lung Transplant Clinic follow-up appointments. Exclusion Criteria: * UCLA unilateral or bilateral lung transplant recipi…