Time to Explore Preventive and Novel Therapies for Bronchiolitis Obliterans Syndrome after Allogeneic Hematopoietic Stem Cell Transplantation

Although allogeneic hematopoietic stem cell transplant (allo-HSCT) is performed to treat otherwise incurable and fatal diseases, transplantation itself can lead to life-threatening complications due to organ damage. Pulmonary complications remain a significant barrier to the success of allo-HSCT. Lung injury, a frequent complication after allo-HSCT, and noninfectious pulmonary deaths account for a significant proportion of non-relapse mortality. Bronchiolitis obliterans syndrome (BOS) is a common and potentially devastating complication. BOS is now considered a diagnostic criterion of chronic graft-versus-host-disease (cGVHD), and National Institutes of Health (NIH) consensus has been published to establish guidelines for diagnosis and monitoring of BOS. It usually occurs within the first 2 years but may develop as late as 5 years after transplantation. Recent prevalence estimates suggest that BOS is likely underdiagnosed, and when severe BOS does occur, current treatments have been largely ineffective. Prevention and effective novel approaches remain the primary tools in the clinician's arsenal in managing BOS. This article provides an overview of the currently available and novel strategies for BOS, and we also discuss specific preventive interventions to reduce severe BOS after allo-HSCT. Therapeutic trials continue to be needed for this orphan disease.