Update on Bronchiolitis Obliterans Syndrome in Lung Transplantation

Lung transplantation has become an important therapeutic option for patients with end-stage organ dysfunction; however, its clinical usefulness has been limited by the relatively early onset of chronic allograft dysfunction and progressive clinical decline. Obliterative bronchiolitis is characterized histologically by luminal fibrosis of the respiratory bronchioles and clinically by bronchiolitis obliterans syndrome (BOS) which is defined by a measured decline in lung function based on forced expiratory volume (FEV₁). Since its earliest description, a number of risk factors have been associated with the development of BOS, including acute rejection, lymphocytic bronchiolitis, primary graft dysfunction, infection, donor specific antibodies, and gastroesophageal reflux disease. However, despite this broadened understanding, the pathogenesis underlying BOS remains poorly understood and once begun, there are relatively few treatment options to battle the progressive deterioration in lung function.