An obligatory role for club cells in preventing obliterative bronchiolitis in lung transplants

Obliterative bronchiolitis (OB) is a poorly understood airway disease characterized by the generation of fibrotic bronchiolar occlusions. In the lung transplant setting, OB is a pathological manifestation of bronchiolitis obliterans syndrome (BOS), which is a major impediment to long-term recipient survival. Club cells play a key role in bronchiolar epithelial repair, but whether they promote lung transplant tolerance through preventing OB remains unclear. We determined if OB occurs in mouse orthotopic lung transplants following conditional transgene-targeted club cell depletion. In syngeneic lung transplants club cell depletion leads to transient epithelial injury followed by rapid club cell-mediated repair. In contrast, allogeneic lung transplants develop severe OB lesions that are largely devoid of club cells despite immunosuppression treatment. Lung allograft club cell ablation also triggers the recognition of alloantigens, and pulmonary restricted self-antigens reported associated with BOS development. However, CD8⁺ T cell depletion restores club cell reparative responses and prevents OB. In addition, ex vivo analysis reveals a specific role for alloantigenprimed CD8⁺ T cells in inhibiting club cell proliferation and maintenance. Taken together, our results demonstrate a vital role for club cells in maintaining lung transplant tolerance and propose a model to identify the underlying mechanisms of OB.