Assessment of Airway Epithelial Damage Related to B-grade Airway-Centered Acute Rejection

Purpose Long-term survival after a lung transplantation (LTx) remains limited by Chronic Lung Allograft Dysfunction (CLAD). B-grade airway-centered acute rejection (AR) has been associated with subsequent CLAD. B-grade AR is considered a cause of airway epithelial damage, but the type of injury and specific epithelial cells at risk are poorly understood. We aimed to assess the detailed morphology of lung allograft epithelium during B-grade AR. Methods We retrospectively identified all transbronchial biopsies (TBBx) with airway-centered AR (B-grade ≥B1), collected 2-25 months after LTx from patients with a first bilateral LTx performed 2010-2015: 38 TBBx from 36 patients. 15 A0B0 TBBx from separate patients were matched to the ≥B1 TBBx according to time post LTx. Blinded semi-quantitative (scores 0-4) grading was performed of each airway using Hematoxylin & Eosin-stained sections to assess features of airway fibrosis and epithelial changes previously associated with CLAD. Immunofluorescence staining was performed using antibodies against club cell secretory protein (CCSP) and Muc-5AC. Results B-grade AR with concurrent ≥10% decline in lung function was associated with an increased risk of CLAD compared to stable B-grade AR and stable B0 TBBx (p=0.01) (figure 1A). Obliterative airway fibrosis (p=0.001) and epithelial flattening (p=0.0004) scores were higher in patients with ≥B1 compared to B0 (figure 1B). We found that epithelial hyperplasia increased over time after transplant (p=0.003) (figure 1C). The percentage of cells positive for CCSP and Muc-5AC was not different between ≥B1 and B0 TBBx (figure 1D), was not associated with time between LTx and TBBx, and did not correlate with our epithelial grading results. Conclusion The combination of B-grade AR and declining lung function is a predictor of CLAD. B-grade AR is associated with histologic obliterative airway fibrosis and epithelial flattening. Further analyses of specific epithelial cell types and changes during B-grade AR are ongoing.