Lung Allograft Dysfunction in a COVID-19 Transplanted Patient is Associated with a Peculiar Immunopathological Phenotype

PURPOSE: Lung transplantation (LT) after severe SARS-CoV-2 infection is emerging as a life-saving medical procedure for selected patients who experience acute respiratory distress syndrome (ARDS). We present the first immunopathological evaluation of a lung allograft rejection in a patient who underwent LT because of irreversible ARDS related to COVID-19. METHODS: Two male patients with irreversible ARDS caused by COVID-19 underwent bilateral LT at our Institution. A surveillance transbronchial biopsy (TBB) was performed 2 months after LT in the first patient (Pt#1), while the second patient (Pt#2) died because of allograft rejection at day 62 post LT and explanted lungs were retrieved. CT imaging of the lungs was performed three days before death. Morphological examination was performed by H&E, whereas the immunophenotyping was performed by immunohistochemistry. RESULTS: Imaging and morphological examination of Pt#2 lungs indicated the presence of a graft dysfunction with features of a restrictive, widespread usual interstitial pneumonia-like syndrome (Fig. 1A, B). The immunophenotyping showed that B-lymphocytes (CD20-positive) were nearly absent, CD8-T-cells were not particularly expanded (mean positive cells within the lung stroma=13.8%; Fig. 1C), and the CD4/CD8 ratio was not decreased (Fig. 1D). The T-regs (Foxp3-positive) were 6% of the overall population (Fig. 1E). Analysis of the immune checkpoint molecules PD1, Tigit, CTLA4 and PDL1 showed that the expression of PD-L1 alone was highly increased in vases and in alveolar cells of rejected lungs, whereas it was nearly undetectable in the TBB from Pt#1 (Fig. 1F, G). CONCLUSION: PDL1 expression in vases was previously documented as a sign of indirect ARDS. Together with our preliminary data, we can hypothesize that PDL1 may play a role in tissue effacement and graft failure, possibly indicating poor allograft prognosis.