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bioRxiv2024

Aberrant and Ectopic Cell Populations of the Fibrotic Pushing Border in Restrictive Allograft Syndrome after Lung Transplantation

RationaleRestrictive allograft syndrome (RAS) is a major cause of mortality in patients following lung transplantation due to rapid progressive fibrosis in the pulmonary graft. We have only limited knowledge of the cellular and molecular mechanisms that characterize the fibrosis in the RAS lung. ObjectiveTo elucidate cellularly-resolved transcriptomic and histologic characteristics of the structural cells in human RAS lungs. MethodsSingle-nuclei RNA-sequencing was performed in peripheral lung tissues from 15 RAS patients undergoing lung re-transplantation, and from 9 healthy control lungs. Findings were validated and complemented by various histologic techniques, including immunofluorescence, RNAscope, combined Elastica van Gieson-immunohistochemistry stains, and micro-CT scans. Measurement and Main resultsDifferential gene expression analysis of our single-nuclei RNA-sequencing data revealed in human RAS lungs previously undescribed and uniquely distributed aberrant basaloid cells, ectopic COL15A1+ vascular endothelial cells, and CTHRC1+ fibrotic fibroblasts, all first characterized in idiopathic pulmonary fibrosis (IPF). In contrast to IPF, RAS lacks the cellular equivalent of bronchiolization. Histologic stains confirmed our transcriptomic discoveries and disclosed distinctive distribution patterns: Aberrant basaloid cells are primarily localized at the edge of the fibrotic pushing border, forming together with the juxtaposed CTHRC1+ fibrotic fibroblasts the fibrotic niche of alveolar fibroelastosis (AFE), the histopathological hallmark in RAS lungs. On the endothelial side, PRX+ alveolar microvasculature is lost in AFE areas. Micro-CT scans revealed that blood supply, now facilitated by expanded and ectopic COL15A1+ VE cells, changes from pulmonary to systemic perfusion. Last, our data reveals potential therapeutically-modifiable expression patterns in RAS, including genes coding for the integrin subunits v{beta}6, activators of TGF{beta}. ConclusionConsidering the marked clinical, histologic and etiologic dissimilarities of RAS and IPF, our snRNAseq study revealed a surprising general principle of cellular and molecular pathogenesis in the fibrosing lung: the entity-spanning composition of the fibrotic niche by a) aberrant basaloid cells localized at the fibrotic pushing border, b) ectopic COL15A1+ vascular ECs and c) effector CTHRC1+ fibrotic fibroblasts. This general principle justifies a flexible but cellular pathogenesis-guided transferability of potential therapeutic approaches between progressive fibrotic lung diseases.

cell biology↗

bioRxiv2023

Donor tissue-resident memory-like T and NK cells generate a transient peripheral chimerism in lung transplant recipients, potentially protective from chronic lung allograft dysfunction

Lung transplantation (LTx) is the only definite treatment option of patients suffering from end- stage lung disease. Long-term outcome is hampered by chronic allograft dysfunction resulting from poorly defined immune mechanisms. In this study of 97 lung recipients, we demonstrate dynamic changes of T, B and NK cell subsets early after lung transplantation with a selective decrease in memory CD4+ and CD8+ T cells accompanied by a relative increase in NK cells. Simultaneously, donor-derived T and NK cells were detected in recipient blood (n=44) immediately after LTx, persisting for three weeks. Donor T and NK cells displayed a CD69+ but CD103-CD49a- CD25- phenotype, which was shared by T and NK cells in lung perfusion solutions. In order to uncover the origin of these donor T and NK cells, the immune compartment of human lung explant tissue, i.e. trachea and parenchyma, was analyzed and it revealed three major subsets: classical circulating CD69-CD103-CD49a- T and NK cells, CD69+CD103+CD49a+ tissue-resident memory (TRM) T and NK cells and CD69+CD103-CD49a- TRM-like T and NK cells. Single-cell RNA sequencing confirmed the presence of TRM-like subsets with unique features, which reflected the phenotypes of donor T and NK cells and created a transient chimerism in recipient blood. Higher frequencies of donor T cells within the first three weeks showed a tendency for protection from chronic lung allograft dysfunction (CLAD) two years after transplantation although the correlation analyses did not reach statistical significance. To the best of our knowledge, we show for the first time that a transient chimerism is established within the first weeks after lung transplantation by donor TRM- like T and NK cells, which may contribute to protection from chronic lung allograft dysfunction (CLAD) development. Single Sentence SummaryDonor TRM-like T and NK cells cause a transient chimerism in lung recipients and potentially contribute to protection from CLAD.

immunology↗