*Purpose: The occurence of bronchiolitis obliterans syndrome (BOS) accounts for a poor long term prognosis after lung transplantation (LTx). Despite immunosuppressive T cell-targeting therapies the survival rate after LTx remains as low as 50% after 5 years. The T cell centric paradigm is being increasingly challenged in solid organ transplantation. We recently demonstrated in a new mouse model of BOS, characterized by the onset of lymphocytic bronchiolitis (LB) after orthotopic LTx, that B cells played a central role in the development of BOS. Alarming experiences from the past strongly suggest that a systemic B cell depletion must be considered with caution if at all. We hypothesized that a subclassification of B cells based on their individual expression profiles in BOS versus non-rejecting murine lung grafts can provide insights into which B cell subset should be specifically targeted in priority to prevent BOS.

*Methods: C57BL/6J mice received C57BL/6J (non-rejecting group) or HLA-A2 knock-in (mismatched group, developing BOS) by an orthotopic LTx surgery. One month later, single cell suspensions prepared from mouse lung grafts were submitted to single cell RNA-sequencing.

*Results: An atlas of 15 cell clusters, separated according to distinct top marker genes, was generated. While the general distribution of cells amongst the different clusters was homogenous between the two groups, major quantitative shifts were observed. As such, classical monocyte, leukocyte and T cell numbers were increased respectively by 3.93-, 2.78- and 2.27-fold in the grafts with BOS. B cells, identified based on the expression of Cd79a, Cd79b and Ig genes, were further subdivided into 7 clusters. Clusters 0 and 2 were respectively enriched by 4.12- and 2.92-fold in the grafts that developed BOS versus syngeneic lung grafts, while clusters 3 and 4 were overrepresented by 5.21- and 6.78-fold in the absence of BOS. Markers for cluster 0 appeared redundant with other clusters, making it difficult to consider for further investigations. Cluster 2 was characterized by the expression of genes involved either in B cell activation, or differentiation into antibody-producing plasma cells, or regulatory/inhibitory roles, or a combination of the functions above depending on the context.

*Conclusions: Since this set of markers does not clearly relate to any described B cell subtype, we plan to characterize by flow cytometry and functionally investigate cells from cluster 2 by using classical immunology assays (mixed lymphocyte reaction and ex vivo antibody production).

« Back to 2020 American Transplant Congress