Donor T and NK Cells with a Special Tissue-Resident Memory Phenotype Migrate into the Periphery of Lung Transplant Recipients - A Potential Feature for Tolerance Development

Abstract

<h3>Purpose</h3> After lung transplantation (LuTx), a transient chimerism of donor cells can be observed in recipient blood due to the migration of lymphocytes from the transplanted lung into the periphery. We aimed to characterize the phenotype of donor T and NK cells and to investigate their potential origin from tissue-resident memory (TRM) T and NK cells. <h3>Methods</h3> Lymphocyte dynamics in recipient blood were determined in n=97 LuTx patients directly (T0), 24 hours (T24) and 3 (wks) weeks after LuTx using flow cytometry. Donor T and NK cells were analyzed by HLA class I allele-specific mAb in n=44 LuTx recipients. T and NK cell markers were used to discriminate circulating from TMR subsets in blood, organ storage solutions (perfusates, n=97), explanted lung parenchyma (n=28) and donor trachea (n=17). Single cell mRNA sequencing of explant lung parenchyma was conducted (n=16). <h3>Results</h3> In peripheral blood of all recipients, donor-derived T and NK cells were detected at T0, T24 and 3 wks after LuTx, showed higher CD69 expression compared to recipient cells (p=0.01 to 0.04) and were mostly CCR7⁻ memory cells. This phenotype was similar to T and NK cells in corresponding perfusates. In recipient parenchyma and donor trachea, most CD69⁺ T and NK cells showed coexpression of TRM markers (CD103, CD49a, PD-1) with significant enrichment in trachea (p<0.05). These other TRM markers were not found in circulating donor T and NK cells or in perfusates, arguing for different memory T and NK cell subsets. Sc-mRNA sequencing confirmed distinct TRM and TRM-like T cell subsets in lung parenchyma according to separate expression profiles. The presence of TRM T and NK cells did not have an impact on primary graft dysfunction (PGD) 24h after LuTx. Yet, patients with high frequencies of donor T cells showed a trend towards CLAD-free survival 2 years post LuTx, although no statistical significance was reached (p=0.15). <h3>Conclusion</h3> Our results demonstrate that donor T and NK cells found in recipient blood immediately after LuTx are separate subsets from circulating as well as pulmonary TRM T and NK cells, since they express CD69 but lack expression of other classical TRM markers. Donor T cells may be clinically relevant for tolerance induction and long-term survival after transplantation due to their unique features.