Cytomegalovirus-specific T cells restricted for shared and donor human leukocyte antigens differentially impact on Cytomegalovirus reactivation risk after allogeneic hematopoietic stem cell transplantation

Abstract

After allogeneic hematopoietic stem cell transplantation (allo-HSCT), the emergence of circulating Cytomegalovirus(CMV)-specific T cells correlates with protection from CMV reactivation, an important risk factor for non-relapse mortality. However, functional assays measuring CMV-specific cells are time-consuming and often inaccurate at early timepoints. We report results of a prospective single-center non-interventional study which identifies the enumeration of Dextramer-positive CMV-specific lymphocytes as a reliable and early predictor of viral reactivation. We longitudinally monitored 75 consecutive patients for 1 year after allo-HSCT (n=630 samples). The presence of ≥0.5 CMV-specific CD8+ cells//L at day+45 was an independent protective factor from subsequent clinicallyrelevant reactivation in univariate(p<0.01) and multivariate(p<0.05) analyses. Dextramer quantification correlated with functional assays measuring IFN-&&production, and allowed earlier identification of high-risk patients. In mismatched transplants, the comparative analysis of lymphocytes restricted by shared(S), donor(D) and host(H) specific HLAs revealed the dominant role of thymic-independent CMV-specific reconstitution. S- and Drestricted CMV-specific T cells reconstituted with similar kinetics in recipients of CMVseropositive donors, while D-restricted T-cell reconstitution from CMV-seronegative grafts was impaired, indicating that in primary immunological responses the emergence of viralspecific T cells is largely sustained by antigen encounter on host infected cells rather than by cross-priming/presentation by non-infected donor-derived APCs. Multiparametric flow cytometry and high-dimensional analysis showed that S-restricted CMV-specific lymphocytes display a more differentiated phenotype and increased persistence than Drestricted counterparts. This study shows that monitoring CMV-specific cells by Dextramer assay after allo-HSCT sheds light on immunoreconstitution mechanisms and permits patients’ risk stratification, eventually improving the clinical management of post-transplant CMV reactivations.