Characterization of High-Avidity Cytomegalovirus-Specific T Cells with Differential Tetramer Binding Coappearing after Allogeneic Stem Cell Transplantation

Abstract

CMV reactivation is a major complication after allogeneic stem cell transplantation (SCT). Immune reconstitution of CMV-specific CTLs (CMV-CTLs) is essential for virus control. During CMV-CTL monitoring using mutated HLA/CMV tetramers selectively detecting high-avidity T cells, we observed coappearance of CMV-CTLs with low (CMV tet^low CTLs) and high tetramer binding (CMV tet^high CTLs) in 53/115 CMV IgG⁺ patients stem cell transplanted from CMV IgG⁺ donors. However, the relevance of these coappearing differentially tetramer binding ("dual") CMV-CTLs was unclear. In this study, we investigated the kinetics, properties, and clinical impact of coappearing CMV tet^low and tet^high CTLs after allogeneic SCT. Patients with dual CMV-CTLs had more CMV tet^high than tet^low CTLs. Chimerism analysis of isolated CMV tet^low and tet^high CTLs revealed their exclusive donor origin. CMV tet^low and tet^high CTLs had an identical effector memory CD45RA^-CCR7^- and CD45RA⁺CCR7^- T cell distribution, equal differentiation, senescence, and exhaustion marker expression and were negative for regulatory CD8⁺ T cell markers. Isolated CMV tet^low and tet^high CTLs were equally sensitive to CMV peptides in IFN-γ release and cytotoxicity assays. However, CMV tet^high CTLs proliferated more in response to low CMV peptide concentrations than tet^low CTLs. TCR repertoire analysis revealed that CMV tet^low and tet^high CTLs use different TCRs. Finally, dual CMV-CTLs were not associated with CMV antigenemia. In conclusion, these data show for the first time, to our knowledge, that both CMV tet^low and tet^high CTLs are functional effector T cells differing by proliferation, numbers in peripheral blood, and probably by their precursors without increasing the CMV reactivation risk after allogeneic SCT.