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

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-gamma 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. The Journal of Immunology, 2017, 199: 792-805.