Deep Profiling of the CD8+ T-cell Compartment Identifies Activated Cell Subsets and Multifunctional Responses Associated with Control of Cytomegalovirus Viremia

Abstract

Background. Human cytomegalovirus (HCMV) is a common opportunistic pathogen in transplant recipients. Patterns of viremia and reactivation are influenced by the host immune response, including CD8+ T cells. However, the cellular deficits or phenotypic differences that account for differential outcomes during HCMV viremia are incompletely understood. Methods. Peripheral blood mononuclear cells were collected from 20 transplant recipients (10 viremia controllers and 10 noncontrollers) at onset of HCMV viremia and 4 weeks postonset. We used mass cytometry to perform in-depth characterization of cell surface and intracellular CD8+ T cell markers and to compare frequencies of these cells between groups. Results. Deep profiling identified 2 central memory T cell subsets at onset and 5 terminally differentiated memory T (TEMRA) cell subsets at 4 weeks that were associated with control of HCMV viremia, in addition to 6 TEMRA subsets at onset and 4 weeks associated with relapsing or remitting HCMV viremia. In general, CD8+ T-cell clusters associated with poorly controlled HCMV viremia lacked markers of activation or terminal differentiation including CD38, CD69, CD25, CD57, and HLA-DR. We also measured the production of 8 HCMV-specific effector molecules (TNFα, IFNγ, interleukin 2, granzyme B, perforin, macrophage inflammatory protein 1β, interleukin 10, and CD107a) in CD8+ T cells. Viremia controllers had greater diversity of HCMV-specific multifunctional responses at both time points, including significantly higher frequencies of HCMV-specific TNFα+IFNγ+ CD8+ T cells at onset. These multifunctional cells had a phenotype consistent with activated TEM/TEMRA cells. Conclusions. Uncontrolled CMV viremia is associated with specific clusters of memory T-cell subsets and lower frequencies of HCMV-specific multifunctional CD8+ T cells.