Cytomegalovirus Infection Leads to Development of High Frequencies of Cytotoxic Virus-Specific CD4+ T Cells Targeted to Vascular Endothelium

Abstract

Cytomegalovirus (CMV) infection elicits a very strong and sustained intravascular T cell immune response which may contribute towards development of accelerated immune senescence and vascular disease in older people. Virus-specific CD8+ T cell responses have been investigated extensively through the use of HLA-peptide tetramers but much less is known regarding CMV-specific CD4+ T cells. We used a range of HLA class II-peptide tetramers to investigate the phenotypic and transcriptional profile of CMV-specific CD4+ T cells within healthy donors. We show that such cells comprise an average of 0.45% of the CD4+ T cell pool and can reach up to 24% in some individuals (range 0.01–24%). CMV-specific CD4+ T cells display a highly differentiated effector memory phenotype and express a range of cytokines, dominated by dual TNF-α and IFN-γ expression, although substantial populations which express IL-4 were seen in some donors. Microarray analysis and phenotypic expression revealed a profile of unique features. These include the expression of CX3CR1, which would direct cells towards fractalkine on activated endothelium, and the β2-adrenergic receptor, which could permit rapid response to stress. CMV-specific CD4+ T cells display an intense cytotoxic profile with high level expression of granzyme B and perforin, a pattern which increases further during aging. In addition CMV-specific CD4+ T cells demonstrate strong cytotoxic activity against antigen-loaded target cells when isolated directly ex vivo. PD-1 expression is present on 47% of cells but both the intensity and distribution of the inhibitory receptor is reduced in older people. These findings reveal the marked accumulation and unique phenotype of CMV-specific CD4+ T cells and indicate how such T cells may contribute to the vascular complications associated with CMV in older people.

Cytomegalovirus (CMV) Epitope–Specific CD4+ T Cells Are Inflated in HIV+ CMV+ Subjects

“…Dual IFN-γ and TNF-α intracellular cytokine staining of Subject 10027’s PBMCs, which produced the largest IFN-γ ELISpot response to DYS, confirmed that the ELISpot responses originated from CD4s and not CD8s, and suggested that these inflated cells were likely polyfunctional (Fig. 2F), as previously reported (11, 35). …”

“…gB-loaded endosomes are also secreted as immunogenic exosomes that stimulate CD4 + memory T cells (36, 37). In HLA-DRB1*07:01 (DR7 + ) persons, the most immunogenic gB epitope is the extremely conserved DYSNTHSTRYV (DYS) epitope that is recognized by cytotoxic, CX 3 CR1 + CD4 + T cells (11, 38). …”

Human Cytomegalovirus (HCMV)-Specific CD4 + T Cells Are Polyfunctional and Can Respond to HCMV-Infected Dendritic Cells In Vitro

“…lished (16,47,52); however, this analysis indicates that CD4 ϩ T cells specific for the other 5 proteins also possess this capacity. CMV-specific CD4 ϩ T cells from all the donors examined expressed a CD107a response to at least 1 of the 6 HCMV proteins.…”

How does cytomegalovirus factor into diseases of aging and vaccine responses, and by what mechanisms?

“…Production of pro-inflammatory cytokines in turn activates p38 in T cells, inhibits T cell telomerase activity, and promotes loss of CD28 and T cell differentiation, further creating a vicious cycle of immunosenescence (Macaulay et al 2013). CMVspecific T cells are found to express high levels of CX3CR1, which binds to injuried vascular endothelium-expressing fractalkine, and the β2-adrenergic receptor, which permits rapid response toward stress (Pachnio et al 2016;van de Berg et al 2012). It is important to note that not all persistent virus infections result in terminally differentiated T cells.…”