Diverse Specificities, Phenotypes, and Antiviral Activities of Cytomegalovirus-Specific CD8⁺T Cells

Abstract

CD8؉ T cells specific for pp65, IE1, and IE2 are present at high frequencies in human cytomegalovirus (HCMV)-seropositive individuals, and these have been shown to have phenotypes associated with terminal differentiation, as well as both cytokine and proliferative dysfunctions, especially in the elderly. However, more recently, T cell responses to many other HCMV proteins have been described, but little is known about their phenotypes and functions. Consequently, in this study, we chose to determine the diversity of HCMVspecific CD8؉ T cell responses to the products of 11 HCMV open reading frames (ORFs) in a cohort of donors aged 20 to 80 years old as well as the ability of the T cells to secrete gamma interferon (IFN-␥). Finally, we also tested their functional antiviral capacity using a novel viral dissemination assay. We identified substantial CD8 ؉ T cell responses by IFN-␥ enzyme-linked immunospot (ELISPOT) assays to all 11 of these HCMV proteins, and across the cohort, individuals displayed a range of responses, from tightly focused to highly diverse, which were stable over time. CD8؉ T cell responses to the HCMV ORFs were highly differentiated and predominantly CD45RA ؉ , CD57 ؉ , and CD28 ؊ , across the cohort. These highly differentiated cells had the ability to inhibit viral spread even following direct ex vivo isolation. Taken together, our data argue that HCMV-specific CD8 ؉ T cells have effective antiviral activity irrespective of the viral protein recognized across the whole cohort and despite viral immune evasion. IMPORTANCEHuman cytomegalovirus (HCMV) is normally carried without clinical symptoms and is widely prevalent in the population; however, it often causes severe clinical disease in individuals with compromised immune responses. HCMV is never cleared after primary infection but persists in the host for life. In HCMV carriers, the immune response to HCMV includes large numbers of virus-specific immune cells, and the virus has evolved many mechanisms to evade the immune response. While this immune response seems to protect healthy people from subsequent disease, the virus is never eliminated. It has been suggested that this continuous surveillance by the immune system may have deleterious effects in later life. The study presented in this paper examined immune responses from a cohort of donors and shows that these immune cells are effective at controlling the virus and can overcome the virus' lytic cycle immune evasion mechanisms.

Identification of immediate early gene products of bovine herpes virus 1 (BHV-1) as dominant antigens recognized by CD8 T cells in immune cattle

“…In this regard, the CD8 T-cell lines examined in the current study were derived from blood T cells harvested 15 days after virus challenge of animals previously vaccinated with a live attenuated vaccine. Previous longitudinal studies of CD8 T-cell responses to human CMV and EBV indicated that the range of CD8 T-cell specificities remains relatively stable over time [13,46,47], although in some instances a less pronounced dominance hierarchy has been observed in the memory pool compared to the active response [48]. It is possible that the detection in the current study of prominent responses to BHV-1 IE proteins reflects preferential expansion of pre-existing memory T cells specific for the IE antigens in the 15-day period immediately following virus challenge.…”

“…However, certain proteins tend to be recognized more consistently and generate stronger responses than others, eg. pp65 and IE1 in CMV [13]. Analyses of CD8 T cells from humans infected with herpes simplex virus type 1 (HSV-1), an alpha herpesvirus most closely related to BHV-1, have identified CD8 T-cell reactivity with over half the viral proteins, including proteins with diverse expression dynamics [7,8].…”

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

“…A UL83 (pp65) ORF 15-mer peptide library was synthesized by JPT Peptide Technologies GmbH (Berlin, Germany). The individual lyophilized peptides from each ORF library were reconstituted and used as previously described (54).…”

Cytomegalovirus-Associated CD4+CD28null Cells in NKG2D-Dependent Glomerular Endothelial Injury and Kidney Allograft Dysfunction

“…Regarding this, knowledge of specific viral proteins to which CMV-specific CD4 + cells respond would be informative but is not currently available and was beyond the current study's scope. However, of relevance, many healthy CMV-seropositive individuals control CMV effectively with a CD8 + T cell repertoire predominantly directed against early-expressed viral proteins, rather than later structural components (22 …”