Abstract
Human herpesviruses are antigenically rich agents that induce strong CD8+T cell responses in primary infection yet persist for life, continually challenging T cell memory through recurrent lytic replication and potentially influencing the spectrum of antigen-specific responses. Here we describe the first lytic proteome-wide analysis of CD8+ T cell responses to a gamma1-herpesvirus, Epstein-Barr virus (EBV), and the first such proteome-wide analysis of primary versus memory CD8+ T cell responses to any human herpesvirus. Primary effector preparations were generated directly from activated CD8+ T cells in the blood of infectious mononucleosis (IM) patients by in vitro mitogenic expansion. For memory preparations, EBV-specific cells in the blood of long-term virus carriers were first re-stimulated in vitro by autologous dendritic cells loaded with a lysate of lytically-infected cells, then expanded as for IM cells. Preparations from 7 donors of each type were screened against each of 70 EBV lytic cycle proteins in combination with the donor’s individual HLA class I alleles. Multiple reactivities against immediate early (IE), early (E) and late (L) lytic cycle proteins, including many hitherto unrecognised targets, were detected in both contexts. Interestingly however, the two donor cohorts showed a different balance between IE, E and L reactivities. Primary responses targeted IE and a small group of E proteins preferentially, seemingly in line with their better presentation on the infected cell surface before later-expressed viral evasins take full hold. By contrast, target choice equilibrates in virus carriage with responses to key IE and E antigens still present but with responses to a select subset of L proteins now often prominent. We infer that, for EBV at least, long-term virus carriage with its low level virus replication and lytic antigen release is associated with a re-shaping of the virus-specific response.
Highlights
Human herpesviruses are ancient pathogens that have co-evolved with our species and its antecedents over millions of years, producing a finely balanced virus-host relationship in which both primary infection and subsequent life-long virus carriage are typically asymptomatic
Herpesviruses are carried by most people as lifelong asymptomatic infections but become life-threatening in immunocompromised individuals
Pathogenic of the human herpesviruses, with primary infection producing a severe flulike illness called infectious mononucleosis, and persistent infection being causally linked to a range of Epstein-Barr virus (EBV)-associated cancers
Summary
Human herpesviruses are ancient pathogens that have co-evolved with our species and its antecedents over millions of years, producing a finely balanced virus-host relationship in which both primary infection and subsequent life-long virus carriage are typically asymptomatic. Our limited understanding of those responses reflects the antigenic complexity of these large DNA viruses with, depending on the agent, 60 to >150 proteins being expressed during the virus replicative (lytic) cycle. While all of these proteins are potentially immunogenic, they include viral evasins which partially shield infected cells from T cell (especially cytotoxic CD8+ T cell) recognition and whose effects upon the immunogenicity of lytic cycle proteins remain unclear [2]. We describe studies on Epstein-Barr virus (EBV), an oncogenic gamma1-herpesvirus, whose spectrum of lytic antigen-induced CD8+ T cell responses has never been rigorously analysed With this virus, proteome-wide screening can be conducted both on long-term virus carriers and on individuals in whom primary infection is clinically manifest as infectious mononucleosis (IM)
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