Specific Mutation of a Gammaherpesvirus-Expressed Antigen in Response to CD8 T Cell SelectionIn Vivo

Abstract

Herpesviruses are thought to be highly genetically stable, and their use as vaccine vectors has been proposed. However, studies of the human gammaherpesvirus, Epstein-Barr virus, have found viral isolates containing mutations in HLA class I-restricted epitopes. Using murine gammaherpesvirus 68 expressing ovalbumin (OVA), we examined the stability of a gammaherpesvirus antigenic locus under strong CD8 T cell selection in vivo. OVA-specific CD8 T cells selected viral isolates containing mutations in the OVA locus but minimal alterations in other genomic regions. Thus, a CD8 T cell response to a gammaherpesvirusexpressed antigen that is not essential for replication or pathogenesis can result in selective mutation of that antigen in vivo. This finding may have relevance for the use of herpesvirus vectors for chronic antigen expression in vivo.V iruses utilize diverse mechanisms for escaping the host immune response. Many RNA viruses can rapidly alter immunogenic viral antigens, whereas large double-stranded DNA (dsDNA) viruses, such as herpesviruses, are thought to rely on subversion and evasion instead. Factors that contribute to this difference include the longer replication cycle for herpesviruses, greater fidelity of DNA-dependent DNA polymerases, and the ability of herpesviruses to encode immunomodulatory molecules in their large genomes. Herpesviruses can also establish latent infections during which virus-infected cells are less effectively recognized by the host immune response. These strategies facilitate establishment of the lifelong persistence in hosts that is a characteristic of herpesvirus infection. Thus, herpesviruses are believed to remain genetically stable in spite of a strong host adaptive immune response. Because the use of herpesviruses in vaccine protocols as a means of expressing heterologous antigens from persistent viral vectors has been previously proposed (11,12), the stability of herpesvirus genomes under immune pressure is an important consideration.There is evidence for mutation of immunodominant herpesvirus epitopes in response to immune pressure. A bone marrow transplant patient with Epstein-Barr virus (EBV)-associated lymphoproliferative disease who was treated with adoptively transferred EBV-specific cytotoxic T lymphocytes (CTLs) developed progressive disease and died. Tumor cells from this patient were found to be resistant to cytolysis by the EBV-specific CTLs, and sequence analysis revealed a mutation that deleted the two immunodominant epitopes recognized by the CTLs (10). Studies have also examined EBV sequence variations in human populations with differing prevalences of specific human leukocyte antigen (HLA) alleles. EBV isolates from populations with a high frequency of the HLA A11 allele were found to contain mutations in an immunodominant A11-restricted viral epitope (7,8,18). These mutations abrogate both peptide binding to the A11 molecule and CTL recognition of lymphoblastoid cell lines (LCL) carrying these EBV mutants. Although these data are consistent with the hyp...

Autophagy Genes Enhance Murine Gammaherpesvirus 68 Reactivation from Latency by Preventing Virus-Induced Systemic Inflammation

“…We did not find increased secretion of IL-12p70 or IL-18 or changes in cell surface expression of CD80, CD86, or MHC class II in macrophages from Atg5 f/f and Atg5 f/f -LysMcre mice that might explain these observations ( Figures S3 B and S3C). We adoptively transferred transgenic CD4 T cells expressing a T cell receptor (TCR) specific for MHV68 glycoprotein gp150 ( Freeman et al., 2011 ) and CD8 T cells expressing a TCR specific for ovalbumin ( Loh et al., 2012 ) into Atg5 f/f and Atg5 f/f -LysMcre mice followed by infection with MHV68 expressing ovalbumin ( Braaten et al., 2005 ). PECs were harvested 28 days later and stimulated with specific (gp150 or ovalbumin) and control (influenza NP 366-374 ) peptides ( Figures S3 D and S3E).…”

Defining Immune Engagement Thresholds for In Vivo Control of Virus-Driven Lymphoproliferation

“…Thus, vE1 showed a strong acute reduction in total viral DNA + cell frequencies, but relative sparing of GC B cells and consequently high long-term virus loads. A position 1 mutation also impairs the control by Rag-1 −/− OT-I mice of MuHV-4 expressing OVA from an HCMV IE1 promoter [59] . However such mice lack B cells or CD4 + T cells, and without CD4 + T cells MuHV-4 causes a lethal, chronic lytic infection even with a strong, polyclonal CTL response [60] , [61] .…”

Characterization of In Vitro Expanded Virus-Specific T cells for Adoptive Immunotherapy against Virus Infection

“…tion mutants have been reported for gamma herpesvirus (28,29). Elucidation of target regions and their HLA restriction of virus-specific T cells, and quantification of the number of T cells for each target region would provide us with essential information for quality control for cellular therapy products.…”