Identification of equine herpesvirus-1 antigens recognized by cytotoxic T lymphocytes

Abstract

Equine herpesvirus-1 (EHV-1) causes serious disease in horses throughout the world, despite the frequent use of vaccines. CTLs are thought to be critical for protection from primary and reactivating latent EHV-1 infections. However, the antigen-specificity of EHV-1-specific CTLs is unknown. The aim of this study was to identify EHV-1 genes that encode proteins containing CTL epitopes and to determine their MHC I (or ELA-A in the horse) restriction. Equine dendritic cells, transfected with a series of EHV-1 genes, were used to stimulate autologous CTL precursor populations derived from previously infected horses. Cytotoxicity was subsequently measured against EHV-1-infected PWM lymphoblast targets. Dendritic cells were infected with EHV-1 (positive control) or transfected with plasmids encoding the gB, gC, gD, gE, gH, gI, gL, immediateearly (IE) or early protein of EHV-1 using the PowderJect XR-1 research device. Dendritic cells transfected with the IE gene induced CTL responses in four of six ponies. All four of these ponies shared a common ELA-A3.1 haplotype. Dendritic cells transfected with gC, gD, gI and gL glycoproteins induced CTLs in individual ponies. The cytotoxic activity was ELA-A-restricted, as heterologous targets from ELA-A mismatched ponies were not killed and an MHC I blocking antibody reduced EHV-1-specific killing. This is the first identification of an EHV-1 protein containing ELA-A-restricted CTL epitopes. This assay can now be used to study CTL specificity for EHV-1 proteins in horses with a broad range of ELA-A haplotypes, with the goal of developing a multi-epitope EHV-1 vaccine.

Equine viral vaccines: the past, present and future

“…In order to use recombinant technology, it is essential to identify those proteins containing CTL epitopes. As was shown for equine infectious anemia virus [57] and equine herpesvirus 1 [87], CTL responses in the horse are MHC class I (or ELA-A in the horse) restricted. The latter molecules are highly polymorphic, meaning that epitopes inducing strong CTL responses in horses expressing one MHC allele might not be immunogenic in horses expressing a different allele.…”

“…Research has just started to address this issue [87]. In addition, little is known about the EHV virulence genes that could be candidates for targeted deletions in order to develop safe and efficacious vaccines.…”

“…The latter molecules are highly polymorphic, meaning that epitopes inducing strong CTL responses in horses expressing one MHC allele might not be immunogenic in horses expressing a different allele. The identification of broadly recognised, dominant epitopes that induce strong CTL responses in horses with different genetic backgrounds is a major challenge and the subject of future research [57,87]. However, it is realistic to assume that a single protein most probably will not fulfil this requirement.…”

Intramuscular Immunization of Mice with the Live-Attenuated Herpes Simplex Virus 1 Vaccine Strain VC2 Expressing Equine Herpesvirus 1 (EHV-1) Glycoprotein D Generates Anti-EHV-1 Immune Responses in Mice

“…These results indicate that the VC2-EHV-1-gD vaccination generated a strong Th1 response priming the animals prior to challenge. Cytotoxic T lymphocytes (CTLs) are thought to be primarily responsible for eliminating EHV-1-infected cells (34)(35)(36)(37). The VC2-EHV-1-gD vaccine increased the numbers of IFN-␥-producing CD8 ϩ cells after stimulation by peptide 3, indicating elicitation of anti-EHV-1 gD CD8 ϩ T cell responses (Fig.…”

Equine Herpes Virus-1: Virus, Immunity and Vaccines

“…Products of the single EHV-1 IE gene (ORF 64) have already been identified as CTL targets [83,84]. Dendritic cells (DC) transfected with ORF 64 can induce a CTL response from cells purified from EHV-1 primed ponies that express the MHC class I A3 serological haplotype.…”