Potential of Equine Herpesvirus 1 as a Vector for Immunization

Abstract

Key problems using viral vectors for vaccination and gene therapy are antivector immunity, low transduction efficiencies, acute toxicity, and limited capacity to package foreign genetic information. It could be demonstrated that animal and human cells were efficiently transduced with equine herpesvirus 1 (EHV-1) reconstituted from viral DNA maintained and manipulated in Escherichia coli. Between 13 and 23% of primary human CD3 ؉ , CD4 ؉ , CD8 ؉ , CD11b ؉ , and CD19 ؉ cells and more than 70% of CD4 ؉ MT4 cells or various human tumor cell lines (MeWo, Huh7, HeLa, 293T, or H1299) could be transduced with one infectious unit of EHV-1 per cell. After intranasal instillation of EHV-1 into mice, efficient transgene expression in lungs was detectable. Successful immunization using EHV-1 was shown after delivery of the human immunodeficiency virus type 1 Pr55 gag precursor by the induction of a Gag-specific CD8 ؉ immune response in mice. Because EHV-1 was not neutralized by human sera containing high titers of antibodies directed against human herpesviruses 1 to 5, it is concluded that this animal herpesvirus has enormous potential as a vaccine vector, because it is able to efficiently transduce a variety of animal and human cells, has high DNA packaging capacity, and can conveniently be maintained and manipulated in prokaryotic cells.Equine herpesvirus 1 (EHV-1), an alphaherpesvirus, causes infections in equines. Usually the disease induced by the virus is mild, and approximately 90% of equines worldwide harbor the agent, whose persistence in animals is lifelong. One of the peculiarities of EHV-1 is its tropism for blood mononuclear cells, which are the primary site for establishment of EHV-1 latency. Neuronal tissues, including the trigeminal ganglion and the brain, are only rarely infected by the agent. Neurological symptoms after infection of equines with certain EHV-1 strains are caused by infection of endothelial cells and subsequent hypoxia and neuronal degradation and are consistent with myeloencephalopathy and not myeloencephalitis (40,62).Herpesviridae enter target cells by fusion of the viral envelope with the plasma membrane at neutral pH after attachment of virions to cell surface glycosaminoglycans (47,51). Glycoproteins are crucially involved in these early stages of infection, and 11 glycoproteins in the prototype member of the Alphaherpesvirinae subfamily, Herpes simplex virus type 1 (HSV-1), have been identified. The herpesvirus glycoproteins involved in attachment, receptor binding, and fusion (i.e., gB, gC, gD, and the gH-gL complex) also appear to largely determine the mostly very restricted host tropism of Alphaherpesvirinae, i.e., the inability of animal viruses to naturally infect species other than those they have coevolved with (23). While the first contact and heparin-sensitive attachment of the studied alphaherpesviruses, including EHV-1, is mainly mediated by gC, receptor binding of HSV-1, pseudorabies virus, and bovine herpesvirus 1 (BHV-1) is via interaction of gD with cellular receptors th...

Evaluation of a vectored equine herpesvirus type 1 (EHV-1) vaccine expressing H3 haemagglutinin in the protection of dogs against canine influenza

“…As a result of the conservative design of the dog experiment, which did not include a vector-only control, we cannot formally exclude that innate and unspecific responses not directed to H3 contribute to the protection conferred by the EHV-1 recombinant virus. Based on the notion that herpesviruses in general and EHV-1 in particular will dampen and subvert rather than induce innate responses, and based on experiments using RacH-derived modified live virus vaccines in horses, bovines and mice, we view the induction of an unspecific protective response as highly unlikely [11][12][13][14]. In addition and as discussed earlier, the rH_EIV vector induced a robust H3-specific antibody response as measured by ELISA and HI.…”

“…the nucleoprotein [27]. Although such a vectored combination vaccine would first need to be fully re-characterized for proper growth in vitro and expression, we do not foresee major problems since EHV-1 is known to accommodate large amounts of foreign DNA [14].…”

“…RacH-based vaccine vectors stably and efficiently deliver immunogenic proteins, induce both humoral and cellular immune responses, and they may also protect vaccinated animals from heterologous challenge [11][12][13]. EHV-1 RacH has a broad host range in cultured cells and infects both dividing and non-dividing cells from different hosts including canine cells [14].…”

Equine Herpesvirus Type 1-Mediated Oncolysis of Human Glioblastoma Multiforme Cells

“…The lack of expression on Hs 683 cells was particularly noteworthy, as this cell line is highly refractory to EHV-1 infection. Previous work by Trapp et al showed that EHV-1 could infect a broad array of cell lines from multiple species (25). The ability of this virus to exhibit such a broad tropism could be attributed to its use of the MHC-I receptor, which is expressed on most cell types across species.…”

“…EHV-1 is an enveloped, double-stranded DNA virus that causes upper respiratory infection in horses and in rare cases causes paralysis and abortigenic disease (1,20). While EHV-1 does not infect humans, cells obtained from a wide array of species, including humans, are readily infected in tissue culture (25). Recently, we showed that equine major histocompatibility complex class I (MHC-I) is a cellular entry receptor for EHV-1 (12).…”