Herpes Simplex Virus (HSV) as Vaccine-vectors

With a deeper understanding of viral biology and the immune system, the field of viral vector vaccines has expanded rapidly in recent years. At present, a wide range of viral vectors has been developed and applied to various types of diseases ranging from certain cancers to a large number of infectious diseases. Creative Biolabs has been committed to the development and production of new vaccine vectors for many years and provided many types of highly efficient viral vaccine vectors to customers around the world. As a service provider, our goal is to provide the highest level of service, confidentiality and customer support.

The Structure of HSV

Herpes simplex virus (HSV) is an enveloped, double-stranded (ds) DNA virus. Mature virions consist of different components: an outer envelope containing about 12 glycoproteins that participate in different functions; an amorphous layer known as the tegument containing about 20 different proteins with structural and regulatory effects; and an icosadeltahedral capsid of dsDNA. The HSV-1 genome is a 152 kb of linear dsDNA arranged as long and short unique segments (UL and US) flanked by inverted repeats. The HSV genome encodes approximately 90 genes that can be classified into essential or non-essential genes based on their requirements for viral replication in tissue culture. The essential genes are critical to the growth of the virus, and viral mutants lacking these genes can only establish a lytic infection when these deletions are provided by the engineered cell line in trans. Non-essential genes are typically required for viral-host cell interactions, such as escape of host immune responses and host cell shut-off, which are important for growth during infection in vivo, but are not essential for growth in tissue culture.

Fig.1 (a) The position of the gene encoding the HSV-1 glycoprotein within the HSV-1 genome. Those listed below the viral genome are essential for viral replication, and those above are non-essential genes. (b) HSV particles consist of an icosahedral capsid containing a 152-kb double-stranded linear DNA genome. The viral nucleocapsid is surrounded by an amorphous tegument layer of virus and cellular proteins. The viral envelope contains 12 viral glycoproteins, those necessary for entry (gD, gB, gH/gL) and modifications for vector retargeting (gD, gB, gC, gH). (Goins. 2016)

Why HSV Can Be Used as Vaccine-vectors?

Different aspects of HSV biology render this virus attractive for designing of gene therapy vectors:

• HSV displays a broad range of host cells and its cellular receptors are widely expressed on the cell surface of numerous cell types.
• Non-dividing cells may be efficiently infected and transduced by HSV.
• Almost half of approximately 90 known viral genes are not essential for growth in tissue culture, and their deletion can produce a sufficiently large genomic space for exogenous transgenes.
• Recombinant HSV vectors can be easily produced to high titer and purity without wild-type contaminants.
• The potential behavior of the virus may be exploited for stable long-term expression of therapeutic transgenes in neurons.
• HSV has interesting features that are retrogradely transported in neurons and metastasized in synapses and can be utilized to track neuronal pathways.

The Design of HSV as Vaccine-vectors

The primary HSV-1 vectors used to date for experimental or gene therapy include the following three types of vectors, amplicons, replication-defective and replication-competent vectors.

• Amplicon vectors
  The amplicon is a plasmid-derived vector engineered to contain the origin of HSV DNA replication (ori) and HSV cleavage packaging recognition sequences (pac). When amplicon is transfected into mammalian cells with HSV helper function, they are replicated, form head-to-tail linked concatamers and are then packaged into viral particles. However, the use of standard HSV-1 as a helper results in the production of helper‑contaminated vector stocks. Contaminant helper particles may cause significant cytotoxicity and inflammatory responses that prevent their use in gene therapy or vaccination protocols. To overcome these obstacles, Creative Biolabs offers different helper systems that do not require a helper vector, such as the helper system consisting of the entire HSV-1 genome, without the pac signal, cloned into a bacterial artificial chromosome (BAC) in E. coli providing a full set of transacting HSV‑1 function. Another different helper system recently developed is based on the deletion of the packaging signal of the helper virus in the cells producing the amplicon by site-specific recombination based on Cre/loxP.
• Replication-defective vectors
  The replication-defective virus is a viral vector in which an “essential” gene for viral replication in vitro is mutated or deleted. Therefore, these mutants cannot grow unless they are complementary in trans in the transformed cell line. To date, several replication-defective vectors have been constructed where the immediate early (IE) genes, expressing infectious cell proteins (ICP) 0, 4, 22, 27 and 47 have been deleted in various combinations.
• Replication-competent vectors
  Several genes involved in HSV replication, virulence, and immune evasion have been identified, which are not essential for the in vitro viral life cycle. These genes are often involved in multiple interactions with cellular proteins to optimize the ability of the virus to grow within the cell. Typically, the deletion/modification of these genes, alone or in combination, are used to produce HSV mutants with reduced ability to replicate in normal resting cells, but which can replicate in tumor or dividing cells. so far, many of the HSV-1 and HSV-2 genes that are not essential in culture and alter the virulence in animal models. Among these genes, genes encoding thymidine kinase (TK), ribonucleotide reductase (RR), the virion-host shut off (Vhs) and the ICP34.5 proteins have been extensively studied.

Creative Biolabs is one of the world's leading leaders in vaccine technology development, providing the highest quality and most comprehensive vaccine vector design services. If you need it, we are your best choice.

Reference

1. Goins W F, et al. (2016). Retargeting of herpes simplex virus (HSV) vectors. Current Opinion in Virology, 21: 93-101.

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