The Mutation of the Genes Related to Neurovirulence in HSV-2 Produces an Attenuated Phenotype in Mice

Abstract

HSV-2 (Herpes simplex virus type 2) is a critical viral agent that mainly causes genital herpes and life-long latent infection in the dorsal root ganglia. Gene modification via CRISPR/Cas9 Clustered regularly interspaced short palindromic repeat sequences/CRISPR associated 9) was used here to construct HSV-2 mutant strains through the deletion of fragments of the RL1 (Repeat Long element 1) and/or LAT (Latency-associated Transcript) genes. The HSV-2 mutant strains LAT-HSV-2 and RL1-LAT-HSV-2 present different biological properties. The proliferation of RL1-LAT-HSV-2 in nerve cells was decreased significantly, and the plaques induced by RL1-LAT-HSV-2 in Vero cells were smaller than those induced by LAT-HSV-2 mutant and wild-type strains. The observation of mice infected with these two mutants compared to mice infected with the wild-type strain indicated that the mutant RL1-LAT-HSV-2 has an attenuated phenotype with reduced pathogenicity during both acute and latent infections and induces a stronger specific immune response than the wild-type strain, whereas the attenuation effect was not found in mice infected with the LAT-HSV-2 mutant containing the LAT gene deletion. However, the simultaneous mutation of both the RL1 and LAT genes did not completely restrict viral proliferation in nerve cells, indicating that multiple HSV genes are involved in viral replication in the neural system. This work suggests that the HSV-2 genes RL1 and/or LAT might be involved in the virulence mechanisms in mouse infections.

The Role of DNA Viruses in Human Cancer

“…Chromosomal rearrangements are typical of cancers that are associated with DNA tumor viruses have been reported in HSV-1 infections. 129,130 The region of the genome of HSV-1 that encodes MUT has not been analyzed but MUT it has been shown that MUT increases the frequency of histidine reversion mutation. 131,132 The transforming region of HSV-1 also encodes the gB, ICP-18.5, ICP-8, and DNA pol genes.…”

“…Chromosomal rearrangements are typical of cancers that are associated with DNA tumor viruses have been reported in HSV-1 infections. 129 , 130 …”

The State-of-the-Art of Gene Editing and its Application to Viral Infections and Diseases Including COVID-19

“…Similar encouraging results were obtained regarding HSV-2; CRISPR/Cas9 system was used to produce a deletion mutation of the two strains of HSV-2, RL1 (Repeat Long element 1) and/or LAT (Latency-associated Transcript) genes. Compared to the wild type, The infected mice with the two mutated strains demonstrated a lower pathogenic phenotype during both phases of infections, acute and latent, and a more competent immune system ( Liu et al., 2020 ).…”

Modulation of Equid Herpesvirus-1 Replication Dynamics In Vitro Using CRISPR/Cas9-Assisted Genome Editing

“…Random indels (insertions and deletions) occur during NHEJ, leading to mutations and frameshifts in the target DNA, which lead to truncated proteins due to the premature stop codon in a different frame and prevent the translation of the active native protein. Lately, various studies have used the CRISPR/Cas9 technology to impair herpesvirus replication in vitro by targeting specific DNA sequences encoding viral proteins, such as HSV-1 [ 35 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ], human alphaherpesvirus 2 (HSV-2) [ 50 , 51 , 52 ], human betaherpesvirus 5 (cytomegalovirus (CMV)) [ 35 ], human gammaherpesvirus 4 (Epstein–Barr virus (EBV) [ 35 , 53 , 54 ], and bovine alphaherpesvirus type 1 (BHV-1) [ 55 , 56 ].…”