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

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 theRL1(Repeat Long element 1) and/orLAT(Latency-associated Transcript) genes. The HSV-2 mutant strainsLAT-HSV-2 andRL1-LAT-HSV-2 present different biological properties. The proliferation ofRL1-LAT-HSV-2 in nerve cells was decreased significantly, and the plaques induced byRL1-LAT-HSV-2 in Vero cells were smaller than those induced byLAT-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 mutantRL1-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 theLAT-HSV-2 mutant containing theLATgene deletion. However, the simultaneous mutation of both theRL1andLATgenes 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.