Safety and immunogenicity of a TK/gI/gE gene-deleted feline herpesvirus-1 mutant constructed via CRISPR/Cas9 in feline

Feline herpesvirus-1 (FHV-1) is the aetiological agent of feline viral rhinotracheitis, which accounts for approximately 50 % of all viral upper respiratory diseases in cats. Commercially available modified live vaccines containing FHV-1 are generally safe and effective, but these FHV-1 vaccines retain full virulence genes and can establish latency and reactivate to cause infectious rhinotracheitis in vaccine recipients, raising safety concerns. To address this shortcoming, we constructed a novel TK/gI/gE -gene-deleted recombinant FHV-1 (WH2020?TK/gI/gE) through CRISPR/Cas9-mediated homologous recombination. The growth kinetics of WH2020-?TK/ gI/gE were slightly delayed compared to those of the parent strain WH2020. Recombinant FHV-1 had severely impaired pathogenicity in cats. Felines immunized with WH2020-?TK/gI/gE produced high levels of gB-specific antibodies, neutralizing antibodies and IFN-S. Additionally, WH2020-?TK/gI/gE provided greater protection against challenge with FHV-1 field strain WH2020 than did the commercial modified live vaccine. After challenge, the cats vaccinated with WH2020-?TK/gI/gE showed significantly fewer clinical signs, pathological changes, viral shedding, and viral loads in the lung and trigeminal ganglia than those vaccinated with the commercial vaccine or unvaccinated. Our results suggest that WH2020-?TK/gI/gE is a promising candidate as a safer and more efficacious live FHV-1 vaccine, with a decreased risk of vaccine-related complications, and could inform the design of other herpesvirus vaccines.

Automated summary

Feline herpesvirus-1 (FHV-1) is a common causative agent of feline viral rhinotracheitis. Current commercial FHV-1 vaccines have safety concerns due to the retention of virulent genes. A novel recombinant FHV-1 (WH2020?TK/gI/gE) was constructed through CRISPR/Cas9-mediated homologous recombination, which showed reduced pathogenicity and provided better protection against FHV-1 challenge compared to the commercial vaccine.