Construction, identification, and immunogenic assessments of an HSV-1 mutant vaccine with a UL18 deletion

HSV-1 is a mucosal and nerve pathogen, whose morbidity shows an increasing tendency. Although several antiviral drugs exist, there is no cure for viral latency for virtually all carriers. There is an urgent need for an HSV-1 vaccine to control infection and limit its spread and recurrence. The UL18 gene, encoding a vital component of capsids, is one of the essential genes of HSV-1. Deletion of UL18 from HSV-1 may be exploited as a new approach to develop an attenuated vaccine. The purpose of this study was to construct a DNA vaccine with a full-length UL18 gene deletion of the HSV-1 genome that can induce an effective immune response. A UL18-knockdown plasmid (BAC-HSV-1ΔUL18) was constructed using the bacterial markerless gene knockout system, consisting of the functional pREDI plasmid and BAC-HSV-1 plasmid. Mice were immunized weekly for 3 weeks, and at 1 week post immunization, blood and splenocyte samples of vaccinated and control groups of mice were prepared for immunogenicity assessment. The level of immune response was evaluated using a DTH assay, cytokine determination, and splenocyte proliferation assay. Combination of the pREDI plasmid and BAC-HSV-1 plasmid provides an effective bacterial markerless gene knockout system. Using two-step homologous recombination with the UL18 homologous recombination fragment constructed by multistep PCR amplification, BAC-HSV-1ΔUL18 plasmid vaccine was successfully constructed and was found to significantly enhance cellular immune responses.