Since seroconversion is an appropriate primary outcome in prophylactic vaccine studies, constructs based on whole virus will need to include a serologic marker that identifies the immune response as vaccine – rather than natural infection-specific. Several candidates have yielded promising results in animal models. An HSV-2 ICP0 deletion mutant protected mice from infection, and was more potent than a gD2 subunit approach [95].

HF10 is a highly attenuated naturally occurring HSV-1 mutant that does not express latency associated transcripts and other important HKI-272 manufacturer viral proteins such as the UL49.5 product and which prevented genital symptoms, systemic disease, and death after intravaginal HSV-2 challenge in mice [96]. Another attractive replication-competent candidate is an HSV-2 glycoprotein E mutant, which is unable to spread from epithelial cells to neuronal cells [97]. In learn more the guinea pig model, the HSV-2 glycoprotein E mutant has shown potential both as a prophylactic

and therapeutic vaccine, although it was unable to completely prevent challenge virus infection or recurrent vaginal shedding [98]. Importantly, infectious glycoprotein E mutant virus was not recovered from dorsal root ganglia or spinal cord in mouse models, although vector DNA was found in the DRG in a minority of animals [98]. AD472, a vaccine strain with deletions Bay 11-7085 in γ34.5 and several other genes designed to improve genetic stability of the virus also protected guinea pigs, but similar to the glycoprotein E mutant, was not able to prevent wild-type infection [99]. These candidates cannot replicate in normal human cells and therefore, cannot establish latency. This inherent safety advantage may be counterweighed by weaker immunogenicity, possibly requiring higher doses

and/or repeated dosing. dl5-29 is a double mutant with deletions in UL5 and UL29, two genes which are essential for viral replication [100]. This construct protected against infection and recurrences in the guinea pig model [101]. In both HSV-1 seropositive and HSV-1 seronegative animals, vaccination with dl5-29 resulted in decreased vaginal shedding after challenge compared with gD2 subunit vaccines [102]. Recently described improvements in production and purification of this construct may make it scalable for clinical testing [103] and Phase I studies have been initiated (NCT01915212). Another novel replication-incompetent mutant is CJ-gD2, in which both copies the ICP0 gene are replaced by gD2 controlled by HSV-1 ICP4 promoter, resulting in gD2 expression at wild type levels and protection from HSV-2 in the murine model [104].