The first non-neuroinvasive live-attenuated bovine herpesvirus type 1 vaccine

PROJECT SUMMARY / SPECIFIC AIMSBovine alphaherpesvirus 1 (BoHV-1) is endemic in the USA cattle population and responsible for significanteconomic loss to the milk and beef industries. Although vaccines are commercially available none arecompetent to protect the animal's nervous system from BoHV-1 invasion and the subsequent establishment oflife-long latent infections. In addition to being the source of infectious bovine rhinotracheitis (IBR) BoHV-1 is acausative agent of "shipping fever" which results from stress placed on cattle during shipping that reactivateslatent infection. In fact current modified-live virus (MLV) vaccines retain neuroinvasive and latency propertiesand can become a complicating factor contributing to stress induced reactivations. The failure of existingproducts to offer adequate protection to cattle (from weaning to feed yards) has highlighted the need for avaccine that affords a combination of strong humoral and cell-mediated immune responses while lacking theability to establish life-long latent infections in the nervous system. We recently demonstrated that MLVvaccines that replicate in non-neural tissue but are ablated for transmission into the nervous system elicitprotective immune responses without evoking neurologic complications or establishing life-long infections. Thisvaccine design referred to as "R2" is based on the removal of a critical neuroinvasive effector region of thepUL37 tegument protein. The safety of R2 vaccines is based on their inability to invade the nervous systemand establish life-long latent infections as opposed to broader replicative attenuation strategies thattraditionally try to balance vaccine safety with efficacy. Unlike traditional BoHV-1 MLV designs R2 vaccines arecleared from the body by the induced immune response. By avoiding attenuation of BoHV-1 replication in themucosa R2 non-invasive vaccines break the safety-efficacy dilemma by producing the strongest possibleimmune response while maintaining an unprecedented degree of safety. In this application we will apply theR2 design to the development of a next-generation BoHV-1 vaccine. This will entail producing an infectiousclone of a native isolate of BoHV-1 and using this clone to make the R2 non-neuroinvasive vaccine. Theresulting recombinant strain will be tested for loss of neuroinvasive potential and vaccine efficacy in calves.This work will provide critical data for a Phase II application and to bring this much needed product to market.Aim 1: Establish a self-excising BAC infectious clone from a BoHV-1 isolate.This new clone be used to produce a vaccine free of intellectual property constraints.Aim 2: Introduce R2 mutations into the BAC and delete the US9 gene to make a marker vaccine derivative.Our established recombination methods will be used to modify the BoHV-1 BAC clone first tomutate the UL37 gene in the R2 effector coding region and second to delete the US9 gene.Propagation of the recovered viruses will be assessed in cell culture.Aim 3: Validate the safety and efficacy of the BoHV-1 live-attenuated vaccine in calves.A Go/No-Go decision to advance the BoHV-1 vaccine will be based on confirmation that the R2mutations ablate the neuroinvasive property of the virus and its virulence while also providingunprecedented protection against native BoHV-1 challenge.