Immune Protection against Staphylococcal Enterotoxin–Induced Toxic Shock by Vaccination with a Venezuelan Equine Encephalitis Virus Replicon

A candidate vaccine against staphylococcal enterotoxin B (SEB) was developed using a Venezuelan equine encephalitis (VEE) virus vector. This vaccine is composed of a self-replicating RNA, termed "replicon," containing the VEE nonstructural genes and cis-acting elements and a gene encoding mutagenized SEB (mSEB). Cotransfection of baby hamster kidney cells with the mSEB replicon and 2 helper RNA molecules resulted in the release of propagation-deficient mSEB-VEE replicon particles (mSEB-VRPs). Mice inoculated subcutaneously with mSEB-VRPs were protected (15 of 20 mice) from a challenge with 5 median lethal dose units of wild-type (wt) SEB. T cells from mice vaccinated with mSEB-VRP responded normally both in vitro to wt SEB and in recall response to the inactivated mSEB polypeptide. The profile of cytokines measured after challenge with wt SEB suggested that the mode of protection was predominantly Th1 dependent. Our results suggest that the VEE replicon is a practical and convenient model system for evaluating efficacy of vaccines for the control of bacterial diseases.