Improved protection against Venezuelan equine encephalitis by genetic engineering of a recombinant vaccinia virus

An improved vaccine is needed against Venezuelan equine encephalitis (VEE) virus because the existing live attenuated vaccine, TC-83, causes a high in cidence of adverse effects, and the Formalin-inactivated vaccine, C-84, doe s not protect against airborne infection. A recombinant vaccine had previou sly been constructed in which the VEE structural proteins were expressed by vaccinia virus. Although protection against subcutaneous challenge with VE E was achieved, the vaccine had limited efficacy against aerosolized virus. We made a similar construct (WR100) and compared its performance with that of a recombinant vaccinia virus which had been altered in two ways (WR103) in order to improve its performance as a vaccine: a synthetic promoter was inserted upstream of the VEE coding sequence to increase the amount of VEE proteins produced, and a single nucleotide in the E2 glycoprotein gene was altered to enhance immunogenicity, The WR103 virus expressed greater amoun ts of VEE proteins on the surface of infected cells than did WR100, and thi s difference was found to correspond to a 3.5-fold increase in VEE protein production. Sera from mice immunized with WR103 contained elevated levels o f antibody to VEE, and enhanced protection against subcutaneous challenge w ith the pathogenic Trinidad donkey strain was achieved. This altered constr uct could form the basis for a better vaccine against VEE.