Preconceptual administration of an alphavirus replicon UL83 (pp65 homolog) vaccine induces humoral and cellular immunity and improves pregnancy outcome in the guinea pig model of congenital cytomegalovirus infection

Development of a vaccine against congenital cytomegalovirus (CMV) infection is a major public health priority. We report the use of a propagation- defective, single-cycle, RNA replicon vector system, derived from an attenuated strain of the alphavirus Venezuelan equine encephalitis virus, to produce virus-like replicon particles (VRPs) expressing GP83, the guinea pig CMV (GPCMV) homolog of the human CMV pp65 phosphoprotein. Vaccination with VRP-GP83 induced antibodies and CD4⁺ and CD8⁺ T cell responses in GPCMV-seronegative female guinea pigs. Guinea pigs immunized with VRP-GP83 vaccine or with a VRP vaccine expressing influenza hemagglutinin (VRP-HA) were bred for pregnancy and subsequent GPCMV challenge during the early third trimester. Dams vaccinated with VRP-GP83 had improved pregnancy outcomes, compared with dams vaccinated with the VRP-HA control. For VRP-GP83-vaccinated dams, there were 28 live pups and 4 dead pups (13% mortality) among 10 evaluable litters, compared with 9 live pups and 12 dead pups (57% mortality) among 8 evaluable litters in the VRP-HA-vaccinated group (P<.001, Fisher's exact test). Improved pregnancy outcome was accompanied by reductions in maternal blood viral load, measured by real-time polymerase chain reaction. These results indicate that cell-mediated immune responses directed against a CMV matrix protein can protect against congenital CMV infection and disease.