Replication-deficient whole-virus vaccines against cytomegalovirus induce protective immunity in a guinea pig congenital infection model

Vaccines are needed to prevent congenital human cytomegalovirus (HCMV) infections. This study used the guinea pig cytomegalovirus (GPCMV) model to examine replication-deficient whole-virus vaccines for protection against maternal viremia and congenital CMV infection. Two recombinant GPCMVs, GP51-DD and GP52-DD, were engineered with destabilization domains fused to the essential viral late proteins GP51 and GP52. These viruses, predicted to replicate in the presence of the synthetic ligand Shield-1 but not in its absence, were evaluated for Shield-1 dependence <i>in vitro</i> and for safety, immunogenicity, and efficacy in the GPCMV model. GP52-DD was profoundly Shield-1-dependent, producing no detectable infectious progeny in its absence. In contrast, the replication of GP51-DD was delayed in the absence of Shield-1 but reached similar peak titers with or without the compound. GPCMV-seronegative guinea pigs received two subcutaneous injections of phosphate-buffered saline, GP51-DD, GP52-DD, or wild-type GPCMV (WT-GPCMV). DNAemia attributable to vaccination was noted in 10/10 (100%) of WT-GPCMV-immunized animals but in only 10/28 animals (36%) immunized with DD vaccines (<i>P</i> < 0.001). GPCMV-specific ELISA and interferon-gamma ELISpot responses were similar in all vaccinated groups. When immunized animals were bred and challenged during pregnancy with virulent GPCMV, DNAemia was detected in all sham-immunized controls and in 44% of GP52-DD-immunized dams (at significantly reduced levels) but was absent in dams immunized with GP51-DD or WT-GPCMV. Immunization with GP52-DD, GP51-DD, or WT-GPCMV significantly reduced congenital GPCMV transmission compared to placebo (protective efficacies of 89, 94, and 100%, respectively). Thus, replication-impaired GP51-DD and replication-deficient GP52-DD vaccines were comparable to WT-GPCMV in immunogenicity and protective efficacy.IMPORTANCECongenital HCMV infections could potentially be prevented by a vaccine, but most vaccines that have advanced in clinical trials have been modestly effective, at best. Subunit HCMV vaccines chiefly target envelope glycoproteins, but none has proven effective at engendering durable protective immunity. A vaccine that confers immune responses to a broader repertoire of immunogens than a subunit vaccine, such as a whole-virus, live-attenuated vaccine, could confer improved protection. However, there are safety concerns for live-attenuated HCMV vaccines. Using the GPCMV model of congenital infection, this study demonstrates that two replication-impaired whole virus vaccines, though attenuated in animals, are highly immunogenic and induce preconception immunity that protects against maternal viremia and fetal infection after wild-type GPCMV challenge during pregnancy.