Abstract 1013 Poster Session IV, Tuesday, 5/4 (poster 145)

Since preconceptual maternal immunity against human cytomegalovirus (HCMV) protects against symptomatic neonatal infection, subunit vaccines which target immunogenic CMV proteins may provide protection against congenital CMV disease. Optimal vaccines for CMV may require inclusion of antigens capable of eliciting neutralizing antibody responses, such as envelope glycoproteins, and also antigens capable of eliciting cytotoxic T-lymphocyte (CTL) responses, such as the virion tegument phosphoproteins. In addition, novel vaccine technologies, such as nucleic acid immunization (so-called "DNA vaccines"), deserve careful consideration. Ideally, preclinical efficacy evaluations should be performed in relevant animal models of infection. The best animal model for the study of congenital CMV infection is the guinea pig cytomegalovirus (GPCMV) model, and the recent molecular characterization of immunogenic GPCMV proteins has created the opportunity to evaluate such subunit vaccines in vivo. These studies investigated the immunogenicity of DNA vaccines which contain a GPCMV glycoprotein, gB, and also a GPCMV tegument phosphoprotein, GP83. The GP83 gene is the homologue of the major HCMV CTL target, UL83 (pp65), and has recently been cloned, identified and sequenced in our laboratory. The GPCMV gB open reading frame (ORF) was cloned into a plasmid vector utilizing the major immediate early promoter (MIEPr) of HCMV, and immunogenicity was analyzed after both intramuscular and intradermal injection. Optimal immunogenicity was observed 1) when the DNA vaccine was delivered intradermally conjugated to gold particles using a PowderJet particle delivery device and 2) when the gB ORF was truncated short of the putative transmembrane domain. BALB/c mice immunized with the gB construct uniformly mounted both ELISA and Western blot responses to gB (n=15). In addition, virus-neutralizing antibody responses were detected in some animals. Radioimmunoprecipitation experiments using antisera from DNA vaccine-immunized animals confirmed that anti-gB antibodies were capable of precipitating the native gB complex. Studies were extended to immunogenicity evaluation in Hartley guinea pigs. Intradermal immunization resulted in antibody responses in 100% (6/6) of immunized guinea pigs as assessed by ELISA and Western blot experiments. A DNA vaccine was also constructed utilizing the GP83 ORF under control of the HCMV MIEPr. This vaccine was found to elicit ELISA responses following intradermal administration in 50% (3/6) of Hartley guinea pigs. Western blot assays confirmed that these antibodies were immunoreactive with the native 70 kDa virion-associated GP83 protein. These data extend our previous observations about the efficacy of DNA vaccines in animal models, and provide justification for further evaluation of subunit vaccines for protection against congenital CMV infection.