Recombinant Expression of Guinea Pig Cytomegalovirus (GPCMV) Glycoprotein B: Analysis of Antibody Responses Following Vaccination of Guinea Pigs for Prevention of Experimental Congenital CMV Infection • 1474

Preconceptual maternal immunity to human cytomegalovirus (HCMV) protects against adverse fetal outcome. A major target of the protective maternal immune response against HCMV is the glycoprotein B complex (gB). The only available animal model for the study of congenital CMV infection is the guinea pig cytomegalovirus (GPCMV) model, but unfortunately relatively little is known about GPCMV gene products. We expressed the GPCMV gB in E. coli as a series of fusion proteins with glutathione-S-transferase (GST). Immunoreactivity by Western blot with high titer GPCMV antisera was found to be strongest with a fusion protein spanning Val₅₂₇ to Leu₆₃₆ of the gB protein. This region of the GPCMV gB protein is colinear with the major antigenic domain of HCMV gB (AD-1). A polyclonal antisera raised in rabbits against this fusion protein (GEX-AD1) identified the gB in virions. In a pregnancy/challenge experiment, seronegative female Hartley guinea pigs were serially immunized with 50 μg of lectin column purified viral glycoprotein or placebo. Pregancy outcomes were monitored following subcutaneous viral challenge in the late second to early third trimester. Immunization significantly improved pregnancy outcome, with 54/63 liveborn pups in the immunization group compared to 21/48 in the control group (p<0.00001). However there were no significant differences between the two groups in the percentage of animals with congenital infection as assessed by viral culture. The anti-gB response in immunized animals was assessed by Western blot, and by ELISA using the GEX-AD1 protein as the target antigen. All dams immunized with lectin column purified glycoprotein had antibody by ELISA to GEX-AD1. The anti-gB antibody responses in pups born to lectin column-glycoprotein immunized dams were compared in representative litters in which transmission of virus occurred and litters in which there was no congenital infection(n=26). Animals with congenital infection tended to have lower anti-GEX-AD1 ELISA titers than animals without congenital infection (3.32 log₁₀ anti-GEX-AD1 titer vs. 2.73 log₁₀ anti-GEX-AD1 titer), but this difference was not statistically significant (p=0.08). These results confirm that glycoprotein vaccines which target gB improve pregnancy outcome in the guinea pig model of congenital CMV. The availability of recombinantly expressed forms of GPCMV gB should prove useful in dissecting the epitopes involved in this protection.