Immunization with a Vaccine Combining Herpes Simplex Virus 2 (HSV-2) Glycoprotein C (gC) and gD Subunits Improves the Protection of Dorsal Root Ganglia in Mice and Reduces the Frequency of Recurrent Vaginal Shedding of HSV-2 DNA in Guinea Pigs Compared to Immunization with gD Alone

Abstract

Attempts to develop a vaccine to prevent genital herpes simplex virus 2 (HSV-2) disease have been only marginally successful, suggesting that novel strategies are needed. Immunization with HSV-2 glycoprotein C (gC-2) and gD-2 was evaluated in mice and guinea pigs to determine whether adding gC-2 to a gD-2 subunit vaccine would improve protection by producing antibodies that block gC-2 immune evasion from complement. Antibodies produced by gC-2 immunization blocked the interaction between gC-2 and complement C3b, and passive transfer of gC-2 antibody protected complement-intact mice but not C3 knockout mice against HSV-2 challenge, indicating that gC-2 antibody is effective, at least in part, because it prevents HSV-2 evasion from complement. Immunization with gC-2 also produced neutralizing antibodies that were active in the absence of complement; however, the neutralizing titers were higher when complement was present, with the highest titers in animals immunized with both antigens. Animals immunized with the gC-2-plus-gD-2 combination had robust CD4؉ T-cell responses to each immunogen. Multiple disease parameters were evaluated in mice and guinea pigs immunized with gC-2 alone, gD-2 alone, or both antigens. In general, gD-2 outperformed gC-2; however, the gC-2-plus-gD-2 combination outperformed gD-2 alone, particularly in protecting dorsal root ganglia in mice and reducing recurrent vaginal shedding of HSV-2 DNA in guinea pigs. Therefore, the gC-2 subunit antigen enhances a gD-2 subunit vaccine by stimulating a CD4 ؉ T-cell response, by producing neutralizing antibodies that are effective in the absence and presence of complement, and by blocking immune evasion domains that inhibit complement activation.

Protection Provided by a Herpes Simplex Virus 2 (HSV-2) Glycoprotein C and D Subunit Antigen Vaccine against Genital HSV-2 Infection in HSV-1-Seropositive Guinea Pigs

“…Animals were mock immunized with the CpG oligonucleotide TCGTCGTTGTCGTTTTGT CGTT (Trilink Inc.) and alum (Alhydrogel; Accurate Chemical and Scientific Corp.) or immunized with 10 g bac-gC2(426t) (gC2), 5 g bacgD2(306t) (gD2), or 10 g gC2 combined with 5 g gD2 (gC2/gD2). The doses of gC2 and gD2 were based on our prior studies indicating that higher doses of gC2 immunization are needed to generate robust C3b-blocking antibody responses (21). Subunit antigens were mixed with CpG at 100 g/guinea pig and with alum at 20 g/g protein in a total volume of 50 l per immunization (46).…”

“…HSV-1 strain NS and HSV-2 strain MS were grown in Vero cells (20,21). In study 1, glycoprotein subunit antigens were prepared in baculovirus.…”

“…Plates were coated with 50 ng of antigen, and serial dilutions of serum were added (21). The endpoint titer was considered the highest dilution of serum resulting in an optical density (OD) of Ն0.1 that was at least 2-fold higher than the OD of sera obtained from mock-immunized animals at that dilution.…”

“…We reported that HSV-1 glycoprotein C (gC1) and HSV-2 glycoprotein C (gC2), used in combination as subunit antigens with gD1 and gD2, respectively, prevented the virus from evading immune responses mediated by complement (20,21). HSV-1 and HSV-2 gC proteins bind complement component C3b generated by activation of the classical, lectin, or alternative complement pathway.…”

“…By binding to C3b, HSV-1 and HSV-2 gC proteins inhibit activation of the complement cascade (26)(27)(28)(29)(30)(31)(32). We previously reported that antibodies induced by immunization of animals with gC1 or gC2 bind to gC and block its ability to interact with C3b; thus, complement remains active in host defense against the virus (20,21,33). In mouse and guinea pig vaginal infection models, a bivalent gC2/gD2 subunit antigen vaccine provided significantly better protection than monovalent gC2 or gD2 subunit antigen vaccines in preventing DRG infection and recurrent vaginal shedding of HSV-2 DNA (21).…”