Yeast-derived glycoprotein B-1 of herpes simplex virus (HSV) as a candidate for an HSV vaccine

Antibody responses, cytokine levels and protection of mice immunised with HSV-2 antigens formulated into NISV or ISCOM delivery systems

The immunogenicity of a type 2 herpes simplex virus (HSV-2) antigen preparation following its formulation into immunostimulating complexes (ISCOMs) or non-ionic surfactant vesicles (NISV) was investigated in a murine model. The immune responses induced by each formulation were characterised by antigen specific total and subclass serum responses, and by lymphocyte proliferation and cytokine (interleukin-2 (IL-2), interleukin-4 (IL-4) and interferon-gamma (IFN-gamma)) production by in vitro restimulated spleen cells. The degree of protection afforded to mice by these various HSV-2 vaccine preparations against homologous (HSV-2) and heterologous (HSV-1) challenge infection was also determined. The findings suggest that formulation of the HSV-2 glycoprotein antigens with ISCOM or NISV delivery vehicles, and the methods used to prepare these formulations, influenced the immunogenicity of the final preparation. Higher IgG2a and neutralising antibody levels, IL-2 and IFN-gamma levels and lymphoproliferative responses were noted in mice immunised with the HSV-2 ISCOM formulated vaccine preparation. Furthermore, although HSV-2 antigens formulated in dehydration-rehydration NISV, or entrapped in NISV by freeze-thawing at 30 degrees C (HSV-2 NISV 30), also elicited relatively high antibody, IL-2 and IFN-gamma levels and relatively high lymphoproliferative responses, formulation of HSV-2 antigens by freeze-thawing with NISV at 60 degrees C (HSV-2 NISV 60) did not. There were no differences between any of the HSV-2 vaccine formulations in terms of IL-4 induction in in vitro stimulated spleen cell cultures. Almost complete protection against HSV-2 challenge was afforded by the HSV-2 ISCOM preparation, while partial protection against challenge infection was afforded by the HSV-2 NISV 30 vaccine formulation. The findings are discussed in relation to the nature of the immune mechanisms, particularly Th1- or Th2-like responses, that may be elicited by HSV-2 antigen preparations formulated into various delivery systems and the relevance of these immune responses to protection against HSV infection in the murine model.

Yeast-secreted bovine herpesvirus type 1 glycoprotein D has authentic conformational structure and immunogenicity

Bovine herpesvirus-1 (BHV-1) glycoprotein D (gD), an envelope glycoprotein, engenders mucosal and systemic immunity protecting cattle from viral infection. Production of gD with authentic immunogenicity is required for a subunit vaccine. We placed the truncated BHV-1 gD gene, lacking its putative transmembrane and cytoplasmic domains, under the control of the methanol-inducible AOX1 promoter in the yeast Pichia pastoris. Truncated BHV-1 gD (tgD) was efficiently secreted into the culture medium as a 68 kDa protein using either the yeast alpha prepro or native BHV-1 gD signal sequences. The yeast-secreted tgD had N-linked glycosylation and appears to have authentic conformational structure and immunogenicity based on the following observations A panel of monoclonal antibodies recognizing five neutralizing epitopes reacted with yeast tgD. Sera from yeast tgD-immunized mice immunoprecipitated native BHV-1 gD and neutralized BHV-1 infection in vitro. Yeast tgD competitively blocked all reaction between native gD and monospecific gD polyclonal sera from cattle. Based on these data, yeast-derived BHV-1 tgD is an excellent candidate for a subunit vaccine.