Cholera toxin conjugates for intragastric vaccination against herpes simplex virus type 2

In this study, we tested the hypothesis that enteric immunization with cholera toxin (CTX) conjugated to glycoprotein D (gD) of herpes simplex virus type 2 (HSV-2) or a peptide corresponding to residues (1-23) of gD (gD(1-23)) would induce relevant antiviral immunity. Intraperitoneal (IP) immunization of mice with CTX-gD(1-23) conjugate induced anti-HSV-2 sera antibody responses which correlated with protection from a lethal IP challenge with HSV-2. Intragastric (IG) immunization of mice with the same conjugate or a CTX-gD conjugate did not result in measurable anti-HSV-2 responses in sera or vaginal washings and only small numbers of anti-HSV-2 antibody-secreting cells (ASC) were found in intestinal lamina propria cell and splenocyte preparations. In comparison, anti-CTX responses were detected in sera and vaginal washings after IG immunization with CTX and anti-CTX ASC in lamina propria cell preparations accounted for 5-10% of total ASC detected at this site. No significant differences in the survival of mice immunized with the conjugates were noted after a lethal intravaginal (IVAG) challenge with HSV-2. The poor enteric immunogenicity of gD(1-23) and gD conjugated to CTX was attributable to proteolysis in the gastrointestinal tract. These results indicate that although peptide-CTX conjugates can induce protective immune responses when administered parenterally, it may not be feasible to use peptides as the basis of an oral vaccine unless methods are developed to protect these antigens from degradation in the gastrointestinal tract.