Vaccination by cholera toxin conjugated to a herpes simplex virus type 2 glycoprotein D peptide

Immunization of BALB/cJ mice with a peptide corresponding to residues 1 to 23 of glycoprotein D [gD(1-23)] from herpes simplex virus type 2 (HSV-2) elicits antibody responses which correlate with protection against lethal HSV-2 infection. In the present study, we examined the ability of cholera toxin (CTX) to act as an immunogenic carrier for gD(1-23). The number of gD(1-23) residues conjugated to CTX affected its binding to GM1 ganglioside and physiological toxicity, both of which are factors affecting oral immunogenicity. The antibody response elicited after intraperitoneal (i.p.) immunization with the CTX-gD(1-23) conjugate was protective against a lethal i.p. challenge with HSV-2. In other experiments, mice were immunized i.p. on day 0 and subsequent immunizations conducted on days 14 and 28 were administered either intragastrically or intravaginally (i.vag.). Intraperitoneal priming followed by either i.p or intragastric boosting resulted in anti-HSV-2 antibodies in vaginal washings and in protection against a lethal i.vag. challenge with HSV-2. Intraperitoneal priming followed by i.vag. boosting did not elicit anti-HSV-2 antibodies in vaginal washings and did not protect mice against a lethal i.vag. challenge with HSV-2. These results suggest that CTX can act as a systemic and an oral delivery molecule for the covalently linked gD(1-23) peptide and that such conjugates can elicit protective immune responses against systemic and genital HSV-2 infection.