Immunogenicity and efficacy of recombinant subunit vaccines against phocid herpesvirus type 1

Phocid herpesvirus type 1 (PhHV-1) is an α-herpesvirus that causes significant morbidity and mortality among young and immunocompromised harbour seals (Phoca vitulina) and therefore represents a major problem for seal rehabilitation centres. Consequently, there is a need for a safe and effective PhHV-1 vaccine. We tested an ISCOM-based recombinant PhHV-1 gB vaccine alone (gB) or with the addition of recombinant PhHV-1 gD (gBD) for (i) immunogenicity and protective efficacy against feline herpesvirus (FHV) infection in cats and (ii) their immunogenicity in seals. The FHV-cat model was chosen based on the close antigenic relationship between PhHV-1 and FHV. Upon challenge, all vaccinated (gB and gBD) cats excreted significantly less FHV (P<0.01) and gBD vaccinated cats showed less weight loss (P=0.05) than the mock-vaccinated cats. However, adding gD to the gB vaccine did not result in significantly better protection. Based on these data, immunogenicity studies in seals under rehabilitation were performed with the gB vaccine only. To this end, gB vaccine was tested at two different doses (20 or 40μg). PhHV-1 specific antibody titres and in vitro proliferative T cell responses were measured in all seals upon vaccination. No differences were observed in antibody titres between seals vaccinated with either 20 or 40μg gB, but the higher gB concentration did result in higher specific proliferative T cell responses (P<0.01). Based on the close antigenic relationship between PhHV-1 and FHV, the safety and efficacy data in the FHV-cat model, and the immunogenicity data in the vaccinated seals, the gB based vaccine is expected to be safe and effective in protecting against PhHV-1 related disease in harbour seals.

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