ENHANCEMENT OF FELINE IMMUNODEFICIENCY VIRUS-INFECTION AFTER IMMUNIZATION WITH ENVELOPE GLYCOPROTEIN SUBUNIT VACCINES

Cats were immunized three times with different recombinant feline immu nodeficiency virus (FIV) candidate vaccines. Recombinant vaccinia viru s (rVV)-expressed envelope glycoprotein with (vGR657) or without (vGR6 57x15) the cleavage site and an FIV envelope bacterial fusion protein (beta-Galactosidase-Env) were incorporated into immune-stimulating com plexes or adjuvanted with Quil A. Although all immunized cats develope d antibodies against the envelope protein, only the cats vaccinated wi th the rVV-expressed envelope glycoproteins developed antibodies which neutralized FIV infection of Crandell feline kidney cells. These anti bodies failed to neutralize infection of thymocytes with a molecularly cloned homologous FIV. After the third immunization the cats were cha llenged with homologous FIV. Two weeks after challenge the cell-associ ated viral load proved to be significantly higher in the cats immunize d with vGR657 and vGR657x15 than in the other cats. The cats immunized with vGR657 and vGR657x15 also developed antibodies against the Gag p roteins more rapidly than the cats immunized with beta-Galactosidase-E nv or the control cats. This suggested that immunization with rVV-expr essed glycoprotein of FIV results in enhanced infectivity of FIV. It w as shown that the observed enhancement could be transferred to naive c ats with plasma collected at the day of challenge.