ENHANCEMENT OF FELINE IMMUNODEFICIENCY VIRUS (FIV) INFECTION AFTER DNA VACCINATION WITH THE FIV ENVELOPE

Despite intensive experimentation to develop effective and safe vaccin es against the human immunodeficiency viruses and other pathogenic len tiviruses, it remains unclear whether an immune response that does not afford protection may, on the contrary, produce adverse effects. In t he present study, the effect of genetic immunization with the env gene was examined in a natural animal model of lentivirus pathogenesis, in fection of cats by the feline immunodeficiency virus (FIV). Three grou ps of seven cats were immunized by intramuscular transfer of plasmid D NAs expressing either the wild-type envelope or two envelopes bearing mutations in the principal immunodominant domain of the transmembrane glycoprotein. Upon homologous challenge, determination of plasma virus load showed that the acute phase of viral infection occurred earlier in the three groups of cats immunized with FIV envelopes than in the c ontrol cats. Genetic immunization, however, elicited low or undetectab le levels of antibodies directed against envelope glycoproteins. These results suggest that immunization with the FIV env gene may result in enhancement of infection and that mechanisms unrelated to enhancing a ntibodies underlay the observed acceleration.