Induction of protective immune response in cats by vaccination with feline leukemia virus iscom.

An effective candidate subunit vaccine consisting of the gp 70/85 of feline leukemia virus (FeLV) was prepared by using the immunostimulating complex (iscom) method for the presentation of membrane proteins of enveloped viruses. Two 32-wk-old specific pathogen-free (SPF) cats were immunized with a FeLV iscom vaccine prepared from the supernatant fluid of the FL74 tumor cell line without adjuvant. Both cats developed FeLV serum antibodies, as measured in an enzyme-linked immunosorbent assay (ELISA) and in a virus neutralization test. A proportion of the antibodies were directed to an epitope located on gp70/85, which was shown in competition ELISA with a peroxidase-labeled virus-neutralizing monoclonal antibody to be shared by all three subtypes of FeLV. The protective effect of FeLV iscom was studied by vaccinating six 8-wk-old SPF cats with iscom prepared from cell culture supernatant of another tumor cell line F422, followed by oronasal challenge with 10(6) ffu FeLV-A (strain Glasgow-1). Six unvaccinated cats were also challenged with the same dose of FeLV. The vaccinated cats developed FeLV serum antibodies, some of which were directed to the shared epitope on gp70/85. At 10 wk after challenge, none was viremic, whereas three of the control cats had developed FeLV viremia. The potential of FeLV iscom as a vaccine against FeLV-associated disease in cats, and of iscom vaccines for protection against mammalian retrovirus infections, is discussed.