Feline leukemia virus DNA vaccine efficacy is enhanced by coadministrationwith interleukin-12 (IL-12) and IL-18 expression vectors

The expectation that cell-mediated immunity is important in the control of feline leukemia virus (FeLV) infection led us to test a DNA vaccine adminis tered alone or with cytokines that favored the development of a Th1 immune response. The vaccine consisted of two plasmids, one expressing the gag/pol genes and the other expressing the env gene of FeLV-A/Glasgow-1. The genet ic adjuvants were plasmids encoding the feline cytokines interleukin-12 (IL -12), IL-18, or gamma interferon (IFN-gamma). Kittens were immunized by thr ee intramuscular inoculations of the FeLV DNA vaccine alone or in combinati on with plasmids expressing IFN-gamma, IL-12, or both IL-12 and IL-18. Cont rol kittens were inoculated with empty plasmid. Following immunization, ant i-FeLV antibodies were not detected in any kitten. Three weeks after the fi nal immunization, the kittens were challenged by the intraperitoneal inocul ation of FeLV-A/Glasgow-1 and were then monitored for a further 15 weeks fo r the presence of virus in plasma and, at the end of the trial, for latent virus in bone marrow. The vaccine consisting of FeLV DNA with the IL-12 and IL-18 genes conferred significant immunity, protecting completely against transient and persistent viremia, and in five of six kittens protecting aga inst latent infection. None of the other vaccines provided significant prot ection.