Development of swinepox virus vectors delivering feline leukemia virus Gag and Env structural proteins and feline B7.1 and B7.2 costimulatory ligands

Feline leukemia virus (FeLV) causes fatal disease in domestic cats worldwide. Although FeLV vaccines are commercially available, none provide complete protection and aluminum-based adjuvants have been associated with development of life-threatening sarcomas. Hence, there is a need for a more efficacious and safer FeLV vaccine.; The replication and expression of swinepox virus (SPV) in feline cells was studied as a first step in exploring the potential use of SPV in cats. Feline cells were permissive to SPV infection and supported expression of foreign proteins driven by synthetic poxvirus promoters. However, SPV viral DNA was not replicated in feline cells and infectious virus was not recovered. FeLV Gag retrovirus-like particles were detected in swine and feline cells infected with an SPV vector containing FeLV Gag-Env, and foreign proteins were incorporated into SPV intracellular mature virions.; Feline costimulatory ligands, B7.1 and B7.2, were utilized as non-chemical adjuvants in SPV/FeLV Gag-Env vectors. Soluble and full-length feline B7 proteins were natively processed in SPV vectors grown in swine cells. Truncated soluble feline B7.1 and B7.2 proteins containing poly-histidine tags (sB7-his) were purified and used to generate feline B7 type-specific antibodies in rabbits. Feline sB7-his proteins possessed greater affinity for CTLA-4, compared to CD28, but retained the ability to partially block CD28-mediated costimulation of IL-2 from Jurkat cells. Full-length B7.1 and B7.2 proteins expressed from SPV vectors costimulated the production of IL-2 from Jurkat cells in a dose-dependant manner.; SPV vectors co-expressing FeLV Gag and Env and feline B7.1 and/or B7.2 were constructed. SPV/Gag-EnvB7 vectors produced properly processed FeLV Gag and Env and biologically active B7.1 and B7.2. SPV/Gag-EnvB7 vectors were stable over several passages and have valuable potential for development as live, non-chemically adjuvanted vaccines for protection of cats from FeLV infection.