Priming immunization with a vif-deleted feline immunodeficiency virus proviral DNA vaccine boosted with a killed whole virus vaccine

Feline immunodeficiency virus (FIV) is the etiological agent of acquired immunodeficiency syndrome in domestic cats. FIV and HIV have similar genomic organization and disease progression. Thus, FIV provides an animal model to study lentiviral pathogenesis and vaccine development. Multiple FIV subtypes, based on genetic diversity in the envelope glycoprotein, poses a challenge in developing vaccines capable of protection against diverse FIV isolates. Therefore, a protein immunogen, expressing FIV Env, was generated for use in a polyvalent vaccine strategy. This approach is based on attenuated subtype A, FIV-PPRDeltavif (FIVDeltavif) DNA vaccine that demonstrated homologous protection. Construction of a mammalian expression vector encoding FIV env was attempted. Generation of this expression plasmid was unsuccessful due to instability, despite using various cloning strategies. Instability may be associated with a possible cryptic bacterial promoter driving inappropriate expression of FIV env. Alternative strategies, including use of tightly regulated bacterial plasmids require further investigation.;A whole killed virus (WKV), FIV-B, vaccine was generated as part of a polyvalent vaccine strategy that included a FIVDeltavif DNA prime and a WKV boost. This strategy was compared to DNA immunization only or WKV vaccine only. This polyvalent approach resulted in improved antibody and T-cell proliferation responses. Protection against FIV-B challenge was not evident in any vaccine group. Furthermore, vaccine-induced enhanced infectivity was observed in three cats vaccinated with the polyvalent vaccine.;Induction of a cytotoxic T-lymphocytes (CTL) response may mediate a decrease in FIV pathogenesis. However, CTL responses in vaccinated cats are not fully characterized. Consequently, development of a feline IFN-gamma ELISPOT assay to measure virus specific CD8 T-cell IFN-gamma expression was attempted. This ELISPOT assay did not detect spot forming cells, despite the use of diverse stimulating antigens. This assay may not posses the sensitivity to detect individual T-cell INF-gamma expression in FIV infected peripheral blood mononuclear cells. Stimulating antigens and feline anti-INF-gamma antibodies require further investigation. Results of these studies reveal increased immunogenicity with a polyvalent vaccine approach of DNA prime and protein boost. However, immune correlates including FIV-specific T-cell responses will require optimized cellular response assays including a feline INF-gamma ELISPOT.