FELINE IMMUNODEFICIENCY VIRUS SUBUNIT VACCINES THAT INDUCE VIRUS NEUTRALIZING ANTIBODIES BUT NO PROTECTION AGAINST CHALLENGE INFECTION

Three experimental vaccines against feline immunodeficiency virus (FIV ), all based on viral antigens presented via immune stimulating comple xes (iscoms), were tested for their capacity to induce protection in c ats from FIV infection. The respective vaccines consisted of FN propag ated in Crandell feline kidney (CrFK) cells (FIV-iscoms); FIV-iscoms s piked with recombinant vaccinia virus expressed FIV envelope glycoprot ein incorporated into iscoms (FN-iscoms + vGR657x15-iscoms) and vGR657 x15-iscoms spiked with recombinant FIV Gag protein incorporated into i scoms (vGR657x15-iscoms + FIV-Gag-iscoms), Simian immunodeficiency vir us envelope glycoprotein incorporated into iscoms, iscoms prepared wit h uninfected CrFK cells, and PBS sewed as controls, All cats vaccinate d with vGR657x15-iscoms combined with FN-iscoms or FIV-Gag-iscoms deve loped Env-specific plasma antibody responses, These antibodies neutral ised FIV infection in CrFK cells, but failed to neutralise FIV infecti on in primary feline thymocytes. FIV-iscoms induced poor Env-specific responses and only one out of six cats developed antibodies that neutr alised FIV in the CrFK cell based assay, Four weeks after challenge al l cats proved to be infected, showing that none of the vaccine prepara tions provided protection. In contrast, 2 weeks after infection, virus infected peripheral blood mononuclear cells were only observed in cat s vaccinated with FN-iscoms + vGR657x15-iscoms or Cr-FK-iscoms and to a lesser extent in cats vaccinated with FIV-iscoms and vGR657x15-iscom s + FIV-Gag-iscoms, but not in cats vaccinated with SN-iscoms or PBS, The differences found in cell associated virus loads amongst the respe ctive groups are discussed in the light of antibody mediated enhanceme nt of infectivity and protective effects provided by Gag-specific T ce ll responses, (C) 1997 Elsevier Science Ltd, All rights reserved.