Abstract
Nonprimate animal models of HIV-1 infection are prevented by missing cellular cofactors and by antiviral actions of species-specific host defense factors. These blocks are profound in rodents but may be less abundant in certain Carnivora. Here, we enabled productive, spreading replication and passage of HIV-1 in feline cells. Feline fibroblasts, T-cell lines, and primary peripheral blood mononuclear cells supported early and late HIV-1 life cycle phases in a manner equivalent to that of human cells, except that produced virions had low infectivity. Stable expression of feline immunodeficiency virus (FIV) Vif-green fluorescent protein (GFP) in HIV-1 entry receptor-complemented feline (CrFK) cells enabled robust spreading HIV-1 replication. FIV Vif colocalized with feline APOBEC3 (fA3) proteins, targeted them for degradation, and prevented G-->A hypermutation of the HIV-1 cDNA by fA3CH and fA3H. HIV-1 Vif was inactive against fA3s as expected and even paradoxically augmented restriction in some assays. In an interesting contrast, simian immunodeficiency virus SIVmac Vif had substantial anti-fA3 activities, which were complete against fA3CH and partial against fA3H. Moreover, both primate lentiviral Vifs colocalized with fA3s and could be pulled down from cell lysates by fA3CH. HIV-1 molecular clones that encode FIV Vif or SIVmac Vif (HIV-1(VF) and HIV-1(VS)) were then constructed. These viruses replicated productively in HIV-1 receptor-expressing CrFK cells and could be passaged serially to uninfected cells. Thus, with the exception of entry receptors, the cat genome can supply the dependency factors needed by HIV-1, and a main restriction can be countered by vif chimerism. The results raise the possibility that the domestic cat could yield an animal model of HIV-1 infection.