The Range of Human APOBEC3H Sensitivity to Lentiviral Vif Proteins

The APOBEC3H gene is polymorphic in humans, with four major population-dependent haplotypes that encode proteins with different levels of antiviral activity. Haplotype II, present most frequently in African populations, encodes the most stable protein and is most active against human immunodeficiency virus type 1 (HIV-1). In contrast to human APOBEC3G, which can be completely counteracted by HIV-1 Vif, the protein encoded by APOBEC3H haplotype II is only partially sensitive to Vif, while the protein encoded by APOBEC3H haplotype I is completely resistant to HIV-1 Vif. We mapped a residue on APOBEC3H that determines this partial Vif sensitivity. However, it is unclear how HIV-1 can replicate in vivo without the ability to neutralize APOBEC3H antiviral activity. In order to directly address this question, we cloned vif genes from HIV-1-infected individuals with different APOBEC3H genotypes and tested them for their ability to inhibit human APOBEC3H. We found that while the APOBEC3H genotype of infected individuals significantly influences the activity of Vif encoded by their virus, none of the Vif variants tested can completely neutralize APOBEC3H as well as they neutralize APOBEC3G. Consistent with this genetic result, APOBEC3H protein expression in human peripheral blood mononuclear cells was below our limit of detection using newly developed antibodies against the endogenous protein. These results demonstrate that human APOBEC3H is not as strong of a selective force for current HIV-1 infections as human APOBEC3G.