A new approach to an AIDS vaccine: creating antibodies to HIV vif will enable apobec3G to turn HIV-infection into a benign problem.
For a decade, attempts to produce a vaccine that prevents HIV infection have been fruitless, and fresh approaches are required. Apobec3G is a natural defensin and a cytidine deaminase. Apobec3G induces a high rate of dC to dU mutation in the first minus strand of cDNA, causing degradation throughout the HIV genome that renders the virus effete. The viral infectivity factor (vif) of HIV is essential for efficient replication of that virus. Vif binds to apobec3G and induces its polyubiquitination, which enables HIV to evade apobec3G. This suggests that a vif-based vaccine which induced anti-vif antibodies, would prevent the neutralizing action of vif upon apobec3G. Then, with HIV-vif ineffective, apobec3G could act without hindrance to create a less aggressive, non-lethal HIV infection. Mutated vif impedes HIV infection. Slow progressors with vif 132S had 4-fold lower viral loads than those with vif 132R; and introducing vif 132S into HIV-1 caused a 5-fold decrease in viral replication. And in the absence of vif, HIV virions accumulate multiple defects in structural, enzymatic, and regulatory viral proteins. The success of a vif-based vaccine depends upon (1) a vif-antibody response, and (2) vif antibodies entering the cells that harbor HIV. First, antibodies to vif have been seen in frequencies ranging between 25% and 100% in patients infected with HIV-1. Second, transport of anti-vif antibodies into cells might occur via several mechanisms. Likeliest is that in viremic persons, antibodies would attach to cell-free virions which would piggyback the antibodies into CD4+ cells. Alternatively, a fusion protein between vif and a cell-surface receptor, e.g., CD4 or CCR5, might be used as vaccine antigen. Also, anti-vif antibodies might internalize after ligation of HIV virions budding on the cell surface, in the same way as monoclonal antibodies against porcine pseudorabies virus induced viral glycoproteins on the cell surface to internalize. Finally, monoclonal antibodies, using unknown mechanisms to enter cells, have been effective against several other intracellular pathogens. In summary, HIV-vif might be effective in a vaccine intended to ameliorate either preexisting or subsequent HIV infection.
Jeffrey Fessel
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HIV Research Unit, Kaiser Permanente Medical Care Program, University of California, 2238 Geary Blvd., San Francisco, CA 94123, USA. jeffrey.fessel@kp.org
D016915:AIDS Vaccines / Q000276:immunology* / Q000627:therapeutic use; D000071480:APOBEC-3G Deaminase; D003564:Cytidine Deaminase; D016346:Gene Products, vif / Q000235:genetics / Q000276:immunology*; D015483:HIV Antibodies / Q000276:immunology*; D015658:HIV Infections / Q000235:genetics / Q000276:immunology / Q000628:therapy*; D006801:Humans; D009700:Nucleoside Deaminases; D011506:Proteins / Q000235:genetics*; D012097:Repressor Proteins; D054320:vif Gene Products, Human Immunodeficiency Virus
D016915:AIDS Vaccines; D016346:Gene Products, vif; D015483:HIV Antibodies; D011506:Proteins; D012097:Repressor Proteins; D054320:vif Gene Products, Human Immunodeficiency Virus; D009700:Nucleoside Deaminases; D000071480:APOBEC-3G Deaminase; C464924:APOBEC3G protein, human; D003564:Cytidine Deaminase