Strategy to Reduce Latent Reservoirs of HIV-1.

DH Hamer, PM Blumberg, S Bocklandt, S Hu, K Lueders, V Marquez, and L McHugh.

National Cancer Institute, National Institutes of health, Bethesda MD 20892 (USA)

We are developing a two-stage strategy to reduce the size of the latent reservoir of HIV-1 that is responsible for viral persistence.  The first step of this strategy is to induce the expression of latent infectious virus in the presence of highly active antiviral therapy to prevent spreading infection by newly synthesized virus.  The second step is to kill the induced HIV+ cells with a targeted toxin.  The first step uses either HIV-1 antigens to activate HIV-1-specific CD4+ cells or analogues of the lipid second messenger diacylglycerol to activate transcription through the protein kinase C pathway.  Recently we have found that synthetic diacylglycerol lactones in which the entropic penalty for ligand binding is reduced by constraining the glycerol backbone into a five-member ring induce HIV-1 with high potency with only minimal side effects such as CD4 dowregulation and inflammatory cytokine production.  The second step of the strategy utilizes recombinant toxins that recognize the viral envelope glycoprotein Env.  Toward this end we have constructed toxins that bind to Env through an engineered antibody that recognizes the CD4-binding site of gp120 with picomolar affinity, a sCD4-17B construct that simultaneously binds to both the receptor and coreceptor binding sites of gp120, and a 5-Helix toxin that recognizes an exposed and conserved binding element of the gp41 ectodomain.  This 5-Helix construct recognizes cells expressing Env from a broad spectrum of HIV-1 strains including primary isolates from clades B, D, E, G, and H and blocks spreading infection while still maintaining potent inhibitory activity against membrane fusion.   The ability of these reagents to reduce the size of the HIV-1 reservoir has been demonstrated in latently infected cell lines, SCID-hu mice, and PBMC from infected humans.