The envelope of the human immunodeficiency virus type 1 (HIV-1) plays a central role in the process of virus entry into the host cell and in the cytopathicity of the virus for lymphocytes bearing the CD4 molecule. Mutations that affect the ability of the envelope glycoprotein to form syncytia in CD4+ cells can be divided into five groups: those that decrease the binding of the envelope protein to the CD4 molecule, those that prevent a post-binding fusion reaction, those that disrupt the anchorage of the envelope glycoprotein in the membrane, those that affect the association of the two subunits of the envelope glycoprotein, and those that affect post-translational proteolytic processing of the envelope precursor protein. These findings provide a functional model of the HIV envelope glycoprotein.

Mutations in sequences at the C terminus of the capsid precursor protein of human immunodeficiency virus type 1 that affect the viral p6 protein prevent release of budded virus particles from the cell surface. The experiments reported here define an important step in the life cycle of the virus, the release of the budded particle from a tether that binds the assembled particle to the cell surface. Inhibition of the release of the viral capsid proteins by interferon a indicates that this step of virus maturation may be sensitive to inhibition by antiviral drugs.

Long-term in vivo expression of a broad and potent entry inhibitor could circumvent the need for a conventional vaccine for HIV-1. Adeno-associated virus (AAV) vectors can stably express HIV-1 broadly neutralizing antibodies (bNAbs)1,2. However even the best bNAbs neutralize 10–50% of HIV-1 isolates inefficiently (IC80 > 5 μg/ml), suggesting that high concentrations of these antibodies would be necessary to achieve general protection3–6. Here we show that eCD4-Ig, a fusion of CD4-Ig with a small CCR5-mimetic sulfopeptide, binds avidly and cooperatively to the HIV-1 envelope glycoprotein (Env) and is more potent than the best bNAbs (geometric mean IC50 < 0.05 μg/ml). Because eCD4-Ig binds only conserved regions of Env, it is also much broader than any bNAb. For example, eCD4-Ig efficiently neutralized 100% of a diverse panel of neutralization-resistant HIV-1, HIV-2, and SIV isolates, including a comprehensive set of isolates resistant to the CD4-binding site bNAbs VRC01, NIH45-46, and 3BNC117. Rhesus macaques inoculated with an AAV vector stably expressed 17 to 77 μg/ml of fully functional rhesus eCD4-Ig for 40 weeks, and these macaques were protected from multiple infectious challenges with SHIV-AD8. Rhesus eCD4-Ig was also markedly less immunogenic than rhesus forms of four well characterized bNAbs. Our data suggest that AAV-delivered eCD4-Ig can function like an effective HIV-1 vaccine.