We have developed and characterized eCD4-Ig, an exceptionally broad and potent HIV-1 entry inhibitor. eCD4-Ig is a fusion of CD4-Ig - a safe but ineffective therapeutic - with a short CCR5- mimetic sulfopeptide. eCD4-Ig is qualitatively different from CD4-Ig or broadly neutralizing antibodies (bNAbs) because it avidly binds two highly conserved and functionally important receptor-binding regions of the HIV-1 envelope glycoprotein, and only those sites. As a consequence, eCD4-Ig, but not CD4-Ig or bNAbs, neutralized 100% of isolates tested, including both R5- and X4-isolates, and two large panels of antibody-resistant HIV-1, HIV-2 and SIV isolates, all with IC50s < 1.2 g/ml and IC80s less < 5.2 g/ml. Moreover, in unpublished data, we show that eCD4-Ig is much harder to escape than CD4-Ig or a well characterized CD4-binding site bNAb, and in fact we have yet to identify isolates fully resistant to eCD4-Ig. Most importantly, and again in contrast to bNAbs, eCD4-Ig could provide long- term protection in vivo. When four rhesus macaques were inoculated intramuscularly with an adeno- associated virus (AAV) vector expressing a rhesus form of eCD4-Ig, these macaques were protected from six infectious and escalating challenges with SHIV-AD8. The last of these challenges, also unpublished, were 8- and 16-times the 50% animal infectious dose of SHIV-AD8, and were administered more than one year after inoculation. Here our primary goal is to understand the strengths and limitations of passively administered and AAV-delivered eCD4-Ig as potential alternatives to current antiretroviral regimens. These studies will also help to understand the risks and improve the safety of AAV-eCD4-Ig, perhaps facilitating its use as an alternative vaccine.

Public Health Relevance

eCD4-Ig is a very broad and potent HIV-1 entry inhibitor that works well with a safe and established gene-therapy vector. We will determine whether eCD4-Ig, as a passively administered protein or with this gene-therapy vector, can suppress infection in rhesus macaques. We will also improve eCD4-Ig and its delivery system, and lay the foundations for human studies of eCD4-Ig.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Method to Extend Research in Time (MERIT) Award (R37)
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AIDS Discovery and Development of Therapeutics Study Section (ADDT)
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Conley, Tony J
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Scripps Florida
United States
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Fetzer, Ina; Gardner, Matthew R; Davis-Gardner, Meredith E et al. (2018) eCD4-Ig Variants That More Potently Neutralize HIV-1. J Virol 92:
Otsuka, Yuka; Schmitt, Kimberly; Quinlan, Brian D et al. (2018) Diverse pathways of escape from all well-characterized VRC01-class broadly neutralizing HIV-1 antibodies. PLoS Pathog 14:e1007238
Mou, Huihui; Zhong, Guocai; Gardner, Matthew R et al. (2018) Conditional Regulation of Gene Expression by Ligand-Induced Occlusion of a MicroRNA Target Sequence. Mol Ther 26:1277-1286
Fellinger, Christoph H; Gardner, Matthew R; Bailey, Charles C et al. (2017) Simian Immunodeficiency Virus SIVmac239, but Not SIVmac316, Binds and Utilizes Human CD4 More Efficiently than Rhesus CD4. J Virol 91:
Gardner, Matthew R; Farzan, Michael (2017) Engineering antibody-like inhibitors to prevent and treat HIV-1 infection. Curr Opin HIV AIDS :
Zhong, Guocai; Wang, Haimin; Li, Yujun et al. (2017) Cpf1 proteins excise CRISPR RNAs from mRNA transcripts in mammalian cells. Nat Chem Biol 13:839-841
Zhong, Guocai; Wang, Haimin; Bailey, Charles C et al. (2016) Rational design of aptazyme riboswitches for efficient control of gene expression in mammalian cells. Elife 5:
Gardner, Matthew R; Fellinger, Christoph H; Prasad, Neha R et al. (2016) CD4-Induced Antibodies Promote Association of the HIV-1 Envelope Glycoprotein with CD4-Binding Site Antibodies. J Virol 90:7822-32