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Journal of Virology, June 2003, p. 6965-6978, Vol. 77, No. 12
0022-538X/03/$08.00+0     DOI: 10.1128/JVI.77.12.6965-6978.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

A Novel Human Antibody against Human Immunodeficiency Virus Type 1 gp120 Is V1, V2, and V3 Loop Dependent and Helps Delimit the Epitope of the Broadly Neutralizing Antibody Immunoglobulin G1 b12

Michael B. Zwick,1 Robert Kelleher,1 Richard Jensen,1 Aran F. Labrijn,1,{dagger} Meng Wang,1 Gerald V. Quinnan Jr.,2 Paul W. H. I. Parren,3 and Dennis R. Burton1*

Departments of Immunology and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037,1 Department of Preventive Medicine and Biometrics, Uniformed Services University of the Health Sciences, Bethesda, Maryland 208142,2 and Genmab, Utrecht, The Netherlands3

Received 17 December 2002/ Accepted 13 March 2003

The V1/V2 and V3 loops are proximal to the CD4 binding site (CD4bs) of human immunodeficiency virus type 1 (HIV-1) gp120 and undergo conformational change upon CD4 receptor engagement by the HIV-1 envelope spike. Nearly all of the reported monoclonal antibodies (MAbs) against the CD4bs exhibit a very limited capacity to neutralize HIV-1. However, one such human MAb, immunoglobulin G1 (IgG1) b12, is uniquely able to neutralize primary isolates across subtypes with considerable potency. The molecular basis for the anti-HIV-1 activity of b12 is not fully understood but is relevant to vaccine design. Here we describe a novel human MAb, 4KG5, whose binding to monomeric gp120 is moderately enhanced by IgG1 b12. In sharp contrast, 4KG5 binding to gp120 is inhibited by soluble CD4 (sCD4) and by all other (n = 14) anti-CD4bs MAbs tested. 4KG5 is unable to recognize gp120 in which either V1, V2, or V3 has been deleted, and MAbs against the V2 or V3 loops inhibit the binding of 4KG5 to gp120. Moreover, 4KG5 is able to inhibit the binding of the CD4-induced MAbs 17b and X5 in the absence of sCD4, whereas 17b and X5 only weakly inhibit the binding of 4KG5 to gp120. Mutagenesis of gp120 provides further evidence of a discontinuous epitope of 4KG5 that is formed by the V1/V2 loop, the V3 loop, and a portion of the bridging sheet (C4). 4KG5 was isolated as a single-chain Fv from a phage display library constructed from the bone marrow of an HIV-1-seropositive subject (FDA2) whose serum neutralizes HIV-1 across subtypes. Despite its source, we observed no significant neutralization with 4KG5 against the autologous (R2) virus and several other strains of HIV-1. The results suggest a model in which antibody access to the CD4bs on the envelope spike of HIV-1 is restricted by the orientation and/or dynamics of the V1/V2 and V3 loops, and b12 avoids these restrictions.


* Corresponding author. Mailing address: The Scripps Research Institute, Department of Immunology (IMM-2), 10550 North Torrey Pines Rd., La Jolla, CA 92037. Phone: (858) 784-9298. Fax: (858) 784-8360. E-mail: burton{at}scripps.edu.

{dagger} Present address: Genmab, 3584 CK Utrecht, The Netherlands.


Journal of Virology, June 2003, p. 6965-6978, Vol. 77, No. 12
0022-538X/03/$08.00+0     DOI: 10.1128/JVI.77.12.6965-6978.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.




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