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Journal of Virology, December 2001, p. 12161-12168, Vol. 75, No. 24
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.24.12161-12168.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Effector Function Activities of a Panel of Mutants of a Broadly Neutralizing Antibody against Human Immunodeficiency Virus Type 1

Marjan Hezareh,1 Ann J. Hessell,1 Richard C. Jensen,1 Jan G. J. van de Winkel,2 and Paul W. H. I. Parren1,*

Department of Immunology, The Scripps Research Institute, La Jolla, California,1 and Department of Immunology and Genmab, University Medical Center Utrecht, Utrecht, The Netherlands2

Received 3 July 2001/Accepted 20 September 2001

The human antibody immunoglobulin G1 (IgG1) b12 neutralizes a broad range of human immunodeficiency virus-type 1 (HIV-1) isolates in vitro and is able to protect against viral challenge in animal models. Neutralization of free virus, which is an antiviral activity of antibody that generally does not require the antibody Fc fragment, likely plays an important role in the protection observed. The role of Fc-mediated effector functions, which may reduce infection by inducing phagocytosis and lysis of virions and infected cells, however, is less clear. To investigate this role, we constructed a panel of IgG1 b12 mutants with point mutations in the second domain of the antibody heavy chain constant region (CH2). These mutations, as expected, did not affect gp120 binding or HIV-1 neutralization. IgG1 b12 mediated strong antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) of HIV-1-infected cells, but these activities were reduced or abrogated for the antibody mutants. Two mutants were of particular interest. K322A showed a twofold reduction in Fcgamma R binding affinity and ADCC, while C1q binding and CDC were abolished. A double mutant (L234A, L235A) did not bind either Fcgamma R or C1q, and both ADCC and CDC functions were abolished. In this study, we confirmed that K322 forms part of the C1q binding site in human IgG1 and plays an important role in the molecular interactions leading to complement activation. Less expectedly, we demonstrate that the lower hinge region in human IgG1 has a strong modulating effect on C1q binding and CDC. The b12 mutants K322A and L234A, L235A are useful tools for dissecting the in vivo roles of ADCC and CDC in the anti-HIV-1 activity of neutralizing antibodies.

* Corresponding author. Mailing address: Department of Immunology, The Scripps Research Institute, 10550 N. Torrey Pines Rd., IMM2, La Jolla, CA 92037. Phone: (858) 784-8602. Fax: (858) 784-8360. E-mail: parren{at}scripps.edu.

Journal of Virology, December 2001, p. 12161-12168, Vol. 75, No. 24
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.24.12161-12168.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.