title: A dimeric form of the HIV-1 antibody 2G12 elicits potent antibody-dependent cellular cytotoxicity.
abstract: OBJECTIVE
  Increasing data support a role for antibody-dependent cellular cytotoxicity (ADCC) in controlling HIV-1 infection. We recently isolated a naturally occurring dimeric form of the anti-HIV-1 antibody 2G12 and found it to be significantly more potent than 2G12 monomer in neutralizing primary virus strains. However, given the unusual structure of dimeric 2G12 with two Fc regions, it was not clear whether 2G12 dimer could bind to the CD16 Fc receptor on ADCC effector cells or trigger ADCC. Here we compared the in-vitro ADCC activities of 2G12 monomer and dimer and investigated the effects of including ADCC-enhancing mutations in both forms of 2G12.
  
  
  METHODS
  An in-vitro ADCC assay using target cells stably expressing gp160 was developed to evaluate the activities of 2G12 monomer and dimer with and without ADCC-enhancing mutations that increase the CD16-binding affinity of the 2G12 Fc region.
  
  
  RESULTS
  Both 2G12 monomer and 2G12 dimer elicited ADCC, although the dimer showed increased potency [lower half-maximal concentration (EC(50))] in triggering ADCC, thus confirming its ability to bind CD16 and trigger ADCC. The ADCC-enhancing mutations improved the ADCC activity of 2G12 monomer more than 2G12 dimer such that their EC(50) values were nearly equal. However, no increase in nonspecific ADCC activity was observed using 2G12 IgGs with these mutations.
  
  
  CONCLUSIONS
  Given the likelihood that ADCC plays a role in protecting against initial infection and/or controlling chronic infection, these data suggest 2G12 dimers and/or addition of ADCC-enhancing mutations could augment the prophylactic and/or therapeutic potential of 2G12.
authors.affiliation: Division of Biology, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Klein
authors.forename: Alexandre
authors.initials: A
authors.lastname: Webster
authors.forename: Priyanthi N P
authors.initials: PN
authors.lastname: Gnanapragasam
authors.forename: Rachel P
authors.initials: RP
authors.lastname: Galimidi
authors.forename: Pamela J
authors.initials: PJ
authors.lastname: Bjorkman
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology*; D000920:Antibody-Dependent Cell Cytotoxicity / Q000235:genetics / Q000276:immunology*; D000080908:Broadly Neutralizing Antibodies; D015815:Cell Adhesion Molecules / Q000235:genetics; D002478:Cells, Cultured; D058851:GPI-Linked Proteins; D015483:HIV Antibodies / Q000276:immunology*; D019302:HIV Envelope Protein gp160 / Q000378:metabolism; D015658:HIV Infections / Q000276:immunology*; D015497:HIV-1 / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D009154:Mutation; D055503:Protein Multimerization; D017452:Receptors, IgG / Q000378:metabolism
chemical_list: C529157:2G12 monoclonal antibody; D000911:Antibodies, Monoclonal; D000080908:Broadly Neutralizing Antibodies; D015815:Cell Adhesion Molecules; C106607:FCGBP protein, human; C428200:FCGR3B protein, human; D058851:GPI-Linked Proteins; D015483:HIV Antibodies; D019302:HIV Envelope Protein gp160; D007074:Immunoglobulin G; D017452:Receptors, IgG; C514797:gp160 protein, Human immunodeficiency virus 1