Design and Expression of a Dimeric Form of the Human Immunodeficiency Virus Type 1 Antibody 2G12 with Increased Neutralization Potency

Abstract

The antigen-binding fragment of the broadly neutralizing Human Immunodeficiency Virus Type 1 (HIV-1) antibody 2G12 has an unusual 3D domain-swapped structure with two aligned combining sites that facilitates recognition of its carbohydrate epitope on gp120. When expressed as an intact IgG, 2G12 formed typical IgG monomers containing two combining sites and a small fraction of a higher molecular weight species, which showed a significant increase in neutralization potency (50- to 80-fold compared to 2G12 monomer) across a range of clade A and B strains of HIV-1. Here we show that the higher molecular weight species corresponds to a 2G12 dimer containing four combining sites, and present a model for how intermolecular 3D domain swapping could create a 2G12 dimer. Based on the structural model for a 3D domain-swapped 2G12 dimer, we designed and tested a series of 2G12 mutants predicted to increase the ratio of 2G12 dimer to monomer. We report a mutation that effectively increases the 2G12 dimer/monomer ratio without decreasing the expression yield. Increasing the proportion of 2G12 dimer compared with monomer could lead to a more potent reagent for gene therapy or passive immunization.