Characterization of Molecular Features,Antigen-Binding,and in Vitro Properties of IgG and IgM Variants of 4E10,an Anti-HIV Type 1 Neutralizing Monoclonal Antibody

Abstract

The human monoclonal antibody 4E10 has been generated previously by immortalization of peripheral blood cells from an HIV-1-infected individual. This antibody binds to the linear epitope NWFDIT on gp41 and exhibits exceptional neutralizing activity against a broad spectrum of primary HIV-1 isolates. In the present study, molecular features, immunoreactivity, and functional activity of 4E10 were studied. The original hybridoma-derived 4E10 was of subtype IgG₃. Analysis of the variable segment of the heavy chain (VH) demonstrated extensive somatic mutations compared to the closest homologous germline gene VH1-69. Most amino acid substitutions occurred in the complementarity-determining region (CDR) 2, characteristic for an antigen-driven somatic maturation. The heavy chain of the CDR3 (H3) is of unusual length and cannot be attributed with certainty to any specific D(H) locus. To enable mass production and to prolong the in vivo half-life, 4E10 was subsequently cloned as IgG₁ in Chinese hamster ovary (CHO) cells. In additional studies, 4E10 was class switched to the IgM isotype. Binding to the linear epitope NWFDIT was not significantly changed after the cloning procedures. However, in vitro studies revealed dramatic differences in the neutralizing potential. The antiviral activity could be greatly enhanced by change of IgG₃ to IgG₁. In contrast, the IgM isotype almost completely lost its neutralizing potential.