Impact of Immunoglobulin Isotype and Epitope on the Functional Properties of Vibrio cholerae O-Specific Polysaccharide-Specific Monoclonal Antibodies

• Authors: Robert C Kauffman, Emory University; Oluwaseyi Adekunle, Emory University; Hanyi Yu, Emory University; Alice Cho, Emory University; Lindsay E Nyhoff, Emory University; Meagan Kelly, Massachusetts General Hospital; Jason B Harris, Harvard Medical School; Taufiqur Rahman Bhuiyan, International Centre for Diarrhoeal Disease Research; Firdausi Oadri, International Centre for Diarrhoeal Disease Research; Stephen B Calderwood, Massachusetts General Hospital; Richelle C Charles, Massachusetts General Hospital; Edward T Ryan, Massachusetts General Hospital; Jun Kong, Emory University; Jens Wrammert, Emory University
• Journal Title: MBIO
• Volume: Volume 12, Number 2
• Publisher: AMER SOC MICROBIOLOGY | 2021-03-01
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.1128/mBio.03679-20
• Subjects: Mathematics; Statistics
• Keywords: Science & Technology; Life Sciences & Biomedicine; Microbiology; immunoglobulin isotype; OSP antibody; Vibrio cholerae; B-CELL RESPONSES; HOUSEHOLD CONTACTS; IMMUNE-RESPONSES; SECRETORY IGA; X-RAY; ANTIGEN; INFECTION; LIPOPOLYSACCHARIDE; PROTECTION; IMMUNIZATION

Abstract

Vibrio cholerae causes the severe diarrheal disease cholera. Clinical disease and current oral cholera vaccines generate antibody responses associated with protection. Immunity is thought to be largely mediated by lipopolysaccharide (LPS)-specific antibodies, primarily targeting the O-antigen. However, the properties and protective mechanism of functionally relevant antibodies have not been well defined. We previously reported on the early B cell response to cholera in a cohort of Bangladeshi patients, from which we characterized a panel of human monoclonal antibodies (MAbs) isolated from acutely induced plasmablasts. All antibodies in that previous study were expressed in an IgG1 backbone irrespective of their original isotype. To clearly determine the impact of affinity, immunoglobulin isotype and subclass on the functional properties of these MAbs, we re-engineered a subset of low-and high-affinity antibodies in different isotype and subclass immunoglobulin backbones and characterized the impact of these changes on binding, vibriocidal, agglutination, and motility inhibition activity. While the high-affinity antibodies bound similarly to O-antigen, irrespective of isotype, the low-affinity antibodies dis-played significant avidity differences. Interestingly, despite exhibiting lower binding properties, variants derived from the low-affinity MAbs had comparable agglutination and motility inhibition properties to the potently binding antibodies, suggesting that how the MAb binds to the O-antigen may be critical to function. In addition, not only pentameric IgM and dimeric IgA, but also monomeric IgA, was remarkably more potent than their IgG counterparts at inhibiting motility. Finally, analyzing highly purified F(ab) versions of these antibodies, we show that LPS cross-linking is essential for motility inhibition. IMPORTANCE Immunity to the severe diarrheal disease cholera is largely mediated by lipopolysaccharide (LPS)-specific antibodies. However, the properties and protective mechanisms of functionally relevant antibodies have not been well defined. Here, we have engineered low and high-affinity LPS-specific antibodies in different immuno-globulin backbones in order to assess the impact of affinity, immunoglobulin isotype, and subclass on binding, vibriocidal, agglutination, and motility inhibition functional properties. Importantly, we found that affinity did not directly dictate functional potency since variants derived from the low-affinity MAbs had comparable agglutination and motility inhibition properties to the potently binding antibodies. This suggests that how the antibody binds sterically may be critical to function. In addition, not only pentameric IgM and dimeric IgA, but also monomeric IgA, was remarkably more potent than their IgG counterparts at inhibiting motility. Finally, analyzing highly purified F(ab) versions of these antibodies, we show that LPS cross-linking is essential for motility inhibition.