Biochemical characterization of monoclonal antibodies to the Bordetella pertussis Filamentous hemagglutinin (FHA) and Pertussis toxin (PTx) : implications for improved acellular pertussis vaccine design

Abstract

Incidence rates of whooping cough were dramatically decreased by immunization with whole cell pertussis (wP) vaccines in the 1940s. However, concerns about the safety of the wP vaccine resulted in development of new pertussis vaccines using acellular components of B. pertussis. However, B. pertussis continues to circulate and cause whooping cough disease, even with the safer acellular pertussis (aP) vaccines. Over the last decade, in spite of the high vaccination coverage in many countries, there has been a significant rise in whooping cough infection in industrialized countries. The filamentous hemagglutinin (FHA) and pertussis toxin (PTx) are two antigens included in all currently licensed aP vaccines. Both FHA and PTx induce an immune response sufficient for protection, although anti-PTx antibodies correlate more with protection. Most studies assessing the efficacy of aP vaccines have used serum titers as the primary means to measure an antibody response to a given antigen. Single cell techniques however offer an opportunity to better understand the biochemical attributes of individual antibodies induced upon aP vaccination. In this study, we characterized the antibody responses to FHA and PTx after adult aP booster vaccination. Monoclonal antibodies derived from single B cells which responded to FHA and PTx were purified, the binding affinities to the antigens evaluated, mechanisms of neutralization of FHA and PTx toxicity evaluated, and the binding epitopes of the antibodies analyzed. This study is the first to provide insight into the anti-FHA and PTx antibody repertoire after pertussis vaccination, and also identifies useful antibodies for further elucidation of the structure and function of these antigens. In addition, the mechanisms of neutralization of two potently neutralizing anti-PTx monoclonal antibodies, 1B7 and 11E6 are presented. Antibody binding to live B. pertussis, inhibition of PTx binding to a model receptor fetuin and effects on PTx trafficking in CHO-K1 cells were evaluated. Further understanding of the molecular mechanisms of 1B7 and 11E6 neutralization provides a platform for engineering or isolating such unique anti-PTx antibodies for passive immunization therapies.