Functional classes of naturally occurring human antibodies developed against Gram-negative bacterial pathogens
Fowler, Benjamin Dylan
Gram-negative bacteria are frequently opportunistic pathogens that cause significant morbidity and mortality in humans. Escherichia coli and Klebsiella pneumoniae are two common Gram-negative pathogens that often acquire multi-drug resistance. Other pathogens, such as Bordetella pertussis, are concerning as they re-emerge due to vaccine denialism and vaccine formulation changes. Human monoclonal antibodies (mAbs) are powerful tools and potential therapies that may inform novel antimicrobial strategies to combat these dangerous multi-drug resistant and re-emerging diseases. Four mAbs to E. coli were isolated from human donor memory B cells and the mAbs were demonstrated to bind specifically to E. coli outer membrane protein A (OmpA). One mAb to the N-terminal porin domain of OmpA, ECOL-11, causes the bacteria to aggregate and impairs the adhesion of E. coli to mammalian phagocytes. Using B cells from a different donor, four mAbs that bind K. pneumoniae were generated. These mAbs bind diverse antigens of K. pneumoniae and one mAb, KPNA-14, is specific for capsular polysaccharide. This mAb to the capsular polysaccharide induces complement-mediated killing and increases phagocytosis by murine macrophage-like cells. Multiple mAbs that bind B. pertussis toxin were tested and found to neutralize pertussis toxin using a novel real-time cellular analysis technique called xCELLigence. This innovative assay significantly improves upon antiquated microscopy-based toxin neutralization assays. Together, these diverse mAbs, which interact with three different bacterial pathogens, inform vaccine designs for Gram-negative bacteria and demonstrate the diversity of antibacterial mAbs that bind unique antigenic classes and induce distinctive effector functions.