Thesis (Ph.D.)--University of Washington, 2023Emerging viruses and antibiotic-resistant bacteria are major threats to human health. Despite well-established benefits of the passive transfer of immunity in animal models, engineered monoclonal antibodies (mAbs) have struggled to achieve consistently positive results for the treatment of infectious disease in humans. We hypothesized that a strategy of building mAbs based on human immune memory B cells (MBCs) could be advantageous. This thesis describes efforts to develop mAbs with plausible therapeutic potential against two microbes that drive severe morbidity in vulnerable patients: Pseudomonas aeruginosa and SARS-CoV-2. Diverging from historical, animal-based methods for mAb discovery, we used the B cell receptor sequences of human, antigen-specific B cells, with special focus on MBCs, as templates for novel mAbs. Focusing first on P. aeruginosa, we generated anti-bacterial mAbs using source B cells obtained from patients seen at a cystic fibrosis (CF) clinic. CF is a genetic condition associated with unusually frequent P. aeruginosa infections, but not defects in adaptive immunity. In an in vivo pneumonia model with a highly virulent strain, 2 of 2 human-derived mAbs exhibited prominent protective activity. Notably, our new mAbs were noninferior to an extensively engineered mAb that comprises half of the bi-specific clinical candidate, gremubamab. A second panel of MBC-derived mAbs that showed promise in vitro remain to be tested in future work, highlighting the efficiency of our mAb discovery strategy. Further, we believe our study contributes to understanding of immunity in CF, being the first to confirm the presence of P. aeruginosa-specific MBCs in CF patients.
In contrast to P. aeruginosa, mAbs targeting SARS-CoV-2 were developed from human B cells contemporaneously by multiple groups including our team. However, circulating escape variants have significantly limited clinical use. Importantly, consistent with nearly all mAbs in clinical use, these vulnerable mAbs were of the monomeric isotype, IgG. Building on our prior studies of MBCs and evidence that an alternative isotype, IgM, was an important component in virus-neutralizing human serum, we cloned new mAbs from SARS-CoV-2-specific IgM MBCs. We also found that diverse MBC-derived mAbs gained greater neutralizing potency when expressed as the naturally pentameric IgM isotype. Importantly, we showed that IgM mAbs retained neutralizing activity against viral variants that evaded otherwise identical mAbs made in the IgG isotype. These results suggest a biological role for IgM MBCs in protection against rapidly mutating pathogens, and illuminate the potential for IgM mAbs in the search for new treatments for infectious diseases
