Biology subjects

Gallant, R. M.

Publications and source records attributed to Gallant, R. M..

3 recordsLinked to original sources

bioRxiv2025

Protective and pathogenic antibody responses from a primate Shigella outbreak inform vaccine design

There is currently no approved vaccine for Shigella spp., a leading cause of diarrhea that are increasingly resistant to antimicrobials. Shigella vaccine development is complicated in part by an incomplete understanding of the structural and molecular determinants of immunity. To address this, we isolated monoclonal antibodies (mAbs) against candidate Shigella vaccine antigens using samples from a Shigella flexneri outbreak in a non-human primate (NHP) research facility. We found that antibodies targeting the Shigella O-antigen (O-Ag) can undergo significant affinity maturation (>10%) to acquire broad cross-reactivity across S. flexneri serotypes. We also found that the virulence-associated type III secretion system (T3SS) proteins IpaD and IpaB elicit moderate T cell and robust antibody responses. T3SS antibodies either inhibit, or - surprisingly - enhance bacterial virulence in vitro and in vivo depending on their epitope specificity. These findings provide key insights into protective and deleterious immune responses against Shigella that directly inform vaccine immunogen design.

immunology↗

bioRxiv2025

Improvement of affinity and potency of a monoclonal antibody against Shigella flexneri 3a O-antigen via phage display and whole-cell in-solution panning

As rates of antimicrobial resistance (AMR) among bacterial pathogens continue to rise, the discovery and development of novel classes of therapeutics that can serve as alternatives or adjuncts to traditional small-molecule antibiotics, such as monoclonal antibodies (mAbs), is a public health priority. Some of the most promising antigen targets for antibacterial mAbs are surface polysaccharides such as O-antigen (O-Ag), a component of the lipopolysaccharide found on the outer membrane of gram-negative bacteria. However, developing mAbs against bacterial surface polysaccharides with sufficient breadth and potency to be clinically viable is difficult in part because antibodies against polysaccharides are generally low affinity, and the challenging biochemistry of polysaccharides often precludes further affinity maturation of mAbs against these targets in vitro. Here, we use a phage display library and a whole-cell in-solution panning strategy to successfully improve the affinity of a mAb against Shigella flexneri 3a O-Ag in vitro without requiring the purification of the target antigen. We demonstrate that a single mutation can improve apparent affinity approximately 10-fold without detectably increasing polyreactivity, and increased affinity correlates with enhanced potency in antibacterial effector function and anti-virulence assays. In addition, the most potent variants also gained increased breadth, successfully coordinating complement deposition and complement-independent opsonophagocytosis against S. flexneri 3b, a serotype weakly recognized by the parent mAb. Altogether, this work represents an important first step towards expanding the antibody engineering toolkit for bacterial surface polysaccharides, which will aid the development of novel mAb therapeutics against AMR bacterial pathogens.

bioengineering↗

bioRxiv2023

Fluoxetine promotes immunometabolic defenses to mediate host-pathogen cooperation during sepsis

Selective serotonin reuptake inhibitors (SSRIs) are some of the most prescribed drugs in the world. While they are used for their ability to increase serotonergic signaling in the brain, SSRIs are also known to have a broad range of effects beyond the brain, including immune and metabolic effects. Recent studies have demonstrated that SSRIs are protective in animal models and humans against several infections, including sepsis and COVID-19, however the mechanisms underlying this protection are largely unknown. Here we mechanistically link two previously described effects of the SSRI fluoxetine in mediating protection against sepsis. We show that fluoxetine-mediated protection is independent of peripheral serotonin, and instead increases levels of circulating IL-10. IL-10 is necessary for protection from sepsis-induced hypertriglyceridemia and cardiac triglyceride accumulation, allowing for metabolic reprogramming of the heart. Our work reveals a beneficial "off-target" effect of fluoxetine, and reveals a protective immunometabolic defense mechanism with therapeutic potential.

immunology↗