Inhibition of Invasive Salmonella by Orally Administered IgA and IgG Monoclonal Antibodies
Authors: Richards Angelene F. , Doering Jennifer E. , Lozito Shannon A. , Varrone John J. , Pauly Michael , Whaley Kevin , Zeitlin Larry , Mantis Nicholas J. 
Published: September 2019

Background

Non-typhoidalSalmonella entericastrains, including serovar Typhimurium (STm), are an emerging cause of invasive disease among children and the immunocompromised, especially in regions of sub-Saharan Africa. STm invades the intestinal mucosa through Peyer’s patch tissues before disseminating systemically. While vaccine development efforts are ongoing, the emergence of multidrug resistant strains of STm affirms the need to seek alternative strategies to protect high-risk individuals from infection.

Methodology/Principal Findings

In this report we investigated the potential of an orally administered O5 serotype-specific IgA monoclonal antibody (mAb), called Sal4, to protect mice against invasiveSalmonella entericaserovar Typhimurium (STm) infection. Sal4 IgA was delivered to mice prior to or concurrently with STm challenge. Infectivity was measured as bacterial burden in Peyer’s patch tissues one day after challenge. Using this model, we defined the minimal amount of Sal4 IgA required to significantly reduce STm uptake into Peyer’s patches. The relative efficacy of Sal4 in dimeric and secretory IgA (SIgA) forms was compared, as was a second lower avidity O5-specific IgA mAb that we produced from STm immunized mice. To assess the role of isotype in oral passive immunization, we engineered a recombinant IgG1 mAb carrying the Sal4 variable regions and evaluated its ability to block invasion of STm into epithelial cellsin vitroand Peyer’s patch tissues.

Conclusions/Significance

Our results demonstrate the potential of orally administered monoclonal IgA and SIgA, but not IgG, to passively immunize against invasive Salmonella. Nonethless, the prophylactic window of IgA/SIgA in the mouse was on the order of minutes, underscoring the need to develop formulations to protect mAbs in the gastric environment and to permit sustained release in the small intestine.

Author Summary

The bacteriumSalmonella entericais responsible for significant morbidity and mortality in the developed and developing worlds. While the pathogen is most renowed as the causative agent of typhoid fever, the emergence of invasive non-typhoid strains likeS. entericaserovar Typhimurium (STm) are of great concern because of their propensity to cause severe disease in children under the age of five. In this report, we demonstrate in a mouse model that oral administration of a monoclonal antibody targeting the surface of STm is able to prevent the bacterium from infecting gastrointestinal tissues, the first step in the dissemination process. We show that IgA antibodies (which are normally found in the gut) were far superior than an equivalent IgG antibody (normally found in blood) at protecting the intestine from STm infection. These results lay the foundation for future studies aimed at the development of an orally administered antibody cocktail capable of providing temporary immunity to pathogens likeS. enterica.