# Maternal expression and breast milk transfer of an mRNA- encoded monoclonal antibody in a murine model of cholera

## TL;DR

This study explores using mRNA to produce antibodies in breast milk to protect newborns from cholera, showing that maternal mRNA can transfer functional antibodies to infants through breastfeeding.

## Contribution

The study introduces a novel approach of using mRNA-lipid nanoparticles to stimulate monoclonal antibody production in breast milk for neonatal protection.

## Key findings

- A single intravenous administration of mRNA-LNPs resulted in high and sustained expression of functional ZAC-3 IgG1 in the blood and breast milk of lactating dams.
- ZAC-3 IgG1 was detected in the serum of suckling pups, demonstrating successful transfer of functional antibodies to newborns.
- Breastfeeding pups challenged with V. cholerae showed a significant reduction in bacterial burden when continuously nursing, suggesting protective effects of transferred antibodies.

## Abstract

Breast milk confers infants with immunity to a multitude of pathogens reflective of prior maternal infections and vaccinations. However, in outbreak situations where infants may be vulnerable to lethal infections due to gaps in the maternal immune repertoire, a case can be made for supplementing breast milk with one or more pathogen-specific monoclonal antibodies (mAbs) with known prophylactic or therapeutic activity. As oral delivery of recombinant IgG and IgA mAbs to infants has proven challenging, we investigated the use of mRNA-lipid nanoparticle (LNP) technology to stimulate pathogen-specific mAbs in milk. mRNA encoding the Vibrio cholerae O1 specific mAb, ZAC-3, as a human IgG1 or dimeric IgA2, was encapsulated in lipid nanoparticles (LNP) and administered parenterally to lactating and non-lactating female mice. A single intravenous administration of mRNA-LNPs resulted in high and sustained expression of functional ZAC-3 IgG1 in the blood and breast milk of lactating dams. ZAC-3 IgA2 levels were lower and more transient. ZAC-3 IgG1 (but not IgA2) was also detected in the serum of suckling pups at levels proportional to those in the mothers, demonstrating successful transfer of functional antibodies to newborns. Levels of ZAC-3 IgG1 and IgA2 were not sufficient to limit intestinal colonization of V. cholerae O1 when pups were separated from dams following intragastric challenge; however, a significant reduction in bacterial burden was observed when challenged pups remained with dams for continuous breastfeeding. Our findings highlight the potential of mRNA-based mAb platforms in the maternal-newborn context, while acknowledging the need for optimized antibody isotypes, dosing, and tissue-specific delivery to improve mucosal immunity.

For newborns, breastfeeding is one of the most effective defenses against diarrheal diseases. Human milk contains a myriad of bioactive compounds, including cytokines, defensins, lactoferrin, and milk oligosaccharides that collectively hinder opportunistic and pathogenic bacteria from colonizing the neonatal intestinal epithelium. Breast milk is also enriched in antibodies that afford immunity to newborns against enteric pathogens encountered in the first years of life. However, there are situations where supplementing breast milk with additional pathogen-specific antibodies could protect otherwise vulnerable newborns from newly emerged or rapidly evolving pathogens. In this report we investigate in a mouse model the potential of mRNA as a platform for delivery of human monoclonal antibodies into breast milk.