A preclinical model to assess the potential of microbiome-targeted interventions to improve vaccine immunogenicity in malnourished children

Lower respiratory tract infections and enteric diseases persists as top ten leading causes of death in LICs1, with these deaths disproportionately impacting infants. One important factor that likely contributes to these unacceptably high rates of mortality and morbidity in infants living in LICs is the impaired vaccine effectiveness/immunogenicity that is frequently observed in these populations compared to infants in HICs2-4. Environmental enteric dysfunction (EED) is a gastrointestinal disease characterised by stunting, intestinal villi atrophy, impaired intestinal barrier function, and reduced absorption of nutrients5,6. While this condition is rare in resource-rich countries, an estimated 150 million children under 5 in resource-poor countries are at risk of EED7. Given the profound effects of EED on the intestine, it is perhaps not surprising that EED has been associated with the reduced effectiveness of a range of oral vaccines including the oral rotavirus vaccine8, the live-attenuated oral cholera vaccine9-11 and the oral polio vaccine12. The recent development of a mouse model that recapitulates many of the features of EED including growth stunting, intestinal villi shortening and reduced intestinal barrier function13, has enabled preclinical investigation of the mechanisms through which EED leads to impaired oral vaccine immunogenicity. In this model, mice are subjected to a diet low in fat and protein that mimics malnutrition and are concurrently colonised with an adherent invasive E. coli strain. EED mice have significantly reduced responses to an orally administered attenuated E. coli heat labile toxin (LT) in a manner that was dependent on the induction of intestinal microbiota-dependent RORγT+FOXP3+ Treg T cells in the small intestine13, but whether parenteral vaccine immunogenicity is also comprised in these mice has not been investigated to date.
Malnutrition and stunting are associated with dramatic changes to the composition of the gut microbiota including increases in phylum Proteobacteria and decreases in Bifidobacterium and Lactobacillus species14 and small intestinal bacterial overgrowth by bacteria that normally reside in the oropharyngeal cavity15. Given that mounting evidence suggests that the composition of the microbiota is a major factor influencing immune responses to both oral and parenteral vaccination 4, we hypothesised that EED would also lead to impaired parenteral vaccine immunogenicity. To investigate this, we successfully recapitulated this model of EED (Figure 1a-b) and parenterally immunised EED and control mice with the 13-valent pneumococcal conjugate vaccine (PCV13), a vaccine against Streptococcus pneumoniae infection which is administered to >70 million infants each year. PCV13 immunised EED mice had significantly impaired PCV13-specific antibody responses (Figure 1c-d), but not total IgG (Figure 1e), indicating that vaccine-induced but not humoral immunity overall is compromised in these mice. These unpublished data are the first to indicate that EED can lead to impaired vaccine immunogenicity. Furthermore, T cell cytokine responses and germinal centre B cell and Tfh cell responses were also significantly impaired compared to control mice (Figure 1h-i). These data suggest that microbiota-targeted interventions could be beneficial to enhance vaccine immunogenicity in children with EED.