Maternal vaccination to prevent Klebsiella pneumoniae gut colonization and neonatal sepsis

PROJECT SUMMARY This project will advance our efforts in the development of maternal vaccines to prevent Klebsiella pneumoniae (Kp) neonatal sepsis. Kp is the leading cause of neonatal sepsis and an urgent worldwide threat due to rising antimicrobial resistance. Vaccines targeting Kp, specifically ones that can be delivered maternally to prevent neonatal sepsis, are considered highest priority by the World Health Organization. This multi-PI project builds on the expertise of both the Rosen and Schwartz labs in bacteriology, humoral immunity, murine modeling, gnotobiotics, and microbiome analyses to interrogate immune responses to maternal bioconjugate vaccines targeting Kp's polysaccharide capsule (K-antigen) or O-antigen. To our knowledge, we have developed the first murine model of Kp neonatal sepsis demonstrating pup bacteremia protection after dam vaccination and we intend to leverage this model to answer fundamental questions imperative for the development of a human vaccine. In preliminary studies, maternal vaccination led to high levels of antigen-specific IgGs in pups, secretory IgAs in breastmilk, resistance of gastrointestinal Kp colonization in pups, and near complete protection from Kp bacteremia challenge. As we have already developed several candidate K-antigen or O-antigen bioconjugate vaccines with our collaborator Dr. Harding at Omniose, we will utilize both K- and O-vaccines and compare the relative efficacy of pup protection from matched K:O Kp strains. ELISAs will be used to quantify IgG in both dams and pups over time and determine the specific IgG subtypes passed vertically. Functionality and durability will be determined over time using serum bactericidal and opsonophagocytic killing assays. As isolates leading to neonatal sepsis are thought to originate either from the mother via vertical passage to the baby or from exogenous environmental sources, we will evaluate how vaccination alters susceptibility to Kp gastrointestinal colonization. In addition to gavage challenge of pups, we will also use gnotobiotic mice transplanted with human microbiota to most closely mimic human conditions. Maternal and pup Kp gut colonization will be analyzed after Kp bioconjugate vaccination or control (protein-only) vaccination using selective culture and shotgun metagenomic sequencing. To determine the relative contributions of passively transferred IgG and secretory IgA to protection of pups, we will cross-foster pups. Pups, either with circulating Kp-specific IgG (via passive transfer prior to delivery) or nursing from dams with Kp-specific immunity, will be challenged intraperitoneally with Kp and monitored for protection. Further, we will leverage mutant mice incapable of producing IgA to gauge the importance of breastmilk IgA to pup immunity. At the conclusion of these studies, we will have preclinical data on the efficacy of K- vs. O-bioconjugate maternal vaccination, the effect of these immunizations on Kp colonization dynamics, and the relative contributions of IgG and sIgA to protection, to be leveraged for human trials.