A capsule-based bioconjugate vaccine to prevent Klebsiella pneumoniae infections

PROJECT SUMMARY Klebsiella pneumoniae is a Gram-negative, encapsulated human pathogen capable of causing community- acquired and healthcare-associated infections across all age groups. Further, K. pneumoniae antimicrobial resistance is alarmingly high with isolates frequently resistant to last-line antibiotic therapies. Currently there are no licensed vaccines available or in clinical trials for K. pneumoniae, yet preliminary data from our group demonstrate that K. pneumoniae disease and death can be prevented with polysaccharide-protein conjugate vaccines that target its capsular polysaccharide. Over the last six years, VaxNewMo has been developing a platform to produce a multivalent conjugate vaccine targeting the capsular polysaccharides of most K. pneumoniae clinical isolates encountered. Conjugate vaccines, composed of a polysaccharide covalently linked to a carrier protein, are life-saving vaccines used to prevent disease from multiple bacterial pathogens. Conventionally, conjugate vaccines are manufactured using chemical conjugation, which is notoriously complex, labor intensive, and imprecise, hindering the development of new conjugate vaccines against existing and emerging bacterial threats, like K. pneumoniae. Well aware of these drawbacks, VaxNewMo has been advancing an alternative method for manufacturing conjugate vaccines that utilizes prokaryotic glycosylation systems in a process termed bioconjugation. VaxNewMo's proprietary bioconjugation platform relies on a conjugating enzyme to transfer a bacterial polysaccharide to a carrier protein using E. coli as a platform. Moreover, since bioconjugation is an enzyme driven process, the conjugates produced are non-derivatized and are therefore structurally identical to those presented to immune cells by the pathogen itself. Bioconjugation can be used to rapidly produce new conjugates simply by introducing new genetic information encoding for a different polysaccharide serotype into a bioconjugation competent strain of E. coli. As an example of this, we developed a tetravalent capsule-based bioconjugate vaccine in Phase I STTR activities and demonstrated its ability to elicit serotype specific immunoglobulins that mediate bactericidal activity towards K. pneumoniae clinical isolates. In this Phase II SBIR proposal, we will further expand the serotype coverage to include at a minimum 50% of all K. pneumoniae isolates clinically encountered thereby promoting future commercialization potential of the vaccine. In Aim 1, we will glycoengineer and analytically characterize an additional eight unique capsule-based bioconjugate vaccines resulting in the production of a dodecavalent (12-valent) formulation. In Aim 2, immunogenicity will be assessed in monovalent and dodecavalent dose-finding studies using murine immunization models and, subsequently, determine functional antibody responses via a serum bactericidal assay (SBA) and secondarily using an opsonophagocytic killing assay (OPKA) as well as perform challenge studies in mice vaccinated with a mouse optimized dose. Finally, in Aim 3, we will confirm immunogenicity and functional antibody responses (SBA and OPKA) of monovalent and multivalent capsule-based bioconjugate formulations in rabbits, a widely utilized animal model for conjugate vaccine development.