A promising bioconjugate vaccine against hypervirulentKlebsiella pneumoniae

Abstract

HypervirulentKlebsiella pneumoniae(hvKp) is globally disseminating as a community-acquired pathogen causing life-threatening infections in healthy individuals. The fact that a dose as little as 50 bacteria is lethal to mice illustrates the dramatic increase of virulence associated with hvKpstrains compared with classicalK. pneumoniae(cKp) strains, which require lethal doses greater than 107bacteria. Until recently, these virulent strains were mostly antibiotic-susceptible. However, multidrug-resistant (MDR) hvKpstrains have been emerging, spawning a new generation of hypervirulent “superbugs.” The mechanisms of hypervirulence are not fully defined, but overproduction of capsular polysaccharide significantly impedes host clearance, resulting in increased pathogenicity of hvKpstrains. While there are more than 80 serotypes ofK. pneumoniae, the K1 and K2 serotypes cause the vast majority of hypervirulent infections. Therefore, a glycoconjugate vaccine targeting these 2 serotypes could significantly reduce hvKpinfection. Conventionally, glycoconjugate vaccines are manufactured using intricate chemical methodologies to covalently attach purified polysaccharides to carrier proteins, which is widely considered to be technically challenging. Here we report on the recombinant production and analytical characterization of bioconjugate vaccines, enzymatically produced in glycoengineeredEscherichia colicells, against the 2 predominant hypervirulentK. pneumoniaeserotypes, K1 and K2. TheK. pneumoniaebioconjugates are immunogenic and efficacious, protecting mice against lethal infection from 2 hvKpstrains, NTUH K-2044 and ATCC 43816. This preclinical study constitutes a key step toward preventing further global dissemination of hypervirulent MDR hvKpstrains.