A promising bioconjugate vaccine against hypervirulent Klebsiella pneumoniae

Significance

Klebsiella pneumoniae is considered a nosocomial pathogen, usually infecting immunocompromised patients. However, a pathotype of K. pneumoniae, termed hypervirulent K. pneumoniae (hv Kp), has emerged and is spreading throughout the community, causing severe, often fatal, disease in healthy individuals. Moreover, reports on multidrug-resistant hv Kp isolates are increasing in frequency. It is imperative that strategies to combat hv Kp begin immediately to prevent further dissemination of this new class of “superbugs.” Here, we show that bioconjugate vaccines targeting the capsule of hv Kp can provide immunity and protection against extremely lethal hv Kp strains. Further, we demonstrate that bioconjugation is a promising technology for rapid development of efficacious vaccines against emerging bacterial threats.

Abstract

Hypervirulent Klebsiella pneumoniae (hv Kp) 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 hv Kp strains compared with classical K. pneumoniae (c Kp) strains, which require lethal doses greater than 10 ⁷ bacteria. Until recently, these virulent strains were mostly antibiotic-susceptible. However, multidrug-resistant (MDR) hv Kp strains 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 hv Kp strains. While there are more than 80 serotypes of K. pneumoniae, the K1 and K2 serotypes cause the vast majority of hypervirulent infections. Therefore, a glycoconjugate vaccine targeting these 2 serotypes could significantly reduce hv Kp infection. 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 glycoengineered Escherichia coli cells, against the 2 predominant hypervirulent K. pneumoniae serotypes, K1 and K2. The K. pneumoniae bioconjugates are immunogenic and efficacious, protecting mice against lethal infection from 2 hv Kp strains, NTUH K-2044 and ATCC 43816. This preclinical study constitutes a key step toward preventing further global dissemination of hypervirulent MDR hv Kp strains.