Immunogenicity and safety of a tetravalent E. coli O-antigen bioconjugate vaccine in animal models

Vaccine. 2016 Jul 29;34(35):4152-4160. doi: 10.1016/j.vaccine.2016.06.067. Epub 2016 Jul 6.


Background: Extra-intestinal pathogenic Escherichia coli (ExPEC) are major human pathogens; however, no protective vaccine is currently available. We assessed in animal models the immunogenicity and safety of a 4-valent E. coli conjugate vaccine (ExPEC-4V, serotypes O1, O2, O6 and O25 conjugated to Exotoxin A from Pseudomonas aeruginosa (EPA)) produced using a novel in vivo bioconjugation method.

Methods: Three doses of ExPEC-4V (with or without aluminum hydroxide) were administered to rabbits (2μg or 20μg per O-antigen, subcutaneously), mice (0.2μg or 2μg per O-antigen, subcutaneously) and rats (0.4μg or 4μg per O-antigen, intramuscularly). Antibody persistence and boostability were evaluated in rats using O6-EPA monovalent conjugate (0.4μg O-antigen/dose, intramuscularly). Toxicity was assessed in rats (16μg total polysaccharide, intramuscularly). Serum IgG and IgM antibodies were measured by ELISA.

Results: Robust antigen-specific IgG responses were observed in all animal models, with increased responses in rabbits when administered with adjuvant. O antigen-specific antibody responses persisted up to 168days post-priming. Booster immunization induced a rapid recall response. Toxicity of ExPEC-4V when administered to rats was considered to be at the no observed adverse effect level.

Conclusions: ExPEC-4V conjugate vaccine showed good immunogenicity and tolerability in animal models supporting progression to clinical evaluation.

Keywords: Conjugate vaccine; Escherichia coli; Extra-intestinal pathogenic E. coli (ExPEC); Immunogenicity; Safety; Vaccine.

MeSH terms

  • ADP Ribose Transferases / immunology
  • Adjuvants, Immunologic / administration & dosage
  • Animals
  • Antibodies, Bacterial / blood
  • Bacterial Toxins / immunology
  • Escherichia coli
  • Escherichia coli Infections / prevention & control*
  • Escherichia coli Vaccines / immunology*
  • Exotoxins / immunology
  • Female
  • Immunization, Secondary
  • Immunogenicity, Vaccine*
  • Mice
  • Mice, Inbred ICR
  • No-Observed-Adverse-Effect Level
  • O Antigens / immunology*
  • Pseudomonas aeruginosa Exotoxin A
  • Rabbits
  • Rats
  • Rats, Sprague-Dawley
  • Toxicity Tests
  • Vaccines, Conjugate / immunology
  • Virulence Factors / immunology


  • Adjuvants, Immunologic
  • Antibodies, Bacterial
  • Bacterial Toxins
  • Escherichia coli Vaccines
  • Exotoxins
  • O Antigens
  • Vaccines, Conjugate
  • Virulence Factors
  • ADP Ribose Transferases