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

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.

Bioneedles as vaccine carriers.

Bioneedles are small hollow mini implants fabricated from biodegradable polymers which can be filled with antigen. Bioneedles can be used for vaccination without syringes and needles. Formulations have been prepared containing tetanus toxoid with and without aluminum phosphate. Stability and immunogenicity of Bioneedles were compared with liquid formulations. The antigen, when formulated in Bioneedles, retained fully its antigenicity up to 60 degrees C for 1 week whereas the antigen, in its liquid form, lost all activity at 60 degrees C after 1 week. After 3 weeks at 60 degrees C, a recovery of 60% was still found in the Bioneedles. Mice injected with Bioneedles with adjuvanted tetanus toxoid showed a comparable functional antibody response to the group receiving conventional liquid injections. This response was achieved with a four times lower antigen concentration when using the Bioneedles compared to the regular injections. We conclude that Bioneedles are good alternatives for injections using needles and syringes.