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Protein and Polysaccharide Conjugate Vaccines to Enteric Diseases

Szu, Shousun
DHHS/NIH - National Institute of Child Health and Human Development
Start date
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The capsular polysaccharide of S. typhi (Vi) is a licensed vaccine but with limited efficacy in children less than 5 years old. To provide a vaccine for younger children, Vi was conjugated to recombinant exoprotein A of Pseudomonas aeruginosa (rEPA). An efficacy of 89% at 47 months was shown in 2-to-5-year olds injected with Vi-rEPA. Vi-rEPA, administered concurrently with routine vaccines in the Expanded Program of Immunization (EPI) at 2, 4, 6 and 12 months showed Vi-rEPA was safe, compatible with EPI immunization and 95% infants had higher than the estimated protective antibody level after the last injection; Vi-rEPA is suitable for routine immunization of infants.

It was found that high maternal antibody levels impede the infants antibody response. In collaboration with the International Vaccine Institute, Korea and the Novartis Institute for Global Health, Italy,Vi was conjugated to licensed vaccines such as DT. In mice, these conjugates elicited similar IgG anti-Vi levels to those induced by Vi-rEPA.

In collaboration with the Lanzhou Institute of Biologics, China, a high tittered human plasma pool from volunteers immunized with Vi-rEPA was purified and the level of IgG anti-Vi determined in weight units. It will be available for distribution globally as a human IgG anti-Vi reference standard.Vibrio cholerae O1 remains a major health problem in developing countries; especially in the Indian subcontinent and in Africa.

A cholera outbreak started in Haiti in October 2010. Up to July 2011, there were more than 420,000 cases and 6,000 deaths. No vaccine is available to control the spread. Field studies showed that serum vibriocidal activity is directed toward its LPS.

In a phase 1 trial, V. cholerae O-SP conjugates elicited IgG anti-LPS with vibriocidal activity. A hexamer and octamer corresponding to the O-SP were chemically synthesized and conjugated to TT. In mice these conjugate elicited higher vibriocidal activities than the native O-SP conjugate used in the Phase I study. Octamer conjugates elicited higher antibody levels than the hexamer conjugates. Various linkers were studied. A conjugate synthesized with a heptadecamer linker was more immunogenic than the one with a nonamer linker. Linkers with various hydrocarbon or hydroxyl chains were compared for efficiency, stability, and solubility.

Rotavirus is the most common cause of infantile diarrhea worldwide. Two licensed oral rotavirus vaccines conferred limited protection and some lots were contaminated with small amounts of porcine circovirus 1 and 2 DNA.

We are designing a parenteral vaccine based on capsid proteins. Recombinant capsid proteins with truncated C or N termini were expressed in E. coli and elicited neutralizing antibodies in mice and guinea pigs. Conjugation of the recombinant proteins to a polysaccharide vaccine improved protein solubility. The double truncated (both C and N terminals) core region of the capsid protein provided a high yield antigen that elicited neutralizing antibody to the P4, P6 and P8 serotypes in the plaque-forming assay.

To improve immunogenicity, conjugates of capsid proteins-based peptides were prepared. In collaboration with the Lanzhou Institute of Biologics, whole cell killed rotavirus parenteral vaccine was prepared and elicited higher neutralizing antibody levels than the corresponding live oral vaccine. Combination of capsid protein with the killed whole cell rotavirus for broader P serotype coverage is under study.Enterohemorrahagic E. coli (EHEC) infections are the leading cause of E. coli deaths in developed countries. In the US, the prevalent serotype is O157H:7.

An outbreak in Germany and neighboring countries in 2011 was caused by O104. The EHEC strains contain the Shiga toxin (Stx) gene and the released toxin can cause serious manifestations; from diarrhea, hemorrhagic colitis, to hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura. HUS is a major cause of acute and chronic kidney damage in young children and could lead to death. In a phase II study in 2-5 years old children in the US, an LPS based conjugate vaccine elicited a >10 fold rise of antibodies with bactericidal activity in 98% of children. Most EHEC infections are caused by strains secreting Stx2. The non-toxic B-subunit of Stx2 was purified in high yield by an improved recombinant technique. Stx2B could serve as a carrier protein for the E. coli O157 O-SP and provide a broader coverage of non-O157 EHEC infections.

Funding Source
Nat'l. Inst. of Child Health and Human Devel.
Project source
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Escherichia coli
Bacterial Pathogens
Natural Toxins
Meat, Poultry, Game