• Vaccine Name: E. coli vaccine using verocytotoxin toxoid
• Target Pathogen: Escherichia coli
• Target Disease: Hemorrhagic colitis
• Vaccine Ontology ID: VO_0000501
• Type: Subunit vaccine
• Antigen: The antigens for these vaccines are either verocytoxin 1 (VT1) or verocytoxin 2 (VT2). The prototype toxin VT1 is virtually identical to Shiga toxin produced by Shigella dysenteriae type 1. By using in vitro neutralization tests in Vero cells, VT1 has been shown to be serologically distinct from VT2 in that these toxins showed no cross-neutralization by heterologous antisera (Bielaszewska et al., 1997).
• Adjuvant: incomplete Freund's adjuvant
  • Adjuvant name: incomplete Freund's adjuvant
  • VO adjuvant ID: VO_0000142
  • Description: Freund’s incomplete adjuvant was used in the making of these vaccines (Bielaszewska et al., 1997).
• Preparation: VT1 was purified from JB28, an E. coli TB1 strain. VT2 was purified from E. coli R82pJES 120DH5a. The purity of these toxin preparations was established by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoretic analysis. The labeled toxins were characterized for specific activity (1.7 x 10^5 to 2.3 x 10^5 cpm/mg) and biological activity (3.8 x 10^5 and 1.9 x 10^3 50% cytotoxic doses [CD50s]/mg for VT1 and VT2, respectively). The Vero cell binding activities, which represent the percentage of the input activity bound to the 25-sq cm monolayers after 1h of incubation and three washes, were 48% for VT2 preparations and 75% for VT1 preparations. For the subunit immunizations, VT1 and VT2 were separated into the A and B subunit fractions by SDS-polyacrylamide gel electrophoresis. (Bielaszewska et al., 1997).

Rabbit Response

• Host Strain: New Zealand White
• Vaccination Protocol: Rabbits weighing approximately 2 kg were immunized subcutaneously with doses of 60 mg of toxoid mixed with equal volumes adjuvant in four sequential weekly intervals (Bielaszewska et al., 1997).
• Immune Response: Rabbits immunized with the VT A and B subunits developed NAb to the homologous toxin but not to the heterologous toxin. Rabbits immunized with the A subunits were reactive by ELISA with the homologous toxin but were less, if at all, reactive to the heterologous toxin. Immunization with the B subunits led to the appearance of ELISA antibodyto the homologous toxin in the case of VT1 but did not lead to a detectable level of antibody in the case of VT2. Immunization with VT1 and VT2 toxoids resulted in strong ELISA antibody responses to both homologous and heterologous toxins (Bielaszewska et al., 1997).
• Challenge Protocol: 125 I-labeled VT1 and VT2 were administered to rabbits which had been immunized, in groups of three, with either the A or B subunit of VT1, the A or B subunit of VT2, or with VT1 or VT2 holotoxoids and to nonimmune controls. Following administration of approximately 4 x 10^6 cpm of labeled VT through the ear vein, a 1- to 2-ml blood specimen was collected from the ear artery (Bielaszewska et al., 1997).
• Efficacy: Animals immunized by either the VT1 A subunit or the VT2 A subunit were protected from target tissue uptake of both the homologous and heterologous125 I-labeled holotoxins. In contrast, in animals immunized with the toxin B subunits, protection was extended only against challenge by the homologous toxin. Findings indicate that the in vivo cross-neutralization is a predominant function of antibodies directed to the VT A subunits. This suggests that the VT1 A or VT2 A subunit may be a suitable immunogen for immunizing humans against systemic VT-mediated disease (Bielaszewska et al., 1997).