Preliminary Studies on a Derivative Verotoxin as Oral Adjuvant

Jose Matías, Oscar Landeta, Paula Esquivias and Carlos Gamazo

Most vaccines are still delivered by injection. Mucosal vaccination would increase compliance and decrease the risk of spread of infectious diseases due to contaminated syringes. However, most antigens are unable to induce immune responses when administered mucosally and require the use of strong adjuvant or effective delivery systems. Vibrio cholerae toxin (CT) is a powerful mucosal adjuvants when co-administered with soluble antigens, but present important drawbacks such as residual toxicity. In the current report, a recombinant verotoxin, rVTX1 from Escherichia coli O157 has been tested to be used as oral adjuvant. A common antigen, BSA (bovine serum albumin), was orally co-administered with the toxoid rVTX1 in BALB/c mice. Commercial CT was used as a reference adjuvant. In this study, the specific antibody response was determined in sera (IgG1, IgG2a, IgA and IgE) and in fecal samples (IgA). In addition, the oral toxicity of the new adjuvant candidate was studied in mice. Results indicated that rVTX1 possesses a higher mucosal adjuvant activity than CT when administered orally without inducing any toxic symptoms. These preliminary results support further experiments to demonstrate the potential applications of this protein in oral vaccine development.