A mucosal vaccine against diphtheria: formulation of cross reacting material (CRM197) of diphtheria toxin with chitosan enhances local and systemic antibody and Th2 responses following nasal delivery

The development of new generation vaccines against diphtheria is dependent on the identification of antigens and routes of immunization that are capab le of stimulating immune responses similar to, or greater than, those obtai ned with the parenterally-delivered toroid vaccine, while reducing the adve rse effects that have been associated with the traditional-vaccine. In this study, we examined the cellular and humoral immune responses in mice gener ated after both parenteral and mucosal immunizations with cross-reacting ma terial (CRM197) of diphtheria toxin. We found that both native and mildly f ormaldehyde-treated CRM197 and conventional diphtheria toroid (DT) induced mixed Th1/Th2 responses and similar levels of anti-DT serum IgG following p arenteral immunization. In contrast, CRM197 preparations were poorly immuno genic when administered intranasally in solution. However, formulation of t he antigens with chitosan significantly enhanced their immunogenicity, indu cing high levels of antigen-specific IgG, secretory IgA, toxin-neutralizing antibodies and T cell responses, predominately of Th2 subtype. Furthermore , intranasal immunization with CRM197 and chitosan induced protective antib odies against the toxin in a guinea pig passive challenge model. We also fo und that priming parenterally with DT in alum and boosting intranasally wit h CRM197 was a very effective method of immunization in mice, capable of in ducing high levels of anti-DT IgG and neutralizing antibodies in the serum and secretory IgA in the respiratory tract. Our findings suggest that boost ing intranasally with CRM197 antigen may be very effective in adolescents o r adults who have previously been parenterally immunized with a conventiona l diphtheria toroid vaccine. (C) 2000 Elsevier Science Ltd. All rights rese rved.