A mucosal vaccine against diphtheria: formulation of cross reacting material (CRM(197)) 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 capable of stimulating immune responses similar to, or greater than, those obtained with the parenterally-delivered toxoid vaccine, while reducing the adverse effects that have been associated with the traditional vaccine. In this study, we examined the cellular and humoral immune responses in mice generated after both parenteral and mucosal immunizations with cross-reacting material (CRM(197)) of diphtheria toxin. We found that both native and mildly formaldehyde-treated CRM(197) and conventional diphtheria toxoid (DT) induced mixed Th1/Th2 responses and similar levels of anti-DT serum IgG following parenteral immunization. In contrast, CRM(197) preparations were poorly immunogenic when administered intranasally in solution. However, formulation of the antigens with chitosan significantly enhanced their immunogenicity, inducing high levels of antigen-specific IgG, secretory IgA, toxin-neutralizing antibodies and T cell responses, predominately of Th2 subtype. Furthermore, intranasal immunization with CRM(197) and chitosan induced protective antibodies against the toxin in a guinea pig passive challenge model. We also found that priming parenterally with DT in alum and boosting intranasally with CRM(197) was a very effective method of immunization in mice, capable of inducing high levels of anti-DT IgG and neutralizing antibodies in the serum and secretory IgA in the respiratory tract. Our findings suggest that boosting intranasally with CRM(197) antigen may be very effective in adolescents or adults who have previously been parenterally immunized with a conventional diphtheria toxoid vaccine.