Nonclinical safety evaluation of Escherichia coli heat-labile toxin mucosal adjuvant as a component of a nasal influenza vaccine

Conventional influenza vaccines currently in use are administered parenterally and generally confer good protection against systemic disease through the induction of high titers of serum virus-neutralizing antibodies. Parenteral vaccines are suboptimal in that they fail to induce a local mucosal response that may prevent the early stages of virus infection. Thus, the intranasal administration of a vaccine may provide a viable alternative to the parenteral route. Indeed, intranasal administration of vaccine antigens when formulated with an appropriate mucosal adjuvant (e.g., bacterial toxins), results in a vigorous local and systemic immune response. This review discusses the nonclinical safety evaluation of Escherichia coli heat-labile toxin as a mucosal adjuvant for an intranasally administered influenza vaccine.