The intranasal adjuvant Endocine™ enhances both systemic and mucosal immune responses in aged mice immunized with influenza antigen

Despite availability of annual influenza vaccines, influenza causes significant morbidity and mortality in the elderly. This is at least in part a result of immunosenescence; the age-dependent decrease in immunological competence that results in greater susceptibility to infections and reduced responses to vaccination. To improve protective immune responses in this age group, new vaccines strategies, such as the use of adjuvants, are needed. Here, we evaluated the mucosal vaccine adjuvant Endocine™, formulated with split influenza antigen and administered intranasally in aged (20-month old) mice. Humoral immune responses were assessed and compared to unadjuvanted intranasal and subcutaneous vaccines. We show that formulation with Endocine™ significantly enhances hemagglutination inhibition (HI) titers, as well as serum IgG and mucosal IgA antibody titers, compared to both types of unadjuvanted vaccines. Thus, our results indicate that intranasal vaccination with Endocine™ is a possible approach for the development of mucosal influenza vaccines for the elderly.