Intranasal c-di-GMP-adjuvanted plant-derived H5 influenza vaccine induces multifunctional Th1 CD4+ cells and strong mucosal and systemic antibody responses in mice

The present study investigated the detailed humoral and cellular immune responses in mice vaccinated intranasally or intramuscularly with plant-derived influenza H5N1 (A/Anhui/1/05) antigen alone or formulated with bis-(3′,5′)-cyclic dimeric guanosine monophosphate (c-di-GMP) as adjuvant. The use of c-di-GMP as intramuscular adjuvant did not enhance the immune response to plant-derived influenza H5 antigen. However, intranasal c-di-GMP-adjuvanted vaccine induced strong mucosal and systemic humoral immune responses. Additionally, the intranasal vaccine elicited a balanced Th1/Th2 profile and, most importantly, high frequencies of multifunctional Th1 CD4+ cells. Our results highlight that c-di-GMP is a promising mucosal adjuvant for pandemic influenza vaccine development.