The novel adjuvant IC31 strongly improves influenza vaccine-specific cellular and humoral immune responses in young adult and aged mice.

The compromised immune responses in the elderly as well as the threat of pandemic influenza necessitate the development of improved influenza vaccines. This study provides evidence that IC31, a two-component synthetic adjuvant signalling through TLR-9, augments humoral and cellular immune responses to seasonal influenza vaccines. Experiments performed in young adult mice showed increased HI titres and higher levels of IgG2a antibodies that were accompanied by the induction of IFN-gamma producing CD4(+) T cells after single vaccination with reduced doses of vaccine antigens, even 200 days after single immunisation. Importantly, similar effects were seen in aged mice, although most pronounced upon booster immunisation. Thus, IC31 fulfils important criteria of novel influenza vaccine adjuvants.