Maximal immune response and cross protection by influenza virus nucleoprotein derived from E. coli using an optimized formulation

•The nucleoprotein is a promising antigen to develop a universal influenza A virus vaccine.•Maximal cross protection by E. coli-derived NP was observed with the formulation of Alum plus CpG.•10 µg of NP combined with Alum and CpG induced higher protection than 90 µg of NP without any adjuvant.•A combination of Al(OH)3 and CpG may be an efficient adjuvant in the NP formulation.

The highly conserved internal nucleoprotein (NP) is a promising antigen to develop a universal influenza A virus vaccine. In this study, mice were injected intramuscularly with Escherichia coli-derived NP protein alone or in combination with adjuvant alum (Al(OH)3), CpG or both. The results showed that the NP protein formulated with adjuvant was effective in inducing a protective immune response. Additionally, the adjuvant efficacy of Al(OH)3 was stronger than that of CpG. Optimal immune responses were observed in BALB/c mice immunized with a combination of NP protein plus Al(OH)3 and CpG. These mice also showed maximal resistance following challenge with influenza A virus PR8 strain. Most importantly, 10 µg NP formulated with Al(OH)3 and CpG induced higher protection than did 90 µg NP. These findings indicated that a combination of Al(OH)3 and CpG may be an efficient adjuvant in the NP formulation.

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