Soluble recombinant influenza antigens

A nucleic acid comprising:

• a) a nucleotide sequence encoding a hemagglutinin domain selected from the group consisting of hemagglutinin subtypes H1, H2, H3, H4, H5, H6, H7, H8, H9, H10, H11, H12, H13, H14, H15, and H16;
• b) a nucleotide sequence encoding an oligomerization domain selected from the group consisting of a GCN4-pII peptide, a proline rich domain (PRD) of maize γ-zein, and a bacteriophage T4 fibritin;
• wherein amino acid residues are added to the C-terminal end of the oligomerization domain such that the oligomerization domain from GCN4-pII or bacteriophage T4 fibritin does not terminate in an α-helix and the oligomerization domain from the PRD of maize γ-zein does not terminate in an amphipathic polyproline II helix;
• c) a nucleotide sequence encoding a signal peptide;
• and
• d) a nucleotide sequence encodinng an endoplasmic reticulum (ER) retention signal;
• wherein the nucleic acid encodes a soluble recombinant hemagglutinin (rHA) that forms a homotrimer.