Immunogenic reagents from west nile virus

An immunogenic composition comprising a purified complex of at least 4 West Nile Virus (WNV) PrM/E heterodimers, each heterodimer consisting of a recombinant WNV PrM polypeptide and (ii) a recombinant WNV E polypeptide wherein the composition comprising the purified complex is substantially free of free WNV M polypeptide obtained by the method comprising:

• (a) culturing a population of mammalian host cells comprising a recombinant polynucleotide vector comprising a nucleic acid encoding a WNV polyprotein, wherein said nucleic acid encodes, in 5′-3′ order, a eukaryotic leader sequence, a WNV PrM polypeptide, a WNV E polypeptide and a translational stop codon, under conditions that provide for intracellular expression of recombinant PrM/E polypeptide;
• (b) recovering an insoluble portion from the cells, wherein the insoluble portion contains substantially all of the membrane component of the cells;
• (c) treating the insoluble portion with a non-ionic detergent, thereby to solubilize the membrane component and release the PrM/E polypeptide;
• and
• (d) purifying the released PrM/E polypeptide, to provide a composition comprising said purified complex substantially free of free WNV M polypeptide.