Patent ID: 8778357

Claim:
A method for producing an influenza virus particle, comprising the steps of: a) providing a linear expression construct free of amplification sequences needed for amplification of plasmids in bacterial cells, selection markers, or both amplification sequences and selection markers, wherein the construct comprises an RNA polymerase I (polI) promoter and a polI termination signal, the polI promoter and polI termination signal being inserted between an RNA polymerase II (polII) promoter and a polyadenylation signal, wherein the linear expression construct further comprises a gene segment selected from the group consisting of an HA gene segment of an influenza virus, an NA gene segment of an influenza virus, or both an HA gene segment and an NA gene segment of an influenza virus, and wherein the gene segment is inserted between the polI promoter and the polI termination signal; b) transfecting a host cell with the linear expression construct; c) infecting the host cell with a helper virus, wherein the helper virus is an influenza virus, and wherein the helper virus comprises genomic RNA encoding a protein selected from the group consisting of HA protein of an influenza virus, NA protein of an influenza virus or both HA protein and NA protein of an influenza virus, the helper virus further comprising other viral segments needed to produce progeny virus particles; d) cultivating the host cell, thereby producing progeny virus particles, wherein at least some of the progeny virus particles comprise HA protein or NA protein derived from the linear expression construct; and e) selecting a candidate virus particle from among the progeny virus particles, wherein the candidate virus particle comprises: i) HA protein derived from the linear expression construct and not HA protein derived from the helper virus, if the linear expression construct comprises an HA gene segment; and ii) NA protein derived from the linear expression construct and not NA protein derived from the helper virus, if the linear expression construct comprises an NA gene segment.