The present invention relates to immortalized avian cell lines suitable for production of biologicals or viruses for vaccination. In particular, the cell lines are derived from primary cells which are transformed with at least two viral or cellular genes, one of which causes cell cycle progression whereas the other interferes with innate protective mechanisms of the cell induced by dysregulated replication. The invention moreover relates to the production of said immortalized cell lines and their use for producing biologicals or viruses for vaccination.
