The present invention provides novel MDCK-derived adherent non-tumorigenic cell lines that can be grown in the presence or absence of serum. The cell lines of the present invention are useful for the production of vaccine material (e.g., viruses). More specifically, the cell lines of the present invention are useful for the production of influenza viruses in general and ca/ts influenza viruses in particular. The invention further provides methods and media formulations for the adaptation and cultivation of MDCK cells such that they remain non-tumorigenic. Additionally, the present invention provides methods for the production of vaccine material (e.g., influenza virus) in the novel cell lines of the invention.