A U.S. Patent for “Selection Marker for Cell Transfection and Protein Production” was awarded to Sanofi on February 11th, 2020. The present invention is within the field of industrial protein production. The invention provides a novel expression system using dihydroorotate dehydrogenase (DHODH) as a selection marker in combination with leflunomide or a metabolite thereof, notably for use in mammalian cell lines. Expression vectors encoding DHODH, cell lines comprising said vectors and methods of producing recombinant proteins are also provided. Learn More