Complex sentence: The stable growth of HeLa enabled a researcher at the University of Minnesota hospital to successfully grow polio virus, enabling the development of a vaccine, and by 1954, Jonas Salk developed a vaccine for polio using these cells.
Split into simpler sentences: The stable growth of HeLa enabled a researcher at the University of Minnesota hospital to successfully grow polio virus, enabling the development of a vaccine. By 1954 Jonas Salk developed a vaccine for polio using these cells.