Ever since human embryonic stem (ES) cells were first isolated in 1998, a debate over their use has raged. Proponents of ES cell research say that the promise of the cells in treating diseases ranging from heart failure to paralysis is invaluable. Critics, on the other hand, argue that the ethical cost of using ES cells, which are derived from human embryos, is too high. Scotland-based PPL Therapeutics hopes to end the debate once and for all by developing an unlimited source of stem cells-without ever creating or destroying an embryo.

Select from the choices above to read the entire article.