Two scientists who were awarded the Nobel Prize in Physiology or Medicine on Monday helped lay the foundation for regenerative medicine, the hotly pursued though still distant idea of rebuilding the body with tissues generated from its own ells. They are John B. Gurdon of the University of Cambridge in England and Shinya Yamanaka of Kyoto University in Japan. Their discoveries concern the manipulation of living cells and lie at the heart of the techniques for cloning animals and generating stem cells, the primitive cells from which the mature tissues of the body develop.