The promise of using stem cells to treat disease has moved a tantalizing step closer to reality, without the ethical shackles that have long hindered its progress.

In a compelling scientific feat, independent teams of researchers in Japan and the U.S. have created human embryonic stem cells without destroying any human embryos. Scientists said they "reprogrammed" mature human cells and returned them to a primordial, embryonic-like state in a laboratory dish.

The...