For the first time, scientists have created human embryos that are genetic copies of living people and used them to make stem cells — a feat that paves the way for treating a range of diseases with personalized body tissues but also ignites fears of human cloning. If replicated in other labs, the methods detailed Wednesday in the journal Cell would allow researchers to fashion human embryonic stem cells that are custom-made for patients with Alzheimer's disease, diabetes and other health problems. Theoretically capable of reproducing themselves indefinitely, these stem cells could be used to grow replacements for a wide variety of diseased cells — those of the blood, skin, heart, brain, muscles, nerves and more — that would not risk rejection by the patient's immune system. The report also raises the specter that, with a high-quality donor egg, a bit of skin, some careful tending in a lab and the womb of a willing surrogate, humans have cracked the biological secret to reproducing themselves. That is an objective American scientists have squarely renounced as unethical and scientifically irresponsible. At the same time, most acknowledge that such "reproductive cloning" will one day prove too tempting to resist. In the hope that other researchers will validate and extend their results, the scientists at Oregon Health & Science University provided an exceptionally detailed account of their techniques. For anyone with a well-equipped fertility lab, the comprehensive guide could also be a useful handbook for cloning a baby. OHSU cell biologist Shoukhrat Mitalipov led a team of 23 scientists who methodically culled the lessons learned from stem cell research on amphibians, mice and rhesus monkeys — as well as from the abundant failures of others in the field. They devised a welter of new techniques to use the DNA of a fully formed skin cell in its most primitive embryonic form. The approach they used — called somatic cell nuclear transfer — effectively strips an egg of i