One of the obstacles to human cloning has been cleared by scientists who successfully used skin to generate embryonic stem cells.
The advance, described as a “milestone”, is expected to aid the development of stem cell therapies that avoid fertilised human embryos.
But since it employs a cloning technique it is certain to fuel controversy over “brave new world” science.
The US scientists said they were not interested in cloning humans and did not believe their methods could successfully be used in this way.
But the therapeutic cloning technique they employed would also be the start of the process of making duplicate humans.
It is the first time scientists have managed to create human embryos through cloning developed enough to provide stem cells.
The same somatic cell nuclear transfer (SCNT) technique was employed by researchers at the Roslin Institute in Edinburgh to produce Dolly, the first mammal to be cloned from an adult cell. During SCNT, a donor cell nucleus is transferred to an egg cell whose own nuclear DNA has been removed.
The egg develops into an early-stage embryo that is a clone of the donor, containing the same genes.
Stem cells taken from the embryo are “pluripotent”, having the ability with the right coaxing to mature into any kind of tissue in the body, from brain to bone.
In the new study, reported in the journal, Cell, scientists transferred nuclei from human skin cells into human egg cells.
They generated “blastocysts”, early embryos consisting of a cluster of 150 cells, from which human embryonic stem cells (hESCs) were obtained and grown in the laboratory.
Scientists have previously cloned monkey embryos and mined them for stem cells, but until now been frustrated in their attempts to do the same with humans.
Lead researcher Professor Shoukhrat Mitalipov, from Oregon Health and Science University, said: “Our finding offers new ways of generating stem cells for patients with dysfunctional or damaged tissues and organs,
“Such stem cells can regenerate and replace those damaged cells and tissues and alleviate diseases that affect millions of people.
“The stem cells demonstrated an ability to convert into several different cell types, including nerve, liver and heart cells.”