Israeli scientists have grown heart tissue from human embryo stem cells, while others in the US have used stem cells to produce insulin - possibly leading to new treatments for heart disease and even a cure for type 1 diabetes.
The joint announcement yesterday follows hard on the vote by the US Congress to ban use of embryo stem cells in research, along with any form of human cloning. No country permits human reproductive cloning, but Britain this year gave the go-ahead for limited studies with stem cells from embryos left over from fertility treatment. Japan is to follow Britain's lead.
Researchers at the Technion-Israel Institute of Technology announced in the Journal of Clinical Investigation they had grown cardiomyocytes, the precursors of heart cells. If injected into an adult human heart, they say, these cells would produce mature muscle cells.
"Patients with end-stage heart failure often depend on availability of heart donors," said Mr Rafael Beyar, dean of medicine at the institute. "This research may lead to tools to treat this devastating disease." Sir Charles George, medical director of the British Heart Foundation, called it "a fascinating and important milestone".
The US find, reported in the journal Diabetes, "offers the promise that stem cells might provide a rich source of insulin-producing cells and put us closer to a cure for this serious disease", said Mr Christopher Saudek, president of the American Diabetes Association.
But so far, the research offers only promise - and controversy. Through embryo stem cells, a single fertilised egg turns into 100 trillion cells of more than 200 kinds of tissue over nine months in the womb. Three years ago a US team found how to grow these cells in a laboratory and raised the prospect of treatments for incurable diseases. They also provoked alarm from religious and political groups and concern from some governments.
Campaigners argue that by using stem cells from adults, researchers could sidestep the ethical issues involved in embryos and achieve the same ends.