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IT HAS been 10 frustrating years since human embryonic stem cells were first isolated from spare human embryos and grown in the lab – frustrating, because ESCs have completely failed to live up to their promise of providing an inexhaustible source of transplantable tissues and organs. Instead, they have remained mired in moral and political controversy because they are obtained from embryos that perish in the process.

Only one company, of Menlo Park, California, has made significant progress on the medical front, having successfully turned ESCs into cells that could be used to repair spinal cords, hearts, livers, bones and pancreases. Unfortunately its most advanced plans for a clinical trial – to treat damaged spinal cords – keep getting rebuffed by the US , most recently in May. The FDA is not satisfied that the cells will be safe. Will patients’ immune systems react against them? Will they turn cancerous?

Now, at long last, researchers have managed to turn ESCs into something with obvious practical potential: an inexhaustible supply of red blood cells. A supply that, in future, could be transplanted into anyone, irrespective of their blood type (see “First red blood grown in the lab”). Like true red blood cells they don’t have nuclei, so they cannot multiply and cause cancers. There is still work to do to create truly “universal” cells and ensure they work in animals and people. But it is an important breakthrough, and a timely response to those in the US trying to turn the use of cells from embryos into an election issue.