A previously incurable blood disorder – sickle-cell disease – has been successfully treated in 9 of 10 adults who received stem cells transplanted from tissue-matched siblings.

The inherited disease causes the bone marrow to churn out blood cells that are shaped like crescents, or sickles, rather than the round shape of healthy cells. This causes painful blockages in blood vessels, depletion of blood and severe anaemia.

Transplants have worked well in around 200 children but don't succeed in adults because the technique requires that cells in the recipient's own bone marrow are destroyed first – children can usually tolerate this, but adults can't.

Even when adults have got past this obstacle, they have gone on to develop the fatal condition graft-versus-host disease (GVHD), in which the donated cells attack and destroy other tissue.