UNTIL THE 1940s, blood transfusions often went wrong because some of the main blood-group systems, such as the Rhesus factor, had yet to be discovered. This hit or miss approach to matching donors with recipients is now a thing of the past, as tests for all sorts of characteristics of an individual’s blood have become available. But finding a well-matched donor can still be difficult. Some patients have blood types so rare that there may be but a handful of appropriate donors in the country where they live.

On November 7th a consortium of researchers at several British institutions, co-ordinated by NHS Blood and Transplant, a government health authority, and Bristol University, announced a step towards solving this problem. They have successfully transfused into two healthy volunteers red blood cells grown from appropriate stem cells donated by others.