For nearly half a century, the idea of using human stem cells to grow healthy specialised cells and tissue has been evolving from science fiction towards practicable medicine. The successful treatment in Brazil of a small group of type 1 diabetes patients with their own stem cells does not mean this evolution is complete. But it is, at the very least, a landmark trial on the way to what optimists hope will be a new era of “regenerative medicine”.

Fourteen of 15 subjects in a study by the University of São Paulo, reviewed in the Journal of the American Medical Association, were able to stop injecting themselves with insulin for significant periods after treatment that involved extracting healthy stem cells from their bone marrow, suppressing their overactive immune systems, then reinjecting the stem cells. The trial provided the first clinical evidence for long-held theories that diabetes could be among many conditions suitable for new stem-cell treatments. As such, the results are an unqualified fillip for type 1 diabetes sufferers and for stem-cell research as a whole. It may, however, be seized on by opponents of embryonic stem-cell research as evidence that adult stem cells are just as useful as those harvested from embryos. Such a hasty judgment would be unhelpful to those living with chronic afflictions ranging from Alzheimer’s and Parkinson’s disease to rheumatoid arthritis. And it would be unfounded in science.

The mechanism by which stem-cell reinjection helped the patients in the Brazilian trial is poorly understood. The process may simply have saved so-called “beta cells” — crucial to the body’s production of its own insulin — that would otherwise have been destroyed by the subjects’ malfunctioning immune systems. There is also a chance that some of the stem cells fulfilled scientists’ most cherished hopes by regenerating once back in the body, to produce new beta cells. This would bear out what is already known from lab tests — that adult stem cells can indeed regenerate and could have myriad therapeutic uses as a result. But the balance of evidence still points to a central role for responsibly harvested embryonic stem cells in this fast-moving area of research, not least because these cells alone contain what has been called the full “software of life”, and thus the ability to develop into any of the more than 200 different types of tissue in the body. As Elias Zerhouni, director of the National Institutes of Health in the US, put it last month, studies claiming as much potential for adult as for embryonic cells “do not hold scientific water”.

Dr Zerhouni’s words were carefully chosen and politically significant. Shortly before this week’s renewed congressional debate on federal US funding for stem-cell research, he broke ranks with the White House, calling for more embryonic stem-cell lines for publicly funded US scientists. With Democratic majorities in both chambers and a compromise Bill before the Senate, a fundamental change in federal policy could follow. Yet state legislatures and the private sector are already answering the call of science, most recently with research grants worth $76 million to Californian universities.

Britain, which leads the world in stem-cell research, thanks to its encouragement of scientific inquiry, may not do so for long. But this race is against debilitating diseases, not between national scientific elites or rival claimants to moral superiority. The news from Brazil brings us all a step closer to a significant social victory.