DURING THE past two decades, scientists, politicians and conservative activists have been fighting over stem cells, which can morph into any type of cell in the body, with the right coaxing. Some activists objected to how scientists harvest the cells they use in much of the most promising research — from human embryos. Researchers argued that embryonic stem cell science has incredible promise to alleviate human suffering caused by disease and organ failure. But until now the scientists didn’t have many big payoffs to tout.

On Thursday, a group of Harvard researchers announced that they had effectively cured diabetes in lab mice using human embryonic stem cells. The team painstakingly exposed stem cells to various chemicals until they figured out which ingredients to use and in which order, finally inducing undifferentiated stem cells to become beta cells, which specialize in detecting rises in blood sugar and releasing insulin in response. Beta cells are nature’s natural insulin pumps, but they are much better at finely tuning blood sugar than artificial insulin delivery methods. The Harvard scientists transplanted the beta cells they created into diabetic mice, which were asymptomatic within 10 days.

This dramatic result is particularly promising for victims of type I diabetes, a disorder in which the body’s immune system kills off all of its beta cells, but it also potentially offers relief to those suffering with type 2 diabetes, also known as adult-onset diabetes. Many laboratory discoveries take years or decades to yield therapies . The Harvard scientists are more optimistic. With partners at the University of Chicago, they are planning tests on primates, and they hope to begin human transplant trials within three years.

After the Harvard team reported its findings in the journal Cell, its leader, Doug Melton, pointedly thanked the philanthropists who donated to his project. The George W. Bush administration, he noted, had ruled out federal funding for embryonic stem cell research except on a few lines of cells that were already in use. The Obama administration correctly reversed that policy shortly after coming to office. Without private support in the interim, this advance on diabetes would have been significantly delayed, if not stopped altogether.

Embryonic stem cells have been the “gold standard” in research to date, lead study author Felicia Pagliuca explained. Scientists haven’t established that non-embryonic stem cells are as useful. “We don’t know what we don’t know” about them, she said. Until they do, it is crucial that scientists preserve the flexibility to explore the huge potential of stem cell research.