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arvard stem cell researchers announced today that they have made a giant leap forward in the quest to find a truly effective treatment fortype 1 diabetes, a disease that affects an estimated 3 million Americans at a cost of about $15 billion annually.

With human embryonic stem cells as a starting point, the scientists were for the first time able to produce, in the kind of massive quantities needed for cell transplantation and pharmaceutical purposes, human insulin-producing beta cells equivalent in most every way to normally functioning beta cells.

Doug Melton, who led the work, said he hopes to have human transplantation trials using the cells under way within a few years. Twenty-three years ago, when his infant son Sam was diagnosed with type 1 diabetes, Melton dedicated his career to finding a cure for the disease.

“We are now just one preclinical step away from the finish line,” said Melton, whose daughter Emma also has type 1 diabetes.