Methods of differentiating unmodified adult stem cells into functional beta-like cells are provided, as well as compositions, tissues and devices containing such cells. The method requires inducing sequential expression of PDX1, NGN3, and MAFA in these stem cells to form reprogrammed beta cells. Methods of treating diabetes are also provided, comprising obtaining stem cells, preferably from a patient with diabetes, inducing sequential expression of PDX1, NGN3, and MAFA, in said stem cells to form reprogrammed beta cells, and introducing said reprogrammed beta cells into a pancreas of said patient. Alternatively, it may be possible to inject such cells systemically, if the cells are targeted for the pancreas. In yet another embodiment, the reprogrammed beta cells are placed into an artificial pancreas that is surgically placed or injected into the patient.
