Researchers at the University of Texas Health Science Center at San Antonio have cured Type 1 diabetes in mice without side effects. The treatment would also allow people with Type 2 diabetes to stop insulin shots.

Diabetes is classified as either Type 1 or Type 2. Type 1 diabetes is a lifelong autoimmune condition that develops when the beta-cells — the cells in the pancreas that produce insulin — are destroyed, causing a person's blood sugar level to become too high.

 Type 2 diabetics produce insulin, but can't properly use the insulin they produce. The majority of people who have diabetes have Type 2,  and obesity caused by overeating is generally recognized as the major cause.

The new discovery increases the number of pancreatic cells that secrete insulin.

"It worked perfectly," said Bruno Doir, Ph.D, co-inventor of the technique. "We cured mice for one year without any side effects. That's never been seen. But it's a mouse model, so caution is needed. We want to bring this to large animals that are closer to humans in physiology of the endocrine system."

"The pancreas has many other cell types besides beta cells, and our approach is to alter these cells so that they start to secrete insulin, but only in response to glucose [sugar]," said Ralph DeFronzo, M.D., the other co-inventor of the technique. "This is basically just like beta cells."

The therapy uses a technique called gene transfer. A virus is used as a vector, or carrier, to introduce selected genes into the pancreas. These genes become incorporated into the organ and cause digestive enzymes and other cell types to make insulin.

Gene transfer using a viral vector has been approved nearly 50 times by the U.S. Food & Drug Administration to treat various diseases, said DeFronzo, and is a proven treatment for rare childhood diseases.

Unlike beta cells, which the body rejects in Type 1 diabetes, the other cell populations of the pancreas co-exist with the body's immune defenses.

"If a Type 1 diabetic has been living with these cells for 30, 40 or 50 years, and all we're getting them to do is secrete insulin, we expect there to be no adverse immune response," DeFronzo said.

The new therapy precisely regulates blood sugar in mice and could be a major advance over traditional insulin therapy and some diabetes medications that can make blood sugar drop too low.

"A major problem we have in the field of Type 1 diabetes is hypoglycemia (low blood sugar)," Doiron said. "The gene transfer we propose is remarkable because the altered cells match the characteristics of beta cells. Insulin is only released in response to glucose."

People don't have symptoms of diabetes until they have lost at least 80 percent of their beta cells, Doiron said.

"We don't need to replicate all of the insulin-making function of beta cells," he said. "Only 20 percent restoration of this capacity is sufficient for a cure of Type 1."

The next step will be to test the new therapy on larger animals, and hopefully advance to large-scale human studies within three years.

According to the Centers for Disease Control and Prevention, 29.1 million Americans had diabetes in 2014.