LOS ANGELES (Reuters) - An experimental vaccine may be able to stop the progression of type 1, or juvenile, diabetes, according to results from a mid-stage clinical trial of the injected drug presented on Saturday.

"The vaccine prolonged what little ability people with advanced diabetes had to make insulin. We are optimistic of better efficacy in younger people, who don't have full-blown disease," said Daniel Kaufman, professor in the department of molecular and medical pharmacology at the University of California, Los Angeles, whose research team first developed and tested the vaccine in diabetes-prone mice.

Diabetes, which can lead to heart disease, kidney failure and blindness, is caused by a shortage of insulin, a hormone that regulates blood sugar levels, or by the body's failure to respond to it.

In type 1 diabetes, the body's immune system attacks cells in the insulin-making parts of the pancreas. The body is then unable to control blood sugar levels and insulin must be injected daily. Juvenile diabetes affects about one in 300 people, with the average onset age of 12.

Type 2 diabetes, which is more common, arises when the body becomes resistant to insulin, often as a result of obesity.

The UCLA researchers discovered the autoimmune response that causes type 1 diabetes may be due to the immune system attacking a protein called GAD in the insulin-producing cells in the pancreas. They then developed a diagnostic test for identifying individuals who were developing type 1 diabetes based on antibodies to that protein in their blood.

The vaccine research was licensed by the university to Sweden's Diamyd Medical AB, which conducted a trial of 47 adults recently diagnosed with late onset type 1 diabetes. The study results were unveiled at a meeting of the American Diabetes Association in New Orleans.

The vaccine, injected at four different dose levels up to three times over a six-month period, successfully prolonged patients' ability to make insulin, compared with patients who received a placebo, the researchers said.

Kaufman said the vaccine worked best at a low-to-medium dosage and the trial showed no safety concerns.

"The study shows that it is possible to inhibit the autoimmune attack on the cells that make insulin, thereby slowing the progression of type 1 diabetes," said Kaufman. Further studies are planned, the researcher said.

Diamyd expects the vaccine to first be used to prevent diabetes patients being treated with oral drugs from becoming dependent on insulin injections. Further applications are expected to be the prevention of insulin dependency in children and young people who run the risk of developing the illness and increasing the survival capability of insulin producing cells after transplantation.