Diabetes researchers have expressed optimism for the efficacy of a vaccine used to treat tuberculosis to also treat type 1 diabetes. The FDA has given green signal to go ahead with a mid-stage trial to test the vaccine. The century-old vaccine is called bacillus Calmette-Guerin (BCG). The trial of the vaccine to treat type 1 diabetes will involve 150 adults with advanced cases of the disease.

The announcement for the approval came on Sunday at the 75th Scientific Sessions of the American Diabetes Association by Dr. Denise Faustman, director of the Massachusetts General Hospital Immunobiology Laboratory in Boston and principal investigator of the study.

The American Diabetes Association says type 1 diabetes affects 5% of all diabetics. In type 1 diabetes insulin-producing beta cells are attacked and killed by the immune system in the pancreas.

"In the phase I (preliminary) trial we demonstrated a statistically significant response to BCG, but our goal in (this trial) is to create a lasting therapeutic response", Faustman said in a statement.

Faustman added that the focus would be on people who have had type 1 diabetes for many years. The BCG vaccine was originally approved in 1921 to treat tuberculosis patients.

According to Faustman, levels of a substance called tumor necrosis factor, or TNF, are temporarily increased by the BCG vaccine. The diabetes-causing T cells in the blood of individuals with type 1 diabetes can be eliminated by the higher TNF levels. The BCG vaccine can also cause temporary return of insulin secretion.