Just announced this week, five diabetic beagles were injected with two extra genes about four years ago and have not needed insulin injections since. Two are still alive and living without diabetes.
This is the first long-term research cure with large animals and seems to have been a success. One aspect that was interesting to me, was that when dogs were injected with only one of the two genes, they remained diabetic and insulin dependent. Each gene has a specific job: one makes insulin and the other an enzyme that regulates glucose into the muscles.
More information can be read by searching Google for “Gene Therapy in Diabetic Dogs”.