Effect of AC2993 With or Without Immunosuppression on Beta Cell Function in Patients With Type I Diabetes

This study will determine 1) the safety of AC2993 in patients with type I diabetes; 2) the ability of AC2993 to improve beta cell function; and 3) the effects of immunosuppression on beta cell function. Type I diabetes is an autoimmune disease, in which the immune system attacks the beta cells of the pancreas. These cells produce insulin, which regulates blood sugar. AC2993 may improve the pancreas's ability to produce insulin and help control blood sugar, but it may also activate the original immune response that caused the diabetes. Thus, this study will examine the effects of AC2993 alone as well as in combination with immunosuppressive drugs. Patients between 18 and 60 years of age who have type I diabetes mellitus may be eligible for this 20-month study. They must have had diabetes for at least 5 years and require insulin treatment. Candidates will be screened with a questionnaire, followed by medical history and physical examination, blood and urine tests, a chest x-ray and skin test for tuberculosis, electrocardiogram (EKG), and arginine stimulated C-peptide test (see description below). Participants will undergo the following tests and procedures: Advanced screening phase: Participants undergo a diabetes education program, including instruction on frequent blood glucose monitoring, dietary education on counting carbohydrates, intensive insulin therapy, review of signs and symptoms of low blood sugar (hypoglycemia), and potential treatment with glucagon shots. Patients must administer insulin via an insulin pump or take at least four injections per day including glargine (Lantus) insulin. 4-month run-in phase * Arginine-stimulated C-peptide test: This test measures the body's insulin production. The patient is injected with a liquid containing arginine, a normal constituent of food that increases insulin release from beta cells into the blood stream. After the injection, seven blood samples are collected over 10 minutes. * Mixed meal stimulated C-peptid