CTLA4-Ig (Abatacept)for Prevention of Abnormal Glucose Tolerance and Diabetes in Relatives At -Risk for Type 1

Study Purpose and Rationale: In this study, relatives who are confirmed to have two or more antibodies, not including mIAA, and normal glucose tolerance will be eligible for randomization to experimental treatment or placebo groups with the aim to determine whether experimental treatment will prevent or delay the occurrence of abnormal glucose tolerance and type 1 diabetes mellitus. Individuals with normal glucose tolerance are earlier in the disease process; that is, have less beta cell destruction than those with abnormal glucose tolerance or frank diabetes, yet will inevitably progress to clinical disease and essentially complete beta cell loss. Treatment at this early stage in a population who will inevitably progress to type 1 diabetes provides the greatest opportunity for a clinically important impact on disease prevention. With abnormal glucose tolerance rather than diabetes as the primary endpoint, study participants, regulators, funders, and investigators will be able to determine whether the therapy can alter disease progression. Therefore, the rationale for this study is that individuals with immunologic markers of T1DM and normal glucose tolerance will inevitably develop clinical T1DM. Prior to development of clinical T1DM they will progress from normal glucose tolerance to abnormal glucose tolerance; and abnormal glucose tolerance results in clinical T1DM within 5 years in almost 80% of subjects. They have a condition that differs from overt diabetes only in the duration of the autoimmune process that results in beta cell destruction. Intervention early in the course of disease may be more effective than intervention in those with abnormal glucose tolerance or clinical T1DM. Description of Treatment Groups Subjects will be randomized to receive either Abatacept or placebo infusions along with close monitoring for abnormal glucose tolerance or diabetes. The infusions will be conducted at approved TrialNet clinical sites with appropriate facilities. All blood and serum samples for the primary and secondary outcome determinations will be sent to the Core Laboratories for analysis. Clinical laboratory studies may be done at the local sites. Participants will be randomly assigned in a 1:1 ratio (within the two strata defined by age at enrollment: \<18 and 18 or older) to the following 2 groups: * to receive Abatacept (intravenous infusion at 0, 2, and 4 weeks following randomization, and then every 28+/-7 days) thereafter for a total of 14 doses. Close monitoring for diabetes development through the duration of study. * to receive placebo intravenous infusion at 0, 2, and 4 weeks following randomization and then every 28+/- 7 days thereafter for a total of 14 doses. Close monitoring for diabetes development through the duration of study. Treatment Assignment After participants sign the consent form, complete the screening visit(s), and meet all of the inclusion criteria and none of the exclusion criteria, participants will be randomized to receive either Abatacept and close monitoring or placebo with close monitoring. Participants will be randomized in equal allocations to each group. The randomization method will be stratified by TrialNet study site and whether the participant is less than 18 years of age or 18 years and older. This approach ensures that study site will not be a potential confounder. The TNCC will generate the randomization numbers and tables. Study Assessments During the course of the study, participants will frequently undergo assessments of their glucose tolerance status, insulin production, immunologic status, and overall health and well-being. Samples will be drawn for storage in the National Institute for Diabetes and Digestive and Kidney Disease (NIDDK) Repository and at TrialNet Laboratory Sites for future analysis related to T1DM. Study Duration The study has been designed to provide 80% power to detect a 40% risk reduction in the occurrence of abnormal glucose tolerance using a two-sided test at the 0.05 level after six years of study duration. A total of approximately 206 patients will be allocated in a 1:1 ratio to the two groups.