Inclusion Criteria:

• Mentally stable and able to comply with study procedures
• Clinical history compatible with type 1 diabetes with onset at less than 40 years of age, insulin dependence for at least 5 years at study entry, and a sum of age and insulin dependent diabetes duration of at least 28
• Absent stimulated C-peptide (less than 0.3 ng/ml) 60 and 90 minutes post-mixed-meal tolerance test

• Involvement of intensive diabetes management, defined as:

  1. Self-monitoring of glucose values no less than a mean of three times each day averaged over each week
  2. Administration of three or more insulin injections each day or insulin pump therapy
• Under the direction of an endocrinologist, diabetologist, or diabetes specialist with at least three evaluations the 12 months prior to study enrollment
• At least one episode of severe hypoglycemia in the past 12 months, defined as an event with one of the following symptoms: memory loss; confusion; uncontrollable behavior; irrational behavior; unusual difficulty in awakening; suspected seizure; seizure; loss of consciousness; or visual symptoms in which the participant was unable to treat him/herself and which was associated with either a blood glucose (BG) level < 54 mg/dL [3.0 mmol/L] or prompt recovery after oral carbohydrate, intravenous glucose, or glucagon administration, in the past 12 months prior to study enrollment
• Reduced awareness of hypoglycemia. More information about this criterion, including specific definition of hypoglycemia unawareness, is in the protocol.

Exclusion Criteria:

• Body mass index (BMI) greater than 30 kg/m2 or weight less than or equal to 50 kg
• Insulin requirement of more than 1.0 IU/kg/day or less than 15 U/day
• HbA1c greater than 10%
• Untreated proliferative diabetic retinopathy
• Systolic blood pressure higher than 160 mmHg or diastolic blood pressure higher than 100 mmHg
• Measured glomerular filtration rate using iohexol of less than 80 ml/min/1.73m2. More information about this criterion is in the protocol.
• Presence or history of macroalbuminuria (greater than 300 mg/g creatinine)
• Presence or history of panel-reactive anti-HLA antibody levels greater than 20% by flow cytometry. More information about this criterion is in the protocol.
• Pregnant, breastfeeding, or unwilling to use effective contraception throughout the study and 4 months after study completion
• Active infection, including hepatitis B, hepatitis C, HIV, or tuberculosis. More information about this criterion is in the protocol.
• Negative for Epstein-Barr virus by IgG determination
• Invasive aspergillus, histoplasmosis, or coccidioidomycosis infection within one year prior to study enrollment
• History of malignancy except for completely resected squamous or basal cell carcinoma of the skin
• Known active alcohol or substance abuse
• Baseline Hgb below the lower limits of normal, lymphopenia, neutropenia, or thrombocytopenia
• History of Factor V deficiency
• Any coagulopathy or medical condition requiring long-term anticoagulant therapy after transplantation or individuals with an INR greater than 1.5

• Severe coexisting cardiac disease, characterized by any one of the following conditions:

  1. Heart attack within the last 6 months
  2. Evidence of ischemia on functional heart exam within the year prior to study entry
  3. Left ventricular ejection fraction less than 30%
• Persistent elevation of liver function tests at the time of study entry
• Symptomatic cholecystolithiasis
• Acute or chronic pancreatitis
• Symptomatic peptic ulcer disease
• Severe unremitting diarrhea, vomiting, or other gastrointestinal disorders that could interfere with the ability to absorb oral medications
• Hyperlipidemia despite medical therapy (fasting LDL cholesterol greater than 130 mg/dl, treated or untreated; and/or fasting triglycerides greater than 200 mg/dl)
• Receiving treatment for a medical condition that requires chronic use of systemic steroids, except the use of 5 mg or less of prednisone daily, or an equivalent dose of hydrocortisone, for physiological replacement only
• Treatment with antidiabetic medication other than insulin within the past 4 weeks
• Use of any investigational agents within the past 4 weeks
• Received a live attenuated vaccine(s) within 2 months of study entry
• Any medical condition that, in the opinion of the investigator, will interfere with safe participation in the trial
• Treatment with any immunosuppressive regimen at the time of enrollment
• A previous islet transplant
• A previous pancreas transplant, unless the graft failed within the first week due to thrombosis, followed by pancreatectomy and transplant occurred more than 6 months prior to enrollment