Patient description: The patient is a 24-year-old man who has had type 1 diabetes for 11 years. He presents to the emergency room with hyperglycemia and concern for possible diabetic ketoacidosis after not taking his insulin for 3 days. The patient reports that he is currently homeless and has lost his supply of insulin, syringes, glucometer, and glucose testing supplies. The patient states that at the time of his initial diagnosis with type 1 diabetes he was hospitalized with a glucose value >1000 mg/dL. At the time, he was experiencing polyuria, polydipsia, and polyphagia. He reports that he has been on insulin since the time of his diagnosis, and he has never been prescribed oral agents for diabetes management. Most recently, he has been using insulin glargine 55 units once daily, and insulin aspart sliding scale 3 times daily. The patient has had previous episodes of diabetic ketoacidosis, for which he was hospitalized. With this episode of hyperglycemia, he is not experiencing any nausea, vomiting, or abdominal discomfort, and he appears well. His lab studies showed: A1c: 11.3% Creatinine: 0.9 mg/dL with eGFR >60 mL/min Aspartate aminotransferase (AST): 17 U/L Alanine aminotransferase (ALT): 14 U/L Beta-hydroxybutyrate: 0.1 mmol/L Bicarbonate: 25 mEq/L Anion

Clinical trial eligibility criteria: eligible ages (years): 2.0-6.0,  Type 1 Diabetes Mellitus Age between 2 and 6 years (inclusive) 2. Type 1 diabetes as defined by WHO for at least 6 months [WHO definition: 'The aetiological type named type 1 encompasses the majority of cases which are primarily due to beta-cell destruction, and are prone to ketoacidosis. Type 1 includes those cases attributable to an autoimmune process, as well as those with beta-cell destruction for which neither an aetiology nor a pathogenesis is known (idiopathic). It does not those forms of beta-cell destruction or failure to which specific causes can be assigned (e.g. cystic fibrosis, mitochondrial defects, etc.).'] 3. Insulin pump user (with or without continuous glucose monitoring or flash glucose monitoring system) for at least 3 months, with parent/guardian good knowledge of insulin self-adjustment as judged by the investigator 4. Treated with U-100 rapid or ultra-rapid acting insulin analogue 5. Screening HbA1c ≤ 11% (97mmol/mol) on analysis from local laboratory 6. Able to wear glucose sensor 7. Able to wear closed-loop system 24/7 8. The parent/guardian is willing to follow study specific instructions 9. The parent/guardian is proficient in English  Physical or psychological disease likely to interfere with the normal conduct of the study and interpretation of the study results as judged by the investigator 2. Untreated coeliac disease or thyroid disease based on local investigations prior to study enrolment 3. Current treatment with drugs known to interfere with glucose metabolism, e.g. systemic corticosteroids 4. Known or suspected allergy to insulin 5. Parent/guardian's lack of reliable telephone facility for contact 6. Parent/guardian's severe visual impairment 7. Parent/guardian's severe hearing impairment 8. Medically documented allergy towards the adhesive (glue) of plasters or subject is unable to tolerate tape adhesive in the area of sensor placement 9. Serious skin diseases (e.g. psoriasis vulgaris, bacterial skin diseases) located in parts of the body which could potentially be used for localisation of the glucose sensor)