Research Study to Look at Fast-acting Insulin Aspart With the Insulin Pump System 'iLet™' in Adults With Type 1 Diabetes

The iLet™ is a new insulin pump that is programmed to work with a Continuous Glucose Monitoring (CGM) device. This is to give participants insulin automatically. The CGM device is already available for sale. The iLet™ is not yet approved for use. Fast-acting insulin aspart is a type of insulin that doctors can already prescribe for use with insulin pens, but not for use in an insulin pump. This study is to test how safe fast acting insulin aspart is when used with different insulin delivery settings in the iLet™ in people with type 1 diabetes. Participants will get fast-acting insulin aspart as participants' insulin and use the iLet™ as participants' insulin pump with a CGM device. Participants' iLet™ will be set to 2 different insulin delivery settings for 7 days on each setting. The setting participants get first is decided by chance. The study will last for about 5 to 9 weeks. Participants will have 4 visits and 1 phone contact with the study or staff.


Eligibility Criteria:
Inclusion Criteria:

* Informed consent obtained before any trial-related activities. Trial-related activities are any procedures that are carried out as part of the trial, including activities to determine suitability for the trial
* Male or female, age more than or equal to 18 years and less than or equal to 75 years at the time of signing informed consent
* Diagnosed with type 1 diabetes mellitus more than or equal to 1 year prior to the day of screening
* Treated with continuous subcutaneous insulin infusion more than or equal to 1 year prior to the day of screening
* Have a mean total daily dose of insulin more than or equal to 20 units
* Familiar with continuous glucose monitoring as judged by the investigator
* Has someone over 18 years of age who (i) lives with them, (ii) has access to where they sleep, (iii) is willing to be in the house when the subject is sleeping, and (iv) is willing to receive calls from the study staff and check the welfare of the study subject
* Body mass index (BMI) less than or equal to 35.0 kg/m\^2 at screening
* Glycated haemoglobin (HbA1c) more than or equal to 6.5% (47 mmol/mol) and less than or equal to 9% (75 mmol/mol) at screening
* Able and willing to remain in a designated place for the specified duration of the 'in-patient' periods
* Lives within a 120-minute drive away from the central monitoring location (site)

Exclusion Criteria:

* Known or suspected hypersensitivity to trial product(s) or related products
* Previous participation in this trial. Participation is defined as signed informed consent
* Female who is pregnant, breast-feeding or intends to become pregnant or is of child-bearing potential and not using an adequate contraceptive method (adequate contraceptive measures as required by local regulation or practice)
* Participation in any clinical trial of an approved or non-approved investigational medicinal product within 30 days before screening
* Any disorder, except for conditions associated with diabetes mellitus, which in the investigator's opinion might jeopardise subject's safety or compliance with the protocol
* Anticipated initiation or change in concomitant medications known to affect weight or glucose metabolism during the trial
* Impaired liver function, defined as Alanine Aminotransferase (ALT) more than or equal to 2.5 times or Bilirubin more than 1.5 times upper normal limit at screening
* Renal impairment measured as estimated Glomerular Filtration Rate (eGFR) value of eGFR less than 60 ml/min/1.73 m\^2
* Any episodes of diabetic ketoacidosis within the past 90 days prior to the day of screening
* Known hypoglycaemic unawareness as indicated by the Investigator according to Clarke's questionnaire question 8
* Recurrent severe hypoglycaemic episodes within the last year as judged by the Investigator
* Any of the following: myocardial infarction, stroke, hospitalization for unstable angina pectoris or transient ischaemic attack within the past 180 days prior to the day of screening
* Subjects presently classified as being in New York Heart Association (NYHA) Class IV
* Planned coronary, carotid or peripheral artery revascularisation known on the day of screening
* Inadequately treated blood pressure defined as Grade 3 hypertension or higher (systolic more than or equal to 180 mmHg or diastolic more than or equal to 110 mmHg) at screening
* Unwilling or unable to avoid acetaminophen throughout the trial