This trial is conducted in Europe. The aim of this trial is to investigate Pharmacodynamics (the effect of the investigated drug on the body) , Pharmacokinetics (the exposure of the trial drug in the body), and Safety of NNC0143-0406 in Subjects with Type 1 Diabetes Mellitus

Inclusion Criteria:

• Male or female aged 18-55 years (both inclusive) at the time of signing informed consent
• Subjects diagnosed (clinically) with type 1 diabetes mellitus at least 365 days prior to the day of screening
• Treated with continuous subcutaneous insulin infusion at least 90 days prior to the day of screening

Exclusion Criteria:

• Known or suspected hypersensitivity to trial product(s) or related products
• Males who are sexually active and not surgically sterilised (vasectomy or otherwise) and their partners that are not using a highly effective contraception method, from randomisation until 90 days after dosing, such as double barrier contraception (e.g. condom and spermicide) or combination of either an oral ontraceptive, a contraceptive patch, a diaphragm or intrauterine device, together with a physical barrier such as condom. Male subjects must also agree to refrain from sperm donation from randomisation until 90 days after last dosing
• Female who is pregnant, breast-feeding or intends to become pregnant or is of child-bearing potential and not using adequate contraceptive methods (adequate contraceptive measures as required by local regulation or practice) (adequate contraceptive measures are defined as sterilisation, hormonal intrauterine device, oral contraceptives, condom with spermicide sexual abstinence or vasectomised partner)