A Study to Look at How Safe NNC0268-0965 is in Healthy People and People With Type 1 Diabetes

Inclusion Criteria: * Part 1 (healthy subjects): 1\. Male, aged 18-55 years (both inclusive) at the time of signing informed consent. * Part 2 (subjects with type 1 diabetes mellitus): 1. Male or female, aged 18-55 years (both inclusive) at the time of signing informed consent. 2. Diagnosed with type 1 diabetes mellitus equal to or more than1 year prior to the day of screening. 3. Male subject or female subject of non-child bearing potential. Non-child bearing potential being surgically sterilized (i.e. documented hysterectomy, bilateral salpingectomy or bilateral oophorectomy or being postmenopausal (as defined as no menses for 12 months without an alternative medical cause). 4. Current daily total insulin treatment between 0.2 (I)U/kg/day and 1.2 (I)U/kg/day (both inclusive). 5. HbA1c equal to or below 8.5%. 6. Fasting C-peptide below 0.30 nmol/L. Exclusion Criteria: * (Part 1 and Part 2) 1. Male of reproductive age who or whose partner(s) is not using adequate contraceptive methods (adequate contraceptive measures as required by local regulation or practice). Adequate contraceptive measures include that the male subject uses a condom during intercourse and that the partner practices adequate contraception (risk of pregnancy must be lower than 1%). In addition, subjects must not donate sperm for the duration of the trial.