BACKGROUNDMYL-1601D is a proposed biosimilar of originator insulin aspart, Novolog®/NovoRapid® (Ref-InsAsp-US/Ref-InsAsp-EU).OBJECTIVEThis study assessed the immunogenicity, efficacy, and safety of MYL-1601D with Ref-InsAsp-US in patients with type 1 diabetes mellitus (T1D).METHODSThis was a 24-week, open-label, randomized, phase III study. Patients were randomized 1:1 to mealtime MYL-1601D or Ref-InsAsp-US in combination with insulin glargine (Lantus SoloSTAR®) once daily. The treatment-emergent antibody response (TEAR) rate (defined as patients who were anti-insulin antibody [AIA] negative at baseline and became positive at any timepoint post-baseline or patients who were AIA positive at baseline and demonstrated a 4-fold increase in titer values at any timepoint post-baseline) was the primary endpoint. The study also compared the change from baseline in glycated hemoglobin (HbA1c), fasting plasma glucose (FPG), prandial, basal, and total daily insulin, 7-point self-monitored blood glucose (SMBG) profiles, immunogenicity, and adverse events (AEs) including hypoglycemia.RESULTSIn total, 478 patients were included in the intent-to-treat analysis (MYL-1601D: 238; Ref-InsAsp-US: 240) set. The 90% confidence interval (CI) for the primary endpoint was within the pre-defined equivalence margin of ±11.7% and the treatment differences (SE) in TEAR responders between the treatment groups was - 2.86 (4.16) with 90% CI - 9.71 to 3.99. The mean (SD) changes from baseline for HbA1c, FPG, and insulin dosages were similar in both groups at week 24. The safety profiles including hypoglycemia, immune-related events, AEs, and other reported variables were similar between the treatment groups at week 24.CONCLUSIONSMYL-1601D demonstrated similar immunogenicity, efficacy, and safety profiles to Ref-InsAsp-US in patients with T1D over 24 weeks. CLINICAL TRIAL REGISTRATION CLINICALTRIALS.GOV: NCT03760068.