This is a multicenter, Phase Ib, open-label, siplizumab dose-finding study in individuals aged 8-45 years with a Type 1 diabetes mellitus (T1DM) diagnosis. within 18 months of V0. Participants will be randomized 1:1:1:1 to one of four possible siplizumab dosing arms. All dosing arms will receive weekly siplizumab doses for a total of 12 weeks. After the completion of treatment, participants will undergo follow-up visits at weeks 12, 24, 36 and 52 which include longitudinal MMTTs. If indicated, participants will enter into long-term safety monitoring for up to an additional 48 weeks. Blood samples for mechanistic analyses will be obtained during the treatment phase and thereafter. Adults aged 18- 45 will be enrolled initially at the study sites.
The primary objective is to identify a safe, metabolically favorable, dosing regimen for siplizumab in patients with type 1 diabetes that induces changes in T cell phenotypes observed with alefacept therapy in new-onset T1DM.
The secondary objectives are to:
1. Assess the safety profile of siplizumab in recently diagnosed T1DM.
2. Assess the effects of siplizumab on residual beta cell function in recently diagnosed T1DM participants.