Rezpegaldesleukin (NKTR-358) in New Onset Type 1 Diabetes Mellitus

This Phase 2 study is a 2-arm, multi-center, double-masked (masking of the participant, care provider and investigator), placebo-controlled, 2:1 randomized trial design in new onset T1D participants (within 100 days of diagnosis). Participants will be administered rezpegaldesleukin/placebo once every 14 days over 26 weeks with an additional 6-month follow-up period.

Inclusion Criteria: * Provide informed consent or assent as appropriate and if \< 18 years of age have a parent or legal guardian provide informed consent. * Age ≥ 8 and ≤ 45 years at the time of signing informed consent and (as applicable) assent A. * Diagnosis of T1D within 100 days of randomization. * Positive for at least one islet cell autoantibody; GAD65A, mIAA (if obtained within 10 days of the onset of insulin therapy), IA-2A, ICA, or ZnT8A. * Stimulated C-peptide of ≥ 0.2 pmol/mL measured during MMTT conducted at least 21 days from diagnosis of diabetes. * Participants ≥ 18 years old to have body weight ≥ 35 kg and ≤ 130kg. * Participants \< 18 years old to have body weight \> 5th and \ 2 times the upper limit of normal * Current or ongoing use of non-insulin pharmaceuticals that affect glycemia within 7 days of the screening visit or any prohibited concomitant medication as listed in section 3.7. * Concurrent treatment with systemic immunosuppressive agents (including biologics or steroids) - intranasal and inhaled corticosteroids are permitted as well as eye and ear drops containing corticosteroids. * Have active signs or symptoms of acute infection at the time of randomization. * Active acute or chronic infection requiring medical treatment (antibiotics, antiviral, antifungal) within 4 weeks of baseline visit unless approved by the Infectious Disease Committee. * Have evidence of prior or current tuberculosis infection as assessed by Purified Protein Derivative (PPD), interferon gamma release assay (IGRA) or by history. * Any present malignancies or history of malignancy within the past 5 years, other than a successfully treated nonmelanoma skin cancer. * Be currently pregnant or lactating or anticipate becoming pregnant during the study. * History of severe cardiac disease (i.e. myocardial infarction, unstable ischemic heart disease, cerebrovascular accident, stroke, stage 3 or 4 heart failure). * Have evidence of current or past HIV or Hepatitis B infection. * Have evidence of active Hepatitis C infection. * History of organ allograft. * Hypersensitivity to IL-2, PEG, or any components of the active drug. * Had major surgery within 12 weeks before the screening visit or anticipates requiring major surgery during the study. * Has any autoimmune disease other than T1D, stable thyroid, stable asthma, inactive Graves' disease or celiac disease (e.g., rheumatoid arthritis, polyarticular juvenile idiopathic arthritis, psoriatic arthritis, ankylosing spondylitis, multiple sclerosis, systemic lupus erythematous) or has any other disease that may be affected by immunotherapy. * Screening 12-lead electrocardiogram (ECG) with findings suggestive/indicative of acute ischemia, clinically important heart disease or clinically important arrhythmias. * Current or history thrombotic events within six months prior to randomization * Known or untreated clinically significant hyperthyroidism or hypothyroidism * Prior treatment within 12 months of randomization with an immune modulating/immune depleting agents, such as teplizumab (TZield), thymoglobulin (ATG) or rituximab. * Prior treatment within 6 months of randomization with a metabolic therapy intended to alter the disease course of T1D (e.g. teplizumab). * Has significant and uncontrolled disease/condition in the investigator's opinion that may adversely affect study participation or may compromise the study results or increase participant risk.