The main purpose of this study is to evaluate the safety and tolerability of CUG252 following multiple ascending doses in participants with Systemic Lupus Erythematosus (SLE).

CUG252 is a potential best-in-class engineered IL-2 compound, designed to have improved Treg selectivity while reducing undesired IL-2 activity.

This study will evaluate safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and immunologic effects of CUG252 following subcutaneous administration of multiple ascending doses in participants with mild-to-moderate SLE. The effects of SLE disease activity and biomarkers will also be evaluated.. The SLE participants will receive randomized multiple subcutaneous doses of CUG252 or placebo. After receiving the last dose of CUG252 or placebo, participants will be followed to study day 64 post first dose administration to evaluate safety, PK, PD and preliminary efficacy.

Inclusion Criteria:

• Male or female participant, aged 18 to 65 years (inclusive), at time of consent
• BMI greater than or equal to 18 and less than 39 kg/m2 at Screening
• Diagnosis of SLE at least 6 months prior to Screening
• Minimal to moderate SLE disease activity
• If a participant is taking oral prednisone, the dose must be less than or equal to 20 mg/day for a minimum of 8 weeks prior to Screening and at a stable dose for a minimum of 2 weeks prior to Screening
• If a participant is taking azathioprine, antimalarial, mycophenolate mofetil, or methotrexate, the medication(s) must have been started a minimum of 12 weeks prior to Screening and at a stable dose for a minimum of 8 weeks prior to Screening

Exclusion Criteria:

• Have one or more of the following medical conditions: SARS-CoV-2 infection 30 days prior to drug administration, evidence of Grade 3 or greater hematologic, hepatic, or rental dysfunction, active severe or unstable neuropsychiatric SLE, active severe renal disease, history of severe active lupus nephritis with proteinuria levels greater than 1.0 g/24 hours, or dialysis in the last 6 months. History of current diagnosis of other autoimmune/inflammatory diseases, history of any non-SLE disease that has required treatment with corticosteroids for more than 2 weeks within the last 12 weeks prior to Screening, active clinically significant bacterial, viral, or fungal infection at Screening, active or latent TB at Screening, pulmonary infection or active lung disease besides those related to lupus, or severe pulmonary disease requiring oxygen therapy. History of condition that predisposes participant to infection, confirmed positive serology at Screening, history of opportunistic infection requiring hospitalization or IV antimicrobial treatment within the last year, history of organ or hematopoietic stem cell transplant, history of major surgery within 12 weeks of Screening, history of significant cardiovascular disease, history of gastrointestinal bleeding, history of cancer apart from successfully treated squamous or basal cell carcinoma or cervical cancer in situ.
• Are on one or more of the following medications: have received vaccination within 30 days prior to Screening (including COVID-19 vaccination), Aldesleukin or other IL-2 derivatives at any time, T cell depleting agents and inhibitors of T cell activation at any time, Anti-BLyS/BAFF inhibitors, IL-1 receptor antagonist, anti-TNF therapy, and anti-interferon alpha receptor inhibitor within 3 months prior to Screening, rituximab or other B-cell depleting agent within 6 months, glucocorticoids within 6 weeks prior to Day 1, other immunosuppressant drugs within 8 weeks, history of cytotoxic medications within 12 months, receipt of blood products within 6 months, plasmapheresis within 30 days of Screening.