Study of Daxdilimab (HZN-7734) in Participants With Active Proliferative Lupus Nephritis (LN)

Inclusion Criteria: * Willing and able to understand and provide written informed consent * Adult men or women 18 to 80 years of age * Willing and able to comply with the prescribed treatment protocol and evaluations for the duration of the trial * Fulfill the 2019 European League Against Rheumatism/American College of Rheumatology Classification Criteria for Systemic Lupus Erythematosus (SLE) * Have at least one of the following at Screening per central lab: * Antinuclear antibodies (ANA) ≥ 1:80 * Anti-dsDNA antibodies elevated to above normal range as established by the central laboratory (ie, positive results) * Anti-Smith antibodies elevated to above normal (ie, positive results). * Diagnosis of proliferative LN based on a renal biopsy obtained within 6 months prior to signing the informed consent form (ICF) or during the Screening Period: * Class III (± class V) or class IV (± class V) LN according to the World Health Organization (WHO) or 2003 International Society of Nephrology (ISN)/Renal Pathology Society (RPS) classification (based on local evaluation of renal biopsy). * Urine protein to creatinine ratio ≥113.17 mg/mmol, obtained via a 24-hour urine collection at Screening. * Estimated glomerular filtration rate ≥35 mL/min/1.73 m2 * Negative serum beta-human chorionic gonadotropin test at Screening (females of childbearing potential only). Key Exclusion Criteria: * History of allergy, hypersensitivity reaction, or anaphylaxis to any component of the investigational product or to a previous monoclonal antibody or human immunoglobulin therapy. * Known intolerance to ≤1.0 gm/day of MMF or equivalent dose of mycophenolic acid (MPA). * A diagnosis of pure Class V membranous LN based on a renal biopsy obtained within 6 months prior to signing ICF or during the Screening Period. * History of dialysis within 12 months prior to signing the ICF or expected need for renal replacement therapy (dialysis or renal transplant) within a 12-month period after enrollment. * History of, or current renal diseases (other than LN) that in the opinion of the Investigator could interfere with the LN assessment and confound the disease activity assessment (eg, diabetic nephropathy). * Known history of a primary immunodeficiency or an underlying condition such as known human immunodeficiency virus (HIV) infection, a positive result for HIV infection per central laboratory, splenectomy, or any underlying condition that in the opinion of the Investigator significantly predisposes the participant to infection. * Hepatitis B, Hepatitis C, active tuberculosis (TB), any severe herpes infection, clinically active infection, or opportunistic infection. * Clinically significant cardiac disease including unstable angina, myocardial infarction, congestive heart failure within 6 months prior to Randomization. * History of cancer within the past 5 years, except in situ carcinoma of the cervix, cutaneous basal cell or squamous cell carcinoma with curative therapy. * Receipt of a live vaccine within 4 weeks prior to Day 1. * The use of immunosuppressants, biologics, and DMARDS within the protocol defined washout periods.