A Study to Learn More About the Safety and Effects of Felzartamab in Adults With Lupus Nephritis Aged 18 to 75 Years Old

Study Sponsor, originally HI-Bio, Inc., is now HI-Bio, A Biogen Company.

Inclusion criteria

Part 1

• Diagnosis of Systemic Lupus Erythematosus (SLE) according to the 2019 European League Against Rheumatism (EULAR)/ American College of Rheumatology (ACR) criteria
• Diagnosis of International Society of Nephrology/ Renal Pathology Society (ISN/RPS) 2003 Class III or IV LN as evidenced by renal biopsy performed within 1 year prior to or during screening, either with or without the presence of Class V LN
• Proteinuria (urine protein to creatinine ratio) > 1.0 gram per gram (g/g), based on 24-hour urine collection during screening
• eGFR ≥ 45 milliliter/minute/1.73 square meters (mL/min/1.73 m^2) (as calculated by the Chronic Kidney Disease Epidemiology Collaboration formula)

• If eGFR is ≥35 to <45 mL/min/1.73m^2, renal biopsy must be within 6 months of screening and must not have >50% of glomeruli with sclerosis. If the renal biopsy was performed more than 6 months prior to screening, a repeat biopsy must be done during screening after all the other eligibility criteria are met
• If eGFR is ≥45 mL/min/1.73 m^2, renal biopsy must be within 1 year prior to screening. If the renal biopsy was performed more than 1 year prior to screening, a repeat biopsy must be done during screening after all the other eligibility criteria are met
• History of inadequate response, for lack of efficacy or intolerance, to at least a three-month course of one standard of care treatment for lupus nephritis, as determined by the treating physician

Part 2

• Participants must complete Part 1 of the study to be eligible to participate in Part 2.

Exclusion criteria

Part 1

• Presence of rapidly progressive glomerulonephritis, as defined by at least one of the following: crescent formation in > 50% of glomeruli on renal biopsy, sustained doubling of serum creatinine within 12 weeks of screening, or the investigator's opinion that the participant has rapidly progressive glomerulonephritis
• Greater than 50% of glomeruli with sclerosis on renal biopsy
• Currently requiring hemodialysis or peritoneal dialysis or expected to require dialysis during the study treatment period
• A previous kidney transplant or other organ transplant, or planned transplant within study treatment period

Part 2

• Did not complete Part 1 of the study
• Received protocol-prohibited medications in Part 1 such as calcineurin inhibitors (e.g., cyclosporine, tacrolimus, or voclosporin), alkylating agents including cyclophosphamide, or biologic agents other than felzartamab
• Progression of LN (as measured by worsening proteinuria and/or decreasing eGFR) has been observed such that in the opinion of the investigator the participant will not benefit from continuing in Part 2 of the study

Other protocol-defined inclusion/exclusion criteria may apply.