Study of ALXN2050 in Proliferative Lupus Nephritis (LN) or Immunoglobulin A Nephropathy (IgAN)

Proteinuria, the presence of excess proteins in the urine, was assessed using 24-hour urine collections obtained at designated timepoints. A negative change from baseline indicated an improvement in symptoms.

Proteinuria, the presence of excess proteins in the urine, was assessed using 24-hour urine collections obtained at designated timepoints. A reduction from baseline indicated an improvement in symptoms.

Changes in kidney function were monitored using measurements of eGFR and calculated based on the Chronic Kidney Disease Epidemiology Collaboration formula. Results are reported in milliliters/minute/1.73 meters squared (mL/min/1.73 m^2). Estimates of change from baseline are least-square means based on a mixed-effect model for repeated measures model that included change from baseline as the response variable, treatment as independent variable and adjusts for covariates of baseline and the stratification factor at randomization. An increase in eGFR in response to treatment indicated an improvement in symptoms.

Complete renal response was defined as a decrease in urine protein to creatinine ratio (UPCR) to ≤0.5 gram/gram (g/g), an eGFR rate >60 mL/min/1.73 m^2 or no eGFR reduction ≥20% from baseline, and no treatment failure. Treatment failure was defined as the receipt of additional standard of care therapy at any time during the study for protocol-defined renal flare, severe extrarenal systemic lupus erythematosus (SLE) flare, or suboptimal response.

Partial renal response was defined as a decrease in UPCR ≥50% compared to baseline, an eGFR rate >60 mL/min/1.73 m^2 or no eGFR reduction ≥20% from baseline, and no treatment failure. Treatment failure was defined as the receipt of additional standard of care therapy at any time during the study for protocol-defined renal flare, severe extrarenal SLE flare, or suboptimal response.

UPCR was assessed using 24-hour urine collections obtained at designated time points. The time to the first occurrence of UPCR ≤0.5 g/g was summarized by spot urine sample analysis.

A corticosteroid taper was carried out per protocol at the clinical discretion of the investigator.

Renal flare was determined in the opinion of the investigator and additional protocol-specified criteria. For participants who achieved a complete renal response, a renal flare was the reproducible recurrence of proteinuria ≥1g/g. For all other participants, a renal flare was either of the following: a reproducible increase of serum creatinine >25% higher than baseline or above the upper limit of normal (plus additional protocol-specified criteria) or a reproducible doubling of the UPCR from a 24-hour urine collection compared with the lowest previous value obtained after the first dose of study intervention.

Extrarenal SLE flare was defined as an increase in the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) Safety of Estrogens in Lupus Erythematosus National Assessment modification ≥4 points that was not accounted for by proteinuria, hematuria, urinary cellular casts, hypocomplementemia, or an increase in anti-double-stranded DNA antibody level. The SLEDAI-2K is an instrument that was used to assesses the disease activity of extrarenal SLE flare across 18 disease descriptors. Each descriptor carried a weighted value ranging from 1-8, with the reported score calculated as the sum of these descriptors and ranging from 0 to 85. Higher scores represent increased degrees of disease activity.

Treatment failure was defined as the receipt of additional standard of care therapy at any time during the study for protocol-defined renal flare, severe extrarenal SLE flare, or suboptimal response.

For the determination of serum albumin, blood samples were obtained at designated time points. Results reported as grams/liter (g/L).

A suboptimal response was to be determined in the opinion of the investigator in addition to the following criterion: reproducible proteinuria ≤25% decreased compared to baseline based on UPCR on a 24-hour urine collection performed by a central laboratory.

Partial remission was defined as mean proteinuria <1 g/24 hours, based on two valid 24-hour urine collections obtained within 2 weeks prior to the study visit.