Interim Analysis of a Phase 3 Trial of Povetacicept in IgA Nephropathy

BACKGROUND: B-cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL) have distinct roles in IgA-producing B-cell populations and appear to be central to the pathogenesis of IgA nephropathy. Povetacicept, an enhanced, variant transmembrane activator and calcium-modulator and cyclophilin-ligand interactor (TACI)-Fc fragment fusion therapeutic, is engineered for dual inhibition of BAFF and APRIL. METHODS: In this ongoing, phase 3, double-blind, placebo-controlled trial, participants with biopsy-proven IgA nephropathy receiving stable background therapy were randomly assigned in a 2:1 ratio to receive povetacicept at a dose of 80 mg or placebo subcutaneously every 4 weeks. The primary end point of this prespecified interim analysis was the change in the 24-hour urinary protein-to-creatinine ratio at week 36. Secondary end points were the change at week 36 in galactose-deficient IgA1 levels and hematuria resolution at week 36 among participants with baseline hematuria. RESULTS: A total of 557 participants received povetacicept (372 participants) or placebo (185 participants). Efficacy analyses included the first 199 participants who had undergone randomization (131 in the povetacicept group and 68 in the placebo group). The 24-hour urinary protein-to-creatinine ratio decreased by 52.0% with povetacicept and by 4.3% with placebo by week 36 (adjusted difference, -49.8 percentage points; 95% confidence interval [CI], -58.6 to -39.2; P<0.001). Galactose-deficient IgA1 levels decreased by 77.4% with povetacicept and increased by 9.1% with placebo (adjusted difference, -79.3 percentage points; 95% CI, -82.2 to -75.9; P<0.001). Among the participants with baseline hematuria, resolution occurred in 85% with povetacicept and in 23% with placebo (adjusted difference, 62 percentage points; 95% CI, 45 to 78; P<0.001). The incidence of adverse events (75% with povetacicept and 78% with placebo) and serious adverse events (3% and 4%, respectively) were similar in the trial groups. CONCLUSIONS: Povetacicept led to a significantly greater reduction in the 24-hour urinary protein-to-creatinine ratio than placebo by week 36 in participants with IgA nephropathy. (Funded by Vertex Pharmaceuticals; RAINIER AIS-D08 ClinicalTrials.gov number, NCT06564142.).