Sibeprenlimab

Vertex Pharmaceuticals announced positive results from a pre-specified Week 36 interim analysis of the RAINIER Phase III trial evaluating povetacicept in adults with IgA nephropathy, meeting the primary endpoint and all secondary endpoints. IgAN is the most common form of primary glomerulonephritis, affecting an estimated 330,000 people in the US and Europe, with up to 72% of adult patients progressing to end-stage renal disease or death within two decades of diagnosis. The data position Vertex’s povetacicept as a potential first dual BAFF+APRIL inhibitor to reach registration in this disease. RAINIER is a global, randomized, double-blind, placebo-controlled Phase III trial evaluating povetacicept 80 mg administered subcutaneously every four weeks versus placebo on top of standard of care. A total of 605 patients were randomized: 557 in the main cohort and 48 in an exploratory cohort with lower baseline eGFR (20 to <30 mL/min/1.73m²). The interim analysis population comprised 199 patients from the main cohort (131 povetacicept, 68 placebo). Background supportive care rates were high, with 97.8% of patients on ACEi/ARBs and 67.7% on SGLT2 inhibitors, a proportion the company described as the highest in any contemporary IgAN trial. For the primary endpoint, povetacicept-treated patients achieved a 52.0% reduction from baseline in 24-hour urine protein to creatinine ratio (UPCR), compared with a 4.3% reduction in the placebo arm, yielding a 49.8% reduction versus placebo (P<0.0001). The povetacicept Phase III results on secondary endpoints were similarly consistent: serum galactose-deficient IgA1 (Gd-IgA1) fell 77.4% from baseline versus a 9.1% increase with placebo (79.3% reduction versus placebo; P<0.0001), and 85.1% of povetacicept-treated patients with baseline hematuria achieved resolution compared with 23.4% on placebo (P<0.0001). An exploratory endpoint showed 42.2% of povetacicept patients achieved UPCR below 0.5 g/g versus 6.2% on placebo. Povetacicept was generally well tolerated. Adverse event rates were similar between arms (75.0% versus 78.4% for placebo). Injection site reactions occurred in 14.5% of the povetacicept group, all mild or moderate. There were no deaths, no drug-related serious adverse events, and no opportunistic infections. Treatment discontinuations were lower in the povetacicept arm (3.8%) than placebo (8.8%). The US FDA has granted rolling review of the Biologics License Application for povetacicept in IgAN, and Vertex stated it will complete the full BLA submission by the end of March, using a priority review voucher to shorten the review timeline from ten to six months. Reshma Kewalramani, Vertex’s CEO, said the data “bring us one step closer to realizing povetacicept’s pipeline-in-a-product promise”. The RAINIER trial continues blinded toward a final two-year analysis with a primary endpoint of total eGFR slope through Week 104. Vertex is also advancing povetacicept in the Phase II/III OLYMPUS trial in primary membranous nephropathy and plans to initiate a Phase II trial in generalized myasthenia gravis in H1 2026. Povetacicept is an engineered TACI-Fc fusion protein that simultaneously inhibits BAFF and APRIL, two cytokines that drive B cell activation, differentiation, and survival. In IgAN, pathogenic B cells produce Gd-IgA1, which forms immune complexes that deposit in the kidney’s glomerular mesangium, triggering inflammation and fibrosis. By neutralizing both cytokines, povetacicept aims to suppress the upstream immunological drivers of disease rather than managing downstream consequences alone. IgAN treatment has historically relied on supportive care with renin-angiotensin system blockade. Recent approvals have begun to change the landscape: the US FDA approved Travere Therapeutics’ sparsentan (Filspari), a dual endothelin and angiotensin receptor antagonist, under accelerated approval in 2023 for IgAN with proteinuria. Calliditas Therapeutics’ budesonide delayed-release (Tarpeyo) received accelerated approval in 2021 as a targeted-release corticosteroid. Neither of these agents shares povetacicept’s mechanism. Key competitors targeting BAFF and/or APRIL in IgAN include: Vera Therapeutics’ atacicept, a TACI-Ig fusion protein and dual BAFF/APRIL inhibitor in the Phase III ORIGIN trial for IgAN, which represents the most direct mechanistic competitor to povetacicept. Otsuka/ Visterra, Inc.’s sibeprenlimab (VIS649), an anti-APRIL monoclonal antibody that reported Phase III data in IgAN and targets only one of the two cytokines inhibited by povetacicept. China-based RemeGen’s telitacicept, another dual BAFF/APRIL TACI-Fc fusion protein approved in China for systemic lupus erythematosus and in Phase II development for additional autoimmune indications, though its IgAN program is less advanced. Vor Bio secured a license to telitacicept’s ex-China rights in a June 2025 deal. GSK’s belimumab, a BAFF-only monoclonal antibody approved for SLE and lupus nephritis, is not in active IgAN development. The povetacicept proteinuria reduction of nearly 50% over placebo at 36 weeks, combined with the depth of Gd-IgA1 suppression and hematuria resolution, will be measured against atacicept and sibeprenlimab data as physicians and regulators assess the emerging class. Whether these surrogate endpoint improvements translate into durable preservation of kidney function will depend on the two-year eGFR data still to come from RAINIER.