Ionis Pharmaceuticals (IONS) stock declined 2.23% to $42.93 in regular trading, shedding $0.98, before rebounding 2.33% to $43.93 in after-hours activity. The regular-session drop came despite positive Phase 3 kidney disease trial results announced by its partner Roche, whose experimental treatment sefaxersen significantly reduced proteinuria in patients with primary IgA nephropathy.

Roche Reports 43.1% Proteinuria Reduction in Phase 3 Kidney Trial

Roche reported positive results from the ongoing Phase 3 IMAgINATION study involving adults with primary IgA nephropathy. The trial evaluated sefaxersen alongside optimized standard care and measured its effectiveness against a placebo. At week 37, the treatment achieved a statistically significant 43.1% reduction in proteinuria relative to placebo, with a 95% confidence interval of 32.5% to 52.0% and a P-value below 0.0001.

Researchers assessed treatment effect using the 24-hour urine protein-to-creatinine ratio, a key marker of kidney damage. Lower proteinuria levels generally correlate with better long-term kidney function.

The findings were presented at the American Society of Nephrology Kidney Week 2026 conference. A greater proportion of patients receiving sefaxersen experienced resolution of blood in the urine compared with placebo recipients. The treatment also demonstrated consistent effectiveness across predefined patient subgroups and introduced no new safety concerns.

Ionis-Developed Therapy Advances Through Roche Partnership

Sefaxersen was developed by Ionis as an RNA-targeted treatment that reduces production of factor B in the liver. Factor B contributes to the activity of the alternative complement pathway, which plays a role in IgA nephropathy. By lowering this protein, sefaxersen targets a biological process associated with kidney inflammation and damage. RNA-targeted design of this kind, which aims to reduce disease-driving proteins at their source, is the core of Ionis's drug development approach.

The experimental medicine is administered as a monthly injection beneath the skin and supports potential self-administration by patients, an administration profile that matches the long-term treatment demands of a disease that often requires management over many years. Roche is continuing the blinded IMAgINATION study to measure changes in kidney function over two years, and researchers will assess estimated glomerular filtration rate at week 105 to evaluate longer-term treatment outcomes.

Roche licensed sefaxersen from Ionis under an agreement covering complement-mediated diseases. Ionis has previously received upfront payments, licensing fees, and development milestone payments through the partnership. The agreement also provides for potential regulatory milestones, sales milestones, and tiered royalties on future net sales.

IONS Stock Declines as Roche Prepares Regulatory Discussions

Despite the clinical progress, Ionis shares finished the regular session lower before recovering part of their losses after hours. The contrasting price movements followed Roche's announcement of the latest Phase 3 findings, although the available trading information does not establish a specific cause for the regular-session decline.

IgA nephropathy causes progressive kidney damage and commonly affects adults before the age of 40. The disease affects at least 25 adults per million worldwide each year and can eventually lead to kidney failure. Within 20 years of diagnosis, up to half of affected patients may develop end-stage kidney disease.

Roche plans to share the latest trial findings with health authorities to support further development discussions. The ongoing study is expected to provide additional evidence about sefaxersen's effects on kidney function. Regulatory decisions and future commercial milestones will determine the treatment's potential contribution to Ionis Pharmaceuticals' business.