Ionis Pharmaceuticals (NASDAQ:IONS) shares hovered near 52-week highs Wednesday after partner GSK (NYSE:GSK) announced that its experimental drug, bepirovirsen, successfully met the primary endpoints in two pivotal Phase 3 trials, B-Well 1 and B-Well 2.
The results represent a potential paradigm shift for the 250 million people living with chronic hepatitis B (CHB), offering a statistically significant "functional cure" rate after a finite, six-month course of therapy—a sharp contrast to the lifelong medication required by current standards of care.
The studies, which enrolled over 1,800 patients globally, demonstrated that bepirovirsen plus standard of care was vastly superior to standard of care alone.
While current treatments achieve functional cure rates of only about 1%, bepirovirsen produced "clinically meaningful" responses, particularly in patients with lower baseline viral surface antigens (HBsAg) ≤1000 IU/ml, where the effect was even more pronounced.
Functional cure is defined as the sustained loss of the hepatitis B surface antigen (HBsAg) and undetectable viral DNA for at least 24 weeks after stopping treatment.
GSK plans to begin global regulatory filings in the first quarter of 2026.
The drug already holds Fast Track designation from the U.S. FDA, Breakthrough Therapy designation in China, and SENKU designation in Japan.
For Ionis, the success triggers a clear path toward $150 million in upcoming milestones and tiered royalties in the 10-12% range, marking the first of five major Phase 3 readouts expected for the company’s partnered programs this year.