Biogen Phase Ib Data Positions Salanersen for SMA Treatment Sequencing

Biogen presented new Phase Ib data showing that its investigational antisense oligonucleotide, salanersen, produced motor improvements and reductions in neurodegeneration biomarkers in children with spinal muscular atrophy (SMA) previously treated with gene therapy. The findings, presented in March 2026 at the Muscular Dystrophy Association Clinical & Scientific Conference, included at least one year of follow-up for all participants and evaluated salanersen in patients who continued to experience disease burden despite prior treatment with the gene therapy onasemnogene abeparvovec.¹

According to the company, the therapy was generally well tolerated and was associated with slowing of neurodegenerative processes and functional gains, including achievement of new motor milestones defined by the World Health Organization. Biogen also presented the design of a global Phase III clinical development program intended to evaluate once-yearly salanersen dosing across a broad SMA population.

“Spinal muscular atrophy has benefited from extraordinary therapeutic progress, but across the treatment landscape there remains room for improvement,” said Thomas Crawford, MD, co-director, Muscular Dystrophy Association Clinic at Johns Hopkins Medicine, in a company press release.¹ “There is growing scientific and clinical enthusiasm about the advances that salanersen offers. These additional Phase [I] data add confidence in the emerging salanersen clinical profile. We have more reason to look forward to results of the Phase [III] program."

What did the Phase Ib data reveal about salanersen’s clinical activity?

The ongoing Phase Ib study enrolled 24 participants aged six months to 12 years who had previously received gene therapy but remained in suboptimal clinical condition. All participants received at least two doses of salanersen at either 40 mg or 80 mg.

Among patients with elevated baseline levels of neurofilament light chain, a biomarker associated with neurodegeneration, investigators observed meaningful reductions of approximately 75% within six months of treatment initiation. These reductions were sustained throughout the follow-up period.¹

The company reported that functional outcomes also improved across the study population. All 24 participants demonstrated improvement from baseline on at least one clinical endpoint, and half of the cohort achieved at least one new motor milestone. All participants maintained previously achieved motor functions during the observation period.

The therapy was generally well tolerated at both dose levels, with most adverse events reported as mild to moderate. Upper respiratory tract infections and vomiting were the most commonly reported adverse events in the 40 mg dose group, while pyrexia and upper respiratory tract infection were most common in the 80 mg cohort.

How will the Phase III salanersen program evaluate treatment strategies in SMA?

The three-study global Phase III clinical program will evaluate once-yearly 80 mg salanersen across multiple SMA populations.

The Phase III program includes STELLAR-1, an open-label study evaluating salanersen in presymptomatic infants younger than six weeks with a confirmed genetic diagnosis of SMA. STELLAR-2 is a randomized, double-blind, sham-controlled study evaluating salanersen initiated approximately six months after gene therapy in infants treated presymptomatically with the onasemnogene abeparvovec gene therapy. A third trial, SOLAR, will evaluate the therapy in adolescents and adults aged 15 to 60 years who are treatment-naïve or previously treated with risdiplam.

The STELLAR studies are designed to compare multiple early treatment strategies in presymptomatic newborns, including salanersen alone, gene therapy alone, and combination approaches, with the goal of informing optimal treatment sequencing in SMA.

“With the encouraging Phase [Ib] results in hand, we are initiating the Phase [III] STELLAR-1, STELLAR-2, and SOLAR salanersen studies as quickly as possible,” said Stephanie Fradette, PharmD, head of the Neuromuscular Development Unit at Biogen, in the release.¹ “Together with the SMA community, we have designed these studies to confidently answer the most relevant questions for the field and establish salanersen’s role in the future treatment landscape.”

Salanersen is designed to correct SMN2 pre-messenger RNA splicing and increase production of survival motor neuron protein. The therapy incorporates a modified backbone chemistry intended to enable high potency and support once-yearly dosing.²

References

1. Biogen. Biogen Presents Additional Salanersen Data Showing New Motor Milestones Achieved in Children with SMA Previously Treated with Gene Therapy. Press Release. March 11, 2026
2. Weng W-C, Lee W-T, Chien Y-H, Tsai L-K. Updates of spinal muscular atrophy in advanced therapies. J. Formosan Med. Assoc. 2025. doi: 10.1016/j.jfma.2025.10.018