Biogen’s Phase 1b results for salanersen showed a pronounced drop in a neurodegeneration biomarker and measurable motor gains in children who had already received gene therapy—but those early signals are not the same as proof of clinical advantage. The company has launched a three‑trial Phase 3 program to answer whether those biomarker and milestone changes translate into durable, meaningful benefit across newborns, post‑gene‑therapy infants, and older patients.
What the Phase 1b data actually showed in treated children
The open Phase 1b enrolled 24 children aged 0.5 to 12 years who had previously received gene therapy yet still had suboptimal clinical status. Biogen reported about a 75% reduction in neurofilament light chain (NfL) at six months in participants with elevated baseline NfL, and those lower levels were sustained through the follow‑up period—an objective signal consistent with reduced ongoing nerve‑cell injury.
Twelve of the 24 children achieved at least one new WHO motor milestone after starting once‑yearly salanersen, and every participant maintained the motor abilities they had at baseline. Safety was mostly mild to moderate: the common adverse events were upper respiratory infections, pyrexia, and vomiting. The trial tested 40 mg and 80 mg doses; Biogen plans to continue development with the 80 mg dose in the Phase 3 program.
How the Phase 3 program will separate signal from uncertainty
Biogen is running three complementary Phase 3 studies to define salanersen’s role across the SMA spectrum: STELLAR‑1 for presymptomatic newborns, STELLAR‑2 for infants who received gene therapy and start salanersen later, and SOLAR for teens and adults (including those treated with risdiplam). STELLAR‑1 has begun screening, while SOLAR and STELLAR‑2 are planned to start later in 2026; each study targets distinct timing and clinical questions rather than repeating the same population.
| Study | Population | Primary purpose | Timing / note |
|---|---|---|---|
| STELLAR‑1 | Presymptomatic infants <6 weeks | Test early monotherapy vs other sequences for maximal motor outcomes | Screening started (Biogen statement) |
| STELLAR‑2 | Infants starting salanersen ~6 months after gene therapy | Assess add‑on or sequencing benefit post‑gene therapy | Planned to start later in 2026 |
| SOLAR | Teens and adults (15–60), including risdiplam‑treated | Measure functional and safety outcomes in older SMA populations | Planned to start later in 2026 |
Practical implications for clinicians and families now
For children who already received gene therapy and still show elevated NfL or residual motor function, the Phase 1b results identify a plausible candidate group for salanersen—one where you can reasonably expect a biomarker response and some motor gains based on the 24‑patient cohort. That is not the same as recommending switching established treatment plans: Biogen’s data are preliminary and do not demonstrate superiority or interchangeability with nusinersen, onasemnogene abeparvovec (gene therapy), or risdiplam.
Concrete thresholds and stop signals to watch in practice: a clear fall in NfL by six months (Phase 1b median ~75% in those with high baseline levels) would be an early indicator of biological effect; conversely, absent NfL decline plus no motor improvement would be a practical reason to reassess therapy. Serious adverse events or patterns of new safety concerns in the broader Phase 3 cohorts would also justify pausing or changing course for individuals.
Near‑term checkpoints that will define salanersen’s role
The critical next readouts are the Phase 3 efficacy and safety endpoints—especially whether presymptomatic infants in STELLAR‑1 show superior motor development, and whether the post‑gene‑therapy and older cohorts in STELLAR‑2 and SOLAR translate the Phase 1b biomarker drops into lasting functional benefit. Regulators and clinicians will be watching timelines around enrollment completion and primary‑endpoint analyses once those studies get under way.
Q&A
Q: Does Phase 1b prove salanersen is better than existing SMA treatments?
A: No. The Phase 1b data are encouraging on NfL and motor milestones in a small, specific group (24 children post‑gene therapy), but Phase 3 comparisons and larger safety databases are required before any claim of superiority or interchangeability.
Q: Who might be the earliest appropriate candidates?
A: Based on the study population, children who previously received gene therapy but still have residual motor function and elevated NfL appear most likely to show a response — the trial showed new WHO milestones in 12 of 24 such participants.
Q: What should clinicians watch for next?
A: Watch STELLAR‑1 screening and the planned 2026 starts for SOLAR and STELLAR‑2, and track whether Phase 3 demonstrates durable motor improvement tied to sustained NfL reduction without unexpected safety signals. Those outcomes will determine clinical suitability and any changes to treatment sequencing.