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Safety and Efficacy of Intrathecal BIIB115 in Infants with Spinal Muscular Atrophy Previously Treated with Onasemnogene Abeparvovec

Fast replyInvestigationalNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

Spinal Muscular Atrophy is a rare genetic condition that makes the muscles very weak, often starting in infancy. Some babies receive an early gene‑therapy called Onasemnogene Abeparvovec that can improve outcomes. This study looks at adding another medicine, Salanersen (code name BIIB115), which is given as a small injection into the fluid that surrounds the spinal cord.

The purpose of the study is to find out whether giving Salanersen about six months after the gene‑therapy is safe and can be tolerated well. Children who take part will receive the injection and then be seen regularly for several years. At each visit they will have simple blood draws and brief examinations to check how they are doing.

During the study doctors will watch for any side effects and will also look at a protein called neurofilament light chain that can show nerve damage, and they will perform a test called compound muscle action potential that measures how nerves and muscles work together. The children’s ability to reach basic movement goals such as sitting, standing and walking will be recorded using the World Health Organization motor milestones and other easy‑to‑understand scales like the Hammersmith Infant Neurological Examination, CHOP INTEND, Hammersmith Functional Motor Scale Expanded and Revised Upper Limb Module. The follow‑up continues until the children are several years old, allowing researchers to see long‑term safety and any signs of benefit.

The research process

The trial runs in 5 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Baseline assessments

    After joining the study, study staff will review your medical history to confirm a diagnosis of spinal muscular atrophy (sma) and record your current abilities.

    A blood sample will be taken to measure baseline levels of neurofilament light chain (nfl), a protein that indicates nerve cell damage.

    A sample of cerebrospinal fluid (csf) may be collected to assess the concentration of the study medication.

    Electrical testing called compound muscle action potential (cmap) will be performed on specific nerve‑muscle pairs to evaluate muscle response.

    Standard motor assessments will be completed, including the world health organization (who) motor milestones, the hammersmith infant neurological examination section 2 (hine‑2), and the chop intend motor function scale.

  2. Step 2

    First dose of salanersen

    Approximately six months after your previous gene therapy (onasemnogene abeparvovec), you will receive a single dose of salanersen.

    The dose is 80 mg and will be given as an intrathecal injection, which means the medication is injected into the fluid surrounding the spinal cord.

    The medication is supplied as a solution for injection and will be administered by qualified medical personnel according to the study schedule.

  3. Step 3

    Early safety monitoring (up to day 365)

    Following the injection, you will attend regular clinic visits to monitor for any adverse events, including serious adverse events.

    Blood will be drawn at day 180 and day 365 to measure nfl levels and the concentration of salanersen in the serum.

    A csf sample may be collected at these time points to assess the drug concentration in the spinal fluid.

    The cmap test will be repeated at day 365 to track changes in muscle response.

    Motor function will be re‑evaluated at day 365 using the who milestones, hine‑2, and the chop intend scale.

  4. Step 4

    Intermediate assessments (days 365 to 1825)

    Throughout the next four years, you will continue to have scheduled visits to check safety and collect data.

    Blood samples will be taken periodically to monitor nfl and drug levels in the serum.

    Additional csf collections may be performed to measure the concentration of salanersen in the spinal fluid.

    Motor assessments will be repeated at various intervals, including the who milestones, hine‑2, the chop intend scale, the hammersmith functional motor scale expanded (hfmse), and the revised upper limb module (rulm).

    The study will also record whether participants remain free of clinically manifested sma, any development of sma subtypes, and survival outcomes such as time to death or need for permanent ventilation.

  5. Step 5

    Final study completion

    At the end of the study period (up to day 1825), a final set of assessments will be performed, repeating all previously described tests.

    The collected information will be used to evaluate the overall safety, tolerability, and effect of salanersen when added after gene therapy in infants with sma.

Who can join the trial?

7 criteria

  • Have a confirmed genetic test showing a 5q spinal muscular atrophy (SMA) change, either both copies of the gene are missing or mutated (homozygous) or two different mutations are present (compound heterozygous).
  • Have exactly 2 copies of the SMN2 gene, which helps produce a protein important for motor nerve cells.
  • Received the gene‑therapy medicine called Onasemnogene Abeparvovec (OA) when you were 42 days old or younger, and the study screening began less than 6 months after that treatment.
  • Were still without any signs of SMA when the OA dose was given. This means:
    • No obvious symptoms that doctors think are related to SMA at the time of treatment.
    • All normal tendon reflexes (such as the reflexes in the biceps, knee, and ankle) were present when the treatment was given, as checked by a standard infant exam called the Hammersmith Infant Neurological Examination (HINE) or an equivalent test.
    • If a nerve test called Compound Muscle Action Potential (CMAP) was done at that time, the result for the ulnar nerve was at least 2 millivolt (mV) (a measure of nerve signal strength).
    • The study may have other requirements that are defined in the trial protocol.

Who cannot join the trial?

5 criteria

  • If blood tests after the initial treatment still show liver enzymes called ALT or AST that are more than twice the normal range, or if the platelet count (the cells that help blood clot) is lower than normal, or if a heart‑related protein called troponin‑I remains high, you cannot take part in the study.
  • If an electrocardiogram (a test that records the heart’s electrical activity) shows a corrected QT interval longer than 450 milliseconds using Fridericia’s correction, you are not eligible.
  • If you have received any other approved SMA medicines such as nusinersen or risdiplam, a drug that blocks a protein called myostatin (myostatin inhibitor), or any experimental SMA drug besides the initial treatment, you cannot join.
  • If you have taken steroids to treat problems that occurred after the initial treatment within the 14 days before the study drug is given, you are excluded.
  • Other reasons defined by the study protocol may also prevent participation.
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Investigated drugs

  • Salanersen

    (also known by its code name BIIB115) is a medication that is injected directly into the spinal fluid. It is given as a liquid solution and is being tested to see if it can help improve muscle strength and function in infants with spinal muscular atrophy (SMA) after they have already received an earlier gene‑therapy treatment. In the study, doctors will watch carefully for any side effects and check how well the drug is tolerated.

  • Onasemnogene abeparvovec

    is a one‑time gene‑therapy medicine that delivers a healthy copy of the SMN gene to the body. It is given to infants with SMA before they show symptoms, with the aim of preventing or reducing the loss of muscle function caused by the disease. In this trial, all participants have already received this therapy, and the study is looking at how adding Salanersen later may affect their safety and health.

What is already known about the treatment

BIIB115 - This medication is given as an 80 mg solution for injection that is administered directly into the spinal fluid (intrathecal injection). It is currently an investigational drug being studied in Phase 3 trials and is not yet approved for general medical use. The drug is intended for patients with spinal muscular atrophy, a rare nervous‑system disease that causes muscle weakness. It works by attaching to the genetic instructions for the SMN2 protein and helping the body produce more of the functional SMN protein, which supports nerve and muscle health. It belongs to the class of antisense oligonucleotides, a type of therapy that modifies how genes are read.

Investigated diseases

Spinal Muscular Atrophy - Spinal Muscular Atrophy is a genetic disorder that causes loss of motor neurons in the spinal cord, leading to muscle weakness and reduced movement. It usually appears in early childhood, but the age of onset can vary. As the disease progresses, children may have difficulty sitting, standing, and walking. Over time, muscle weakness can spread to the trunk and respiratory muscles.
Trial detailsLast updated 7 Oct 2026
Age0-17PhasePhase IIITrial ID2025-523857-32-00Protocol code277SM301Estimated enrolment42 patientsSponsorBiogen Idec Research Limited

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