Biogen's Bet on a Twisted Piece of Chemistry

If those claims hold up in practice, it could make ASOs viable for a much wider range of diseases than current technology allows.

Biogen Already Has ASO Street Cred

This isn't Biogen dabbling in unfamiliar territory. The company has been in the ASO business since Spinraza launched, and its pipeline tells the story of a company doubling down.

The clearest example is salanersen (BIIB115), a next-generation ASO for SMA licensed from Ionis Pharmaceuticals. Salanersen uses novel backbone chemistry that could allow once-yearly dosing, a massive upgrade over Spinraza's more frequent intrathecal injections. Phase 1b data presented in March 2026 showed the drug was generally well-tolerated in 24 children previously treated with gene therapy. Participants with elevated baseline levels saw a 75% reduction in neurofilament light chain (a marker of nerve damage) at six months, and 12 of 24 hit new motor milestones.

Phase 3 trials are expected to kick off in Q2 to Q3 of 2026. If salanersen works, it positions Biogen to replace its own blockbuster with something better.

Beyond SMA, Biogen has QALSODY (tofersen) approved for ALS and a collaboration with Stoke Therapeutics on zorevunersen for Dravet syndrome, a severe form of childhood epilepsy. The company now has 10 Phase 3 or Phase 3-ready programs in its pipeline, up from just one at the end of 2024.

Why Alloy, Why Now

Biogen and Alloy aren't strangers. The two companies have worked together since 2020 on antibody treatments using Alloy's AI-enabled platforms. This new deal expands the relationship into genetic medicines, a category Alloy has been building out aggressively.

And Biogen isn't the only big pharma knocking on Alloy's door. Sanofi signed a deal valued at up to $400 million with Alloy for developing a CNS antisense therapy, with Sanofi bringing its blood-brain barrier penetration expertise to the table. Since 2017, Alloy has built over 200 partnerships, with more than 60 resulting in licensed programs and 9 antibodies reaching clinical development.

For a company most people haven't heard of, those are serious numbers.

The Bigger ASO Arms Race

Biogen's move fits into a broader industry trend. The antisense oligonucleotide market was worth roughly $3 billion in 2024 and is projected to reach $5.3 billion by 2033. The wider oligonucleotide therapeutics space (which includes siRNA and other RNA-targeting drugs) could hit $17.7 billion by 2030.

Ionis Pharmaceuticals remains the 800-pound gorilla, with partnerships spanning Biogen, Novartis, and others. Wave Life Sciences is pushing exon-skipping ASOs for Duchenne muscular dystrophy. Novartis has pelacarsen in Phase 3 for a cholesterol-related condition.

The competitive pressure explains why Biogen can't just rely on its existing Ionis relationship. Licensing Alloy's AntiClastic platform gives Biogen a second source of ASO innovation, one with potentially differentiated chemistry that could open up targets its current toolkit can't reach.

The Bridge to Growth

CEO Chris Viehbacher has framed Biogen's current chapter as a "bridge to growth." The company's legacy multiple sclerosis franchise is declining. Spinraza faces competitive pressure from gene therapies and newer treatments. Revenue from growth products like Leqembi (for Alzheimer's, with Eisai) and Zurzuvae (for postpartum depression, with Sage) reached $3.3 billion in 2025, but Biogen needs pipeline hits to sustain momentum.

The Alloy partnership is a relatively low-risk way to diversify the toolbox. Biogen isn't acquiring a company or betting billions on a single program. It's paying for access to a platform that could feed multiple programs across multiple disease areas. If even one or two targets pan out, the deal pays for itself many times over.

No analyst commentary on the partnership has surfaced yet, though recent Biogen coverage has been mixed: RBC Capital lowered its price target to $213 on April 7, while HC Wainwright bumped it to $237 on April 2. Neither action was tied to the Alloy deal.

The Bottom Line

Biogen built its reputation on being early to antisense oligonucleotides. But being first isn't the same as being best, and the ASO field has evolved dramatically since Spinraza's approval. The Alloy deal is a bet that next-generation chemistry (specifically, drugs with a different physical shape) can solve the delivery and potency problems that have limited ASOs for years.

It's not flashy. There's no billion-dollar headline or dramatic Phase 3 readout to point to. But the best infrastructure investments rarely make the front page. If AntiClastic delivers on its promise, this quiet April announcement could look very different in hindsight.

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