$60 million. Nine investors around the table. One protein that has already survived more clinical failures than most drug targets ever see.
Oyster Therapeutics, the London company until this week known as Kesmalea, closed a $60 million Series A-2 on November 10. 4BIO Capital led the round. Eli Lilly joined as a new investor, alongside CE Ventures, Actium Group and TOHO Ventures. Syncona, Oxford Science Enterprises, Mission BioCapital and MGB Ventures all came back.
The obvious read is that tau is investable again. The more useful read is narrower. This is platform capital, not a verdict on the lead asset.
Oyster's tau programme has no disclosed start date for human trials and no published preclinical efficacy numbers. What the company does have is a delivery mechanism that could matter well beyond Alzheimer's: a degrader that enters the body as two small molecules and only assembles into a drug after it crosses the blood-brain barrier.
The scientific bet is pharmacokinetics, not biology: can two halves meet inside the brain at useful concentrations?
The next real catalyst is first-in-human data. No public date exists for it.
What sixty million dollars actually buys
The company's history suggests this is not a first cheque. Kesmalea raised £25 million in 2022, co-led by Syncona and Oxford Science Enterprises, then added £5 million in 2023, according to European Biotechnology. The new round is labelled Series A-2 in the release and described by BioPharma Dive as an extension of the Series A. The labelling is housekeeping. The syndicate is the signal.
Oyster Therapeutics financing
Announced 10 November 2026. 4BIO Capital led; Eli Lilly joined as a new investor. · Oyster Therapeutics, 2026
The proceeds have three jobs, according to the company. Move the oral tau degrader into clinical development. Keep building the SELFTAC platform. And fund a sponsored research agreement with Massachusetts General Hospital, where Catarina Silva's lab will supply patient-derived neuronal lines and assays for oligomeric tau.
That last item deserves a closer look. The MGH collaboration buys better biology, not a shortcut to the clinic. Oyster is paying for a sharper read on which forms of tau actually damage neurons. Useful, but not the same as a clinical milestone.
Eight other investors joined 4BIO in the syndicate, BioPharma Dive reported. The mix matters. Lilly is strategic money from a company already selling an amyloid drug. Syncona and Oxford Science Enterprises are long-duration life-science capital that has stayed with the company since its earlier rounds. CE Ventures brings Gulf corporate venture exposure. None of them disclosed individual cheques.
The tau graveyard is real
Tau is the defining pathology of tauopathies, with Alzheimer's as the best-known member. It is also where some of the most expensive neuroscience programmes have gone to die.
Pharmaphorum lists Johnson & Johnson's antibody posdinemab, Eli Lilly's zagotenemab and the OGA inhibitor LY3372689 among the failures. In May 2026, Biogen's antisense therapy diranersen, also known as BIIB080, missed its primary endpoint in a Phase 2 Alzheimer's study despite encouraging reductions in tau biomarkers, European Biotechnology reported.
That last result is the one to keep in mind. Lowering tau is not the same as helping patients. A degrader can clear the protein and still fail the functional endpoint if the damage is already done or if the wrong form of tau was removed.
Oyster is also behind. BioPharma Dive notes that medicines from Biogen and Arrowhead Pharmaceuticals able to lower tau substantially are much further ahead in clinical testing. Oyster's candidate has not entered the clinic.
Two halves that meet in the brain
Most targeted protein degraders are bifunctional molecules: one warhead binds the target, another recruits the cell's disposal machinery, and a linker holds the pair together. The design is rational and modular. It also produces large molecules that struggle to cross the blood-brain barrier and often need to be injected.
Molecular glues are smaller and more drug-like. But their discovery is less predictable, because they work by inducing a protein interaction rather than by a modular design the chemist can reason about.
Oyster's SELFTAC platform tries to take both advantages. The two warheads travel as separate small molecules, cross the gut wall, cell membranes and the blood-brain barrier, then reassemble through a reversible linker into an active bifunctional degrader. Once assembled, the molecule behaves like a conventional PROTAC and sends tau to the cell's protein-clearance machinery.
| Design | Bifunctional degrader | Molecular glue | SELFTAC (company claim) |
|---|---|---|---|
| Size | Large | Small | Travels as two small molecules |
| CNS penetration | Poor | Better | Designed for it |
| Design logic | Rational, modular | Less predictable | Rational, modular |
| Clinical proof | Some approved outside CNS | Approved in oncology | None yet |
Based on Oyster Therapeutics, pharmaphorum and European Biotechnology reporting, November 2026.
The modular design also lets Oyster screen combinations of warheads rather than rebuild a whole molecule each time. That is the industrial argument: shorter design cycles, more shots on goal, a platform that can be pointed at proteins beyond tau.
Owen Smith, a partner at 4BIO Capital, was careful about the gap between mechanism and medicine. "Much remains to be shown in the clinic, but this is where science meets unmet medical need," he said in the company's release.
He is right to be careful. The clever part of SELFTAC is not the degradation. It is the logistics. Getting two halves to the right place, at the right concentration, at the right time is a pharmacokinetic problem, and pharmacokinetics is where elegant degraders usually meet their limits.
Why Lilly is hedging its own franchise
Lilly already sells Kisunla, an anti-amyloid antibody. The drug generated $484 million in worldwide sales in the first nine months of 2026, pharmaphorum reported. That is a real business. It is not a cure.
Amyloid drugs modestly affect cognition and do not stop or reverse Alzheimer's, as BioPharma Dive put it. That leaves room for a complementary approach aimed at tau, the protein that correlates more closely with cognitive decline in many patients.
Lilly has been here before. Its own tau antibody, zagotenemab, failed. Backing Oyster is a second route into the same biology, this time through degradation rather than blockade, and through a private company rather than an internal programme.
"Big pharma investors are very interested in tau," Oyster chief executive Rob Johnson told BioPharma Dive, likening experimental drugs for chronic diseases such as Alzheimer's to "the next obesity opportunity". The comparison is telling. Obesity became a venture category once the biology produced drugs that clearly worked. Tau has not had that moment yet.
The venture math is turning, unevenly
Neuroscience venture funding has been rebuilding. Startups focused on the central nervous system took in $1.09 billion in 2023, $1.58 billion in 2024 and $1.9 billion in 2025 from 26 prolific venture firms, according to BioPharma Dive's analysis. The 2026 total stood at $664 million by mid-November.
Five neurology-focused rounds in recent weeks added around $450 million, the same analysis found. Oyster's $60 million sits in the middle of that cluster, not at the top.
The comparison with VectorY is unavoidable. As we wrote in November, the Dutch biotech raised $83.5 million to push a TDP-43 gene therapy through ALS, with Eli Lilly also participating. That round bought a clinical-stage asset. Oyster's round buys a platform and a preclinical programme.
That difference explains the structure. Platform companies raise extension rounds when the science is promising but the clinical proof is not yet financeable at a higher price. The A-2 label is honest about where Oyster sits.
What would falsify the story
Three things have to be true for SELFTAC to become more than a clever delivery idea.
The three conditions behind the platform
2. Selectivity. The degrader must remove pathological tau while sparing healthy tau. Tau has normal functions; clearing all of it is not obviously safe.
3. Manufacture. An oral medicine has to be stable, absorbable and cheap enough for a large population. That is a formulation problem as much as a chemistry one.
None of those conditions is proven in humans. The company has not disclosed a clinical timeline, and BioPharma Dive reported that Oyster has not said when its top drug will enter the clinic.
What investors can watch is narrow and specific. An IND filing. A first-in-human study with pharmacokinetic data from the brain. A selectivity readout comparing pathological and healthy tau. Any one of those would move the platform from story to evidence.
The tau graveyard is not a reason to avoid this round. It is the reason the round is priced the way it is. Lilly and 4BIO are paying for a delivery mechanism that, if it works, applies to proteins that have been out of reach for every other modality. The money is real. The proof is still ahead.