Oyster Therapeutics raises £44.7m led by 4BIO Capital with Eli Lilly
This article covers Oyster Therapeutics, a biotech startup, which has closed a series A funding round of £44.7m to advance an oral tau degrader and broader programmes built on its SELFTAC platform. The financing is intended to support progress towards clinical trials in tau-driven neurodegenerative diseases such as Alzheimer’s and to advance brain-penetrant, orally available targeted protein degraders.
Oyster Therapeutics (formerly Kesmalea Therapeutics), a biotech startup focused on brain-penetrant targeted protein degraders, has closed a series A funding round of £44.7m to advance an oral tau degrader and wider programmes built on its SELFTAC platform. The financing is intended to push the company towards clinical trials in tau-driven neurodegenerative diseases such as Alzheimer’s.
Why it matters
Targeted protein degradation is an increasingly prominent therapeutic approach that repurposes the cell’s own disposal machinery to remove disease-causing proteins. Translating that approach to the central nervous system is technically difficult because many existing degraders are large bifunctional molecules that struggle to cross the blood–brain barrier. Oyster’s funding signals renewed investor appetite for solutions that make degraders small and orally available, which could broaden how neurodegenerative diseases are treated if the science translates in humans.
Inside the product
Oyster’s lead programme is an oral, small-molecule degrader aimed at pathological forms of tau, the protein central to Alzheimer’s and other tauopathies. The company says its SELFTAC platform converts larger bifunctional degraders into smaller molecules intended to improve brain penetrance and selectivity for disease-associated protein species while sparing the healthy form.
The company has a sponsored research agreement with Massachusetts General Hospital to access patient-derived neuronal cell lines and assays for oligomeric tau, work supervised by Dr Catarina Silva at the Mass General Brigham Neuroscience Institute and Harvard Medical School. Oyster argues an oral formulation would suit large patient populations because of ease of administration, room-temperature storage and potentially lower manufacturing costs.
Who are the investors?
The round was led by 4BIO Capital, a London-based life science venture fund. New strategic participants include Eli Lilly and Company, CE Ventures, Actium Group and TOHO Ventures (managed by Global Brain). Existing backers Syncona, Oxford Science Enterprises (OSE), Mission BioCapital and MGB Ventures also took part.
4BIO positioned itself as a conviction-led life science investor willing to support technologies before every clinical question is answered. In the announcement, Owen Smith, Partner at 4BIO Capital, said:
Alzheimer’s and other tau-driven diseases remain among the hardest problems in medicine and Oyster is taking them on with a clear scientific rationale. Targeted protein degradation has real promise and SELFTAC is an ambitious effort to solve its critical technical challenges so that degraders can reach the brain. Alongside it, Oyster’s lead program aims to remove disease-associated tau while preserving healthy tau. Much remains to be shown in the clinic, but this is where science meets unmet medical need. At 4BIO Capital we back teams like this with conviction before every question is answered, helping to build companies with the potential to make a real difference in medicine.
The investor mix combines deep-pocketed pharma expertise (Eli Lilly), cross-border venture capital (TOHO/Global Brain) and specialist life science backers (Syncona, OSE), offering both strategic development knowledge and sector-specific funding.
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Founder perspective
In the announcement, Rob Johnson, Chief Executive Officer of Oyster Therapeutics, said:
This financing accelerates our progress towards the clinic and enables us to validate a new approach to targeted protein degradation, or TPD, that solves some of its major limitations through the use of smaller molecules. Millions of people living with diseases such as Alzheimer’s need new approaches such as TPD to address the root cause of disease. At Oyster we are defining next-generation TPD medicines that can reliably reach the brain and are orally available to better meet the needs of global patient populations. We welcome this support from both new and existing investors for our vision of building the world’s leading neuroscience TPD company.
Johnson’s comments underscore the company’s clinical focus and its intent to demonstrate both CNS exposure and selective clearance of pathological tau species—key hurdles for any degrader aimed at neurodegeneration.
The bigger picture
Oyster’s raise comes amid broader interest in converting targeted protein degradation from a mostly oncology-leaning field into neurology applications. Delivering brain-penetrant, orally bioavailable degraders would be a technical step-change with implications beyond tau: other neurodegenerative targets could become addressable if the platform proves generalisable.
The participation of international and strategic investors also reflects growing cross-border flows into UK biotech and the willingness of large pharma to seed neuroscience propositions early. For the UK and European ecosystem, the deal is another data point that investors are prepared to back platform plays that combine chemistry innovation with clear translational plans, even in some of the hardest areas of medicine.
They've invested in Oyster Therapeutics
Get to know these biotech investors
| Investors | Investment Focus | Startup Investments | Round Size | Connect |
|---|---|---|---|---|
 4BIO Capital( ) We are a London-based venture capital firm specialising in life sciences, with a... London  | ||||
 Eli Lilly and Company( ) Indianapolis, US  | ||||
 Oxford Science Enterprises( ) The firm focuses on investing in Life Sciences, Health Tech, and Deep Tech, prim... Oxford | ||||
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