Oyster Therapeutics raises $60M to bring Alzheimer’s tau degrader to clinic
London-based Kesmalea Therapeutics has raised $60 million (about €53.5 million) in a Series A-2 financing and rebranded as Oyster Therapeutics. The funding will support the development of an oral, brain-penetrant protein degrader targeting tau, a protein implicated in Alzheimer’s disease and other neurodegenerative disorders.
Why it matters: Approved disease-modifying treatments for Alzheimer’s, including Leqembi and Kisunla, target amyloid plaques in the brain. Oyster is pursuing another hallmark of the disease: abnormal accumulations of tau inside neurons, which are associated with neuronal damage and cognitive decline.
The company aims to develop a treatment that selectively removes harmful forms of tau while preserving the protein’s normal functions. Unlike antibody treatments administered by infusion, Oyster’s candidate is being developed as an oral medicine.
How it works: Targeted protein degradation (TPD) uses the cell’s natural protein disposal machinery to eliminate unwanted proteins. Conventional bifunctional degraders contain two components: one binds the target protein, while the other recruits the machinery responsible for destroying it.
However, connecting these components often produces relatively large molecules that struggle to cross biological barriers, particularly the blood-brain barrier that protects the central nervous system.
Oyster’s proprietary SELFTAC platform uses a reversible linker that allows the two components to exist as smaller molecules capable of crossing cell membranes. They can then reassemble into active bifunctional degraders that direct the cell to destroy the target protein. The company believes this approach could overcome limitations of conventional degraders, particularly for neurological diseases where brain penetration is essential.
The financing: The round was led by London-based 4BIO Capital, with new investors including Eli Lilly, CE Ventures, Actium Group and TOHO Ventures, managed by Global Brain. Existing backers Syncona, Oxford Science Enterprises, Mission BioCapital and MGB Ventures also participated.
Lilly’s participation is particularly notable given its existing position in Alzheimer’s disease with Kisunla (donanemab), an approved anti-amyloid antibody.
Founded in 2020 by medicinal chemist Harry Finch, Kesmalea raised £25 million in a Series A financing in 2022, co-led by Syncona and Oxford Science Enterprises, followed by another £5 million in 2023.
Also notable: Alongside the financing, Oyster has established a sponsored research agreement with Massachusetts General Hospital, working with neurologist Catarina Silva, an assistant professor at Harvard Medical School. The collaboration will use patient-derived neuronal cell lines and methods to study oligomeric tau, small aggregates of the protein considered particularly harmful to neurons. The research is expected to support Oyster’s understanding of tau biology and its drug development efforts.
What to watch: Oyster has not disclosed a timeline for entering clinical trials or detailed preclinical results for its lead candidate.
Tau remains a challenging therapeutic target. In May 2026, Biogen’s tau-targeting antisense therapy diranersen (BIIB080) missed its primary endpoint in a Phase 2 Alzheimer’s study despite encouraging reductions in tau biomarkers.
For Oyster, the next challenge will be to establish whether SELFTAC can deliver sufficient drug exposure in the brain, selectively eliminate pathological tau and ultimately translate that activity into clinical benefits.
