Estuary Raises $103 Million to Pursue Gene Therapy for ADPKD

Estuary Biotherapeutics has launched with $103 million in committed funding and a difficult scientific goal: develop a one-time genetic treatment for autosomal dominant polycystic kidney disease, or ADPKD. The financing comprises a $93 million Series A led by RA Capital Management and an earlier $10 million seed round.

ADPKD is an inherited disorder in which mutations disrupt polycystin proteins, allowing cysts to grow and progressively damage the kidneys. Tolvaptan can slow disease progression for some patients, but Estuary is pursuing a treatment designed to address the underlying protein deficiency.

Its lead program, EST-201, is intended to deliver a functional version of the PKD2 gene. A second candidate, EST-101, would deliver a shortened, functional part of the protein produced by PKD1. The company's founders point to mouse research showing that restoring polycystin activity can shrink cysts and reverse inflammation and scarring. The truncated PKD1 approach is meant to solve a packaging problem because the full gene is too large for standard viral vectors.

Both programs remain preclinical. Estuary expects EST-201 to enter human testing in 2027 and EST-101 in 2028, but kidney delivery remains the central technical hurdle. Success in mice does not establish safe, durable expression in people, and local administration must reach enough kidney tissue to alter disease progression.

Biogen's venture arm participated in the financing, and several Estuary executives previously worked at Biogen. That connection is strategically interesting but does not make Estuary a material Biogen program or justify a direct earnings impact for BIIB.

The funding gives Estuary time to test delivery, manufacturing and toxicology before clinical trials. For investors following the kidney-disease field, the next meaningful evidence will be an investigational new drug clearance, human dosing and biomarkers showing that restored polycystin activity changes cyst growth without unacceptable immune or safety problems.