Estuary Biotherapeutics, a gene therapy developer working on inherited kidney disease, came out of stealth on 16 October 2026 with a $93m Series A round led by RA Capital Management.
Deep Track Capital, Biogen New Ventures, UPMC Enterprises, Pivotal bioVenture Partners and the National Kidney Foundation Innovation Fund joined the round, as did a family office connected to a person living with the disease. Seed investors 4BIO Capital and GV, Alphabet's venture arm, also took part.
Together with an earlier $10m seed round, the company has $103m in total committed financing. No valuation was disclosed.
“Estuary's programs have the potential to transform the care of patients with ADPKD.”Emily Minkow, Managing Director, RA Capital Management
What Estuary does
Estuary is developing one-time treatments for autosomal dominant polycystic kidney disease (ADPKD), an inherited condition in which cysts build up in the kidneys. The company said ADPKD affects more than 8 million people worldwide. It is caused by mutations in the PKD1 or PKD2 genes, which make proteins called polycystins.
Its approach uses an adeno-associated virus (AAV) to carry genetic material directly to the cells lining the kidney, with the aim of restoring polycystin levels along the nephron. Estuary said that keeping delivery confined to the kidney may avoid some of the problems of AAV therapies that are given systemically.
Co-founder and chief executive Wayne Sackett said the company is focused on "the most crucial remaining barrier to kidney gene therapy: delivery."
The science and the pipeline
The company is built on work from the Yale School of Medicine labs of co-founders Stefan Somlo and Michael Caplan. Somlo published a mouse study in Nature Genetics in 2021 showing that restoring polycystin expression reversed structural and functional signs of disease in kidneys that already had cysts. Caplan reported in Nature Communications in 2023 that a compact part of the polycystin-1 protein was enough to suppress cystic disease in mice.
Estuary has two lead programmes. EST-201 delivers a full-length copy of the PKD2 gene and is aimed at patients with PKD2 mutations; the company expects it to enter the clinic in 2027. EST-101 delivers the functional region of polycystin-1 for patients with PKD1 mutations and is expected to follow in 2028.
Neither programme has been tested in people yet.
Who is running it
Several of Estuary's executives come from Biogen, according to BioPharma Dive. Chief scientific officer Jeremy Duffield was a Biogen vice president of research and development, chief medical officer Uptal Patel headed Biogen's west coast hub, and head of regulatory Kiley Keelin was a Biogen director of regulatory affairs. Co-founder Xavier Anguela previously ran gene therapy work at Eli Lilly.
Emily Minkow, a managing director at RA Capital Management, and Owen Smith, a partner at 4BIO Capital, join the board alongside Sackett, with Jake Bauer as independent chair. Spark Therapeutics co-founder Jeff Marrazzo is among the company's advisers.
What the money is for
Estuary said the financing will take EST-201 and EST-101 through clinical proof of concept, develop its kidney-targeting delivery platform and support a wider pipeline in both inherited and common kidney diseases.
Options for ADPKD patients are limited. BioPharma Dive noted that tolvaptan is the only drug specifically approved for the disease, and that Novartis agreed last year to buy Regulus Therapeutics for $800m to gain an RNA-targeting ADPKD candidate.
Company website: estuarybio.com