Estuary Biotherapeutics launches with $103 million to advance targeted gene therapies for kidney disease

·         Paradigm-shifting approach targeting the root cause of autosomal dominant polycystic kidney disease (ADPKD), with the goal of durably halting or reversing the structural and functional manifestations of the disease

·         Proceeds will advance two lead gene therapies designed to treat the root cause of autosomal dominant polycystic kidney disease (ADPKD)

·         Science originates from the research of scientific co-founders Dr. Stefan Somlo and Dr. Michael Caplan of Yale School of Medicine

London, United Kingdom, 16 October 2026 – 4BIO Capital, a specialist biotech venture firm transforming innovative technologies into breakthrough precision therapies, today announces that it has participated in the USD 93M Series A financing of Estuary Biotherapeutics (Estuary), following its co-lead of the company’s USD 10M Seed round with GV. The financings provide USD 103M as Estuary launches to develop targeted gene therapies for kidney disease.

Proceeds from the Series A will be used to advance Estuary’s two lead programmes, EST-201 and EST-101, through clinical proof of concept and to further develop the company’s kidney targeting platform. Estuary’s technology is based on landmark discoveries demonstrating that restoring polycystin expression in mouse kidneys with established cystic disease can reverse both kidney structure and function, and that a compact functional region of the polycystin-1 (PC1) protein is sufficient to suppress cystic disease. Estuary’s programmes use a potentially one-time, locally delivered adeno-associated virus (AAV) to restore polycystin protein levels across the entire nephron, and are designed to address the underlying genetic cause of ADPKD directly. This kidney-confined approach is designed to avoid the systemic toxicities that have limited AAV gene therapies elsewhere in the body.

Owen Smith, Partner at 4BIO Capital and Estuary Board member, said: “4BIO exists to back breakthrough therapies that can change the course of disease for patients who do not yet have good options. Having partnered with Wayne from Estuary’s earliest days, co-leading the seed financing and helping shape the initial business plan, we have seen first-hand how effectively the team has translated ambitious science into a focused development strategy. In a short period, Estuary has generated strong data, advanced both programmes materially and built the organisation needed for the next stage. We are excited to continue supporting the company in the Series A as it moves towards the clinic.”

Wayne Sackett, co-founder and CEO, added: “ADPKD is one of the world’s most common genetic diseases, yet patients are still awaiting a therapy that can transform the course of their disease. We paired our scientific co-founders’ landmark breakthroughs in disease biology with a dedicated and passionate team focused on solving the remaining barrier to kidney gene therapy: delivery. By pioneering fit-for-purpose local administration and an efficient global development strategy, our team is moving with urgency to bring these important medicines into the clinic.”

Estuary is developing locally delivered genetic medicines for ADPKD, starting with two lead programmes. EST-201 is a full-length PKD2 gene therapy delivered through AAV, which will be evaluated in patients with ADPKD with a PKD2 mutation and is anticipated to enter the clinic in 2027. EST-101 is a gene therapy delivering a PC1-derived functional region via the same AAV, which will be evaluated in patients with ADPKD with a PKD1 mutation and is anticipated to enter the clinic in 2028. The programmes build on the findings of Estuary’s scientific co-founders from Yale School of Medicine: Dr. Stefan Somlo, who established the in vivo reversal biology underlying Estuary’s approach, and Dr. Michael Caplan, who showed that a compact functional region of the polycystin-1 (PC1) protein is sufficient to suppress cystic disease, providing the scientific basis for an AAV-based approach to ADPKD-PKD1.

The Series A was led by RA Capital Management, with follow-on participation from the company’s seed co-leads, 4BIO Capital and GV. Other participants include Deep Track Capital, Biogen New Ventures, UPMC Enterprises, Pivotal bioVentures, the National Kidney Foundation and a family office connected to an individual living with ADPKD.