Estuary Biotherapeutics seeds kidney gene therapy push with $10M as launch financing reaches $103M

Estuary Biotherapeutics has launched with $103 million in committed financing to develop genetic medicines targeting serious kidney diseases, beginning with autosomal dominant polycystic kidney disease (ADPKD). At the base of that total sits a $10M seed round co-led by 4BIO Capital and GV, both of which also participated in the larger raise.

The bulk of the financing is a $93 million Series A led by RA Capital Management, with participation from Deep Track Capital, Biogen New Ventures, UPMC Enterprises, Pivotal bioVenture Partners, the National Kidney Foundation Innovation Fund and a family office connected to an individual living with ADPKD.

Proceeds will support Estuary's two lead programs, EST-201 and EST-101, through clinical proof of concept, along with further development of the company's kidney-targeting platform. Both programs are designed to address the two most common genetic subtypes of ADPKD, an inherited disease characterized by progressive cyst growth in the kidneys.

EST-201 is a full-length PKD2 gene therapy delivered through an adeno-associated virus and is intended for patients whose ADPKD is caused by a PKD2 mutation; Estuary anticipates bringing it into the clinic in 2027. EST-101 delivers a functional region derived from the polycystin-1 protein using the same AAV approach and is aimed at PKD1 mutations, with the company expecting a 2028 clinical entry.

Rather than targeting downstream pathways, the programs are designed to address the underlying genetic causes of ADPKD. Estuary plans to use locally delivered AAV to target kidney epithelial cells and restore polycystin protein levels across the nephron while limiting systemic exposure. CEO Wayne Sackett described delivery as "the most crucial remaining barrier to kidney gene therapy."

The approach builds on research from scientific co-founders Dr. Stefan Somlo and Dr. Michael Caplan of Yale School of Medicine. Their work demonstrated the potential to reverse structural and functional manifestations of polycystic kidney disease in preclinical models and helped establish the scientific basis for the company's gene therapy strategy.

The market is substantial: ADPKD affects more than eight million people worldwide and ranks among the most common inherited kidney diseases, with more than 90% of patients carrying mutations in either PKD1 or PKD2. Estuary estimates initial U.S. treatment populations of approximately 100,000 to 140,000 rapidly progressing patients with PKD1 mutations and 10,000 to 15,000 with PKD2 mutations.

For 4BIO Capital, the seed was an early bet on a team it helped build. Partner Owen Smith said the firm co-led the seed financing and helped shape the initial business plan, adding that the company has "translated ambitious science into a focused development strategy."