Hillstar Bio, founded in 2023 and based in Boston, Massachusetts, is a biotechnology company specializing in precision immunology therapies for autoimmune diseases. The company's approach focuses on selectively targeting and depleting pathogenic immune cells while preserving healthy ones, aiming to provide durable relief and potentially reset the immune system in patients with autoimmune conditions. ​

In March 2025, Hillstar Bio announced the successful closing of a $67 million Series A financing round. The funding was led by a syndicate of investors from the U.S., Europe, and Asia, including Droia Ventures, Frazier Life Sciences, Novo Holdings A/S, LifeArc Ventures, and Hummingbird Bioscience. ​

The proceeds from this financing are allocated to advance Hillstar Bio's lead program targeting TRBV9+ T cells, a subset implicated in various autoimmune conditions. The initial focus is on developing treatments for axial spondyloarthritis (AxSpA), with plans to initiate clinical proof-of-concept studies in 2026. Additionally, the company aims to expand its pipeline to address other immune and inflammatory diseases associated with HLA-B27. ​