Siren Biotechnology

Market position

The company describes itself as the first to develop an AAV gene therapy for cancer and the first universal AAV gene therapy, with a stated vision of AAV immuno-gene therapy becoming a cornerstone treatment for solid tumors. Investors backing the company have cited the potential for its off-the-shelf, universal design to shorten clinical development and manufacturing timelines and to support a pipeline across multiple brain and eye cancer indications before expansion into other solid tumors.

Siren contrasts its approach with both conventional cytokine immunotherapy and conventional AAV gene therapy: vectorization is intended to provide durable, steady cytokine expression instead of short half-life dosing; local intratumoral delivery confines cytokine production to the tumor microenvironment; low doses and self-limiting genomes are intended to reduce toxicity; and the universal, off-the-shelf drug product is designed for reuse across indications rather than being tailored to a single disease.

Technology

Siren's platform vectorizes engineered cytokines into AAV genomes that are infused locally into tumors rather than administered systemically. The design is described as universal, meaning a single drug product can be applied across multiple solid tumor types regardless of tumor mutations, which the company says reduces clinical development, manufacturing timelines and per-trial capital needs. Stated safety features include low dosing enabled by local delivery; self-limiting payload activity, as AAV genomes do not survive tumor cell death; immunological optimization of the entire AAV genome to limit non-specific immune activation; insensitivity to widespread pre-existing anti-AAV immunity that affects systemically delivered AAV therapies; and a production process optimized for vector integrity to minimize empty capsids, genomic fragments and other viral componentry. The approach is framed as addressing cytokine immunotherapy's short half-lives, non-specificity and systemic toxicity at high doses.

Go-to-market

Patients with solid tumor cancers, with initial focus on brain tumors, including high-grade glioma, and eye tumors identified as an early area of focus at launch.

Geography

Headquartered in the Mission Bay district of San Francisco, California.

History

The company emerged from stealth on May 17, 2023, concurrent with its first preclinical data presentation at the American Society of Gene & Cell Therapy (ASGCT) 26th Annual Meeting in Los Angeles, describing itself as the first AAV gene therapy for cancer and the first AAV gene therapy able to be manufactured once and used across numerous indications. Initial funding was led by Founders Fund and Lux Capital, with participation from Innovation Endeavors, ARTIS Ventures, Civilization Ventures, Savantus Ventures and others. In 2025 the company ran a Regulation Crowdfunding community round on Wefunder, seeking up to $5 million and ultimately raising $4.2 million from more than 1,600 investors. Company announcements subsequently reported FDA clearance of its first IND, advancing Siren to clinical stage; publication of foundational AAV immuno-gene therapy data alongside presentations at ASGCT 2026; and an $8 million non-dilutive grant from the California Institute for Regenerative Medicine (CIRM) supporting clinical development of SRN-101 in high-grade glioma.

Risks & controversies

Board members and investors initially questioned the use of a public crowdfunding campaign as unusual for biotech. The Regulation Crowdfunding Form C filing required Siren to publicly disclose information private biotechs typically withhold, including cash on hand, burn rate and employee count, and required a first-time independent financial audit that took about three months.