Mestag Therapeutics, a Cambridge, UK-based developer of antibody therapies targeting fibroblast-immune interactions in cancer and inflammation, has raised $40M in financing backed by SV Health Investors, Johnson & Johnson Innovation – JJDC, Forbion, GV and Northpond Ventures. The company engineers antibodies like MST-0312, a FAP-LTBR bispecific that induces tertiary lymphoid structures (TLS) in solid tumors. The capital funds the Phase 1 STARLYS trial of MST-0312 starting mid-2026.
TLS Momentum Draws Oncology Capital
The raise aligns with rising interest in TLS induction for immunotherapy. Unnatural Products secured $45M in Series B financing in October 2024 for oncology therapeutics. CytomX Therapeutics has raised $136M targeting the tumor microenvironment with proteolytically-activated antibodies. Mestag's fibroblast focus differentiates by reprogramming immune access in cold tumors.
Cold Tumors Resist Checkpoint Drugs
Solid tumors in barrier organs like lung and gut often evade PD-1/PD-L1 therapies due to poor immune cell infiltration. Fibroblasts in the tumor microenvironment exclude T cells, limiting responses. Chronic inflammatory diseases such as RA and IBD similarly feature overactive stromal fibroblasts driving persistent inflammation without durable remission.
Fibroblast Antibodies Reshape Immunity
Mestag's RAFT platform discovers targets on fibroblast subsets. MST-0312 bispecifically engages FAP on cancer-associated fibroblasts and LTBR to form TLS and high endothelial venules (HEV), enabling immune cell recruitment and activation. Preclinical data demonstrate robust anti-tumor effects, particularly in combinations.
As Susan Hill, CEO noted:
"This financing advances Mestag to the clinical stage… We believe MST-0312 is well positioned to overcome these hurdles by enabling better access of immune cells, through formation of HEVs, and local education and activation to tumor antigen through formation of TLS."
Stromal Agonists Target Inflammation
M402 acts as a stromal agonist antibody inhibiting myeloid cells in inflammatory diseases. Recent deals validate the platform: licensing a novel target to Johnson & Johnson in December 2024 and a collaboration with MSD in October 2024 potentially worth up to $1.9B. These partnerships de-risk expansion into RA, IBD, lupus and kidney disease.
Elite VCs Signal Clinic Confidence
SV Health Investors, which founded Mestag, leads with a track record in UK immuno-oncology including Bicycle Therapeutics' IPO. JJDC brings J&J R&D resources, aligning with their recent inflammatory deals. GV and Northpond add AI-biotech and immunotherapy conviction, while Forbion bolsters European life sciences support. This syndicate reflects de-risked path to IND filing early 2026.
Immunotherapy Market Doubles by 2033
Cancer immunotherapy stands at $153.27B in 2025, projected to reach $305.80B by 2033 at 9.1% CAGR per Grand View Research. Competitors like Bicycle Therapeutics ($555M raised) pursue bicyclic peptides for tumors, while Protagonist Therapeutics ($400M+) focuses GI peptides. Mestag carves a niche in fibroblast-driven TLS, ahead of peers like Candel Therapeutics in viral approaches.
Academic Founders Pioneer Fibroblasts
Founders include Harvard's Michael Brenner, Oxford's Mark Coles and Chris Buckley, and Cold Spring Harbor's David Tuveson—pioneers in stromal immunology and cancer fibroblasts. CEO Susan Hill brings execution from Gyroscope Therapeutics' Novartis acquisition. Recent hires like CMO Lindsey Rolfe (30+ years oncology) and CSO Matthew Sleeman (ex-Regeneron) prepare for clinic.
Phase 1 Trial Leads Pipeline Push
Proceeds support MST-0312's Phase 1 STARLYS in barrier organ cancers mid-2026, with IND early 2026. Leadership expanded with CDO Pascal Merchiers and ongoing pharma collaborations. The 43-person team pursues RAFT platform targets across oncology and inflammation.