Third Harmonic Bio is a clinical-stage biopharmaceutical company developing oral small-molecule inhibitors of KIT, a receptor that controls mast cell function and survival. Mast cell overactivation drives a range of allergic and inflammatory diseases, and Third Harmonic Bio's approach aims to directly deplete and inactivate mast cells — rather than blocking individual inflammatory mediators like histamine. The company's sole active program is THB335, a next-generation oral KIT inhibitor targeting chronic spontaneous urticaria (CSU), a chronic condition characterized by persistent hives and itch affecting an estimated 1.5M+ patients in the U.S. Third Harmonic Bio has no approved products and generates no revenue. THB335 is a redesigned version of a prior candidate, THB001, which was discontinued after liver toxicity emerged in a Phase 1b study; THB335 incorporates structural modifications intended to address that toxicity risk. Phase 1 data showed a roughly 40-hour half-life enabling once-daily dosing and dose-dependent reductions in a mast cell biomarker. Third Harmonic Bio plans to initiate a Phase 2 study in CSU and sees potential future indications in respiratory and gastrointestinal diseases. The company funds operations through equity raises and licenses its KIT inhibitor compounds from Novartis, owing Novartis development and sales milestones plus royalties on net sales. Third Harmonic Bio has engaged TD Cowen to run a strategic review that could result in a partnership, asset sale, or merger.