Third Harmonic Bio Launches with $155M to Tackle Mast Cell-Driven Diseases

On Wednesday, Third Harmonic Bio closed on Series B financing, bringing the total capital raised to $155 million. This capital will fund the development of the company’s lead candidate, THB001, as it commences the next phase of human studies for the initial indication of chronic urticaria.

This follows a $50 million Series A, led by Atlas Venture, which upstarted Third Harmonic Bio in 2019. Atlas was accompanied in that round by OrbiMed, receiving an extra boost from BVF Partners. The current round was co-led by General Atlantic and BVF, with participation from Atlas and Orbimed. Boxer Capital, RA Capital, RTW, Deep Track Capital, Ajax Health/Zeus and Commodore Capital contributed funding as well.

“We are excited to continue to support Third Harmonic Bio’s fantastic team in bringing a powerful new potential medicine to patients affected by diverse mast cell-driven diseases,” said Michael Gladstone, partner at Atlas Venture and Third Harmonic Bio founder. “We are delighted to partner with Third Harmonic Bio’s new investors as the company advances and expands the THB001 clinical development program.”

THB001, a novel allergy medication taken orally, inhibits the cell surface receptor that regulates mast cell function and maintenance, known as KIT. Mast cells are the first-line defense against foreign bodies known as allergens, reacting to the external stimuli with inflammatory responses such as hives, wheezing and gastrointestinal distress. By inhibiting KIT, THB001 eases these inflammatory responses, providing broad allergy relief.

The drug demonstrated promising drug-like properties in preclinical studies, displaying the high accuracy that is essential to safety and effectively reduced mast cell count in a variety of tissues.

“Achieving the selectivity required to target KIT with an oral small-molecule therapy for allergy and inflammation has until now been an intractable drug development challenge,” said Natalie Holles, chief executive officer of Third Harmonic Bio. “As a first-in-class, highly selective KIT inhibitor, we believe THB001 has the potential to revolutionize the treatment of a broad range of mast cell-mediated allergic and inflammatory diseases of the skin, airway and GI tract.”

For now, researchers at the company are focusing on developing applications of the therapy in treating chronic urticaria, a skin disease affecting up to 1% of the population that causes red, itchy, painful welts or hives in response to a stimulus, or even none at all. Current treatments are effective only half the time at best, and when antihistamine therapy fails, the majority either do not respond to biologics or simply do not consider them as an option.

“Allergic and inflammatory diseases represent a significant unmet medical need, and although available therapies have been commercially successful, only a fraction of the diagnosed patient population is adequately treated,” said Rob Perez, operating partner at General Atlantic. “THB001, with its unique attributes and oral formulation, represents a true pipeline-in-a-product opportunity with the potential to offer an important new therapeutic option to millions of underserved patients.”

Later this year, the company plans to conduct a Phase 1b proof-of-concept study, looking at the therapy's ability to mitigate allergic reactions of the skin such as hives upon contact with cold surfaces.

In the future, the company plans to broaden the range of THB001 treatments available for various diseases of the skin, airway and gastrointestinal tract in which mast cells play a known role in the pathophysiology of the condition.