In 2013, renowned Boston Children’s Hospital pain researcher Clifford Woolf, MD, PhD, and Kai Johnsson, PhD, his fellow co-founder at Quartet Medicine, believed they held the key to non-narcotic pain relief. Woolf had shown that tetrahydrobioptrin — a protein also known as BH4 — is a primary natural modulator of neuropathic and inflammatory pain sensitivity. Quartet was founded on the premise that inhibiting BH4 production could prevent the progression of acute pain to chronic pain in millions of patients, without threat of addiction or tolerance.

With solid human genetic data and chemical biology, plus $17 million in series A funding, Quartet looked primed for success. But in the summer of 2017, toxicology studies of the company’s lead candidate revealed neurologic side effects. Hope for the promising pain drug cratered, taking Quartet with it.

Now, however, a surprising discovery about BH4 will likely rekindle interest in the once-promising pathway and could have profound implications for treating autoimmunity and cancer. In yesterday’s Nature, Woolf and his team at Boston Children’s Hospital, together with immunologists from the Institute of Molecular Biotechnology (IMBA) in Vienna report that BH4 also functions as a kind of immunological thermostat in the body, raising and lowering the activity levels of T cells. …