Researchers at Columbia University Medical Centre (CUMC) identified the immune cells responsible for destroying hair follicles in people with alopecia areata, a common autoimmune disease that causes hair loss.
They report initial results from an ongoing clinical trial of an FDA-approved drug, which has produced complete hair regrowth in several patients with moderate-to-severe alopecia areata.
Three of the participants experienced total hair regrowth within five months of the start of treatment.
"We've only begun testing the drug in patients, but if the drug continues to be successful and safe, it will have a dramatic positive impact on the lives of people with this disease," said Raphael Clynes, who led the research, along with Angela M Christiano, professor in the Departments of Dermatology and of Genetics and Development at CUMC.
Alopecia areata is a common autoimmune disease that causes disfiguring hair loss. The disease can occur at any age and affects men and women equally.
Hair loss in alopecia areata occurs when cells from the immune system surround and attack the base of the hair follicle, causing the hair to fall out and enter a dormant state.
A major clue was uncovered four years ago in Christiano's genetic study of more than 1,000 patients with the disease.
That study suggested that a "danger signal" in the hair follicles of patients attracts the immune cells to the follicle and sparks the attack.
In the current research, the team first studied mice with the disease, then tracked backward from the danger signal to identify the specific set of T cells responsible for attacking the hair follicles.
Further investigation of mouse and patient cells revealed how the T cells are instructed to attack and identified several key immune pathways that could be targeted by a new class of drugs, known as JAK inhibitors.
Two JAK inhibitors tested separately by the researchers - ruxolitinib and tofacitinib - were able to block these immune pathways and stop the attack on the hair follicles.
In mice with extensive hair loss from the disease, both drugs completely restored the animals' hair within 12 weeks. Each drug's effect was also long-lasting, as the new hair persisted for several months after stopping treatment.
The researchers rapidly initiated a small open-label clinical trial of ruxolitinib - which is FDA approved for the treatment of a blood disorder - in patients with moderate-to-severe alopecia areata.
In three of the trial's early participants, ruxolitinib completely restored hair growth within four to five months of starting treatment, and the attacking T cells disappeared from the scalp.
The results appear the journal Nature Medicine.