Growing Hairy Skin from Human Stem Cells

Building on years of groundbreaking discoveries in stem cell research, scientists from Indiana University School of Medicine and Harvard Medical School have determined how to grow hairy skin using human stem cells—developing one of the most complex skin models in the world.

The study, published yesterday in Nature, shows that skin generated from pluripotent stem cells can be successfully grafted onto a nude mouse to grow human skin and hair follicles. The discovery could lead to future studies in skin reconstruction, disease modeling, and treatment.

“This is the first study to show that human hair can be grown completely from stem cells in a dish, which has been a goal of the skin biology community for decades,” says senior author Karl Koehler, of Harvard.

Using the three-dimensional culture technique that they developed in past experiments, the researchers incubated human stem cells for about 150 days in a ball-shaped cluster of cells called a skin organoid. The interior of the aggregate of cells represent the top layer of skin (the epidermis) and the outside of the cluster develops the bottom layer of skin (the dermis).

“We’ve developed a new cooking recipe for generating human skin that produces hair follicles after about 70 days in culture,” Koehler says. “When the hair follicles grow, the roots extend outward radially. It’s a bizarre-looking structure, appearing almost like a deep-sea creature with tentacles coming out from it.”

After the incubation period, researchers tested whether skin organoids could integrate on the skin of nude mice. More than half of the organoids they grafted on the mice grew human hair follicles. According to Koehler, the skin organoid developed from culture is akin to fetal facial skin and hair.

The experiments show that organoid-generated hairy skin can integrate into mouse skin, which suggests potential applications in skin and facial reconstruction. Physicians typically perform skin grafts in surgery, meaning the removal of skin from one area of the body to transplant on skin that’s been wounded.

“This could be a huge innovation, providing a potentially unlimited source of soft tissue and hair follicles for reconstructive surgeries," says first author Jiyoon Lee of Harvard.

The researchers’ next step is to analyze the development of sensory neurons and Merkel cells that are bundled with the organoid hair follicles. “We’re setting up experiments where we wiggle the hairs and see if the neurons activate," Koehler says, “as proof of concept that our skin can respond to touch in some way.”