Being able to tell the difference between hot and cold or feeling the embrace of a loved one are experiences that many of us take for granted in our daily lives. But paralyzed patients who have lost their sense of touch don’t have this luxury.

Sensory nerves are cells in the spinal cord that send signals from outside of the body to the brain where they are translated into senses like touch, temperature and smell. When someone is paralyzed, their sensory nerves can be damaged, preventing these sensory signals from reaching the brain and leaving patients at risk for severe burns or not knowing when they’ve cut themselves because they can’t feel the pain.

A Journey to Restore Touch

A group of scientists led by Dr. Samantha Butler at the  Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA are on a research journey to restore the sense of touch in paralyzed patients and people with sensory neuron damage. In their earlier work, which we blogged about back in September, the team discovered that signaling proteins called BMPs played an important role in the development of sensory nerve cells in chicken embryos.

With the help of CIRM-funding, Butler and her team have made significant progress since this earlier study, and today, we bring you an exciting update on their latest findings published in the journal Stem Cell Reports.

Using a similar strategy to their previous study, Butler and her team attempted to make sensory nerve cells from human stem cells in a dish. They exposed human pluripotent stem cells to a specific BMP protein, BMP4, and a chemical called retinoic acid. This combination treatment created two types of sensory nerve cells: Dl1 cells, which allow you to sense your body’s position and movement, and Dl3 cells, which allow you to feel pressure.

Human embryonic stem cell-derived neurons (green) showing nuclei in blue. Left: with retinoic acid added. Right: with retinoic acid and BMP4 added, creating proprioceptive sensory nerve cells (pink). (Image source: UCLA Broad Stem Cell Research Center/Stem Cell Reports)

This is the first time that researchers have reported the ability to make sensory nerve cells from human stem cells. Another important finding was that the UCLA team was able to make sensory nerve cells from both human embryonic stem cells and human induced pluripotent stem cells (iPSCs), which are pluripotent stem cells derived from a patient’s own cells. The latter finding suggests a future where paralyzed patients can be treated with personalized cell-based therapies without the need for immune suppressing drugs.

Feeling the Future

This study, while still in its early stages, is an important step towards a future where paralyzed patients can regain feeling and their sense of touch. Restoring a patient’s ability to move their limbs or walk has dominated the field’s focus, but Butler argues in a UCLA news release that restoring touch is just as important:

Samantha Butler

“The field has for a long time focused on making people walk again. Making people feel again doesn’t have quite the same ring. But to walk, you need to be able to feel and to sense your body in space; the two processes really go hand in glove.”

 

Butler and her team are continuing on their journey to restore touch by transplanting the human sensory nerve cells into the spinal cords of mice to determine whether they can incorporate into the spine and function properly. If the transplanted cells show promise in animal models, the team will further develop this cell-based therapy for clinical trials.

Butler concluded,

“This is a long path. We haven’t solved how to restore touch but we’ve made a major first step by working out some of these protocols to create sensory interneurons.”