An experimental stem cell therapy at Mayo Clinic is helping people with spinal cord injuries regain movement and feeling, though results have varied and doctors don't yet understand why.

In a case report that was released this week, Mayo researchers described the results of the therapy on the first of 10 patients to receive it. A California man who was injured in 2017 in a surfing accident made remarkable progress, going from complete paralysis and no feeling below his neck to walking with increasing speed and for longer distances.

"The first patient was a super-responder, but there are other patients in the trial who are moderate responders and nonresponders," said Dr. Mohamad Bydon, a Mayo neurosurgeon and lead author of the case study in the journal Mayo Clinic Proceedings. "One of our objectives … is to better delineate who will be a responder and why patients respond differently to stem cell injections."

The stem cells, which are so-called master cells that produce other needed cells in the body, were extracted from the patients' own fat tissue and multiplied in a lab before they were injected. The study seeks to determine the ideal timing and dosage of injections, and whether they are safe or produce side effects.

In the first case, the California man had surgery to decompress his spine and fuse his cervical vertebrae. Therapy exercises helped him gain some mobility, but his progress plateaued after about six months.

The stem cell injection took place 11 months after his injury. At that time, it took him 58 seconds to walk 10 meters. Three months later, he had cut that time to 23 seconds. Strength and dexterity had improved as well.

Testing the injections after patients have plateaued in therapy exercises is important, Bydon said, because the researchers don't want to mistake any gains made in therapy as evidence of the stem cells working.

The injected stem cells appear to migrate to the highest level of inflammation at the site of the spinal cord injury. Exactly what they do at that point is not fully understood, Bydon said, but researchers are taking spinal fluid samples from patients to find out. Biological markers in the fluid could explain why patients are healing after the stem cell injections, and why some make more progress than others.

The stem cell therapy is just one of many being tested by researchers to improve treatment of the roughly 500,000 spinal cord injuries that occur worldwide each year. Mayo and other institutions reported progress last year in patients using a spinal cord stimulator.