For years, a Japanese man lay motionless, paralyzed from the neck down after a devastating spinal cord injury. Doctors doubted he would ever stand again. Today, he can not only stand independently but is learning to walk once more, thanks to an injection of laboratory-grown stem cells into his spinal cord.

Researchers at Keio University in Tokyo treated four fully paralyzed patients using neural stem cells derived from induced pluripotent stem cells (iPS). Remarkably, half of the patients showed significant improvements. One can now stand, while the other can move his arms and legs.

“That’s a great positive outcome. It’s very exciting for the field,” says James St John, a translational neuroscientist at Griffith University in the Gold Coast, Australia.

From Paralysis to Movement

The trial began cautiously in December 2021, led by stem-cell scientist Hideyuki Okano and orthopedic surgeon Masaya Nakamura. The team transplanted approximately two million neural precursor cells into each patient’s spinal cord injury site. These cells, created from donor-derived iPS cells — adult cells reprogrammed to behave like embryonic stem cells — can develop into neurons and supporting glial cells.

All four participants were men treated two to four weeks after their injuries. They received immune-suppressing medication for six months to ensure their bodies wouldn’t reject the cells. One year later, the researchers assessed their progress using the American Spinal Injury Association Impairment Scale (AIS), which ranks impairment from A (complete paralysis) to E (normal function).

Initially, all four patients were classified as grade A — completely paralyzed. But one patient dramatically improved to grade D, able to stand independently. He now actively trains to walk again. Another improved to grade C, regaining partial movement in arms and legs. Even the two patients who remained at grade A demonstrated subtle motor improvements, such as being able to feed themselves — a huge step up for quality of life.

“This is a dramatic recovery,” Okano told Nature.

Magnetic resonance imaging (MRI) scans from one patient provided clues about the mechanics at play in these recoveries. A previously hollow, damaged spinal region had filled with new tissue within a year. According to Prof. Toru Ogata of the University of Tokyo, “It’s possible that the transplanted cells have engrafted and are increasing the number of nerves.” Ogata calls the outcome “groundbreaking,” especially given the severe initial condition of these patients.

Cautious Optimism and Challenges Ahead

While these results sound extraordinary, the Japanese scientists remain cautious. The study involved only four patients, too small a number to establish definitive effectiveness. Spontaneous recovery sometimes occurs naturally in spinal cord injury patients, though dramatic improvements like those seen in this trial are exceedingly rare. It sounds preposterous that the results may be owed to chance, but new trials involving more people will settle many things.

However, the major differences in patient outcomes are something to carefully consider. The reasons for these differences remain unclear, though severity and specific nature of injury likely are involved. Each spinal cord injury is unique, the researchers added.

Okano’s startup, K Pharma, aims to initiate new, larger trials soon. They’ll focus on varying injury types and chronic paralysis cases as early as 2027.

Prof. Kinichi Nakashima of Kyushu University believes that increasing the number of cells injected may enhance success. “The key will be whether the team can prove the treatment’s efficacy by increasing the number of successful cases,” he said.

A Leap Forward for Paralysis treatment

In Japan alone, about 6,000 new spinal cord injuries occur annually, most often because of traffic accidents. Globally, nearly one million new injuries occur each year, with approximately 20 million people currently living with the devastating effects of spinal paralysis.

Makoto Ohama, chairman of the Japan Spinal Cord Foundation and himself affected by spinal injury, reacted with hope. “I feel like I can see a beacon of hope,” he said after hearing the results. For people previously facing a lifetime of dependence, even modest improvements can profoundly transform their lives.

In the delicate art of repairing damaged nerves, this new approach represents not just medical innovation but a powerful leap forward in restoring mobility — and dignity — to thousands waiting for a cure.

The results have not yet been peer-reviewed. They were presented at a press conference on 21 March.