The research, led by scientists at the University of California San Diego School of Medicine, built on previous work in rodents showing that grafting human neural progenitor cells (NPCs) was able to improve motor function after injury.

In the most recent trial, it was shown that rhesus monkeys that were treated with stem cells were better able to grasp an orange compared with monkeys that had not been treated.

The findings open up the possibility that this form of treatment may, one day, be able to cure the paralysis that can occur when people experience spinal cord injuries.

“For more than three decades, spinal cord injury research has slowly moved toward the elusive goal of abundant, long-distance regeneration of injured axons, which is fundamental to any real restoration of physical function,” said Mark Tuszynski, Professor of neuroscience and Director of the UC San Diego Translational Neuroscience Institute. “While there was real progress in research using small animal models, there were also enormous uncertainties that we felt could only be addressed by progressing to models more like humans before we conduct trials with people”.

In particular, researchers noted that using NPCs, stem cells that would otherwise become nerve cells in the central nervous system, from eight-week-old human foetuses meant that the graft promoted axon extension and did not respond to naturally occurring inhibitors.

Over a nine month period, the grafts were shown to measurably grow, expressing key neural markers and also was shown to send out the fibres that nerve cells use to communicate, axons, through the injury site.

Image: Mark Tuszynski, University of California San Diego School of Medicine

Of particular interest to the researchers was the regeneration of corticospinal axons, which are responsible for voluntary movement in humans and was the first time this had been seen in a primate model.

“We seem to have overcome some major barriers, including the inhibitory nature of adult myelin against axon growth,” Tuszynski said. “Our work has taught us that stem cells will take a long time to mature after transplantation to an injury site, and that patience will be required when moving to humans. Still, the growth we observe from these cells is remarkable -- and unlike anything I thought possible even ten years ago. There is clearly significant potential here that we hope will benefit humans with spinal cord injury.”

There is still some work to be done before human clinical trials can be launched. The team that worked on this project are looking further into how to improve the growth of the cells, before ensuring production of neural stem cells that are able to meet FDA requirements and the completion of additional safety tests.