In what seems like something found in a work of science fiction rather than a medical journal, a team of neuroscientists, surgeons, and other researchers successfully grafted human neural progenitor cells into several rhesus monkeys suffering from spinal cord injuries. The team was amazed to find that the grafts not only survived but grew into a natural network of new electrical activity, allowing some monkeys to regain use of their forelimbs.
The findings of the study were published in the February issue of Nature Medicine. The study represents another step in utilizing human stem cells and is the largest jump since similar experiments on rodents. “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, MD, PhD, professor of neuroscience and director of the UC San Diego Translational Neuroscience Institute.
Tuszynski spoke on the study and its goals. He acknowledged the progress of stem cell trials on rodents, but also knows the challenges that lay ahead, and the incremental steps needed before human trials for certain therapies. To Tuszynski and the team, the small step up to successful grafts in primates like the rhesus monkeys is more of a leap forward.
“We discovered, for example, that the grafting methods used with rodents didn’t work in larger, non-human primates. There were critical issues of scale, immunosuppression, timing and other features of methodology that had to be altered or invented,” said Tuszynski.
Managing to grow and proliferate grafted stem cells for spinal cord injuries is a difficult undertaking due to several challenges. An extracellular matrix surrounds injuries and makes proliferation of cells challenging since the inhibitory proteins created around an injury are meant to fortify, not nurture new growth. Though these challenges are always present, Tuszynski and team were able to accomplish grafting in the rodents, then the monkeys. They utilized neural progenitor cells for the primate trials. They are hopeful that testing on human subjects is close to fruition, though there are still several biological challenges ahead. For now, the team is happy with their progress.
“We seem to have overcome some major barriers, including the inhibitory nature of adult myelin against axon growth,” said Tuszynski.