Spinal injuries are often permanent, but new research suggests such injuries may be healed, at least in part. Researchers were able to stimulate limb function in paralyzed mice by implanting human stem cells into their spinal cords. We're not close to repeating the test in people, but the study shows it may be possible some day with further research.

The University of California-San Diego team grafted human neural stem cells (NSCs) into the spinal cord injuries of mice who were purposely injured to impair the use of their front legs. The stem cells grew slowly, yet steadily, over the course of 18 months, retaining their original function despite being in a strange and challenging environment for an extended period of time. What’s more, eventually the rodents were able to use their front legs again.

"The bottom line is that clinical outcome measures for future trials need to be focused on long time points after grafting," said study researcher Mark Tuszynski in a recent statement. Relying on shorter time frames might produce misleadingly negative results considering how long it takes neural stem cells to develop, he added.

For the study, the team used H9 human NSCs, which are a type of stem cell derived from human embryonic stem cells, as commonly used in scientific research, the statement reported. They then grafted these human stem cells into the spinal injuries of mice. The researchers observed the rodents’ recovery over the course of 18 months, noting that significant cell growth did occur soon after grafting, and continued up to a year after the initial implantation.

The most important observation was that these cells were able to continue to do what they were designed to do—regrow neural cells—despite the fact that they were transplanted into an entirely different species. This suggests the cells have resilience and similar experiments may also work in human subjects.

We’re Not There Yet

Before you get too excited about these results, the researchers emphasized that there were a number of caveats. First, humans and mice are entirely different species, and though the results observed in the rodents are promising, we don't know if they could be repeated in people.

Also, the researchers observed that some astrocytes, star-shaped neural cells associated with electrical impulse transmission, did migrate from the original implantation site to other areas of the rodents. These brain cells are classified as glial cells, which are noted to lead to devastating and difficult to treat cancers when they are dysregulated, Harvard University reported. However, there were no tumors or abnormal growths observed in the mice in the study and the researchers are trying to figure out way to make sure cancer doesn't develop.

Ultimately, the team believe that these results stand as a good foundation on which to build further research.

“Success, it would seem, will take time," concluded Tuszynski.

Source: Lu P, Ceto S, Wang Y, et al. Prolonged human neural stem cell maturation supports recovery in injured rodent CNS. The Journal of Clinical Investigation . 2017