Researchers take step toward using stem cells to repair spinal cord injuries
Researchers at the University of California San Diego’s School of Medicine (UCSD) have taken a step toward using stem cells to repair spinal cord injuries, having successfully grafted human neural cells into the spinal cords of injured rhesus monkeys. The grafted cells produced new human neural connections and resulted in improved forelimb function. The team announced its findings in the February 26 issue of the journal Nature Medicine.
Earlier rat studies used transplanted human stem cells
Previously, research teams used rodent subjects when attempting to study the repair of significant spinal cord injuries. However, in this experiment, UCSD worked with rhesus monkeys to produce a better model for potential human treatments. Researchers first refined and developed new grafting techniques to accommodate significant central nervous system differences between primates and rodents. Close management of a host of primate-specific supportive factors had a significant positive impact on grafting success.
Previous research teams, both at UCSD and elsewhere, completed much of the work in developing primate-specific grafting techniques. A related team at UCSD conducted an earlier experiment using human stem cells in laboratory rats. For example, during that 18-month study, the rats began to show motor improvement after about a year. The team also noted that the transplanted cells maintained a rate of growth that was consistent with human development. That’s significant, given the substantial differences between rat and human development. Typical rat gestation last about 21 days. Comparatively, human gestation takes place over about 280 days.
To produce successful human stem cell grafts, researchers addressed a primate’s natural absence of growth promoting factors in mature nerve cells, and developed techniques that overcame the nerve’s inability to regenerate naturally.
Stem cell grafting and growth takes time
The team monitored the primate grafts over a period of nine months. During that time, the grafts both grew and developed new pathways to reach undamaged nerve cells on the other side of the injury. According to researchers, the monkeys began to display partial recovery of movement in their affected limbs. The team also documented the regeneration of corticospinal axons into the injury sites. This is essential to restore voluntary movement, and it is the first documented regeneration in primate subjects.
The development rate of neural stem cells is significant. Most neural stem cell studies to date have observed grafting and development over a period of weeks or months. The UCSD studies showed that the grafting and regeneration process occurs over a longer period of time.
Researchers are quick to caution that the process produced only a limited recovery of movement during the trial. They also say that the monkeys may have displayed additional recovery over a longer period of observation. The process of growing new nerve cells is time consuming and involves many factors. Additionally, a primate body does not naturally support nerve regeneration after birth.
The future of human stem cell transplant trials
Despite the apparent success of the process, the team is not yet ready to progress to human clinical trials. Before a human trial could proceed, researchers must develop at least one human stem cell line that the Food and Drug Administration will approve. Although the stem cells in the UCSD trials were not dental stem cells, it may be possible to form the same sort of neural stem cells from dental pulp. Additionally, researchers must fully assess other safety issues prior to seeking approval for a human clinical trial.
Nonetheless, the work is a valuable step towards the possibility of using stem cells to repair spinal cord injuries in humans. It demonstrates techniques to overcome the body’s response to nerve injuries, which does not naturally support nerve tissue regeneration.