The experiments creating the biggest buzz among spinal cord researchers are those involving fetal cell, stem cell or embryonic stem cell transplants. So far, most of the research is in animals, though some studies are beginning in people.
In all three methods, the idea is essentially the same: To implant in the damaged spinal cord immature cells that can be nudged to grow into many, perhaps all, of the thousands of different types of nerve cells in the body. The immature cells can also be genetically engineered to produce large quantities of the chemical messengers believed to stimulate new nerve growth.
Ideally, the cells would be transplanted into a patient within a week or two of injury, but the ultimate goal is to use them months or even years later to stimulate nerve growth.
In embryonic stem cell transplantation, cells are taken from embryos at the 8- to 12 cell-stage, says Dr. John W. McDonald, director of the spinal cord injury program at Washington University in St. Louis. These cells, isolated for the first time only a year ago, then differentiate into every type of cell in the body, including spinal nerve cells.
In fetal cell transplants, tissue is taken from the spinal cords of aborted fetuses. Researchers at the University of Florida are already trying this method in a few patients to see if it yields new nerve growth.
At Cedars-Sinai Medical Center in Los Angeles, researchers are gearing up for a study in which they would take nerve stem cells from the brains of patients with spinal cord injuries, grow them in large numbers in the lab, and re-inject them to trigger new nerve growth. Once thought non-existent in adults and still tough to identify in the lab, neural stem cells – presumably left over from fetal development – have been shown to exist in the brain in the lining of spaces called ventricles, in the hippocampus, a memory center, and in the spinal cord.
If the basic cell transplant strategy works in humans – and researchers should know in two to five years – it could eclipse everything else now in testing.
Already, researchers have been able to insert into neural stem cells “marker” genes that show where the cells migrate after being injected into animals and what kinds of nerve cells they become, says Dr. Evan Snyder, a neuroscientist at Children’s Hospital in Boston.
In fact, preliminary research shows that if human neural stem cells are injected into mice three or four days after a spinal cord injury, the cells move to exactly where they’re needed and start replacing the cells that were damaged, Snyder notes.
At a neuroscience meeting next month, McDonald’s team will present data showing that embryonic stem cells can restore function by replacing cells lost after spinal cord injury in rats, even if they’re transplanted as long as nine days later.