Stem Cell Transplants Help Repair Spinal Cord Injuries in Rats
Nov. 29, 1999 (Indianapolis) -- Between 250,000 and 500,000 Americans have
spinal cord injuries, and because many of them are young, they will spend
decades in a wheelchair unless new treatments can be developed. Research in
rats that is being reported in the December issue of the journal Nature
Medicine may lead to new therapies in humans.
The neurons that make up the spinal cord have extensions, called axons, that
resemble telephone wires and carry messages between the brain and the rest of
the body. Traumatic injury can kill neurons or interrupt the axon connections,
causing a loss of function. Unlike the heart, parts of the adult spinal cord do
not survive transplantation.
In this study, the researchers used embryonic stem cells which have the
potential to become any cell type in the body depending on what chemical
signals they get when they mature. The researchers hoped that by triggering
embryonic stem cells to become nerve cell precursors and then transplanting
these precursor cells into the injured area they could promote healing of the
"Establishing regenerative therapies that promote substantial
improvements in locomotion when instituted after the injury process is complete
has been a difficult obstacle," says John W. McDonald, MD, PhD. McDonald is
an assistant professor of neurology at Washington University School of Medicine
in St. Louis. "This is a key threshold that had not before been
The researchers treated rats nine days after an injury to the spinal cord by
transplanting stem cells from mice into the injury site. In another control
group, the rats underwent a fake operation and were given only the culture
medium with no cells.
Two to five weeks following the procedure, the researchers found various
markers that showed the transplanted cells were alive and functioning. They
also used special techniques to identify any axons that had grown from the
transplanted cells. At two weeks, transplanted cells had not only filled the
cavity at the point of injury, but had migrated up to 1 cm in each direction.
By the five week follow-up, the cells were not as dense but the injured regions
still contained mouse axons. None of the cells had developed into tumors.
The researchers also looked at the motor skills of transplanted rats vs. the
controls. One month after the surgery, the control rats were not able to move
their hind limbs in a coordinated fashion and the limbs could not support their
bodies. The hind limbs of the treated animals had regained some movement and
were able to partially support the weight of the rats' bodies.
"Their walking certainly wasn't normal," says McDonald. "But
this functional recovery was especially encouraging because the cells were
transplanted nine days after the spinal cord injury -- a time period that had
not yet been explored."