Biomedical Engineering Reference
In-Depth Information
derive undifferentiated embryonic stem cells (ES cells) from fetal spinal cord tissue
and then mature them into cells that are suitable to implant into the damaged spinal
cord [
16,
17
]. When using ES cells, researchers have two options: they can treat ES
cells, allowing them to mature into CNS cells in vitro before transplantation, or they
can directly implant differentiated cells and depend on signals from the brain mature
the cells. This technique became possible when Reynolds and Weiss found that stem
cells taken from the brain could be propagated in vitro. This allowed labs to dupli-
cate what occurs naturally in the brain, and attempt to use the product to regrow the
damaged cells.
In December of 1999 McDonald and colleagues from Washington University
School of medicine successfully implanted ES cells in laboratory rats. McDonald
induced thoracic spinal cord injury in rats using a metal rod 2.5 mm in diameter
resulting in paralysis [
80
]. Nine days after the injury McDonald and colleagues
transplanted roughly 1 million ES embryoid bodies pretreated with retinoic acid
into the syrinx that had formed around the contusion. During the 9 days that passed
between injury and transplantation, all the standard events following a spinal cord
injury occurred. At the time of injury some cells died immediately, followed by a
second wave of apoptosis within the first 24 h [
80
]. The center of the bruised spine
filled with fluid becoming a cyst referred to as syrinx. McDonald injected the ES
cells into this cavity. Two weeks after the transplantation ES stem cells filled the
area normally occupied by glial scarring. After 5 weeks the stem cells had migrated
further away from the implantation site. Although a number of them had died, there
was still enough for the rats to have a growing supply of neurons and glial cells.
Most of the surviving cells were oligodendrocytes and astrocytes, but some neurons
were found in the middle of the cord. The rats regained limited use of their legs.
Paralysis had been cured.
McDonalds work in 1999 represented new successes in stem cell technology, but
there are still many years of work ahead of us before any of this technology can be
tested in humans. A major obstacle remains: although scientists are achieving
results, they do not understand the factors responsible for what occurs. In McDonalds
study, the regaining of functions could result from the few differentiated neurons.
Another possibility could be that the high differentiation of oligodendrocytes remy-
elinated enough axons to reestablish communication. Or perhaps functions regained
due to ES cells producing growth factors—more research will have to be done
before these options are narrowed down. Additional to unclear understanding of the
process, other complications exist. Any introduction of foreign cells into the body
triggers the immune system. ES cells would not simply be accepted into the host
CNS. McDonald used cyclosporine to prevent rejection in the rats, but things get
more complicated when testing begins on humans. The brain and spinal cord are
complex, mysterious realms of the body—until science can predict the exact affect
of evolving technologies, no testing on humans can occur.
A major motivation behind spinal cord research has been Christopher Reeve
[
91
]. Injured in a horseback riding incident, Christopher Reeve suffered a cervical
spinal cord injury that left him quadriplegic. Thus, he began the Christopher Reeve
Paralysis Foundation (CRPF). CPRF funds research to treat or cure paralysis result-
ing from spinal cord injury or other CNS disorders. CPRF supports a Research
