University of Wisconsin News:

http://www.news.wisc.edu/11063.html
Scientists infuse rat spinal cords with brain-derived human stem cells
(Posted: 4/19/2005)
Paroma Basu
Unveiling a delivery method that may one day help surgeons treat the
deadly neurodegenerative disease amyotrophic lateral sclerosis (ALS),
researchers at the UW-Madison have inserted engineered human stem cells
into the spinal cords of ALS-afflicted rats.

Reporting their work today (April 19) in the journal Human Gene Therapy,
the scientists directed certain types of neural stem cells to secrete a
neuron-protecting protein before injecting them into the rat spinal cord
where motor neurons reside. Motor neurons dictate muscle movement by
relaying messages from the spinal cord and brain to the rest of the body.
ALS causes the neurons to progressively decay and die.

Notably, the UW-Madison stem cell researchers did not work with human
embryonic stem cells, blank-slate cells that arise during the earliest
stages of development and can develop into any of the 220 tissue and cell
types in humans. Scientists have long regarded these cells as a crucial
ingredient in the quest to cure spinal injuries and neurodegenerative
disease.

Rather, the scientists worked with more specialized neural stem cells -
known as neural progenitor cells - that arise from primitive stem cells
during the first few weeks of human brain development. Unlike embryonic
stem cells, they can only develop into neural tissue and they are
incapable of living forever, as embryonic stem cells can. But the neural
progenitor cells are much more appropriate for clinical use because,
unlike embryonic stem cells, they can grow in the absence of animal
derivatives that are considered a potential source of contamination, says
co-author Clive Svendsen, a professor of anatomy based at the
university's Waisman Center, and a leading authority on neural progenitor
cells.

"This is the first study that shows that certain types of stem cells can
survive and release powerful protective proteins in the spinal cord of
rats with a genetic form of ALS," says Svendsen.

Once inside the brain or spinal cord, neural progenitor cells grow into
neuron-supporting stem cells called astrocytes. Some researchers believe
that ALS causes astrocyte malfunction, which in turn causes motor neurons
to degenerate and eventually die.

Several research groups around the world are trying to unleash the
therapeutic potential of neural progenitor cells. But the UW-Madison work
is the first "double whammy," says Svendsen, because the injected neural
progenitor cells develop into astrocyte-like cells and simultaneously
secrete glial cell-line derived neurotrophic factor (GDNF), a naturally
occurring protein that preserves motor neurons during development. The
twofold approach has a better chance of protecting healthy neurons that
haven't already succumbed to ALS, he says.

Approximately 5,600 people in the United States are annually diagnosed
with ALS. Also known as Lou Gehrig's disease, ALS is not well understood,
though mutations in the SOD-1 gene - or superoxide dismutase-1 - are
known to play a role. ALS attacks nerve cells in the brain and spinal
cord, and as motor neurons progressively die, the brain can no longer
initiate and control muscle movement.

The UW-Madison researchers tackled several technical barriers trying to
ensure that the progenitor cells correctly gather near the motor neurons
in the spinal cord, while continuing to pump GDNF once there, says Sandra
Klein, lead author of the study and a UW-Madison doctoral researcher.

But making GDNF-emitting stem cells was the first puzzle to grapple with.
Svendsen and his team approached the problem using a genetically
engineered viral structure known as a lentivirus. Collaborating with
Patrick Aebischer, a researcher in Switzerland, the scientists
manipulated the lentivirus' genetic machinery, directing it to secrete
GDNF. The team then infected neural progenitor cells with the
GDNF-pumping lentivirus. Once the cells were infected, the scientists
washed the virus away, leaving self-sustaining colonies of GDNF-producing
progenitor cells.

The next problem was actually getting the cells into the right location
of the ALS rat spinal cord.
"Nobody had shown that human progenitors could be delivered right into
the region of the dying motor neurons," says Klein, who chose to work
with rats because they have a larger spinal cord.

Klein bore into the base of the rat spine, using a micro-pipette, or tiny
dropping device, to deliver the progenitor cells into the bottom region
of the spinal cord where motor neurons are located. After months of trial
and error, Klein finally ascertained through staining tests that the
progenitor cells were indeed gathering near the neurons and releasing
GDNF in the area.

Svendsen says the approach could be regarded as a novel form of gene
therapy where progenitor cells are used as "mini pumps" to deliver
protein.

It is crucial now to see whether greater numbers of GDNF-bearing
progenitor cells can actually prolong the life of an ALS-ridden rat, says
Svendsen. If so, he aims to plan a human safety trial with a small group
of patients. Ordinarily, the researchers would first test the work in
primates, but good ALS primate models do not exist due to the ravaging
nature of the disease, he says.

Compared to small rats, humans will most likely require more extensive
spinal cord transplants, the researchers predict. If successful, a
similar progenitor cell protein delivery method could radically help to
combat several other ailments, including Huntington's disease,
Parkinson's disease and stroke.

The UW-Madison work was supported by the ALS Association and the UW
Foundation.
(View a full news release version of this story)

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