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THIS PAGE FROM TOP: RICHARD CARRASCO/KECK MEDICINE OF USC; GREG IGER/KECK MEDICINE OF USC. OPPOSITE: SOPHIE JACOPIN/SCIENCE SOURCEInstitute in Los Angeles. He worries that “having an
incorrect connection is worse than just doing nothing.”
Svendsen is more optimistic about his team’s work
involving human tests of a novel stem cell approach to
treat ALS, a degenerative motor neuron disease in which
cells that transmit messages from the brain and spinal
cord to the muscles wither or die.
Challenges in the field certainly remain. While recent
human trials have shown tantalizing promise, they’re
still at an early stage. Moreover, studies have involved
a relatively small number of patients, and scientists
aren’t sure what complications may emerge.
Even so, Charles Liu, the bioengineer and neurosur-geon heading the stem cell trial at USC, feels confident
about the overall direction of the research. “The idea
that you can restore function back to where it was lost
is relatively new,” he says broadly, not just concerning
stem cells. “This is the first time when all of us dared
think it might be possible to regenerate, restore and
repair.”RESTORING LOST FUNCTION
The modern era of regenerating brain function began
in the late 1980s and early ’90s with a battle against
Parkinson’s disease. The movement disorder stemsfrom the death of neurons that produce dopamine, a
neurochemical that dispatches messages to parts of
the brain that control motor skills and coordination.
People with Parkinson’s develop tremors, rigidity in
the limbs and loss of muscle control, and sometimes
exhibit signs of dementia.
To fight the disorder, Swedish researchers pioneered
the transplantation of fetal stem cells into the brain.
The fetal cells the researchers used came from the
brains of aborted fetuses 6 to 9 weeks old. Experts rea-
soned that since these cells had not yet fully matured,
there must be some way to coax them to transform
into the neurons that Parkinson’s destroys. Studies
published in 1992 showed that the grafts of fetal tissue
made a significant difference. In two cases, severely dis-
abled patients who had required round-the-clock care
before treatment were able to live independently again.
But scientists were stumped on how to best integrate
the cell grafts into the brain’s complex circuitry, where
they would be more targeted and do the most good.
Back then, the prevailing wisdom in neuroscience
was that adults can’t form new neurons. In 1998,
however, a team of American and Swedish scientists
announced their discovery that the human brain does
indeed generate them. It’s a process called neurogenesis,
in which cells continually divide and produce new ones.
This finding came on the heels of similar observations
in rodents, monkeys and birds. “The door has been
opened,” Fred Gage, the research team leader at the
Salk Institute for Biological Studies in San Diego, told
The New York Times at the time. The finding raised the
possibility of harnessing this regenerative capacity to
mend damaged brains, which could translate into more
effective treatments for Alzheimer’s and Parkinson’s.
But how? Acquiring fetal stem cells was proving dif-
ficult. “You needed eight aborted fetuses to get enough
tissue,” recalls Svendsen, who was working on his
postdoc at the University of Cambridge in his native
England at the time. “It struck me as impractical.Kris Boesen, who was paralyzed from the neck down after
a car accident, lifts a dumbbell to demonstrate his recovery.Charles Liu, a neurosurgeon at USC’s Keck School
of Medicine, performed the procedure on Boesen.