October 2017 Discover

You’re not going to go around collecting aborted fetuses
for thousands of patients.” And although using fetal
stem cells wasn’t controversial in Sweden, it was in the
United States.
The next logical step was to figure out how neurons
are generated and use them to repair or replace dam-
aged cells. Embryonic stem cells seemed to offer a solu-
tion. Culled from embryos barely 4 or 5 days old, these
cells are versatile shape-shifters that can mature into
any type of cell in the body — a trait that’s made them
crucial to research. And neural embryonic stem cells are
more targeted; in the formative stages of brain develop-
ment, they can be chemically coaxed into generating
neurons that have a host of different functions. Plus,
neural stem cells can migrate to brain regions where
they’re needed most.
Although British researchers had discovered embry-
onic stem cells in laboratory animals in 1981, it wasn’t
until 1998 that a Wisconsin team announced it had iso-
lated stem cells from human embryos for the first time.
It was an achievement many thought would quickly
usher in medical advances.

Svendsen, who joined the Cambridge faculty in 1998,

was inspired by this work and thought it could apply

to his Parkinson’s research. He began looking at how

to transform stem cells into neurons that would pump

out dopamine. He ran a small pilot study of five people

with Parkinson’s. Svendsen injected into their brains a

protein known to enhance neural development, called

glial cell line-derived neurotrophic factor (GDNF). The

treatment stopped dopamine-producing neurons from

dying, and the patients’ motor skills markedly improved.

Meanwhile, outside forces were derailing promising

studies. In the U.S., the use of embryonic stem cells,

often derived from embryos discarded by in vitro fertil-

ization clinics, became a flashpoint of intense political

debate. This led to a near-total ban in 2001 of their use

in government-funded research, an act that held back

advances by about five years, scientists say. Research

ground to a virtual standstill because of the lack of

institutional and financial support, and the onerous

restrictions on how research could be done.

In 2006, Japanese scientists figured out how to repro-

gram specialized cells, such as those in skin, so that they

October 2017^ DISCOVER^35

“The idea that you can restore function back to where

it was lost is relatively new,” Charles Liu 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.”

Cell Transformation

The promise of stem cells is their ability to become any cell in the

body. When treating brain injuries, the stem cells can become neurons

(which transmit information throughout the body), astrocytes (which

help maintain the central nervous system) or oligodendrocytes (which

protect nerve fibers).

Produce neuronal

precursor cells

Some neuronal

precursor cells die off

Astrocytes

Neurons

Oligodendrocytes

Neural stem cells

Produce more

stem cells