Stem cells take knocks
Negative results provide reality check
for stem-cell therapies.
06
September 2002 HELEN PEARSON
 |
| Blood
stem cells' properties
are called into question.
|
| ©
SPL |
|
|
Fresh concerns have been raised over the usefulness
of adult stem cells after a spate of papers
throwing doubt on their regenerative abilities.
Reports claiming that stem cells from adults
are capable of repairing every tissue in the
have raised hopes that these cells could prove
a panacea for conditions from Parkinson's to
heart disease.
But the recent rash of studies dispute these
claims. Stem-cell biologist Irving Weissman
of Stanford University in California has now
dealt a blow to the suggested repair properties
of blood stem cells.
All stem-cell experiments need to be repeated
before clinicians pursue potential therapies,
Weissman says. Some trials are already underway.
"I worry that non-experts just accept and practise
it," he says. "We do not have solid science
for that."
Experiments from researchers outside the stem-cell
establishment are under particular scrutiny.
Scientific journals may also be at fault, says
stem-cell biologist Tariq Enver of the Institute
of Cancer Research in London, UK. In their eagerness
to publish the hottest papers, "perhaps people
weren't as rigorous as they ought to have been",
he says.
Cell division
Scientists agree that some cells are 'multipotent'
- capable of making many other tissue types.
What they are squabbling over is whether these
cells exist naturally in the adult body, or
whether they are artefacts of lab treatments.
This is crucial if the right cells are to be
selected for stem-cell therapies.
| Transdifferentiation
may be vastly overblown
|
| Stuart
Orkin
Harvard Medical School
|
|
|
Last year, for example, a celebrated paper
by Diane Krause of Yale University and co-workers
reported that a single stem cell from bone marrow
that normally makes only blood had transdifferentiated
- switched to making liver, lung and skin1.
Weissman and his team dispute those results.
Using slightly different methods they isolated
a single mouse blood stem cell, injected it
into mice and tracked its progeny with a green
fluorescent protein. They found that, apart
from blood, it made only eight cells of any
other tissue in three mice2.
"It's very difficult to compare one [experiment]
with another," comments Stuart Orkin, who studies
blood stem cells at Harvard Medical School in
Boston. But "transdifferentiation may be vastly
overblown", he agrees.
The slew of negative results do not spell the
end for stem-cell therapies - they merely provide
a reality check.
Other cells in the bone marrow or elsewhere
may be genuinely multipotent; one of these cells
could explain Krause's results, she herself
admits. But some suspect that these stem-cell
types may be very rare, making them harder to
extract and use in treatments.
Alternatively, cells may be converted into
multipotent ones in the lab. Some think that
this phenomenon explains findings earlier this
year from Catherine Verfaillie at the University
of Minnesota, Minneapolis3.
She cultured her adult stem cells for weeks
before showing that they are multipotent when
transplanted into mice. Cultured cells may,
however, have a greater risk of forming cancers
or otherwise behaving oddly.
Many in the field now want more rigorous experimental
standards for all stem-cell experiments. "We
need to step back and do definitive experiments
rather than flashy ones," says Orkin. |
