Good article from Scientific American, on some problems with adult 
stem cell research.

June 12, 2007   
 
Can Adult Stem Cells Do It All?   
 
Scientists may have turned mouse skin cells into embryolike stem 
cells, but prior claims for the power of adult cells have yet to 
stand the test of time   
 
By JR Minkel    
 
Stem cells have been hailed by scientists as the great hope to one 
day prevent, halt and even reverse damage from diabetes, spinal cord 
injuries and degenerative diseases like Parkinson's and Alzheimer's. 
Stem cells obtained from human embryos seem to offer the best chance 
of new therapies, because unlike other stem cells they have the 
ability to morph into almost any type of tissue. But researchers 
complain that political roadblocks are keeping them from determining 
the full potential of these cells. 

Six years ago, President Bush limited federally funded research to 
about 20 viable lines of cells that had been extracted from embryos 
prior to August 9, 2001. The stem cell community has repeatedly 
called for the restrictions to be lifted, charging that the 
designated cell colonies have been compromised or corrupted and that 
failure to ease the ban is hobbling U.S. efforts to discover new life-
saving treatments. But opponents say such research is immoral, 
because embryos must be destroyed to obtain their cells. 

Last week, Congress sent legislation to Bush that would allow 
federally funded scientists to study cells from frozen embryos that 
fertility clinic patients no longer need and have chosen to donate 
instead of discard. The Stem Cell Research Enhancement Act of 2007 
also spells out ethical guidelines governing such research. 

Bush immediately renewed his pledge to veto the bill (as he did 
similar legislation that reached his desk last year)—and it is 
questionable whether the Senate can muster the votes to override it. 
The Senate passed the measure in April by a 63-to-34 margin—just four 
votes shy of the two thirds majority needed to nix a veto—on a day 
when two supporters of the bill were absent. 

In vetoing the measure, Bush said it would be "a grave mistake" 
for "American taxpayers [to] be compelled to support the deliberate 
destruction of human embryos." 

Critics argue further that embryonic stem cell research is 
unnecessary because stem cells from adults are purportedly just as 
promising. In fact, just a day before the House vote last week, 
researchers announced that they had coaxed plain old skin cells taken 
from adult mice to mimic embryonic cells, which—if they learn to do 
the same for humans—could offer a simple and seemingly less 
controversial way to create scores of stem cells. 

Although researchers said the finding did not negate the need for 
studies on true embryonic stem cells, critics seized on it as further 
proof that such research is superfluous: If adult cells could be 
transformed into embryolike cells, they argued, then why not use them 
instead of destroying embryos? 

The claim echoes those made many times in the emotional debate over 
federal funding of new human embryonic work. In particular, opponents 
of embryonic stem cell research have repeatedly pointed to the 
supposed power of stem cells extracted from the adult body, which in 
the hands of at least one laboratory seemed to nearly match that of 
embryonic stem cells. 

In contrast to last week's study other laboratories have never 
reproduced the dramatic findings on which such arguments are based. 
And in the past six months investigations have exposed strange flaws 
in the data from one lab that claimed to have successfully 
manipulated adult stem cells to act like embryonic tissue. 

At first blush, a flurry of unreproducible results might suggest 
problems within the field itself. 

In recent interviews top stem cell experts said that the failures 
reflect the field's high public profile and its politicization, which 
obscure real progress. "I hate it when [big claims go unreplicated], 
because it makes our field look like a field full of shams and 
frauds," says stem cell biologist Irving Weissman of Stanford 
University. 

Conventional wisdom has long held that adult stem cells are only 
capable of forming their tissue of origin. Researchers have isolated 
stem cells from only some of the body's organs and tissues, including 
the blood, brain, skeletal muscle, heart muscle and most recently 
from skin. They hope to discover whether stem cells also exist for 
other key organs such as the pancreas, liver and spinal cord. Much 
adult stem cell research focuses on identifying the genes and 
molecules that define such cells and allow them to replenish 
themselves indefinitely as they produce the various cell types of 
their organs—the defining characteristics of a stem cell. Learning to 
grow and manipulate adult stem cells in the lab might also allow 
researchers to create tissue regenerating treatments from them. 

A series of headline-grabbing results in the late 1990s and early 
this decade suggested that specific adult stem cells such as those 
from the blood seemed able to exceed expectations and transform 
themselves into other organs and tissues. When engineered to glow 
green and injected into mice, these studies revealed glowing cells in 
unexpected organs such as the brain, heart and liver. The discoverers 
dubbed the process transdifferentiation. 

Within a few years, however, laboratories that tried to replicate the 
findings either failed or came up with simple explanations for them 
such as fusion between the injected cells and those in the identified 
organs. A September 2002 follow-up study found no evidence for 
widespread transdifferentiation of blood-forming stem cells in brain, 
liver, kidney, gut and other tissues. Transdifferentiation may occur, 
but if so it must be a rare event, says stem cell and cardiovascular 
researcher Kenneth Chien of the Harvard Stem Cell Institute. 

Scientists were even more stunned in July 2002 when researchers led 
by stem cell biologist Catherine Verfaillie at the University of 
Minnesota reported that bone marrow–derived cells they had injected 
into young embryos contributed to all three embryonic layers, just as 
embryonic stem cells would do. 

Verfaillie and colleagues were trying to grow stem cells extracted 
from rodent mesenchyme, a component of bone marrow that contributes 
to fat, skeleton and muscle. Bone marrow cells do not normally grow 
in the lab, but the team reported that by carefully controlling the 
amount of oxygen the cells received along with other growth 
conditions, they could keep the cells alive for at least a year. In 
the process, the cells seemed to turn into something else, the 
experiments indicated. Rather than showing up only in the mesoderm, 
or middle layer of the embryo where future mesenchymal cells reside, 
the cells had spread to the two adjacent layers, which form other 
tissues such as skin, brain and gut, according to the group's report 
in Nature. 

The researchers speculated that their cells, which they called 
multipotent adult precursor cells (MAPCs), might have regressed to a 
more primitive state in culture or were left over from embryonic 
development. "That started a lot of excitement that there might be 
these adult stem cells that had the potential of embryonic stem 
cells,'' says stem cell researcher Amy Wagers of the Joslin Diabetes 
Center in Boston. 

Hoping to confirm the result by replicating it, other laboratories 
tried unsuccessfully to grow the cells. Wagers, then a postdoctoral 
fellow in the Stanford University lab of stem cell biologist Irving 
Weissman, spent a week in Verfaillie's lab in 2002 trying to learn to 
culture MAPCs. "They're very fussy," she says. Even Verfaillie, who 
announced she would teach a course on growing the cells in lab 
dishes, had problems culturing them at times, according to Weissman. 

(con't)

----------------------------------------------------------------------
To sign-off Parkinsn send a message to: mailto:[log in to unmask]
In the body of the message put: signoff parkinsn