SCIENCE
Revisiting Stem Cells
By Dr. Rizwana Rahim
Chicago, IL
Stem cell research
had an important anniversary last week (9 August).
Not as much of any specific advance in research
as of the restrictions placed on it.
Perhaps the best way to update my article on ‘Stem
Cells: Science and Ethics’ that appeared little
over a year ago in the Pakistan Link (24 June 2005,
http://www.pakistanlink.com/Commentary/2005/Jun05/24/02.HTM
) would be to say: The politics still drives the
science in this area, while the science –
enormously complicated, to begin with – has
much unrealized potential for cell therapy.
Stem cells are unlike any other kinds of cells in
the body: they are unspecialized cells, which are
capable of dividing for long without any change,
but they can become or grow into any cell in any
organ (about 200 tissues, including heart, brain,
or skin) and perform specialized functions there
(i.e., their pluri-potency or plasticity). In humans,
they were first isolated in 1998 from an early embryo
(or blastocyst) and successfully grown in the laboratory.
Any group of cells that are so maintained for longer
than 6 months are considered an established ‘cell
line’, and till 2001 there were about 78 such
cell lines in the world.
Most efficient stem cells are present in early (3-5
day-old) embryo, a microscopic hollow ball, consisting
of a trophoblast (outer layer), blastocoel (the
hollow cavity), and an inner cell mass (about 30
stem cells) in blastocoel (See Figure 1). Most human
embryonic stem cells (HESC) are created with embryos
from in-vitro fertilization (IVF) clinics where
they are kept frozen.
HESC procedures destroy the embryo, which is the
major source of moral and ethical objections from
various conservative groups, besides the President.
The fact that these embryos, willing created by
couple with reproductive difficulties, were leftover
and would eventually be destroyed doesn’t
appease the objections. Even in reviving them for
the initial IVF purpose, some will be lost.
Five years ago, President Bush restricted federal
funding for HESC research to only those HESC lines
created by the date of that announcement (9 August
2001), provided these lines were derived from an
embryo created for reproductive purposes, but no
longer needed, and obtained after informed consent
of the donor who received no financial inducement
for the purpose. This reflected the pro-life, conservative
pressure from groups. Initially, under this restriction,
only about 78 HESC lines were eligible. These restrictions
do not, however, affect research supported by private
funds, but there can be no commingling of federal
funds in any shape or form. For institutions that
use both sources of research funds, this was an
enormous burden -- creating separate airtight compartments
for federal and private research.
The other shoe fell when it became clear that more
and more eligible HESC lines were so contaminated
(apart from being ‘old’ and weak) that
many scientists have serious doubts if the information
and material obtained from them could ever be safely
used for therapeutic and other purposes in humans.
Now only about 21 HESC lines are eligible, which
seriously limits genetic diversity. According to
a 2003 survey, there are about 400,000 unwanted
IVF embryos in the US. Congress recently passed
a bill that would have included leftover IVF embryos
donated for federal funding, but the President vetoed
it.
There are other sources for stem cells, involving
procedures that do not involve an embryo, and thereby
wouldn’t upset the conservative groups: (i)
from blood, skin and brain (or adult stem cells),
which can become specialized, but only into a limited
number of cell types, and they are not easy to grow
in culture, (ii) from umbilical cord which contains
some stem cells that can grow into heart, liver,
brain, bone, or cartilage, but umbilical cord is
neither long nor does it contain a big supply of
stem cells, and (iii) by somatic cell-nuclear transfer
(SCNT) techniques (similar to those used in creation
of ‘Dolly’ the sheep), in which a skin
cell is fused with an egg from which its nucleus
has been removed (or enucleated), but success-rate
in this is very low, requiring numerous fresh human
ova which would be impractical, and it hasn’t
been tried yet in humans.
Frustration has led some prominent US research groups
to migrate to UK, Singapore and Taiwan. California,
Connecticut and other states are trying to provide
additional funding to stem the outbound tide.
Some new strategies are being developed. Harvard
University is trying to develop 100 new HESCs from
IVF embryos, using private funds, in addition to
the SCNT procedures toward the same end. Claims
by South Korean researchers of success through SCNT,
later found to be not true, was a serious blow to
the effort. A Kyoto University team now claims that
treating skin cells by different growth factors
turns them into an embryo-like entity that can provide
stem cells. If true, this would bypass human embryos
and make the emotional-moral argument over HESC
moot. No matter the success so far or the prospects,
the major hurdle still remains: human trials to
test the worth of even the most successful procedures
in animals.
Regardless of the prospects of HESCs for regenerative
therapy, they will feature big in the mid-term elections.
This issue has for once united the Democrats with
a split in the Republican ranks!
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