Biomedical Engineering Reference
In-Depth Information
“stembrid” technique. He has applied for a patent on the so-called
stembrid
method (US 2004/0259249)
insisting that he does not intend to stop other
researchers from using the method (
10
). However, Verlinsky did not reveal the
details of his technique, which were later on patented. It is known that other
teams are trying to attach cells to a surface and spin them until the denser nucleus
is forced out (
11
). The cells from adults are taken afterwards and fused with the
enucleated ESCs (
11
). The idea is that the cytoplasm of an enucleated ESC will
reprogram the donor nuclei, turning the fused cell into an ESC, too. The result,
as Verlinsky told at a Conference in an oral presentation on preimplantation
genetics in London, is new lines of ESCs that are genetically identical to the
adult donor (
11
). He called the new cells
stembrids.
How one could be sure that
the stembrids contain only the genetic material of the adult donors? Verlinsky's
response was that he fused male adult cells with a female ESC line (not the egg),
with resulting male cells. However, his team has not yet tested the HLA proteins
on the cell surface to prove that the stembrids are an immune match for the adult
donors. By contrast, Hwang's team has shown that the ESCs derived via thera-
peutic cloning have the surface markers that make them compatible with the
donor's immune system. The biggest question, though, is whether the stembrids
really are true ESCs. Verlinsky stated (
11
) that cells express a number of ESC
markers, but we do not know which of them. His team has also shown that cells
can differentiate into a number of cell types, including heart muscle cells, neu-
rons, and blood stem cells, although the results have not yet been published.
Apparently, far more detailed studies will be needed in the future to prove this
method, especially since it is not published, yet. Besides looking at further cell
surface markers, Verlinsky's team was to show that, like true ESCs, the stem-
brids are capable of forming cancers called teratomas, which contain a mixture
of different cell types, when injected into immune-compromised mice (
12
) . Until
these studies are done, we must remain very skeptical. Potentially, these result-
ing stem cells could be stockpiled for use in researching any number of genetic
diseases, including stem cells that will specifically develop seven diseases
(including two forms of muscular dystrophy, thalassemia, Fanconi anemia, frag-
ile X syndrome, Marfan syndrome, and a type of neurofibromatosis). Researchers
could choose cells directly affected by a disease (parts of the brain impaired by
Fragile X) without having to take samples of living tissue from people who suf-
fer from the disease.
These ESCs are also far superior to the cells of animals with diseases similar
to those of humans (
11
). Verlinsky's method would have huge advantages if it
really did work. Obtaining the large number of fresh human eggs needed for
therapeutic cloning is not possible for legal reasons in many countries and is very
expensive in countries where it is legal, such as the USA. By contrast, there is a
virtually limitless supply of existing ESCs for fusion with adult cells. With
Verlinsky's method, federally funded researchers could try to derive stembrids
using already approved ESC lines. However, Verlinsky died recently, and the
question is how quickly the research can go without him.
