Biomedical Engineering Reference
In-Depth Information
sophisticated knowledge of the workings also of the human
body and mind. Such knowledge of how things work often
leads to new technological powers to control or alter these
workings, powers generally sought in order to treat
human disease and relieve suffering. But, once available,
powers sought for one purpose are frequently usable for
others. The same technological capacity to influence and
control bodily processes for medical ends may lead
(wittingly or unwittingly) to non-therapeutic uses,
including ''enhancements'' of normal life processes or even
alterations in ''human nature.'' Moreover, as a result of
anticipated knowledge of genetics and developmental
biology, these transforming powers may soon be able to
transmit such alterations to future generations.
of that species (
Homo sapiens,
sheep, cat, dog, etc.) is
produced. Cloning is a type of reproduction wherein off-
spring result not from the chance of the union of ovum and
sperm (sexual reproduction); rather it results from the
deliberate replication of the genetic makeup of another
single individual (asexual reproduction).
Human cloning is accomplished by introducing the
nuclear material of a human somatic cell (donor) into an
oocyte (egg) that has had its own nucleus removed or
inactivated. This yields a product with a human genetic
constitution virtually identical to the donor of the somatic
cell. This technique is known as SCNT. Since SCNT uses
human genetic material, the developing embryo is of the
species
H. sapiens.
Bioethics Question: Is research using human pluri-
potent stem cells ethical?
So, let us consider some of these technological areas
important to engineers and their attendant bioethical
concerns.
A ''pluripotent'' cell can be differentiated into more than
one alternative type of mature cell; so it is able to pro-
duce all the cell types of the developing organism's body.
Thus, a pluripotent stem cell has the same functional
capacity (i.e., pluripotency) as an embryonic stem cell,
though it does not necessarily share the same origin.
''Stem cell research'' involves isolating human embryonic
stem cells from embryos at the blastocyst stage
(
Figure 8.2-1
) or from the germinal tissue of fetuses
(
Figure 8.2-2
). As of this writing, such harvesting kills the
donor. The embryonic stem cells have been harvested
from
in vitro
fertilization (IVF). Human adult stem
Cloning and stem cell research
[C]loning represents a turning point in human
history
d
the crossing of an important line separating
sexual from asexual procreation and the first step
toward genetic control over the next generation.
It thus carries with it a number of troubling
consequences for children, family, and society.
Leon R. Kass, Chair, The President's Council on Bioethics
8
Researchers in the United States asserted in late 2001
that they were able to produce the first cloned human
embryos, merely reaching a six-cell stage before the cells
stopped division and died. In the meantime, a number of
fertility specialists had declared a strong intent to clone
human beings. In response to the technical and societal
uncertainties and anxieties, the United States Congress
had already begun in 1998 to consider these issues, with
the House of Representative in July 2001 passing a strict
ban on all human cloning, including the production of
cloned human embryos. Since then, a number of cloning-
related bills have been considered in the US Senate and
several state legislations. Numerous nations have banned
human cloning, with the United Nations considering an
international convention on the issue. It suffices to say
that the political and societal aspects of cloning are as
challenging as the technical demands.
The biology of cloning begins with the ovum (egg). A
human ovum consists of a single gamete cell, having only
23 active chromosomes. This means that the sex has not
yet been determined. Once the ovum contains a complete
nucleus from any species that is activated and developing -
whether that has occurred by sexual fertilization or by
asexual somatic cell nuclear transfer (SCNT) - an embryo
Zona pellucida
Inner
Cell mass
Blastocoele
(A)
(B)
Trophoblast
Inner cell mass
Blastocoele
(C)
Figure 8.2-1 Three stages of blastocyst formation in the pig,
drawn from sections to show the formation of the inner cell mass.
Adapted from: The President's Council for Bioethics, 2004,
Monitoring Stem Cell Research, Appendix A, Washington, DC.
