The term cloning
is used by scientists to describe many different processes that involve making
duplicates of biological material. In most cases, isolated genes or cells are
duplicated for scientific study, and no new animal results. The experiment that
led to the cloning of Dolly the sheep in 1997 was different: It used a cloning
technique called somatic cell nuclear transfer and resulted in an
animal that was a genetic twin -- although delayed in time -- of an adult
sheep. This technique can also be used to produce an embryo from which cells
called embryonic stem (ES) cells could be extracted to use in
research into potential therapies for a wide variety of diseases.
Thus, in the
past five years, much of the scientific and ethical debate about somatic cell
nuclear transfer has focused on its two potential applications: 1) for
reproductive purposes, i.e., to produce a child, or 2) for producing a source
of ES cells for research.
The technique
of transferring a nucleus from a somatic cell into an egg that produced Dolly
was an extension of experiments that had
been ongoing for over 40 years. In the simplest terms, the technique used to
produce Dolly the sheep - somatic cell nuclear transplantation cloning -
involves removing the nucleus of an egg and replacing it with the diploid
nucleus of a somatic cell. Unlike sexual reproduction, during which a new
organism is formed when the genetic material of the egg and sperm fuse, in
nuclear transplantation cloning there is a single genetic "parent."
This technique also differs from previous cloning techniques because it does
not involve an existing embryo. Dolly is different because she is not
genetically unique; when born she was genetically identical to an existing
six-year-old ewe. Although the birth of Dolly was lauded as a success, in fact,
the procedure has not been perfected and it is not yet clear whether Dolly will
remain healthy or whether she is already experiencing subtle problems that
might lead to serious diseases. Thus, the prospect of applying this technique
in humans is troubling for scientific and safety reasons in addition to a
variety of ethical reasons related to our ideas about the natural ordering of
family and successive generations.
Several
important concerns remain about the science and safety of nuclear transfer
cloning using adult cells as the source of nuclei. To date, five mammalian
species -- sheep, cattle, pigs, goats, and mice -- have been used extensively
in reproductive cloning studies. Data from these experiments illustrate the
problems involved. Typically, very few cloning attempts are successful. Many
cloned animals die in utero, even at late stages or soon after birth,
and those that survive frequently exhibit severe birth defects. In addition,
female animals carrying cloned fetuses may face serious risks, including death
from cloning-related complications.
An additional
concern focuses on whether cellular aging will affect the ability of somatic cell
nuclei to program normal development. As somatic cells divide they
progressively age, and there is normally a defined number of cell divisions
that can occur before senescence. Thus, the health effects for the resulting
liveborn, having been created with an "aged" nucleus, are unknown.
Recently it was reported that Dolly has arthritis, although it is not yet clear
whether the five-and-a-half-year-old sheep is suffering from the condition as a
result of the cloning process. And, scientists in
The
announcement of Dolly sparked widespread speculation about a human child being
created using somatic cell nuclear transfer. Much of the perceived fear that
greeted this announcement centered on the misperception that a child or many
children could be produced who would be identical to an already existing
person. This fear is based on the idea of "genetic determinism" --
that genes alone determine all aspects of an individual -- and reflects the
belief that a person's genes bear a simple relationship to the physical and
psychological traits that compose that individual. Although genes play an
essential role in the formation of physical and behavioral characteristics,
each individual is, in fact, the result of a complex interaction between his or
her genes and the environment within which he or she develops. Nonetheless,
many of the concerns about cloning have focused on issues related to
"playing God," interfering with the natural order of life, and
somehow robbing a future individual of the right to a unique identity.
Several groups
have concluded that reproductive cloning of human beings creates ethical and
scientific risks that society should not tolerate. In 1997, the National
Bioethics Advisory Commission recommended that it was morally unacceptable to
attempt to create a child using somatic cell nuclear transfer cloning and
suggested that a moratorium be imposed until safety of this technique could be
assessed. The commission also cautioned against preempting the use of cloning
technology for purposes unrelated to producing a liveborn child.
Similarly, in
2001 the National Academy of Sciences issued a report stating that the
The cloning
debate was reopened with a new twist late in 1998, when two scientific reports
were published regarding the successful isolation of human stem cells. Stem
cells are unique and essential cells found in animals that are capable of
continually reproducing themselves and renewing tissue throughout an individual
organism's life. ES cells are the most versatile of all stem cells because they
are less differentiated, or committed, to a particular function than adult stem
cells. These cells have offered hope of new cures to debilitating and even
fatal illness. Recent studies in mice and other animals have shown that ES
cells can reduce symptoms of Parkinson's disease in mouse models, and work in
other animal models and disease areas seems promising.
In the 1998
reports, ES cells were derived from in vitro embryos six to seven days
old destined to be discarded by couples undergoing infertility treatments, and
embryonic germ (EG) cells were obtained from cadaveric fetal tissue following
elective abortion. A third report, appearing in the New York Times,
claimed that a
For those who
believe that the embryo has the moral status of a person from the moment of
conception, research or any other activity that would destroy it is wrong. For
those who believe the human embryo deserves some measure of respect, but disagree
that the respect due should equal that given to a fully formed human, it could
be considered immoral not to use embryos that would otherwise be destroyed to
develop potential cures for disease affecting millions of people. An additional
concern related to public policy is whether federal funds should be used for
research that some Americans find unethical.
Since 1996,
Congress has prohibited researchers from using federal funds for human embryo
research. In 1999, DHHS announced that it intended to fund research on human ES
cells derived from embryos remaining after infertility treatments. This
decision was based on an interpretation "that human embryonic stem cells
are not a human embryo within the statutory definition" because "the
cells do not have the capacity to develop into a human being even if
transferred to the uterus, thus their destruction in the course of research
would not constitute the destruction of an embryo." DHHS did not intend to
fund research using stem cells derived from embryos created through cloning,
although such efforts would be legal in the private sector.
In July 2001,
the House of Representatives voted 265 to 162 to make any human cloning a
criminal offense, including cloning to create an embryo for derivation of stem
cells rather than to produce a child. In August 2002, President Bush,
contending with a DHHS decision made during the
Prepared by Kathi E. Hanna, M.S., Ph.D.,
Science and Health Policy Consultant