Human cloning is the creation of a genetically identical copy (or
clone
Clone or Clones or Cloning or Cloned or The Clone may refer to:
Places
* Clones, County Fermanagh
* Clones, County Monaghan, a town in Ireland
Biology
* Clone (B-cell), a lymphocyte clone, the massive presence of which may indicate a pathologi ...
) of a
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
. The term is generally used to refer to artificial human
cloning, which is the reproduction of human
cells and
tissue. It does not refer to the natural conception and delivery of
identical twins. The possibility of human cloning has raised
controversies. These ethical concerns have prompted several nations to pass
laws
Law is a set of rules that are created and are enforceable by social or governmental institutions to regulate behavior,Robertson, ''Crimes against humanity'', 90. with its precise definition a matter of longstanding debate. It has been vario ...
regarding human cloning.
Two commonly discussed types of human cloning are ''therapeutic cloning'' and ''reproductive cloning''.
Therapeutic cloning would involve cloning cells from a human for use in medicine and transplants. It is an active area of research, but is not in medical practice anywhere in the world, as of . Two common methods of therapeutic cloning that are being researched are
somatic-cell nuclear transfer and (more recently)
pluripotent stem cell induction.
Reproductive cloning would involve making an entire cloned human, instead of just specific cells or tissues.
History
Although the possibility of
cloning humans had been the subject of speculation for much of the 20th century, scientists and policymakers began to take the prospect seriously in 1969.
J. B. S. Haldane was the first to introduce the idea of human cloning, for which he used the terms "clone" and "cloning", which had been used in agriculture since the early 20th century. In his speech on "Biological Possibilities for the Human Species of the Next Ten Thousand Years" at the ''
Ciba Foundation Symposium on Man and his Future'' in 1963, he said:
Nobel Prize-winning geneticist
Joshua Lederberg advocated cloning and
genetic engineering
Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of technologies used to change the genetic makeup of cells, including ...
in an article in ''
The American Naturalist'' in 1966 and again, the following year, in ''
The Washington Post
''The Washington Post'' (also known as the ''Post'' and, informally, ''WaPo'') is an American daily newspaper published in Washington, D.C. It is the most widely circulated newspaper within the Washington metropolitan area and has a large n ...
''. He sparked a debate with conservative bioethicist
Leon Kass, who wrote at the time that "the programmed reproduction of man will, in fact, dehumanize him." Another
Nobel Laureate,
James D. Watson, publicized the potential and the perils of cloning in his ''
Atlantic Monthly'' essay, "Moving Toward the Clonal Man", in 1971.
With the cloning of a sheep known as
Dolly
Dolly may refer to:
Tools
*Dolly (tool), a portable anvil
* A posser, also known as a dolly, used for laundering
* A variety of wheeled tools, including:
**Dolly (trailer), for towing behind a vehicle
**Boat dolly or launching dolly, a device fo ...
in 1996 by
somatic cell nuclear transfer (SCNT), the idea of human cloning became a hot debate topic.
Many nations outlawed it, while a few scientists promised to make a clone within the next few years. The first
hybrid human clone was created in November 1998, by
Advanced Cell Technology. It was created using SCNT; a nucleus was taken from a man's leg cell and inserted into a cow's egg from which the nucleus had been removed, and the hybrid cell was cultured and developed into an
embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...
. The embryo was destroyed after 12 days.
In 2004 and 2005,
Hwang Woo-suk, a professor at
Seoul National University, published two separate articles in the journal
'' Science'' claiming to have successfully harvested pluripotent,
embryonic stem cells from a cloned human blastocyst using SCNT techniques. Hwang claimed to have created eleven different patient-specific stem cell lines. This would have been the first major breakthrough in human cloning. However, in 2006 ''Science'' retracted both of his articles on clear evidence that much of his data from the experiments was fabricated.
In January 2008, Dr. Andrew French and
Samuel Wood of the biotechnology company
Stemagen Stemagen is a corporation headed by Dr. Samuel Wood, notable for cloning adult skin cells On January, 2008, Dr. Andrew French, Stemagen's chief scientific officer and Wood in California, announced that they successfully created the first 5 mature h ...
announced that they successfully created the first five mature human embryos using SCNT. In this case, each embryo was created by taking a nucleus from a skin cell (donated by Wood and a colleague) and inserting it into a human egg from which the nucleus had been removed. The embryos were developed only to the
blastocyst stage, at which point they were studied in processes that destroyed them. Members of the lab said that their next set of experiments would aim to generate embryonic stem cell lines; these are the "holy grail" that would be useful for therapeutic or reproductive cloning.
In 2011, scientists at the New York Stem Cell Foundation announced that they had succeeded in generating embryonic stem cell lines, but their process involved leaving the
oocyte
An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The femal ...
's nucleus in place, resulting in
triploid cells, which would not be useful for cloning.
In 2013, a group of scientists led by Shoukhrat Mitalipov
Shoukhrat Mitalipov (, russian: Шухрат Музапарович Миталипов; born 1961) is an American biologist who heads the Center for Embryonic Cell and Gene Therapy at the Oregon Health & Science University in Portland. He is a we ...
published the first report of embryonic stem cells created using SCNT. In this experiment, the researchers developed a protocol for using SCNT in human cells, which differs slightly from the one used in other organisms. Four embryonic stem cell lines from human fetal somatic cells were derived from those blastocysts. All four lines were derived using oocytes from the same donor, ensuring that all mitochondrial DNA inherited was identical. A year later, a team led by Robert Lanza at Advanced Cell Technology reported that they had replicated Mitalipov's results and further demonstrated the effectiveness by cloning adult cells using SCNT.
In 2018, the first successful cloning of primates
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter includin ...
using SCNT was reported with the birth of two live female clones, crab-eating macaques named Zhong Zhong and Hua Hua.[*
*]
Methods
Somatic cell nuclear transfer (SCNT)
In somatic cell nuclear transfer ("SCNT"), the nucleus of a somatic cell is taken from a donor and transplanted into a host egg cell
The egg cell, or ovum (plural ova), is the female reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete is ...
, which had its own genetic material removed previously, making it an enucleated egg. After the donor somatic cell genetic material is transferred into the host oocyte with a micropipette, the somatic cell genetic material is fused with the egg using an electric current. Once the two cells have fused, the new cell can be permitted to grow in a surrogate or artificially. This is the process that was used to successfully clone Dolly the sheep (see section on History in this article). The technique, now refined, has indicated that it was possible to replicate cells and reestablish pluripotency, or "the potential of an embryonic cell to grow into any one of the numerous different types of mature body cells that make up a complete organism".
Induced pluripotent stem cells (iPSCs)
Creating induced pluripotent stem cells ("iPSCs") is a long and inefficient process. Pluripotency refers to a stem cell that has the potential to differentiate into any of the three germ layers: endoderm (interior stomach lining, gastrointestinal tract, the lungs), mesoderm (muscle, bone, blood, urogenital), or ectoderm (epidermal tissues and nervous tissue). A specific set of genes, often called "reprogramming factors", are introduced into a specific adult cell type. These factors send signals in the mature cell that cause the cell to become a pluripotent stem cell. This process is highly studied and new techniques are being discovered frequently on how to improve this induction process.
Depending on the method used, reprogramming of adult cells into iPSCs for implantation could have severe limitations in humans. If a virus
A virus is a wikt:submicroscopic, submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and ...
is used as a reprogramming factor for the cell, cancer-causing genes called oncogenes may be activated. These cells would appear as rapidly dividing cancer cells that do not respond to the body's natural cell signaling process. However, in 2008 scientists discovered a technique that could remove the presence of these oncogenes after pluripotency induction, thereby increasing the potential use of iPSC in humans.
Comparing SCNT to reprogramming
Both the processes of SCNT and iPSCs have benefits and deficiencies. Historically, reprogramming methods were better studied than SCNT derived embryonic stem cells (ESCs).[ However, more recent studies have put more emphasis on developing new procedures for SCNT-ESCs. The major advantage of SCNT over iPSCs at this time is the speed with which cells can be produced. iPSCs derivation takes several months while SCNT would take a much shorter time, which could be important for medical applications. New studies are working to improve the process of iPSC in terms of both speed and efficiency with the discovery of new reprogramming factors in oocytes. Another advantage SCNT could have over iPSCs is its potential to treat mitochondrial disease, as it utilizes a donor oocyte.][ No other advantages are known at this time in using stem cells derived from one method over stem cells derived from the other.]
Uses and actual potential
Work on cloning techniques has advanced our basic understanding of developmental biology in humans. Observing human pluripotent stem cells grown in culture provides great insight into human embryo development, which otherwise cannot be seen. Scientists are now able to better define steps of early human development. Studying signal transduction
Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellular ...
along with genetic manipulation within the early human embryo has the potential to provide answers to many developmental diseases and defects. Many human-specific signaling pathways have been discovered by studying human embryonic stem cells. Studying developmental pathways in humans has given developmental biologists more evidence toward the hypothesis that developmental pathways are conserved throughout species.
iPSCs and cells created by SCNT are useful for research into the causes of disease, and as model systems used in drug discovery
In the fields of medicine, biotechnology and pharmacology, drug discovery is the process by which new candidate medications are discovered.
Historically, drugs were discovered by identifying the active ingredient from traditional remedies or by ...
.
Cells produced with SCNT, or iPSCs could eventually be used in stem cell therapy, or to create organs to be used in transplantation, known as regenerative medicine. Stem cell therapy is the use of stem cells to treat or prevent a disease or condition. Bone marrow transplantation is a widely used form of stem cell therapy.[Bone Marrow Transplantation and Peripheral Blood Stem Cell Transplantation]
In National Cancer Institute Fact Sheet web site. Bethesda, MD: National Institutes of Health, U.S. Department of Health and Human Services, 2010. Cited August 24, 2010 No other forms of stem cell therapy are in clinical use at this time. Research is underway to potentially use stem cell therapy to treat heart disease, diabetes
Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level (hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...
, and spinal cord injuries.[Cell Basics: What are the potential uses of human stem cells and the obstacles that must be overcome before these potential uses will be realized?](_blank)
. In Stem Cell Information World Wide Web site. Bethesda, MD: National Institutes of Health, U.S. Department of Health and Human Services, 2009. cited Sunday, April 26, 2009 Regenerative medicine is not in clinical practice, but is heavily researched for its potential uses. This type of medicine would allow for autologous transplantation, thus removing the risk of organ transplant rejection by the recipient. For instance, a person with liver disease could potentially have a new liver grown using their same genetic material and transplanted to remove the damaged liver. In current research, human pluripotent stem cells have been promised as a reliable source for generating human neurons, showing the potential for regenerative medicine in brain and neural injuries.
Ethical implications
In bioethics, the ethics of cloning refers to a variety of ethical
Ethics or moral philosophy is a branch of philosophy that "involves systematizing, defending, and recommending concepts of morality, right and wrong action (philosophy), behavior".''Internet Encyclopedia of Philosophy'' The field of ethics, alo ...
positions regarding the practice and possibilities of cloning, especially human cloning. While many of these views are religious
Religion is usually defined as a social- cultural system of designated behaviors and practices, morals, beliefs, worldviews, texts, sanctified places, prophecies, ethics, or organizations, that generally relates humanity to supernatural, ...
in origin, for instance relating to Christian views of procreation and personhood, the questions raised by cloning engage secular perspectives as well, particularly the concept of identity.
Advocates support development of therapeutic cloning in order to generate tissues and whole organs to treat patients who otherwise cannot obtain transplants, to avoid the need for immunosuppressive drugs, and to stave off the effects of aging. Advocates for reproductive cloning believe that parents who cannot otherwise procreate should have access to the technology.
Opposition to therapeutic cloning mainly centers around the status of embryonic stem cells, which has connections with the abortion debate.
Some opponents of reproductive cloning have concerns that technology is not yet developed enough to be safe – for example, the position of the American Association for the Advancement of Science , while others emphasize that reproductive cloning could be prone to abuse (leading to the generation of humans whose organs and tissues would be harvested), and have concerns about how cloned individuals could integrate with families and with society at large.
Members of religious groups are divided. Some Christian theologians perceive the technology as usurping God's role in creation and, to the extent embryos are used, destroying a human life; others see no inconsistency between Christian tenets and cloning's positive and potentially life-saving benefits.
Current law
In 2018 it was reported that about 70 countries had banned human cloning.
In popular culture
Science fiction has used cloning, most commonly and specifically human cloning, due to the fact that it brings up controversial questions of identity. Humorous fiction, such as '' Multiplicity'' (1996) and the Maxwell Smart feature '' The Nude Bomb'' (1980), have featured human cloning. A recurring sub-theme of cloning fiction is the use of clones as a supply of organs for transplantation. Robin Cook's 1997 novel '' Chromosome 6'', Michael Bay's ''The Island The Island(s) may refer to:
Places
* Any of various islands around the world, see the list of islands
* The Island (Cache County, Utah), an island on the Bear River, Utah
* The Island, Chennai, a river island in India
* The Island, Chicago, a n ...
'', and Nancy Farmer's 2002 novel ''House of the Scorpion'' are examples of this; ''Chromosome 6'' also features genetic manipulation and xenotransplantation. The '' Star Wars'' saga makes use of millions of human clones to form the Grand Army of the Republic that participated in the Clone Wars. The series '' Orphan Black'' follows human clones' stories and experiences as they deal with issues and react to being the property of a chain of scientific institutions. In the 2019 horror film '' Us'', the entirety of the United States' population is secretly cloned. Years later, these clones (known as The Tethered) reveal themselves to the world by successfully pulling off a mass genocide of their counterparts.
See also
* Homunculus
* CRISPR gene editing
Notes
References
Further reading
* Araujo, Robert John, "The UN Declaration on Human Cloning: a survey and assessment of the debate," 7 The National Catholic Bioethics Quarterly 129 – 149 (2007).
* Seyyed Hassan Eslami Ardakani, ''Human Cloning in Catholic and Islamic Perspectives'', University of Religions and Denominations
The University of Religions and Denominations ( fa, دانشگاه اديان و مذاهب ) is a teaching and research center focusing on the study of religions and Islamic sects. The president of the university is Sayyid Abulhasan Navab, on ...
, 2007
* Oregon Health & Science University. "Human skin cells converted into embryonic stem cells: First time human stem cells have been produced via nuclear transfer." ScienceDaily. ScienceDaily, 15 May 2013
External links
"Variations and voids: the regulation of human cloning around the world"
academic article by S. Pattinson & T. Caulfield
United Nation declares law against cloning.
* ttps://web.archive.org/web/20130502125744/http://www.ornl.gov/sci/techresources/Human_Genome/elsi/cloning.shtml Cloning Fact Sheet
How Human Cloning Will Work
{{DEFAULTSORT:Human Cloning
Biotechnology
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