Therapeutic cloning. See what “Therapeutic cloning” is in other dictionaries
, (cell nuclear replacement, research cloning and embryo cloning), which consists of removing an egg (oocyte) from which the nucleus has been removed, and replacing this nucleus with the DNA of another organism. After many mitotic divisions in the culture (culture mitoses), a given cell forms a blastocyst (an early stage embryo consisting of approximately 100 cells) with DNA almost identical to the original organism.
The purpose of this procedure is to obtain stem cells that are genetically compatible with the donor organism. For example, embryonic stem cells can be obtained from the DNA of a patient with Parkinson's disease, which can be used to treat it, and they will not be rejected by the patient's immune system.
Application
Stem cells obtained through therapeutic cloning are used to treat many diseases. In addition, currently a number of methods using them are under development (treatment of certain types of blindness, spinal cord injuries, Parkinson's disease, etc.)
Discussions about therapeutic cloning
This method often causes controversy in the scientific community, and the term describing the created blastocyst is called into question. Some believe that it is incorrect to call it a blastocyst or embryo, since it was not created by fertilization, but others argue that, under the right conditions, it can develop into a fetus, and ultimately a child - so it is more appropriate to call the result an embryo.
The potential for therapeutic cloning in the medical field is enormous. Some opponents of therapeutic cloning object to the fact that the procedure uses human embryos and destroys them in the process. Others feel that such an approach instrumentalizes human life or that it would be difficult to allow therapeutic cloning without allowing reproductive cloning.
Legal status of the technology
According to data from 2006, cloning for therapeutic purposes is used in the UK, Belgium and Sweden. Research in this area is permitted in Japan, Singapore, Israel and Korea.
In many other countries, therapeutic cloning is prohibited, although laws are constantly being debated and changed. On December 8, 2003, UN countries voted against a ban on reproductive and therapeutic cloning proposed by Costa Rica.
In Russia, such therapy is currently not carried out, its legal status has not been determined, but the development of the technology has been suspended until the status is determined.
See also
Write a review about the article "Therapeutic cloning"
Links
Notes
Excerpt describing Therapeutic Cloning
Afterwards, I couldn’t come to my senses for a very long time, I became withdrawn, and spent a lot of time alone, which saddened all my family to the core. But, little by little, life took its toll. And, after some time, I slowly began to emerge from that deeply isolated state into which I had plunged myself, and from which it turned out to be very, very difficult... My patient and loving parents tried to help me as best they could. But with all their efforts, they did not know that I was truly no longer alone - that, after all my experiences, an even more unusual and fantastic world suddenly opened up to me than the one in which I had already lived for some time. . A world that surpassed any imaginable fantasy in its beauty, and which (again!) was given to me with its extraordinary essence by my grandfather. This was even more amazing than everything that happened to me before. But for some reason this time I didn’t want to share it with anyone...Days passed by. In my Everyday life I was an absolutely normal six-year-old child who had my own joys and sorrows, desires and sorrows and such unfulfillable rainbow childhood dreams... I chased pigeons, loved going to the river with my parents, played children's badminton with friends, helped, to the best of my ability , mother and grandmother in the garden, read my favorite books, learned to play the piano. In other words, I lived the most normal life ordinary life all small children. The only trouble was that by that time I already had two Lives... It was as if I lived in two completely different worlds: the first was our ordinary world, in which we all live every day, and the second, it was my own “hidden” world, in which only my soul lived. It became more and more difficult for me to understand why what was happening to me was not happening to any of my friends?
I began to notice more often that the more I shared my “incredible” stories with someone from my environment, the more often they felt a strange alienation and childish wariness. It hurt and it made me very sad. Children are curious, but they don't like the unknown. They always try as quickly as possible with their childish minds to get to the bottom of what is happening, acting on the principle: “what is it and what do they eat it with?”... And if they cannot understand it, it becomes “alien” for their everyday environment and is very quickly fades into oblivion. This is how I started to become a little “alien”...
I gradually began to understand that my mother was right in advising me not to tell my friends about everything. But I just couldn’t understand why they didn’t want to know this, because it was so interesting! So, step by step, I came to the sad realization that I must not be exactly like everyone else. When I once asked my mother about this “head-on”, she told me that I shouldn’t be sad, but on the contrary, I should be proud, because this is a special talent. To be honest, I couldn’t understand what kind of talent it was that all my friends were shying away from?.. But it was reality and I had to live with it. Therefore, I tried to somehow adapt to it and tried to talk as little as possible about my strange “opportunities and talents” among my acquaintances and friends...
Although sometimes it slipped against my will, as, for example, I often knew what would happen on this or that day or hour with one or another of my friends and wanted to help them by warning them about it. But, to my great surprise, they preferred not to know anything and got angry with me when I tried to explain something to them. Then I realized for the first time that not all people like to hear the truth, even if this truth could somehow help them... And this discovery, unfortunately, brought me even more sadness.
Six months after my grandfather's death, an event occurred that, in my opinion, deserves special mention. It was a winter night (and winters in Lithuania at that time were very cold!). I had just gone to bed when I suddenly felt a strange and very soft “calling”. It was as if someone was calling me from somewhere far away. I got up and went to the window. The night was very quiet, clear and calm. The deep snow cover shone and shimmered with cold sparks throughout the sleeping garden, as if the reflection of many stars was calmly weaving its sparkling silver web on it. It was so quiet, as if the world had frozen in some strange lethargic sleep...
Introduction
Messages about the permission of work on cloning human organs flashed in the media mass media, sound intriguingly fantastic. Everyone seems to have become accustomed to cloned frogs and sheep. Is the stamping of the liver, kidneys, heart and lungs on the way?
In order to grow, for example, a human kidney in the laboratory and successfully transplant it into a patient, two problems must be solved. The first is the problem of rejection of foreign cells and tissues. Why make an artificial organ when you can take a natural one? Unfortunately, the high mortality rate in the world from all kinds of accidents provides material for such transplants. The trouble is that the immune system of the recipient (that is, the person who has had an organ transplanted) will react to foreign cells in the same way as it reacts to influenza or rubella viruses - it will kill these cells. Let's not go into the details of why this happens. Many popular articles and books have been written on this topic. There are three ways to get around the rejection problem.
You can suppress the recipient's immunity with special medications - immunosuppressants. Not bad for preventing rejection, but then the patient will suffer from unwanted side effects.
The second option is to select an organ from a donor whose cells will resemble the recipient’s cells in a number of ways. In other words, you need to find a double organ. For this purpose in developed countries entire data banks are being created around the world. The chances of success are still slim. Biologists count dozens of parameters by which the immune system can distinguish “friends” from “strangers.” Therefore, you can stand in line for a kidney transplant for years.
Finally, the third way, the most promising and least developed, is to create an organ from cells that are not rejected by the immune system. These are some fetal cells. They have not yet acquired specific marks by which both their own and others can recognize them. immune systems. The possibility of growing such cells, taken at the earliest stages of embryo development, was mainly studied in Lately discussion in scientific and pseudo-scientific circles. However, the distance between growing such cells in bulk and obtaining an organ from them is approximately the same as from the first smelting furnaces to a spaceship.
The idea that if an organ for transplantation cannot be obtained, then it must be done was expressed back in the late 1980s. Director of the liver transplant program at Boston Children's Hospital, Dr. Charles Vacanti. However, the organ is very a complex system: it includes many different tissues, it is penetrated by blood vessels and nerves. How to recreate this system and how to reproduce the desired shape of the organ in the laboratory? This is the second and so far practically unsolved problem in the creation (cloning) of organs for transplantation.
Some approaches to solving it, however, are being outlined. Take the nose and ears for example. Their shape is created by cartilage, and cartilage is structured quite simply. It has no blood vessels or nerve endings. To get an artificial ear, do the following. The desired shape is cast from a porous polymer and “populated” with chondrocytes - cells that create natural cartilage. Chondrocytes themselves can be grown outside the body, but ears and noses do not grow in plastic cups. Chondrocytes themselves cannot create such complex spatial forms. However, they can be helped by arranging them in the space in the right way. After some time, the polymer fibers from which the template was made dissolve, and “living” cartilage of the desired shape is obtained.
This is already something, although the kidney or liver is still a long way off. They consist of different tissues, and it is unlikely that it will be possible to “assemble” these organs from them in the same way as a car is assembled from individual parts on an assembly line. This is where human and biological technologies diverge. Human technology is built on the assembly of complex units from blocks that are created in advance and separately. Biological technology is based on the gradual, step-by-step “growing” of structures from developing rudiments. There are no pre-created parts. All of them are formed in the process of development. If scientists can get isolated cells to act in the same way, there will be a chance, albeit a remote one, of producing complex artificial organs like livers or kidneys.
Finally, there is another way to develop transplantology. The “artificial kidney” device has been created and is working. There are no living cells in it yet. But perhaps in the future it will be possible to create a kind of “centaur” - an organ filled with electronics, which will include living tissue. It will not be a copy of a natural kidney, but it will perform its functions perfectly.
Therapeutic cloning
Therapeutic cloning is a cloning technology for the purpose of obtaining embryonic stem cells for scientific research and, potentially, use in the treatment of various human diseases. During therapeutic cloning, the embryo is not transferred for further development into the woman's uterine cavity, and is used as an object scientific research and experiments and obtaining stem cells. The zygote is othipotent, i.e. from any of its cells, under appropriate conditions, an embryo can develop. At the blastocyst stage, pluripotent cells are formed, from which all organs and tissues of the body are subsequently formed. In the process of therapeutic cloning, the embryo is inevitably destroyed after the formation of the primary “strip” (“trunk”) of cells, because their further development occurs in different conditions artificial environment in accordance with what kind of tissue is expected to be obtained.
Its goal is to use therapeutic cloning or parthenogenesis-based cell therapy to help sick people. Current efforts are focused on diseases of the nervous and cardiovascular systems, autoimmune disorders, diabetes and blood and bone marrow diseases.
When nerve cells can be grown from cloned embryos, it may be possible to treat not only spinal cord injuries, but also brain disorders such as Parkinson's disease, Alzheimer's disease, stroke and epilepsy.
In addition, stem cells can be turned into pancreatic cells for the treatment of diabetes, cardiac muscle cells for the treatment of heart attacks.
Even more interesting would be to direct the development of the messengers in such a way that they differentiate into blood and bone marrow cells.
Ethical considerations for using stem cells
However, the issue of freedom of research and use of stem cells in different countries has not yet been clearly resolved. At the same time, the importance of cell transplantology for science and medicine is obvious and not in dispute. In contrast, the only question raised is the ethics of using human embryos. The World Health Organization has taken a very clear position on this matter: what is important and valuable for human health must be accepted and allowed.
Two major ethical issues can be identified: the consistency of stem cell research with what is considered acceptable and ethical regarding natural reproduction, and the consistency with positions and moral beliefs regarding abortion and assisted human reproduction. Ethical principle- “the principle of avoiding unnecessary spending” - suggests that it is right to benefit people and wrong to harm them. The postulate fully applies to the use of embryos in stem cell research.
In his article “Stem Cells and Reproduction,” John Harris (Professor of Bioethics, Research Director of the Center for Social Ethics and Policy at the University of Manchester, Director of the Institute of Medicine, Law and Bioethics) defends the ethical principle that the natural is not related to the moral. The processes occurring in nature cannot be completely transferred to human society with its moral principles. Therefore, embryos produced only to be killed naturally may be justifiably killed. And if in nature all processes occur naturally, without contradicting its laws, then in similar circumstances it is moral to allow the same result for something deliberately created by man. It is then possible to accept the sacrifice of embryos in natural reproduction to achieve the result of prolonging the life of another. According to the scientist, society evaluates certain moral costs and benefits. And if this is done in the case of natural reproduction, then for the same reasons it should be done in the case of embryo sacrifice for stem cell research.
Church view
There are prohibitions of the church, which are based on the fact that:
1. introduction of the nucleus of a somatic cell into an egg cell deprived of a nucleus, that is, cloning is an “unauthorized creation of life,” and
2. The destruction of a hundred-cell, five-day-old blastocyst is the “killing of a living being.”
A person has no moral right to either - this is the logic of the majority of members of the Presidential Council on Bioethics, whose opinion on the inadmissibility of all types of cloning of human embryonic cells underlies the church position.
“Experiments with the cloning of a human embryo are a challenge to human nature itself,” commented priest Mikhail Dudko (Secretary for Interaction of the Russian Orthodox Church and Society of the Department for External Church Relations) on the message about permission to obtain stem cells issued by the British government to Newcastle University for the purpose of growing organ fragments and tissues for therapeutic purposes.
On the other hand, the church in some cases allows transplant cloning.
“Fundamentals of the social concept of the Russian Orthodox Church”, MOSCOW, 2000:
XII.6. The cloning (obtaining genetic copies) of animals carried out by scientists raises the question of the admissibility and possible consequences of human cloning. The implementation of this idea, which is met with protest from many people around the world, can become destructive for society. Cloning, to an even greater extent than other reproductive technologies, opens up the possibility of manipulating the genetic component of the individual and contributes to its further devaluation. A person does not have the right to claim the role of creator of creatures similar to himself or to select genetic prototypes for them, determining their personal characteristics at his own discretion. The idea of cloning is an undoubted challenge to the very nature of man, the image of God inherent in him, an integral part of which is the freedom and uniqueness of the individual. “Replication” of people with given parameters may seem desirable only for adherents of totalitarian ideologies.
Human cloning can pervert the natural principles of procreation, consanguinity, motherhood and paternity. A child can become his mother's sister, his father's brother, or his grandfather's daughter. The psychological consequences of cloning are also extremely dangerous. A person who was born as a result of such a procedure may not feel like an independent person, but only a “copy” of someone living or previously living people. It must also be taken into account that “by-products” of experiments with human cloning would inevitably be numerous failed lives and, most likely, the birth of a large number of non-viable offspring. At the same time, cloning isolated cells and tissues of the body is not an infringement on the dignity of the individual and in some cases turns out to be useful in biological and medical practice.
Legal view
There are two types of cord/placental blood stem cell banks: donor (public), where cord/placental blood is donated for public use - their work is funded by the state, so that after immunological selection, stem cells can be used to treat any person, and private banks personal storage, in which umbilical cord/placental blood stem cells are the property of a specific person and can be used only for him, accordingly he assumes all costs associated with procurement and storage.
The activities of banks are regulated by Order of the Ministry of Health of Russia dated July 25, 2003 No. 325 “On the development of cell technologies in the Russian Federation,” which approved the Regulations on the Bank of Human Umbilical Cord/Placental Blood Stem Cells. In development of the above order, at the level of the constituent entities of the Russian Federation, there is also the order of the Moscow Department of Health dated December 8, 2003 No. 702 “On organizing the work of the State Institution “Stem Cell Bank of the Moscow Department of Health”” (as amended and supplemented), a government decree Samara region dated January 21, 2003 No. 14 “On the creation of the State Unitary Enterprise “Volga Region Bank of Hematopoietic Cells””, etc.
In accordance with the Decree of the Government of the Russian Federation dated January 22, 2007 No. 30 “On approval of the Regulations on licensing of medical activities” (as amended and supplemented) in order to begin work in the field of cell technologies (collection, transportation, storage of hematopoietic stem cells, use cell technologies), the organization must obtain a license.
Umbilical cord blood biologically belongs to the newborn, but according to Art. 28 of the Civil Code of the Russian Federation, a child, due to his infancy, is not able to express his consent to its use. Therefore, in accordance with Art. 32 of the Fundamentals of the legislation of the Russian Federation on the protection of the health of citizens, the consent of a legal representative is required for the collection, storage and use of donor stem cells, in in this case- mother of a newborn. Once transferred to a third party, cord blood ceases to be the property of the child. If the mother decides to store the blood privately, the biological material becomes the property of the client, who receives the exclusive right to dispose of it
The necessary trigger for collecting cord blood cells is the woman's written informed consent. This is established by the Fundamentals of the legislation of the Russian Federation on the protection of the health of citizens (Article 32), the Law of the Russian Federation dated 06/09/1993 No. 5142-1 “On the donation of blood and its components” (as amended and additionally), the latter notes that “donation blood and its components is a freely expressed voluntary act” (Article 1). The task of medical workers is to clearly and correctly inform the woman about the meaning and procedure for the upcoming procedure. It is important to explain that blood is taken from the vessels of the umbilical cord and placenta after the birth of the child and its separation from the mother, therefore this procedure does not pose any danger to the health of the mother and the newborn. If complications arise during childbirth, the blood sampling procedure is canceled, since doctors need to focus on fulfilling their direct responsibilities - saving the life and health of the child and mother.
The Moscow Department of Health has developed informed consent for the collection of cord blood from a woman who is proposed to become a stem cell donor.
etc.................
Eddie Lawrence, for BBCRussian.com
Recently, there has been active debate in political, scientific circles and in the media about the two types of cloning: therapeutic and reproductive, as well as about the so-called “stem cells” and their significance for the further development of modern medicine.
What does all this mean from a specialist’s point of view?
Reproductive cloning
This is an artificial reproduction in laboratory conditions of a genetically accurate copy of any living creature. Dolly the sheep, born at Edinburgh's Roslyn Institute, is an example of the first such cloning of a large animal.
The process is divided into several stages. First, an egg is taken from a female individual, and the nucleus is extracted from it using a microscopic pipette. Then any cell containing the DNA of the cloned organism is injected into the anucleated egg. In fact, it mimics the role of sperm in fertilizing an egg. From the moment the cell merges with the egg, the process of cell reproduction and embryo growth begins (Scheme 1).
In many countries around the world, including the UK, human reproductive cloning for the purpose of producing cloned children is prohibited by law.
Therapeutic cloning
This is the same reproductive cloning, but with the embryo growth period limited to 14 days, or, as experts say, a “blastocyst.” After two weeks, the process of cell reproduction is interrupted.According to most scientists, after 14 days, the central core begins to develop in embryonic cells. nervous system and a conglomerate of cells (embryo, blastocyst) should already be considered a living being.
Such cloning is called therapeutic only because the embryonic cells formed during the first 14 days are capable of subsequently turning into specific tissue cells of individual organs: heart, kidneys, liver, pancreas, etc. - and used in medicine for the treatment of many diseases.
Such cells of future organs are called “embryonic stem cells.”
In the UK, scientists are allowed to use therapeutic cloning and conduct research on stem cells for medical purposes.
In Russia, many scientists (for example, Academician of the Russian Academy of Medical Sciences N.P. Bochkov, Professor V.Z. Tarantul from the Institute of Molecular Genetics) do not like to use the expression “therapeutic cloning” and prefer to call this process “cellular reproduction.”
Embryonic stem cells
They are formed in the embryo (blastocyst) in the first days of reproduction. These are the ancestors of the cells of almost all tissues and organs of an adult.They have been known to embryologists for a long time, but in the past, due to the lack of biotechnology for their laboratory cultivation and preservation, such cells were destroyed (for example, in abortion clinics).
Over the past decades, not only the biotechnology of artificially obtaining embryonic stem cells by cloning has been developed, but also special nutrient media have been created for growing living tissues from them.
Future medicine - medicine of "spare parts"
The development of many areas of medicine in the next century will be based on the use of embryonic stem cells.
That is why today in scientific and political circles so much attention is paid to the issues of therapeutic cloning and research on stem cells for medical purposes.
What are the practical benefits?
Development of biotechnology for obtaining large quantities Stem cells will enable doctors to treat many previously incurable diseases. First of all - diabetes (insulin dependent), Parkinson's disease, Alzheimer's disease (senile dementia), heart muscle diseases (myocardial infarction), kidney disease, liver disease, bone disease, blood disease and others.
New medicine will be based on two main processes: growing healthy tissue from stem cells and transplanting such tissue to the site of damaged or diseased tissue.The method of creating healthy tissues is based on two complex biological processes: the initial cloning of human embryos to the stage of the appearance of “stem” cells and the subsequent cultivation of such cells and the cultivation of the necessary tissues and, possibly, organs in nutrient media.
Professor Vyacheslav Tarantul from the Moscow Institute of Molecular Genetics of the Russian Academy of Sciences even proposes, from the moment of birth of any child, to create a bank of stem cells for each child from embryonic cells (for example, his own umbilical cord). After 40-50 years, if any organs or tissues become diseased or damaged, it will always be possible to grow from this bank a replacement for the damaged tissue, which will be genetically completely identical to this person. In this case, no foreign donor organs or transplants are needed (Scheme 2).
What is the danger?
If the process of reproduction of cells obtained as a result of cloning (including for therapeutic purposes) does not stop at the 14-day limit, and the embryo is placed in the woman’s uterus, then such an embryo will turn into a fetus and subsequently into a child. Thus, under certain conditions, “therapeutic” cloning can turn into “reproductive” cloning.
Some specialists are already trying to use cloning biotechnology, for example, to treat infertility in childless families by creating child clones of infertile parents (Italian professor Severino Antinori, American professor Panos Zavos and others).
In the UK, reproductive cloning of children is punishable by up to 10 years in prison.
Recently, there has been active debate in political, scientific circles and in the media about the two types of cloning: therapeutic and reproductive, as well as about the so-called “stem cells” and their significance for the further development of modern medicine.
What does all this mean from a specialist’s point of view?
Reproductive cloning
This is an artificial reproduction in laboratory conditions of a genetically accurate copy of any living creature. Dolly the sheep, born at Edinburgh's Roslyn Institute, is an example of the first such cloning of a large animal.
The process is divided into several stages. First, an egg is taken from a female individual, and the nucleus is extracted from it using a microscopic pipette. Then any cell containing the DNA of the cloned organism is injected into the anucleated egg. In fact, it mimics the role of sperm in fertilizing an egg. From the moment the cell merges with the egg, the process of cell reproduction and embryo growth begins (Scheme 1).
In many countries around the world, including the UK, human reproductive cloning for the purpose of producing cloned children is prohibited by law.
Therapeutic cloning
This is the same reproductive cloning, but with the embryo growth period limited to 14 days, or, as experts say, a “blastocyst.” After two weeks, the process of cell reproduction is interrupted.
According to most scientists, after 14 days, the central nervous system begins to develop in embryonic cells and the conglomerate of cells (embryo, blastocyst) should already be considered a living being.
Such cloning is called therapeutic only because the embryonic cells formed during the first 14 days are capable of subsequently turning into specific tissue cells of individual organs: heart, kidneys, liver, pancreas, etc. - and used in medicine for the treatment of many diseases.
Such cells of future organs are called “embryonic stem cells.”
In the UK, scientists are allowed to use therapeutic cloning and conduct research on stem cells for medical purposes.
In Russia, many scientists (for example, Academician of the Russian Academy of Medical Sciences N.P. Bochkov, Professor V.Z. Tarantul from the Institute of Molecular Genetics) do not like to use the expression “therapeutic cloning” and prefer to call this process “cellular reproduction.”
Embryonic stem cells
They are formed in the embryo (blastocyst) in the first days of reproduction. These are the ancestors of the cells of almost all tissues and organs of an adult.
They have been known to embryologists for a long time, but in the past, due to the lack of biotechnology for their laboratory cultivation and preservation, such cells were destroyed (for example, in abortion clinics).
Over the past decades, not only the biotechnology of artificially obtaining embryonic stem cells by cloning has been developed, but also special nutrient media have been created for growing living tissues from them.
Future medicine - medicine of "spare parts"
The development of many areas of medicine in the next century will be based on the use of embryonic stem cells.
That is why today in scientific and political circles so much attention is paid to the issues of therapeutic cloning and research on stem cells for medical purposes.
What are the practical benefits?
The development of biotechnology for obtaining large quantities of stem cells will enable doctors to treat many still incurable diseases. First of all - diabetes (insulin dependent), Parkinson's disease, Alzheimer's disease (senile dementia), heart muscle diseases (myocardial infarction), kidney disease, liver disease, bone disease, blood disease and others.
New medicine will be based on two main processes: growing healthy tissue from stem cells and transplanting such tissue to the site of damaged or diseased tissue.
The method of creating healthy tissues is based on two complex biological processes: the initial cloning of human embryos to the stage of the appearance of “stem” cells and the subsequent cultivation of such cells and the cultivation of the necessary tissues and, possibly, organs in nutrient media.
Professor Vyacheslav Tarantul from the Moscow Institute of Molecular Genetics of the Russian Academy of Sciences even proposes, from the moment of birth of any child, to create a bank of stem cells for each child from embryonic cells (for example, his own umbilical cord). After 40-50 years, if any organs or tissues become diseased or damaged, it will always be possible to grow from this bank a replacement for the damaged tissue, which will be genetically completely identical to this person. In this case, no foreign donor organs or transplants are needed (Scheme 2).
What is the danger?
If the process of reproduction of cells obtained as a result of cloning (including for therapeutic purposes) does not stop at the 14-day limit, and the embryo is placed in the woman’s uterus, then such an embryo will turn into a fetus and subsequently into a child. Thus, under certain conditions, “therapeutic” cloning can turn into “reproductive” cloning.
Some specialists are already trying to use cloning biotechnology, for example, to treat infertility in childless families by creating child clones of infertile parents (Italian professor Severino Antinori, American professor Panos Zavos and others).
In the UK, reproductive cloning of children is punishable by up to 10 years in prison.
Authors
Sviridova-Chaylakhyan T.A., Chailakhyan L.M.
The review is devoted to the current biomedical direction in cell replacement therapy - therapeutic cloning, which is the most universal approach for obtaining patient-specific lines of embryonic stem cells (ESCs) with enormous potential for maintaining and restoring human health. The review also presents alternative approaches and trends in obtaining human ESCs, which, unlike therapeutic cloning, are still far from entering clinical practice. The unique value of ESCs in medicinal purposes identifies a serious need for the development of therapeutic cloning in our country.
Introduction
The basis for the emergence of one of the most promising biomedical trends in cell replacement therapy - therapeutic cloning - were two important discoveries of the late 20th century. This is, firstly, the creation of a cloned sheep Dolly, and secondly, the production of embryonic stem cells (ESCs) from human blastocysts and primordial germ cells. In the first case, it has been convincingly shown for mammals that if the nucleus of a somatic cell of an adult organism is introduced into an enucleated oocyte, then under the influence of the cytoplasm of the oocyte, the nucleus of such a cell is reprogrammed and is capable of giving rise to the development of an embryo (clone), the genome of which is identical to the genome of the organism - the donor of the nuclei. In the second case, it is shown how human ESCs can be obtained and cultivated. The combination of these two important achievements creates the fundamental possibility of obtaining patient-specific ESC lines and, on their basis, progenitor cells determined in a certain direction (for example, cells of the hematopoietic series), which, in essence, will be the cells of the patient himself, and completely with them immunocompatible. This is the main meaning and the main objective therapeutic cloning. Currently, the main sources of obtaining stem cells directly for biomedical work are stem cells from umbilical cord blood and adult stem cells. Both sources have serious limitations: umbilical cord blood stem cells are autogenous only to the newly born, and receiving stem cells from the patient himself is unsafe for him. In addition, the general consensus is that the differentiation potential of these cells is lower than that of ESCs. Obviously, the most universal and reliable source obtaining human stem cells (SC) using cloning technologies.
Future needs for therapeutic cloning
It can be confidently stated that the future needs for therapeutic cloning are unlimited, since this approach allows almost every person to create their own bank of SC lines. Since these cells multiply quickly, they can be obtained in any quantity. A person will essentially have an unlimited supply of his own stem and progenitor cells of various determinations.
Based on modern ideas about the huge role in normal functioning Since the human body has a natural pool of stem cells, which sharply depletes with age, the enormous possibilities of therapeutic cloning in maintaining and restoring human health during his life, in overcoming various ailments and in prolonging his active age become completely obvious. The life opportunities of each individual person are greatly enriched.
A number of countries have now passed laws allowing research with human ESCs, although the moral and ethical issues associated with the use of human embryos for this purpose still continue to cause the most heated public debate in the history of biomedical science. Typically, in reproductive practice, approximately 24 oocytes are obtained from each female client and only two to four embryos are then used for implantation in the hope that one of them will develop normally during pregnancy. Many embryos remaining after artificial insemination will be destroyed in any case, even after years of storage in cryobanks. Less than 3% of these embryos are currently available for research. At the same time, a special analysis carried out in the USA, Canada, England, Australia and other countries showed that patients of reproduction centers in the overwhelming majority would prefer to donate the remaining oocytes and embryos for scientific research, including receiving IC,
More recently, in March 2009, research with human embryos and hESCs for biomedical purposes was legally permitted in the United States with the conduct of appropriate clinical trials, although, in fact, experiments in this direction began in 2006 at Harvard University. Multimillion-dollar projects to create cloned human embryos to obtain hESCs have also been launched in Australia. Given these facts, there is no doubt that therapeutic cloning will soon become a leading trend in cell replacement therapy and biomedical practice in the world. The unique value of ESCs for medicinal purposes determines the serious need for the development of therapeutic cloning in our country. It is obvious that legislative permission in Russia to carry out such research work within certain strict ethical frameworks is now the most important and pressing need. It should be noted that therapeutic human cloning and reproductive cloning are fundamentally different directions in their goals, and, of course, human reproductive cloning should be strictly prohibited due to fundamental principles biological reasons, not to mention the complex ethical, legal and social issues that arise.
Global trends in the development of therapeutic cloning
The enormous potential of therapeutic cloning technologies has so far been demonstrated in animal model objects. The first work on therapeutic cloning was published in 2000 and was performed on mice. The work showed that ESC lines from cloned embryos consist of cells with the same pluripotent properties as conventional ESCs. Then dozens of such works appeared and successful attempts were made, using cloning technology, to correct the pathologies existing in experimental animals, in particular, combined immunodeficiency. This demonstrated the serious possibilities of combining therapeutic cloning with gene therapy For successful treatment various genetic diseases.
To date, fundamental scientific and technological aspects do not create barriers to therapeutic cloning [14-17]. And although there are already about 500 lines of human ESCs in the world, not one of them has been obtained using cloning technologies - the method of nuclear transplantation. Two sensational publications in the journal Science in 2004 and 2005 by South Korean scientists on obtaining individual lines of ESCs for 11 seriously ill patients turned out to be unreliable. There is a report of obtaining a patient-specific line from activated parthenogenetic human oocytes containing histocompatible stem cells for an oocyte donor - a potential patient, in whose treatment it is already possible to use autogenous cells without an immune rejection reaction. Another achievement is the production of cloned human embryos with fibroblast nuclei that have developed to the blastocyst stage, but no ESC lines have been created from them.
Alternative approaches to obtaining patient-specific ESC lines
At the same time, the world is actively searching for alternative options for obtaining patient-specific ESC lines for biomedical purposes. One possibility is to transplant human somatic cell nuclei into animal oocytes. The rapidly growing interest in therapeutic cloning for the treatment of various diseases requires the production of ESCs in large quantities. However, even under legislatively favorable conditions, human oocytes and embryos for this will always be a very limited number, and their production will be expensive. The shortage of human oocytes needed for research purposes can be made up by using animal oocytes, which are more readily available. Hybrid heteroplasmic embryos with the human genome and mixed human and animal cytoplasm represent an attractive and convenient model system for solving many fundamental and practical issues of therapeutic cloning. When conducting research, it is strictly prohibited to implant the resulting hybrid embryos into the uterus of a person or animal, as well as to grow them in vitro for a long time (more than 14 days).
First successful work in this direction belongs to a group of Chinese scientists who, using the method of transferring nuclei of human somatic cells (fibroblasts) into enucleated rabbit oocytes, obtained hybrid reconstructed embryos and then ESC lines. Careful analysis showed that these ESCs are phenotypically similar to normal human ESCs, including the ability to undergo a variety of cellular differentiation. Thus, it turned out to be possible to obtain human stem cell lines without the participation of human oocytes. The same researchers then transferred human fibroblast nuclei into enucleated bovine oocytes and showed that in such hybrids, reprogramming of human cell nuclei with corresponding activation of embryonic gene expression was observed. Hybrid embryos developed to late preimplantation stages, which is important for the future generation of ESCs.
Conducting similar studies was allowed in England, but all efforts to repeat the work of Chinese scientists were unsuccessful: it was not possible to achieve the development of the same reconstructed hybrid human-animal embryos to the stage of producing blastocysts and ESCs using interspecies nuclear transplantation. Similar attempts at interspecies human nuclear transplantation undertaken in the United States were also unsuccessful. Based on a large series of experiments on the transfer of nuclei of human somatic (cumulus) cells into oocytes of humans and various animals: cows, rabbits and mice, it was shown that in human-animal hybrids the corresponding reprogramming of nuclei is not achieved, as in cloned human embryos, in which the gene expression pattern was almost identical to normal human embryos. It is especially critical that the hybrid embryos lacked expression of pluripotency genes, which is necessary for the production of SCs.
According to a number of researchers, defects in the development of human-animal hybrids may be associated not only with insufficient reprogramming of the epigenetic status of human somatic nuclei, but also with complete incompatibility of the human nuclear genome and the animal mitochondrial genome. Reconstructed hybrid embryos survive for a short time only due to human mitochondria, since the nuclei of human somatic cells are usually transferred into the animal's oocytes along with the cytoplasm. Thus, based on all these data, it was concluded that animal oocytes are not suitable for use as recipients of human cell nuclei, and obtaining human ESCs from such embryos is practically impossible.
Another approach to create patient-specific pluripotent stem cells is to induce dedifferentiation of somatic cells using ESCs themselves, as demonstrated by somatic hybridization first in mice and then with human ESCs. Stem cells, when fused with somatic cells, provide factors required for epigenetic reprogramming of the genome of somatic cells with the corresponding induction of pluripotent properties and characteristics. The possibility of reprogramming the nuclei of somatic cells using ESC extract has been demonstrated and attempts have been made to selectively eliminate HSC chromosomes, however, the removal of all chromosomes is still technically difficult to achieve, and the considered method of obtaining stem cells is generally far from being put into therapeutic practice.
The most promising alternative approach for generating patient-specific somatic cell lines for biomedical purposes is the generation of HSC-like cells or induced pluripotent CiPSD SC lines. This is a new direction of research in cell replacement therapy, which began with the work of scientists from Japan in 2006 on mice to reprogram fibroblasts to a status similar to pluripotent. Soon the possibility of such a transformation was demonstrated for human fibroblasts. Genetic modification of fibroblasts was carried out using retroviral transfection of four key pluripotency factors: 0ct3/4, Sox2, Klf4, c-Myc, and subsequent expression of these genes induced reprogramming of somatic cells with a return to the pluripotent state. Although the effectiveness of this approach was very low, and it is also known that the use of viral vectors can lead to malignancy of iPS cells, these works became a sensation. A whole series of studies with induction factors followed and an active search was undertaken for other ways of introducing genes into somatic cells (without resorting to retroviruses) while minimizing genome modification. As a result, the possibility was shown in mice in a safe way reprogramming cells using transposons and just one factor Klf4.
However, it is premature to consider iPS cells as an adequate alternative replacement for ESCs for regenerative therapy. For biomedical purposes, it is necessary to reprogram cells’ own genes instead of adding new copies, and only therapeutic cloning technologies provide a unique opportunity for such reprogramming of somatic cell nuclei. The reversibility of the gene expression program under the influence of the oocyte cytoplasm and the return to the embryonic expression pattern in somatic donor nuclei allows us to currently consider reconstructed human embryos as the main source of obtaining patient-specific ESC lines.
State of research on therapeutic cloning in Russia
Despite the boom about the great potential of ESCs in the treatment of various diseases, work on therapeutic cloning is still practically not being carried out in Russia. This is primarily due to the lack legislative framework for conducting research using human oocytes and embryos. With the adoption of such laws, there is a real opportunity for Russia to develop therapeutic cloning very quickly. Our country has effective cellular technologies for obtaining reconstructed embryos using nuclear transplantation. Basically, the basics modern technologies nuclear transfer of somatic cells, combining microsurgery and electrofusion were first developed here in the 80s of the last century. There are also effective technologies for obtaining human ESC lines.
It is possible to implement the tasks of therapeutic cloning on the basis of reproduction centers, which, in addition to their direct purpose, can become centers for obtaining ESC lines, first of all, directly for female patients of this center and any members of their families. It can be expected that with the development of therapeutic technologies, obtaining one’s own ESCs will become available to every person. It is necessary to carry out close cooperation between reproduction centers and relevant research laboratories focused on solving fundamental problems and developing new technologies. Such technologies include the reconstruction of embryos using non-invasive optical-laser micromanipulation techniques for the purposes of therapeutic cloning and cell replacement therapy. The development of such techniques will lead to the emergence of a new class of micromanipulation equipment that combines various optical laser microtools (optical tweezers, laser scalpel, etc.) with computerized control. It should be expected that with appropriate consistent scientific and organizational work regarding the development of therapeutic cloning in our country, Russia can reach a foreign level in this area of biomedical research in the foreseeable future.