Despite the fact that much has been discussed, there is still a lot of confusion regarding the concepts of cloning (reproductive and therapeutic), stem cells (embryonic and non-embryonic) and cell therapy as well as this can affect our lives. Therefore the purpose of this article is to try to define these concepts and express my position on ethical aspects not only as a scientist but also as representative of countless families who see in this new technology a future hope of cure for numerous neurodegenerative diseases, often lethal or severely disabling.
What is cloning?
CLONING IS A common mechanism of propagation of the species in plants or bacteria. According to Webber (1903) a clone is defined as a population of molecules, cells or organisms that originated from a single cell and that are identical to the original cell and between them. In humans, natural clones are the identical twins that originate from the division of a fertilized egg. Dolly's great revolution, which paved the way for the possibility of human cloning, was the first demonstration that it was possible to clone a mammal, that is, to produce a genetically identical copy from a differentiated somatic cell . To understand why this experience was surprising, we need to remember a bit of embryology.
We have all been a single cell, resulting from the fusion of an egg and a sperm. This first cell already has in its nucleus the DNA with all the genetic information to generate a new being. The DNA in the cells becomes extremely condensed and organized into chromosomes. With the exception of our sex cells, the egg and the sperm that have 23 chromosomes, all the other cells of our body have 46 chromosomes. In each cell, we have 22 pairs that are the same in both sexes, called autosomes and a pair of sex chromosomes: XX in the female sex and XY in the male sex. These cells, with 46 chromosomes, are called somatic cells. Let us return now to our first cell resulting from the fusion of the ovum and the spermatozoid. Immediately after fertilization, it begins to divide: a cell in two, two in four, four in eight, and so on. At least up to the eight cell phase, each of them is capable of developing into a complete human being. They are called totipotent . In the eight to sixteen cell phase, the embryo cells differentiate into two groups: a group of external cells that will originate the placenta and the embryonic attachments, and a mass of internal cells that will originate the embryo itself. After 72 hours, this embryo, now with about one hundred cells, is called a blastocyst. It is at this stage that implantation of the embryo occurs in the uterine cavity. The inner cells of the blastocyst will originate the hundreds of tissues that make up the human body. They are called pluripotent embryonic stem cells . From a certain moment, these somatic cells - which are still all the same - begin to differentiate in the various tissues that will make up the organism: blood, liver, muscles, brain, bones, etc. The genes that control this differentiation and the process by which this occurs are still a mystery. What we do know is that once differentiated, somatic cells lose the ability to originate any tissue. Descending cells from a differentiated cell will retain the same characteristics as the one that originated them, ie, liver cells will originate liver cells, muscle cells will originate muscle cells and so on. Although the number of genes and DNA is the same in all cells of our body, genes in differentiated somatic cells express themselves differently in each tissue, that is, gene expression is tissue-specific. With the exception of the genes responsible for the maintenance of the cellular metabolism ( housekeeping genes ) that remain active in all the cells of the organism, only the genes important for the maintenance of this tissue will function in each tissue or organ. The others remain "silenced" or inactive.
The process of reproductive cloning
The great news of Dolly was precisely the discovery that an already differentiated somatic mammalian cell could be reprogrammed to the initial stage and returned to being totipotent. This was achieved by transferring the nucleus of a somatic cell from the mammary gland of the sheep that originated Dolly to an enucleated ovum. Surprisingly, it began to behave like a newly fertilized egg by a spermatozoon. This has probably occurred because the egg, when fertilized, has mechanisms, for us as yet unknown, to reprogram the DNA in order to make all of its genes active again, which occurs in the normal process of fertilization.
To obtain a clone, this enucleated egg into which the somatic cell nucleus was transferred was inserted into a uterus of another sheep. In the case of human reproductive cloning, the proposal would be to remove the nucleus of a somatic cell, which could theoretically be of any tissue of a child or adult, insert this nucleus into an ovule and implant it into a uterus (which would function as a belly for rent). If this egg develops we will have a new being with the same physical characteristics of the child or adult from whom the somatic cell was removed. It would be like an identical twin born later.
We already know that it is not an easy process. Dolly was only born after 276 failed attempts. In addition, of the 277 "mother of Dolly" cells that were inserted into a nucleus-free ovum, 90% did not reach the blastocyst stage. Further attempts to clone other mammals such as mice, pigs, calves, a horse and a stag have also shown very low efficiency and a very large proportion of malformed abortions and embryos. Penta, the first Brazilian heifer cloned from a somatic cell died adult, in 2002, with a little over a month. Also in 2002, it was announced the cloning of the copycat the first pet cat cloned from an adult somatic cell. For this we used 188 eggs that generated 87 embryos and only one live animal. In fact, recent experiments with different types of animals have shown that this reprogramming of genes to the embryonic stage, which originated Dolly, is extremely difficult.
The group led by Ian Wilmut, the Scottish scientist who became famous for this experiment, states that virtually all animals that have been cloned in recent years from non-embryonic cells are in trouble (Rhind, 2003). Among the different defects observed in the very few animals that were born alive after numerous attempts, we can observe: abnormal placentas, gigantism in sheep and cattle, heart defects in pigs, pulmonary problems in cows, sheep and pigs, immunological problems, leukocyte production failure , muscular defects in sheep. According to Hochedlinger and Jaenisch (2003), recent advances in reproductive cloning allow four important conclusions: 1) most clones die early in gestation; 2) cloned animals have similar defects and abnormalities, regardless of donor cell or species; 3) these abnormalities probably occur due to failures in reprogramming the genome; 4) The efficiency of cloning depends on the differentiation stage of the donor cell. In fact, reproductive cloning from embryonic cells has shown an efficiency of ten to twenty times greater, probably because the genes that are fundamental at the beginning of embryogenesis are still active in the donor cell genome (Hochedlinger and Jaenisch, 2003).
Interestingly, among all mammals that have already been cloned, the efficiency is slightly higher in calves (about 10% to 15%). On the other hand, an intriguing fact is that there is still no news of monkey or dog that has been cloned. Perhaps this is why the British scientist Ann McLaren has stated that failures in reprogramming the somatic nucleus may constitute an insurmountable barrier to human cloning.
Even so, people like the Italian doctor Antinori or the Raelian sect advocate human cloning, a procedure that has been banned in all countries. In fact, a document signed in 2003 by the science academies of 63 countries, including Brazil, calls for a ban on human reproductive cloning. The fact is that the simple possibility of cloning humans has elicited ethical discussions in all segments of society, such as: Why clone? Who should be cloned? Who would decide? Who will be the father or mother of the clone? What to do with clones that are born defective?
In fact, the major ethical problem today is the enormous biological risk associated with reproductive cloning. In my view, it would be the same as discussing the pros and cons of releasing a new medication whose effects are devastating and still totally unmanageable.
Despite all these arguments against human reproductive cloning, experiments with cloned animals have taught us a lot about cell function. On the other hand, core transfer technology for therapeutic purposes, called therapeutic cloning, can be extremely useful for obtaining stem cells.
The therapeutic cloning technique for obtaining stem cells
If instead of inserting into the uterus the ovum whose nucleus has been replaced by one of a somatic cell let it divide in the laboratory we will be able to use these cells - which in the blastocyst stage are pluripotent - to make different tissues. This will open fantastic prospects for future treatments, because today you can only grow cells in the laboratory with the same characteristics of the tissue from which they were removed. It is important for people to understand that in cloning for therapeutic purposes only tissues will be generated in the laboratory without implantation in the uterus. It is not about cloning a fetus up to a few months inside the uterus and then removing the organs as some believe. There is also no reason to call this embryo egg after core transfer because it will never have that destiny.
A study published in the journal Sciences by a group of Korean scientists (Hwang et al., 2004) confirms the possibility of obtaining pluripotent stem cells from the technique of therapeutic cloning or nucleus (TN) transfer. The work was done thanks to the participation of 16 volunteer women who donated, in all, 242 eggs and cumulus cells (cells surrounding the eggs) to contribute to research aimed at therapeutic cloning. Cumulus cells, which are already differentiated cells, were transferred to the eggs from which the nuclei had been removed. Of these, 25% were able to divide and reach the stage of blastocyst, thus able to produce pluripotent stem cell lines.
Therapeutic cloning would have the advantage of avoiding rejection if the donor were the person himself. It would be the case, for example, of reconstituting the bone marrow in someone who became paraplegic after an accident or to replace the heart tissue in a person who suffered a heart attack. However, this technique has its limitations. The donor could not be the same person when it was someone affected by genetic disease, because the pathogenic mutation that causes the disease would be present in all cells. If someone else's embryonic stem cell lines were used, there would also be a problem of donor-recipient compatibility. This would be the case, for example, of someone affected by progressive muscular dystrophy, as there would be a need to replace their muscle tissue. He could not use his own stem cells, but a compatible donor who could possibly be a close relative. In addition, we do not know if, in the case of cells obtained from an elderly person affected by Alzheimer's disease, for example, if the cloned cells would be the same age as the donor or if they were young cells. Another open question concerns the reprogramming of genes that could render the process unfeasible depending on the tissue or organ to be replaced. In summary, however much we favor therapeutic cloning, it is a technology that needs a lot of research before being applied in clinical treatment. For this reason, the great hope in the short term for cell therapy comes from the use of stem cells from other sources
Cell therapy with other sources of stem cells
a) Adult individuals
There are stem cells in various tissues (such as bone marrow, blood, liver) in children and adults. However, the quantity is small and we do not know yet in which tissues are able to differentiate. Recent research has shown that stem cells taken from the spinal cord of individuals with heart problems have been able to rebuild their heart muscle, which opens up fantastic prospects of treatment for people with heart problems. But the major limitation of the autotransplantation technique is that it would not serve genetic carriers. It is important to remember that genetic diseases affect 3-4% of children born. That is, more than five million Brazilians for a current population of 170 million people. It is true that not all genetic diseases could be treated with stem cells, but if we only think about degenerative neuromuscular diseases, which affect one in every thousand people, we are talking about two hundred thousand people.
b) Umbilical cord and placenta
Recent research has shown that umbilical cord blood and the placenta are rich in stem cells. However, we also do not yet know the potential differentiation of these cells in different tissues. If umbilical cord stem cell research provides the expected results, that is, if they are truly capable of regenerating tissues or organs, this will certainly be fantastic news because it would not involve ethical questions. We would then have to solve the compatibility problem between donor and recipient stem cells. For this, it will be necessary to create, with the greatest urgency, public cordon banks, similar to blood banks. This is because it is known that the greater the number of cord samples in a bank, the greater the chance of finding a compatible one. Recent experiments have shown that umbilical cord blood is the best material to replace the marrow in cases of leukemia. Therefore, the creation of cord blood banks is a priority that is already justified only for the treatment of blood diseases, even before we confirm the results of other research.
c) Embryonic cells
If cord stem cells have the desired potential, the alternative will be the use of embryonic stem cells obtained from unused embryos that are discarded in fertilization clinics. Opponents of the use of embryonic cells for therapeutic purposes argue that this could lead to a trade in eggs or that there would be destruction of "human embryos" and it is unethical to destroy one life to save another.
Despite all these arguments, the use of embryonic stem cells for therapeutic purposes, obtained by both nucleus transfer and discarded embryos in fertilization clinics, is advocated by the many people who will benefit from this technique and most scientists. The 63 science academies around the world that have positioned themselves against reproductive cloning advocate embryonic stem cell research for therapeutic purposes. Regarding those who think that therapeutic cloning can open the way for reproductive cloning, we must remember that there is an insurmountable difference between the two procedures: implantation or not in a human uterus. Just prohibit implantation in the womb! If we think that any human cell can be theoretically cloned and generate a new being, we can go so far as to think that every time we pull the cuticle or pull a hair out, we are destroying a potential human life. After all, the nucleus of a cuticle cell could be placed in an enucleated egg, inserted into a womb and generate a new life!
On the other hand, tissue culture is a common practice in the laboratory, supported by all. The only difference, in this case, would be the use of ova (which when not fertilized are just cells) that would allow the production of any tissue in the laboratory. That is, instead of being able to produce only one type of tissue, already specialized, the use of ovules would allow to manufacture any type of fabric. What is anti-ethical about it?
As for egg trading, would not it be the same thing that happens today with organ transplants? Is not it easier to donate an egg than a kidney? Each of us may wonder: Would you give an egg to help someone? To save a life?
Regarding the destruction of "human embryos," again we must remember that we are talking about growing tissues or, in the future, organs from embryos that are normally discarded, which will never be inserted into a uterus. We know that 90% of the embryos generated in fertilization clinics and that are inserted in a uterus, under the best conditions, do not generate life. In addition, recent work (Mitalipova et al. , 2003) has shown that cells obtained from poor embryos, which would not have the potential to generate a life, maintain the ability to generate embryonic stem cell lines and thus generate tissues . In short, is it fair to let a child or young man affected by a deadly neuromuscular disease die to preserve an embryo whose destination is garbage? An embryo that, even if implanted in a womb, would have a very low potential to generate an individual? By using embryonic stem cells to regenerate tissues in a person convicted of a lethal disease, are not we actually creating life? This is not comparable to what is done today in transplantation when organs are removed from a person with brain death (but could remain in vegetative life)
It is extremely important that people understand the difference between human cloning, therapeutic cloning and cell therapy with embryonic stem cells or not. Most countries in the European Community, Canada, Australia, Japan, China, Korea and Israel have recently approved embryonic stem cell research. This is also the position of science academies in 63 countries, including Brazil. It is vital that our legislation also approve these searches because they can save countless lives!