The embryo is a hybrid of a human and a pig. Biologists from the United States, Japan and Spain have injected human stem cells into a pig's egg. Scientists called the embryo grown in the womb of an animal chimera - in honor of a creature from ancient mythology. In the future, these studies will allow scientists to grow organs for transplantation and study nature. genetic diseases... In order for research to move forward, scientists must not only prove the effectiveness of the experiments, but also their ethics.

What is the essence of the experiment

A group of American scientists from the Salk Institute for Biological Research in California injected human stem cells into a pig embryo on early stage development and placed it in the womb of an animal. A month later, stem cells developed into embryos with the rudiments of human tissues: heart, liver and neurons.

Of the 2,075 transplanted embryos, 186 developed to the 28-day stage. The resulting embryos were "extremely unstable," scientists admit, but so far this is the most successful human hybrid. Scientists write that the resulting chimera is the most important step towards creating animal embryos with functioning human organs.

Source: Cell Press

The ultimate goal is to grow functional and transplant-ready organs, the experiments carried out are the first step towards this, writes WP, citing scientists from California.

The results of a similar study are reported in the first issue of the journal Nature for 2017. As follows from the publication, a group of scientists from Japan and the United States managed to grow a mouse pancreas inside a rat, and then transplant an insulin-producing organ into diabetic mice, which did not cause immune rejection. This was the first confirmation that interspecies organ transplantation is possible, writes Nature.

Why is it needed

The main goal of scientists is the cultivation of human organs using the embryos of large animals. According to the US Department of Health, 22 people die each day while waiting for organs for transplantation. Scientists have long tried to grow artificial tissues outside the human body, but the organs that develop in a Petri dish (the so-called container for growing microorganisms) are very different from those grown inside a living organism.

The technology for growing artificial organs is likely to be similar to the experiment with mice and rats, writes The Washington Post. The rats that were implanted with new cells as part of the studies described in Nature were genetically modified. They could not grow their own pancreas, so the stem cells “filled the empty space”. Some of the glands appearing in rats were transplanted into sick mice. After surgery, the mice lived with healthy glucose levels for a year - half human life, writes WP.

The study proved that interspecies transplantation is not only possible, but also effective, said senior study author Hiromitsu Nakauchi of Stanford University. Scientists in the same way managed to "grow" the heart and eyes.

What are the difficulties

Scientists from California achieved their first results four years after the start of research. According to them, pigs are ideal animals for experimentation. Their organs are about the same size, but they grow much faster than humans. The time factor should become the main factor in further research, the researchers admit.

“While the number of human cells in the resulting embryo is very small, and the whole process takes place at an early embryonic stage, it is too early to talk about creating a full-fledged chimera,” commented Nakauchi's colleagues on the result. In the resulting embryos, there was only one human per 100,000 pig cells (efficiency 0.00001%). "It is enough to achieve an efficiency of 0.1% to 1% of cells," one of the authors of the California study explained to the BBC.

After four weeks of development, scientists at the Salk Institute ethically destroyed the resulting embryos to prevent the chimera from fully developing. “We just wanted to answer the question of whether human cells will be able to adapt at all,” explained one of the authors.

Ethical issues

In 2015, the US National Institutes of Health imposed a moratorium on research funding that crosses human and animal cells. Since stem cells can develop into any human tissue, an animal with human brain, according to some bioethics. Others point to the violation of the "symbolic border" between man and animal, writes WP.

Californian scientists believe the fears surrounding "chimeras" are more mythical than controlled experiments, but admit that the possibility of an animal being born with human cells is worrying.

In August, the US National Institutes of Health allowed a return to funding for chimera research. The organization proposes to allow the introduction of human stem cells into embryos at an early stage of development in large animals, with the exception of other primates.

“We have finally managed to prove that this approach to organ creation is possible and safe. Hope people will understand this. Many people think that this is from the section of science fiction, but now it is becoming a reality, "- commented on the possible lifting of the ban Nakauchi.

Daniil Sotnikov

Preview photo: still from the movie "Chimera"

Header photo: WikiCommons

An international group of scientists led by the Spaniard Juan Balmonte, known for his work in the field of stem cells, managed to create embryos of human and pig chimeras, which in the future may become a source of donor organs. Another team of researchers cured congenital deafness in mice using viruses. talks about the success of genetic engineering related to medicine.

The creation of genetically modified organisms is not the only way that genetic engineering can please humanity. Biotechnology makes it possible not only to change genes to improve agricultural plants and animals, but also to treat previously incurable diseases. Ironically, for this, scientists use the eternal enemies of man - viruses. The latter are used to create vectors that deliver DNA to desired cells... Another direction that may frighten people who are not too knowledgeable in science is the creation of chimera embryos that combine cells of humans and other organisms. However, what appears to be ominous at first will actually turn out to be in a convenient way creating organs.

Kidneys or lungs that have been obtained by growing chimeric embryos will be suitable for transplantation to people in need. Those fearing a mutant uprising should think that the real benefits of this technology outweigh the vague fears of pessimistic science fiction writers.

Image: Nakauchi et al. / The University of Tokyo

To dispel fears, you need to understand what and how scientists who create chimeras are doing. The main material that researchers work with is stem cells, which have pluripotency - the ability to transform into other cells in the body (nerve, fat, muscle, and so on) with the exception of the placenta and yolk sac. They are introduced into the embryos of other organisms, after which the embryo develops further.

Pigmen

This is how an international team of scientists from the USA, Spain and Japan managed to create the pig-man, rat-mouse and cow-man chimeras. They reported this in an article published in the journal Cell, which became the first document to support the successful "chimerization" of related species.

The main problem is that it is not enough to introduce pluripotent cells into the embryo and wait for something good to come out. Instead, it can end up with an organism with catastrophic developmental disabilities, including the formation of teratomas. It is necessary to turn off genes in recipient embryos so that they cannot form specific tissues. In this case, the implanted stem cells take on the task of growing the missing organ.

First, scientists injected rat stem cells into mouse embryos at the blastocyst stage, when the fetus is a ball of several dozen cells. This method is called embryo complementation. The aim of the experiment was to find out which factors play a leading role in interspecies chimerism. The embryos were transferred into the body of female mice, after which they developed into living chimeras, one of which survived until the age of two.

Genes in embryos were turned off using CRISPR / Cas9 technology, which introduces breaks in specific regions of DNA. For example, the researchers, when testing their approach, blocked the activity of a gene that plays an important role in the formation of the pancreas. The mice that were born died as a result, however, when the pluripotent cells of rats were introduced into the embryos, the missing organ developed. The scientists also turned off the Nkx2.5 gene, without which the embryos suffered from serious heart defects and turned out to be underdeveloped. Chimerization helped the embryos achieve normal growth, but no live chimeras were obtained.

Photo: Juan Carlos Izpisua Belmonte / Salk Institute for Biological Studies

The study of the resulting rat-mice showed that different mouse tissues contained a different proportion of rat cells. When scientists tried to inject rat cells into pig blastocysts and then conducted genetic analysis four week old embryos, they found no rodent DNA. This suggests that not all animals are suitable for chimerization with each other, and the successful grafting of stem cells from some embryos to others may depend on genetic, morphological or anatomical factors.

The main goal of scientists was to create a chimera of a man and a pig, in order to trace how human tissues will develop inside the embryo of a non-ruminant cloven-hoofed animal. They used pig blastocysts and, using a laser beam, made microscopic holes for the subsequent injection of various groups of pluripotent cells, which were grown under different conditions. Then the embryos were transferred to sows, where they developed successfully. Tracking the dynamics of human material was carried out using a fluorescent protein, for the production of which human stem cells were programmed.

As a result, precursor cells were formed in the porcine embryo. of various kinds tissues, including the heart, liver and nervous system... The pig-human hybrids were allowed to develop for three to four weeks, after which they were destroyed for ethical reasons.

Deaf mice

American scientists from Boston were recently able to return hearing to mice suffering from a rare genetic function disorder inner ear... To do this, they used a biological gene delivery system (vector) based on neutralized viruses. Researchers have modified an adeno-associated virus that infects humans but does not cause disease.

The infectious agent is able to penetrate hair cells - receptors of the auditory system and vestibular apparatus in animals. Biotechnologists have used the vector to repair the defective Ush1c gene in the cells of newly born live mice. This mutation causes deafness, blindness, and imbalance. As a result, the animals' hearing improved, which allowed them to distinguish even quiet sounds.

Genetic engineering, therefore, is not a way to create mutants that threaten humanity. This is a constantly improving set of methods and means to improve the life and health of people, especially those who are in great need of it. Since the creation of chimeras and gene therapy are not so easy to implement and sometimes require ingenious solutions, the development of biotechnology is not going as fast as we would like. However, dozens of scientific papers are published annually that deepen and enrich our knowledge and skills.

However, something akin to a revolution in medical science did happen. At the end of January, the scientific journal Cell published an article by molecular biologist Juan Carlos Ispisua Belmonte, who runs a laboratory at the Salk Institute in California (USA), and 38 of his coauthors. The article describes how scientists managed to create viable embryos, consisting of a mixture of pig and human cells.

Who are they

If these creatures were allowed to be born (and biologists did not do this, not least for ethical reasons), they could not be formally attributed to any biological species. Such organisms are called chimeras. In chimeras, which we know from medieval miniatures, eagle wings are attached to the body of a lion, and a snake sting is attached to the goat's hooves. Who remembers the mouse from the human auricle on the back - the result of a high-profile experiment 20 years ago, it is easy to admit that you can expect something else from biologists. But in this sense, the new creatures from the Belmonte laboratory hardly had a chance to surprise anyone: after birth, they would look like the most ordinary pigs. It's just that some of the cells in their body - about one thousandth of a percent - would contain pure human DNA. And in this, the piglets would have favorably distinguished from the 1997 eared mouse, which was rather an experiment on plastic surgery and did not have a single human cell.

According to recent estimates, a person has 30-40 trillion cells, and about the same in a pig. A thousandth of a percent of such an astronomical figure - is it a lot or a little? To conceive a child, just one cell is enough. Therefore, in theory, a chimera pig could become a parent to a human baby.

Donor without a motorcycle

Doctors see pigs not as potential relatives, but as potential donors for transplanting their organs to humans. In the United States alone, 27,000 kidneys, lungs, hearts and intestines are transplanted per year. And in all 27 thousand cases, surgeons deal with organs of living or dead people. But who in their right mind would dare to ask to be transplanted into the place of their own refusing heart, taken from a pig, when the procedure with the usual, human, is debugged and works perfectly? Those who will not reach the queue for a transplant: 118 thousand people are registered in the United States on the so-called waiting list. According to statistics, about 22 of them will die today (and the same number will die tomorrow, and the same number will die next Sunday) without waiting for their transplant.

There are too few human donors - and it's not even that volunteers are rare. (Unlike the United States, in Russia, according to the law, a potential donor is anyone who has not explicitly prohibited the removal of his or her organs. The law does not require consent from relatives.) Only three people out of a thousand, according to British data from New Scientist magazine, die in circumstances that make their organs are suitable for transplantation. The numbers, obviously, vary from country to country - they depend on how quickly the ambulance arrives at the scene of an accident or shootout, as a result of which the most promising donors appear, and on how many transplant centers nearby, where organs can be properly disposed of. Finally, it is necessary to find and prepare a patient from the “waiting list” for the operation in a few more hours - there are much stricter compatibility rules than for blood transfusion with its four different groups.

The cells that are least susceptible to rejection are our own. What if we use animals as incubators for kidneys and pancreas grown from human cells (and ideally from the cells of exactly the patient to whom the organ will be transplanted)? Solving the problem head-on is hindered by the same problem with rejection: for the ready immune system of an adult pig, human cells are no less alien than for us - pork cells.

This means that we must act somehow differently.

Cut and glue

Imagine that in front of you two people are cut in half at the same time - say, with a combat laser from a bad science fiction movie. Then they connected half of one with half of the other, and the glued halves would then live a whole life as if nothing had happened. The option is even more paradoxical: they took two thin ones, pressed them to each other - and got one fat man. If both people have not yet turned four days from the moment of conception, nothing is impossible here. At this stage, the future organism is a ball of identical cells. "You remove the outer protective layer from inanimate matter and physically connect the embryos," Virginia Papaioannou, a professor at Columbia University (USA), explained in an interview how scientists have been producing chimera mice with a full set of genes from two individuals at the same time since the 1960s. Having touched, the two embryos simply form a new larger ball - almost like soap bubbles meeting in the air. The immune system The ball of cells does not yet have a ball of cells that could prevent this - as, indeed, all other systems: they will develop much later.

A more subtle intervention is to add a foreign biomaterial to the embryo when its cells have already divided into different varieties. At the blastocyst stage, the embryo - whether in a mouse or in a person - is a hollow ball with a small portion of cells locked inside. Only this internal portion is to become the future lungs, liver, kidneys, brain, skin and other details of the adult body, and the entire external portion will turn into a placenta that will not survive childbirth. Biologists prefer to introduce foreign cells at this stage.

This is not to say that this scenario in its purest form opens up exciting opportunities for transplantologists. The need for donor organs usually arises later - when a person has already passed the age of the embryo. How to breed it with another embryo? Take such cells of an adult organism that have not acquired a clear mission (like brain or liver cells) and have not lost the ability inherent in the cells of the embryo to turn into anything. They are called stem cells, but they are very rare in the body. In 2012 Nobel Prize in medicine was awarded to the Japanese scientist Shinye Yamanaka for the fact that he came up with a way to turn ordinary body cells into stem cells - to forget your prehistory and "fall into childhood." The full name is induced (because they were forced to change) pluripotent (that is, "capable of anything" - of any transformation) stem cells. Researchers of chimeras use them.

Is it possible to combine embryos like this different types- for example, rats and mice? This is exactly what the team of Toshihiro Kobayashi from the University of Tokyo did first with stem cells in 2010 - and the American team, which published their results seven years later, perfected the method. How can you be sure that you actually bred a chimera? Take as a basis the embryos doomed to death with specially damaged DNA. Using the recently invented "gene scalpel" CRISPR-Cas9, a DNA point-editing technique, scientists have disabled the genes responsible for the growth of the pancreas or heart. With such a defect, there is no chance of surviving (and even being born alive). But then rat stem cells were implanted into the embryo. And if the chimera mouse was still born, scientists could be sure that a rat's heart was beating inside him.

But the most surprising result concerned the gallbladder. Rats do not have it, but mice do. But chimeras, in which the mouse genes responsible for this organ were disabled, were still born with a working gallbladder- from rat cells. The mouse cells somehow suggested the correct context to the rats, and they, succumbing to the influence, formed an organ impossible in the rat.

Closer to pigs than rats

It was not possible to cross a pig and a rat in this way - because these organisms are too different from each other. Different gestation times and different organ sizes suggest that cells are programmed to divide at different rates. Finally, can a chimera's tiny rat heart pump blood through a huge pig's liver?

But with people there is no such difficulty: we are much closer to pigs - primarily in terms of organ size. Therefore, pigs (and mini-pigs as a separate option) have always been the # 1 candidates for xenotransplantation. In parallel with the cultivation of human cells in a porcine body, biologists are considering other possibilities - for example, simply to take and hide from human immunity those proteins on the surface of pig cells that cause the most acute reaction. Such studies have been going on for a long time, so a pig as a candidate for organ transplant is not new.

The new experiment showed that there is a possibility, and it is not at all speculative - and not even an incredible accident. 2075 embryos were planted in pigs, and 186 of them have reached sufficient, according to scientists, maturity. Human cells were labeled with a special label in their DNA, which makes them produce a fluorescent protein - and 17 mature, healthy embryos glowed confidently in ultraviolet light, proving to scientists that they are definitely chimeras.

From now to organs in a living incubator - years, the researchers say. And the point is not only that the proportion of human cells in the chimera's body is too small. It would be difficult for scientists to see how they grow and what happens to cells in an adult body anyway.

We are much closer to pigs - primarily in terms of organ size. Therefore, pigs have always been the # 1 candidate for xenotransplantation.

Chimeras of mice and rats, bred earlier, lived a full-fledged mouse life in two years. There is no reason to think that human and pig chimeras would have serious health problems preventing them from reaching maturity. They were not prevented from being born biological problems rather ethical. And so serious that the team from the Salk Institute was forced to conduct research with private money, because the rules of the US National Institutes of Health - an analogue of the Ministry of Health, which finances most of biomedical research in the country - prohibit spending money on any experiments with the introduction of human stem cells into animal embryos.

What is unethical about giving birth to a pig with a human spleen? Our uncertainty about the results of such an experiment. The proportions of cells in an adult embryo are not the same as in the embryo. And if pig cages prevail in a million to one ratio, it's not as bad as if human cages take over. And a creature will be born that looks more like a human than a pig, with a human brain, but with deformities caused by the circumstances of the experiment. For medics to be able to save people, it seems, there needs to be a more precise definition of a person - and a more accurate answer to the question of where people come from.

It is quite possible to come to this conclusion after a successful bold experiment that experts conducted in China. Its main goal is to test the possibilities of growing organs for transplanting them to humans.

Chinese scientists crossed a pig with primates. Thus, they actually succeeded in what was previously considered incredible. Consequently, it is not at all excluded that chimeras really existed in a distant time.

A team of specialists succeeded in crossing pig and primate cells. According to the latest information received, two piglets were born alive. However, their death after that came within only one week.

The main thing in this experiment is that never before in history have fully-term chimeras been born. This could be a significant step in providing humanity with the organs for the necessary transplants.

However, it seems that achieving this goal is still a long way off.

Chinese scientists first started modifying monkey cells to produce a specific fluorescent protein. This allowed specialists to trace the genetic cells of their offspring.

Then, they set about extracting embryonic stem cells from the modified ones. This was done to introduce them into pig embryos five days after fertilization took place.

It is reported that the specialists introduced more than four thousand embryos obtained in this way to the sows.

As a result, the female pigs gave birth to ten piglets. Two of them had both types of cells. In fact, they were the most real chimeras.

As a result, the researchers note that in the chimeras that were born, part of the tissues, including the tissues of the heart, liver, spleen, lungs and skin, consisted of monkey cells. However, their ratio was rather low.

Also, Chinese science is still at a loss to give an answer to what actually was the cause of the unexpected death of newborns and fully matured pigs.

However, it is also noted that at the same time, other piglets born during the experiment and who were not chimeras died. Scientists tend to assume that the reason for this lies in the special processes associated with IVF.

It has long been known that this method does not work as well in animals as in humans. However, in spite of this, experts are going to continue their bold experiment.

In doing so, they propose to use a much larger number of monkey cells. The next attempt will have as its goal the creation of completely healthy and viable animals.

The main task is to have one of their organs completely composed of primate cells. Then it will be a real breakthrough in the possibilities of transplantation.