Members of the Bioethics Expert Team of the Polish Bishops’ Conference present their reflections on the experiments conducted with human-animal organisms.

Alongside a positive assessment of some biomedical projects, the Team also presents some objections to them. At the forefront of the latter are the attempts to mix human and animal biological material.

The Team’s members believe that “disrespect for the personal dignity of man may never accompany scientific research. Man must never be a victim of medical experimentation.”

“Respect for the dignity of the human being excludes […] his objectification, treating him (including the embryo and fetus) as mere biological material, changing his personal identity, and reference to his psychosomatic structure according to similar criteria which are considered sufficient in experiments on animals,” we read in the statement.

In this regard, the Team’s members also cite the statements of the recent Popes Benedict XVI and Francis. “We need constantly to rethink the goals, effects, overall context and ethical limits of this human activity, which is a form of power involving considerable risks. This, then, is the correct framework for any reflection concerning human intervention plants and animals, which at present includes genetic manipulation by biotechnology for the sake of exploiting the potential present in material reality,” writes Pope Francis in the encyclical Laudato si’ (131-132).

Press Office of the Polish Bishops’ Conference

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Stance of the Team for Bioethics of the Polish Bishops’ Conference
on Research with Human-Animal Organisms

  1. The medicine of the future promises wonderful prospects and raises new hopes. Unfortunately, it also sometimes raises serious doubts. They do not always originate from the goals of scientific research and related experiments per se if they are of a beneficial nature and respond to human health needs. Doubts are raised regarding the technologies used in research and interventions that violate the personal dignity of the human being, which involves an integral understanding of the human being, that is, not only his spirit but also his body. For some time now, a particular source of concern has been the research developing, especially in the 21st century, that now involves on creating human-animal cells and will, in the future, include that of beings.
  2. The dangers of interfering with the genetic heritage were already pointed out by Pope Francis in his encyclical Laudato si’: “Here I would recall the balanced position of Saint John Paul II, who stressed the benefits of scientific and technological progress as evidence of ‘the nobility of the human vocation to participate responsibly in God’s creative action,’ while also noting that ‘we cannot interfere in one area of the ecosystem without paying due attention to the consequences of such interference in other areas.’ He made it clear that the Church values the benefits which result ‘from the study and applications of molecular biology, supplemented by other disciplines such as genetics, and its technological application in agriculture and industry.’ But he also pointed out that this should not lead to ‘indiscriminate genetic manipulation’ which ignores the negative effects of such interventions” (LS 131).
  3. The Question of Concepts
  4. In modern terminology, the terms hybrid and chimera need to be clarified. In popular scientific literature and journalism these terms are sometimes used interchangeably. In the present document, they are employed in accordance with the terminology commonly used in the biological sciences. In simple terms, a hybrid has “mixed” DNA from two organisms in each of its cells. This concerns two situations. First, sexual interbreeding of organisms, but also the situation of a cell nucleus with human DNA being introduced into an animal egg cell without a cell nucleus (but with conserved mitochondria).
  5. Unlike a hybrid, a chimera contains two types of cells with differing DNA. In other words, a chimera has cells whose genotypes differ.
  6. A typical hybrid among mammals is an organism that results from the crossing of two beings of different species, by sexual reproduction. Nowadays, a hybrid is also understood as an organism created by crossing animals of two races, subspecies, or genera, so that each cell of the hybrid contains genetic information from both these beings. Hence, hybrids usually have characteristics of both animal species or breeds. This mixture of DNA can produce a new organism called a hybrid. The mule, the hawk or the bison are just some examples of hybrids.
  7. As already emphasized, a chimera is an organism made of cells that have different genotypes. This means that some cells have the correct set of individual A’s chromosomes, and some have the set of individual B’s chromosomes. Within interspecies chimeras, for example, some cells may have a human karyotype, and some may have a monkey’s karyotype. Chimeras can thus be single species, but also interspecies. A single-species chimera come to exist in many ways. It can result from the fertilization of a single female gamete by two male gametes, from the fusion of two zygotes, or from the fusion of two early embryos. As a result of this combination, the formed being has cells with different genotypes. This is also sometimes called mosaicism. In the case of the mother’s cells, the child’s genotype is not the same as of the mother. Medicine has also come across rare cases of fetal-maternal microchimerism.
  8. In a broad sense, a chimera is a being in which organs, tissues, or cells taken from a donor of the same species have been implanted. An example of this kind of chimera would be a human being who has received a homologous (also called allogeneic) transplant of cells, tissues, or organs from another human being. However, because of the respect due to the donor and to the recipient of organs, tissues or cells, the term is not used for the recipient of transplants.
  9. In modern biology, interspecies chimeras are organisms created by combining embryonic fragments of different organisms at the embryonic stage, or creatures that have been implanted with stem cells taken from others of another species. The creation of interspecies embryonic chimeras has recently been a much-debated subject, but research has been conducted in only a few cases, and it is in fact not approved and accepted by society.
  10. Biological Aspects
  11. The production of human-animal hybrids and chimeras already has a history. These procedures are characterized by ever new ideas and research aimed at overcoming human health problems. However, there are times when research and experiments involving the creation of new organisms are motivated by unethical benefits. Here are a few examples.
  12. The Russian biologist Ilya Ivanovich Ivanov, who in 1910 proposed crossing a human being with a monkey, can be considered a precursor to the idea of making human-animal beings. This idea was supported, among others, by the authorities of the Soviet Union and the Pasteur Institute in Paris. One of the aims of these experiments was to fabricate „living robots.” Fortunately, this kind of work was rapidly abandoned.
  13. The development of microbiology, embryology, genetics, and the knowledge of stem cells has opened a new path the production of human-animal organisms. In 2006, English scientists at Newcastle University and Kings College in London attempted to make human-animal embryos by introducing genetic material from an adult human cell into the oocytes of a cow. The experiment was designed to produce human embryonic stem cells. These were intended to enable therapies involving the development from stem cells of a patient’s cells, tissues or organs destroyed by disease or injury. If the new cells or tissues had the same genetic information as the human donor’s DNA, they would avoid being rejected by the transplant recipient’s immune system. This type of research has reached the exploratory stage and is not currently used to produce organs for transplantation.

12 Not all genetic research and experimentation provoke strong opposition. One of the many examples of the production of organisms that not all representatives of biological, agricultural, and ecological sciences approve of is the work on GMOs, such as the transgenic cows created by Argentine scientists at the biotech company Bio Sidus. They reported on an experiment involving the implantation into a cow embryo of human genes responsible for producing human insulin. These embryos were transferred into cow mothers. The resulting organisms would produce human insulin extracted from their milk. Currently, this technology is used to generate protein-like drugs that cannot be obtained by methods of chemical synthesis.

  1. Compared to this work, that of Esmail Zanjani of the University of Nevada is quite different; his experiment involves the introduction of human stem cells, taken from bone marrow, into a sheep fetus. As a result, selected organs of the sheep, including the heart, were to be largely human. The authors’ intention was to produce organs that would be suitable for transplantation to the human from whom the stem cells were taken. The recipient’s immune system would recognize these transplants as foreign.
  2. Steve Goldman’s team at the University of Rochester Medical Center injected human glial progenitor cells into donkey mice. These cells developed into astrocytes, i.e., the largest glial cells that are a component of nervous tissue. The researchers announced that, in the experiment, they had obtained mouse-chimeras with the human cells in their brains.
  3. A paper recently published in the journal “Cell” has had a resounding effect on the scientific world. Professor Juan Carlos Izpisua Belmonte from California’s Salk Institute recounted, together with his Chinese collaborators, the first successful attempt to grow human stem cells in a macaque blastocyst. This means that the organism of this chimera consisted of cells derived from a human and from a macaque. As in the above-mentioned experiments, the experimentation is expected to be the next step in developing a method for producing needed tissues and organs for transplant procedures that would not trigger a rejection by the recipient’s immune system.
  4. There have also been significant developments in transplanting pig organs to humans. Surgeons in New York City attached a kidney taken from a genetically modified pig to a human in a groundbreaking operation. Importantly, the human body did not reject the transplanted organ, and the kidney from the pig took on its functions. This is a major step in the years-long effort to use animal organs in life-saving transplants, given the shortage of organs for transplantation. Moreover, researchers at the University of Maryland, Baltimore, reported transplanting a pig heart into a patient for whom a donor could not be found. This is the first animal-to-human heart transplant. The U.S. Food and Drug Administration (FDA) has granted emergency approval for the surgery, which solely applies when an experimental medical product—in this case a genetically modified pig heart—is the only treatment option available that may allow the patient to survive.

III. Ethical aspects

17 The Bioethics Expert Team of the Polish Bishops’ Conference has great esteem for the efforts being made by representatives of medical science in their search for ever more perfect and effective therapeutic methods. We are also aware that progress in these sciences is not possible without conducting experiments, which are at times very innovative and may even be dangerous to man. Not all these experiments necessarily raise moral objections. However, the Team’s members believe that scientific research can never be accompanied by disrespect for the personal dignity of man may never accompany scientific research. Man must never be a victim of medical experimentation. The methods used should raise a minimum of hope, and the risk associated with their use must not be greater than resulting from the abandonment of a therapeutic procedure with proven methods. Respect for the dignity of the human person also precludes his objectification, treating him (including the embryo and fetus) as mere biological material, changing his personal identity, and reference to his psychosomatic structure according to similar criteria which are considered sufficient in experiments on animals. In other words, “By themselves [science and technology] cannot disclose the meaning of existence and of human progress. [They] are ordered to man, from whom they take their origin and development; hence they find in the person and in his moral values both evidence of their purpose and awareness of their limits” (CCC 2293). Consequently, the conscious and uncoerced consent of the participant in the experiment itself has its limits. There are also limits to the experimentation with of human body parts, for they are always connected to the individual person and, so, marked by his dignity which transcends the right of appropriation by another human being, and even more that of the world of other creatures. For the faithful, the incommunicability of his own body and the body of another person derives, moreover, from the fact that the life of God is present in him, and he is the temple of the Holy Spirit (cf. CCC 2300; 1 Cor. 6:19).

  1. From the foregoing axiological assumptions derive the principles of using cells and organs of the human body in medical experiments and research. This is especially true of the experiments discussed above, which involve combining or “mixing” elements of the human body with elements of an animal body.
  2. In response to a statement issued in September 2007 and the subsequent official report published on 1 October 2007 by The Human Fertilization and Embryology Authority (HEFA) in the United Kingdom, suggesting a policy regarding the production and use of human-animal cytoplasmic embryos (which prompted the UK government to introduce appropriate legislation), the former President of the Pontifical Academy for Life, Archbishop Elio Sgreccia, stated that such experiments are “a monstrous act against human dignity.” A similar stance on this issue was taken by the Scientific Council of the Polish Bishops’ Conference on 19 October 2007. On 28 October 2019, our Team (of Experts of the Polish Bishops’ Conference on Bioethics) also expressed its opinion a related topic, publishing a document entitled “Stance of the PBC Bioethics Team of Experts on creating human-animal hybrids” ( In 2011, a similar statement was made by the CJEU (Judgment of the Court of Justice of the European Union (Grand Chamber) dated 18 October 2011; Case C34/10 Oliver Brüstle vs. Greenpeace).
  3. In the present document, our Team refers to the work cited above on creating human-animal (macaque-human) embryonic chimeras. Our Team’s stance has two dimensions. The first, presented above, is ontological in nature. It points to the unethical character of experiments aimed at creating new beings—even if only at the embryonic stage—by combining elements of human genetic information or human cells with animal gametes or implanting them in animals, thus fundamentally violating human dignity, which is reduced to the level of an animal. In the document’s second dimension, which is biological-ethical, indicates the dangers of such experiments.
  4. In general, it must be stated that many scientists are opposed to producing human-animal embryonic chimeras. They point to the dangers associated with such attempts. These include the risk of transmitting animal pathogens, including pathogenic viruses, to humans. This could occur, among other things, when putting into a human organism human stem cells grown in an animal, through the transfer of the nucleus from a human somatic cell into the cytoplasm of an animal oocyte previously deprived of its cell nucleus, and as well as the transplantation into humans of organs grown in an animal as a result of the introduction of human stem cells. In each of these situations, the possibility of transmitting new pathogens (new zoonoses) arises, thus endangering humans.
  5. Objections to such practices include the use of human embryos and justifying the needs or benefits of experimenting on human-animal embryos. The effects of such research are difficult to predict and are associated with biological risks. Undoubtedly, as Pope Francis notes in his encyclical Laudato si’, “A good part of our genetic code is shared by many living beings. It follows that the fragmentation of knowledge and the isolation of bits of information can actually become a form of ignorance unless they are integrated into a broader vision of reality” (LS 138).
  6. Previous research results confirm the possibility the possibility of generating human neuronal activity in the brains of animal organisms. Su Chun Zhang produced human-animal embryonic cells in 2007 in model research on chimeras, yet not with the goal of generating chimeric brains with both animal-derived and human-derived cells. There is concern, however, about uncontrolled colonization of animal brains with human nerve cells, which may be one of the possible scenarios in projects to generate embryonic human-animal chimeras. Moreover, individual Positive individual research results are often accidental in nature, and do not yet prove that the technology has been mastered and is error-free. The broad participation of Bioethics Committees that grant permission to conduct research solely for cognitive and modeling purposes should be recommended.
  7. The ecological dimension must also be considered in these experiments. It is concerned with the risk of disrupting the natural biodiversity of species by producing artificial organisms with a biological and moral status that is difficult to determine. These issues were raised by Julian J. Koplin and Julian Savulescu in 2019 in a study, in which they found brain cell treatments to be the most challenging from this perspective.
  8. The interspecies chimeras generated during embryogenesis will likely produce human gametes (female oocytes organisms, male sperm organisms), although their phenotypes (shape and appearance) will be essentially animal. If such animals are allowed to reproduce, human organisms may develop in their uteri. It should be noted that the article cited above (Tao Tan, 2021) raised so much controversy that the institutions overseeing this type of research immediately banned the use of gametes of chimeric organisms in reproduction (we use the term “procreation” to refer to human gametes).
  9. Bearing in mind the whole spectrum of problems and risks connected with the research in question, the members of the Bioethics Expert Team of the Polish Bishops’ Conference once again express their firm opposition to experiments aimed at generating human-animal embryonic organisms. An additional reason for opposition to such research is the attempt to use in it cells and tissues obtained from aborted fetuses. In the context of Eglio Sgreccia’s protest, mentioned above, we remind you that the CJEU’s judgment in 2011 (Oliver Brüstle vs. Greenpeace) prohibits the patenting of biotechnological solutions related to the early stages of embryonic development that undermine human dignity.
  10. Finally, the members of the Team would like to recall two important statements by recent popes. On 31 January 2008, Benedict XVI addressed the following words at the Plenary Session of the Congregation for the Doctrine of the Faith: “The Church’s Magisterium certainly cannot and ought not address every scientific innovation, but has the task of reaffirming the important values at stake and of suggesting to the faithful and to all people of good will the ethical and moral principles and guidelines for new and important issues” ( The reminder of the Magisterium’s role is somehow complemented by the words of Pope Francis in his encyclical Laudato si’: “Human creativity cannot be suppressed. If an artist cannot be stopped from using his or her creativity, neither should those who possess particular gifts for the advancement of science and technology be prevented from using their God-given talents for the service of others. We need constantly to rethink the goals, effects, overall context, and ethical limits of this human activity, which is a form of power involving considerable risks. This, then, is the correct framework for any reflection concerning human intervention plants and animals, which at present includes genetic manipulation by biotechnology for the sake of exploiting the potential present in material reality” (LS 131-132).

On behalf of the Team

Bishop Józef Wróbel SCJ

Warsaw, 28 Jan. 2022