Chimeras - a medical miracle or Pandora's box

In a groundbreaking experiment, the results of which were published earlier this month, scientists succeeded in creating an embryo that contained both human and monkey cells. The scientists destroyed the embryo after 20 days of study in the laboratory, but their achievement is interpreted by some ethicists as the opening of Pandora's box.

There is a name for the type of life scientists have created, which is a chimera, and it comes from a monster from Greek mythology that was part lion, part goat, and part snake.

The US-China study, led by scientist Juan Carlos Izpisua Belmonte, is the culmination of decades of work to understand early embryonic development in non-human species, which Belmonte hopes can now be applied to humans.

However, the experiment has raised serious ethical questions about the consequences of combining human cells with cells from other species, and ethicists around the world are debating how the work should be interpreted and considering next steps.

Some ethicists fear that scientists will rush into the future with chimeras without adequate preparation. Their main concern is the ethical status of chimeras containing human and non-human cells - especially if the human cells are integrated into sensitive regions such as the monkey brain. Among other things, the question arises as to what rights such beings would have.

Professor Julian Savulescu of the Center for Practical Ethics at Oxford believes this research opens Pandora's box.

"These embryos are destroyed after 20 days of development, but it is only a matter of time before the human-non-human chimeras are successfully developed, perhaps as a source of organs for humans. The key ethical question is: what is the moral status of these new creatures? Before any experiments are conducted on live-born chimeras, or their organs are harvested, it is crucial that their mental capacities and lives are adequately assessed."

Belmonte, a professor at the Salk Institute for Biological Studies who enjoys a high reputation thanks to his work on embryo development, clearly indicated what the goals of his experiment are and in which direction he wants to go. Creating mutants with specific physical characteristics in the table of heroes of the X-Men films is definitely not his goal.

He explained to "Time" that the first steps of the human embryo are "the greatest mystery of human development." "While we know a lot about development after we're born, even what happens during pregnancy, we really know nothing about human development during the first two to three weeks after fertilization. "Everything we know about early embryogenesis comes from different laboratory models - hamsters, mouse worms - but we know nothing about us," said Belmonte.

In a study published in the journal Cell, Belmonte described how his team's creation of a human-monkey chimera, which was maintained for 20 days, allowed him to study these key stages of development. In particular, scientists have looked for and studied the various signals that new cells send to trigger the development from a single fertilized cell to millions of cells and the multiple tissues and organs that make up a human. The evolutionary closeness of primates and humans made this possible. Belmonte previously tried to conduct a similar experiment with human and pig embryos, but failed.

Scientists agree that there are several reasons why this type of research should continue. Human-monkey chimeras can be used to study parts of the brain, for example to better understand Alzheimer's disease. Another goal is to grow human organs for transplantation by "deleting" the relevant organ from the animal's genetic makeup and replacing it with human stem cells.

Belmonte says he is fully aware of the moral and ethical issues his work raises. "We will not use monkeys to grow human organs in them," he said. He claims he plans to learn the "language" of human embryo development using a human-monkey model, then use it to better understand a particular disease — and potentially create human tissue for organ transplants in less controversial species, such as pigs.

Belmonte is already working with scientists and pig farmers in his native Spain to prepare for further studies. In preparing to work on the human-monkey chimera, he consulted three independent ethicists and obtained permission from international regulatory boards.

Hank Greeley, director of the Center for the Law and Nature of Science at Stanford University, claims that the experiment itself did not pose a problem, because the embryo was not planned for implantation and further development. However, he admits that such experiments can upset people and be misinterpreted if they are not adequately explained. Greeley points out that one of the biggest concerns is about consent to study. He says that it is most important that cell donors are informed in detail that their cells can be used for chimeric research. "One of the most controversial issues in research ethics is whether certain forms of research are so controversial that they require special approval," said Greely.

Belmonte used stem cells in his research that were approved by the ethics committee of Peking University and have been used in previous research as well. However, it remained unclear whether the approval form specifically indicated that the research involved a chimera.

On the other hand, some ethicists warn that this type of research can lead to the design of human beings to suit social desires and needs, and cite numerous examples throughout history when science has been misused in order to fulfill authoritarian and cultural expectations.

Belmonte is willing to participate in all discussions. He claims that he was unfairly criticized when the news about his work was leaked to the media prematurely and when it was commented out of context by those who do not understand his work.

"I am not arguing that we should conduct every experiment we can, but that we should move forward in ways that are legally and ethically permissible," he said. He believes that his work is not only limited to the academic understanding of early human development, or even to the science fiction possibility of creating human tissue for organ transplantation, but that it can reveal how they begin and thus help in the treatment of diseases such as cancer and Alzheimer's.

"Thus, we can study not only the earliest but also the later stages of life with these chimeric platforms," ​​he said. Of course, provided that our ethical, cultural and sociological norms can keep up with the rapid pace of scientific progress.