In a groundbreaking development, scientists have successfully created the first human-monkey chimera, raising critical ethical questions surrounding this controversial scientific achievement.
What if you could grow a human organ inside an animal? This may sound like science fiction, but it is one of the goals of a controversial field of research called chimera science. A chimera is an organism that contains cells from two or more different species. In this case, the aim is to create chimeras that have both human and monkey cells, and use them to study human development and the possibilities of organ transplantation.
Recently, a team of researchers from the U.S., China and other countries reported the first successful creation of human-monkey chimeric embryos in a study published in the journal Cell. The researchers injected 25 human stem cells, which can develop into any type of cell, into macaque monkey embryos. They then cultured the mixed embryos in test tubes for up to 20 days, and observed how the human and monkey cells interacted and differentiated.
The monkey embryos received the injections of human cells six days after they were created. Within one day, 132 embryos exhibited human cell presence. After 10 days, 103 chimeric embryos were still progressing, but survival declined. By day 19, only three chimeras remained alive, yet the proportion of human cells in the embryos remained consistently high.
The researchers, led by Juan Carlos Izpisua Belmonte from the Salk Institute for Biological Studies in California, said that their work was motivated by a desire to understand the early stages of human development, which are largely unknown due to ethical and technical limitations. They also hoped that their findings could pave the way for generating human organs in animals for transplantation purposes, as there is a severe shortage of donor organs worldwide.
However, the study also raised serious ethical concerns about the implications and consequences of creating such chimeras. Some critics argued that mixing human and animal cells could blur the boundaries between species and compromise their dignity and identity. Others worried that human cells could end up in the brain or reproductive system of the chimeras, raising questions about their cognitive abilities and potential offspring. Moreover, some pointed out that conducting such experiments in China, where the regulations are less strict than in other countries, could pose risks of abuse and exploitation.
The researchers acknowledged these ethical challenges and said that they followed strict guidelines and oversight from their institutions and countries. They also stressed that their goal was not to create hybrid creatures or organs for transplantation, but to use human-monkey chimeras as a model system to study human development and disease. They argued that this approach could provide valuable insights into how humans evolved from primates, and how genetic and environmental factors affect embryonic development.
At the same time, they hinted that study had the potential to be used to create human tissues for organ transplantation in a species with fewer ethical concerns, like pigs. Pigs are evolutionarily more distant from humans and offer greater accessibility for conducting experiments.
More recently, Chinese scientists have achieved a groundbreaking feat in creating the first true chimeric monkey, incorporating cells from a different embryo and marked with green fluorescent protein. The resulting monkey exhibited high levels of chimerism, with 67% of its tissues originating from donor cells, ranging from 21% to 92% in different parts of the body. The donor cells were found in 26 types of tissue, including the brain, heart, kidneys, liver and testes. The monkey’s eyes and fingertips showed green fluorescence, indicating the presence of donor cells.
Unfortunately, the monkey did not survive for long. It died after 10 days due to respiratory failure and hypothermia. The exact cause of its death is unclear, but it could be related to the epigenetic differences between the cell types.
Again, the method, involving injecting stem cells into an embryo and tracking their development, presents ethical challenges but offers a potential avenue for advancing research on neurological and biomedical issues in humans.
hese studies represent a milestone in chimera science, but also open up new dilemmas and debates about its applications and implications. As this field advances, it will require careful regulation and public dialogue to ensure that it is conducted responsibly and respectfully.
