Lab-grown embryos mix human and monkey cells for the first time
Researchers at the Salk Institute for Biological Studies in the US have for the first time grown human cells in monkey embryos. The results of their work were published in the journal Cell on 15 April 2021. While the results might imply progress for this particular field of research called “chimera research”, they have also ignited a debate about how ethical studies of this kind are.
By integrating human cells into the embryos of macaque monkeys, researchers have created what is called a chimeric tool. Chimeras are organisms that are made up of the cells of two distinct species, in this case humans and monkeys. For instance, if this hybrid embryo was placed in the womb of a monkey, it could possibly grow into a new kind of an animal (however this was not the aim of this study).
In this study, the monkey embryos containing human stem cells stayed alive and grew outside the body for a period of 19 days.
Previously, in a 2017 study researchers integrated human cells into pig tissues as they thought that pigs, whose organ size, physiology and anatomy are similar to that of humans, could help them in creating organs that could ultimately be transplanted to humans.
But this experiment failed and they believe it is because of the large evolutionary distance between pigs and humans(about 90 million years). Therefore, after this experiment, they decided to pick a species that was more closely related to humans, hence macaque monkeys were chosen.
Researchers believe that this ability to grow cells of two different species together offers scientists a powerful tool for research and medicine, advancing current understanding about early human development, disease onset and progression and ageing. Further, research of this kind could also help in drug evaluation and address the critical need for organ transplantation.
Researchers note how chimeric tools provide a new platform to study how certain diseases arise. For instance, a particular gene that is associated with a certain type of cancer could be engineered in a human cell. Researchers could then study the course of disease progression using the engineered cells in a chimeric model, which may be able to tell them more about the disease than results obtained from an animal model.
Some rare hybrid animals exist naturally and were probably the result of unintentional cross breeding between animals of different species. In 2014, a rare hybrid animal called “Geep” was born on an Irish farm. Geep was a hybrid between a goat and a sheep, a result of the two mating. However, the birth of this geep was not artificially induced and the cross-breeding is believed to have happened unintentionally. Generally, different species don’t cross-breed and if they do, their offspring don’t survive for long and are prone to infertility.
Mules are another example of a hybrid animal that is the result of mating between a female horse and a male donkey. As per the Mule Museum, these hybrid animals are the result of intentional breeding by humans, which they first undertook in the ancient times. While mules can live a long healthy life, they are infertile which means that they cannot have offspring of their own.
Even so, research that concerns itself with gene editing or something like chimera research, which involves artificially integrating cells from two distinct species concerns some scientists on ethical grounds. The reason is that while further research into chimeras might lead to progress, which could mean that they could be used as a source of organs for humans, these chimeras would still be a mix of human and non-human cells, a thought that makes many uncomfortable.
Writing in Pursuit, Professor Julian Savulescu and Dr Julian Koplin, of the University of Melbourne, note that chimeric research raises “the philosophical and ethical issue of moral status: how should we treat other life forms?”. They argue that chimera research has the potential to worsen injustice against animals and also point out the fairness in using part-human animals to meet human needs.
In the case of the recent research at Salk, researchers have made it clear that the chimeras created with macaques will not be used for human organ transplants but that they “nevertheless reveal invaluable information about how human cells develop and integrate, and how cells of different species communicate with one another.” Some scientists, however, are still skeptical since they feel that one of the goals of chimera research is to create organs that can be transplanted to humans.
In 2018, Dr He Jiankui made headlines when he claimed to have produced genetically modified babies using the gene editing technique CRISPR. Jiankui claimed that he had altered the genes of a human embryo that eventually resulted in the birth of twin girls with specific desired attributes — supposedly the first instance of human offspring so produced— using newly-developed tools of gene “editing”. The genes of the twins were “edited” to ensure they do not get infected with HIV, the virus that causes AIDS, according to the claims.
In December 2020 a court in China sentenced him to prison for three years, with a fine of 3 million yuan (approx. Rs 3 crore), for illegal medical practice.
Therefore, genetic modification like chimera studies continues to be a subject of major debate. In developing countries like India, genetically modified crops are also a contentious topic. Tampering with the genetic code in human beings is more controversial, as any such change can be passed down to future generations.
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