Some scientists argue that the sheer moral ambiguity on these topics is a string enough to justify the slowing down/halting of further advancements within the field until proper legislation is introduced (Koplin & Savulescu, 2019). However, with the close evolutionary relationship between humans and primates it is impossible to ignore the questions surrounding cognitive similarities between humans and these chimeric organisms. Up until now, most chimeric research occurred in non-primate organisms however many scientists believe human-monkey chimeras could act as the ‘holy-grail’ model to study human disease response (De Los Angeles et al., 2019). Recently the scientific world was met with a huge breakthrough following the successful production of a human-monkey chimeric embryos (Tan et al., 2021). In fact, it is not just specific organs that scientists are cautious about developing with these techniques but also in what organisms. Henceforth, some scientists go as far to say research in this field should be prohibited in its entirety to eliminate any possible developments (Koplin & Wilkinson, 2019). The key issue raised concerns the potential of such non-human animals developing a human like consciousness. Many medical ethics councils believe the restriction on brain chimera research needs to be more tightly regulated. Amongst scientists, there are many questions concerning how chimeric brain development is controlled. Some of the ethical concerns over chimera produced organs specifically is surrounding specific organs. Therefore, is it completely justified to suggest one is any more ethical than the other? Ultimately both consumption and experimentation for organ culture on animals are both used for human gain at the expense of the animal. In addition to this, many also argue that this sort of experimentation should face no more ethical backlash than what animal consumption does (Bourret et al., 2016). This high level of regulation is maintained to ensure animals are not suffering and that they are properly cared for. The experimentation on pigs for human organ production is a process that is strictly controlled. Over the years many questions have arisen as to how one can justify the production of human organs in animal hosts. Researchers have also found that even if the embryos do end up being viable, they often end up uncontrollably developing into tumours that have the potential of becoming cancerous (Kroon et al., 2008). In most trials, only about 25% of the injected embryos developed into chimeric organisms (Wu et al., 2017).
It is often quite difficult to predict if and how the embryo develops. A further issue with the technology is that often the probability of producing viable chimeric embryos is quite low.
The understanding of the technology for chimeric organ culture is relatively new therefore it is understandable as to why people are dubious towards the feasibility and safety of such techniques.
One of the major concerns with interspecific chimeras is that the research surrounding them is quite recent. However, production of lymphoid tissue in animal models could further our medical understanding about immunology (Porsdam Mann et al., 2019). It is often very difficult to study virus pathogenesis in animals due to our distinct immune systems. The ultimate benefit for using human-animal chimeric models is the immense research potential. However, the true ethical concerns lie in crossing the human-animal species barrier (Bourret et al., 2016). The use of chimeric organisms is nothing new for the scientific world, with rat-mouse chimeras being some of the first model organisms to be used. The injected iPSCs from the human embryos can then develop into the organs that are ‘missing’ from the pig embryo ultimately allowing for the formation of functional human organs inside the pig (Koplin & Wilkinson, 2019). Human stem cells (specifically iPSCs) are then injected into this embryo which is then implanted into a pig. Using CRISPR-Cas9 technology, the genes to develop certain organs are knocked out of the pig embryo.
One of most common chimeras is the human-pig embryo used to grow human organs in a pig. The technique of generating a chimera works by the fusion of two animal embryos, where each has been slightly altered to allow the two to become compatible. However, as with all animal-related experimentation technologies, there are numerous ethical concerns that must be considered in the debate to justify such techniques. Providing a solution for the time-old issue of organ availability for transplantation, chimeras allow scientists to synthesise organs in an animal model that can then be inserted into humans. Chimeras are organisms that are composed of two distinct interspecific cell types and since their initial discovery they have forever changed the medical world.
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