Author: Attabey Rodríguez Benítez
Editors: Sarah Kearns, Jimmy Brancho, and Whit Froehlich
Can you imagine a future where humans could receive organs from animals instead of having to wait for a donor? Well, this could be possible thanks to evidence from an international collaboration between labs in Harvard and China which resulted in a publication in the prestigious journal Science.
What is Xenotransplantation?
Currently, there is a medical shortage of organs and tissue. Xenotransplantation could be a viable option for the future. This terminology in “rice and beans”, as I like to say, is when organs are transplanted from one species to another, e.g. pigs to humans. Trans-species organ donation could be possible because the organs of pigs and humans are similar in size and function. However, there is a possibility for incompatibility where the human body rejects the organ transplant, and there is also the chance that humans could contract a porcine virus. In some cases, endogenous retroviruses could cause autoimmune diseases or cancer.
This new study, cited above, uses the gene editing tool CRISPR-Cas9 to remove the genes that generate the porcine virus, resulting in virus-free pigs that could be used for xenotransplantation.
What is CRISPR-Cas9?
CRISPR-Cas9 is a type of scissors that cut DNA in a specific manner. The scissors essentially have a WANTED poster with a detailed description of its target in order to remove it. For example, picture an editor in charge of looking for a specific paragraph that starts with a blue line (Figure 1, below). After locating this line, they have to find an orange phrase within it, specifically the word GENE. It is then that this molecular scissors are allowed to cut at each side of the word GENE shown in the image below.
This is precisely what happens when CRIPR-Cas9 is used in pigs. The scissors are designed to have their WANTED poster directed at the porcine virus. The study team proceeded onward and did a somatic cell transfer. In “rice and beans,” somatic cells are the ones capable of growing organs and tissue. This process requires the nucleus, where the somatic DNA is located. This nucleus is removed and the rest of the cell is discarded. At the same time the nucleus of a female pig egg is removed, and the somatic nucleus (with the virus-free DNA) is then transferred to the egg to replace the old nucleus. This means that DNA without the porcine virus is transferred to the sow’s egg. After the transfer the egg is stimulated with a shock and will begin to divide. After a time, a blastocyst is formed which is an early stage embryo. The blastocyst is transferred to a sow with in-vitro fertilization which leads to the first virus-free pig. Therefore, the organs of this pig can be harvested and transplanted to a human without the fear of contracting the porcine virus. This could open the door for a future supply to alleviate the current organ crisis.
CRISPR-Cas9 has a great potential in science and it’s a great invention. I think that it is pretty close to winning the Nobel Prize, since is a total improvement over previous methods. However, it still has its flaws; for example off-target modifications. Aside from its defects, xenotransplantation is far from reality because the only way to test this in clinical trials is by actually transplanting the organs to a human. Nonetheless, it is in the hands of government agencies to decide if this research can be pushed forward.
In conclusion, the scientists in this article managed to create a porcine virus-less pig. However, a major roadblock lies ahead. This needs to be further tested in humans and there is no other way to test it other than making the actual transplant in a human. A way to convince the government agencies is by doing a transplant from pigs to monkeys, an animal closer to humans, and observe how they react to the transplant.
Niu, D.; Wei, H.-J.; Lin, L.; George, H.; Wang, T.; Lee, I.-H.; Zhao, H.-Y.; Wang, Y.; Kan, Y.; Shrock, E.; Lesha, E.; Wang, G.; Luo, Y.; Qing, Y.; Jiao, D.; Zhao, H.; Zhou, X.; Wang, S.; Wei, H.; Güell, M.; Church, G. M.; Yang, L. Science (80-. ). 2017, 4187, 1–8.
About the author:
Attabey completed her bachelor’s degree at the University of Puerto Rico, Río Piedras. Currently, she is a doctoral student in the program of Chemical Biology at the University of Michigan. After her first year she joined the labs of Prof. Alison R.H Narayan and Prof. Janet L. Smith. She focuses on using enzymes as chemical tools for the synthesis of natural products and elucidating their mechanisms of action through structural biology. In addition to research and contributing to MiSciWriters Attabey has a Spanish science blog, En Arroz y Habichuelas, where she writes about science for the general public and in Spanish! She also enjoys reading comics (Saga, Paper Girls, Bitch Planet, etc.), watching movies with a scoring above 7 on IMDB, and eating disgusting amounts of popcorn! You can follow her on Twitter and connect on LinkedIn.
Read all posts by Attabey here.