Over 107,000 adults and children are on the national transplant waiting list as of February 2021 according to the Health Resources and Services Administration (HRSA), and tragically, around 17 people die each day waiting for a transplant. The demand for organ transplants has increased rapidly over the past decade. And while there has been much greater success in these operations than in the past, there are more people on the waiting list than there are organs that are available to be transplanted, thus resulting in a major organ shortage crisis. Currently, doctors rely primarily on human parts for transplants, especially with regards to life-or-death organs such as the heart or liver. However, new research is leading us closer to being able to solve the transplant crisis through gene-edited pigs.
Since the United States alone already consumes around 120 million pigs every year, using their organs seems a bit more ethical to most people than using the organs of other animals. The organs of pigs are right around the same size as humans and have a similar anatomy as well. Additionally, pigs reach adulthood in about six months, which is quicker than primates. However, the issue lies in viruses that pigs carry that humans are unable to combat. When formerly tested in monkeys, the pig organs did not hold up for long because the genes were too foreign. But with newer technology and the help of CRISPR, a tool used to alter DNA sequences to modify the function of genes, scientists are getting closer to being able to use pig organs for human transplants.
CRISPR refers to the cellular machinery used to recognize and remove the DNA of harmful viruses.
Image from ndla
As mentioned, the genome of the pig possesses DNA sequences from viruses that likely infected the species a long time ago, causing the virus’ genes to be inserted into the chromosomes and passed down through generations. These sequences of DNA are known as porcine endogenous retroviruses, or PERVs for short. While scientists are uncertain of the PERVs actual risk to humans, they believe that the PERVs would likely produce infectious viral particles and cause damage, resulting in an unsuccessful transplant. But thanks to the help of clustered regularly interspaced short palindromic repeats, or CRISPR, scientists were able to make refined changes to the pig’s genes to attempt to solve this problem. In 2017, scientists revealed that they were able to create healthy pigs whose genomes no longer contained the PERV sequences. They then put this modified pig cell’s DNA-containing nuclei into eggs of pig ovaries from a slaughterhouse. The eggs developed into embryos and were implanted into a surrogate mother. The piglets born from this process went through another round of removing the PERVs, and the process was repeated. The new generation of pigs seemed healthy and fully functioning and, according to the researchers, the “tendency of the pig cells to bind to certain human antibodies was reduced by 90%, and the modified cells better survived interactions with human immune cells” – a major achievement.
Despite this success, however, PERVs are just one of the issues keeping us from xenotransplants – transplants between members of different species. There is always the possibility that the human immune system will attack genes from the foreign organ, a way to prevent toxic interactions with human blood needs to be found, and the general idea of xenotransplantation raises many ethical and social concerns.
Scientists of xenotransplantation still have a hefty amount of research to complete before it will be ready to perform with humans. But until then, human transplantation is our only option. Every nine minutes, a new person is added to the waiting list for a transplant, but we simply do not have enough available organs to fulfill this need. Just one donor can save up to eight lives! So if you aren’t already registered, I encourage you to go register as an organ donor – before the pigs beat you to it.