Animal-to-human organ transplantations have been carried out for decades, but due to complications with organ rejection the technique has seen limited success. The potential, however, for having an effectively unlimited source of donor organs has seen a continued effort to create more favorable outcomes. The recent development of the gene editing technology known as CRISPR/Cas9 could finally be the solution for this long-standing problem.
Using this new method, scientists have managed to edit an incredible 62 separate genes in pig embryos to make the animals' organs more likely to be accepted by the human immune system. This is 10 times the number of genes that have ever been edited in any other animal at one time. In addition to these, the team also edited a further 20 genes in separate embryos. The researchers predict that for any pig organs to be fully viable in humans, they would need both these sets of modifications.
One of the biggest worries holding back the widespread use of animals as organ donors is the threat of infecting the recipient with a foreign, potentially dangerous, animal virus. These viruses, known as endogenous retroviruses, are found embedded in the genomes of all animals, and it was because those in primates are so similar to those in humans, and thus more likely to cause infection, that scientists stopped using primates as donors and turned instead to pigs. The potential dangers of those from pigs, however, remained unknown.
With the rise of CRISPR/Cas9 gene editing, new opportunities have been born. The technique allows scientists to add and remove sections of DNA to any organism's genome with comparative ease and precision. Researchers from Harvard Medical School set out to do this to pig embryos on a scale not yet seen before. They were able to inactivate 62 porcine endogenous retroviruses (PERVs) which could potentially cause disease if activated in transplanted organs.
They then went on to focus on genes in the pig genome that are thought to play a role in the rejection of organs by the human immune system. Here, they modified over 20 genes that encode proteins found on the surface of pig cells, and which are known to provoke an immune response or cause blood clotting. According to Nature News, the specific genes targeted have not yet been revealed as the findings are yet to be published.
The exact details of how the team has managed to achieve this unprecedented scope of gene editing is still unknown, but the lead researcher, George Church, told Nature that they are close to implanting the edited embryos into mother pigs. It is only when these piglets are born will we know the full extent that this massive amount of editing will have on the living animals.
[H/T: Nature News]