The idea is to tweak the DNA of pigs just enough to make their organs safe for transplanting into people. If scientists could get this kind of “xenotransplantation” to work, there would be enough organs for everyone.
And we may have just got much closer to this science fiction reality. On October 5, geneticist George Church of Harvard Medical School in Boston, Massachusetts announced that his group may have engineered enough genetic changes into a pig embryo to make its organs safe for transplanting into people. We will need to wait until the embryos develop and grow into adult pigs to know for sure but in any event, we are definitely getting close.
Scientists have been trying to do this for decades with little success. What has made it possible after all this time is the availability of the super gene editing tool CRISPR/Cas9. With this tool in hand, scientists can make multiple changes at once to an animal’s DNA.
And they definitely needed this powerful tool! Church and his group made over 80 genetic changes to these pig embryos which is a record breaking number. It is over ten times what has been changed in animals thus far.
With CRISPR/Cas9, even if this huge number of changes isn’t enough, it is only a matter of time until he or someone else engineers suitable pigs. CRISPR/Cas9 is that simple and that powerful.
So it really isn’t a question of if we can do this but when. Sometime in the near future, you may be walking around with a pig heart.
Humanizing a Pig
The first big problem to overcome in using pig organs in people is rejection. Our bodies even reject mismatched human organs so you can imagine what happens with an animal organ.
One way to get around this rejection is to change key genes in an animal so that its organs look more like a human’s (at least to our immune systems). In other words, to create a humanized pig.
This is as tricky as it sounds. Because pigs and people are very different from one another, scientists need to make a lot of changes. Church and his group started out by changing more than 20 different pig genes in a pig embryo.
We will need to wait and see if these are enough changes to fool our immune systems. But even if all of this genetic engineering solves the rejection problem, these organs still won’t be safe. There is still the problem of potentially dangerous viruses lying in wait in the pig genome.
Getting Rid of PERVs
Animals have relatively harmless viruses (called endogenous retroviruses or ERVs) that hang out in their DNA. Pigs have the porcine variety and so their viruses are called PERVs.
These viruses are for the most part inactive and are passed down safely from parents to offspring. A few, however, are still able to form infectious viruses but they are usually harmless to the host species. In the lab, one of these viruses from pigs can infect human cells.
What we don't know is if these viruses can infect human cells in a live person or if that would make the patient sick. Or even worse, be infectious and spread and make lots of people sick.
No one wants a new Ebola to come out of something like an organ transplant. This is why Church’s group used CRISPR/Cas9 to shut off 62 of these PERVs in a pig cell.
This reduced the danger of infection of human cells in the lab by over 1000-fold. Hopefully that will be enough to make the procedure safe.
Humanized and De-PERVed
Right now these researchers have two separate pig cells. One has the genetic changes to deal with rejection and the other has the changes that inactivate the viruses in the pig’s DNA.
The next step will be to make all of the changes in a single pig embryo. This pig can then be grown and its organs tested for safety.
If it turns out that its organs are still rejected or are not safe, then scientists will have to keep using CRISPR/Cas9 until they get safe organs. Eventually, thousands of lives could be saved each year in the U.S., all thanks to these genetically modified pigs.
Nice explanation of how CRISPR/Cas9 works
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