If you’re like me and your knowledge of science fiction far outweighs your knowledge of actual science, when you hear the word “xenotransplantation,” what comes to mind first is the deadly xenomorph from the Alien movies.
In reality, though, it’s more closely connected to another, far less acclaimed movie. Who would have thought that Rob Schneider vehicle The Animal — about a horrifically wounded man put back together with animal parts — may actually have gone some way toward predicting the future of medical science?
But let’s start with a bit of etymology. The word xenotransplantation stems from the Greek word “xeno,” which means “foreign.” Defined as “the surgical transfer of cells, tissues or whole organs from one species to another,” it’s literally the practice of replacing faulty or damaged human organs with those taken from another (i.e., foreign) species.
First attempted back in the early 1900s, scientists originally tried using the organs of pigs, goats, lambs and monkeys to help those with failing human organs. Unfortunately, none of these worked, and xenotransplantation was abandoned as a concept for several decades. In 1944, however, it was discovered that when organs are transplanted from one human to another, it triggers a response from the immune system — essentially, the immune system sees the foreign organ the same way it would a disease or a virus and attacks it. So the first successful human-to-human transplantation wouldn’t end up taking place until 1954, and even then, it only worked because it was between a pair of identical twins, meaning rejection wasn’t an issue due to their genetic similarity.
Transplants began to be more successful in the 1960s with the advent of immunosuppressive drugs, and had become commonplace by the 1980s. The problem, however, is that there aren’t enough organs for all of the people who need them — hence the need for revisiting the idea of xenotransplantation.
While much of this science is still experimental, some practical versions exist in the form of “xenografts,” aka, the transplanting of animal tissue to humans (as opposed to an entire organ). “People may not realize it, but before recombinant human-insulin was produced, diabetic people were injecting bovine and porcine insulin to lower their blood sugar,” explains Aseda Tena, a PhD student at Harvard University in the biological and biomedical sciences program who has extensive training in xenotransplantation research. “Porcine skin is being used to treat severe burn patients, and porcine aortic valve replacements have also been used in human hearts.”
If the latter sounds familiar, it’s because they’ve been used in a few notable cases, including Arnold Schwarzenegger, Mick Jagger and Barbara Walters, who, upon receiving a cow valve as opposed to a pig, joked to Vanity Fair, “I was happy when I learned that. A pig valve wouldn’t be kosher.”
The hope is that in the near future, full organs — like kidneys and hopefully even hearts — will be able to be transplanted from pigs to humans, even if only as a temporary replacement until a human donor can be found. With an estimated 20 people dying every day on organ-donation waiting lists, it’s easy to see why xenotransplantation could be a great help to those who need it.
In many ways then, our future rests mostly in the hands — or rather, trotters — of our porky pals. “Pigs are readily available, their organs are anatomically comparable in size and function to humans, and new infectious agents are less likely since they’ve been in close contact with humans through domestication for many generations,” Tena explains. However, you can’t just grab pig organs off the rack, so to speak: First, the pigs must be modified, or as Tena puts it, “humanized.”
Sadly, this does not (or at least, not yet) involve the creation of hideous mutant pig-men. These pigs, says Tena, look perfectly normal, changed only on the genetic level. For one, they lack a key sugar molecule that human and primate immune systems have been known to attack. Tena adds, “Gene editing has proven to be efficacious in eliminating potentially disease-causing viruses from the pig genome, as well as inserting human genes with the intent to create ‘human friendly’ organs.”
As promising as the future of xenotransplantation looks, there are more hurdles ahead. For one, rejection is still a serious problem in human-to-human transplantation, so for it to work consistently from pigs is still going to take some figuring out. Additionally, Tena notes, “The impact of xenotransplantation on the human race is still unknown. It’s hard to predict what exactly may go wrong but the main concern is that the procedure leaves open the potential for new types of infection to be introduced, which we might not know how to control.” Which, yeah, sounds kind of terrifying.
Tena says that it’s hard to say exactly when xenotransplantation will be ready to extend to full organs, but she believes it will come about sooner than other procedures being developed for the same purpose. “Other options for overcoming the shortage of human donors in general have not made as much progress as xenotransplantation, including stem-cell research, tissue engineering and regenerative medicine. Although I support the ongoing research in these fields to overcome the barriers each of them face, I strongly believe that xenotransplantation is the best near-term solution to the organ shortage that’s preventing thousands of people on the waiting list to receive an organ transplant.”
With approximately 114,000 Americans waiting for an organ right now, it’s a goal that seems well worth pursuing. And one we’ll certainly celebrate when the time comes.