A medical first. That is how the first transplant of a genetically-modified pig heart into a human patient has been described. A pig’s heart is very similar to a human heart; it has the same shape, the large blood vessels can be successfully connected and it has a similar heart rhythm. The heart was made a bit more ‘human’ in order to prevent a rejection response from occurring, says Carlijn Bouten, professor of Cell-Matrix Interactions in Cardiovascular Regeneration. “Researchers have added six human genes and removed four pig genes. That reduces the risk of rejection, but it also prevents the heart from growing.”

Decades of research have led to this transplant, Bouten stresses. “The step from pig to human remains a risk. In my field, surgeons have been successfully transplanting pig heart valves into humans for a number of years now. But these valves are specially treated and no longer contain living pig cells. This transplant, however, involves an entire organ. If this gene editing works, it will open up a whole new world of possibilities.”

The operation was a success, the heart appears to be working well and the patient is recovering, but there’s still a risk that the patient’s immune system might reject the organ or that other complications might occur. But even if this doesn’t happen, both Bouten and professor of Cardiovascular Biomechanics Frans van de Vosse don’t expect to see pig heart transplants on a large scale in the future. “In first instance, it’s still an experiment. But even when everything works technologically, we are still left with a serious ethical issue. Do we want pigs to become a depot of spare organs for humans? On the other hand: we’re also allowed to eat pigs. And should we mix organs from different species? To what extent should we be allowed to modify animals, and how you do raise these animals?”

Organ depots

In order to address these kinds of issues from various angles, Van de Vosse participated in the focus discussion group ‘Animals as donors,’ which is part of a social debate initiated by knowledge institute Rathenau and Kennislink. The media attention surrounding this transplant certainly encourages the ethical discussion, Bouten believes. “Does this mean that we will need to have entire stables in the future where we breed genetically modified animals under sterile conditions? Animals as organ depots? I have some reservations about that. This is a discussion that should be held society-wide, not just among researchers. Apart from that, this kind of transplant is a highly complex and expensive procedure, which is why I don’t expect large numbers of operations. I do however believe that it will be a springboard to various technological procedures that might actually lead to a solution to the problem of donor shortage.”

Both Van de Vosse and Bouten are in the process of developing a heart alternative. They currently collaborate in a large nationwide consortium on a hybrid heart: an artificial heart with a lining made of human tissue created in the lab. Van de Vosse says that the artificial heart will develop rapidly, especially since UMC Utrecht implanted an artificial heart in a patient last fall for the first time in the Netherlands. “It can save the lives of patients who can’t wait for a heart transplant due to a critical situation.”