In an attempt to use pigs as "incubators" of human organs to be used in transplants, a group of US scientists created chimera embryos partly of pig, partly human.

Researchers at the University of California, Davis have inserted pluripotent human stem cells into the DNA of pig embryos, and allowed these to grow in the wombs of sows for 28 days, before destroying them and analyzing their tissues.

Potential. According to the authors of the controversial experiment, of which many implications are not yet known, the embryos would have developed into pigs similar to others in appearance and behavior, but with human organs (in this case, pancreas).

Cut and (re) sew. The research, to which the US National Institutes of Health have denied funding, was essentially carried out in two phases before knowing its developments. Using the "molecular scissors" for CRISPR genetic editing, the portions of DNA that would have allowed the development of the pancreas were removed from the pig embryos.

In this genetic niche, pluripotent human stem cells were then injected, capable of potentially developing in any organ, and obtained by reprogramming adult cells. The hope was that, taking advantage of the genetic "void" created, a pancreas made exclusively of human cells would develop in pigs.

Starting from the recipient's cells, the technique could allow, according to its proponents, to obtain organs completely compatible with those of the patient.

Image The moment when human stem cells (in the syringe, on the right) are injected into a pig embryo. | Pablo Ross / UC Davis

The risks. But beyond the intent to compensate for an objective lack of transplant organs, the experiment remains very controversial. One of the major concerns is that pluripotent human cells can migrate from the genetic niche created and contribute to the development of the animal's brain, making it, in some way, partly "human". A possibility, this, that Pablo Ross, at the head of the study, defines as "very low potential".

Then there is the discourse of animal suffering: before using pigs as incubators of human organs, it would perhaps be better, suggest different organizations for the protection of animals, to encourage the culture of organ donation among human beings.

Only the bare essentials. Walter Low, a neurosurgeon at the University of Minnesota, explained to the BBC that research like this could also be used to obtain low-risk hearts, livers, lungs, kidneys and corneas. But he also specified that we are in a preliminary phase of these studies, in which we are still trying to "take aim" at the right genetic targets, to avoid that undesired extra organs also develop in animal embryos.

For now, the only thing certain is that genetic editing techniques have revitalized the field of xenotransplantation, that is the possibility of using animal organs for human patients, which had suffered a setback in clinical trials.