We don’t have enough organs for transplant, but it’s not as though governments and scientists are sitting back idly. Incentives to encourage donation are being considered and urged, and various labs are working on and succeeding in creating organs from stem cells. But is growing human organs in animals a step too far? That’s currently being debated, after MIT Technology Review revealed that at least three groups in the U.S. are doing just that.

The controversial technique involves the creation of so called “chimeras,” or mixtures between humans and farm animals. Although the work has yet to be published, the information gathered by MIT from the scientists themselves indicates that roughly 20 successful pregnancies were established in either pigs or sheep last year, but all were terminated before reaching full-term.

And at work presented last November at the National Institutes of Health facility in Maryland, scientists revealed just how far their research has progressed. For instance, one group at the University of Minnesota used human cells in an attempt to treat an eye abnormality in a pig fetus, and showed evidence of success in the two-month-old pig.

Creating these species fusions involves both the use of stem cells and gene-editing technologies, both of which have progressed massively in recent years. First off, scientists tweak the DNA inside sheep or pig cells so that the developing embryo lacks certain organs or tissues. These ordinarily wouldn’t survive, but scientists have demonstrated it’s possible to help them develop by adding normal cells from a different embryo, which fill in the gaps.

Taking this a giant stride further, scientists are now substituting the extra cells for human stem cells and implanting the embryos in farm animals, thus creating a hybrid that could potentially provide a source for transplant organs. While you may now have concocted pictures of bipedal pigs or sheep with opposable thumbs, according to Stanford scientist Hiromitsu Nakauchi, this “embryo complementation” technique leads to fetuses with relatively few human cells.

“If the extent of human cells is 0.5 percent, it’s very unlikely to get thinking pigs or standing sheep,” Nakauchi told MIT. “But if it’s large, like 40 percent, then we’d have to do something about that.”

^{None of the chimeras have been carried to term so far due to ethical considerations. saoirse2013/Shutterstock}

Scientists have already been adding human genes to pig DNA to make the animals' organs more compatible for transplantation, but this technique goes significantly further than that. Debates on the ethics of the situation have therefore been ignited. Some have expressed concerns over such humanization of animals, in particular regarding the effects on their cognitive abilities. But currently, we still don’t even know whether the resulting animals would be viable, nor the extent of human cell contribution, as institutions only permitted the research if the developing animals were terminated at an early stage. So at present, the research is being used to optimize techniques and examine feasibility.

Don’t expect such experiments to become commonplace in a hurry, though. The National Institutes of Health, the world’s biggest funder for medical research, won’t provide grants for any such research, although that might change when more evidence becomes available from groups who have sourced money elsewhere. Ultimately, in the face of a global organ shortage, such experimental techniques are at least worthy of consideration, and blanket bans on funding seem myopic when the research is still in such a premature stage and impacts on the animals haven’t had a chance to be assessed.