27 Enero 2017 17:47
Scientists have taken the first step towards being able to grow human organs in pigs.
It wasn’t easy, but scientists have grown the first ever human-pig hybrid. The team created what’s known among scientists as a ‘chimera’ – an allusion to the mythical monster with a lion’s head, a goat’s body, and a serpent’s tail – in a laboratory. The international team of researchers is now one step closer to being able to cultivate human organs inside animals to use for transplants.Although this final goal is still some way off, the embryo that the team created – which grew to be four weeks old – has proved that it’s possible to combine the cells of two different species, suggesting that one day in the future an animal could be born with functional human organs. Meanwhile, these techniques can also be used to test drugs on organs grown in pigs. The report, published in the journal Cell, explains that the achievement has been made possible by a combination of techniques using stem cells and genome modification. The experiment involved injecting human stem cells into pig embryos at an early stage and then transferring the hybrid embryos to adult pigs, which carried the embryos for between three and four weeks. The embryos were then removed and analysed so that researchers could see how the cells mixed. A decade ago, scientists figured out how to grow the heart, eyes and pancreas of a rat inside a mouse. Since then, various attempts have been made to inject human cells into large mammals, but none have been fruitful until now. The complexity of the process resides in the fact that the gestation rate of pig organs differs markedly from that of humans. Human gestation takes about 280 days, while that of pigs is just 122. The team had to get the timing just right in order to introduce the human cells into the pigs without killing them.
‘At this point, we wanted to know whether human cells can contribute at all to address the “yes or no” question. Now that we know the answer is yes, our next challenge is to improve efficiency and guide the human cells into forming a particular organ in pigs,’ says Juan Carlos Izpisúa, a professor at the Salk Institute’s Gene Expression Laboratory.To take this next step, a greater human contribution will be required, in which specific genes are deactivated in the pig embryos, thus giving rise to significant ethical concerns. ‘The idea of having an animal being born composing of human cells creates some feelings that need to be addressed,’ admitted the author of the report. The team makes it clear that the chimera did not develop human traits. They also state that the injected cells can be manipulated to prevent them from contributing to the development of the brain. Nonetheless, the prospect of creating human-pig chimeras has provoked fierce debate within the scientific community. It also raises ethical questions about the morality of using animals as hosts for human organs. The experiment, carried out in California and Spain, was paid for with private donations. The US government last year banned funding for this type of research.