Towards the goal of growing life-saving organs inside animals for use in transplants, scientists have successfully created a human-pig hybrid embryo – by inserting human stem cells into the embryo of a pig. The embryos are less than 0.001% human, and the rest pig, have been analyzed by the scientists.
However, the research remains at a very early stage and proved more difficult than expected. The breakthrough experiment, described Thursday in the journal Cell, was the first demonstration that such an interspecies of two large, distantly-related species organ transplant is possible. Using stem cell technologies, researchers generated human cells and human tissues in the embryos of pigs and cattle. It was described as an “exiting publication” by other researchers.
“This is an important first step,” said lead investigator Juan Carlos Izpisua Belmonte, a professor in the Salk Institute of Biological Studies’ Gene Expression Laboratory. “The ultimate goal is to grow functional and transplantable tissue or organs, but we are far away from that.”
The human-pig hybrid is the first proof chimeras – named after the Greek mythical lion-goat-serpent monster – can be made by combining material from humans and animals. It is the creation of scientists at the Salk Institute for Biological Studies in La Jolla – a biological research organization in California.
Scientists implanted adult human cells, known as intermediate induced pluripotent stem cells — into pig embryos and allowed them to grow for four weeks. The effort involved some 1,500 pig embryos and took four years, far longer than initially estimated, due to the complicated nature of the experiments.
They found that the human cells began to form into muscle tissue in the pig embryos. The process appears very inefficient – of the 2,075 embryos implanted only 186 continued to develop up to the 28-day stage.
“This is the first time that human cells are seen growing inside a large animal,” Prof Belmonte from the Salk Institute, told the BBC News.
Despite the milestone, integrating cells from human and animal species is proving difficult, and developing human organs remains at a considerable distance, said Dr. Jun Wu, a staff scientist in the gene expression laboratory at the Salk Institute and first author of the research.
“Species evolve independently, and many factors dictating the developmental programs might have diverged, which makes it difficult to blend cells from one species to a developing embryo from another,” Wu said. “The larger the evolutionary distance, the more difficult for them to mix.”
The notion of creating human-animal mixtures has stoked controversy and raised ethical questions, particularly since the experiments could theoretically lead to the creation of animals with human qualities, and possibly intelligence.
The researchers have only done research that is legal, but they are aware of the controversy.
Prof Belmonte said, “We are restricting development to one month in the pig, the reason is this is enough for us now to understand how cells mix, differentiate and integrate. One possibility is to let these animals be born, but that is not something we should allow to happen at this point. Not everything that science can do we should do, we are not living in a niche in lab, we live with other people – and society needs to decide what can be done.”
Dr Wu said: “When the public hears the world chimera it is always associated with Greek mythology, there is always this associated fear. But angels are chimeras, it can be a positive image and hopefully help with a worldwide shortage of organs, not create a monster.”