CALIFORNIA • Scientists in the US have injected human stem cells into pig embryos, creating human-pig embryos known as chimeras as part of efforts to determine whether human organs grown inside pigs can be used for transplants.
Once mature, the chimeras should look and behave like normal pigs, except that one organ will be composed of human cells, said the team from the University of California, Davis, reported the BBC.
The embryos are part of research aimed at overcoming the worldwide shortage of transplant organs.
Creation of the chimeric embryos is done in two stages: first, a gene editing technique know as Crispr is used to remove DNA from a newly fertilised pig embryo.
This creates a genetic void or "niche". To fill this, human induced pluripotent (iPS) stem cells are injected into the embryo. These iPS cells are derived from adult cells and "dialled back" to become stem cells capable of developing into any tissue in the body.
The team at UC Davis hopes the pig thus created from the chimera embryo will grow a human organ. The university was focused on growing a human pancreas.
But so far, none of the human-pig embryos has been allowed to develop within sows for more than 28 days - with the pregnancies terminated and the tissue removed for analysis - as the research remains controversial .
Last year, the National Institutes of Health, the main US medical research agency, imposed a moratorium on funding of all such experiments, according to the BBC.
The main worry is that human cells might migrate to the developing pig's brain and make it more human. Consequently, the university team is proceeding with caution. They have injected human stem cells into pig embryos but without creating a genetic niche.
However, they found that human cells in several parts of the developing foetus struggled to compete with the pig cells. They hope that by deleting a key gene involved in the creation of the pig pancreas, human cells will have more success creating a human-like pancreas.
Other teams have also created human-pig embryos, but none has allowed the foetuses to be born.
University of Minnesota Department of Neurosurgery's Professor Walter Low said pigs are an ideal "biological incubator" for growing human organs, including hearts, livers, kidneys, lungs and corneas.
But Prof Low stressed that his university's research, using another form of gene editing called Talens, was still at the preliminary stages.
Xenotransplantation, the concept of using animal organs for humans, has been seen as the solution to a worldwide shortage of organs for transplantation.
However, clinical trials have never been conducted over fears that humans might be infected with animal viruses as a result. In April last year, China approved the marketing of corneas grown in pigs for use in transplants.
