Now scientists move step closer to growing human organs in pigs

HUMAN-PIG embryos have successfully grown human tissue – taking scientists a step closer to the prospect of organ transplants between species.

The so-called ‘chimeras’ were created by injecting human stem cells into pig embryos and then implanting them in a sow.

The cells formed part of the tissue of the pig embryos, with scientists hoping the pigs will eventually develop a human pancreas. However, these embryos did not become piglets as they were removed at 28 days. Researchers said the amount of human tissue was ‘low’. But it has been hailed as an ‘important first step’ towards the goal of one day growing whole human organs in pigs – or other animals – which would not be rejected by the recipient’s immune system.

However, the project is not without controversy. There are fears that if too much human DNA is introduced to a pig’s embryo, it will also contribute to tissues in other organs – particularly the brain.

This could affect the animal’s behaviour, although as yet these concerns are a long way from being realised.

The Daily Mail reported in June that the team had created human-pig embryos. Today the researchers have published the first scientific report of their findings in the journal Cell.

It follows a study published earlier this week, in which scientists cured diabetes in mice by giving them a transplant from a mouse pancreas grown inside a rat. Around 1,500 pig embryos were used in the research, carried out by the Salk Institute of Biological Studies in San Diego, in the US, and the Catholic University of Murcia in Spain.

One of the problems they faced is that pigs and humans are five times more distant in evolutionary terms than mice and rats. Pig embryos also develop three times faster than human embryos.

The researchers injected several different forms of human stem cells, which have the potential to grown into any type of tissue, into pig embryos to see which would survive best.

The cells that were found to survive longest, and had most potential were ‘intermediate’ human pluripotent stem cells.

Dr Juan Carlos Izpisua Belmonte, a professor at Salk, said that 28 days was ‘long enough for us to try to understand how the human and pig cells mix together early on without raising ethical concerns about mature chimeric animals’. Dr Izpisua Belmonte added: ‘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.’

He added: ‘The ultimate goal is to grow functional and transplantable tissue or organs, but we are far away from that. This is an important first step.’

Animal sciences researcher Professor Bruce Whitelaw, of Edinburgh’s Roslin Institute, said: ‘This is an exciting publication. It clearly demonstrates that human stem cells introduced into the early pig embryo can form a human-pig chimera.’

But Philip Lymbery, the chief executive of Compassion in World Farming, said: ‘I fully understand the longing of those who need transplants.

‘However, growing human organs in animals is not the solution, and could open up a whole

‘Functional and transplantable’ ‘Carries terrible consequences’

new source of animal suffering. We should be focusing our efforts on getting more people to donate their organs.

‘Genetically editing and cloning animals carries terrible consequences for their welfare.

‘Those animals who do make it past the embryo stage ... often die shortly after birth. This seems like a very high price to pay when there are quite clearly other reliable solutions to turn to.’

Dr David King, director of watchdog group Human Genetics Alert, added: ‘I find these experiments disturbing.

‘I am concerned that human organs or tissues produced in pigs might carry pig viruses into the human population.