Subscribe to the BioNews newsletter for free

Advanced Search

Search for

Like the Progress Educational Trust on Facebook



US scientists create first human-pig embryo chimeras

30 January 2017

By Annabel Slater

Appeared in BioNews 886

The first early human–pig embryo chimeras have been created by researchers in the US.

The embryos, which were less than 0.001 percent human, could provide insight into early development and are a first step towards creating animals that could grow human organs for transplantation.

'This is the first time that human cells are seen growing inside a large animal,' Professor Juan Carlos Izpisua Belmonte, from the Salk Institute in La Jolla, California, told BBC News.

The team aimed to create human–animal chimeras using pig and cow embryos as the size of these animals' organs is relatively close to those of humans. Although cow embryos proved to be too expensive and complex to use, 2075 early-stage pig embryos were injected with intermediate-stage human pluripotent stem cells. These were found to be the most successful type of stem cell to produce the chimeras.  

The embryos were then implanted into sows – 185 embryos continued to develop, resulting in human–pig chimeras comprising approximately of one human cell per 10,000 pig cells.

Although the rate of success was low, Professor Izpisua Belmonte considered this a positive sign as ethical concerns could arise in particular if human cells contribute to brain tissue.

No embryonic development was allowed to proceed past four weeks.

'One possibility is to let these animals be born, but that is not something we should allow to happen at this point,' said Professor Izpisua Belmonte. '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.'

Previous chimeras were typically created by inserting human cells at a later stage of development. The researchers say their work shows human cells can contribute to the development of a pig embryo. Next they plan to use CRISPR/Cas9 to edit the pig genome in order to improve the development of the human cells.

'The ultimate goal is to grow functional and transplantable tissue or organs, but we are far away from that,' said Professor Izpisua Belmonte. 'This is an important first step.'

Professor Bruce Whitelaw of the University of Edinburgh, who was not involved in the study, called it 'an exciting publication' which 'paves the way for significant advances in our understanding of development in the embryo and hints towards future novel biotech applications'. Reflecting on the production of the first live rat–mouse chimeras, he said, 'The 10 years between these two studies is a testament of how difficult it has been to achieve the human–pig result.'

In the study, published in Cell, the team also reported the production of several rat–mouse chimeras using CRISPR/Cas9 genome editing. Another study in Nature this week also reports creation of rat–mouse chimeras, producing functional mouse pancreases in rats (see BioNews 886).

The Guardian | 26 January 2017
CNN | 27 January 2017
BBC News | 26 January 2017
Cell | 26 January 2017
Science Daily | 26 January 2017


14 August 2017 - by Cara Foley 
Ancient viral genes have been eliminated from pigs using the genome editing tool CRISPR, according to research...

05 September 2016 - by Anneesa Amjad 
A prominent bioethicist in the USA has suggested that most of the ethical concerns surrounding the creation of animal-human chimera embryos using human pluripotent stem cells could be reasonably addressed...
08 August 2016 - by Antony Blackburn-Starza 
The US National Institutes of Health is considering lifting a ban on the funding of research to create human-animal 'chimeras' and replacing it with an ethical review process...
13 June 2016 - by Dr Jane Currie 
Scientists have used CRISPR to create part-pig, part-human embryos in an attempt to grow human organs for transplant...
11 May 2015 - by Dr Tamara Hirsch 
Scientists have identified a new type of stem cell that shows distinct advantages over those discovered to date, and which could potentially be used to grow human organs in animals such as pigs or cows...

Be the first to have your say.

You need to or  to add comments.

By posting a comment you agree to abide by the BioNews terms and conditions

- click here to enquire about using this story.

Published by the Progress Educational Trust


Public Conference
8 December 2017

Speakers include

Professor Azim Surani

Professor Magdalena Zernicka-Goetz

Professor Robin Lovell-Badge

Sally Cheshire

Professor Guido Pennings

Katherine Littler

Professor Allan Pacey

Dr Sue Avery

Professor Richard Anderson

Dr Elizabeth Garner

Dr Andy Greenfield

Dr Anna Smajdor

Dr Henry Malter

Vivienne Parry

Dr Helen O'Neill

Dr César Palacios-González

Philippa Taylor

Fiona Fox

Sarah Norcross

Sandy Starr


Good Fundraising Code

Become a Friend of PET HERE and give the Progress Educational Trust a regular donation