Chimaeric human-animal hybrid embryos

On Wednesday 5th September, the UK's Human Fertilisation and Embryology Authority (HFEA) announced their decision that British scientists can press ahead with research to generate animal / human hybrid embryos, also known as embryo chimaeras. Certain sections of the media have got very overexcited about this type of research, drawing unhelpful cartoons of humans with rabbit heads and the like - but what exactly is this technology all about?

Put simply, creating chimaeric animal / human embryos means taking an unfertilised animal egg - such as from a cow or rabbit - and removing the DNA from it. Then the empty egg is fused with a human cell, and the process of development re-activated.  The embryo is then allowed to grow for just a couple of days, until it is a tiny ball of cells. 

At this stage, the scientists can extract embryonic stem cells from the developing embryo, which can be used to generate all the different tissues of the body.  Many scientists believe that such embryonic stem cells could be the key to treating many human diseases - for example, using them to replace the brain cells lost or damaged in conditions such as Parkinson's or Alzheimer's.

Because the animal egg's DNA would be removed before the human cell is added, the resulting stem cells will be essentially human.  However, there will be a small amount of animal DNA present. This is because egg cells have structures called mitochondria, which provide energy.  These contain their own miniature chromosome in the form of a small circle of DNA, which controls how they behave. It too would be passed on in the stem cells. But any fears that rabbits with human heads will be hopping around the place are unfounded, because in any case the embryos would be destroyed at the stage when the stem cells are harvested, and not be implanted into the womb to develop further.

At the moment, human embryonic stem cells can only be created from human embryos, which are understandably in short supply.  Many people also raise significant ethical objections to the use of human embryos in research.  By using these hybrid embryos, scientists would totally avoid the need to use human eggs or embryos to generate stem cells.   Although there are still people who have ethical objections to this technique, it is important to point out that such technology would effectively reduce the need for experiments on human embryos. 

Many scientists and research organisations around the world believe that research using animal/human hybrid embryos is important - especially given the practical and ethical limitations of working with human embryos.  If we truly believe that stem cells are a viable technology for treating serious human diseases in the future, then embracing hybrids may have to be a necessary step along the road of scientific progress.