The process involves the insertion of the nucleus of a single human skin cell into the empty egg of an animal, for example a rabbit. By use of an electric stimulus, the cell can then be triggered to begin dividing.

Is this really a ‘hybrid embryo’?

Strictly speaking, no.  A 'hybrid' is an organism which is formed by mixing the chromosomes of two separate organisms.  That is not what is happening here.  Here the nucleus of the animal egg - or its DNA - has been removed before the implantation of the human cell.  The resulting cell block is more than 99.99% human.  The miniscule element of the animal which remains is in the shell only and forms no part of the human cell development.

If it isn’t really a hybrid embryo, what is it?

Scientists are agreed that ‘hybrid embryo’ is a misleading description, but don’t seem able to agree on what would be a better description.  The process is best described as ‘cell nuclear transfer’.  The result of the process is, I think, perhaps best described as a ‘hosted human cell.’

Where have the human eggs come from?

They are donted by women undergoing IVF treatment.  IVF treatment is given to infertile couples to help with conception.  The process requires collecting eggs from the woman.  These are then fertilised outside the body and then re-implanted.  Many eggs are collected from the woman for this process, but only one, or a small number, will ever work and become successfully implanted and develop.  The ‘spare’ eggs are either destroyed are made available for scientific research.  Stem cell research to date has been based on the use of human eggs, but only 3% of therapeutically cloned embryos derived from a human egg are capable of producing the stem cells they need.  It would therefore take 30 human eggs to have a reasonable chance of producing sufficient appropriate stem cells.  Human eggs are just not available in that quantity, and should in any event be directed towards IVF assistance wherever possible.

What do scientists obtain from these eggs?

Stem cells.  These are the very basic building blocks of our body.  Stem cells are known as ‘pluripotent’.  That means they can develop into anything which eventually forms some part of us.  But while still stem cells they are raw material.  They have not yet taken on any specific direction of development or any particular identity.

Could these ‘hosted’ embryos develop into a foetus?

No.  They are only needed for a few days in any event because the stem cells have been formed by then.  The rest of the material is then destroyed.  The law requires destruction within 14 days. By that time, the cell cluster is no bigger that this full stop.  Also, to develop into a foetus, the eggs would have to be implanted into the uterus.  This is banned by law. Furthermore, as normal fertilisation has not occured, normal development would be highly unlikely in any event.

Why are stem cells so important?

Stem cells are our basic building block. They have two key properties. They can multiply indefinitely and the are pluripotent - meaning they have the potential to develop into any type of cell. Embryonic stem cells have the greatest potential to aid research into diseases. In nofrmal human development, the stem cells gradually respond to directions to form into all the various component parts of our body. We retain some stem cells in some parts of our bodies and they help repair those aspects of our body if things subsequently go wrong. But only a few parts of our bodies retain stem cells in this way.

What do scientists do with stem cells?

The skin cells that scientists use to implant into the egg are taken from patients who have the diseases that they are trying to study, and hopefully cure.  Once in the egg shell, the human cell carrying the specific disease will divide and generate stem cells.  Scientists can then study those cells in order to understand better the disease process.  If they can work out, by observing the development of the stem cells, how the disease starts and develops, they can hopefully work out what sort of intervention would prevent - or reverse- the disease.  In other words, scientists  may be able to work out how to reprogramme the cells, so that they turn into healthy cells, instead of developing as diseased cells.

What about getting stem cells from other sources?

They are available from other sources.  Scientists could use adult stem cells derived from, for example, bone marrow or the umbilical cord.  Bone marrow collection is an invasive process, better avoided if possible. Umbilical cord stem cells can only be used to treat blood diseases. They do not have the pluripotency of embryonic stem cells. But whether from marrow or from the umbilical cord, adult stem cells are far less successful for this kind of research.  When injected into another person, as part of a ’repair’ treatment, they will trigger a body’s immune response process, and be rejected.  The stem cells might be useful for treating the individual from whom they were sourced - but not anybody else.  Stem cells produced from cell nuclear transfer do not trigger an immune response. 

How do these ‘hosted’ embryos help research into a disease?

Take Motor Neurone Disease as an example.  To understand the disease, scientists need to establish all the genes which make up the disease.  In 20 years of research to date, they have discovered just one of the genes involved - which means they are about 5% of the way to the answer they are seeking.  Research would be a lot quicker if they didn’t have to try to discover genes in the traditional way.  Using cell nuclear transfer, they can use the gene defect that already exists in every MND patient’s cells and derive a supply of stem cells from them.  Then studying the mechanisms of the disease becomes so much easier- and hopefully quicker.

Who is urging this research to be done?

The Association of Medical Research Charities and the Genetic Interest Group - which together represent over 220 medical charities, including Cystic Fibrosis Trust, the Wellcome Trust, Cancer Research UK, Multiple Sclerosis Society, Alzheimer’s Society, Muscular Dystrophy Campaign, Motor Neurone Disease Association, British Medical Association, and Parkinson’s Disease Society.

How many people in the UK currently suffer from the diseases that this research may help to cure?

The potential of embryonic stem cell research is enormous, and if it yields the breakthroughs scientists hope for it could impact obn a wide variety of diseases, including heart disease and cancer, the top two fatal diseases. There are lots more diseases that could be treated through advances achieved using this research, affecting millions of people in the UK and around the world: Dementia - around 700,000; Parkinson’s - around 120,000; Muscular Dystrophy - around 60,000; Huntington’s Disease - around 8,000; Cystic Fibrosis - around 8,000; Motor Neurone Disease - around 5,000.

When might we see progress?

The Human Fertility and Embryology Authority first granted a license to derive human embryonic stem cell lines in 2003.  The first clinical trial is expected to commence later this year to treat spinal cord injuries.  A further trial for a treatment for age related macular degeneration is about two years away.  Progress in tackling all the other diseases will come a lot quicker if cell transfer technology is authorised for the derivation of stem cells.