What are stem cells and how can they help

They offer the prospect of a cure for many degenerative diseases such as diabetes, Parkinson's disease and heart failure.

But what are stem cells, how can they help us and should we use human embryos for this research?

Another question I am often asked is why use human embryos and embryonic stem cells?

Would it not be more ethical to use stem cells from adult bone marrow, babies' cord blood or other tissues?

Many scientists believe only embryonic stem cells have the true capacity to develop into all the different cell types of the body and therefore represent the greatest potential for medical therapies at present.

Embryos are donated, after independent counselling, by couples undergoing or following IVF treatment. They are surplus to their clinical need and would otherwise be destroyed.

These individuals have confidence in the regulatory framework of the Human Fertilisation and Embryology Authority (HFEA) and understand the importance of the research.

Of course this does not mean the potential of other stem cells should not be explored.

Recent experiments suggest adult stem cells may have some capacity to change into other cells for therapy.

In time we may be able to reprogramme many cells to other functions in the body in which case early embryos and embryonic stem cells would not be needed.

But in the meantime I believe the judicious use of embryos and the development of embryonic stem cell lines provide our best route for developing new therapies to treat a range of degenerative diseases.

The drugs currently available can only slow the progression of these diseases, whereas there is the real prospect cells produced from embryos could be transplanted to halt their development and even cure patients with conditions such as diabetes.

This represents an important change in our thinking about how in the future we might treat patients who suffer from illnesses which often require long-term care.

But how much of this is science fact rather than science fiction?

In fact there is now a huge research effort all over the world leading to rapid breakthroughs.

In my own laboratories at the Centre for Stem Cell Biology at Sheffield University, we are investigating both the fundamental biology of embryonic stem cells as well as ways of generating cells for therapies, such as insulin-secreting cells and neurons.

This work is showing great promise but turning early research findings into practical means of delivering a safe, effective therapy to patients will probably take ten years or longer.

Just a few weeks ago scientists from South Korea announced they had made embryonic stem cells from a cloned human embryo.

This technique would be a means of matching up the genetics of stem cells to that of the patient to completely prevent immunological rejection.

In the UK, all this work is regulated by the HFEA and must comply with strict ethical and clinical criteria.

Recently, the National Stem Cell Bank was established to oversee the control and distribution of stem cells for research and eventually clinical trials.

So what are stem cells?

Most of us are familiar with the idea that our cells divide and proliferate as we grow and this process is needed to for us to remain healthy.

Our skin cells continually divide to replace cells lost through wear and tear. Blood cells are replaced about every six weeks.

But even healthy skin cells or most other cell types do not divide indefinitely and they also undergo changes from one cell generation to the next.

Some cells have a limited programme of division and eventually become old and die, including brain cells.

Others may accumulate small genetic mutations that ultimately result in cell death.

So in many cases our tissues need to be replenished by cells that retain the full capacity for making functional cells.

These are called stem cells (or more correctly adult stem cells) and act as a reservoir to allow regeneration of a particular cell type.

A good example are bone marrow stem cells.

These make all the cells of our blood such as red ones to carry oxygen and white ones to protect against infection.

After treatment for cancers such as leukaemia, a bone marrow (stem cell) transplant may be needed to replace those cells killed fighting the illness.

In an auto-immune disease such as juvenile diabetes - Type 1 diabetes - the stem cells that form the cells that secrete insulin are destroyed. As a result the body can no longer regulate blood glucose.

Children who develop this disease must have insulin injections for the rest of their lives and suffer a number of debilitating conditions.

Stem cells are also the basic building blocks of development.

During the very earliest stages, when the embryo is a ball of cells as small as a pinhead and is yet to implant in the uterus, the "master" stem cells are produced.

These cells are destined to divide and proliferate to form all the various cells (liver, nerve, muscle and the rest) that make up our body.

In the last few years, scientists have been able to extract these cells from the early embryo and make them divide in the test tube.

Crucially, these so-called "embryonic" stem cells still have the ability to form all the different cell types.

The properties of embryonic stem cells in the laboratory have made scientists and doctors very excited.

Harry Moore, research professor at the University of Sheffield's school of medicine, has been conducting research into stem cells.