We hear a lot about stem cells these days,

but what are they, where do they come from

and what do we really know about them?

Inside our bodies there's a microscopic world,

busy and complex like the world around us.

Stem cells build and maintain this world.

This is a story of stem cells and their lives

inside and outside our bodies.

Life begins with one cell, the fertilised egg.

Throughout development cells divide over and over again

to produce the billions of cells that make up the body.

At certain stages, most cells stop making copies of themselves

and start to specialise.

When we are fully formed almost all our cells are specialised.

Cells are beautiful things when you see them down a microscope.

Normally they're so miniscule we can't see them,

even though they're what make us.

And each type of cell has its own characteristic.

Some types of cell grow very closely together

and form beautiful patterns.

Other types of cell will move away from one and other.

Some cells become big, others are always very small.

It depends on what type of cell they are.

These different cell types work in specialised teams.

Some carry oxygen through the blood system,

some do the stretching and contracting in our muscles,

some carry messages between our brain and the rest of our body.

Stem cells are very special cells They act as a resevoir,

because the specialised cells

can no longer make copies of themselves.

So, if they die and get used up, they have to be replaced from somewhere.

And this is where the stem cells function.

Stem cells are used in the blood system.

We need to make millions of new blood cells every day

and these are generated from stem cells.

And these cells actually live in the bone marrow.

Altogether a blood stem cell can make eight different types

of specialised cell.

They're used in the skin.

We need to make new skin cells all the time

because we're always wearing away our skin.

And actually now we know they're present even in the brain.

We always have to make new stem cells,

so they're not completely exhausted,

because otherwise we'd lose the capacity to make any new cells.

So the stem cell has to make a decision.

Every time it divides, it produces two daughter cells,

and those daughter cells can be new stem cells,

or they can be specialised cells.

Stem cells in the adult tissues can normally only make

the type of cell in that tissue.

So a stem cell in the skin, can make cells in the skin,

but it can't make blood cells and vice versa.

Stem cells are already useful in medicine.

One skin stem cell alone can produce enough specialised skin stells

to cover the whole body.

This produced a breakthrough in the treatment of extensive burns.

1ST DEGREE BURN...

When a person is heavily burnt, we take a sample

from an unburnt area and we take apart the skin sample

and we get the cells out of it,

and we seed the cells in a culture flask like this one.

We feed the cells with a special liquid, which is full of protein and sugar.

They need to eat like you.

At some point, these cells will divide, will multiply.

And they will cover the entire bottom of the flask.

We remove the cells using a special chemical

and we take this sheet of cells into the surgery room

and transplant the patient with it.

We can do only part of the skin today,

which means we can do the outer most layer of the skin,

which is very important, because without this layer you wouldn't be able to survive.

However, we cannot reconstruct sweat glands our hair follicles.

So these burnt patients have had their lives saved by stem cells,

but they have no hair and they don't sweat.

That is obviously a problem.

They are alive, but I can't say they have a normal life.

That's why many laboratories are trying to understand

how the skin is built to be able to reconstruct it in the lab,

so we can improve the life of these patients.

Stem cells are also used to treat patients with blood disorders,

such as leukaemia.

A transplant of just a few blood stem cells,

is enough to repair the entire blood system.

Stem cells for specific tissues and organs

can only make the cells of that tissue.

We know there are stem cells in skin, blood, guts and muscles,

but we don't know whether other organs have their own stem cells,

or how useful they will be.

Back along the chain of development, there's another kind of stem cell.

It's controversial. It can become any specialised cell.

The embryonic stem cell.

This cell comes from a blastocyst, the stage of development

before implantation in the uterus.

For fertility treatment, blastocysts are produced in the laboratory.

If they are not used for a pregnancy, they can be donated for research.

In the early embryo, there's a group of cells

that can give rise to all the tissues of the body.

These are the cells we're very interested in

because we know that we can take the cells from the early embryo

and grow them in culture, and maintain them in a state

where they can contribute to all the tissues.

What we're seeing here is the blastocyst stage of development.

It's smaller than a pin head.

You can't see it without the microscope.

So at this stage, the cells in the embryo - these are the cells -

they can make any tissue at all.

What we have to do, is isolate these cells.

One way is we can remove the trophectoderm cells

so that we're just left with a clean inner cell mass.

So we can grow these in culture, and they'll multiply

until we have lots of these cells

that still have the capacity to form

any tissue at all.

Embryonic stem cells can become heart, blood, brain or skin cells

depending on the way they are grown.

These stem cells have turned into heart cells.

When you're working with stem cells, you're always observing the cells

and you're trying to understand how it is they can do what they can do.

You're trying, actually, to make them do what you want to do.

It's almost like a battle of wills.

A stem cell goes through a long series

of decisions to become a specialised cell.

A combination of internal and external signals guide each stem cell

along the path towards specialisation.

These signals are normally provided by the body.

By figuring out how to recreate these signals in the lab,

scientists aim to grow pure populations of almost any cell type.

The challenge to us is to understand each decision and how it's controlled.

And then how to provide those signals,

to impose the direction on the sytem.

And once we get to a point where that begins to happen,

then you suddenly see that you could use it

to address medical conditions and problems.

Work that we have been doing recently

has been focussed on trying to make stem cells for the brain

from embryonic stem cells. And it turns out we're able to do this.

These neural stem cells are now no longer able to make all cells,

they can only make three types of cells, the three types that exist in the brain.

So this is an important first step in creating a useful and powerful system,

that can both be applied for drug screening and perhaps in the end for transplantation.

These lab-grown human cells, produced in large numbers,

provide improved models for testing new medical treatments

and may reduce the need for animal testing.

The same cells may help us understand what goes wrong in complex diseases,

like Alzheimer's, Parkinson's and diabetes.

Diabetes is a chronic disease defined by high blood sugar levels

that stay high just because there is not enough insulin.

We know that the insulin is produced by cells in the pancreas.

We call them beta cells.

Transplantations of those cells are now done in clinics.

Those cells are isolated from donor organs.

After transplantation with those cells, you can normalise diabetes.

You can correct diabetes.

The major obstacle to beta cell transplantation in diabetes

is the shortage of donor cells.

We can transplant only 25 patients per year,

while there are more than 50,000 patients in Belgium that are treated with insulin.

We have to look for other techniques

to produce insulin-making cells in the laboratory.

What the researchers try to do

is first examine this path, this evolution

between the embryonic stem cell and the insulin-producing beta cell,

and then to also try to isolate the different stages,

the different kind of stem cells on the way to beta cells.

If one can then isolate them and let them grow in the laboratory

then you can make as many insulin-producing cells as you want.

And that's the goal of many investigators in the world.

The embryonic stem cell area is a very exciting area.

It really has opened a new world, that of regenerative medicine.

We have now bridges between all the laboratories

that have a particular expertise.

Working together, we will be in a good position

to examine, to investigate its enormous potential,

but the enthusiasm should not cover all the technical and scientific

questions and obstacles that exist

and that will have to be studied very carefully.

Stem cell research is a fast-moving field.

Around the world, new findings are constantly reported,

creating new questions and fresh challenges for scientists

seeking to harness these cells and to shape future medicine.

So cells are the building blocks of the tissues and organs of the body.

And many people are interested in this.

What captured my imagination, was when I realised that

in development, cells actually have to make choices

and decide to become different types of cell,

and understanding how that is controlled, how that decision is made...

If you could understand that, it seems to me,

then you would understand the most important thing about life.