Many scientists think that there is a maximum human lifespan
of around 120 years. And that might be because adult
human stem cells can only divide a finite number of times,
so there's a limit to the body's capacity for repair.
But what if there was a way of manipulating stem cells,
of taking them back to the beginning, of rewinding their clocks
so that growth could continue?
Dr Harald Ott, a Harvard researcher, is doing something
that only a few years ago was looked on as science
fiction.
He's working to extend the life of our stem cells, to trick them
into growing long after their natural lifespan.
Operating at the very limits of our scientific knowledge,
he's trying to produce lab-grown human organs
for transplant.
What exactly are you doing, Harald?
Well, Chris, what you're looking at here is a human heart
donated for research.
[Dr Chris] The human heart is a complex structure
and one that would be almost impossible to grow from scratch in the lab.
[Dr Ott] We flushed the organ with detergent to remove
all cells from this heart, by using the organ's own vascular system.
[Dr Chris] So where blood would normally flow through the muscle,
now detergent is flowing through, and that's stripping the cells away?
[Dr Ott] Exactly.
[Dr Chris] Dr Ott is left with a protein shell.
All the capillaries and structure of the heart is preserved,
but without functioning cells, the heart
can't do its job.
It's a bit like an office without staff –
it looks the same, but it lacks the vital components
to become functional.
So the next job is to use stem cells to seed this structure
with healthy heart cells.
[Dr Ott] Chris, what you're looking at here is one of those scaffolds
that is mounted in a bioreactor that enables us to perfuse it
with nutrients and seed it with cells. The heart muscle cells,
we get them into it by injecting them directly into it,
every one to two millimetres.
So there's hundreds of injections.
[Dr Chris] Stem cells have one big limitation –
they can only divide into predetermined cells.
So, for example, skin stem cells
can only produce skin cells.
But in 2008, a Japanese scientist called Shinya Yamanaka
made a major breakthrough.
He took normal adult
skin cells and turned back time.
He tricked them into becoming embryonic stem cells,
cells that can become any cell of the human body.
And it's these that
Dr Ott uses to turn into heart cells.
So why aren't we there yet?
I mean, it sounds to me like you've built a heart.
So while we have something that's the shape of a heart
and it has all the necessary components, we now have to help these components
to come together, teach the heart muscle cells to become heart muscle.
If you think of the foetal heart as it develops, very early on the heart
muscle cells are exposed to stress and strains to that moving environment.
That's why we apply stretch and electrical stimulation to, over time,
help mature these cells into something that's much closer to your or my heart.
[Dr Chris] Do you think within our lifetimes we will see
this heart in the jar move to a human body and be functioning?
Well, that's what I hope for.