Just like you can change a single letter in a word document,

now we can change single letters in the DNA.

It's called CRISPR.

Clustered Regularly Interspaced Short Palindromic Repeats.

The new gene editing platform CRISPR is generating a lot of excitement.

CRISPR...

But this isn't the first time scientists have tried to fix the genes that make us sick.

It started over 30 years ago.

Gene therapy.

Medicine's new frontier.

It was the first time they were going to be altering a human's DNA.

The expectations were crazy.

I like reading as well as playing chess.

And I like to go to different places.

I'd want to make people more aware about sickle cell.

How are you, Pierce?

Pierceton Charles has sickle cell anemia.

It's a painful genetic disease that distorts his red blood cells so they can't deliver

oxygen to his organs.

His first blood transfusion was 7 months old.

He had a stroke.

He lost his spleen and shortly after the gallbladder.

He's had a total of 48 hospitalizations.

He's one of about 100,000 people in the United States with sickle cell.

Most are African-American and, on average, live to their mid-40s.

There is no definite treatment for sickle cell.

Sickle cell was one of the first hereditary diseases to have its gene mutation,

or sequence change, identified.

Ever since I met my first patient with sickle cell disease,

that's been really my challenge to say, let's find a cure that is based on the cause.

We've known the sequence change since the early 1970s.

But I'll point out, that's over 40 years ago, and we don't have any therapy

based on knowing that sequence change.

So in his lab at Stanford University, Matthew Porteus is trying to repair the gene

that causes sickle cell.

So what we have to do is edit some blood stem cells.

He's using a new gene editing technology called CRISPR-Cas9.

Ready to electroporate.

It works like genetic scissors,

cutting out and replacing a gene's misspelled bits of DNA.

We can change single letters in the DNA and convert the disease-causing variant

to a non-disease-causing variant.

The cells that have been edited are these bright green cells.

Pierceton needs monthly treatments to replace his sickle-shaped red blood cells

with normal cells.

He donates the old blood for Porteus's research,

which he hopes could someday help him.

They're attempting to modify the genes so they can cure sickle cell.

I think that it's pretty amazing.

Porteus has applied for approval for a clinical trial.

We think these cells represent cures for patients.

They do everything that they're supposed to do.

So that gives us confidence that it's worth trying in a human patient.

We have our fingers crossed.

We're excited.

But along with CRISPR's promise come fears about its accuracy...

A DNA break could be dangerous.

It could cause other mutations.

...and its potential use editing genes not just in patients but in embryos,

which would impact future generations.

We're talking about something that would affect human evolution.

Critics worry CRISPR could be used to create designer babies.

You may want to make a baby taller, faster, smarter.

The power of this new CRISPR technology has

resurfaced questions that people have been thinking about for 40 years.

If we had a tool that would allow you to change the

DNA that would then be passed along to next generations,

is that something we should or shouldn't do?

Many of the questions, and the controversy, remind Ashanthi De Silva

of her own experience with a different kind of genetic engineering,

called gene therapy, nearly 30 years ago.

Ashanthi, Ashanthi, come baby.

When I was born, the umbilical cord was infected, and I would turn blue a lot.

She was born with ADA deficiency,

a rare genetic disorder that crippled her immune system.

Although there was no cure, her doctor had an idea,

though it could take a lifetime.

He said, "You know, there's this potential trial

going on at the National Institutes of Health.

Let me send her blood."

And he told me, "Mrs. De Silva, this is for

possible gene therapy when your daughter is 60 years old."

And I thought, "Oh, how wonderful!"

Unlike CRISPR, which repairs genes,

gene therapy would send in an

extra healthy gene to do the work of the defective one.

But before Ashanthi could be treated,

there were scientific, and ethical, hurdles to overcome.

They had told my parents there would be risks of leukemia, death.

It was the first time they were going to be altering a human's DNA.

We all went to the NIH.

And they actually didn't have FDA approval yet.

It was really up until that day they were waiting for the phone call,

I was in the room.

This is on the 14th of September,

"A great day for the world, a great day for medicine.

Gene therapy has been approved."

You can read that.

"Our daughter is the first patient in the world to receive gene therapy."

They had taken my cells and injected the vector with the corrected gene into my cells.

They transferred those cells back to me,

to see if they would give me a new immune system.

How about that?

My parents did receive death threats, because there was this idea that

altering someone's DNA is playing God.

There was a historic medical first today.

Genetic engineering as a potential way to cure an illness in a human being.

The gene therapy revolution seemed to come almost instantly,

fueled in part by discoveries from the Human Genome Project,

the national effort to find and sequence all human genes.

Payoff has already begun by the discovery of a long list of genes.

As researchers found more and more of the genes that cause hereditary diseases...

It is only a step toward eventual treatment, but it is a significant one.

Gene in a cancer patient.

...news stories regularly touted gene therapy as the potential cure.

Gene therapy to improve a potentially deadly condition.

Such as muscular dystrophy, sickle cell anemia.

And possibly even AIDS.

We presumed, as a society, that if we had the gene we'd be able to

then quickly move to a treatment.

The expectations were crazy.

James Wilson was one of gene therapy's pioneers.

In these human cells he was able to replace

the defective cystic fibrosis gene with a normal gene.

In 1999, at the University of Pennsylvania,

he began testing a gene therapy for a rare liver disease that mostly affects boys.

Upon their first meal they develop a coma.

And there's 50 percent mortality as a result of that.

To deliver the healthy gene into the patient's body,

Wilson used a specially prepared virus called a vector.

A young man by the name of Jesse Gelsinger received the vector.

Things went terribly wrong.

He mounted this enormous immune response that led to his death.

I had spent almost 10 years trying to make it safe.

That's probably irrelevant.

What is relevant is a young man died.

After hundreds of gene therapy experiments, Gelsinger's death

came as an enormous shock.

Every researcher in America was reminded:

This is messing with the code of life.

Why aren't they reporting these?

Congress held hearings, and federal agencies investigated.

The FDA says Penn researchers failed to report previous

toxic reactions in humans and the death of test animals in similar experiments.

I wasn't given all the information.

And some of the information I was given was not true.

Penn's program was shut down, and Wilson banned from clinical trials

for five years.

Then investigators began uncovering problems at other institutions

around the country.

Several others died, hundreds more had side effects,

but researchers didn't tell federal health officials.

Gene therapy also faced scientific setbacks...

A cystic fibrosis treatment, a muscular dystrophy treatment,

a brain cancer treatment: all failed.

To this date, gene therapy has yet to cure anyone.

...including Ashanthi De Silva.

The benefits from her gene therapy diminished with time.

So she still needed regular enzyme injections to support her immune system.

Gene therapy, at least initially, did give me that boost that I needed.

But it wasn't what they could call a cure.

The tragic death of Jesse Gelsinger

was one of several events that led to a precipitous decline in the support for this field.

Support just evaporated after that.

It seemed that gene therapy's prospects were over,

but a small group of researchers continued on.

Our first responsibility

to everyone, including Jesse Gelsinger, was

to try to figure out what happened and why.

We learned that the problem was immune response, not to the gene,

but to the delivery vehicle itself.

Wilson returned to the lab, hoping to make safer vectors.

And the vectors that we generated seem not only really safe

but were much more efficient.

I knew that they would be a game changer,

and we just distributed these to my colleagues.

And I hoped that there would get traction.

It didn't take long to discover them.

It took a lot longer for there to get traction.

An experimental gene therapy...

Almost 20 years later, gene therapy has been experiencing a revival,

and is showing promise for conditions ranging from hemophilia

to Parkinson's disease.

Peter McConnell has a genetic eye disease called choroideremia.

It leads to tunnel vision, and in some cases blindness.

He's the father of two young children and, hoping to see them grow up,

joined a clinical trial at the University of Pennsylvania.

When I initially was approved, I didn't think twice about it.

I was just going to do it.

They take a genetically mutated virus, and they inject it in the back of your retina.

The goal isn't to miraculously restore eyesight.

What they would consider successful was stopping the eye from progressing

and getting worse.

I'd be more than happy if that was the case.

For the first time ever, the FDA has just approved a gene therapy treatment.

The first gene therapy was recently approved in the United States

for a form of childhood leukemia.

But because gene therapy doesn't actually fix broken genes,

no one knows how long its benefits will last.

What we're asking to do here is to cure diseases.

And whether we can ultimately achieve a permanent genetic graft

that reverses their disease forever, we'll see.

That hope for a permanent cure is why so many are excited about CRISPR.

Wow. Human genetic engineering.

Yesterday was science fiction, and today it's reality.

Get this. It could eliminate chemotherapy.

It's fast, cheap and can cut and paste genetic code with great precision.

All the results say that it is working.

The ultimate test is going to be those first few patients.

They're the ones taking all the risks.

Patients who take risks like Ashanthi De Silva did with gene therapy.

She's grateful for the treatment she got,

but regrets gene therapy's long hiatus.

When you're doing something like altering someone's DNA, there are risks.

But it gave me life.

I was able to complete my master's, get married, you know have a nice home life,

so I've been very lucky.

As for James Wilson, he is now working with CRISPR but remains mindful of the

lessons from gene therapy's early days.

That period of exuberance, early on in the development of a new,

novel, cutting-edge technology, it's very easy to get caught up into that.

The reality is, is this is still science.

And these are still experiments, and we are still learning.