0:00:01.286,0:00:05.317
The most important gift[br]your mother and father ever gave you

0:00:05.341,0:00:08.061
was the two sets[br]of three billion letters of DNA

0:00:08.085,0:00:09.649
that make up your genome.

0:00:10.014,0:00:12.491
But like anything[br]with three billion components,

0:00:12.515,0:00:13.915
that gift is fragile.

0:00:14.815,0:00:18.355
Sunlight, smoking, unhealthy eating,

0:00:18.379,0:00:21.371
even spontaneous mistakes[br]made by your cells,

0:00:21.395,0:00:23.318
all cause changes to your genome.

0:00:24.942,0:00:28.220
The most common kind of change in DNA

0:00:28.244,0:00:32.473
is the simple swap of one letter,[br]or base, such as C,

0:00:32.497,0:00:35.738
with a different letter,[br]such as T, G or A.

0:00:36.744,0:00:40.117
In any day, the cells in your body[br]will collectively accumulate

0:00:40.141,0:00:44.977
billions of these single-letter swaps,[br]which are also called "point mutations."

0:00:46.147,0:00:48.678
Now, most of these[br]point mutations are harmless.

0:00:48.702,0:00:49.860
But every now and then,

0:00:49.884,0:00:53.877
a point mutation disrupts[br]an important capability in a cell

0:00:53.901,0:00:57.256
or causes a cell to misbehave[br]in harmful ways.

0:00:58.099,0:01:01.098
If that mutation were inherited[br]from your parents

0:01:01.122,0:01:03.782
or occurred early enough[br]in your development,

0:01:03.806,0:01:06.772
then the result would be[br]that many or all of your cells

0:01:06.796,0:01:08.708
contain this harmful mutation.

0:01:09.153,0:01:12.423
And then you would be one[br]of hundreds of millions of people

0:01:12.447,0:01:14.058
with a genetic disease,

0:01:14.082,0:01:17.085
such as sickle cell anemia or progeria

0:01:17.109,0:01:20.230
or muscular dystrophy[br]or Tay-Sachs disease.

0:01:22.225,0:01:25.407
Grievous genetic diseases[br]caused by point mutations

0:01:25.431,0:01:27.424
are especially frustrating,

0:01:27.448,0:01:30.352
because we often know[br]the exact single-letter change

0:01:30.376,0:01:34.576
that causes the disease[br]and, in theory, could cure the disease.

0:01:35.268,0:01:38.117
Millions suffer from sickle cell anemia

0:01:38.141,0:01:41.212
because they have[br]a single A to T point mutations

0:01:41.236,0:01:43.597
in both copies of their hemoglobin gene.

0:01:45.529,0:01:48.661
And children with progeria[br]are born with a T

0:01:48.685,0:01:50.853
at a single position in their genome

0:01:50.877,0:01:52.276
where you have a C,

0:01:53.125,0:01:56.564
with the devastating consequence[br]that these wonderful, bright kids

0:01:56.588,0:02:00.564
age very rapidly and pass away[br]by about age 14.

0:02:02.358,0:02:04.041
Throughout the history of medicine,

0:02:04.065,0:02:07.125
we have not had a way[br]to efficiently correct point mutations

0:02:07.149,0:02:08.918
in living systems,

0:02:08.942,0:02:12.142
to change that disease-causing[br]T back into a C.

0:02:13.482,0:02:15.450
Perhaps until now.

0:02:15.474,0:02:19.664
Because my laboratory recently succeeded[br]in developing such a capability,

0:02:19.688,0:02:21.488
which we call "base editing."

0:02:23.277,0:02:25.301
The story of how we developed base editing

0:02:25.325,0:02:27.999
actually begins three billion years ago.

0:02:29.055,0:02:31.715
We think of bacteria[br]as sources of infection,

0:02:31.739,0:02:35.053
but bacteria themselves are also[br]prone to being infected,

0:02:35.077,0:02:36.984
in particular, by viruses.

0:02:37.871,0:02:40.022
So about three billion years ago,

0:02:40.046,0:02:43.926
bacteria evolved a defense mechanism[br]to fight viral infection.

0:02:45.649,0:02:48.434
That defense mechanism[br]is now better known as CRISPR.

0:02:49.008,0:02:51.833
And the warhead in CRISPR[br]is this purple protein

0:02:51.857,0:02:55.635
that acts like molecular[br]scissors to cut DNA,

0:02:55.659,0:02:58.087
breaking the double helix into two pieces.

0:02:59.323,0:03:03.299
If CRISPR couldn't distinguish[br]between bacterial and viral DNA,

0:03:03.323,0:03:05.562
it wouldn't be a very useful[br]defense system.

0:03:06.315,0:03:09.100
But the most amazing feature of CRISPR

0:03:09.124,0:03:14.161
is that the scissors can be[br]programmed to search for,

0:03:14.185,0:03:16.608
bind to and cut

0:03:16.632,0:03:19.370
only a specific DNA sequence.

0:03:20.911,0:03:24.308
So when a bacterium encounters[br]a virus for the first time,

0:03:24.332,0:03:27.705
it can store a small snippet[br]of that virus's DNA

0:03:27.729,0:03:31.373
for use as a program[br]to direct the CRISPR scissors

0:03:31.397,0:03:34.933
to cut that viral DNA sequence[br]during a future infection.

0:03:35.778,0:03:40.691
Cutting a virus's DNA messes up[br]the function of the cut viral gene,

0:03:40.715,0:03:43.417
and therefore disrupts[br]the virus's life cycle.

0:03:46.059,0:03:50.860
Remarkable researchers including[br]Emmanuelle Charpentier, George Church,

0:03:50.884,0:03:53.537
Jennifer Doudna and Feng Zhang

0:03:53.561,0:03:57.530
showed six years ago how CRISPR scissors[br]could be programmed

0:03:57.554,0:04:00.141
to cut DNA sequences of our choosing,

0:04:00.165,0:04:02.534
including sequences in your genome,

0:04:02.558,0:04:05.901
instead of the viral DNA sequences[br]chosen by bacteria.

0:04:06.550,0:04:09.084
But the outcomes are actually similar.

0:04:09.606,0:04:12.074
Cutting a DNA sequence in your genome

0:04:12.098,0:04:16.225
also disrupts the function[br]of the cut gene, typically,

0:04:16.997,0:04:21.464
by causing the insertion and deletion[br]of random mixtures of DNA letters

0:04:21.488,0:04:22.641
at the cut site.

0:04:24.625,0:04:28.506
Now, disrupting genes can be very[br]useful for some applications.

0:04:30.005,0:04:34.306
But for most point mutations[br]that cause genetic diseases,

0:04:34.330,0:04:38.687
simply cutting the already-mutated gene[br]won't benefit patients,

0:04:38.711,0:04:42.679
because the function of the mutated gene[br]needs to be restored,

0:04:42.703,0:04:44.318
not further disrupted.

0:04:45.259,0:04:48.141
So cutting this[br]already-mutated hemoglobin gene

0:04:48.165,0:04:50.688
that causes sickle cell anemia

0:04:50.712,0:04:54.228
won't restore the ability of patients[br]to make healthy red blood cells.

0:04:55.631,0:04:59.972
And while we can sometimes introduce[br]new DNA sequences into cells

0:04:59.996,0:05:03.417
to replace the DNA sequences[br]surrounding a cut site,

0:05:03.441,0:05:07.765
that process, unfortunately, doesn't work[br]in most types of cells,

0:05:07.789,0:05:10.230
and the disrupted gene outcomes[br]still predominate.

0:05:12.297,0:05:14.479
Like many scientists,[br]I've dreamed of a future

0:05:14.503,0:05:17.277
in which we might be able to treat[br]or maybe even cure

0:05:17.301,0:05:18.672
human genetic diseases.

0:05:19.135,0:05:22.936
But I saw the lack of a way[br]to fix point mutations,

0:05:22.960,0:05:25.984
which cause most human genetic diseases,

0:05:26.008,0:05:28.396
as a major problem standing in the way.

0:05:29.434,0:05:32.102
Being a chemist, I began[br]working with my students

0:05:32.126,0:05:37.061
to develop ways on performing chemistry[br]directly on an individual DNA base,

0:05:37.085,0:05:42.704
to truly fix, rather than disrupt,[br]the mutations that cause genetic diseases.

0:05:44.522,0:05:47.070
The results of our efforts[br]are molecular machines

0:05:47.094,0:05:48.482
called "base editors."

0:05:49.618,0:05:55.093
Base editors use the programmable[br]searching mechanism of CRISPR scissors,

0:05:55.117,0:05:58.053
but instead of cutting the DNA,

0:05:58.077,0:06:01.018
they directly convert[br]one base to another base

0:06:01.042,0:06:03.295
without disrupting the rest of the gene.

0:06:04.674,0:06:08.832
So if you think of naturally occurring[br]CRISPR proteins as molecular scissors,

0:06:08.856,0:06:11.642
you can think of base editors as pencils,

0:06:11.666,0:06:15.162
capable of directly rewriting[br]one DNA letter into another

0:06:16.098,0:06:19.901
by actually rearranging[br]the atoms of one DNA base

0:06:19.925,0:06:22.259
to instead become a different base.

0:06:23.513,0:06:25.689
Now, base editors don't exist in nature.

0:06:26.683,0:06:29.913
In fact, we engineered[br]the first base editor, shown here,

0:06:29.937,0:06:31.294
from three separate proteins

0:06:31.318,0:06:33.548
that don't even come[br]from the same organism.

0:06:34.151,0:06:39.248
We started by taking CRISPR scissors[br]and disabling the ability to cut DNA

0:06:39.272,0:06:43.811
while retaining its ability to search for[br]and bind a target DNA sequence

0:06:43.835,0:06:45.369
in a programmed manner.

0:06:46.351,0:06:49.188
To those disabled CRISPR[br]scissors, shown in blue,

0:06:49.212,0:06:51.720
we attached a second protein in red,

0:06:51.744,0:06:56.045
which performs a chemical reaction[br]on the DNA base C,

0:06:56.069,0:06:59.402
converting it into a base[br]that behaves like T.

0:07:00.958,0:07:04.100
Third, we had to attach[br]to the first two proteins

0:07:04.124,0:07:05.474
the protein shown in purple,

0:07:05.498,0:07:09.098
which protects the edited base[br]from being removed by the cell.

0:07:10.466,0:07:13.308
The net result is an engineered[br]three-part protein

0:07:13.332,0:07:17.450
that for the first time[br]allows us to convert Cs into Ts

0:07:17.474,0:07:19.637
at specified locations in the genome.

0:07:21.490,0:07:24.522
But even at this point,[br]our work was only half done.

0:07:24.546,0:07:27.172
Because in order to be stable in cells,

0:07:27.196,0:07:30.855
the two strands of a DNA double helix[br]have to form base pairs.

0:07:32.125,0:07:35.783
And because C only pairs with G,

0:07:35.807,0:07:38.809
and T only pairs with A,

0:07:39.752,0:07:44.598
simply changing a C to a T[br]on one DNA strand creates a mismatch,

0:07:44.622,0:07:47.471
a disagreement between the two DNA strands

0:07:47.495,0:07:51.763
that the cell has to resolve[br]by deciding which strand to replace.

0:07:53.149,0:07:57.490
We realized that we could further engineer[br]this three-part protein

0:07:58.649,0:08:02.515
to flag the nonedited strand[br]as the one to be replaced

0:08:02.539,0:08:04.450
by nicking that strand.

0:08:05.276,0:08:07.805
This little nick tricks the cell

0:08:07.829,0:08:12.776
into replacing the nonedited G with an A

0:08:12.800,0:08:15.125
as it remakes the nicked strand,

0:08:15.149,0:08:19.180
thereby completing the conversion[br]of what used to be a C-G base pair

0:08:19.204,0:08:21.500
into a stable T-A base pair.

0:08:24.585,0:08:26.136
After several years of hard work

0:08:26.160,0:08:30.141
led by a former post doc[br]in the lab, Alexis Komor,

0:08:30.165,0:08:33.347
we succeeded in developing[br]this first class of base editor,

0:08:33.371,0:08:37.037
which converts Cs into Ts and Gs into As

0:08:37.061,0:08:39.220
at targeted positions of our choosing.

0:08:40.633,0:08:45.863
Among the more than 35,000 known[br]disease-associated point mutations,

0:08:45.887,0:08:49.672
the two kinds of mutations[br]that this first base editor can reverse

0:08:49.696,0:08:55.839
collectively account for about 14 percent[br]or 5,000 or so pathogenic point mutations.

0:08:56.593,0:09:01.363
But correcting the largest fraction[br]of disease-causing point mutations

0:09:01.387,0:09:05.022
would require developing[br]a second class of base editor,

0:09:05.046,0:09:09.132
one that could convert[br]As into Gs or Ts into Cs.

0:09:10.846,0:09:14.573
Led by Nicole Gaudelli,[br]a former post doc in the lab,

0:09:14.597,0:09:17.719
we set out to develop[br]this second class of base editor,

0:09:17.743,0:09:23.870
which, in theory, could correct up to[br]almost half of pathogenic point mutations,

0:09:23.894,0:09:27.805
including that mutation that causes[br]the rapid-aging disease progeria.

0:09:30.107,0:09:33.274
We realized that we could[br]borrow, once again,

0:09:33.298,0:09:37.366
the targeting mechanism of CRISPR scissors

0:09:37.390,0:09:42.551
to bring the new base editor[br]to the right site in a genome.

0:09:43.543,0:09:46.635
But we quickly encountered[br]an incredible problem;

0:09:47.896,0:09:50.324
namely, there is no protein

0:09:50.348,0:09:54.400
that's known to convert[br]A into G or T into C

0:09:54.424,0:09:55.585
in DNA.

0:09:56.760,0:09:58.926
Faced with such a serious stumbling block,

0:09:58.950,0:10:01.482
most students would probably[br]look for another project,

0:10:01.506,0:10:03.246
if not another research advisor.

0:10:03.270,0:10:04.434
(Laughter)

0:10:04.458,0:10:06.400
But Nicole agreed to proceed with a plan

0:10:06.424,0:10:09.091
that seemed wildly ambitious at the time.

0:10:09.966,0:10:12.305
Given the absence[br]of a naturally occurring protein

0:10:12.329,0:10:14.490
that performs the necessary chemistry,

0:10:14.514,0:10:17.950
we decided we would evolve[br]our own protein in the laboratory

0:10:17.974,0:10:21.809
to convert A into a base[br]that behaves like G,

0:10:21.833,0:10:26.660
starting from a protein[br]that performs related chemistry on RNA.

0:10:27.230,0:10:31.164
We set up a Darwinian[br]survival-of-the-fittest selection system

0:10:31.188,0:10:35.180
that explored tens of millions[br]of protein variants

0:10:35.204,0:10:37.222
and only allowed those rare variants

0:10:37.246,0:10:40.467
that could perform the necessary[br]chemistry to survive.

0:10:41.883,0:10:44.271
We ended up with a protein shown here,

0:10:44.295,0:10:47.152
the first that can convert A in DNA

0:10:47.176,0:10:49.268
into a base that resembles G.

0:10:49.292,0:10:50.895
And when we attached that protein

0:10:50.919,0:10:53.490
to the disabled CRISPR[br]scissors, shown in blue,

0:10:53.514,0:10:55.522
we produced the second base editor,

0:10:55.546,0:10:58.641
which converts As into Gs,

0:10:58.665,0:11:02.506
and then uses the same[br]strand-nicking strategy

0:11:02.530,0:11:04.450
that we used in the first base editor

0:11:04.474,0:11:09.939
to trick the cell into replacing[br]the nonedited T with a C

0:11:09.963,0:11:11.638
as it remakes that nicked strand,

0:11:11.662,0:11:15.833
thereby completing the conversion[br]of an A-T base pair to a G-C base pair.

0:11:16.845,0:11:18.892
(Applause)

0:11:18.916,0:11:20.086
Thank you.

0:11:20.110,0:11:23.467
(Applause)

0:11:23.491,0:11:25.826
As an academic scientist in the US,

0:11:25.850,0:11:27.997
I'm not used to being[br]interrupted by applause.

0:11:28.021,0:11:31.172
(Laughter)

0:11:31.196,0:11:35.601
We developed these[br]first two classes of base editors

0:11:35.625,0:11:38.399
only three years ago[br]and one and a half years ago.

0:11:39.267,0:11:40.815
But even in that short time,

0:11:40.839,0:11:44.561
base editing has become widely used[br]by the biomedical research community.

0:11:45.776,0:11:50.141
Base editors have been sent[br]more than 6,000 times

0:11:50.165,0:11:54.036
at the request of more than[br]1,000 researchers around the globe.

0:11:55.475,0:11:58.991
A hundred scientific research papers[br]have been published already,

0:11:59.015,0:12:02.743
using base editors in organisms[br]ranging from bacteria

0:12:02.767,0:12:04.901
to plants to mice to primates.

0:12:07.950,0:12:09.557
While base editors are too new

0:12:09.581,0:12:12.466
to have already entered[br]human clinical trials,

0:12:12.490,0:12:17.612
scientists have succeeded in achieving[br]a critical milestone towards that goal

0:12:17.636,0:12:20.485
by using base editors in animals

0:12:20.509,0:12:24.418
to correct point mutations[br]that cause human genetic diseases.

0:12:25.815,0:12:26.966
For example,

0:12:26.990,0:12:30.783
a collaborative team of scientists[br]led by Luke Koblan and Jon Levy,

0:12:30.807,0:12:33.220
two additional students in my lab,

0:12:33.244,0:12:37.363
recently used a virus to deliver[br]that second base editor

0:12:37.387,0:12:39.577
into a mouse with progeria,

0:12:39.601,0:12:43.458
changing that disease-causing[br]T back into a C

0:12:43.482,0:12:47.588
and reversing its consequences[br]at the DNA, RNA and protein levels.

0:12:48.880,0:12:51.626
Base editors have also[br]been used in animals

0:12:51.650,0:12:54.574
to reverse the consequence of tyrosinemia,

0:12:55.642,0:12:59.260
beta thalassemia, muscular dystrophy,

0:12:59.284,0:13:02.974
phenylketonuria, a congenital deafness

0:13:02.998,0:13:04.937
and a type of cardiovascular disease --

0:13:04.961,0:13:09.823
in each case, by directly[br]correcting a point mutation

0:13:09.847,0:13:12.400
that causes or contributes to the disease.

0:13:13.688,0:13:15.744
In plants, base editors have been used

0:13:15.768,0:13:19.840
to introduce individual[br]single DNA letter changes

0:13:19.864,0:13:21.832
that could lead to better crops.

0:13:22.253,0:13:26.842
And biologists have used base editors[br]to probe the role of individual letters

0:13:26.866,0:13:29.683
in genes associated[br]with diseases such as cancer.

0:13:31.046,0:13:35.613
Two companies I cofounded,[br]Beam Therapeutics and Pairwise Plants,

0:13:35.637,0:13:39.462
are using base editing[br]to treat human genetic diseases

0:13:39.486,0:13:41.092
and to improve agriculture.

0:13:41.953,0:13:43.919
All of these applications of base editing

0:13:43.943,0:13:47.037
have taken place in less[br]than the past three years:

0:13:47.061,0:13:49.425
on the historical timescale of science,

0:13:49.449,0:13:50.731
the blink of an eye.

0:13:52.657,0:13:53.910
Additional work lies ahead

0:13:53.934,0:13:56.966
before base editing can realize[br]its full potential

0:13:56.990,0:14:00.604
to improve the lives of patients[br]with genetic diseases.

0:14:01.244,0:14:04.024
While many of these diseases[br]are thought to be treatable

0:14:04.048,0:14:05.897
by correcting the underlying mutation

0:14:05.921,0:14:09.437
in even a modest fraction[br]of cells in an organ,

0:14:09.461,0:14:12.437
delivering molecular machines[br]like base editors

0:14:12.461,0:14:14.228
into cells in a human being

0:14:14.252,0:14:15.421
can be challenging.

0:14:16.962,0:14:20.335
Co-opting nature's viruses[br]to deliver base editors

0:14:20.359,0:14:22.557
instead of the molecules[br]that give you a cold

0:14:22.581,0:14:25.268
is one of several promising[br]delivery strategies

0:14:25.292,0:14:26.951
that's been successfully used.

0:14:28.268,0:14:30.633
Continuing to develop[br]new molecular machines

0:14:30.657,0:14:32.525
that can make all of the remaining ways

0:14:32.549,0:14:35.441
to convert one base pair[br]to another base pair

0:14:35.465,0:14:39.845
and that minimize unwanted editing[br]at off-target locations in cells

0:14:39.869,0:14:41.069
is very important.

0:14:41.782,0:14:46.488
And engaging with other scientists,[br]doctors, ethicists and governments

0:14:46.512,0:14:51.303
to maximize the likelihood[br]that base editing is applied thoughtfully,

0:14:51.327,0:14:53.708
safely and ethically,

0:14:53.732,0:14:55.732
remains a critical obligation.

0:14:57.525,0:14:59.136
These challenges notwithstanding,

0:14:59.160,0:15:02.815
if you had told me[br]even just five years ago

0:15:02.839,0:15:04.490
that researchers around the globe

0:15:04.514,0:15:08.053
would be using laboratory-evolved[br]molecular machines

0:15:08.077,0:15:11.074
to directly convert[br]an individual base pair

0:15:11.098,0:15:12.280
to another base pair

0:15:12.304,0:15:14.923
at a specified location[br]in the human genome

0:15:14.947,0:15:18.772
efficiently and with a minimum[br]of other outcomes,

0:15:18.796,0:15:19.964
I would have asked you,

0:15:19.988,0:15:22.462
"What science-fiction novel[br]are you reading?"

0:15:23.706,0:15:27.166
Thanks to a relentlessly dedicated[br]group of students

0:15:27.190,0:15:31.650
who were creative enough to engineer[br]what we could design ourselves

0:15:31.674,0:15:34.599
and brave enough[br]to evolve what we couldn't,

0:15:34.623,0:15:39.663
base editing has begun to transform[br]that science-fiction-like aspiration

0:15:39.687,0:15:41.544
into an exciting new reality,

0:15:42.250,0:15:45.481
one in which the most important gift[br]we give our children

0:15:45.505,0:15:48.530
may not only be[br]three billion letters of DNA,

0:15:48.554,0:15:51.664
but also the means to protect[br]and repair them.

0:15:52.339,0:15:53.490
Thank you.

0:15:53.514,0:15:58.016
(Applause)

0:15:58.040,0:15:59.190
Thank you.