Can we cure genetic diseases by rewriting DNA? | David R. Liu

翻译人员: jacks peng 校对人员: Bighead Ge

The most important gift your mother and father ever gave you

你父母给你的最重要的礼物

was the two sets of three billion letters of DNA

就是2组包含30亿个碱基的DNA，

that make up your genome.

它们构成了你的基因组。

But like anything with three billion components,

但就像任何包含太多零件的东西一样，

that gift is fragile.

这个礼物非常脆弱。

Sunlight, smoking, unhealthy eating,

太阳光、吸烟、不健康的饮食，

even spontaneous mistakes made by your cells,

甚至是细胞自身出现的错误，

all cause changes to your genome.

都能改变你的基因组。

The most common kind of change in DNA

最常见的DNA改变

is the simple swap of one letter, or base, such as C,

就是一个字母，也叫一个碱基， 比如C（胞嘧啶），

with a different letter, such as T, G or A.

换成了别的碱基，如T(胸腺嘧啶)、 G(鸟嘌呤)或者A(腺嘌呤)。

In any day, the cells in your body will collectively accumulate

每一天，你身体里的细胞 会累计发生数亿次

billions of these single-letter swaps, which are also called "point mutations."

单碱基的改变， 这也被称作“点突变”。

Now, most of these point mutations are harmless.

大部分点突变是无害的。

But every now and then,

但时不时，

a point mutation disrupts an important capability in a cell

点突变会干扰细胞的某项重要功能，

or causes a cell to misbehave in harmful ways.

或者引起细胞出现异常行为。

If that mutation were inherited from your parents

如果这种变异是从父母遗传而来的，

or occurred early enough in your development,

或者发生于你生命早期，

then the result would be that many or all of your cells

那么结果很可能是 你的大部分甚至全部细胞

contain this harmful mutation.

都带有这种有害变异。

And then you would be one of hundreds of millions of people

你可能就会像其他成千上万人一样

with a genetic disease,

患上基因疾病，

such as sickle cell anemia or progeria

像镰刀型红血球病，或者早衰症，

or muscular dystrophy or Tay-Sachs disease.

或者肌肉萎缩症， 或者家族黑蒙性痴呆症。

Grievous genetic diseases caused by point mutations

由点基因突变引起的 这些不幸的遗传疾病

are especially frustrating,

让我们尤其沮丧，

because we often know the exact single-letter change

因为我们往往已经知道 哪个具体字母（碱基）发生了突变，

that causes the disease and, in theory, could cure the disease.

从而导致了疾病。 因此理论上，我们可以治愈它。

Millions suffer from sickle cell anemia

数百万人被镰刀型红血球病折磨，

because they have a single A to T point mutations

因为他们的血红蛋白基因中

in both copies of their hemoglobin gene.

都含有从A到T的点突变。

And children with progeria are born with a T

而患有早衰症的孩子

at a single position in their genome

只不过生来就在基因组中的 某个位置有一个T，

where you have a C,

而正常的基因应该是C，

with the devastating consequence that these wonderful, bright kids

令人悲伤的是，这些聪明美好的孩子

age very rapidly and pass away by about age 14.

衰老得非常快，通常活不过14岁。

Throughout the history of medicine,

纵观整个医药史，

我们还没有找到有效的方法

we have not had a way to efficiently correct point mutations

in living systems,

可以在生命系统中纠正点突变，

to change that disease-causing T back into a C.

将引起疾病的T改回正常的C。

Perhaps until now.

但现在我们有办法了。

Because my laboratory recently succeeded in developing such a capability,

因为我的实验室 最近成功发明了一种技术，

which we call "base editing."

叫做“碱基编辑”。

The story of how we developed base editing

关于我们如何发明“碱基编辑”的故事

actually begins three billion years ago.

可以追溯到30亿年前。

We think of bacteria as sources of infection,

我们通常认为细菌是感染源，

but bacteria themselves are also prone to being infected,

但其实细菌本身也容易被感染，

in particular, by viruses.

特别是被病毒。

So about three billion years ago,

因此大约30亿年前，

bacteria evolved a defense mechanism to fight viral infection.

细菌进化出一种防御机制， 来抵抗病毒感染。

That defense mechanism is now better known as CRISPR.

这种防御机制如今被称为CRISPR。

And the warhead in CRISPR is this purple protein

CRISPR里最强的武器 是这种紫色的蛋白质，

that acts like molecular scissors to cut DNA,

它就像分子剪刀一样， 可以剪断DNA链，

breaking the double helix into two pieces.

将双螺旋结构剪成2条单螺旋链。

If CRISPR couldn't distinguish between bacterial and viral DNA,

如果CRISPR分不清 细菌和病毒的DNA，

it wouldn't be a very useful defense system.

这就不能算是一个好的防御系统。

But the most amazing feature of CRISPR

但CRISPR最神奇之处在于

is that the scissors can be programmed to search for,

剪刀可以被编辑，

专门寻找、锁定和剪断

bind to and cut

only a specific DNA sequence.

特定的DNA片段。

So when a bacterium encounters a virus for the first time,

所以当细菌首次遇到某个病毒时，

it can store a small snippet of that virus's DNA

它会存储一小段病毒的DNA

for use as a program to direct the CRISPR scissors

以此来引导CRISPR的剪刀，

to cut that viral DNA sequence during a future infection.

如果将来发生感染， 就剪断病毒的DNA链。

Cutting a virus's DNA messes up the function of the cut viral gene,

剪断病毒的DNA 会扰乱该病毒基因的表达功能，

and therefore disrupts the virus's life cycle.

从而中断病毒的生命。

Remarkable researchers including Emmanuelle Charpentier, George Church,

许多优秀的研究者，比如 埃马纽埃尔·卡彭蒂耶、乔治·丘奇，

Jennifer Doudna and Feng Zhang

詹妮佛·杜德纳和张锋，

showed six years ago how CRISPR scissors could be programmed

在6年前展示了 CRISPR的剪刀可以被编辑，

to cut DNA sequences of our choosing,

用来剪断我们选择的DNA片段，

including sequences in your genome,

人类的基因片段，

instead of the viral DNA sequences chosen by bacteria.

而不是细菌选的病毒的DNA片段。

But the outcomes are actually similar.

效果是相似的。

Cutting a DNA sequence in your genome

通过剪断基因中的DNA片段

also disrupts the function of the cut gene, typically,

同样会影响被剪基因的功能，

by causing the insertion and deletion of random mixtures of DNA letters

方法就是在被剪的位置上增加或删除

at the cut site.

随机的DNA碱基组合。

Now, disrupting genes can be very useful for some applications.

在某些情况下，扰乱基因非常有用。

But for most point mutations that cause genetic diseases,

但对于大部分引起遗传疾病的 点突变而言，

simply cutting the already-mutated gene won't benefit patients,

仅仅剪断已经发生变异的基因， 对病人而言并没有意义，

because the function of the mutated gene needs to be restored,

因为这些变异基因的功能需要重置，

not further disrupted.

而不是进一步打乱。

So cutting this already-mutated hemoglobin gene

因此，把那些引起镰刀型贫血的，

that causes sickle cell anemia

已经变异的血红蛋白基因剪断，

won't restore the ability of patients to make healthy red blood cells.

并不能恢复病人的造血功能。

And while we can sometimes introduce new DNA sequences into cells

有时候我们可以加入 一些新的DNA片段到细胞中，

to replace the DNA sequences surrounding a cut site,

替代被剪断区域周围的DNA链，

that process, unfortunately, doesn't work in most types of cells,

但可惜的是这一过程 对大部分细胞不起作用，

and the disrupted gene outcomes still predominate.

被影响的基因仍占主导地位。

Like many scientists, I've dreamed of a future

像许多科学家一样， 我梦想着未来有一天，

in which we might be able to treat or maybe even cure

我们可以治疗甚至治愈

human genetic diseases.

人类遗传疾病。

But I saw the lack of a way to fix point mutations,

但我们缺乏修复点突变的方法，

which cause most human genetic diseases,

而点突变是大部分 人类基因疾病的主因，

是我们需要解决的主要问题。

as a major problem standing in the way.

Being a chemist, I began working with my students

我是一名化学家，我跟我的学生们

to develop ways on performing chemistry directly on an individual DNA base,

一起研究将化学反应 应用于单个DNA碱基上的方法，

to truly fix, rather than disrupt, the mutations that cause genetic diseases.

从而真正修复，而不仅仅是 终止引起基因疾病的变异。

The results of our efforts are molecular machines

我们的成果就是分子机器，

called "base editors."

叫做“碱基编辑器”。

Base editors use the programmable searching mechanism of CRISPR scissors,

碱基编辑器使用的是 类似CRISPR剪刀的可编程搜索机制，

but instead of cutting the DNA,

但与剪断DNA不同的是，

they directly convert one base to another base

它们直接将一个碱基变成另一个，

without disrupting the rest of the gene.

而不会破坏基因的其他部分。

So if you think of naturally occurring CRISPR proteins as molecular scissors,

如果将CRISPR蛋白质 比作分子剪刀的话，

you can think of base editors as pencils,

碱基编辑器就像铅笔，

capable of directly rewriting one DNA letter into another

它能直接改写DNA碱基，

by actually rearranging the atoms of one DNA base

通过重新排列DNA碱基上的原子，

to instead become a different base.

而不是将它变成一个不同的碱基。

Now, base editors don't exist in nature.

碱基编辑器在大自然中并不存在。

In fact, we engineered the first base editor, shown here,

实际上，我们制造的 第一个碱基编辑器，如图所示，

from three separate proteins

是由3种独立的蛋白质组成，

that don't even come from the same organism.

它们甚至都不是来自同一个生物体。

We started by taking CRISPR scissors and disabling the ability to cut DNA

我们首先抑制CRISPR剪刀 剪断DNA的功能，

while retaining its ability to search for and bind a target DNA sequence

并通过编程的方法，保持其搜索和锁定

in a programmed manner.

目标DNA片段的能力。

To those disabled CRISPR scissors, shown in blue,

在功能被抑制的CRISPR剪刀上， 图中蓝色的部分，

we attached a second protein in red,

我们加上了第2种蛋白质， 在这里用红色标出，

which performs a chemical reaction on the DNA base C,

它会与DNA碱基C发生化学反应，

converting it into a base that behaves like T.

将其转换成与T行为相似的碱基。

Third, we had to attach to the first two proteins

第3步，我们将图片中 用紫色标出的蛋白质

the protein shown in purple,

加在前2种蛋白质上，

which protects the edited base from being removed by the cell.

来保护被编辑过的碱基不被细胞移除。

The net result is an engineered three-part protein

最终结果就是制造出一个 由3部分组成的蛋白质，

that for the first time allows us to convert Cs into Ts

这也是我们在史上首次 将基因组特定位置的

at specified locations in the genome.

碱基C转换为T。

But even at this point, our work was only half done.

但做到这一步， 我们的工作也仅仅完成了一半。

Because in order to be stable in cells,

因为为了保持细胞的稳定，

the two strands of a DNA double helix have to form base pairs.

DNA双螺旋结构中的两条链 必须形成碱基对。

And because C only pairs with G,

因为C只能跟G配对，

and T only pairs with A,

T只能跟A配对，

simply changing a C to a T on one DNA strand creates a mismatch,

如果只是将一链上的碱基C变成T，

a disagreement between the two DNA strands

会造成DNA双螺旋的不匹配，

that the cell has to resolve by deciding which strand to replace.

要解决这个问题， 细胞需要决定替换哪一条链。

We realized that we could further engineer this three-part protein

我们认识到可以改进 这个由3部分组成的蛋白质，

to flag the nonedited strand as the one to be replaced

将未编辑的那条链标记为

by nicking that strand.

要被切割掉。

This little nick tricks the cell

这个小缺口诱骗细胞

into replacing the nonedited G with an A

用A取代未编辑的G，

as it remakes the nicked strand,

因为它重新生成了完整的单链，

thereby completing the conversion of what used to be a C-G base pair

这样就完成了C-G碱基对

into a stable T-A base pair.

到稳定的T-A碱基对的转变。

After several years of hard work

在实验室前博士后Alexis Komor

led by a former post doc in the lab, Alexis Komor,

领导的几年努力工作之后，

we succeeded in developing this first class of base editor,

我们成功地开发了第一代碱基编辑器，

which converts Cs into Ts and Gs into As

将指定位置的C都转变为T，

at targeted positions of our choosing.

G都转变为A。

Among the more than 35,000 known disease-associated point mutations,

在3.5万多个已知的 与点突变有关的疾病中，

the two kinds of mutations that this first base editor can reverse

第一代碱基编辑器可以逆转的两种突变

collectively account for about 14 percent or 5,000 or so pathogenic point mutations.

总共占致病点突变的 14%或5000种左右。

But correcting the largest fraction of disease-causing point mutations

但是，纠正大部分致病点突变

would require developing a second class of base editor,

需要开发第二代碱基编辑器，

one that could convert As into Gs or Ts into Cs.

一个可以将A都转变为G 或T都转变为C的工具。

Led by Nicole Gaudelli, a former post doc in the lab,

在实验室前博士后 Nicole Gaudelli的领导下，

we set out to develop this second class of base editor,

我们着手开发了这个第二代碱基编辑器，

which, in theory, could correct up to almost half of pathogenic point mutations,

从理论上讲，这样可以 纠正近一半的致病点基因突变，

including that mutation that causes the rapid-aging disease progeria.

包括导致早衰症的突变。

We realized that we could borrow, once again,

我们意识到我们可以再次借助，

the targeting mechanism of CRISPR scissors

CRISPR剪刀的靶向机制，

to bring the new base editor to the right site in a genome.

将新的碱基编辑器 带到基因组的正确位置。

But we quickly encountered an incredible problem;

但我们很快遇到了 一个棘手的难题；

namely, there is no protein

具体来说，在DNA中没有

that's known to convert A into G or T into C

已知的蛋白质 可以将A转化成G

in DNA.

或者T转化成C。

Faced with such a serious stumbling block,

面对如此严重的困难险阻，

most students would probably look for another project,

很多学生可能会寻找其他方案，

if not another research advisor.

而不是咨询其他研究顾问。

(Laughter)

（笑声）

But Nicole agreed to proceed with a plan

但Nicole同意继续实施一项

that seemed wildly ambitious at the time.

当时看来雄心勃勃的计划。

Given the absence of a naturally occurring protein

鉴于缺乏一种自然产生的蛋白质

that performs the necessary chemistry,

来进行必要的化学反应，

we decided we would evolve our own protein in the laboratory

我们决定在实验室里 进化我们自己的蛋白质

to convert A into a base that behaves like G,

来把A转化成一个像G一样的碱基，

starting from a protein that performs related chemistry on RNA.

从一种对RNA进行相关 化学反应的蛋白质开始。

We set up a Darwinian survival-of-the-fittest selection system

我们建立了达尔文适者生存选择体系，

that explored tens of millions of protein variants

探索了数千万种蛋白质变异，

and only allowed those rare variants

只允许那些能够进行

that could perform the necessary chemistry to survive.

必要化学反应的罕见变异存活下来。

We ended up with a protein shown here,

我们最终得到了这里显示的蛋白质，

the first that can convert A in DNA

第一个能把DNA中的A

into a base that resembles G.

转化成类似G的碱基。

And when we attached that protein

当我们把这个蛋白质连接到

to the disabled CRISPR scissors, shown in blue,

受到抑制的CRISPR剪刀上， 这里用蓝色标示，

we produced the second base editor,

第二代碱基编辑器就诞生了，

which converts As into Gs,

可以把A转变为G，

and then uses the same strand-nicking strategy

然后使用第一代碱基编辑器中

that we used in the first base editor

同样的链切割策略

to trick the cell into replacing the nonedited T with a C

诱骗细胞用C取代未编辑的T，

as it remakes that nicked strand,

当它重新生成单链后，

thereby completing the conversion of an A-T base pair to a G-C base pair.

就完成了A-T碱基对 到G-C碱基对的转变。

(Applause)

（鼓掌）

Thank you.

谢谢。

(Applause)

（鼓掌）

As an academic scientist in the US,

作为一个美国学术科学家，

I'm not used to being interrupted by applause.

我还不是很习惯被掌声打断。

（笑声）

(Laughter)

We developed these first two classes of base editors

我们开发的这两代碱基编辑器

only three years ago and one and a half years ago.

分别诞生于3年前和1年半前而已。

But even in that short time,

但在这短短的时间里，

base editing has become widely used by the biomedical research community.

碱基编辑器已经被 生物医学团队广泛使用。

Base editors have been sent more than 6,000 times

碱基编辑器应全球超过 1000位研究者的请求

at the request of more than 1,000 researchers around the globe.

已经被发送到全球各地多达6千次。

A hundred scientific research papers have been published already,

目前发表的相关科研论文多达百篇，

包括了从细菌到植物， 从老鼠到灵长类动物的生物体中

using base editors in organisms ranging from bacteria

to plants to mice to primates.

使用的碱基编辑器。

While base editors are too new

碱基编辑器还太新，

to have already entered human clinical trials,

尚未进入人体临床试验，

scientists have succeeded in achieving a critical milestone towards that goal

科学家们已经在为之努力了，

by using base editors in animals

他们成功使用动物的碱基编辑器

to correct point mutations that cause human genetic diseases.

来纠正导致人类遗传疾病的点突变。

For example,

比如，

a collaborative team of scientists led by Luke Koblan and Jon Levy,

由Luke Koblan和Jon Levy领导 的一个科学家合作小组，

two additional students in my lab,

外加我们实验室的两个学生，

recently used a virus to deliver that second base editor

最近使用了一种病毒 将第二代碱基编辑器

into a mouse with progeria,

植入患有早衰症的老鼠体内，

changing that disease-causing T back into a C

把致病的T变回C，

and reversing its consequences at the DNA, RNA and protein levels.

并在DNA、RNA和蛋白质层面上 逆转了其导致的后果。

Base editors have also been used in animals

碱基编辑器也被用于动物身上

to reverse the consequence of tyrosinemia,

来逆转酪氨酸血症，

beta thalassemia, muscular dystrophy,

地中海贫血，肌营养不良，

phenylketonuria, a congenital deafness

苯丙酮尿症，某种先天性耳聋

and a type of cardiovascular disease --

和某种类型的心血管疾病——

in each case, by directly correcting a point mutation

在这些案例中，通过直接纠正

that causes or contributes to the disease.

导致或者参与致病的点突变 就可以逆转病症。

In plants, base editors have been used

在植物中，碱基编辑器已被用于

to introduce individual single DNA letter changes

引入单个DNA字符的改变

that could lead to better crops.

以带来更好的收成。

And biologists have used base editors to probe the role of individual letters

生物学家也使用了碱基编辑器 来探索单个碱基

in genes associated with diseases such as cancer.

在与癌症等疾病相关的基因中的作用。

Two companies I cofounded, Beam Therapeutics and Pairwise Plants,

我联合创办的两家公司， Beam Therapeutics和Pairwise Plants，

are using base editing to treat human genetic diseases

正使用碱基编辑器治疗人类基因疾病

and to improve agriculture.

和改善农业。

All of these applications of base editing

所有这些对碱基编辑的应用

have taken place in less than the past three years:

都发生在不到三年的时间里：

on the historical timescale of science,

在科学的历史尺度上，

the blink of an eye.

这只是一眨眼的功夫。

Additional work lies ahead

在碱基编辑器

before base editing can realize its full potential

提升基因疾病病人的生命质量前，

to improve the lives of patients with genetic diseases.

我们仍有很多额外的工作要做。

While many of these diseases are thought to be treatable

尽管许多这些疾病被认为是

by correcting the underlying mutation

只需要纠正器官中 很小一部分细胞

in even a modest fraction of cells in an organ,

的潜在突变就能治疗的，

delivering molecular machines like base editors

将分子机器(如碱基编辑器)

into cells in a human being

送入人体细胞

can be challenging.

仍然富有挑战。

Co-opting nature's viruses to deliver base editors

利用自然界的病毒来传递碱基编辑器，

instead of the molecules that give you a cold

而不是让你感冒的分子来做这个，

is one of several promising delivery strategies

是几种已经成功实践的

that's been successfully used.

有前景的传递策略之一。

Continuing to develop new molecular machines

继续研究开发新的分子机器，

that can make all of the remaining ways

找到其他的方法

to convert one base pair to another base pair

将一个碱基对转变成 另一个碱基对，

and that minimize unwanted editing at off-target locations in cells

并尽量减少细胞非目标位置上 不必要的编辑

is very important.

是非常重要的。

And engaging with other scientists, doctors, ethicists and governments

与其他科学家、医生、 伦理学家和政府合作，

to maximize the likelihood that base editing is applied thoughtfully,

最大限度地提高 碱基编辑用于深思熟虑、

safely and ethically,

安全和合乎道德的可能性，

remains a critical obligation.

仍然是一项重要义务。

These challenges notwithstanding,

尽管有这些挑战，

if you had told me even just five years ago

如果你在五年前告诉我

that researchers around the globe

全球的研究人员

would be using laboratory-evolved molecular machines

将使用实验室发明的分子机器

to directly convert an individual base pair

来直接有效地把单个碱基对

to another base pair

转变成另一个碱基对，

at a specified location in the human genome

放在特定的基因组位置，

efficiently and with a minimum of other outcomes,

而且不会产生其他结果，

I would have asked you,

我会反问你，

"What science-fiction novel are you reading?"

“你是不是在读哪本科幻小说？”

Thanks to a relentlessly dedicated group of students

感谢我们孜孜不倦的学生，

who were creative enough to engineer what we could design ourselves

他们有惊人的创造力来设计工具， 使得我们可以改造自身，

and brave enough to evolve what we couldn't,

并勇敢地去进化 原本无法进化出的特征，

base editing has begun to transform that science-fiction-like aspiration

碱基编辑已经开始将 科幻小说般的渴望

into an exciting new reality,

转变成令人兴奋的现实，

one in which the most important gift we give our children

我们给孩子们最重要的礼物

may not only be three billion letters of DNA,

可能不再只是30亿DNA个碱基，

but also the means to protect and repair them.

同时还有保护和修复它们的方法。

Thank you.

谢谢。

(Applause)

（鼓掌）

谢谢。

Thank you.