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

譯者: 易帆 余 審譯者: Congmei Han

The most important gift your mother and father ever gave you

父母親給你的最貴重的禮物，

was the two sets of three billion letters of DNA

就是兩組三十億個字母的 DNA，

that make up your genome.

它們組成了你的基因組。

But like anything with three billion components,

但，跟所有三十億個元件 組成的東西一樣，

that gift is fragile.

這個禮物也很脆弱。

Sunlight, smoking, unhealthy eating,

日曬、抽菸、不健康的飲食，

even spontaneous mistakes made by your cells,

甚至你細胞自發產生的錯誤

all cause changes to your genome.

都有可能會改變你的基因組。

The most common kind of change in DNA

最常見的 DNA 改變

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

就是換掉一個字母，也就是鹼基，

比如把 C 換成一個不同的字母，

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

比如 T、G，或 A。

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

每天，你身體中的細胞 全部加起來累積有

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

數十億次這種單一字母替換， 亦稱為「點突變」。

Now, most of these point mutations are harmless.

大部分的點突變無害。

But every now and then,

但有時候

a point mutation disrupts an important capability in a cell

點突變會干擾細胞裡的 某個重要功能，

or causes a cell to misbehave in harmful ways.

或是導致傷害性的細胞失常行為。

If that mutation were inherited from your parents

如果那個突變遺傳自你的父母親，

or occurred early enough in your development,

或是在你年幼時就發生了，

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

那麼，造成的結果就是 你很多或所有的細胞

contain this harmful mutation.

都含有這種有害的突變。

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

那麼你就得到機率只有數億分之一的

with a genetic disease,

基因（突變）型疾病，

such as sickle cell anemia or progeria

比如鐮刀型紅血球疾病或是早衰症，

or muscular dystrophy or Tay-Sachs disease.

或是肌肉萎縮症， 或精神性痴呆症。

Grievous genetic diseases caused by point mutations

由點突變所造成的 令人痛苦的基因型疾病

are especially frustrating,

特別令人挫折，

because we often know the exact single-letter change

因為我們通常確知 是哪一個字母的改變

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

造成這種理論上可以治癒疾病。

Millions suffer from sickle cell anemia

數百萬人飽受 鐮刀型紅血球疾病之苦，

because they have a single A to T point mutations

因為他們血紅素基因的兩個複本

in both copies of their hemoglobin gene.

都有一個 A 換成 T 的突變。

And children with progeria are born with a T

早衰症的兒童則是在出生時

基因組中的某個單一位置有個 T，

at a single position in their genome

where you have a C,

但那裡本來應該是 C，

with the devastating consequence that these wonderful, bright kids

產生的結果會有很大的影響， 這些美好、聰明的孩子，

age very rapidly and pass away by about age 14.

會以非常快的速度老化， 大約在十四歲時就會過世。

Throughout the history of medicine,

在醫學史上，

we have not had a way to efficiently correct point mutations

我們還沒有方法

可以在活體上有效地校正點突變，

in living systems,

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

將造成疾病的 T 改回原本的 C。

Perhaps until now.

也許現在有辦法了。

Because my laboratory recently succeeded in developing such a capability,

因為我的實驗室最近 成功開發了這種能力，

which we call "base editing."

我們稱之為「鹼基編輯」。

The story of how we developed base editing

關於我們如何開發出 鹼基編輯的故事，

actually begins three billion years ago.

其實始於三十億年前。

We think of bacteria as sources of infection,

我們認為細菌是感染的源頭，

but bacteria themselves are also prone to being infected,

但細菌本身也有可能會受到感染，

in particular, by viruses.

特別是會被病毒感染。

So about three billion years ago,

所以，大約三十億年前，

bacteria evolved a defense mechanism to fight viral infection.

細菌演化出一種防禦機制 來對抗病毒感染。

That defense mechanism is now better known as CRISPR.

這就是如今較為熟知的 CRISPR 防禦機制。

And the warhead in CRISPR is this purple protein

CRISPR 中的導彈頭， 就是這個紫色的蛋白質，

that acts like molecular scissors to cut DNA,

它就像是分子剪刀， 可以剪斷 DNA，

breaking the double helix into two pieces.

把雙股螺旋斷成兩半。

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

如果 CRISPR 無法區別出 細菌和病毒 DNA 的不同，

it wouldn't be a very useful defense system.

它就不會是個很有用的防禦系統。

But the most amazing feature of CRISPR

但 CRISPR 最驚人的特色是

is that the scissors can be programmed to search for,

它的剪刀可以透過編程只去搜尋、

bind to and cut

結合和剪斷

only a specific DNA sequence.

特定的 DNA 序列。

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

所以，當細菌初次遇到病毒時，

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

它能夠儲存病毒的一小段 DNA，

for use as a program to direct the CRISPR scissors

當成引導 CRISPR 剪刀的程式，

to cut that viral DNA sequence during a future infection.

在將來被感染時，能夠剪斷 該病毒的 DNA 序列。

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

剪斷病毒的 DNA， 會打亂它的基因功能，

and therefore disrupts the virus's life cycle.

進而干擾該病毒的生命週期。

Remarkable researchers including Emmanuelle Charpentier, George Church,

出色的研究者，包括埃馬紐埃爾 卡彭蒂耶、喬治丘奇、

Jennifer Doudna and Feng Zhang

詹妮弗杜德納，及張鋒，

showed six years ago how CRISPR scissors could be programmed

六年前就示範過如何 透過編程讓 CRISPR 剪刀

to cut DNA sequences of our choosing,

剪斷我們選定的 DNA 序列，

including sequences in your genome,

包括在你的基因組中的序列，

instead of the viral DNA sequences chosen by bacteria.

將細菌所選擇的 病毒 DNA 序列取代掉。

But the outcomes are actually similar.

但，後果其實蠻相似的。

Cutting a DNA sequence in your genome

剪斷你基因組中的 DNA 序列

also disrupts the function of the cut gene, typically,

通常也會干擾被剪斷的基因的功能，

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

就在我們剪斷點上插入和刪除

隨機混合的 DNA 字母時發生。

at the cut site.

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

干擾基因在某些應用上非常有用。

But for most point mutations that cause genetic diseases,

但，對於大部分會造成 基因型疾病的點突變，

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

單單只剪斷已經突變的基因， 對病人並沒有益處，

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

因為突變基因的功能 必須要被恢復，

not further disrupted.

而不是被進一步干擾。

So cutting this already-mutated hemoglobin gene

所以，剪斷這個已經突變

且造成鐮刀型 紅血球疾病的血紅素基因，

that causes sickle cell anemia

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

並不能夠恢復病人 製造健康紅血球的能力。

And while we can sometimes introduce new DNA sequences into cells

雖然我們可以將新的 DNA 序列放入細胞中，

to replace the DNA sequences surrounding a cut site,

取代剪斷點周圍的 DNA 序列，

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

但不幸的是，這個過程 在大部分類型的細胞中行不通，

and the disrupted gene outcomes still predominate.

被干擾的基因仍主宰病患。

Like many scientists, I've dreamed of a future

和許多科學家一樣， 我也夢想在未來

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

我們可以治療或甚至治癒

human genetic diseases.

人類的基因型疾病。

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

但我沒發現解決點突變問題的方法，

which cause most human genetic diseases,

點突變正是大部分 人類基因型疾病的成因，

as a major problem standing in the way.

是檔在我們前面的大問題。

Being a chemist, I began working with my students

身為化學家，我開始 和我的學生合作，

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

開發新方法，直接對 個別 DNA 鹼基進行化學反應，

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

不是干擾，而是真正修復 導致遺傳疾病的突變。

The results of our efforts are molecular machines

經過努力，我們開發出了分子機器，

called "base editors."

叫做「鹼基編輯器」。

Base editors use the programmable searching mechanism of CRISPR scissors,

鹼基編輯器用 CRISPR 剪刀的 可編程搜尋機制，

but instead of cutting the DNA,

但不是用來剪斷 DNA，

they directly convert one base to another base

而是直接將一個鹼基 轉換成另一個鹼基，

without disrupting the rest of the gene.

不干擾到基因的其它部位。

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

所以，如果你把渾然天成的 CRISPR 蛋白質視為分子剪刀，

you can think of base editors as pencils,

那麼你可以把鹼基編輯器視為鉛筆，

capable of directly rewriting one DNA letter into another

能夠直接改寫 DNA 字母，

by actually rearranging the atoms of one DNA base

做法是重新安排一個 DNA 鹼基的原子，

to instead become a different base.

讓它成為另一個不同的鹼基。

Now, base editors don't exist in nature.

大自然中沒有鹼基編輯器。

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

事實上，我們設計了人類第一個 鹼基編輯器，在這裡可以看到，

from three separate proteins

我們用了三個不同的蛋白質，

that don't even come from the same organism.

它們甚至可以不用是 來自同一個有機體。

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

我們先從 CRISPR 剪刀著手， 讓它失去剪斷 DNA 的能力，

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

保持其以編程方式

搜尋和結合目標 DNA 序列的能力。

in a programmed manner.

To those disabled CRISPR scissors, shown in blue,

藍色標示的是失去 能力的 CRISPR 剪刀，

we attached a second protein in red,

我們黏上第二種 蛋白質，用紅色標示，

which performs a chemical reaction on the DNA base C,

它會在 DNA 鹼基 C 上面 發生化學反應，

converting it into a base that behaves like T.

將它轉換成一個 行為類似 T 的鹼基。

Third, we had to attach to the first two proteins

第三，在之前的兩個蛋白質上， 我們還要再加上

the protein shown in purple,

用紫色標示的蛋白質，

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

它能夠保護被編輯過的鹼基 不會被細胞給移除。

The net result is an engineered three-part protein

最後就會產生一個 人造的三部件融合蛋白質，

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

這是人類第一次製作出

可以在基因組中的特定位置 將 C 轉換成 T 的蛋白質。

at specified locations in the genome.

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

但，即使做到這樣， 我們的工作也才完成一半。

Because in order to be stable in cells,

為要在細胞中達到穩定，

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

DNA 雙股螺旋的兩股 必須要形成鹼基對。

And because C only pairs with G,

因為 C 只能和 G 配對，

and T only pairs with A,

且 T 只能和 A 配對，

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

若只把 DNA 上的 C 改成 T， 會造成無法配對的狀況，

a disagreement between the two DNA strands

當 DNA 的兩股之間產生衝突，

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

細胞為了解決問題 必須選擇一股來替換。

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

我們發現可以進一步 將這個三部件融合蛋白質再改造，

to flag the nonedited strand as the one to be replaced

將未被編輯的那一股 標記為要被取代的目標，

by nicking that strand.

只要在那一股上刻記即可。

This little nick tricks the cell

這個小小刻記便能騙過細胞，

into replacing the nonedited G with an A

細胞便會在重製被刻記的那一股時，

as it remakes the nicked strand,

用 A 來取代未被編輯的 G，

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

這樣就能完成轉換， 將原本的 C-G 配對

into a stable T-A base pair.

轉換為穩定的 T-A 配對。

After several years of hard work

由博士後研究員 艾莉西斯•柯摩爾領軍，

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

在實驗室努力多年後，

we succeeded in developing this first class of base editor,

我們成功開發出了 第一類鹼基編輯器，

which converts Cs into Ts and Gs into As

它能在我們標靶的位置上，

將 C 轉換為 T， 將 G 轉換為 A。

at targeted positions of our choosing.

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

在已知的三萬五千種 和疾病相關的點突變中，

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

第一鹼基編輯器可以 逆轉其中兩類突變，

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

這兩類加總起來就佔了五千種 （14%）點突變疾病。

But correcting the largest fraction of disease-causing point mutations

但若要校正最大部分 造成疾病的點突變，

would require developing a second class of base editor,

需要開發第二類鹼基編輯器，

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

它能將 A 轉換為 G， 將 T 轉換為 C。

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

由博士後研究員妮可•嘉德利領軍，

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

我們在實驗室裡 準備開發第二類鹼基編輯器，

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

理論上，幾乎可以校正 一半以上的點突變疾病。

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

包括會造成快速老化的早衰症突變。

We realized that we could borrow, once again,

我們知道可以再次藉助

the targeting mechanism of CRISPR scissors

CRISPR 剪刀的定位機制，

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

把新的鹼基編輯器 定位到基因組的特定位置。

But we quickly encountered an incredible problem;

但我們很快就會遇到一個大問題；

namely, there is no protein

換句話說，在 DNA 裡

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

沒有已知的蛋白質可以把 A 轉變成 G

in DNA.

或 T 轉變成 C 。

Faced with such a serious stumbling block,

面對這麼大的障礙，

most students would probably look for another project,

大部分學生不是另找專題

if not another research advisor.

就是另找指導教授。

(Laughter)

（笑聲）

But Nicole agreed to proceed with a plan

但妮可同意繼續這個

that seemed wildly ambitious at the time.

當時看起來相當瘋狂的研究計畫。

Given the absence of a naturally occurring protein

由於沒有這個渾然天成的蛋白質

that performs the necessary chemistry,

來完成必要的化學反應，

we decided we would evolve our own protein in the laboratory

我們決定在實驗室自己設計出

to convert A into a base that behaves like G,

能把 A 轉換成 有 G 行為表現的蛋白質 ，

starting from a protein that performs related chemistry on RNA.

我們從 RNA 上尋找有相關 類似化學表現的蛋白質著手。

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

我們建立了一個 達爾文適者生存的選擇系統，

that explored tens of millions of protein variants

它可以從好幾千萬個變體蛋白質中

篩選出稀有的變體，

and only allowed those rare variants

只讓呈現必要化學反應的 蛋白質存活下來。

that could perform the necessary chemistry to survive.

We ended up with a protein shown here,

我們最後找到了這個蛋白質，

the first that can convert A in DNA

第一個在 DNA 裡可以把

into a base that resembles G.

A 轉變成 G 的蛋白質。

And when we attached that protein

當我們把蛋白質黏到

to the disabled CRISPR scissors, shown in blue,

失去剪刀效力的 CRISPR 上， 用藍色顯示，

we produced the second base editor,

就可以做出第二鹼基編輯器，

which converts As into Gs,

它可以把 A 轉變成 G。

and then uses the same strand-nicking strategy

然後利用相同的「股刻記」策略，

that we used in the first base editor

也就是我們在第一鹼基編輯器上 運用的策略，

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

可以在重製刻記股時騙過細胞，

as it remakes that nicked strand,

讓還沒編輯過的 T 變成 C。

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

如此就完成了 AT 鹼基 轉換成 GC 鹼基的過程。

(Applause)

（掌聲）

Thank you.

謝謝。

(Applause)

（掌聲）

As an academic scientist in the US,

身為一位美國的學術科學家，

I'm not used to being interrupted by applause.

我還真不習慣講到一半 被掌聲中斷。

(Laughter)

（笑聲）

We developed these first two classes of base editors

我們開發出這兩個類型的 鹼基編輯器，

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

一個是在三年前， 另一個在一年半之前。

But even in that short time,

雖然問世的時間不長，

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

鹼基編輯已經在生化研究領域 被廣泛運用了。

Base editors have been sent more than 6,000 times

我們的鹼基編輯器 應全球一千多位研究人員的索取，

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

已經送出了六千多組。

A hundred scientific research papers have been published already,

有好幾百篇在有機體裡 運用鹼基編輯器的

相關科學研究論文 已經陸陸續續發佈了，

using base editors in organisms ranging from bacteria

to plants to mice to primates.

範圍從細菌到植物， 老鼠到靈長類動物都有。

While base editors are too new

因為鹼基編輯器的技術還很新，

to have already entered human clinical trials,

目前無法運用在人類的臨床實驗，

scientists have succeeded in achieving a critical milestone towards that goal

但科學家已經在動物身上，

成功地完成了相當重要的目標，

by using base editors in animals

to correct point mutations that cause human genetic diseases.

已經把人類基因型疾病的 點突變校正回來。

For example,

例如，

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

由盧克•寇蘭及瓊•拉維領軍，

two additional students in my lab,

與我實驗室的兩位學生 組成科研團隊，共同參與合作，

recently used a virus to deliver that second base editor

最近利用一個病毒 將第二鹼基編輯器

into a mouse with progeria,

送進患有早衰症的老鼠身上，

changing that disease-causing T back into a C

成功地將肇病的 T 轉換回 C，

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

並把牠的序列逆轉回 DNA、RNA和蛋白質狀態。

Base editors have also been used in animals

鹼基編輯器也已被用在動物身上，

to reverse the consequence of tyrosinemia,

它可以逆轉酪胺酸血症、

beta thalassemia, muscular dystrophy,

乙型地中海貧血症、肌肉萎縮症、

phenylketonuria, a congenital deafness

苯丙酮尿症、先天性耳聾、

and a type of cardiovascular disease --

還有心血管疾病的序列。

in each case, by directly correcting a point mutation

每一個案例，都能直接校正

that causes or contributes to the disease.

肇病的點突變。

In plants, base editors have been used

鹼基編輯器也被運用在植物上，

to introduce individual single DNA letter changes

藉由改變個別的 DNA 字母

that could lead to better crops.

可以生產出更好的農產品。

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

生物學家也已經利用鹼基編輯器

探測出基因裡個別字母所扮演的角色， 例如癌症疾病基因。

in genes associated with diseases such as cancer.

Two companies I cofounded, Beam Therapeutics and Pairwise Plants,

兩家我共同創立的公司： Beam Therapeutics 和 Pairwise Plants,

are using base editing to treat human genetic diseases

正在運用鹼基編輯技術 治療人類的基因型疾病

and to improve agriculture.

及改善農業。

All of these applications of base editing

這些鹼基編輯的應用 發生在過去不到三年的時間裡：

have taken place in less than the past three years:

在科學歷史的時間尺度上 僅僅是眨眼之間。

on the historical timescale of science,

the blink of an eye.

Additional work lies ahead

在全盤了解鹼基編輯器的潛力前，

before base editing can realize its full potential

眼前還要再努力的工作就是

to improve the lives of patients with genetic diseases.

改善基因型疾病病人的生活。

While many of these diseases are thought to be treatable

雖然這些疾病被認為

可由校正潛在的突變來治療，

by correcting the underlying mutation

in even a modest fraction of cells in an organ,

但即使只是在器官裡一小部分細胞，

delivering molecular machines like base editors

傳送鹼基編輯器這類的分子機器

into cells in a human being

到人類的細胞裡面，

can be challenging.

仍充滿著挑戰。

Co-opting nature's viruses to deliver base editors

利用會讓你感冒的自然界病毒，

instead of the molecules that give you a cold

把鹼基編輯器傳送到細胞的方式，

is one of several promising delivery strategies

是其中一個還不錯的傳送策略，

that's been successfully used.

這個策略已經被成功運用。

Continuing to develop new molecular machines

持續開發新的分子機器，

that can make all of the remaining ways

找出剩餘還沒辦法轉換的鹼基，

to convert one base pair to another base pair

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

盡可能不去編輯不在靶區的細胞

is very important.

至關重要。

And engaging with other scientists, doctors, ethicists and governments

而其他科學家、醫生、 倫理學家、政府的參與也很重要，

to maximize the likelihood that base editing is applied thoughtfully,

大家一起深思熟慮看看要如何

最大化、安全地、符合倫理地 應用鹼基編輯技術，

safely and ethically,

remains a critical obligation.

是我們的重責大任。

These challenges notwithstanding,

雖然這些挑戰仍在，

if you had told me even just five years ago

但如果你在五年前問我，

that researchers around the globe

全球的研究人員，

would be using laboratory-evolved molecular machines

正在利用實驗室 設計出來的分子機器，

to directly convert an individual base pair

直接把單一鹼基對還原成

to another base pair

另一鹼基對，

at a specified location in the human genome

而且是在人類基因組裡的特定位置上

efficiently and with a minimum of other outcomes,

有效地且最小化發生其它結果地 執行還原。

I would have asked you,

我可能會問：

"What science-fiction novel are you reading?"

「你在看哪一本科幻小說？」

Thanks to a relentlessly dedicated group of students

感謝這群全力付出、 勤奮努力的學生們，

who were creative enough to engineer what we could design ourselves

他們的創意讓我們可以 透過基因工程設計我們自己。

and brave enough to evolve what we couldn't,

並勇敢地設計出 我們所辦不到的事，

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

鹼基編輯已經開始從 科幻小說裡渴望的夢想

轉變成振奮人心的真實技術，

into an exciting new reality,

one in which the most important gift we give our children

或許我們給後代的最重要禮物，

may not only be three billion letters of DNA,

除了三十億個字母 DNA，

but also the means to protect and repair them.

還有保護及修護它們的方法。

Thank you.

謝謝。

(Applause)

（掌聲）

Thank you.

謝謝。