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TEDGlobal 2011

Elizabeth Murchison: Fighting a contagious cancer

エリザベス・マーチソン:感染性のガンと闘う

July 14, 2011

タスマニアデビルの大量死の原因とは?何千ものタスマニアデビルが悪性のガンにかかっています。他のガンとは異なり、これは感染性のガンなのです。研究者のエリザベス・マーチソンが、タスマニアデビルを救うためどのように奮闘しているのか、またこの特別なガンについての新発見をお話します。(刺激の強い、顔にできたガンの画像を含みます。)

Elizabeth Murchison - Cancer researcher
Elizabeth Murchison studies a mysterious (and contagious) cancer that threatens to wipe out Tasmanian devils. Full bio

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Double-click the English subtitles below to play the video.
Everyone's familiar with cancer,
ガンはなにも特別な疾病ではありません
00:15
but we don't normally think of cancer
しかし通常 ガンが感染するとは
00:19
as being a contagious disease.
考えられていません
00:21
The Tasmanian devil has shown us
タスマニアデビルの事例によって
00:25
that, not only can cancer be a contagious disease,
ガンは感染する可能性があるだけではなく
00:27
but it can also threaten
種の存続を脅かす可能性があることも
00:30
an entire species with extinction.
明らかとなりました
00:32
So first of all, what is a Tasmanian devil?
まず タスマニアデビルとは何でしょう?
00:36
Many of you might be familiar with Taz, the cartoon character,
クルクル回るアニメキャラのタズを
00:40
the one that spins around and around and around.
ご存知の方も多いでしょう
00:43
But not many people know
しかし実際に世界最大の肉食有袋類の
00:45
that there actually is a real animal called the Tasmanian devil,
タスマニアデビルという動物が存在することを
00:47
and it's the world's largest carnivorous marsupial.
知っている方は多くありません
00:50
A marsupial is a mammal with a pouch
有袋類とはカンガルーのように
00:54
like a kangaroo.
腹部に袋をもつ哺乳類です
00:56
The Tasmanian devil got its name
タスマニアデビルという名前は
00:58
from the terrifying nocturnal scream that it makes.
夜に発する恐ろしい叫び声に由来しています
01:00
(Screaming)
(叫び声)
01:04
(Laughter)
(笑)
01:15
The Tasmanian devil is predominantly a scavenger,
タスマニアデビルは清掃動物で
01:17
and it uses its powerful jaws
強力なあごと
01:20
and its sharp teeth
鋭い歯で
01:22
to chomp on the bones of rotting dead animals.
動物の腐った死骸をかみ砕きます
01:24
[The] Tasmanian devil is found only on the island of Tasmania,
タスマニアデビルはオーストラリア南部に
01:27
which is that small island
位置するタスマニア島という
01:30
just to the south of the mainland of Australia.
小さな島だけに生息しています
01:32
And despite their ferocious appearance,
凶暴な外見にもかかわらず
01:34
Tasmanian devils are actually
タスマニアデビルは実際は
01:38
quite adorable little animals.
愛らしい小さな動物です
01:40
In fact, growing up in Tasmania,
実際タスマニアで育った私も
01:43
it always was incredibly exciting
野生のタスマニアデビルに
01:45
when we got a chance to see
出会った時は いつも
01:47
a Tasmanian devil in the wild.
本当に興奮したものです
01:49
But the Tasmanian devil population
しかしタスマニアデビルの数は
01:51
has been undergoing a really extremely fast decline.
ものすごい勢いで減少しています
01:53
And in fact, there's concern
実際に20〜30年以内に
01:57
that the species could go extinct in the wild
野生のタスマニアデビルが絶減するのではと
01:59
within 20 to 30 years.
懸念されています
02:02
And the reason for that
この原因は
02:05
is the emergence of a new disease,
ある感染性のガンの
02:07
a contagious cancer.
出現です
02:09
The story begins in 1996
始まりは 1996年に
02:13
when a wildlife photographer took this photograph here
野生動物の写真家が撮った
02:15
of a Tasmanian devil
顔に大きな腫瘍のある
02:18
with a large tumor on its face.
タスマニアデビルの写真でした
02:20
At the time, this was thought to be a one-off.
当時は偶発的なものと考えられていました
02:22
Animals, just like humans,
動物にも人間同様に
02:25
sometimes get strange tumors.
奇怪な腫瘍ができることがあります
02:27
However, we now believe
しかし私たちは
02:30
that this is the first sighting of a new disease,
これこそが現在タスマニアで蔓延している
02:32
which is now an epidemic spreading through Tasmania.
新型のガンの最初の事例であったと確信しています
02:35
The disease was first sighted
この病気は1996年に
02:39
in the northeast of Tasmania in 1996
タスマニア北東部で初めて確認されて以来
02:41
and has spread across Tasmania like a huge wave.
大きな波のようにタスマニア中に広がりました
02:44
Now there's only a small part of the population,
現在感染せずに残っているデビルは
02:47
which remains unaffected.
ほんの一握りです
02:50
This disease appears first as tumors,
タスマニアデビルがこのガンを発症すると
02:52
usually on the face or inside the mouth
通常 顔面もしくは口内に
02:55
of affected Tasmanian devils.
腫瘍ができます
02:57
These tumors inevitably grow into larger tumors,
これらの腫瘍は この写真のように
02:59
such as these ones here.
大きくなってしまいます
03:02
And the next image I'm going to show
次にお見せする写真は
03:04
is quite gruesome.
本当にひどいものです
03:06
But inevitably, these tumors progress
これらの腫瘍は否応なしに
03:08
towards being enormous, ulcerating tumors like this one here.
このように大きな潰瘍性の腫瘍に進行するのです
03:10
This one in particular sticks in my mind,
これは私が実際に
03:16
because this is the first case of this disease
目にした初めての事例だったので
03:18
that I saw myself.
特に印象に残っています
03:20
And I remember the horror of seeing this little female devil
悪臭を放つ潰瘍性巨大腫瘍のために
03:22
with this huge ulcerating, foul-smelling tumor
下あごが外れてしまった
03:25
inside her mouth
このメスデビルを
03:27
that had actually cracked off her entire lower jaw.
目の当たりにした恐怖は今でも覚えています
03:29
She hadn't eaten for days.
何日も物は食べていません
03:33
Her guts were swimming with parasitic worms.
内臓は寄生虫でいっぱいでした
03:36
Her body was riddled with secondary tumors.
腫瘍は体中に転移しています
03:38
And yet, she was feeding three little baby Tasmanian devils
それでも彼女は小さな3匹の赤ん坊に
03:41
in her pouch.
母乳を与えていました
03:44
Of course, they died along with the mother.
もちろん赤ん坊も死んでしまいました
03:47
They were too young to survive without their mother.
幼すぎて母親なしでは生き残れなかったのです
03:50
In fact, in the area where she comes from,
このメスが生息していた地域では
03:53
more than 90 percent of the Tasmanian devil population
90%以上のタスマニアデビルが
03:56
has already died of this disease.
この病気で死んでしまっています
03:59
Scientists around the world
タスマニアデビルを襲う
04:02
were intrigued by this cancer,
この感染性のガンに
04:04
this infectious cancer,
世界中の科学者たちが
04:06
that was spreading through the Tasmanian devil population.
大変な興味を示しました
04:08
And our minds immediately turned to cervical cancer in women,
私達はすぐにウィルスで感染する
04:11
which is spread by a virus,
子宮頚ガンや
04:14
and to the AIDS epidemic,
色々なガンと関連のある
04:16
which is associated with a number of different types of cancer.
AIDSの流行のことを考えました
04:18
All the evidence suggested that this devil cancer
状況から このガンがウィルスによって
04:22
was spread by a virus.
感染しているように思われたからです
04:25
However, we now know -- and I'll tell you right now --
しかしウイルス感染症でないことが
04:28
that we know that this cancer is not spread by a virus.
今ではわかっています
04:31
In fact, the infectious agent of disease in this cancer
実はこのガンの感染源は
04:34
is something altogether more sinister,
思いもしなかった
04:38
and something that we hadn't really thought of before.
恐ろしいものでした
04:40
But in order for me to explain what that is,
この原因を説明するために
04:43
I need to spend just a couple of minutes
まずガン自体について
04:46
talking more about cancer itself.
もう少しお話しなくてはいけません
04:48
Cancer is a disease
ガンは世界規模で毎年
04:51
that affects millions of people around the world every year.
何百万人もが発症する疾病です
04:53
One in three people in this room
この部屋にいる方の 3分の1は
04:56
will develop cancer at some stage in their lives.
いつかガンにかかるでしょう
04:58
I myself had a tumor removed from my large intestine
私自身は14歳の時
05:01
when I was only 14.
大腸の腫瘍を摘出しました
05:03
Cancer occurs
ガンは 遺伝子内で
05:06
when a single cell in your body
突然変異を生じた
05:08
acquires a set of random mutations in important genes
1つの細胞がガン化し
05:10
that cause that cell to start to produce
次々に増殖することで
05:13
more and more and more copies of itself.
発生します
05:16
Paradoxically, once established,
自然選択は適者生存のはずですが
05:20
natural selection actually favors
おかしなことにこれが
05:23
the continued growth of cancer.
増殖するガンに対して
05:25
Natural selection is survival of the fittest.
有利に働いてしまうのです
05:27
And when you have a population of fast-dividing cancer cells,
増殖力の高いガン細胞の一つが
05:30
if one of them acquires new mutations,
一つ突然変異すると それは
05:33
which allow them to grow more quickly,
より効果的に栄養を吸収し
05:35
acquire nutrients more successfully,
増殖力が増します
05:37
invade the body,
その細胞は自然選択の対象となり
05:39
they'll be selected for by evolution.
体中に一層蔓延するのです
05:41
That's why cancer is such a difficult disease to treat.
このようにガンは自然選択を通じ進化するので
05:44
It evolves.
治療が難しいのです
05:48
Throw a drug at it,
薬物を投与しても
05:50
and resistant cells will grow back.
耐性細胞を成長させるだけです
05:52
An amazing fact is that,
驚くことに
05:55
given the right environment and the right nutrients,
適切な環境と栄養があれば
05:57
a cancer cell has the potential
ガンは永遠に
06:00
to go on growing forever.
成長することが可能なのです
06:02
However cancer is constrained
しかしガンは生物の身体を
06:05
by living inside our bodies,
離れることはできません
06:07
and its continued growth,
ガンが増殖を続けて
06:09
its spreading through our bodies
体中の組織を
06:11
and eating away at our tissues,
むしばんでしまえば
06:13
leads to the death of the cancer patient
患者の身体もガンそのものも
06:15
and also to the death of the cancer itself.
死んでしまうのです
06:18
So cancer could be thought of
ガンは短命で奇妙な
06:22
as a strange, short-lived, self-destructive life form --
自減的側面を持つ進化論的−
06:24
an evolutionary dead end.
行き詰まりとでも言えましょう
06:29
But that is where the Tasmanian devil cancer
しかしガンが
06:33
has acquired an absolutely amazing
驚くべき進化の適応を果たしたのが
06:35
evolutionary adaptation.
タスマニアデビルの事例だったのです
06:38
And the answer came from studying
DNAを解析することで
06:41
the Tasmanian devil cancer's DNA.
この謎が解けました
06:43
This was work from many people,
多くの人との共同研究ですが
06:45
but I'm going to explain it through a confirmatory experiment
私が数年前に行った
06:47
that I did a few years ago.
確認実験を通して説明します
06:49
The next slide is going to be gruesome.
次のスライドは悲惨です
06:51
This is Jonas.
これはジョナスです
06:54
He's a Tasmanian devil that we found
私達の発見した 顔に大きな腫瘍ができた
06:56
with a large tumor on his face.
タスマニアデビルです
06:59
And being a geneticist,
私は遺伝学者として
07:01
I'm always interested to look at DNA and mutations.
DNAや突然変異の分析には興味があります
07:03
So I took this opportunity
この機会にジョナスの顔の腫瘍と
07:06
to collect some samples from Jonas' tumor
身体からいくらか
07:08
and also some samples from other parts of his body.
サンプルを取りました
07:10
I took these back to the lab.
研究所に持ち帰って
07:13
I extracted DNA from them.
ここからDNAを抽出しました
07:15
And when I looked at the sequence of the DNA,
ジョナスの顔にできた腫瘍のDNAと
07:17
and compared the sequence of Jonas' tumor
身体から採取したDNAを
07:20
to that of the rest of his body,
比較してみると
07:23
I discovered that they had a completely different genetic profile.
遺伝子プロファイルは全く異なっていました
07:25
In fact, Jonas and his tumor
事実 ジョナスと
07:30
were as different from each other
彼にできた腫瘍は 皆さん自身と
07:32
as you and the person sitting next to you.
皆さんの隣に座っている人ほど違っていました
07:35
What this told us was that Jonas' tumor
つまりジョナスの腫瘍は
07:38
did not arise from cells of his own body.
自身の体内で生成されたものではなかったのです
07:41
In fact, more genetic profiling
更に遺伝子プロファイルを分析していくと
07:44
told us that this tumor in Jonas
ジョナスの腫瘍はおそらく
07:47
actually probably first arose
まずメスのデビルから
07:49
from the cells of a female Tasmanian devil --
生じたものだと判明しました
07:51
and Jonas was clearly a male.
ジョナスは明らかにオスなのに
07:53
So how come
ではなぜ他の個体で
07:55
a tumor that arose from the cells of another individual
生まれたガンがジョナスの顔で
07:57
is growing on Jonas' face?
増殖していたのでしょうか?
08:00
Well the next breakthrough
何百ものデビルのガンを
08:03
came from studying hundreds of Tasmanian devil cancers
分析していると
08:05
from all around Tasmania.
重大なことが判明しました
08:08
We found that all of these cancers
全てのガンが
08:10
shared the same DNA.
同じDNAを共有していたのです
08:12
Think about that for a minute.
少し考えて下さい
08:14
That means that all of these cancers
つまり一匹のデビルから
08:16
actually are the same cancer
発症したガンが
08:18
that arose once from one individual devil,
その個体を離れた後
08:20
that have broken free of that first devil's body
タスマニア全土のデビルへ
08:23
and spread through the entire Tasmanian devil population.
広がっていったということです
08:26
But how can a cancer spread in a population?
しかし感染は どのように拡大したのでしょうか
08:30
Well the final piece of the puzzle came
野生のデビルの行動特性を
08:33
when we remember how devils behave when they meet each other in the wild.
思い返し 最後の謎が解けました
08:35
They tend to bite each other,
彼らはお互いを 特に顔を
08:38
often quite ferociously and usually on the face.
激しくかじる癖があります
08:40
We think that cancer cells
その時 腫瘍から落ちたガン細胞が
08:43
actually come off the tumor, get into the saliva.
唾液から流入するのだと思います
08:46
When the devil bites another devil,
かじった時に
08:49
it actually physically implants living cancer cells into the next devil,
生きたガン細胞が別の個体に いわば移植され
08:51
so the tumor continues to grow.
腫瘍が生き続けるのです
08:54
So this Tasmanian devil cancer
このタスマニアデビルガンは
08:56
is perhaps the ultimate cancer.
究極のガンかもしれません
08:58
It's not constrained by living within the body that gave rise to it.
突然変異することで
09:00
It spreads through the population,
免疫システムを侵略し
09:03
has mutations that allow it to evade the immune system,
発症した個体外へも拡大を続けます
09:05
and it's the only cancer that we know of
私達の知る限り
09:08
that's threatening an entire species with extinction.
種を全滅させ得る唯一のガンです
09:10
But if this can happen in Tasmanian devils,
しかしタスマニアデビル以外の
09:14
why hasn't it happened in other animals
動物になぜこの現象は
09:17
or even humans?
見られなかったのでしょうか?
09:19
Well the answer is, it has.
実は既に起こっているのです
09:21
This is Kimbo.
これはケニアのムンバサの
09:25
He's a dog that belongs to a family in Mombasa in Kenya.
家族が飼っている犬 キンボです
09:27
Last year, his owner noticed some blood
昨年 股の部分から
09:31
trickling from his genital region.
出血していることに飼い主が気づきました
09:34
She took him to the vet
獣医に連れて行くと
09:37
and the vet discovered something quite disgusting.
ひどいものが見つかりました
09:39
And if you're squeamish, please look away now.
血を見るのがいやな人は目をそらしてください
09:42
He discovered this,
キンボのペニスの付け根には
09:45
a huge bleeding tumor
出血している
09:47
at the base of Kimbo's penis.
巨大な腫瘍があったのです
09:49
The vet diagnosed this as transmissible venereal tumor,
獣医の診断では性交を介して
09:53
a sexually transmitted cancer
感染する犬に特有の
09:56
that affects dogs.
ガンということでした
09:59
And just as the Tasmanian devil cancer is contagious
このガンもタスマニアデビルの事例のように
10:01
through the spread of living cancer cells,
生きたガン細胞の伝播で
10:04
so is this dog cancer.
感染するものです
10:06
But this dog cancer is quite remarkable,
驚くべきはこのガンが
10:08
because it spread all around the world.
世界中に広まったことです
10:10
And in fact, these same cells
実際にキンボが感染したのと
10:12
that are affecting Kimbo here
同じガン細胞が ニューヨーク市や
10:14
are also found affecting dogs
ヒマラヤ山脈の山村部
10:17
in New York City,
またオーストラリアの
10:19
in mountain villages in the Himalayas
奥地にいる犬にも
10:21
and in Outback Australia.
見つかっているのです
10:23
We also believe this cancer might be very old.
大昔から存在しているのでしょう
10:26
In fact, genetic profiling tells
遺伝子指紋法によると
10:28
that it may be tens of thousands of years old,
このガンは何万年も前から存在しており
10:30
which means that this cancer
ネアンデルタール人の時代の
10:33
may have first arisen
オオカミの体内で
10:35
from the cells of a wolf
発症したものである
10:37
that lived alongside the Neanderthals.
可能性もあるのです
10:39
This cancer is remarkable.
驚くべきことです
10:42
It's the oldest mammalian-derived life form that we know of.
知りうる限り哺乳類から派生した最古の生命体です
10:44
It's a living relic
まさに現代に
10:48
of the distant past.
生きる化石なのです
10:50
So we've seen that this can happen in animals.
動物には見られたように
10:54
Could cancers be contagious between people?
ガンは人間の間でも感染するのでしょうか?
10:56
Well this is a question
この疑問に大きな関心を
11:01
which fascinated Chester Southam,
寄せたのが1950年代の
11:03
a cancer doctor in the 1950s.
腫瘍学者 チェスター・サウザンでした
11:05
Ad he decided to put this to the test
彼は赤の他人のガンを
11:08
by actually deliberately inoculating people
人に植え付けるという実験を
11:11
with cancer from somebody else.
行うことにしました
11:14
And this is a photograph of Dr. Southam in 1957
これは1957年 オハイオ州刑務所の
11:17
injecting cancer into a volunteer,
囚人であった志願者に
11:21
who in this case was an inmate
サウザン医師が
11:24
in Ohio State Penitentiary.
ガンを注射している写真です
11:26
Most of the people that Dr. Southam injected
この実験で
11:30
did not go on to develop cancer
ガンに感染した人は
11:32
from the injected cells.
わずかに数えるのみでした
11:34
But a small number of them did,
彼らの免疫力は
11:36
and they were mostly people who were otherwise ill --
低下しておりいずれにせよ
11:38
whose immune systems were probably compromised.
近々何か病気を患ったことでしょう
11:41
What this tells us,
この実験からわかるのは
11:46
ethical issues aside,
道徳の問題は
11:48
is that ...
さておいて
11:50
(Laughter)
(笑)
11:52
it's probably extremely rare
人間の間でのガン感染は
11:54
for cancers to be transferred between people.
非常に珍しいということです
11:57
However, under some circumstances,
しかしある条件下では
12:01
it can happen.
感染する可能性もあります
12:03
And I think that this is something
このことは これから
12:06
that oncologists and epidemiologists
腫瘍学者や疫学者に
12:08
should be aware of in the future.
考慮してほしいことです
12:10
So just finally,
最後に
12:13
cancer is an inevitable outcome
ガンになるのを防ぐ事は
12:15
of the ability of our cells
細胞の分裂能力と
12:17
to divide
環境適応能力からして
12:19
and to adapt to their environments.
不可能です
12:21
But that does not mean that we should give up hope
だからといってガンに
12:24
in the fight against cancer.
屈服する必要はないのです
12:27
In fact, I believe, given more knowledge
実際 ガン成長の
12:29
of the complex evolutionary processes that drive cancer's growth,
複雑な進化の過程を解析することで
12:31
we can defeat cancer.
ガンを撲滅することができると思っています
12:34
My personal aim
私個人の目標は
12:37
is to defeat the Tasmanian devil cancer.
このタスマニアデビルのガンに打ち勝つことです
12:39
Let's prevent the Tasmanian devil
彼らがこのガンで
12:43
from being the first animal
絶滅する最初の動物になるのを
12:45
to go extinct from cancer.
私達の手で防ぎましょう
12:47
Thank you.
ありがとうございました
12:49
(Applause)
(拍手)
12:51
Translator:Masami Mutsukado and Kacie Landrum
Reviewer:Takahiro Shimpo

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Elizabeth Murchison - Cancer researcher
Elizabeth Murchison studies a mysterious (and contagious) cancer that threatens to wipe out Tasmanian devils.

Why you should listen

Elizabeth Murchison grew up in Tasmania, the island home of the small, aggressive marsupial known as the Tasmanian devil. In the mid-'90s, the devils were beset with a terrible new disease -- a contagious facial cancer, spread by biting, that killed the animals just as they reached breeding age. By 2008, half the devil population of Australia had contracted the cancer and died. And as Murchison says: "I didn’t want to sit back and let the devils disappear.”

Leading an international team at Cold Spring Harbor Laboratory, she worked to understand why this cancer was so virulent -- with the goal of saving the Taz, as it is called, but also of understanding how a contagious cancer works. Analyzing gene and microRNA activity in 25 different facial tumors and in healthy tissue, the team found that cancers from animals across Tasmania were identical, and that the cancer stems from Schwann cells, which normally insulate nerve fibers.

Now a Research Fellow in Medical Sciences at King's College, Cambridge, Murchison is using high-throughput DNA sequencing technologies to investigate the genetics and evolution of this disease, one of only three known cancers that spread contagiously.

She says: "This is why cancer is such a difficult disease to treat: It evolves."

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