How bones make blood - Melody Smith

譯者: Ann Chen 審譯者: Bruce Sung

At any given moment, trillions of cells are traveling through your blood vessels,

無時無刻，都有數兆的細胞 在你血管中流動著。

sometimes circling the body in just one minute.

有時繞身體一圈，僅需一分鐘。

Each of these cells has its origins deep in your bones.

這些細胞各來自骨頭內深處。

Bones might seem rock-solid, but they’re actually quite porous inside.

骨頭可能看起來堅硬如石， 其實它們內部是非常多孔的，

Large and small blood vessels enter through these holes.

大大小小的血管穿過這些孔洞。

And inside most of the large bones of your skeleton is a hollow core

骨骼的大部份大骨頭， 其內部是空心，

filled with soft bone marrow.

裡面充滿著柔軟的骨髓。

Marrow contains fat and other supportive tissue,

骨髓含有脂肪及其他輔助的組織，

but its most essential elements are blood stem cells.

但它最主要的成份是造血幹細胞。

These stem cells are constantly dividing.

這些幹細胞不斷地分裂，

They can differentiate into red blood cells,

它們可分化為紅血球、

white blood cells, and platelets,

白血球及血小板，

and send about hundreds of billions of new blood cells

並且每天將數千億的新生血球

into circulation every day.

注入血液循環中。

These new cells enter the bloodstream

這些新生細胞

通過骨髓內 微細血管的孔洞進入血流。

through holes in small capillaries in the marrow.

Through the capillaries,

藉由微血管，

they reach larger blood vessels and exit the bone.

它們到達較大的血管， 並離開了骨頭。

If there’s a problem with your blood,

如果血液出了問題，

there’s a good chance it can be traced back to the bone marrow.

大多可以追究根源到骨髓。

Blood cancers often begin with genetic mutations in the stem cells.

血癌常開始於 幹細胞的基因突變，

The stem cells themselves are not cancerous,

這些幹細胞本身並沒有癌變，

but these mutations can interfere with the process of differentiation

但它們的突變 會干擾到細胞分化的過程，

and result in malignant blood cells.

進而產生惡性的血癌細胞。

So for patients with advanced blood cancers like leukemia and lymphoma,

對於末期血癌患者， 例如白血病及淋巴癌，

the best chance for a cure is often an allogeneic bone marrow transplant,

最有希望的治癒方法通常是 不同個體的骨髓移植，

which replaces the patient’s bone marrow with a donor’s.

也就是用捐贈者的骨髓 來置換病人的骨髓。

Here’s how it works.

原理如下：

First, blood stem cells are extracted from the donor.

首先，從捐贈者取出造血幹細胞。

Most commonly,

最常用的方法是

blood stem cells are filtered out of the donor’s bloodstream

從捐贈者的血中過濾出造血幹細胞，

by circulating the blood through a machine

也就是讓血液流經一台機器，

that separates it into different components.

將血中不同的組成分離出來。

In other cases, the marrow is extracted directly

另外，也可以從髋部的髂嵴 用注射針直接抽取骨髓。

from a bone in the hip, the iliac crest, with a needle.

Meanwhile, the recipient prepares for the transplant.

此時，病人（受捐者） 要作準備接受移植。

High doses of chemotherapy or radiation kill the patient’s existing marrow,

用高劑量的化療或放療 來破壞病人的骨髓，

destroying both malignant cells and blood stem cells.

殺死癌細胞和造血幹細胞。

This also weakens the immune system,

如此也可減弱免疫系統，

making it less likely to attack the transplanted cells.

讓它比較不會攻擊移植的細胞。

Then the donor cells are infused into the patient’s body through a central line.

接著經由中央靜脈導管 將捐贈的骨髓細胞注入病人體內。

They initially circulate in the recipient’s peripheral bloodstream,

一開始，這些細胞 循環於病人的週邊血流中，

but molecules on the stem cells, called chemokines, act as homing devices

但在幹細胞上的分子 ── 趨化激素， 就像自動導向裝置，

and quickly traffic them back to the marrow.

迅速引導它們回到骨髓。

Over the course of a few weeks,

幾週之後，

they begin to multiply and start producing new, healthy blood cells.

它們開始繁衍， 製造新的健全血球細胞，

Just a small population of blood stem cells

只需要少量的造血幹細胞，

can regenerate a whole body’s worth of healthy marrow.

就可以填補整身的健康骨髓。

A bone marrow transplant can also lead to something

骨髓移植也能導致

called graft-versus-tumor activity,

「移植物對腫療效果」，

when new immune cells generated by the donated marrow

就是捐贈的骨髓 製造新的免疫細胞

can wipe out cancer cells the recipient’s original immune system couldn’t.

能殺滅病人原來免疫系統 所不能殺滅的癌細胞。

This phenomenon can help eradicate stubborn blood cancers.

這種情況可協助根除頑強的血癌。

But bone marrow transplants also come with risks,

但是骨髓移植也伴隨著風險，

including graft-versus-host disease.

包括「移植物對抗宿主疾病」，

It happens when the immune system generated by the donor cells

也就是捐贈細胞製造的免疫系統

attacks the patient’s organs.

攻擊病人的器官。

This life-threatening condition occurs in about 30–50% of patients

這致命的情況約有 30-50% 的機率

who receive donor cells from anyone other than an identical twin,

會發生在不是接受 同卵雙胞胎細胞的病人。

particularly when the stem cells are collected

尤其是當幹細胞是取自血中，

from the blood as opposed to the bone marrow.

而非取自骨髓時。

Patients may take immunosuppressant medications

病人可以使用免疫抑制劑，

or certain immune cells may be removed from the donated sample

或可先移除捐贈者檢體的 特定免疫細胞，以降低

in order to reduce the risk of graft-versus-host disease.

「移植物對抗宿主疾病」的風險。

But even if a patient avoids graft-versus-host disease,

但即使病人躲過了 移植物對抗宿主疾病，

their immune system may reject the donor cells.

他們的免疫系統 仍可能排斥捐贈者的細胞。

So it’s crucial to find the best match possible in the first place.

所以最重要的是 儘可能一開始就尋找最佳配對。

Key regions of the genetic code determine how the immune system

遺傳密碼的關鍵區域決定免疫系統

identifies foreign cells.

如何識別外來細胞。

If these regions are similar in the donor and the recipient,

如果捐贈者和病人的關鍵區域相似，

the recipient’s immune system is more likely to accept the donor cells.

則病人的免疫系統 較容易接受捐贈者的細胞。

Because these genes are inherited, the best matches are often siblings.

因為這些基因具有遺傳性， 最佳配對通常是兄弟姊妹。

But many patients who need a bone marrow transplant

但許多需要骨髓移植的病人

don’t have a matched family member.

沒有匹配的家庭成員。

Those patients turn to donor registries of volunteers

這些病人只好轉求 願意捐贈骨髓的志願者名單了。

willing to offer their bone marrow.

All it takes to be on the registry is a cheek swab to test for a genetic match.

欲名列此名單，只需在頰部拭抹 以供基因配對測試即可。

And in many cases, the donation itself

很多時候，捐贈骨髓的過程

isn’t much more complicated than giving blood.

並沒有比捐血過程複雜。

It’s a way to save someone’s life

這是一種拯救性命的方法，

with a resource that’s completely renewable.

而骨髓資源完全可自我複製再生。.