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At any given moment, trillions of cells are traveling through your blood vessels,
在任何時刻，你的血管內 有幾萬億細胞經過，
sometimes circling the body in just one minute.
有時候能在一分鐘內 在身體裡循環一周。
Each of these cells has its origins deep in your bones.
這些細胞中的每一員 都起源於你的骨頭深處。
Bones might seem rock-solid, but they’re actually quite porous inside.
骨頭看上去和石塊一樣堅固， 但它們中心其實有相當多孔。
Large and small blood vessels enter through these holes.
大小血管從這些洞裡進入。
And inside most of the large bones of your skeleton is a hollow core
而你骨骼中的大骨頭大多數是空心的，
filled with soft bone marrow.
其中填滿了柔軟的骨髓。
Marrow contains fat and other supportive tissue,
骨髓中含有脂肪和其它支持組織，
but its most essential elements are blood stem cells.
但它最重要的成分是造血幹細胞。
These stem cells are constantly dividing.
這些幹細胞一直在進行分裂。
They can differentiate into red blood cells,
它們可以分化成紅細胞、
white blood cells, and platelets,
白細胞和血小板，
and send about hundreds of billions of new blood cells
每天能將數千億新生的血細胞
into circulation every day.
投入人體循環。
These new cells enter the bloodstream
這些新細胞
through holes in small capillaries in the marrow.
通過骨髓裡小毛細血管上的洞 進入血液循環。
Through the capillaries,
通過毛細血管，
they reach larger blood vessels and exit the bone.
它們可以抵達更大的血管， 離開骨頭。
If there’s a problem with your blood,
如果你的血液出了問題，
there’s a good chance it can be traced back to the bone marrow.
這個問題很有可能 可以追溯回骨髓。
Blood cancers often begin with genetic mutations in the stem cells.
血癌往往是由幹細胞中 的基因突變開始的。
The stem cells themselves are not cancerous,
幹細胞本身並沒有癌變，
but these mutations can interfere with the process of differentiation
但這些突變會干擾 分化的過程，
and result in malignant blood cells.
產生惡性的血細胞。
So for patients with advanced blood cancers like leukemia and lymphoma,
因此，對於重症血癌， 例如白血病或淋巴癌的患者來說，
the best chance for a cure is often an allogeneic bone marrow transplant,
最有可能治癒的手段 通常是異體骨髓移植，
which replaces the patient’s bone marrow with a donor’s.
能將患者的骨髓替換成捐獻者的骨髓。
Here’s how it works.
以下是它的原理：
First, blood stem cells are extracted from the donor.
首先，從供者的體內採集造血幹細胞。
Most commonly,
最常見的做法是，
blood stem cells are filtered out of the donor’s bloodstream
通過將血液循環通過機器
by circulating the blood through a machine
將其分離成不同成分，
that separates it into different components.
從而將造血幹細胞 從供者的血液中過濾出來。
In other cases, the marrow is extracted directly
另外的做法是，用針直接從供者
from a bone in the hip, the iliac crest, with a needle.
髖部的骨頭髂嵴中抽取骨髓。
Meanwhile, the recipient prepares for the transplant.
與此同時，受者將為移植做準備。
High doses of chemotherapy or radiation kill the patient’s existing marrow,
用高劑量的化療或放射線照射 殺死患者現存的骨髓，
destroying both malignant cells and blood stem cells.
將癌細胞與造血幹細胞同時破壞掉。
This also weakens the immune system,
這也會弱化患者的免疫系統，
making it less likely to attack the transplanted cells.
降低其攻擊移植細胞的機率。
Then the donor cells are infused into the patient’s body through a central line.
接下來，供者的細胞將通過靜脈注射輸注給患者。
They initially circulate in the recipient’s peripheral bloodstream,
這些細胞先在受者的外周血液中循環，
but molecules on the stem cells, called chemokines, act as homing devices
不過幹細胞上被稱為「趨化因子「的分子 起到歸巢作用，
and quickly traffic them back to the marrow.
引導這些幹細胞快速遷移回骨髓中。
Over the course of a few weeks,
在幾個星期的時間裡，
they begin to multiply and start producing new, healthy blood cells.
它們的數量開始增長， 並開始製造新的健康血細胞。
Just a small population of blood stem cells
只需要少許造血幹細胞，
can regenerate a whole body’s worth of healthy marrow.
就能再生整個身體所需的健康的骨髓。
A bone marrow transplant can also lead to something
一次骨髓移植也可以產生
called graft-versus-tumor activity,
所謂的「移植物抗腫瘤」效應，
when new immune cells generated by the donated marrow
即移植骨髓產生的新免疫細胞
can wipe out cancer cells the recipient’s original immune system couldn’t.
能夠抹殺受者原來的免疫系統 無法殺滅的癌細胞。
This phenomenon can help eradicate stubborn blood cancers.
這個現象能幫助患者 清除頑固的血癌細胞。
But bone marrow transplants also come with risks,
但是骨髓移植也伴隨風險，
including graft-versus-host disease.
包括移植物抗宿主病。
It happens when the immune system generated by the donor cells
這種病症會讓由供體細胞生成的免疫系統
attacks the patient’s organs.
攻擊患者的器官。
This life-threatening condition occurs in about 30–50% of patients
這種危機生命的病症 會發生在約 30% - 50% 那些
who receive donor cells from anyone other than an identical twin,
沒有從同卵雙胞胎獲得 供體細胞的患者身上，
particularly when the stem cells are collected
尤其是在幹細胞
from the blood as opposed to the bone marrow.
是從血液中而不是從骨髓中採集的情況下。
Patients may take immunosuppressant medications
通過讓患者服用免疫抑制藥，
or certain immune cells may be removed from the donated sample
或者將特定免疫細胞 從捐獻的樣本中移除，
in order to reduce the risk of graft-versus-host disease.
可以降低移植物抗宿主病的風險。
But even if a patient avoids graft-versus-host disease,
然而即使患者躲過了移植物抗宿主病，
their immune system may reject the donor cells.
他們的免疫系統 還是有可能排斥供體細胞。
So it’s crucial to find the best match possible in the first place.
因此，在第一步找到儘可能 匹配的捐獻者至關重要。
Key regions of the genetic code determine how the immune system
遺傳基因中有關鍵區域
identifies foreign cells.
決定免疫系統如何識別外來細胞。
If these regions are similar in the donor and the recipient,
如果供者和受者的這些區域比較相似，
the recipient’s immune system is more likely to accept the donor cells.
受者的免疫系統就更有可能接受供者的細胞。
Because these genes are inherited, the best matches are often siblings.
因為這些基因是遺傳的， 最好的配型一般是兄弟姐妹。
But many patients who need a bone marrow transplant
但是很多需要骨髓移植的患者
don’t have a matched family member.
並沒有匹配的家庭成員。
Those patients turn to donor registries of volunteers
這些患者轉而求助於願意捐獻骨髓的
willing to offer their bone marrow.
志願者資料庫。
All it takes to be on the registry is a cheek swab to test for a genetic match.
想成為骨髓捐獻者， 只需用棉籤刮口腔進行基因配型。
And in many cases, the donation itself
大多數情況下，骨髓捐獻本身
isn’t much more complicated than giving blood.
並不比獻血麻煩多少。
It’s a way to save someone’s life
這種辦法可以通過完全可再生的資源
with a resource that’s completely renewable.
拯救某個人的生命。
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