At any given moment, trillions of cells are traveling through your blood vessels, sometimes circling the body in just one minute. Each of these cells has its origins deep in your bones. Bones might seem rock-solid, but they’re actually quite porous inside. Large and small blood vessels enter through these holes. And inside most of the large bones of your skeleton is a hollow core filled with soft bone marrow. Marrow contains fat and other supportive tissue, but its most essential elements are blood stem cells. These stem cells are constantly dividing. They can differentiate into red blood cells, white blood cells, and platelets, and send about hundreds of billions of new blood cells into circulation every day. These new cells enter the bloodstream through holes in small capillaries in the marrow. Through the capillaries, they reach larger blood vessels and exit the bone.
無時無刻,都有數兆的細胞 在你血管中流動著。 有時繞身體一圈,僅需一分鐘。 這些細胞各來自骨頭內深處。 骨頭可能看起來堅硬如石, 其實它們內部是非常多孔的, 大大小小的血管穿過這些孔洞。 骨骼的大部份大骨頭, 其內部是空心, 裡面充滿著柔軟的骨髓。 骨髓含有脂肪及其他輔助的組織, 但它最主要的成份是造血幹細胞。 這些幹細胞不斷地分裂, 它們可分化為紅血球、 白血球及血小板, 並且每天將數千億的新生血球 注入血液循環中。 這些新生細胞 通過骨髓內 微細血管的孔洞進入血流。 藉由微血管, 它們到達較大的血管, 並離開了骨頭。
If there’s a problem with your blood, there’s a good chance it can be traced back to the bone marrow. Blood cancers often begin with genetic mutations in the stem cells. The stem cells themselves are not cancerous, but these mutations can interfere with the process of differentiation and result in malignant blood cells. So for patients with advanced blood cancers like leukemia and lymphoma, the best chance for a cure is often an allogeneic bone marrow transplant, which replaces the patient’s bone marrow with a donor’s.
如果血液出了問題, 大多可以追究根源到骨髓。 血癌常開始於 幹細胞的基因突變, 這些幹細胞本身並沒有癌變, 但它們的突變 會干擾到細胞分化的過程, 進而產生惡性的血癌細胞。 對於末期血癌患者, 例如白血病及淋巴癌, 最有希望的治癒方法通常是 不同個體的骨髓移植, 也就是用捐贈者的骨髓 來置換病人的骨髓。
Here’s how it works. First, blood stem cells are extracted from the donor. Most commonly, blood stem cells are filtered out of the donor’s bloodstream by circulating the blood through a machine that separates it into different components. In other cases, the marrow is extracted directly from a bone in the hip, the iliac crest, with a needle.
原理如下: 首先,從捐贈者取出造血幹細胞。 最常用的方法是 從捐贈者的血中過濾出造血幹細胞, 也就是讓血液流經一台機器, 將血中不同的組成分離出來。 另外,也可以從髋部的髂嵴 用注射針直接抽取骨髓。 此時,病人(受捐者) 要作準備接受移植。
Meanwhile, the recipient prepares for the transplant. High doses of chemotherapy or radiation kill the patient’s existing marrow, destroying both malignant cells and blood stem cells. This also weakens the immune system, making it less likely to attack the transplanted cells. Then the donor cells are infused into the patient’s body through a central line. They initially circulate in the recipient’s peripheral bloodstream, but molecules on the stem cells, called chemokines, act as homing devices and quickly traffic them back to the marrow. Over the course of a few weeks, they begin to multiply and start producing new, healthy blood cells. Just a small population of blood stem cells can regenerate a whole body’s worth of healthy marrow.
用高劑量的化療或放療 來破壞病人的骨髓, 殺死癌細胞和造血幹細胞。 如此也可減弱免疫系統, 讓它比較不會攻擊移植的細胞。 接著經由中央靜脈導管 將捐贈的骨髓細胞注入病人體內。 一開始,這些細胞 循環於病人的週邊血流中, 但在幹細胞上的分子 ── 趨化激素, 就像自動導向裝置, 迅速引導它們回到骨髓。 幾週之後, 它們開始繁衍, 製造新的健全血球細胞, 只需要少量的造血幹細胞, 就可以填補整身的健康骨髓。 骨髓移植也能導致
A bone marrow transplant can also lead to something called graft-versus-tumor activity, when new immune cells generated by the donated marrow can wipe out cancer cells the recipient’s original immune system couldn’t. This phenomenon can help eradicate stubborn blood cancers. But bone marrow transplants also come with risks, including graft-versus-host disease. It happens when the immune system generated by the donor cells attacks the patient’s organs. This life-threatening condition occurs in about 30–50% of patients who receive donor cells from anyone other than an identical twin, particularly when the stem cells are collected from the blood as opposed to the bone marrow.
「移植物對腫療效果」, 就是捐贈的骨髓 製造新的免疫細胞 能殺滅病人原來免疫系統 所不能殺滅的癌細胞。 這種情況可協助根除頑強的血癌。 但是骨髓移植也伴隨著風險, 包括「移植物對抗宿主疾病」, 也就是捐贈細胞製造的免疫系統 攻擊病人的器官。 這致命的情況約有 30-50% 的機率 會發生在不是接受 同卵雙胞胎細胞的病人。 尤其是當幹細胞是取自血中, 而非取自骨髓時。 病人可以使用免疫抑制劑,
Patients may take immunosuppressant medications or certain immune cells may be removed from the donated sample in order to reduce the risk of graft-versus-host disease. But even if a patient avoids graft-versus-host disease, their immune system may reject the donor cells. So it’s crucial to find the best match possible in the first place.
或可先移除捐贈者檢體的 特定免疫細胞,以降低 「移植物對抗宿主疾病」的風險。 但即使病人躲過了 移植物對抗宿主疾病, 他們的免疫系統 仍可能排斥捐贈者的細胞。 所以最重要的是 儘可能一開始就尋找最佳配對。 遺傳密碼的關鍵區域決定免疫系統
Key regions of the genetic code determine how the immune system identifies foreign cells. If these regions are similar in the donor and the recipient, the recipient’s immune system is more likely to accept the donor cells. Because these genes are inherited, the best matches are often siblings. But many patients who need a bone marrow transplant don’t have a matched family member. Those patients turn to donor registries of volunteers willing to offer their bone marrow.
如何識別外來細胞。 如果捐贈者和病人的關鍵區域相似, 則病人的免疫系統 較容易接受捐贈者的細胞。 因為這些基因具有遺傳性, 最佳配對通常是兄弟姊妹。 但許多需要骨髓移植的病人 沒有匹配的家庭成員。 這些病人只好轉求 願意捐贈骨髓的志願者名單了。 欲名列此名單,只需在頰部拭抹 以供基因配對測試即可。
All it takes to be on the registry is a cheek swab to test for a genetic match. And in many cases, the donation itself isn’t much more complicated than giving blood. It’s a way to save someone’s life with a resource that’s completely renewable.
很多時候,捐贈骨髓的過程 並沒有比捐血過程複雜。 這是一種拯救性命的方法, 而骨髓資源完全可自我複製再生。.