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.
在任何时刻,你的血管内 有几万亿细胞经过, 有时候能在一分钟内 在身体里循环一周。 这些细胞中的每一员 都起源于你的骨头深处。 骨头看上去和石块一样坚固, 但它们中心其实有相当多孔。 大小血管从这些洞里进入。 而你骨骼中的大骨头大多数是空心的, 其中填满了柔软的骨髓。 骨髓中含有脂肪和其它支持组织, 但它最重要的成分是造血干细胞。 这些干细胞一直在进行分裂。 它们可以分化成红细胞、 白细胞和血小板, 每天能将数千亿新生的血细胞 投入人体循环。 这些新细胞 通过骨髓里小毛细血管上的洞 进入血液循环。 通过毛细血管, 它们可以抵达更大的血管, 离开骨头。
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.
如果你的血液出了问题, 这个问题很有可能 可以追溯回骨髓。 血癌往往是由干细胞中 的基因突变开始的。 干细胞本身并没有癌变, 但这些突变会干扰 分化的过程, 产生恶性的血细胞。 因此,对于重症血癌, 例如白血病或淋巴癌的患者来说, 最有可能治愈的手段 通常是异体骨髓移植, 能将患者的骨髓替换成捐献者的骨髓。
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.
以下是它的原理: 首先,从供者的体内采集造血干细胞。 最常见的做法是, 通过将血液循环通过机器 将其分离成不同成分, 从而将造血干细胞 从供者的血液中过滤出来。 另外的做法是,用针直接从供者 髋部的骨头髂嵴中抽取骨髓。
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.
与此同时,受者将为移植做准备。 用高剂量的化疗或放射线照射 杀死患者现存的骨髓, 将癌细胞与造血干细胞同时破坏掉。 这也会弱化患者的免疫系统, 降低其攻击移植细胞的几率。 接下来,供者的细胞将通过静脉注射输注给患者。 这些细胞先在受者的外周血液中循环, 不过干细胞上被称为“趋化因子“的分子 起到归巢作用, 引导这些干细胞快速迁移回骨髓中。 在几个星期的时间里, 它们的数量开始增长, 并开始制造新的健康血细胞。 只需要少许造血干细胞, 就能再生整个身体所需的健康的骨髓。
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.
一次骨髓移植也可以产生 所谓的“移植物抗肿瘤”效应, 即移植骨髓产生的新免疫细胞 能够抹杀受者原来的免疫系统 无法杀灭的癌细胞。 这个现象能帮助患者 清除顽固的血癌细胞。 但是骨髓移植也伴随风险, 包括移植物抗宿主病。 这种病症会让由供体细胞生成的免疫系统 攻击患者的器官。 这种危机生命的病症 会发生在约 30% - 50% 那些 没有从同卵双胞胎获得 供体细胞的患者身上, 尤其是在干细胞 是从血液中而不是从骨髓中采集的情况下。
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.
通过让患者服用免疫抑制药, 或者将特定免疫细胞 从捐献的样本中移除, 可以降低移植物抗宿主病的风险。 然而即使患者躲过了移植物抗宿主病, 他们的免疫系统 还是有可能排斥供体细胞。 因此,在第一步找到尽可能 匹配的捐献者至关重要。
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.
遗传基因中有关键区域 决定免疫系统如何识别外来细胞。 如果供者和受者的这些区域比较相似, 受者的免疫系统就更有可能接受供者的细胞。 因为这些基因是遗传的, 最好的配型一般是兄弟姐妹。 但是很多需要骨髓移植的患者 并没有匹配的家庭成员。 这些患者转而求助于愿意捐献骨髓的 志愿者资料库。
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.
想成为骨髓捐献者, 只需用棉签刮口腔进行基因配型。 大多数情况下,骨髓捐献本身 并不比献血麻烦多少。 这种办法可以通过完全可再生的资源 拯救某个人的生命。