It may become possible to vaccinate against brain tumours.
接种疫苗预防脑瘤将成为可能。
CERVICAL cancer is caused by a virus. That has been known for some time and it has led to a vaccine that seems to prevent it. Since then, researchers have been looking for other cancers that may be caused by viruses, to see if they too can be prevented. And they seem to have found one—one of the most feared of all. A piece of research expected to be unveiled on June 1st by Duane Mitchell of Duke University in North Carolina, at a meeting of the American Society of Clinical Oncology, hints that glioblastomas, the most lethal form of brain tumour, may also be susceptible to vaccination.
The story began a few years ago when Charles Cobbs of the California Pacific Medical Centre Research Institute in San Francisco found something odd about glioblastomas. He noticed they usually have a form of herpes, called cytomegalovirus, active within them. It is not that catching cytomegalovirus automatically causes a brain tumour—the virus is found, inactive, in about 80% of the population. Nevertheless, there is clearly some connection between virus and tumour, a connection reinforced by Dr Cobbs’s discovery that the virus appears to dwell inside the tumour but not in the healthy tissue surrounding it. This led him to speculate that the virus may be creating the tumour as a safe haven to support its own existence.
After learning about Dr Cobbs’s work, Dr Mitchell and his colleagues first confirmed the basic findings. They discovered cytomegalovirus in the tumours of more than 90% of those people with glioblastoma whom they examined, but not in healthy brain tissue, nor in non-m alignant brain tumours. They then began an experiment on 21 patients who had been diagnosed with glioblastoma.
Their intention was to encourage those patients’ immune systems to attack the tumours by training them to recognise the signs of active cytomegalovirus infection. To do that, they drew blood from their patients and exposed the immune-system cells within each sample to bits and pieces of cytomegalovirus, in order to encourage those cells to develop the power to identify the pathogen. The cells were then injected back into the patients they had come from, in the hope that those patients’ immune systems would react to cytomegalovirus as if they had encountered it naturally within the body.
The results are encouraging. The normal prognosis for glioblastoma is death within two years, even if a patient is treated with chemotherapy and radiation. Such treatment by itself is reckoned to slow the tumour’s growth by between six and eight months. When Dr Mitchell added his crude vaccine to the traditional treatment, this figure rose to more than a year—and in some people the tumours have stopped growing for more than two years, an observation that opens the door to work on a proper vaccine.
Just why active cytomegalovirus is associated with glioblastoma is still unclear. The virus may cause the tumour, as Dr Cobbs suspects, or the tumour may simply provide the virus with a congenial home. From the vaccine-maker’s point of view it hardly matters. If a vaccine causes the immune system to destroy infected cells, the cancer will be killed anyway. And that would be very good news indeed.
宫颈癌是由病毒引起的。这一点人们早已知晓，它促使人们研制出一种疫苗，该疫苗似乎能够预防宫颈癌。从那时起，研究人员一直在寻找其他类型的可能由病毒引起的癌症，看它们是否也可以预防。他们似乎已经找到了一种——让人最为恐惧的癌症之一。一项研究预计于6月1日在美国临床肿瘤学协会的一次会议上由北卡罗来纳州杜克大学的杜南·米切尔公之于众，该研究暗示，成胶质细胞瘤(一种最致命的脑瘤)或许也可以通过接种疫苗来预防。
事情开始于几年前。那时，位于旧金山的加利福尼亚州太平洋医疗中心研究所的查尔斯·考布斯发现了成胶质细胞瘤的一些奇怪现象。他注意到它们内部通常有一种活性的疱疹，叫做巨细胞病毒。并非一旦感染巨细胞病毒，就会引发脑瘤——他们发现，该病毒在80%的人的体内都是不活跃的。然而，病毒与肿瘤之间显然有某种联系，这种联系经考布斯博士的发现得到进一步证实。考布斯发现，该病毒看起来是寄居在肿瘤内，而非寄居在周围健康的组织内。他由此推测，病毒有可能诱发肿瘤，作为维持自己生存的安全天堂。
在了解了考布斯博士的研究工作之后，米切尔博士及其同事首先证实了这一基本发现。他们在所检查过的90%以上患成胶质细胞瘤的病人的肿瘤内发现了巨细胞病毒，而在健康的脑组织和良性脑瘤中均没发现。接着，他们开始在21名此前被诊断患有成胶质细胞瘤的病人身上进行一项实验。
他们的目的是通过训练那些病人的免疫系统，使它们能够辨认活性巨细胞病毒感染的病征，从而将免疫系统激活，使之攻击肿瘤。为了这样做，他们从病人身上抽血，并将每个样本中的免疫系统细胞暴露于零碎的巨细胞病毒。这样做是为了刺激那些细胞，培养它们鉴别病原体的能力。接着，又将这些细胞注射回病人体内，也就是它们来自的地方。希望这样做能使病人的免疫系统作用于巨细胞病毒，就好像它们在体内自然地遇到它一样。
结果是令人鼓舞的。对成胶质细胞瘤，一般预测病人在两年内死亡，即使他接受化疗和放疗。据推算，这种治疗本身可使肿瘤的生长放慢6~8个月。当米切尔博士在传统治疗的基础上加进他未经加工的疫苗时，这个数字上升至一年以上——在一些人中，肿瘤停止生长达两年多。这项观察为研制有效的疫苗开启了大门。
至于活性巨细胞病毒与成胶质细胞瘤为何有联系目前仍不清楚。或许是病毒导致肿瘤的产生（正如考布斯博士怀疑的那样），也可能肿瘤仅仅为病毒提供了一个适宜的生存场所。疫苗研制者认为这无关紧要。假如有一种疫苗能够使免疫系统杀死受感染细胞，无论如何，癌症就可以得到治愈，而那无疑将是个天大的好消息。
