Vaccines：A new health food
GETTING two for the price of one is always a good bargain. And according to a paper in this week’s Proceedings of the National Academy of Sciences, that is what Tomonori Nochi of the University of Tokyo and his colleagues have done. Using genetic engineering, they have overcome two of the limitations of vaccines. One is that they are heat-sensitive and thus have to be transported along a “cold chain” of refrigerators to the clinics where they are used. The other is that, although they stimulate immune responses inside the body, they often fail to extend that protection to the outside, where it might prevent bacteria and viruses getting inside in the first place.In this context, the outside is not the skin: that is dry and hostile to germs. It is the damp and welcoming surface of places such as the lung and the gut that are at risk. Although these are casually called internal, technically they are not. Any nasties in the gut or lungs have to cross the walls of those organs before they can multiply inside the body.
Dr Nochi’s genetic engineering involved growing the vaccine in rice. To prove the principle, he chose cholera, but it should work with other vaccines as well. With cholera, the immune response is induced by what is known as the cholera toxin B-subunit. This is a protein, and Dr Nochi took the gene that encodes it and inserted that gene into the genome of rice. Next to the B-subunit gene itself, he inserted a second piece of DNA called a promoter. This, as its name suggests, promotes activity in an adjacent gene. Promoters themselves are activated by other molecules, and whether they are switched on or not depends on whether the cell they are in provides the necessary stimulation. In this case Dr Nochi picked a promoter that is active in the tissue of rice grains.
It was then just a question of growing the rice and feeding the resulting grains to some experimental mice to find out what would happen. The first thing that happened was that the grains protected the B-subunit from being broken down in the stomach, thus overcoming one of the regular bugbears of protein-based drugs: that they cannot be given by mouth, because they will be digested. This is a problem with today’s cholera vaccine which is indeed taken by mouth and therefore affords poor protection. When the B-subunits got to the intestines they did exactly what Dr Nochi hoped and induced the production of antibodies and the secretion of those antibodies into the mucous coating of the intestinal wall. Dr Nochi’s mice really were protected. When he fed them cholera toxin, they did not get sick.
On top of all this, he got as good a response with rice that had been stored at room temperature for 18 months as he did when he used fresh grains. For a vaccine against a disease that is found predominantly in poor countries—places that tend to lack refrigerators and have only intermittent power to run those that do exist—that is an enormous advance. If Dr Nochi’s finding can be translated into a product that is safe and effective for people, it will be a big boost to the health of the world’s poor.
考研词汇：
overcome[ˌəuvəˈkʌm]
v.战胜，克服
[真题例句]If we do not confront and overcome these internal fears and doubts, if we protect ourselves too much, then we cease to grow.[1995年阅读2]
[例句精译] 如果我们不能去正视并克服这些内在的恐惧和疑虑，如果我们过于自我保护，那么我们就会停止成长。
hostile[ˈhɔstail]
a.敌对的，敌方的，敌意的
[真题例句]Stratford-on-Avon, as we all know, has only one industry—William Shakespeare—but there are two distinctly separate and increasingly hostile branches.[2006年阅读2]
[例句精译] 正如我们所知，埃文河上的斯特福特就只有一个行业——威廉·莎士比亚——但是却有两个界限清楚并各怀敌意的分支部门。
induce[inˈdju:s]
v.①引诱，劝使;②引起，导致;③感应
[真题例句]Indeed, the mere presence of a grape in the other chamber (without an actual monkey to eat it) was enough to induce (②) sullen behaviour in a female capuchin.[2005年阅读1]
[例句精译] 事实上，一个笼舍里葡萄的存在(就算是没有猴子在吃)，就足以引起另一只猴子愤愤不平了。
adjacent[əˈdʒeisənt]
a.(to)邻近的，毗连的
mucous[ˈmju:kəs]
a.黏液的, 黏液似的
enormous[iˈnɔ:məs]
a.巨大的，庞大的
[真题例句]Of course, the use of the Internet isnt the only way to defeat poverty.And the Internet is not the only tool we have.But it has enormous potential.[2001年阅读2]
[例句精译] 当然，使用互联网不是惟一消灭贫困的方法。互联网也不是我们所拥有的惟一工具，但它却有巨大的潜力。
背景常识介绍：
疫苗，是指为了预防、控制传染病的发生、流行，而用于人体预防接种的疫苗类预防性生物制品。
疫苗是将病原微生物(如细菌、立克次氏体、病毒等)及其代谢产物，经过人工减毒、灭活或利用基因工程等方法制成的用于预防传染病的自动免疫制剂。疫苗保留了病原菌刺激动物体免疫系统的特性。当动物体接触到这种不具伤害力的病原菌后，免疫系统便会产生一定的保护物质，如免疫激素、活性生理物质、特殊抗体等;当
动物再次接触到这种病原菌时，动物体的免疫系统便会依循其原有的记忆，制造更多的保护物质来阻止病原菌的伤害。
疫苗的发现可谓是人类发展史上具有里程碑意义的事件。因为从某种意义上来说，人类繁衍生息的历史就是人类不断同疾病和自然灾害作斗争的历史。控制传染性疾病最主要的手段就是预防，而接种疫苗被认为是最行之有效的措施。
参考译文：
疫苗：全新健康食品
“买一送一”一向都是笔好买卖。这个星期的《国家科学院学报》发表的论文中，东京大学的Tomonori Nochi和他的同事就公布了这样一件好的成果。通过基因工程，他们突破了传统疫苗的两大局限。其一是疫苗往往是热敏性的，因此在运往临床使用地的途中，疫苗必须通过“低温运输系统”在冷藏库中低温运输。另一个则是尽管疫苗可以刺激人体内部的免疫反应，但他们往往不能将保护的范围扩大到外部，那里是能够预防细菌和病毒进入内部的第一道防线。在这里，外部不是指皮肤(皮肤过于干燥不适合微生物生存)。而是指潮湿且细菌容易接触的器官表面，例如肺和易感染的内脏就很易受感染。尽管习惯上这些地方被称为体内，但在学术上并不是。任何细菌要进入体内繁殖必须首先通过这些器官的表面粘膜。
Nochi博士进行的基因工程试验包括在大米中培育疫苗。为了证明这一原理可行，他选择霍乱疫苗进行试验，但这也应该同样适用于其他疫苗。应对霍乱，引起免疫系统反应的是被称为霍乱毒素B亚单位的蛋白质。Nochi博士分析出这种蛋白质的基因，并且将其插入大米的染色体组中。他还在邻近B亚单位基因处插入被称为启动子的第二段DNA。就像这段DNA的名字一样，它会激活邻近基因的活性。启动子自身则由其他分子激活，这些启动子能否表达取决于其所在的细胞是否给其必要的刺激。在这个例子中，Nochi博士的启动子就是在大米组织中发挥作用。
现在，要做的就是种植这种大米并且用它们喂养一些试验用老鼠，以研究将会出现什么结果。首先，谷类粮食在胃中保护了B亚单位被直接消化，因此使传统上一直困扰蛋白质药物的一大难题——蛋白质药物会在胃中被消化往往不能直接口服——得到解决。这同样是霍乱疫苗的一大缺点，现今的霍乱疫苗实际上是口服的，因此往往只能起很小的作用。当B亚单位顺利进入肠内，大米疫苗实际上已经完成Nochi博士所希望的工作，同时疫苗会使人体产生抗体并将这些抗体分泌入肠内表面覆盖的黏液中。Nochi博士的老鼠在实验中得到了保护，当喂食它们霍乱毒素后，它们并没有染病。
但最关键的是，Nochi博士使用在室温下保存了18个月的大米与使用新鲜大米所得到的实验结果是一样良好的。由于需要疫苗来抵抗疾病的地方往往是那些贫穷国家，往往缺乏足够的冷藏系统并且没有足够的稳定电力来供这些系统运行。因此相较传统疫苗，大米疫苗的这一特点可以说是一个巨大的进步。如果Nochi博士的发明可以制成安全且对人有效的产品，对世界上广大贫穷人民的健康安全将会是一个巨大的推动。