VOA标准英语2012--Clues Found for AIDS Vaccine Trial Success

Clues Found for AIDS Vaccine¹ Trial Success

In 2009, a study in Thailand proved for the first time that an AIDS vaccine was possible. But scientists were not sure why it offered some protection. Now they have some clues.

The Thailand study looked at a vaccine candidate called RV144. Since the results were announced, researchers have been combing through the data. What was it about this vaccine candidate that offered a protection rate of 31 percent? It was not high enough to go to market, but high enough to cause a lot of excitement for vaccine researchers.

“Once you have a vaccine that works, the next step in terms of the evolution of the vaccine is to try to first understand why it worked, with an idea that if we find out specifically what lab tests seem to correspond with protection we can design a new set of vaccines² that might provide better protection,” said Col. Jerome Kim, senior author of a new follow-up study on RV144.

Antibodies

Kim, a medical doctor with the U.S. Military HIV Research Program, said when the RV144 results were announced scientists thought the success might be due to antibodies. These are proteins that bind³ to viruses and disable them.

“But we didn’t really know,” he said, “and so we looked very, very broadly at a number of different immune responses. And looking very broadly then allowed us to down-select – to pick out only those things which were the most important. Because that statistically⁴ gives us the greatest ability to say after all the testing’s done, this was important.”

The follow-up studies eventually led to two antibodies, one called IgG and the other IgA. Some in the Thai trial had more of one type of antibody than the other. Both, though, were drawn⁵ to a part of HIV called the envelope.

Kim said, “HIV is a member of a group of viruses where the outer coat actually is composed of a little bit of what you call membrane⁶ and then what we call viral spikes⁷. And these viral spikes stick out of the membrane and envelope is contained in those spikes. And very often when vaccines work, the antibody is directed against these spikes because they’re prominent. They stick out and the immune system sees them and says, Ah ha! Let’s make an immune response against it.”

But when it comes to HIV, Col. Kim said that’s easier said than done.

“The virus envelope is very variable. And it’s one of the reasons why we were so worried that no vaccine might ever be possible. Because like the flu virus, the HIV virus changes its envelope and does it very quickly, actually many times faster than the flu virus can,” he said.

A particular region of the envelope called V2 was the target of antibody response. This region may have something to do with how HIV mutates to avoid detection.

“There is a part of the HIV envelope which exposed to the surface. So that’s very important because if it’s buried way, way down in the envelope the antibodies aren’t going to be able to reach it,” he said. 

What’s going on?

The IgG and the IgA antibodies responded differently to the HIV envelope. But IgG was associated with a better vaccine protection rate by binding⁸ to the envelope V2 region. IgA, on the other hand, took a more broad approach to viral envelopes. Initially⁹, it was thought that this resulted in greater risk of infection. Kim says it was both unexpected and confusing, but it raised a number of hypotheses.

“They looked to see, is it actually making infection worse? And in fact it’s not. What it’s doing is it appears to potentially block the beneficial effects that were being seen with other immune responses. So it’s a blocking of the good response rather than something that increases the risk of infection,” he said.

The antibodies were apparently¹⁰ competing with each other to bind to the envelope. Initial studies indicated IgA had a binding advantage over IgG. But Kim says that did not mean people were more likely to be infected with HIV.

“Really, the risk of HIV infection in people who had high levels of IgA was similar to the risk of infection to people who got placebos¹¹. They knocked down the beneficial response. They didn’t create a bad response,” he said.

And that could be one reason why the efficacy rate of RV144 was not higher than 31 percent.

Kim said a lot more research is planned on the RV144 vaccine results, including follow-up studies. In fact, two trials are expected next year using similar vaccines. One would be tested in Thailand on the high risk group called men who have sex with men. The other would be tested against HIV Subtype C, which is a virus that’s predominantly found in southern Africa. Despite the vaccine breakthroughs, an effective AIDS vaccine is still considered years away.

1 vaccine   

n.牛痘苗，疫苗；adj.牛痘的，疫苗的

参考例句：

• The polio vaccine has saved millions of lives.脊髓灰质炎疫苗挽救了数以百万计的生命。
• She takes a vaccine against influenza every fall.她每年秋季接种流感疫苗。

2 vaccines   

疫苗，痘苗( vaccine的名词复数 )

参考例句：

• His team are at the forefront of scientific research into vaccines. 他的小组处于疫苗科研的最前沿。
• The vaccines were kept cool in refrigerators. 疫苗放在冰箱中冷藏。

3 bind   

vt.捆，包扎；装订；约束；使凝固；vi.变硬

参考例句：

• I will let the waiter bind up the parcel for you.我让服务生帮你把包裹包起来。
• He wants a shirt that does not bind him.他要一件不使他觉得过紧的衬衫。

4 statistically   

ad.根据统计数据来看，从统计学的观点来看

参考例句：

• The sample of building permits is larger and therefore, statistically satisfying. 建筑许可数的样本比较大，所以统计数据更令人满意。
• The results of each test would have to be statistically independent. 每次试验的结果在统计上必须是独立的。

5 drawn   

v.拖，拉，拔出；adj.憔悴的，紧张的

参考例句：

• All the characters in the story are drawn from life.故事中的所有人物都取材于生活。
• Her gaze was drawn irresistibly to the scene outside.她的目光禁不住被外面的风景所吸引。

6 membrane   

n.薄膜，膜皮，羊皮纸

参考例句：

• A vibrating membrane in the ear helps to convey sounds to the brain.耳膜的振动帮助声音传送到大脑。
• A plastic membrane serves as selective diffusion barrier.一层塑料薄膜起着选择性渗透屏障的作用。

7 spikes   

n.穗( spike的名词复数 )；跑鞋；（防滑）鞋钉；尖状物v.加烈酒于( spike的第三人称单数 )；偷偷地给某人的饮料加入（更多）酒精（ 或药物）；把尖状物钉入；打乱某人的计划

参考例句：

• a row of iron spikes on a wall 墙头的一排尖铁
• There is a row of spikes on top of the prison wall to prevent the prisoners escaping. 监狱墙头装有一排尖钉，以防犯人逃跑。 来自《简明英汉词典》

8 binding   

有约束力的，有效的，应遵守的

参考例句：

• The contract was not signed and has no binding force. 合同没有签署因而没有约束力。
• Both sides have agreed that the arbitration will be binding. 双方都赞同仲裁具有约束力。

9 initially   

adv.最初，开始

参考例句：

• The ban was initially opposed by the US.这一禁令首先遭到美国的反对。
• Feathers initially developed from insect scales.羽毛最初由昆虫的翅瓣演化而来。

10 apparently   

adv.显然地；表面上，似乎

参考例句：

• An apparently blind alley leads suddenly into an open space.山穷水尽，豁然开朗。
• He was apparently much surprised at the news.他对那个消息显然感到十分惊异。

11 placebos   

n.（给无实际治疗需要者的）安慰剂( placebo的名词复数 )；安慰物；宽心话；（试验药物用的）无效对照剂

参考例句：

• But, eventually, I think they were just kind of like placebos. 但是后来，我想它们只是安慰剂（安慰剂：没有任何药效的药） 来自电影对白
• But comparable numbers of those who received placebos also improved. 但是吃安慰剂的人的病情也改善了。 来自互联网