美國研究人員３１日報告說，他們新開發(fā)出了一種抗非典實驗疫苗,。這種疫苗能有效阻止非典病毒在老鼠體內(nèi)復制,，其開發(fā)為最終研制出適用于人體的非典疫苗“邁出了關(guān)鍵一步”,。
美國研究人員３１日報告說,，他們新開發(fā)出的一種疫苗在實驗中有效地阻止了非典病毒在鼠體內(nèi)復制。這一研究結(jié)果發(fā)表在４月１日正式出版的英國《自然》雜志上,。
美國國家過敏和傳染病研究所內(nèi)貝爾博士領(lǐng)導的小組,，以編碼非典病毒表面一種外殼蛋白的ＤＮＡ片段為基礎開發(fā)出這種疫苗。這一片段本身不會引發(fā)感染,，但能夠刺激機體產(chǎn)生針對非典病毒的保護性免疫反應,。研究人員還對疫苗中采用的ＤＮＡ片段進行了修改，使其與病毒原始基因序列有所差別,，以最大程度降低這種ＤＮＡ片段與非典病毒或其他冠狀病毒遺傳材料發(fā)生重組的危險,。
研究人員用兩種不同形式的疫苗對總共１０只鼠進行了實驗，兩種疫苗中的ＤＮＡ在構(gòu)成上略有區(qū)別,，實驗中還選取了５只接種了無效疫苗的鼠作為對照組,，所有這些鼠在３０天后分別接觸非典病毒。分析結(jié)果發(fā)現(xiàn),，對照組中的實驗鼠肺部存在大量非典病毒,，而接種了兩種疫苗的鼠肺部非典病毒水平分別都只有對照組的百萬分之一左右，幾乎可以忽略不計,。
內(nèi)貝爾在一份新聞公報中說,，新實驗結(jié)果是朝開發(fā)出對人體有效的非典疫苗邁出的關(guān)鍵一步,。研究人員正在與位于美國加利福尼亞州的生物技術(shù)公司“Ｖｉｃａｌ”合作,，制造可用于人體臨床試驗的高純化疫苗,。目前，疫苗的人體臨床試驗尚有待美國食品和藥物管理局批準,。
一些未參與該項研究的專家指出,，新疫苗的實驗結(jié)果雖然令人鼓舞，但也不能過分夸大,。采用ＤＮＡ片段開發(fā)疫苗是一種較新的思路,，此前科學家曾利用這種辦法開發(fā)出一些針對其他病毒的疫苗，并在實驗中刺激動物產(chǎn)生免疫反應,，但迄今還沒有一種ＤＮＡ疫苗真正證明對人體有效,。另外，目前用于研究非典病毒的動物模型有一定局限性,，針對非典的ＤＮＡ疫苗在投入人體臨床試驗前尚有很多研究工作要做,。
SARS vaccine works well in mice
An experimental vaccine developed by federal researchers prevented the SARS (severe acute respiratory syndrome) coronavirus from reproducing in laboratory mice, according to a report published in the Apr 1 issue of Nature.
Gary J. Nabel（http://www.niaid.nih.gov/vrc/labs_nabel.htm,） of the National Institute of Allergy and Infectious Diseases (NIAID), one of the authors of the study, called the vaccine "a critical first step towards developing an effective human SARS vaccine." Nabel was quoted in a news release from the National Institutes of Health, of which NIAID is a part.
The NIAID noted that most vaccines use killed or weakened forms of a whole virus or bacteria. But the new vaccine contains a fragment of SARS virus DNA that codes for a protein on the outer surface of the virus, the agency said. The protein helps the virus enter host cells. Because the DNA in the vaccine codes only for the protein, it can’t cause infection by itself.
The investigators tested two versions of the vaccine in mice, the NIAID said. The two differed in how much genetic material was removed from the original piece of DNA. Two groups of five mice received three doses of one or the other form of the vaccine over 6 weeks. A control group of five mice received an inactive vaccine.
Thirty days later, all the mice were exposed to the SARS virus, the NIAID said. "After two days, the mice in the control group had very high levels of SARS virus in their lungs. The vaccinated mice had nearly negligible levels of SARS virus in their lungs." The controls had a million times as many virus particles as the vaccinated mice, the agency said.
The vaccine caused the mice to generate both antibodies and specialized T cells to defend against the SARS virus, the NIAID reported. But the researchers found that the antibodies alone caused the dramatic reduction in virus in the vaccinated mice.
NIAID Directory Anthony S. Fauci, MD, noted that the SARS coronavirus was identified only a year ago. "This [vaccine] research was done in a remarkably short period of time, a testament to the serious attention and great cooperation the public health community has displayed in response to SARS," he said in the news release.
In their report in Nature, the authors of the study say that DNA vaccines have proved successful in various animal experiments with several infectious diseases. But they add, "This approach has only recently been used in human studies, and its potential to protect against human diseases has yet to be established." In addition, mice are an imperfect model for SARS infections in humans. (Another recent NIAID study showed that unvaccinated mice could be infected with the SARS virus, but they developed antibodies that blocked viral replication.)
Consequently, the report says, it will be important to test whether the experimental SARS vaccine generates an immune response in humans. If the response is unsatisfactory, it could be augmented by using inactivated viral vaccine candidates or other techniques, the researchers say.
The NIAID’s DNA vaccine is one of several potential SARS vaccines under development. For example, Chinese health officials announced in January that they would launch the first human trial of a SARS vaccine developed in China. Also in January, it was reported that the University of British Columbia had developed three candidate SARS vaccines, which were to be tested in animals at the Southern Research Institute in Birmingham, Ala.
Yang Z, Kong W, Huang Y, et al. A DNA vaccine induces SARS coronavirus neutralization and protective immunity in mice. Nature 2004(1 Apr);428:561-4 [Abstract]http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v428/n6982/abs/nature02463_fs.html
