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snowinheart银虫 (正式写手)
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Vaccination against AIV in poultry can play an important role in reducing virus shedding and raising the threshold for infection and transmission. It is believed that vaccination with a high-quality vaccine against AIV can be part of an effective control program. In conjunction with culling, quarantine, improved serological surveillance, and high biosecurity, the control of outbreaks of HPAI in poultry, as well as the prevention of transmission of HPAI to humans, is possible. Because the vaccination of poultry with live vaccines against NDV is mandatory in many countries (19), the development of bivalent vaccines should be made a priority. Such vaccines would reduce the burden of vaccine production and administration in comparison with individual vaccination. For these reasons, we have focused on the development of live bivalent viruses that show potential as vaccines against the major economic pathogens AIV and NDV. First, by reverse genetics, we produced an influenza virus (VN HN) that expresses the ectodomain of the NDV HN protein in place of the influenza virus NA. The HN of NDV has been shown to be the major antigen eliciting a protective immune response in chickens (14, 15). We reasoned that the HN protein would confer protection against NDV and provide the necessary NA activity in the absence of the endogenousNAprotein. TheVNHNvirus grew efficiently in embryonated chicken eggs and stably expressed the cHN segment, both of which characteristics are fundamental requirements for a successful vaccine. However, preliminary experiments using VNHN to vaccinate 2-week-old White Leghorn chickens revealed that this virus is possibly too attenuated in vivo to induce a highly protective immune response in chickens (data not shown). Experiments are needed to examine the ability of VNHN to induce a protective response after immunization of chick embryos in ovo. Such an approach requires a more highly attenuated vaccine strain than that used for vaccination of hatched chickens. Next, we chose NDV as a bivalent vaccine vector because it possesses several properties that make it suitable for use in viral vaccine development. The RNA genome of the virus does not integrate into host cell DNA. Furthermore, the rNDV vector can stably incorporate an inserted foreign gene over multiple passages and, because it is a respiratory virus, it can provide a convenient platformfor rapid, efficient, and economical mass immunization of poultry. These benefits are multiplied in the case of a multivalent vaccine; one immunization can lead to protection from two or more pathogens. Whereas simultaneous vaccination with multiple live attenuated viruses may lead to complications if the presence of one virus interferes with the growth or immunogenicity of another, such problems are circumvented entirely by the use of a single bivalent virus vaccine. Thus we propose that, by using recently developed reverse genetics techniques (20, 21), it is possible to develop a new generation of effective, economical, and convenient bivalent live attenuated vaccines. An outbreak of HPAI H7N7 in The Netherlands in 2003, in which 30 million chickens were slaughtered, involved the transmission of H7N7 to 89 persons and led to the death of a veterinarian. In addition, an HPAI H7N3 virus emerged in Canada in 2004 that also transmitted to humans (2, 3). Accordingly, in the present study we produced rNDV that expressed the H7 HA protein, with the intention of protecting poultry from HPAI H7 and NDV, and showed its efficacy in chickens. We suggest that the HAs from genetic variants of HPAI H5N1 or HPAI H7N7 viruses, as well as from other potential pandemic strains such as H9N2, could be inserted into the rNDV fusogenic vector to develop bivalent vaccines against theseAIVstrains andNDV.In addition, the rNDV vector can potentially harbor two different subtypes of HA as extra transcriptional units, opening the possibility for the development of bivalent vaccines that protect poultry against multiple HPAI strains. |
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zap65535
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2楼2010-01-02 22:53:43
mirror5582
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zap65535(金币+5,VIP+0):助人为乐，再接再厉还有大奖，详见版规。 1-3 12:20
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zap65535(金币+5,VIP+0):助人为乐，再接再厉还有大奖，详见版规。 1-3 12:20
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为家禽接种抗AIV的疫苗对于减少病毒脱落以及提高感染和传染阈值具有重要作用。接种高质量的抗AIV疫苗是一种控制感染的有效方法。结合筛选、检疫、改良血清学监视以及高生物安全性有可能控制家禽HPAI的暴发以及预防HPAI传播至人类。由于在许多国家（19）已经强制性的为家禽接种抗NDV的活疫苗，因此必须优先研制二价疫苗。这种疫苗与个体免疫相比能够减少疫苗生产及给药时的负荷。由于这些原因，我们将集中精力研发具有潜在优势的二价活疫苗以对抗主要常见的AIV和NDV病菌。 首先，通过反向遗传学，我们生产了一种流感病毒（VNHN）用于表达NDV的HN蛋白的外功能区，以替代流感病毒NA。已表明NDV的HV是鸡雏中诱发保护性免疫应答的主要抗原（14，15）。我们有充分的证据说明在内源NA蛋白缺失的时候，HN蛋白能够发挥保护作用以对抗NDV，并且提供必要的NA活性。VNHN病毒在鸡胚中有效生长并稳定的表达其cHN片段，这两个特征是成功获得疫苗的基本要求。但是，通过在预实验中使用VNHN接种2周龄的白来杭鸡结果显示，该病毒可能由于在鸡雏体内过于衰减而不能够诱导高保护性的免疫应答（未展示结果）。应该在鸡胚接种后通过实验检查VNHN是否有能力诱发保护性应答。该方法需要一种衰减度高于鸡胚接种疫苗的疫苗株。 其次，我们选择NDV作为二价疫苗载体是由于其自身的几种特征使其适用于病毒疫苗的研制。该病毒的RNA染色体组不能完整的侵入宿主细胞DNA。此外，rNDV载体能够稳定的跨过多重通道去结合植入的外源基因，且由于它是一种呼吸道病毒，能够为快速、有效和经济的家禽群体免疫提供一种便利的平台。多价疫苗的的益处也是多重的，一次接种就可以保护家禽免受两种或多种病菌的感染。反之，如果一种病毒会干扰另一种病毒的生长或免疫原性，那么同时接种多种减毒活疫苗就可能会导致一些并发症，通过单纯使用二价病毒疫苗就绕过了这个问题。因此我们预计采用近年来发展起来的反向遗传学技术（20，21）可能会研制出一种新一代的有效、经济且便利的二价减毒活疫苗。 2003年，HPAI H7N7在荷兰暴发， 屠杀了30,000,000鸡雏，传染l89个人，还导致一名兽医死亡。此外在2004年，HPAI H7N3病毒在加拿大出现，也传播到了人类（2，3）。据此，在本研究中我们生产的能够表达H7HA蛋白的rNDV，可以保护家禽免受HPAI和NDV的感染，并在鸡雏中显示了其有效性。我们的结果说明，rNDV融合载体能够植入HPAI H5N1或HPAI H7N7的遗传性变型以及其他可能广泛流行的菌株，如H9N2。此外，rNDV载体有可能包含两种不同的HA亚型作为额外的转录单位，使得研制的二价疫苗有可能保护家禽免受多种HPAI菌株感染。 [ Last edited by mirror5582 on 2010-1-3 at 11:22 ] |
3楼2010-01-03 10:27:44
snowinheart
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4楼2010-01-04 17:37:13
