Antigenic characterisation of infectious bursal disease virus to improve vaccination strategies and vaccine design

家禽业对于确保不断扩大的人口获得足够的食物至关重要。然而，传染性法氏囊病病毒（IBDV），负责鸡的Gumboro病，被认为是全球关注的行业。这种疾病可能很严重，导致高死亡率和抑制免疫反应，从而加剧其他感染。人们的担忧如此之大，以至于每年都有数十亿只鸡接种IBDV疫苗，并且对新型疫苗进行了大量投资。疫苗通常通过刺激中和抗体的产生来起作用，这些抗体结合病毒并阻止病毒进入宿主细胞。然而，尽管取得了这些进展，仍有许多疫苗接种失败的报告，一些鸡群尽管接种了疫苗，但由于人们知之甚少的原因，仍出现了高死亡率。当疫苗失效时，确定在禽群中传播的病毒序列（野毒株），如果发现突变，通常假定疫苗毒株与野毒株之间的不匹配是导致失败的原因。然而，虽然病毒序列的某些变化会导致疫苗无效，但并非所有突变都是如此，而且疫苗可能失败的原因还有许多其他潜在原因，包括疫苗接种时机不佳或剂量不足。因此，重要的是确定哪些序列变化导致疫苗失效，哪些不会，以便确定在特定区域是否需要更匹配的疫苗。辨别这一点的一种方法是通过所谓的“中和试验”，确定疫苗诱导抗体来中和野毒株的能力。然而，由于IBDV的野外菌株不感染通常使用的细胞，因此没有常规进行中和试验。IBDV的野外菌株感染被称为法氏囊的器官中的细胞。皮尔布赖特研究所的安德鲁·布罗德本特博士已经证明，当细胞从囊中取出并在实验室中存活时，IBDV的野外菌株会感染并在其中复制。他使用这些细胞与IBDV的野株进行中和试验，以量化中和抗体。此外，他的小组还开发了用小分子（GFP11）标记的IBDV菌株。当标签与另一个更大的分子（GFP1-10）相互作用时，它发出绿色荧光。罗斯林研究所海伦·桑教授的研究小组培育出了每个细胞中都含有GFP1-10分子的鸡。这两个小组之间的合作已经表明，这些鸡的细胞在被标记的IBDV感染时发出绿色荧光，这意味着它们可以用于中和试验，以提高其吞吐量。我们的目标是生成一组来自不同地理区域的不同菌株的标记IBDV，并使用含有GFP1-10的法氏囊细胞来确定IBDV疫苗是否交叉中和不同的IBDV菌株。这将有助于确定疫苗失败在多大程度上是由于病毒序列的变化。此外，我们将筛选病毒组，以确定某些菌株是否会诱导交叉中和其他菌株的抗体，我们将确定抗体结合的共同区域，这些区域在不同菌株之间共享。如果我们在交叉中和的毒株之间确定了共同的抗体结合位点，那么就有可能开发出一种更通用的IBDV疫苗，在未来可以预防多种毒株。

The poultry industry is essential to securing enough food for the expanding human population. However, infectious bursal disease virus (IBDV), responsible for Gumboro Disease in chickens, is recognised as a worldwide concern for the industry. The disease can be severe and lead to high death rates and suppressed immune responses that can exacerbate other infections. So great is the concern that every year billions of chickens are vaccinated against IBDV and there has been considerable investment into new types of vaccine. Vaccines typically work by stimulating the production of neutralising antibodies that bind the virus and prevent it from entering the host cells. However, despite these developments, numerous vaccine failures have been reported, with some flocks experiencing high death rates, despite being vaccinated, for reasons that are poorly understood. When a vaccine failure occurs, the sequence of the virus circulating in the flock (field strain) is determined and if there are mutations found, it is often presumed that a mis-match between the vaccine strain and the field strain is responsible for the failure. However, while some changes in the virus sequence will cause a vaccine to be ineffective, this is not the case for every mutation, and there are many other potential reasons why a vaccine may fail, including poor timing of vaccination or inadequate dosing. It is therefore important to determine which sequence changes result in vaccine failures and which do not, in order to determine whether a more matched vaccine is needed in a particular region. One way to discern this is to determine the ability of the vaccine to induce antibodies that neutralise the field strain, in so-called 'neutralisation assays'. However, neutralisation assays are not routinely conducted, as field strains of IBDV do not infect the cells that are typically used.Field strains of IBDV infect cells in an organ known as the bursa of Fabricius. Dr Andrew Broadbent at The Pirbright Institute has shown that when cells are removed from the bursa and kept alive in the laboratory, field strains of IBDV will infect and replicate in them. He has used these cells to conduct neutralisation assays with field strains of IBDV in order to quantify neutralising antibodies. In addition, his group has developed IBDV strains that are tagged with a small molecule (GFP11). When the tag interacts with another, larger molecule (GFP1-10), it fluoresces green. Professor Helen Sang's group at The Roslin Institute has developed chickens that contain the GFP1-10 molecule in every cell. A collaboration between the two groups has already shown that cells from these chickens fluoresce green when infected with the tagged IBDV, meaning they can be used in the neutralisation assay to make it higher throughput. We aim to generate a panel of tagged IBDVs from diverse strains from different geographical areas, and use bursal cells containing GFP1-10 to determine whether IBDV vaccines cross-neutralise different IBDV strains. This will help determine the extent to which vaccine failure is due to changes in the virus sequence. Moreover, we will screen the panel of viruses to determine whether certain strains induce antibodies that cross-neutralise others, and we will identify common regions that the antibodies bind to that are shared between the different strains. If we identify common antibody binding sites between strains that cross-neutralise, then it may be possible to develop a more universal IBDV vaccine that can protect against multiple strains in the future.