Developing and validating an in-vitro mycobacterial challenge model to facilitate TB vaccine research and minimise in-vivo challenge experiments

牛结核病目前是英国养殖业面临的最大挑战之一，特别是在英格兰西南部和威尔士。这一流行病的规模迫切需要开发新的工具。接种疫苗是控制任何传染病流行的最有效方法之一。牛和人类结核病疫苗开发中的主要挑战之一是，我们不知道什么类型或水平的免疫反应将具有保护性。这意味着候选疫苗必须在受控的牛分枝杆菌(M.bovis)挑战实验中进行评估，在该实验中，接种的动物被故意感染完全毒力的牛分枝杆菌，并在通过尸检评估保护效果之前跟踪几个月。这些都是缓慢且昂贵的实验，会使大量动物感染牛型支原体。该项目旨在开发两种模型：体外分枝杆菌生长抑制试验(MGIA)和体内卡介苗攻击模型，这两种模型都将取代致病性牛型结核分枝杆菌挑战作为候选结核病疫苗的第一筛选试验。体外MGIA包括在实验室的试管中感染接种疫苗或对照动物的血液或细胞，而不是感染动物本身。卡介苗挑战模式包括用减毒但可复制的卡介苗感染淋巴结内的动物，而不是将毒力强的牛型支原体感染到肺部。这两个互补的模型将用于筛选候选疫苗，只有在这些模型中表现出保护作用的疫苗才会进入使用致病性牛型支原体挑战进行评估的阶段。这项工作将实现三件事。首先，也是重要的一点，它将减少遭受牛分枝杆菌感染的牛的数量，每年至少减少1/3和大约30-50头牛。其次，它将完善和改进牛研究中涉及的程序。第三，它将有助于确定免疫保护相关因素，以完善疫苗设计和开发。最终，如果我们有一个经过验证的保护相关性，就可以在少量牛身上进行简单的免疫原性实验，而不是进行大规模的致病性牛分枝杆菌攻击实验。

Bovine TB is currently one of the greatest challenges that the farming industry faces in the UK especially in the southwest of England and Wales. The scale of this epidemic urgently requires the development of new tools. Vaccination is one of the most effective ways to control any infectious disease epidemic. One of the major challenges in bovine and human TB vaccine development is that we do not know what type or level of immune response will be protective. This means that candidate vaccines have to be evaluated in controlled Mycobacterium bovis (M.bovis) challenge experiments, where vaccinated animals are deliberately infected with fully virulent M.bovis and followed for several months before assessment of protection through post-mortem examination. These are slow and costly experiments which subject large numbers of animals to M.bovis infection. This project aims to develop two models; an in-vitro mycobacterial growth inhibition assay (MGIA) and an in-vivo BCG challenge model, both of which will replace pathogenic M.bovis challenge as a first screening test for candidate TB vaccines. The in-vitro MGIA involves infecting blood or cells from a vaccinated or control animal, in a test tube in the laboratory, rather than having to infect the animal itself. The BCG challenge model involves infecting animals in the lymph nodes with the attenuated but replicating BCG vaccine, rather than infecting animals with virulent M.bovis into the lungs. These two complementary models will be used to screen vaccine candidates, and only vaccines demonstrating a protective effect in these models will be progressed to evaluation using pathogenic M.bovis challenge. This work will achieve three things. Firstly, and importantly, it will reduce the number of cattle undergoing pathogenic M.bovis challenge, by at least 1/3 and approximately 30-50 animals per annum. Secondly it will refine and improve the procedures involved in cattle studies. Thirdly, it will facilitate the identification of immune correlates of protection with which to refine vaccine design and development. Ultimately, if we had a validated correlate of protection, simple immunogenicity experiments on small numbers of cattle could be conducted, rather than large pathogenic M.bovis challenge experiments.