Optimising response to oral yeast-based vaccines against coccidiosis in chickens

人类饲养的家禽比以往任何时候都多，人们越来越依赖禽肉和禽蛋来提供供人类食用的膳食蛋白质。与此同时，我们正试图减少对控制病原体的药物的常规依赖，用疫苗或其他策略取而代之。这样的疫苗应该是耐热的，而不是依赖于持续的冷链。不幸的是，许多病原体没有可扩展和成本效益高的疫苗，例如引起鸡球虫病的艾美耳球虫。我们和其他人最近估计，球虫病每年给英国家禽业造成约1亿GB的损失，全球超过100亿GB。英国畜牧业生产中使用的大约40%的药物需要控制这些寄生虫。活疫苗是可用的，但对生产商来说，成本要高出四倍，而且不能以足够的规模生产以取代药物。它们能够进行一些复杂的蛋白质修饰，这是许多其他表达系统无法实现的，并且很容易培养到非常高的密度，产生大量稳定的颗粒。利用酿酒酵母作为癌症、病毒和细菌疫苗的递送载体的想法已经被探索，诱导强大的体液和细胞免疫反应。最近，我们开发了一种酵母递送平台，在该平台中，来自艾美耳球虫的抗原可以以稳定的、非分泌的形式表达，酵母本身作为运输系统和佐剂。我们已经测试了这种酵母来接种一种形式的球虫病，在对鸡进行低水平攻击后，诱导控制寄生虫复制，达到比使用其他疫苗递送系统更好的水平。在这里，我们建议开发酵母递送系统，以提高对高水平挑战的保护，并扩大其范围，以防止另外两种形式的球虫病。这三种疾病加在一起，在欧洲、北美和南美洲、亚洲和非洲造成了绝大多数球虫病负担。这些新疫苗的效力将在商业条件下进行测试，从农场水平的表现和鸡只的福利(免于疾病)来评估价值。重要的是，疫苗接种前酵母细胞的热灭活意味着疫苗在分发或注射时不被归类为转基因生物，因此不受转基因生物监管。另外使用冷冻干燥来保存热灭活的酵母，消除了对冷链的需求，降低了运输和储存成本。我们将表征疫苗接种和寄生虫攻击后诱导的免疫反应，以评估灭活酵母方法在接种家禽其他重要病原体方面的可能效用。以酿酒酵母为基础的疫苗可能对家禽疾病特别有价值，因为在这些疾病中，安全性、可扩展性、稳定性、递送和成本至关重要。

Humankind is farming more poultry than ever before, with an increasing reliance on poultry meat and eggs for provision of dietary protein for human consumption. Concurrently, we are attempting to reduce routine reliance on drugs to control pathogens, replacing them with vaccines or other strategies. For species such as chickens, these vaccines have to be cheap, reliable, easy to administer and (ideally) use existing distribution pathways in such a way that they are accessible to industry as well as backyard farmers in low- and medium-income countries. Such vaccines should be thermostable and not rely on a constant cool-chain. Unfortunately, scalable and cost-effective vaccines are not available for many pathogens such as Eimeria, cause of the disease coccidiosis in chickens. We and others have recently estimated that coccidiosis costs the UK poultry industry ~£100 million every year, exceeding £10 billion globally. Approximately 40% of the drugs used in British livestock production are required to control these parasites. Live vaccines are available, but represent a four-fold higher cost to the producer and cannot be produced at sufficient scale to replace drugs. A robust, cost-effective alternative is required.Yeast species such as Saccharomyces cerevisiae are useful tools for the high yield production of recombinant proteins and have a Generally Regarded As Safe (GRAS) status (e.g. United States Food and Drug Agency). They are capable of performing several complex protein modifications that are not achieved in many other expression systems, and are easily grown to very high densities producing large quantities of stable particles. The idea of using S. cerevisiae as a delivery vehicle for cancer, viral, and bacterial vaccines has been explored, inducing robust humoral and cellular immune responses. Recently, we have developed a yeast-delivery platform in which antigens from Eimeria can be expressed in a stable, non-secreted form, with the yeast itself acting as transport system and adjuvant. We have tested this yeast to vaccinate against one form of coccidiosis, inducing control of parasite replication following low-level challenge of chickens at levels better than achieved using other vaccine delivery systems. Here, we propose to develop the yeast delivery system to improve protection against high-level challenge and expand its range to protect against two additional forms of coccidiosis. Combined, these three forms of disease cause the overwhelming majority of the burden of coccidiosis in Europe, North and South America, Asia and Africa. The efficacy of these new vaccines will be tested under commercial conditions, assessing value in terms of farm-level performance and chicken welfare (freedom from disease).Importantly, heat inactivation of the yeast cells prior to vaccination means that the vaccine is not categorised as a genetically modified organism (GMO) at the time of distribution or administration, and would therefore not be subject to GMO regulations. Additional use of freeze-drying to preserve the heat-killed yeast removes the requirement for a cold chain, reducing transport and storage costs. We will characterise immune responses induced following vaccination and parasite challenge to assess the likely utility of the killed-yeast approach to vaccinate against other important pathogens of poultry. Vaccines based upon S. cerevisiae are likely to be particularly valuable against diseases of farmed poultry, where safety, scalability, stability, delivery and cost are crucial.