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，越来越依赖禽肉和禽蛋为人类消费提供膳食蛋白质。与此同时，我们正在努力减少对控制病原体的药物的例行依赖，代之以疫苗或其他战略。对于鸡等物种，这些疫苗必须便宜、可靠、易于管理，并且（理想情况下）使用现有的分销途径，使工业以及低收入和中等收入国家的后院农民都能获得。这种疫苗应该是热稳定的，不依赖于恒定的冷却链。不幸的是，对于许多病原体，如引起鸡球虫病的艾美耳球虫，没有可扩展的和具有成本效益的疫苗。我们和其他人最近估计，球虫病每年使英国家禽业损失约1亿英镑，全球超过100亿英镑。英国畜牧业生产中使用的药物中约有40%用于控制这些寄生虫。活疫苗是可以得到的，但对生产者来说，成本要高出四倍，而且不能以足够的规模生产，以取代药物。酵母菌种（如酿酒酵母（Saccharomyces cerevisiae））是重组蛋白高产生产的有用工具，并且具有一般公认安全（GRAS）状态（例如美国食品和药物管理局）。它们能够进行在许多其他表达系统中无法实现的几种复杂的蛋白质修饰，并且容易生长到非常高的密度，产生大量稳定的颗粒。利用S.已经探索了作为癌症、病毒和细菌疫苗的递送载体的酿酒酵母，其诱导了强有力的体液和细胞免疫应答。最近，我们开发了一种酵母递送平台，其中来自艾美耳球虫的抗原可以以稳定的非分泌形式表达，酵母本身充当转运系统和佐剂。我们已经测试了这种酵母接种一种形式的球虫病，诱导控制寄生虫复制低水平的挑战后，鸡的水平比使用其他疫苗输送系统。在这里，我们建议开发酵母输送系统，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。这三种形式的疾病加在一起，造成了欧洲、北美和南美、亚洲和非洲绝大多数球虫病的负担。这些新疫苗的有效性将在商业条件下进行测试，评估农场水平性能和鸡福利（免于疾病）方面的价值。重要的是，接种前对酵母细胞进行热灭活意味着疫苗在分销或管理时不被归类为转基因生物（GMO），因此不受GMO法规的约束。额外使用冷冻干燥来保存热灭活的酵母，消除了对冷链的要求，降低了运输和储存成本。我们将研究疫苗接种和寄生虫攻击后诱导的免疫应答，以评估灭活酵母方法对家禽其他重要病原体的疫苗接种的可能效用。基于S.酿酒酵母可能对养殖家禽的疾病特别有价值，其中安全性、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.