Using synthetic biology to generate novel vaccines against avian infectious bronchitis virus (IBV)

鸡在一生中多次接种家禽病原体疫苗，以预防不同的疾病。传染性支气管炎病毒（IBV）导致鸡的呼吸道疾病，使它们更容易受到细菌感染。除此之外，感染IBV的鸡体重增加较少，产优质鸡蛋较少。接种IBV疫苗对于福利和经济原因都很重要。现有的针对IBV的疫苗存在许多问题。有许多不同的IBV毒株在地球仪中传播，然而目前可用的疫苗不能针对所有毒株进行交叉保护。新的疫苗是通过在鸡蛋中多次培养IBV强毒株来生产的。这降低了疫苗株对鸡的致病性，但增加了疫苗株对鸡胚的致病性。针对IBV的疫苗通过用疫苗喷洒家禽群或通过将疫苗置于饮用水中来施用。由于很难保证每只鸡都接种了相同剂量的疫苗，导致疫苗的免疫效果较差。这些菌株不适合在鸡蛋中生长，因此对鸡胚的致病性较低。本研究拟通过对3株IBV弱毒株的安全性、稳定性和有效性进行检测，以确定IBV弱毒株是否可作为疫苗使用。这些新型疫苗有可能在小鸡仍在蛋中发育时给予小鸡，从而保护小鸡即使在孵化之前也免受IBV感染。这将保证每只鸡只接种相同剂量的疫苗，并减少疫苗失效的可能性，这对家禽业非常有利。更安全和更有效的IBV疫苗将减少用于治疗IBV感染引起的继发性细菌感染的鸡的抗生素用量。抗生素在农业中的大量使用可能会导致细菌对抗生素的耐药性，这是一个潜在的破坏性问题。研究的第二部分提出使用分子工具将来自不同IBV毒株的表面蛋白-刺突插入其中一种新型疫苗毒株。刺突是病毒外部的主要结构，鸡产生抗体。它在不同的IBV毒株之间是高度可变的，因此针对一种IBV毒株产生的抗体可能不会对新的IBV毒株产生交叉保护。最具经济破坏性的IBV毒株之一的刺突将被插入疫苗株中。我们将评估用这些重组病毒接种疫苗是否能够防止含有相同加标物或不同加标物的致病性病毒的攻毒。我们将确定这两种含有不同刺突的病毒是否能够在鸡蛋中相互竞争生长。这将研究用两种病毒接种鸡蛋的可能性;在一次剂量中保护两种或更多种重要的IBV毒株。本研究的总体目标是利用合成生物学产生新一代更安全，更有效的疫苗来对抗重要的家禽病原体传染性支气管炎病毒。

Chickens are vaccinated multiple times against poultry pathogens throughout their lives to protect against different diseases. Infectious bronchitis virus (IBV) causes a respiratory disease in chickens making them more susceptible to bacterial infections. In addition to this, chickens infected with IBV gain less weight and produce fewer high quality eggs. It is important to vaccinate against IBV both for welfare and economic reasons. There are a number of problems with the vaccines available against IBV. There are many different strains of IBV circulating around the globe however currently available vaccines do not cross-protect against all strains. New vaccines are produced by growing a virulent strain of IBV in hen's eggs multiple times. This reduces the pathogenicity of the vaccine strain when it is given to chickens but it increases the pathogenicity of the vaccine strain for chicken embryos. Vaccines against IBV are administered by spraying poultry flocks with the vaccine or by putting the vaccine in the drinking water. It is hard to guarantee that each chicken has received the same dose, which make the vaccines less effective.We have rationally attenuated three strains of IBV using molecular tools. These strains have not been adapted to grow in eggs so are less pathogenic for chicken embryos. This study proposes to establish whether the rationally attenuated strains of IBV could be used as vaccines, by testing the safety, stability and efficacy of all three potential vaccine strains. These novel vaccines have the potential to be given to chicks while they are still developing in the egg so that the chicks are protected against IBV infection even before they hatch. This would guarantee that each chick received the same dose of vaccine and reduce the possibility of vaccine breakdown, which would be very beneficial to the poultry industry. Safer and more efficacious vaccines against IBV will reduce the amount of antibiotics given to chickens to treat secondary bacterial infections resulting from IBV infection. The prolific use of antibiotics in farming may contribute to the development of antibiotic resistance in bacteria, a potentially devastating problem.The second part of the study proposes to use molecular tools to insert the surface protein, the spike, from a different strain of IBV into one of the novel vaccine strains. The spike is the major structure on the outside of the virus that chickens develop antibodies against. It is highly variable between different strains of IBV so antibodies produced against one strain of IBV may not cross-protect against a new strain of IBV. The spike of one of the most economically damaging strains of IBV will be inserted into a vaccine strain. We will assess whether vaccinating with these recombinant viruses is able to protect against challenge with pathogenic virus containing the same spike or with a different spike. We will establish whether the two viruses containing different spikes are able to grow in competition with each other in eggs. This will investigate the potential to vaccinate eggs with both viruses; protecting against two or more important strains of IBV in a single dose.The overall aim of this study is to use synthetic biology to generate a new generation of safer, more efficacious vaccines against the important poultry pathogen, infectious bronchitis virus.