Rapid and Scalable Production of SARS-CoV-2 Spike Protein in Plants for Serological Testing of COVID-19

快速检测人群中的SARS-CoV-2感染者对于抗击当前的COVID 19大流行至关重要。血清学检测被广泛接受为SARS-CoV-2诊断测试的最佳方法;它们可以识别无症状和先前感染的个体，用于接触者追踪，并且在正在进行的疫苗开发中非常重要。目前，包括我们的主要合作伙伴bioLytical Laboratories在内的加拿大公司正在开发血清学检测试剂盒。大规模生产这种检测试剂盒需要具有成本效益和可扩展性的SARS-CoV-2刺突蛋白来源，目前这种来源非常短缺。我们的提案旨在开发一种快速和可扩展的方法，用于在植物中生产这种蛋白质，并与我们的合作伙伴组织合作，以证明其在血清学检测中的适用性。我们将使用本氏烟草（Nicotiana benthamiana）农杆菌渗入法进行快速表达，因为它允许在转化（转染）的一周内在温室生长的植物中产生重组蛋白。该方法已成功用于生产许多其他病毒蛋白，包括SARS冠状病毒的刺突蛋白。我们将首先证明这种方法的总体可行性，然后表达SARS-CoV-2刺突蛋白的几种变体。使用标准亲和方法纯化表达的加标物，并测定纯度。我们的合作组织bioLytical Laboratories将在其SARS-CoV-2血清学检测系统中测试植物产生的刺突蛋白，并将其结合特性与哺乳动物细胞产生的刺突蛋白进行比较。与此同时，我们的第二个合作伙伴组织ImmunoPrecise Antibodies（加拿大）将确定植物产生的刺突蛋白如何与现有的SARS-CoV-2抗体反应。这些实验将确定N.本氏菌产生的刺突蛋白可用作血清学测试试剂盒的基础。这种易于规模化和经济的SARS-CoV-2刺突蛋白来源的可用性将直接影响加拿大生产血清学检测试剂盒的能力，并将成为加拿大应对当前COVID-19大流行的关键因素。

Rapid detection of SARS-CoV-2-infected individuals in the population is essential for combating the current COVID 19 pandemic. Serological assays are widely accepted as the best approach for SARS-CoV-2 diagnostic tests; they can identify non-symptomatic and previously infected individuals, be used for contact tracing, and are important in ongoing vaccine development. Serological testing kits are currently under development by Canadian companies, including our primary partner bioLytical Laboratories. The large-scale production of such testing kits requires a cost-effective and scalable source of the SARS-CoV-2 spike protein, which is currently in very short supply. Our proposal aims to develop a rapid and scalable method for producing this protein in plants, and in collaboration with our partner organizations, to demonstrate its suitability in serological testing assays. We will use the Nicotiana benthamiana agro-infiltration method for rapid expression, as it allows for the production of recombinant protein in greenhouse-grown plants within one week of transformation (transfection). The approach has been successfully used for producing many other viral proteins, including the spike protein from the SARS coronavirus. We will first demonstrate the overall feasibility of this approach, and then express several variants of the SARS-CoV-2 spike protein. Expressed spike will be purified using standard affinity methods and assayed for purity. Our partner organization, bioLytical Laboratories, will then test the plant-produced spike protein in their SARS-CoV-2 serological assays system, and compare its binding properties with those of mammalian cell-produced spike protein. In parallel, our second partner organziation, ImmunoPrecise Antibodies (Canada), will determine how the plant-produced spike protein reacts with available SARS-CoV-2 antibodies. These experiments will determine if N. benthamiana-produced spike protein can be used as a basis for serological test kits. The availability of such an easily scaled and economical source of SARS-CoV-2 spike protein would have a direct impact on Canada's capacity to produce serological testing kits, and would be a critical element in Canada's response to the current COVID-19 pandemic.