Scalable purification of heterologously expressed SARS-CoV-2 proteins in the microalgae Phaeodacytlum tricornutum

新冠肺炎疫情突显了对可靠、准确和廉价的诊断测试的需求，以确定接触新冠肺炎的病原体SARS-CoV-2病毒的程度。特别是，血清学检测可以在个人基础上确定谁接触过SARS-CoV-2病毒，并监测加拿大人口对疫苗接种的免疫反应。开发血清学测试的一个关键要求是需要SARS-CoV-2蛋白(或抗原)与人类抗体发生免疫反应。西安大略大学、兰伯顿学院、森科尔能源公司、Lumivi公司和Pond Technologies公司合作的目标是为三角褐指藻微量新冠肺炎抗原开发一种可扩展的正交蛋白质生产系统，用于诊断和用于SARS-CoV-2病毒的基础科学研究。目前新冠肺炎抗原的蛋白质生产系统价格昂贵，难以规模化以满足人群水平测试的要求，或者无法生产免疫反应形式的抗原。三角褐指藻是一种遗传易驯化的生物，在简单、廉价和明确的介质(主要是海水和阳光)中生长，目前正在大量种植，以收获供人类食用的生物制品。再加上三角褐指藻可以产生被人类免疫系统识别的蛋白质，这些特性使其成为生产新冠肺炎抗原的极佳正交平台。SARS-CoV-2很有可能在未来数年内持续构成威胁，并发生变异。此外，SARS-CoV-2免疫往往不会持久，根除将需要通过血清学检测在全球范围内进行长期接触者追踪和多重接触监测。我们正在提议的三角褐指藻生产系统将快速修改和扩展，以应对这些可能发生的情况，以及其他病毒大流行爆发的出现。

The COVID-19 pandemic has highlighted the need for reliable, accurate and cheap diagnostic tests to determine the extent of exposure to the SARS-CoV-2 virus, the causative agent of COVID-19. In particular, serological testing can identify on an individual basis who has been exposed to the SARS-CoV-2 virus and monitor immunological response to vaccination in the Canadian population. A key requirement in developing serological tests is the need for SARS-CoV-2 protein (or antigen) that is immunologically reactive with human antibodies. The goal of the partnership between The University of Western Ontario, Lambton College, Suncor Energy, Lumivi and Pond Technologies is to develop a scalable orthogonal protein-production system for COVID-19 antigens in the microalage, Phaeodactylum tricornutum, for diagnostic purposes and for use in basic science investigations of the SARS-CoV-2 virus. Current protein production systems for COVID-19 antigen are expensive and difficult to scale to meet the requirements of population-level testing, or cannot produce the antigens in an immunologically reactive form. Phaeodactylum tricornutum is a genetically tractable organism, grows in a simple, cheap and defined media (essentially seawater and sunlight), and is currently cultivated in very large volumes for harvesting of bioproducts for human consumption. Coupled with the finding that Phaeodactylum tricornutum can produce proteins that are recognized by the human immune system, these characteristics make it an excellent orthogonal platform for the production of COVID-19 antigens. There is a good chance that SARS-CoV-2 will be a continual threat for years and that it will mutate. In addition, SARS-CoV-2 immunity tends not to be long-lasting, and eradication will require long-term contact tracing and multiple exposure monitoring worldwide by serological testing. The Phaeodactylum tricornutum production system we are proposing will be rapidly modifiable and scalable to respond to these eventualities, and to the emergence of other viral pandemic outbreaks.