SARS-CoV-2 assay using plant protein

South African researchers have developed a serological assay to easily detect antibodies to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) using recombinant viral proteins produced in plants ..

This assay allows the detection of antibodies against the SARS-CoV-2 antigen Spike protein Is expressed as Nicotiana Bensamiana Plants-commonly known as “vents” or “venties”, tobacco and its relatives Nicotiana Native to Australia. Benthamiana It is also a common plant used for “farming” monoclonal antibodies and other recombinant proteins.

Nicotiana Ben Samiana. Image credit: Hanjo Hellmann / Shutterstock

The spike protein is a membrane structure used by SARS-CoV-2 to bind to the human host cell receptor angiotensin converting enzyme 2 (ACE2) and gain viral entry.

The indirect enzyme-linked immunosorbent assay (ELISA) developed here was able to reliably detect antibodies to some of this spike protein in samples taken from patients previously infected with SARS-CoV-2.

Serological assays using such plant-based expression systems provide a convenient and cost-effective tool for measuring serum prevalence and protective immunity to SARS-CoV-2 in resource-poor settings. It’s possible, says Wendy Burgers (University of Cape Town, South Africa) and colleagues.

A preprinted version of the paper is available on the server medRxiv*, Articles undergo peer review.

Serological testing is urgently needed to track pandemic epidemics

The COVID-19 pandemic caused by SARS-CoV-2 has rapidly swept the world since it started in Wuhan, China at the end of last year. Today, the virus infects more than 18.65 million people and causes more than 703,000 deaths, continuing to pose a significant threat to global health and socio-economics.

“The development of serological tests to detect SARS-CoV-2 antibodies is very important,” Burgers and his team wrote. “All population serological studies to estimate the extent of pandemic spread in the community, and studies defining protective immunity to SARS-CoV-2, rely on reliable serology.”

Ideally, these tests should be cost-effective, so the team can apply them in a low-income environment.

Production of recombinant viral proteins

The purified recombinant proteins required for serological assays can be produced using a variety of different protein expression systems, including bacterial, mammalian, yeast, insect, and plant-based systems.

Plant-based systems have several advantages over the more widely used traditional mammalian and insect-based systems. In particular, it is fast, cost-effective and especially desirable in low-income environments because it does not require expensive media or growth conditions. They also outperform bacterial or yeast-based systems because they support post-translational modifications similar to those in mammalian cell systems.

Historically, the main drawback associated with plant-based protein expression systems has been low yields, but advances in plant technology have helped overcome this challenge.

The author says Nicotiana Bensamiana It is recommended as a protein expression system because of its rapid production of biomass, defects in post-transcriptional gene silencing systems, and a wide range of engineering strategies that help overcome low yield issues.

In the new ELISA assay, Nicotiana Bensamiana

The S1 subunit of the viral spike protein is highly immunogenic and its RBD portion is Neutralizing antibody After infection, these spiked protein antigens have become an important focus for many serological studies.

Burgers and colleagues are currently developing an indirect ELISA assay using Spike S1 to test the RBD antigen of SARS-CoV-2. Nicotiana Bensamiana..

The team collected serum samples from 77 South African convalescent patients previously infected with SARS-CoV-2. This was confirmed by the polymerase chain reaction (PCR) test. Samples were taken at a median of 6 weeks post diagnosis, with most patients experiencing mild to moderate COVID-19.

Virus-specific antibody was easily detected

Using a newly developed ELISA with plant-derived viral antigens, researchers have shown that SARS-CoV-2 specific immunoglobulins (Igs) can be easily detected in samples.

Of 77 participants, S1-specific IgG reactivity was detected in 51 cases (66%) and RBD-specific IgG reactivity was detected in 48 cases (62%).

In particular, the team said the results were in good agreement with validated and sensitive commercial ELISA assays.

“Robust detection of SARS-CoV-2 specific antibodies”

“Our study shows that recombinant SARS-CoV-2 proteins produced in plants enable powerful detection of SARS-CoV-2 specific antibodies,” Burgers and colleagues write. I am.

The authors state that one of the main goals was to develop a cost-effective assay that could be used for both large-scale seroepidemiological and SARS-CoV-2 humoral immunity studies.

“We achieve this by utilizing the plant for the production of viral antigens with the advantage of rapid scale-up, and source locally available and therefore low cost available reagents.” They write.

“Serologic studies in an environment like ours in South Africa, where co-morbidities such as HIV and tuberculosis are very prevalent, have not been well investigated and could benefit from this assay.” Concludes the team.

*Important Notices

medRxiv It publishes preliminary, non-peer reviewed scientific reports and should not be considered conclusive and should not guide clinical practice/health-related behaviors or be treated as established information.