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An Infectious cDNA Clone of SARS-CoV-2

Authors: Xie X. et al Link to paper: https://www.sciencedirect.com/science/article/pii/S1931312820302316

Journal/ Pre-Print: Cell Host and Microbe

Key Words: recombinant virus, reporter virus, reverse genetic system, tool for drug screening, tool for viral and immunological studies

Research Highlights

1. First to describe an infectious molecular clone of SARS-CoV2

2. Developed a stable fluorescent reporter virus to be used by the wider scientific community as an experimental model

3. Give an example of how this new tool can be used for drug screening by confirming that SARS-CoV2 replication is sensitive to IFNa treatment

Summary 

An in vitro study describing the first infectious molecular clone of SARS-CoV2 (ic-SARS-CoV2). From a full-genome cDNA, in-vitro transcribed RNA electroporated into cells produces an infectious virus with high titres (2.9x106 PFU/mL) directly from transfection. ic-SARS-CoV2 shows similar characteristics to the original clinical isolate: similar plaque, equivalent replication kinetics and stable genome sequence. Additionally, cloning of mNeonGreen gene into ORF7 region generated a stable reporter virus (ic-SARS-CoV2-mNG) useful for long-term studies. The reporter virus displayed similar characteristics as the ic-SARS-CoV2. Furthermore, ic-SARS-CoV2-mNG replication displayed sensitivity to IFNa treatment. Together, these tools are beneficial for drug screening assays and to study SARS-CoV2.

Impact for SARS-CoV2/COVID19 research efforts

 The highlight of the study is the development of an essential tool that can be used for drug screening and to understand the virology and cell biology of and the immune response to SARS-CoV2

Study Type

· In vitro study

Strengths and limitations of the paper

Novelty: Design of the first infectious molecular clone and the first reporter virus to study SARS-CoV2.

Standing in the field: The authors show that ic-SARS-CoV2-mNG reporter virus is sensitive to Type I interferon treatment. This is consistent with a previously published study using clinical isolates (Lokugamage et al., 2020) and suggests that this new tool can indeed be used to screen drugs for treatment of COVID19.

Appropriate statistics:Yes

Viral model used: infectious molecular clone derived from the SARS-CoV2 clinical isolate 2019-nCoV/USA_WA1/2020

Translatability: No translational potential but can be used to screen drugs and to study immune responses elicited by vaccine candidates

Main limitations: The developed reporter virus has only been shown to infect Vero-E6 cells, a non-human primate kidney epithelial cell line. Although these cells are commonly used to study viruses in vitro, it would have been interesting to show the replication kinetics and antiviral inhibition in another cell type eg. In human lung epithelial cells