Production of Pseudotyped Particles to Study Highly Pathogenic Coronaviruses in a Biosafety Level 2 Setting
March 1st, 2019
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Here, we present a protocol to generate pseudotyped particles in a BSL-2 setting incorporating the spike protein of the highly pathogenic viruses Middle East respiratory syndrome and severe acute respiratory syndrome coronaviruses. These pseudotyped particles contain a luciferase reporter gene allowing quantification of virus entry into target host cells.
Overview
This protocol outlines the generation of pseudotyped particles incorporating spike proteins from MERS and SARS coronaviruses in a BSL-2 environment. These particles enable the study of viral entry into host cells using a luciferase reporter gene for quantification.
Key Study Components
Area of Science
- Virology
- Cell Biology
- Infectious Diseases
Background
- Pseudotyped viruses are safer models for studying pathogenic viruses.
- The technique allows for the examination of viral entry mechanisms.
- HEK293T cells are commonly used for transfection and virus production.
- Monitoring cell health is crucial for successful transfection and infection.
Purpose of Study
- To develop a safe method for studying viral entry of MERS and SARS.
- To quantify the infectivity of pseudotyped particles.
- To assess receptor usage in pseudovirions.
Methods Used
- Transfection of HEK293T cells with plasmids encoding viral proteins.
- Collection and purification of pseudotyped particles.
- Infection of target cells with pseudotyped particles.
- Measurement of luciferase activity to quantify infectivity.
Main Results
- Pseudotyped particles exhibited strong infectivity in target cells.
- Luciferase assays demonstrated a concentration-dependent response.
- Receptor usage was confirmed to be similar to that of native viruses.
- Western blot assays indicated successful incorporation of spike proteins.
Conclusions
- The developed protocol provides a reliable method for studying viral entry.
- Pseudotyped particles serve as effective surrogates for pathogenic viruses.
- This approach can be adapted for other viruses beyond coronaviruses.
Frequently Asked Questions
What are pseudotyped particles?
Pseudotyped particles are virus-like particles that incorporate specific viral proteins, allowing for the study of viral entry without the risk of infection.
Why is monitoring cell health important?
Cell health affects transfection efficiency and the subsequent ability of pseudotyped particles to infect target cells.
What is the role of luciferase in this study?
Luciferase serves as a reporter gene to quantify the infectivity of pseudotyped particles by measuring luminescence.
Can this method be used for other viruses?
Yes, the protocol can be adapted to study other viruses by using different spike proteins.
What cell line is used in this protocol?
HEK293T cells are used for the generation of pseudotyped particles.
How are pseudotyped particles collected?
They are collected from the supernatant of transfected cells and purified through centrifugation and filtration.
Executive Industry Relevance
This protocol enables biopharma R&D teams to study viral entry mechanisms of highly pathogenic coronaviruses under BSL-2 conditions, reducing containment barriers while maintaining biological relevance. By using pseudotyped particles with luciferase readouts, organizations can efficiently evaluate host susceptibility, tropism, and inhibitor effects in early discovery workflows. The approach supports mechanistic de-risking of entry-targeted therapeutics before committing resources to higher-risk models.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of coronavirus spike protein-mediated entry pathways using surrogate particles that mimic native virion behavior.
- Operational Value: Allows screening of receptor usage and entry inhibitors in standard BSL-2 facilities without requiring BSL-3 access.
Screening & Assay Development
- Scientific Value: Provides a quantitative luciferase-based readout to measure infectivity and assess concentration-dependent inhibition of viral entry.
- Operational Value: Supports high-throughput compatible workflows for pseudotype production, purification, and infection using HEK-293T cells.
Translational & Preclinical Research
- Scientific Value: Facilitates assessment of host cell susceptibility and tropism by pseudotyped particles bearing MERS-CoV or SARS-CoV spike proteins.
- Operational Value: Enables cross-functional collaboration between virology, assay development, and pharmacology teams using standardized pseudotype panels.
Pipeline & Workflow Integration
The method fits within the early discovery continuum, supporting target validation through mechanistic interrogation of viral entry prior to lead identification efforts.
- Discovery Biology: Supports hypothesis testing of spike protein function and receptor engagement using pseudotyped surrogates.
- Screening: Enables production of standardized, quantifiable pseudotyped particles for consistent compound screening against viral entry.
- Analytics: Generates luciferase-based luminescence readouts that allow quantitative comparison of infectivity across conditions and inhibitor treatments.
- Translational Research: Connects to preclinical relevance by confirming receptor usage parallels that of native viruses, informing model selection.
- Enterprise Reuse: Establishes a reusable platform applicable to multiple viral fusion proteins (e.g., influenza HA, Ebola GP) beyond coronaviruses.
Operational & Enterprise Impact
- Scientific Value: Predictive confidence in viral entry mechanisms through receptor-specific infection patterns and inhibitor sensitivity profiling.
- Operational Value: Standardized pseudotype production and titration via luciferase assay improves reproducibility across teams and sites.
- Strategic Value: Reduces late-stage attrition by enabling early de-risking of entry-targeted candidates using physiologically relevant surrogates.
- Portfolio Impact: Informs go/no-go decisions on entry inhibitors by providing quantitative data on mechanism of action and potency.
Implementation Considerations
- Requires expertise in mammalian cell culture, transfection, and viral pseudotype production.
- Dependent on access to luminometers and luciferase assay reagents for infectivity quantification.
- Necessitates standardized SOPs for supernatant collection, filtration, and aliquoting to ensure batch consistency.
- Adaptation to non-coronaviral envelope proteins requires validation of pseudotype incorporation and functionality.
- Limited to studying entry steps only; downstream viral life cycle events require complementary methods.
Biopharma FAQs
Why does luciferase reporter quantification matter for viral entry assessment?
Luciferase activity provides a sensitive, quantitative readout of successful pseudotyped particle entry and gene expression in target cells, enabling precise measurement of infectivity levels.
How does receptor expression confirmation support target validation in coronavirus research?
Demonstrating that infectivity increases in receptor-expressing cells (e.g., ACE2 for SARS-CoV, DPP4 for MERS-CoV) confirms that pseudotyped particles use the same entry pathways as native viruses, validating target relevance.
What enables pseudotyped particles to be produced and used in BSL-2 facilities?
Since pseudotyped particles lack viral genetic material and only carry the envelope glycoprotein of interest, they pose minimal biosafety risk, allowing BSL-2 handling instead of requiring BSL-3 containment for pathogenic coronaviruses.
Why is monitoring producer cell health critical before transfection and infection steps?
Optimal cell density and viability directly influence transfection efficiency and pseudotype yield, which in turn affect the consistency and reliability of downstream infectivity assays.
What analytical capability is required to quantify pseudotyped particle infectivity in this workflow?
A luminometer is needed to measure luciferase activity from lysed infected cells, with relative light units serving as a proportional metric of successful viral entry events.
Chapters in this video
0:04
Title
0:41
Cell Seeding for Pseudotyped Particle Production
2:05
Three-plasmid Co-transfection
3:53
Pseudotyped Particles Collection
4:46
Pseudotyped Particle Infection
5:54
Infectivity Quantification by Luciferase Assay Readout
7:04
Results: Infectivity Assays of SARS-CoV S and MERS-CoV S Pseudotyped Particles
8:02
Conclusion
