Engineered SFTSV ΔN Reporter Pseudovirus Enables Safer Antiviral Drug Screening

Severe fever with thrombocytopenia syndrome virus (SFTSV), formally classified as Dabie bandavirus (DBV), has emerged as one of the more concerning zoonotic threats of the past two decades. First identified in China, the virus belongs to the family Phenuiviridae and is transmitted primarily through tick bites, although person-to-person transmission has also been documented in clinical settings. Infection can produce a constellation of severe symptoms, including high fever, a dramatic drop in platelet counts, leukopenia, and in a substantial fraction of cases, multi-organ failure and death. Case fatality rates reported in endemic regions have ranged from roughly five to thirty percent, and the geographic footprint of the virus continues to expand across East and Southeast Asia, with serological evidence suggesting wider circulation than previously appreciated.

One of the principal obstacles to studying SFTSV has always been biosafety. Live virus work demands containment at biosafety level 3 or higher, a requirement that dramatically limits the number of laboratories able to investigate the pathogen’s infection biology. The infrastructure, personnel training, and regulatory oversight associated with BSL-3 facilities make routine experimentation slow and expensive, and they create a bottleneck for drug discovery pipelines that depend on high-throughput screening. A team of researchers led by Chenxiao Huang, Wei Li, and Jianfeng Dai at Soochow University in Suzhou, China, has now developed a solution to this problem, publishing their findings in Cellular and Molecular Life Sciences.

The strategy the team pursued centers on a concept known as conditional replication deficiency. Rather than creating a pseudovirus that can perform only a single round of entry, as is common with HIV-based or VSV-based surrogate systems, the researchers engineered an SFTSV genome that retains the capacity for genuine viral replication but only under specific laboratory conditions. They accomplished this by removing the gene encoding the nucleoprotein (NP) from the viral S segment and replacing it with a reporter gene. The nucleoprotein is essential for viral genome encapsidation and replication, so without it, the engineered virus cannot complete its life cycle unless the missing protein is supplied in trans by the host cell.

This design creates a powerful safety barrier. The SFTSV ΔN pseudovirus can only replicate in cells or tissues that have been deliberately engineered to express the nucleoprotein from a separate plasmid or transgene. In any other environment, including a laboratory worker’s body or a non-complementing cell line, the virus enters but cannot produce infectious progeny. The approach mirrors strategies used in other conditional replication systems, such as the ΔN systems developed for influenza A virus, where the M2 or NS1 gene is deleted and complemented in trans. The elegance of the design lies in the fact that the pseudovirus retains the full complement of viral structural proteins except for the one that has been removed, meaning that entry, genome replication, transcription, and assembly all proceed normally as long as the missing component is provided.

To make the system useful for drug screening, the researchers created two versions of the ΔN genome, each carrying a different reporter gene in place of the nucleoprotein. One version carried the gene for Gaussia luciferase (Gluc), a secreted luciferase that produces a bright and quantifiable luminescent signal. The other carried the gene for green fluorescent protein (GFP), which allows direct visualization of infected cells under a fluorescence microscope. Using a reverse genetics system, the team successfully rescued both reporter pseudoviruses, confirming that the engineered genomes could be packaged into infectious particles and that the reporter genes were expressed upon infection of complementing cells.

The Gaussia luciferase version proved particularly valuable for high-throughput applications. Because Gluc is secreted into the culture medium, the researchers could measure infection levels simply by sampling the supernatant and adding luciferin substrate, a process that is compatible with automated plate readers and robotic liquid handling systems. This means that hundreds or thousands of compounds can be tested in parallel in a single experiment, with luminescence serving as a direct readout of viral replication. Any compound that reduces the luminescent signal relative to untreated controls is a candidate inhibitor of SFTSV replication.

Using this platform, the researchers performed a screen of a natural product library and identified several compounds that effectively inhibited SFTSV replication. Among the hits was sesamin, a lignan compound found in sesame seeds and sesame oil that has previously been reported to possess anti-inflammatory and antioxidant properties. The identification of sesamin as an inhibitor of SFTSV replication demonstrates the practical utility of the ΔN pseudovirus system for discovering antiviral candidates from complex chemical libraries. The researchers note that the platform can be adapted to screen diverse compound collections, including FDA-approved drugs, natural product extracts, and synthetic small molecules.

Beyond drug screening, the SFTSV ΔN pseudovirus offers a safe and versatile tool for studying viral infection mechanisms and tissue tropism. Because the virus can replicate in cells that provide the nucleoprotein in trans, researchers can investigate host factors that influence viral entry, genome replication, and assembly without the need for BSL-3 containment. The system can also be used in mouse models where the nucleoprotein is expressed in specific tissues, allowing researchers to map which organs and cell types are susceptible to SFTSV infection. This capability is particularly important for understanding the pathogenesis of severe fever with thrombocytopenia syndrome, which involves complex interactions between the virus and the host immune system, including dysregulated cytokine responses and impaired platelet function.

The work represents a significant advance in the toolkit available for studying emerging bunyaviruses. As climate change and expanding tick populations continue to push SFTSV into new geographic areas, the need for effective antiviral therapies and vaccines grows more urgent. The conditional replication-deficient pseudovirus platform developed by the Soochow University team provides a bridge between the safety constraints of high-containment research and the practical demands of drug discovery and mechanistic investigation. By enabling routine experimentation with a virus that retains its authentic replication machinery but cannot spread beyond engineered complementing cells, the system opens the door to broader participation in SFTSV research and accelerates the pace at which candidate therapeutics can be identified and validated.

Subject of Research: Development of a conditional replication-deficient SFTSV reporter pseudovirus for antiviral drug screening and viral infection studies

Article Title: Construction of an SFTSV ΔN reporter pseudovirus for antiviral drug screening

Article References: Construction of an SFTSV ΔN reporter pseudovirus for antiviral drug screening. (n.d.). https://doi.org/10.1007/s00018-026-06485-7

Image Credits: AI Generated

DOI: 10.1007/s00018-026-06485-7

Keywords: SFTSV, Dabie bandavirus, pseudovirus, conditional replication deficiency, reporter gene, antiviral screening, Gaussia luciferase, green fluorescent protein, reverse genetics, sesamin, biosafety level 3, nucleoprotein