4. Discussion
The absence of basic research and translational technology has been highlighted since the 2014-2016 EBOV epidemic in West Africa, the reason for which is BSL-4 facility restrictions. It is a priority to develop a safe method for EBOV research with low BSL restrictions and definite applicability.
Although the result of the neutralization assay is a gold standard for antibody detection, BSL-4 laboratories are not available for many research groups. In this situation, many groups developed an increasing number of agents, which are single replication cycle pseudotyped viruses, for hazardous pathogens based on the lentivirus system (Chen et al., 2018; Qiu et al., 2013; Zhao et al., 2013). In addition, the efficient expression of the luciferase reporter gene in infected cells was demonstrated after GP-mediated infection (Fig. 2b, 2c), indicating the infection efficiency. These features make pseudotyped EBOV a safe and quantifiable tool for antiviral drug discovery and neutralizing activity evaluation.
Among the viral proteins, GPs are considered the major pathogenicity factor (Panina et al., 2017). EBOV entry into target cells is initiated by the interaction between the viral GP and receptors on the surface of target cells. As a result, the GP of EBOV was selected to construct the pseudotyped EBOV in this study. As expected, GP endowed the pseudotyped EBOV with similar infectivity of authentic EBOV, as indicated by the result that the pseudotyped EBOV could infect different target cells in this study, except C3/36 cells from mosquitoes (Fig. 2a).
All assays involving live EBOV have to be performed under BSL-4 conditions because of the high lethality of EBOV, which limits the application of these assays. However, the pseudotyped EBOV generated from our two-plasmid system has only a single infection cycle (Fig. 2d, 2e), so that it cannot cause mass infection and death. In addition, based on the pseudotyped EBOV, we developed a neutralization assay to evaluate the neutralizing activity of the antibody products. As our data show (Fig. 3a), the pseudotyped EBOV neutralization assay can successfully be used for neutralizing activity evaluation, having the consistent results with an authentic EBOV-based neutralization assay in neutralizing antibody detection, confirming its potential application value in antiviral drug discovery and neutralizing antibody evaluation.