Pseudoparticles

Pseudoparticles are virus-like particles engineered to mimic specific properties of infectious viruses while lacking replication capabilities. They are used as research tools to study viral entry, cell tropism, and antibody neutralization, as well as in gene delivery and vaccine development. Unlike fully infectious virions, pseudoparticles typically cannot produce progeny and are designed to contain a replication-defective genome or a reporter gene that enables measurement of successful entry or transcription.

Production and design: Pseudoparticles are commonly produced by expressing a viral core or structural proteins (such as Gag/Pol) in combination with an envelope glycoprotein from a chosen virus. A transfer plasmid providing a single-round reporter gene (for example luciferase or GFP) is packaged inside the particle. The envelope determines which cell types can be infected, enabling systematic studies of receptor usage and tropism.

Applications: They are widely used to assess entry pathways, receptor requirements, and neutralizing antibodies in a safer, single-cycle system. In addition, pseudoparticles are used for screening of antiviral compounds, evaluating vaccine-induced antibody responses, and for basic research on viral fusion. They are particularly common in HIV research with various envelopes and in studies of coronaviruses with spike pseudotypes.

Safety and limitations: Because pseudoparticles are replication-incompetent and can be designed to lack certain viral genes, they offer enhanced biosafety. However, results may not fully replicate authentic virus infection, given differences in genome, replication context, and accessory factors. Production efficiency and host range can also vary depending on the envelope and packaging system.

See also: Virus-like particle; Pseudotype; Viral entry; Neutralization assay.