pseudoviruses

Pseudoviruses are engineered viral particles that resemble authentic viruses in their ability to enter cells but are typically replication-defective and carry a heterologous genome or reporter genes. They are used to study viral entry, screen neutralizing antibodies, and enable safe gene delivery experiments outside high biosafety containment.

Construction and features: Pseudoviruses are produced by co-transfecting producer cells with plasmids encoding a core genome from a selected retrovirus or lentivirus lacking essential replication genes, a packaging plasmid providing structural proteins in trans, and an envelope glycoprotein from a virus of interest to determine cell tropism. A reporter gene such as luciferase or GFP is included to quantify entry. The resulting particles are often called pseudoparticles or pseudotypes.

Applications: In vaccine and antiviral research, pseudoviruses enable neutralization assays and high-throughput screens without handling replication-competent pathogens. They are used to investigate receptor use and entry pathways, study cross-species tropism, and deliver reporter constructs in gene transfer assays. They also facilitate laboratory studies of viruses that require higher biosafety levels.

Safety and limitations: Although replication-defective, pseudoviruses require appropriate biosafety practices. The specific envelope and core determine risk; some pseudotypes may require BSL-2 or higher. Limitations include non-identical entry kinetics or cofactor usage compared to the native virus, potential differences in post-entry steps, and the possibility of recombination or rescue under certain production conditions. Results should be interpreted with caveats.

Examples: Common systems include lentiviral-based pseudoparticles with VSV-G envelope, murine leukemia virus pseudotypes, and coronavirus spike-pseudotyped particles.