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Pseudoviruses are recombinant viral particles composed of its own backbone and heterologous envelope proteins from other viruses. The envelope proteins mediate the entry of pseudoviruses as efficiently as that of the live viruses with high pathogenicity and infectivity. Different from the live virus, pseudoviruses have no ability to autonomous replication and can only infect host cells for one cycle due to the deletion of its own envelope protein genes and the absence of pathogenic genes. Studies of high-risk and highly pathogenic enveloped viruses require biosafety level (BSL)-3 or higher laboratories, while pseudoviruses can be handled in BSL‐2 laboratories and are generally easier to manipulate experimentally. Due to the characteristics of strong operability, low biological risk, convenient detection, and high sensitivity, pseudoviruses have been widely used in the study of highly pathogenic viruses such as SARS-associated coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and influenza viruses.

Pseudoviruses are usually based on the genome of low biologic risk virus or modified virus, in which the envelope protein genes are replaced by reporter genes, such as green fluorescent protein (GFP) and luciferase genes. The number of cells infected with pseudoviruses is directly proportional to reporter gene expression, so it is easy to quantitatively analyze pseudoviruses. Assays using fluorescent proteins are less expensive and easier to perform in vitro and in vivo systems than chemiluminescence assays, although they are less sensitive and may have a higher background. Lentiviral vectors are the preferred packaging systems for the production of envelope-pseudotyped viruses due to their high efficiency. The human immunodeficiency virus (HIV) packaging system is the most widely used pseudovirus packaging system. Based on the number of plasmids used in the system, HIV pseudovirus systems can be divided into two-plasmid, three-plasmid, and four-plasmid systems. The two-plasmid system including an expression plasmid and a packaging plasmid is the preferred one. Murine leukemia virus (MLV) is a retrovirus that mainly infects mice and causes leukemia. MLV pseudoviruses and HIV have similar packaging processes. Vesicular stomatitis virus (VSV) packaging system is a universal tool for pseudovirus production. This system has no stringent selectivity for envelope proteins. HIV and MLV packaging methods are simpler and less time-consuming than VSV packaging methods. The advantage of VSV pseudoviruses over HIV and MLV pseudoviruses is that the rapid intracellular replication of the VSV genome enables robust reporter gene expression to be detected within hours of infection. VSV and MLV packaging systems can achieve higher pseudovirus yields compared to HIV systems. In addition, VSV and MLV systems are safer than HIV systems, and live VSV and MLV are less toxic than HIV.

Amerigo Scientific offers highly safe and operable pseudoviruses, which can be widely used in the study of virus infection mechanism, the screening and evaluation of antiviral drugs and vaccines, and the detection of neutralizing antibody titers.