Many different gene delivery systems have been developed to exploit retroviral transduction for stable integration of the desired DNA sequence into the host cell’s genome. It thus enables the inheritable and permanent expression of the transgene over repeated cell divisions. A key feature of all retroviral systems, including lentivrial vector lentivector-based systems, is that they produce replication defective viral particles. This allows for the delivery of the desired transgene without continued viral replication in the target cells, thus, eliminating the dangers associated with the use of a live pathogen. 

The production of replication defective lentivirus is accomplished through trans-complementation. Usually the packaging cells are co-transfected with three or more separate plasmids that together express all viral components necessary to generate infectious particles, containing the DNA sequence of interest packaged for delivery. While many lentivector systems are based on co-transfection of two helper plasmids (2nd generation) with the transfer plasmids (see the graph above), the newer systems (3rd generation & beyond) have the packaging and envelope genes on three helper plasmids. In addition, the accessory gene Tat is deleted and Rev is placed on a separate vector in the 3rd generation. It reduces homology between the packaging constructs and the chance of homologous recombination to produce replication competent virus.

G&P Biosciences Lentiviral Vector Systems

G&P Biosciences provides lentivirus services for your research in cell lines or model organisms. Our services include the construction of transfer vectors (lentivectors) for your target gene, shRNA or miRNA, and the preparation of pre-packaged, ready-to-use, replication-defective, high-titerlentiviralparticles. Our lentiviralsystems are based on the 3rd generation with the most advanced safety features and the packaging genes encoded by three different plasmids. It prevents recombination events from producing replication-competent virus. To produce lentiviral particles, the lentivector and packaging plasmids (offered by G&P Biosciences as an pre-optimized, transfection-ready DNA mixture, LentiPAK) are co-transfected into the packaging cell line. The packaging cells produce infectious particles, whose genome only encodes sequences from the lentivector, which can be used to transduce the target cells.

*Packaging kit includes an optimized lentiviral packaging (LentiPAK) DNA mix, a control vector, & a transfection reagent (QuickFectin) for producing high titers and robust expression levels.

All of our lentivectors contain a deletion in the U3 region from the 3’ LTR which results in self-inactivation (which is safer than an intact LTR that could activate genes adjacent to insertion). The 5’ LTR drives expression of the packaged genomic RNA, while the transgene is driven by a heterologous promoter within the lentivector. We offer RNA Pol II promoters (e.g., CMV, EF-1α, and CAG) for protein-coding gene expression and RNA Pol III promoters (e.g., H1 and U6) for production of shorter transcripts, such as shRNAs. Our lentivectorscan be pseudotyped with different coat proteins to alter their tropism. The most common one is a fusogenic envelope G glycoprotein of vesicular stomatitis virus (VSV-G). Other envelope proteins are also available including those derived from rabies virus, MLV, baculovirus, and measles virus. There are also many options of tags and fusions as well as selectable markers to choose from (see the table above and visit our "Products" and “Virus Services” site to learn more and order).

Important Safety Information

With the safety features in place, our lentiviral/retroviral vectors and viral particles can be employed in standard Biosafety Level 2 tissue culture facilities and should be treated with the same level of caution as any other potentially infectious agent. Any investigator who purchases our lentiviral/retroviral/viral products & services is responsible for following Biosafety Level 2 requirements on the handling of viral particles. For more information on Biosafety Level 2 agents and practices, please refer to NIH’s “Biosafety Considerations for Research with Lentiviral Vectors”.

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