The Trans-Lentiviral Packaging System is based on new generation lentiviral vectors developed by Kappes et al (1,2,3,4). This lentiviral system includes a significant number of safety features designed to enhance its biosafety and to minimize its relation to the wild-type, human HIV-1 virus. Figure 1 illustrates the absence of functional gag-pol recombinants in lentiviral stocks generated from the Trans-Lentiviral Packaging System.

Trans-Lentiviral Packaging System includes the following key safety features:

• The expression vectors contain a deletion in the 3' LTR that does not affect generation of the viral genome in the producer cell line, but results in “self-inactivation” of the lentivirus after transduction of the target cell (5).


• The number of genes from HIV-1 that are used in the system has been reduced (i.e. gag, pol, rev, tat and vpr).


• None of the structural genes are actually present in the packaged viral genome, therefore no new replication-competent virus can be produced.


• The VSV-G gene from Vesicular Stomatitis Virus is used to pseudotype the vector particles (Yee et al., 1994). The HIV-1 envelope has been completely removed from the vector.


• Genes encoding the structural and other components required for packaging the viral genome are separated onto five plasmids minimizing the threat of recombinant replication competent virus production.


• Although the four packaging plasmids allow expression in trans of proteins required to produce viral progeny (e.g. gag, pol, rev, env) in the TLA-HEK293T producer cell line, none of them contain LTRs or the Ψ packaging sequence. This means that none of the HIV-1 structural genes are actually present in the packaged viral genome, and thus, are never expressed in the transduced target cell. No new replication-competent virus can be produced.


• The reverse transcriptase (RT) and integrase (IN) proteins are provided in trans producing a class of vectors that contain split gag-pol components on separate vectors

For more information visit the following links:

http://oba.od.nih.gov/rdna_rac/rac_guidance_lentivirus.html
http://oba.od.nih.gov/oba/rac/Guidance/LentiVirus_Containment/pdf/
Lenti_Containment_Guidance.pdf
http://oba.od.nih.gov/oba/rac/guidelines_02/NIH_Guidelines_Apr_02.htm