Lentiviral Vectors in Gene Therapy


Lentiviruses are a family of retroviruses capable of inserting their genome into the genetic material of dividing and nondividing cells. Retroviral vectors based on lentiviruses retain these properties, and have been developed as candidate therapeutic agents for gene delivery to cells of the central nervous system, muscle and hepatocytes as well as antigenā€presenting cells in the immune system.

Keywords: lentivirus; vector; gene therapy

Figure 1.

Genetic structure of the DNA provirus of HIV‐1 showing the major open reading frames, gag, pol and env, and the accessory and regulatory genes, vpu, vif, vpr, nef, tat and rev. The 5′ long terminal repeat acts as a promoter and the 3′ long terminal repeat as the polyadenylation sequence. Three families of messenger RNAs are produced, a full‐length version which is either singly or multiply spliced as shown. Ψ is the packaging signal sequence allowing encapsidation of the vector RNA into the viral particle. SD: major splice donor.

Figure 2.

Infection and virus production in a single cell. Bold arrows demonstrate transport events and dotted arrows represent transport and regulatory functions. Numbers set events chronologically, although many processes overlap: 1, binding of gp120 to CD4 on the cell surface; 2, coreceptor binding and membrane fusion; 3, entry of viral capsid and subsequent uncoating, reverse transcription begins; 4, completion of reverse transcription and formation of preintegration complex (PIC); 5, translocation of PIC across nuclear membrane through pore complexes; 6, integration of viral genome into host DNA; 7, generation of multiply spliced viral transcripts; 8, production of viral regulatory proteins at rough endoplasmic reticulum (ER); 9, exponential increase of viral transcription mediated by Tat protein; 10, downregulation of surface CD4 by the action of Nef protein; 11, production of singly spliced mRNA by the action of Rev protein; 12, production of viral Env protein on rough ER; 13, production of unspliced genomic mRNA by the action of Rev protein; 14, production of viral structural and replication proteins on polysomes; 15, transport of viral Env protein to cell membrane and cleavage by host cell proteases; 16, packaging of genomic mRNAs into nascent virion at plasma membrane; 17, budding of immature viral particle from cell surface; 18, maturation of virion into infectious particle mediated by viral protease. (Reproduced from Lever, AML and Griffin, SDC (2001) HIV: future and futuristic therapies. Journal ofHIVTherapy6(4): 85–90. Published by Mediscript Limited, London, UK with permission.)

Figure 3.

Examples of vector design. 1: Minimal vector showing the position of the packaging signal (Ψ) and polypurine tract (ppt). Long terminal repeats (LTRs) act as promoter and polyadenylation signals. 2: Vector with RNA nuclear export signal; RRE, Rev response element. 3: Self‐inactivating vector. Mutation in U3 copied to the 5′ LTR inactivates the LTR promoter. The internal promoter alone (Pro) is active in the transduced vector. 4: Dual gene vector. One gene driven from LTR and the second from the internal promoter or internal ribosome entry site (IRES).

Figure 4.

Subdivision of the HIVORFs into separate expressors for packaging lentiviral vector RNA indicates a heterologous promoter distinct from the retroviral LTR. VSV: vesicular stomatitis virus.



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Further Reading

Coffin JM, Hughes SH and Varmus HE (1997) Retroviruses. New York, NY: Cold Spring Harbor Laboratory Press.

Deglon N, Tseng JL, Bensadoun JC, et al. (2000) Self‐inactivating lentiviral vectors with enhanced transgene expression and potential gene transfer system in Parkinson's disease. Human Gene Therapy 11: 179–190.

Griffin SDC, Allen JF and Lever AML (2001) The major HIV‐2 packaging signal is present on all HIV‐2 RNA species: co‐translational RNA encapsidation and limiting Gag protein confer specificity. Journal of Virology 75: 12058–12069.

Jeang K‐T (ed.) (2000) HIV‐1: Molecular Biology and Pathogenesis. Viral Mechanisms, Advances in Pharmacology vol. 48 New York, NY: Academic Press.

Jeang K‐T (ed.) (2000) HIV‐1: Molecular Biology and Pathogenesis. Clinical Applications, Advances in Pharmacology vol. 49. New York, NY: Academic Press.

Schnell T, Foley P, Wirth M, Munch J and Uberla K (2000) Development of self‐inactivating, minimal lentivirus vector based on simian immunodeficiency virus. Human Gene Therapy 11: 439–447.

Sung An D, Wersto RP, Agricola BA, et al. (2000) Marking and gene expression by a lentivirus vector in transplanted human and nonhuman primate CD34(+) cells. Journal of Virology 74: 1286–1295.

Sutton RE, Reitsma MJ, Uchida N and Brown PO (1999) Transduction of human progenitor hematopoietic stem cells by human immunodeficiency virus type 1‐based vectors is cell cycle dependent. Journal of Virology 73: 3649–3660.

Unutmaz D, KewalRamani VN, Marmon S and Littman DR (1999) Cytokine signals are sufficient for HIV‐1 infection of resting human T lymphocytes. Journal of Experimental Medicine 189: 1735–1746.

Wang X, Appukuttan B, Ott S, et al. (2000) Efficient and sustained transgene expression in human corneal cells mediated by a lentiviral vector. Gene Therapy 7: 196–200.

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Lever, AML(Jan 2006) Lentiviral Vectors in Gene Therapy. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0005742]