Investigation of requirements for efficient gene delivery using the HIV-1 based lentiviral transduction system

HIV-based lentiviral vectors: origin and sequence differences

Three gene therapy strategies have received US Food and Drug Administration (FDA) approval; one includes HIV-1-based lentiviral vectors. These vectors incorporate features to provide long-term gene transfer and expression while minimizing generation of a replication-competent virus or pathogenicity. Importantly, the coding regions of viral proteins were deleted, and the cis-acting regulatory elements were retained. With the use of representative vectors developed for clinical/commercial applications, we compared the vector backbone sequences to the initial sources of the HIV-1. All vectors included required elements: 5′ long terminal repeat (LTR) through the Ψ packaging signal, central polypurine tract/chain termination sequence (cPPT/CTS), Rev responsive element (RRE), and 3′ LTR, including a poly(A) signal. The Ψ signaling sequence demonstrated the greatest similarity between all vectors with only minor changes. The 3′ LTR was the most divergent sequence with a range of deletions. The RRE length varied between vectors. Phylogenetic analysis of the cPPT/CTS indicated multiple sources, perhaps because of its later inclusion into lentiviral vector systems, whereas other regions revealed node clusters around the HIV-1 reference genomes HXB2 and NL4-3. We examine the function of each region in a lentiviral vector, the molecular differences between vectors, and where optimization may guide development of the lentiviral delivery systems.

The determination of importance of sequences neighboring the Psi sequence in lentiviral vector transduction and packaging efficiency

A number of lentiviral vector systems have been developed for gene delivery and therapy by eliminating and/or modifying viral genetic elements. However, all lentiviral vector systems derived from HIV-1 must have a viral packaging signal sequence, Psi (Ψ), which is placed downstream of 5' long terminal repeat in a transgene plasmid to effectively package and deliver transgene mRNA. In this study, we examined feasible regions or sequences around Psi that could be manipulated to further modify the packaging sequence. Surprisingly, we found that the sequences immediately upstream of the Psi are highly refractory to any modification and resulted in transgene vectors with very poor gene transduction efficiency. Analysis around the Psi region revealed that there are a few sites that can be used for manipulation of the Psi sequence without disturbing the virus production as well as the efficiency of transgene RNA packaging and gene transduction. By exploiting this new vector system, we investigated the requirement of each of four individual stem-loops of the Psi sequence by deletion mapping analysis and found that all stem-loops, including the SL4 region, are needed for efficient transgene RNA packaging and gene delivery. These results suggest a possible frame of the lentiviral vector that might be useful for further modifying the region/sequence around the packaging sequence as well as directly on the Psi sequence without destroying transduction efficiency.

The HIV-1 nucleocapsid protein does not function as a transcriptional activator on its own cognate promoter

The human immunodeficiency virus type 1 (HIV-1) nucleocapsid (NC) is a multifunctional, zinc finger-containing protein known to be involved in almost every step of the viral life cycle. We therefore examined the effects of NC in vivo as a transcription activator on the basal transcriptional activity of the HIV-1 U3 and Rous sarcoma virus (RSV) promoters, as well as HIV-1 long terminal repeats (LTRs) such as the U3R and U3RU5 regions, using promoter-fused reporter gene assays, Western blot analyses, and quantitative real time-polymerase chain reaction. From these studies, we found that the basal transcriptional levels of the HIV-1 U3 and RSV promoters were barely enhanced by the presence of NC. Placing the U3R region upstream of reporter genes greatly increased transcriptional activity compared to that of the U3 promoter alone, and such activity was further increased by Tat expression. However, neither transcription driven by U3R itself nor Tat-mediated transcriptional activation of the U3R was further increased by the addition of NC. Similar results were also observed with U3RU5 of the HIV-1 LTR region in the presence of either NC or Gag protein. Thus, these results indicate that the HIV NC protein is unable to act as a transcriptional activator on its cognate and possibly other retroviral promoters.

Production of influenza pseudotyped lentiviral particles and their use in influenza research and diagnosis: an update

Pseudotyped viral particles are being used as safe surrogates to mimic the structure and surface of many viruses, including highly pathogenic viruses such as avian influenza H5N1, to investigate biological functions mediated by the envelope proteins derived from these viruses. The first part of this article evaluates and discusses the differences in the production and characterization of influenza pseudoparticles. The second part focuses on the applications that such a flexible tool can provide in modern influenza research, in particular in the fields of drug discovery, molecular biology and diagnosis.