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The CCR5 chemokine receptor is important for most clinical strains of HIV to establish infection. Individuals with naturally occurring polymorphisms in the CCR5 gene who have reduced or absent CCR5 are apparently otherwise healthy, but are resistant to HIV infection. With the goal of reducing CCR5 and protecting CCR5+ cells from R5-tropic HIV, we used Tag-deleted SV40-derived vectors to deliver several anti-CCR5 transgenes: 2C7, a single-chain Fv (SFv) antibody; VCKA1, a hammerhead ribozyme; and two natural CCR5 ligands, MIP-1α and MIP-1β, modified to direct these chemokines, and hence their receptor to the endoplasmic reticulum. These transgenes were delivered using recombinant, Tag-deleted SV40-derived vectors to human CCR5+ cell lines and primary cells: monocyte-derived macrophages and brain microglia. All transgenes except MIP-1α decreased CCR5, as assayed by immunostaining, Northern blotting, and cytofluorimetry (FACS). Individually, all transgenes except MIP-1α protected from low challenge doses of HIV. At higher dose HIV challenges, protection provided by all transgenes diminished, the SFv and the ribozyme being most potent. Vectors carrying these two transgenes were used sequentially to deliver combination anti-CCR5 genetic therapy. This approach gave approximately additive reduction in CCR5, as measured by FACS and protected from higher dose HIV challenges. Reducing cell membrane CCR5 using anti-CCR5 transgenes, alone or in combinations, may therefore provide a degree of protection from R5-tropic strains of HIV. [ABSTRACT FROM AUTHOR]

The article discusses the clinical efficacy of small interfering RNAs (siRNAs). It discusses several recent findings which demonstrate that, under appropriate conditions, siRNAs can trigger interferon responses. It is reported that siRNAs are double stranded, sequence-specific inhibitors of gene expression that act by incorporation into the catalytic domain of an Argonaute family protein.

Highly active antiretroviral therapy (HAART) treatment for HIV has changed the course of AIDS in societies in which the drugs are readily available. Despite the great success of HAART, drug resistance and toxicity issues still remain a concern for some individuals. Thus, a number of investigators have been exploring other approaches for inhibiting HIV-1 replication. One of the most potent of these is the use of RNA interference (RNAi). This review will focus solely on the use of RNAi for the treatment of HIV-1 infection, including the problems, progress and future prospects.

Highly active antiretroviral therapy has greatly reduced the morbidity and mortality from human immunodeficiency virus (HIV) infection, but AIDS continues to be a serious health problem worldwide. Despite enormous efforts to develop a vaccine, there is still no cure, and alternative approaches including gene therapy should be explored. In this study we developed and compared combinatorial foamy virus (FV) anti-HIV vectors that also express a mutant methylguanine methyltransferase (MGMTP140K) transgene to increase the percentage of gene-modified cells after transplantation. These FV vectors inhibit replication of HIV-1 and also the simian immunodeficiency virus/HIV-1 (SHIV) chimera that can be used in monkey AIDS gene therapy studies. We identified a combinatorial FV vector that expresses 3 anti-HIV transgenes and inhibits viral replication by over 4 logs in a viral challenge assay. This FV anti-HIV vector expresses an HIV fusion inhibitor and two short hairpin RNAs (shRNAs) targeted to HIV-1 tat and rev, and can be produced at high titer (3.8 x 10(7) transducing units ml(-1)) using improved helper plasmids suitable for clinical use. Using a competitive repopulation assay, we show that human CD34(+) cells transduced with this combinatorial FV vector efficiently engraft in a mouse xenotransplantation model, and that the percentage of transduced repopulating cells can be increased after transplantation.

Many microRNAs (miRNAs) are encoded within the introns of RNA Pol II transcripts, often as polycistronic precursors. Here, we demonstrate the optimization of an intron encoding three endogenous miRNAs for the ectopic expression of heterologous anti-HIV-1 small interfering RNAs (siRNAs) processed from a single RNA polymerase II primary miRNA. Our expression system, designated as MCM7, is engineered from the intron-embedded, tri-cistronic miR-106b cluster that endogenously expresses miR-106b, miR-93 and miR-25. Manipulation of the miR-106b cluster demonstrated a strict requirement for maintenance of the native flanking primary miRNA (pri-miRNA) sequences and key structural features of the native miRNAs for efficient siRNA processing. As a model for testing the efficacy of this approach, we have replaced the three endogenous miRNAs with siRNAs targeting the tat and rev transcripts of human immunodeficiency virus type 1 (HIV-1). This study has enabled us to establish guidelines for optimal processing of the engineered miRNA mimics into functional siRNAs. In addition, we demonstrate that the incorporation of a small nucleolar RNA TAR chimeric decoy (snoRNA) inserted within the MCM7 intron resulted in a substantial enhancement of HIV suppression in long-term acute infectious HIV-1 challenges.

The current treatment regimen for HIV-infected individuals combines two or more drugs targeting different viral proteins such as RT and gag. Resistance to conventional drugs can develop quickly, and typically persists. The prospect of longer, continuous antiretroviral therapy brings with it the need for new antiretroviral drugs and approaches. In this context, gene therapies have the potential to prolong life and quality of life as an additional therapeutic class and may serve as an adjuvant to traditional treatments. This review focuses on RNA-based hematopoietic cell gene therapy for treatment of HIV infection. Recent advances in our understanding of RNA interference (RNAi) make this an especially attractive candidate for anti-HIV gene therapy although ribozyme and RNA decoy/aptamer approaches can be combined with RNAi to make a combinatorial therapy akin to highly active anti-retroviral therapy.

Lentiviral vectors portend a promising system to deliver antiviral genes for treating viral infections such as HIV-1 as they are capable of stably transducing both dividing and nondividing cells. Recently, small interfering RNAs (siRNAs) have been shown to be quite efficacious in silencing target genes. RNA interference is a natural mechanism, conserved in nature from Yeast to Humans, by which siRNAs operate to specifically and potently down regulate the expression of a target gene either transcriptionally (targeted to DNA) or post-transcriptionally (targeted to mRNA). The specificity and relative simplicity of siRNA design insinuate that siRNAs will prove to be favorable therapeutic agents. Since siRNAs are a small nucleic acid reagents, they are unlikely to elicit an immune response and genes encoding these siRNAs can be easily manipulated and delivered by lentiviral vectors to target cells. As such, lentiviral vectors expressing siRNAs represent a potential therapeutic approach for the treatment of viral infections such as HIV-1. This review will focus on the development, lentiviral based delivery, and the potential therapeutic use of siRNAs in treating viral infections., (Gene Therapy (2006) 13, 553-558. doi:10.1038/sj.gt.3302688; published online 5 January 2006.)