Activity of TAR in inducible inhibition of HIV replication by foamy virus vector expressing siRNAs under the control of HIV LTR

Advances in foamy virus vector systems: Development and applications

Foamy virus (FV) is a retrovirus with a safer integration profile than other retroviruses, rendering it appealing for gene therapy. Prototype FV (PFV) vector systems have been devised to yield high-titer vectors carrying large transgenes. Subsequent iterations of PFV vectors have been engineered to be replication-incompetent, enhancing their safety. A third generation PFV vector system, composed of four plasmids, has been adapted to accommodate large transgenes. Additionally, a novel dual-vector system shows promise for convenient and efficient gene delivery, particularly with the forthcoming development of stable producer cell lines expressing PFV Env. FVs exhibit a broad host spectrum due to the ubiquitous presence of the host factor, heparan sulfate (HS), on their surface. The receptor-binding domain (RBD) of FV Env proteins plays a crucial role in binding to the host cell HS. The FV vector system has been employed in hematopoietic stem cell (HSC) gene therapy to address monogenic diseases in dog and mouse models. In addition, FV vectors safely and efficiently deliver anti-HIV transgenes to HSCs, and vectors carrying HIV epitopes successfully induce antibodies against HIV, offering the promise of anti-HIV gene therapy and vaccine development. In this review, we delve into the development and utilization of FV vector systems, emphasizing their unique advantages in gene therapy, including their non-pathogenic nature, broad host tropism, large transgene capacity, and persistence in resting cells. Furthermore, we discuss the potential of FV vectors in tackling current challenges in gene therapy and their viability as valuable tools for treating genetic diseases.

Chimeric Trojan Protein Insertion in Lentiviral Membranes Makes Lentiviruses Susceptible to Neutralization by Anti-Tetanus Serum Antibodies

This study describes the initial testing of a novel strategy for neutralization of lentiviruses using the fundamental biology of enveloped viruses' assembly and budding. In the field of gene therapy, viral vector surface proteins have been manipulated in order to redirect host cell specificity by alteration of pseudo-types. This study tested whether known viral pseudo-typing proteins or surface proteins known to be recruited to the human immunodeficiency virus (HIV) envelope could be engineered to carry neutralizing epitopes from another microorganism onto the lentiviral surface. The results identify ICAM1 as a novel vehicle for lentiviral pseudo-typing. Importantly, the study shows that in a model lentiviral system, ICAM1 can be engineered in chimeric form to result in expression of a fragment of the tetanus toxoid on the viral membrane and that these viruses can then be neutralized by human serum antibodies protective against tetanus. This raises the possibility of delivering chimeric antigens as a gene therapy in HIV-infected patients.

Prospects for Foamy Viral Vector Anti-HIV Gene Therapy

Stem cell gene therapy approaches for Human Immunodeficiency Virus (HIV) infection have been explored in clinical trials and several anti-HIV genes delivered by retroviral vectors were shown to block HIV replication. However, gammaretroviral and lentiviral based retroviral vectors have limitations for delivery of anti-HIV genes into hematopoietic stem cells (HSC). Foamy virus vectors have several advantages including efficient delivery of transgenes into HSC in large animal models, and a potentially safer integration profile. This review focuses on novel anti-HIV transgenes and the potential of foamy virus vectors for HSC gene therapy of HIV.

Inhibition of HIV-1 by a Lentiviral Vector with a Novel Tat-Inducible Expression System and a Specific Tropism to the Target Cells

Today, lentiviral vectors are favorable vectors for RNA interference delivery in anti-HIV therapeutic approaches. Nevertheless, problems such as the specific recognition of target cells and uncontrolled expression of the transgene can restrict their use in vivo. Herein we present a new HIV-inducible promoter to express anti-HIV short hairpin RNA (shRNA) by RNA Pol II in mammalian cells. We likewise showed a novel third-generation lentiviral vector system with more safety and a specific tropism to the target cells. The new promoter, CkRhsp, was constructed from the chicken β-actin core promoter with the R region of HIV-1 long terminal repeat fused upstream of minimal hsp70 promoter. This system was induced by HIV-1 Tat, and activates transcription of two shRNAs against two conserved regions of HIV-1 transcripts produced in two steps of the virus life cycle. We also mimicked HIV-1 cell tropism by using the HIV-1 envelope in structure of third-generation lentiviral vector. The new fusion promoter efficiently expressed shRNA in a Tat-inducible manner. HIV-1 replication was inhibited in transient transfection and stable transduction assays. The new viral vector infected only CD4+cells. CkRhsp promoter may be safer than other inducible promoters for shRNA-mediated gene therapies against HIV. The use of the wild envelope in the vector packaging system may provide the specific targeting T lymphocytes and hematopoietic stem cells for anti-HIV-1 therapeutic approaches in vivo.

Establishing Restricted Expression of Caveolin-1 in HIV Infected Cells and Inhibition of Virus Replication

Background:

Caveolin-1 (Cav-1) is the major protein of the caveolae and plays a role in multiple cellular functions and implicated to have anti-HIV activity. Regulated expression of Cav-1 is important for safe and effective use in order to exploit Cav-1 for HIV therapeutic applications.

Methods:

A series of Cav-1 and GFP expression vectors were constructed under the control of the HIV LTR for conditional expression or CMV promoter and the expression of Cav-1 was monitored in the presence or absence of Tat or HIV infection in order to establish the restricted expression of Cav-1 to HIV infected cells.

Results:

Cav-1 expression was evident under the control of the HIV LTR in the absence of Tat or HIV infection as demonstrated by immunoblot. Placing two internal ribosomal entry sequences (IRES) and a Rev response element, RRE (5’~ LTR-IRES-GFP-RRE-IRES-Cav-1~3’) resulted in no expression of Cav-1 in the absence of Tat with effective expression in the presence of Tat. Transduction of HIV permissive cells with this construct using a foamy virus vector show that Cav-1 was able to inhibit HIV replication by 82%. Cells that received LTR-IRES-GFP-RRE-IRES-Cav-1 remain healthy in the absence of Tat or HIV infection.

Conclusion:

These results taken together reveal the inclusion of two IRES establishes a significant reduction of leak through expression of Cav-1 in the absence of Tat or HIV infection. Such regulated expression will have therapeutic application of Cav-1 for HIV infection as well as broad applications which can be beneficial for other host-targeted interventions as therapeutics.

Foamy virus vectors for HIV gene therapy

Highly active antiretroviral therapy (HAART) has vastly improved outcomes for patients infected with HIV, yet it is a lifelong regimen that is expensive and has significant side effects. Retroviral gene therapy is a promising alternative treatment for HIV/AIDS; however, inefficient gene delivery to hematopoietic stem cells (HSCs) has so far limited the efficacy of this approach. Foamy virus (FV) vectors are derived from non-pathogenic viruses that are not endemic to the human population. FV vectors have been used to deliver HIV-inhibiting transgenes to human HSCs, and they have several advantages relative to other retroviral vectors. These include an attractive safety profile, broad tropism, a large transgene capacity, and the ability to persist in quiescent cells. In addition, the titers of FV vectors are not reduced by anti-HIV transgenes that affect the production of lentivirus (LV) vectors. Thus FV vectors are very promising for anti-HIV gene therapy. This review covers the advantages of FV vectors and describes their preclinical development for anti-HIV gene therapy.

A Kaposi's sarcoma-associated herpesvirus-encoded ortholog of microRNA miR-155 induces human splenic B-cell expansion in NOD/LtSz-scid IL2Rγnull mice

MicroRNAs (miRNAs) are small noncoding RNA molecules that function as posttranscriptional regulators of gene expression. Kaposi's sarcoma (KS)-associated herpesvirus (KSHV), a B-cell-tropic virus associated with KS and B-cell lymphomas, encodes 12 miRNA genes that are highly expressed in these tumor cells. One viral miRNA, miR-K12-11, shares 100% seed sequence homology with hsa-miR-155, an oncogenic human miRNA that functions as a key regulator of hematopoiesis and B-cell differentiation. So far, in vitro studies have shown that both miRNAs can regulate a common set of cellular target genes, suggesting that miR-K12-11 may mimic miR-155 function. To comparatively study miR-K12-11 and miR-155 function in vivo, we used a foamy virus vector to express the miRNAs in human hematopoietic progenitors and performed immune reconstitutions in NOD/LtSz-scid IL2Rγ(null) mice. We found that ectopic expression of miR-K12-11 or miR-155 leads to a significant expansion of the CD19(+) B-cell population in the spleen. Subsequent quantitative PCR analyses of these splenic B cells revealed that C/EBPβ, a transcriptional regulator of interleukin-6 that is linked to B-cell lymphoproliferative disorders, is downregulated when either miR-K12-11 or miR-155 is ectopically expressed. In addition, inhibition of miR-K12-11 function using antagomirs in KSHV-infected human primary effusion lymphoma B cells resulted in derepression of C/EBPβ transcript levels. This in vivo study validates miR-K12-11 as a functional ortholog of miR-155 in the context of hematopoiesis and suggests a novel mechanism by which KSHV miR-K12-11 induces splenic B-cell expansion and potentially KSHV-associated lymphomagenesis by targeting C/EBPβ.

Nanotherapeutics Using an HIV-1 Poly A and Transactivator of the HIV-1 LTR-(TAR-) Specific siRNA

HIV-1 replication can be efficiently inhibited by intracellular expression of an siRNA targeting the viral RNA. We used a well-validated siRNA (si510) which targets the poly A/TAR (transactivator of the HIV-1 LTR) site and suppresses viral replication. Nanotechnology holds much potential for impact in the field of HIV-1 therapeutics, and nanoparticles such as quantum rods (QRs) can be easily functionalized to incorporate siRNA forming stable nanoplexes that can be used for gene silencing. We evaluated the efficacy of the QR-si510 HIV-1 siRNA nanoplex in suppressing viral replication in the HIV-1-infected monocytic cell line THP-1 by measuring p24 antigen levels and gene expression levels of HIV-1 LTR. Our results suggest that the QR-si510 HIV-1 siRNA nanoplex is not only effective in delivering siRNA, but also in suppressing HIV-1 viral replication for a longer time period. HIV-1 nanotherapeutics can thus enhance systemic bioavailability and offer multifunctionality.

Caveolin 1 inhibits HIV replication by transcriptional repression mediated through NF-κB

Caveolin 1 (Cav-1), the scaffold protein of a specific membrane lipid raft called caveolae, has been reported to suppress HIV-1 replication. However, the mechanism by which Cav-1 inhibits HIV replication remains unclear. In this study, we investigated the mechanism by which Cav-1 inhibits HIV replication at the level of gene expression. Our results show that Cav-1 represses viral gene expression and that this suppression involves the NF-κB pathway. We used several approaches in different cell types, including primary CD4(+) T cells and macrophages, to demonstrate the role of nuclear factor κB (NF-κB) in Cav-1-mediated inhibition of viral expression. A mutational analysis of the cis-acting element shows that the two NF-κB sites in the U3 region of the long terminal repeat (LTR) are critical for Cav-1-mediated inhibition of viral expression. In the presence of Cav-1, phosphorylation of IKKβ, IKKα, IκBα, and NF-κB p65 is dramatically reduced, while viral gene expression is suppressed. In addition, translocation of NF-κB p65 to the nucleus decreases substantially in the presence of Cav-1. Furthermore, significant inhibition of NF-κB activation and binding to target DNA are evident in the presence of Cav-1. These results establish evidence that Cav-1 inhibits HIV replication by transcriptional repression of viral gene expression and contributes to HIV's persistent infection of macrophages.

Expression of interfering RNAs from an HIV-1 Tat-inducible chimeric promoter

The therapeutic value of antiviral interfering RNAs could be improved by technologies that limit their expression to the infected cell population. The HIV-1 Tat-inducible viral LTR and LTR-containing chimeric promoters have previously been used to drive expression of antiviral RNAs and proteins directed against HIV-1. Here, we characterize an alternative promoter, consisting of a chicken β-actin core promoter fused to the viral TAR element, for the conditional expression of interfering RNAs. This promoter, that we refer to as the CK-TAR promoter, can induce levels of silencing comparable to the viral LTR in response to Tat produced from co-transfected plasmids or during viral replication. While the CK-TAR promoter shows a modest level of basal activity, similar to the viral LTR, it is less responsive to the extracellular stimuli tested including LPS, TNFα, and PMA. The CK-TAR promoter is an alternative Tat-inducible promoter with the potential to minimize the risk of vector mobilization and to drive polycistronic expression of interfering RNAs.

HIV infection upregulates caveolin 1 expression to restrict virus production

Caveolin 1 (Cav-1) is a major protein of a specific membrane lipid raft known as caveolae. Cav-1 interacts with the gp41 of the human immunodeficiency virus (HIV) envelope, but the role of Cav-1 in HIV replication and pathogenesis is not known. In this report, we demonstrate that HIV infection in primary human monocyte-derived macrophages (MDMs), THP-1 macrophages, and U87-CD4 cells results in a dramatic upregulation of Cav-1 expression mediated by HIV Tat. The activity of p53 is essential for Tat-induced Cav-1 expression, as our findings show enhanced phosphorylation of serine residues at amino acid positions 15 and 46 in the presence of Tat with a resulting Cav-1 upregulation. Furthermore, inhibition of p38 mitogen-activated protein kinase (MAPK) blocked phosphorylation of p53 in the presence of Tat. Infection studies of Cav-1-overexpressing cells reveal a significant reduction of HIV production. Taken together, these results suggest that HIV infection enhances the expression of Cav-1, which subsequently causes virus reduction, suggesting that Cav-1 may contribute to persistent infection in macrophages.

The foamy virus genome remains unintegrated in the nuclei of G1/S phase-arrested cells, and integrase is critical for preintegration complex transport into the nucleus

Foamy viruses are a member of the spumavirus subfamily of retroviruses with unique mechanisms of virus replication. Foamy virus replication is cell cycle dependent; however, the genome is found in the nuclei of cells arrested in the G(1)/S phase. Despite the presence of genome in the nuclei of growth-arrested cells, there is no viral gene expression, thus explaining its dependency on cell cycle. This report shows that the foamy virus genome remains unintegrated in G(1)/S phase-arrested cells. The foamy virus genome is detected by confocal microscopy in the nuclei of both dividing and growth-arrested cells. Alu PCR revealed foamy virus-specific DNA amplification from genomic DNA isolated in cycling cells at 24 h postinfection. In arrested cells no foamy virus DNA band was detected in cells harvested at 1 or 7 days after infection, and a very faint band that is significantly less than DNA amplified from cycling cells was observed at day 15. After these cells were arrested at the G(1)/S phase for 1, 7, or 15 days they were allowed to cycle, at which time foamy virus-specific DNA amplification was readily observed. Taken together, these results suggest that the foamy virus genome persists in nondividing cells without integrating. We have also established evidence for the first time that the foamy virus genome and Gag translocation into the nucleus are dependent on integrase in cycling cells, implicating the role of integrase in transport of the preintegration complex into the nucleus. Furthermore, despite the presence of a nuclear localization signal sequence in Gag, we observed no foamy virus Gag importation into the nucleus in the absence of integrase.