Comparative Evaluation of the Activity of Various Lentiviral Vectors Containing Three Anti-HIV Genes

A promising direction in the treatment of HIV infection is a gene therapy approach based on the insertion of antiviral genes aimed at inhibiting HIV replication into the genome of host cells. We obtained six constructs of lentiviral vectors with different arrangements of three antiviral genes: microRNAs against the CCR5 gene, the gene encoding the C-peptide, and the gene encoding the modified human TRIM5a protein. We found that despite containing the same genes, these vectors were produced at different titers and had different effects on cell viability, transduction efficiency, and expression stability. Comparative evaluation of the antiviral activity of three of the six developed vectors that showed stable expression was carried out using the continuous SupT1 lymphocytic cell line. All of the vectors protected cells from HIV infection: the viral load was several orders of magnitude lower than in control cells, and with one vector, complete cessation of virus growth in modified cells was achieved.

Optimization of Polycistronic Anti-CCR5 Artificial microRNA Leads to Improved Accuracy of Its Lentiviral Vector Transfer and More Potent Inhibition of HIV-1 in CD4⁺ T-Cells

C-C chemokine receptor type 5 (CCR5) is utilized by human immunodeficiency virus (HIV) as a co-receptor for cell entry. Suppression of the CCR5 gene by artificial microRNAs (amiRNAs) could confer cell resistance. In previous work, we created a lentivector that encoded the polycistron of two identical amiRNAs that could effectively suppress CCR5. However, tandem repeats in lentiviral vectors led to deletions of the repeated sequences during reverse transcription of the vector RNA. To solve this problem, we have created a new amiRNA against CCR5, mic1002, which has a different microRNA scaffold and targets a different sequence. Replacing one of the two identical tandem amiRNAs in the polycistron with the mic1002 amiRNA increased the accuracy of its lentiviral vector transfer while retaining its ability to effectively suppress CCR5. A lentiviral vector containing two heterogenic amiRNAs significantly inhibited HIV replication in a vector-transduced human CD4⁺ lymphocyte culture.

Scaffolds for Artificial miRNA Expression in Animal Cells

Artificial miRNAs (amiRNAs) are molecules that have been developed to promote gene silencing in a similar manner to naturally occurring miRNAs. amiRNAs are generally constructed by replacing the mature miRNA sequence in the pre-miRNA stem-loop with a sequence targeting a gene of interest. These molecules offer an interesting alternative to silencing approaches that are based on shRNAs and siRNAs because they present the same efficiency as these options and are less cytotoxic. amiRNAs have mostly been applied to gene knockdown in plants; they have been examined to a lesser extent in animal cells. Therefore, this article reviews the amiRNAs that have been developed for animal cells and focuses on the miRNA scaffolds that can already be applied to construct the artificial counterparts, as well as on the different approaches that have been described to promote amiRNA expression and silencing efficiency. Furthermore, the availability of amiRNA libraries and other tools that can be used to design and construct these molecules is briefly discussed, along with an overview of the therapeutic applications for which amiRNAs have already been evaluated.

Optimization of Critical Hairpin Features Allows miRNA-based Gene Knockdown Upon Single-copy Transduction

Gene knockdown using micro RNA (miRNA)-based vector constructs is likely to become a prominent gene therapy approach. It was the aim of this study to improve the efficiency of gene knockdown through optimizing the structure of miRNA mimics. Knockdown of two target genes was analyzed: CCR5 and green fluorescent protein. We describe here a novel and optimized miRNA mimic design called mirGE comprising a lower stem length of 13 base pairs (bp), positioning of the targeting strand on the 5' side of the miRNA, together with nucleotide mismatches in upper stem positions 1 and 12 placed on the passenger strand. Our mirGE proved superior to miR-30 in four aspects: yield of targeting strand incorporation into RNA-induced silencing complex (RISC); incorporation into RISC of correct targeting strand; precision of cleavage by Drosha; and ratio of targeting strand over passenger strand. A triple mirGE hairpin cassette targeting CCR5 was constructed. It allowed CCR5 knockdown with an efficiency of over 90% upon single-copy transduction. Importantly, single-copy expression of this construct rendered transduced target cells, including primary human macrophages, resistant to infection with a CCR5-tropic strain of HIV. Our results provide new insights for a better knockdown efficiency of constructs containing miRNA. Our results also provide the proof-of-principle that cells can be rendered HIV resistant through single-copy vector transduction, rendering this approach more compatible with clinical applications.

Beyond Gene Delivery: Strategies to Engineer the Surfaces of Viral Vectors

Viral vectors have been extensively studied due to their great transduction efficiency compared to non-viral vectors. These vectors have been used extensively in gene therapy, enabling the comprehension of, not only the advantages of these vectors, but also the limitations, such as the activation of the immune system after vector administration. Moreover, the need to control the target of the vector has led to the development of chemical and non-chemical modifications of the vector surface, allowing researchers to modify the tropism and biodistribution profile of the vector, leading to the production of viral vectors able to target different tissues and organs. This review describes recent non-genetic modifications of the surfaces of viral vectors to decrease immune system activation and to control tissue targeting. The developments described herein provide opportunities for applications of gene therapy to treat acquired disorders and genetic diseases and to become useful tools in regenerative medicine.