Non-viral ex vivo transduction of human hepatocyte cells to express factor VIII using a human ribosomal DNA-targeting vector

Ectopic Expression of FVIII in HPCs and MSCs Derived from hiPSCs with Site-Specific Integration of ITGA2B Promoter-Driven BDDF8 Gene in Hemophilia A

Hemophilia A (HA) is caused by mutations in the coagulation factor VIII (FVIII) gene (F8). Gene therapy is a hopeful cure for HA; however, FVIII inhibitors formation hinders its clinical application. Given that platelets promote coagulation via locally releasing α-granule, FVIII ectopically expressed in platelets has been attempted, with promising results for HA treatment. The B-domain-deleted F8 (BDDF8), driven by a truncated ITGA2B promoter, was targeted at the ribosomal DNA (rDNA) locus of HA patient-specific induced pluripotent stem cells (HA-iPSCs). The F8-modified, human induced pluripotent stem cells (2bF8-iPSCs) were differentiated into induced hematopoietic progenitor cells (iHPCs), induced megakaryocytes (iMKs), and mesenchymal stem cells (iMSCs), and the FVIII expression was detected. The ITGA2B promoter-driven BDDF8 was site-specifically integrated into the rDNA locus of HA-iPSCs. The 2bF8-iPSCs were efficiently differentiated into 2bF8-iHPCs, 2bF8-iMKs, and 2bF8-iMSCs. FVIII was 10.31 ng/10⁶ cells in lysates of 2bF8-iHPCs, compared to 1.56 ng/10⁶ cells in HA-iHPCs, and FVIII was 3.64 ng/10⁶ cells in 2bF8-iMSCs lysates, while 1.31 ng/10⁶ cells in iMSCs with CMV-driven BDDF8. Our results demonstrated a high expression of FVIII in iHPCs and iMSCs derived from hiPSCs with site-specific integration of ITGA2B promoter-driven BDDF8, indicating potential clinical prospects of this platelet-targeted strategy for HA gene therapy.

OUP accepted manuscript

Mesenchymal stem cells (MSCs) are a promising cellular vehicle for transferring anti-cancer factors to malignant tumors. Currently, a variety of anti-cancer agents, including the tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), have been loaded into MSCs derived from a range of sources through different engineering methods. These engineered MSCs exhibit enormous therapeutic potential for various cancers. To avoid the intrinsic defects of MSCs derived from tissues and the potential risk of viral vectors, TRAIL was site-specifically integrated into the ribosomal DNA (rDNA) locus of human-induced pluripotent stem cells (iPSCs) using a non-viral rDNA-targeting vector and transcription activator-like effector nickases (TALENickases). These genetically modified human iPSCs were differentiated into an unlimited number of homogeneous induced MSCs (TRAIL-iMSCs) that overexpressed TRAIL in both culture supernatants and cell lysates while maintaining MSC-like characteristics over continuous passages. We found that TRAIL-iMSCs significantly induced apoptosis in A375, A549, HepG2, and MCF-7 cells in vitro. After intravenous infusion, TRAIL-iMSCs had a prominent tissue tropism for A549 or MCF-7 xenografts and significantly inhibited tumor growth through the activation of apoptotic signaling pathways without obvious side effects in tumor-bearing mice models. Altogether, our results showed that TRAIL-iMSCs have strong anti-tumor effects in vitro and in vivo on a range of cancers. This study allows for the development of an unlimited number of therapeutic gene-targeted MSCs with stable quality and high homogeneity for cancer therapy, thus highlighting a universal and safe strategy for stem cell-based gene therapy with high potential for clinical applications.

PiggyBac transposase and transposon derivatives for gene transfer targeting the ribosomal DNA loci of CHO cells

Integrative non-viral vectors such as transposons engineered to mediate targeted gene transfer into safe harbor sites in the genome may be a promising approach for the production of therapeutic proteins or for gene therapy in an efficient and secure way. In this context, we designed and evaluated two strategies for targeting the nuclear ribosomal DNA (rDNA) loci. One approach relied on the co-location of the transposase and transposon near transcriptionally active rDNA copies using a nucleolar localization signal (NoLS). Another one consisted of targeting the 18S-coding region in the rDNA loci using a NoLS-FokI-dCas9 endonuclease to perform targeted transgene knock-in. We show that integration into the rDNA of Chinese hamster ovary (CHO) cells can be achieved at a high frequency using the piggyBac transposon system, indicating that the rDNA is highly accessible for transposition. Consistently, rDNA-targeted transposition events were most frequently obtained when both the piggyBac transposon DNA and the transposase were nucleoli-targeted, yielding cells displaying stable and homogeneous expression of the transgene. This approach thus provides an alternative strategy to improve targeted transgene delivery and protein expression using CHO cells.

Mesenchymal stem cells derived from iPSCs expressing interleukin-24 inhibit the growth of melanoma in the tumor-bearing mouse model

Background

Interleukin-24 (IL-24) is a therapeutic gene for melanoma, which can induce melanoma cell apoptosis. Mesenchymal stem cells (MSCs) show promise as a carrier to delivery anti-cancer factors to tumor tissues. Induced pluripotent stem cells (iPSCs) are an alternative source of mesenchymal stem cells (MSCs). We previously developed a novel non-viral gene targeting vector to target IL-24 to human iPSCs. This study aims to investigate whether MSCs derived from the iPSCs with the site-specific integration of IL-24 can inhibit the growth of melanoma in a tumor-bearing mouse model via retro-orbital injection.

Methods

IL-24-iPSCs were differentiated into IL-24-iMSCs in vitro, of which cellular properties and potential of differentiation were characterized. The expression of IL-24 in the IL-24-iMSCs was measured by qRT-PCR, Western Blotting, and ELISA analysis. IL-24-iMSCs were transplanted into the melanoma-bearing mice by retro-orbital intravenous injection. The inhibitory effect of IL-24-iMSCs on the melanoma cells was investigated in a co-culture system and tumor-bearing mice. The molecular mechanisms underlying IL-24-iMSCs in exerting anti-tumor effect were also explored.

Results

iPSCs-derived iMSCs have the typical profile of cell surface markers of MSCs and have the ability to differentiate into osteoblasts, adipocytes, and chondroblasts. The expression level of IL-24 in IL-24-iMSCs reached 95.39 ng/10⁶ cells/24 h, which is significantly higher than that in iMSCs, inducing melanoma cells apoptosis more effectively in vitro compared with iMSCs. IL-24-iMSCs exerted a significant inhibitory effect on the growth of melanoma in subcutaneous mouse models, in which the migration of IL-24-iMSCs to tumor tissue was confirmed. Additionally, increased expression of Bax and Cleaved caspase-3 and down-regulation of Bcl-2 were observed in the mice treated with IL-24-iMSCs.

Conclusion

MSCs derived from iPSCs with the integration of IL-24 at rDNA locus can inhibit the growth of melanoma in tumor-bearing mouse models when administrated via retro-orbital injection.

Gene Therapy for Hemophilia and Duchenne Muscular Dystrophy in China

Gene therapy is a new technology that provides potential for curing monogenic diseases caused by mutations in a single gene. Hemophilia and Duchenne muscular dystrophy (DMD) are ideal target diseases of gene therapy. Important advances have been made in clinical trials, including studies of adeno-associated virus vectors in hemophilia and antisense in DMD. However, issues regarding the high doses of viral vectors required and limited delivery efficiency of antisense oligonucleotides have not yet been fully addressed. As an alternative strategy to classic gene addition, genome editing based on programmable nucleases has also shown promise to correct mutations in situ. This review describes the recent progress made by Chinese researchers in gene therapy for hemophilia and DMD.

Ectopic expression of factor VIII in MSCs and hepatocytes derived from rDNA targeted hESCs

Hemophilia A is an X-linked recessive bleeding disorder caused by FVIII gene deficiency, which may result in spontaneous joint hemorrhages or life-threatening bleeding. Currently, cell-based gene therapy via ex vivo transduction of transplantable cells with integrating gene-expressing vectors offers an attractive treatment for HA. In present study, we targeted an expression cassette of B-domain-deleted FVIII into the ribosomal DNA (rDNA) locus of human embryonic stem cells (hESCs) by transfection with a nonviral targeting plasmid pHrn. The targeted hESCs clone could be expanded and retained the main pluripotent properties of differentiation into three germ layers both in vitro and in vivo. Importantly, under defined induction conditions, the targeted hESCs could differentiated into functional mesenchymal stem cells (MSCs) and hepatocytes, as validated by relevant specific cell markers and functional examination. Tumorgenesis assay demonstrated that these cells are relatively safe for future applications. Analysis on gene expression revealed that exogenous FVIII mRNA and FVIII proteins were both present in differentiated MSCs and hepatocytes. These results indicated that through gene targeting at hESCs rDNA locus a persistent cell source of transplantable genetic-modified cells can be accomplished for HA therapy.

Enhanced tumor growth inhibition by mesenchymal stem cells derived from iPSCs with targeted integration of interleukin24 into rDNA loci

Induced pluripotent stem cells (iPSCs) are a promising source of mesenchymal stem cells (MSCs) for clinical applications. In this study, we transformed human iPSCs using a non-viral vector carrying the IL24 transgene pHrn-IL24. PCR and southern blotting confirmed IL24 integration into the rDNA loci in four of 68 iPSC clones. We then differentiated a high expressing IL24-iPSC clone into MSCs (IL24-iMSCs) that showed higher expression of IL24 in culture supernatants and in cell lysates than control iMSCs. IL24-iMSCs efficiently differentiated into osteoblasts, chondrocytes and adipocytes. Functionally, IL24-iMSCs induced in vitro apoptosis in B16-F10 melanoma cells more efficiently than control iMSCs when co-cultured in Transwell assays. In vivo tumor xenograft studies in mice demonstrated that IL24-iMSCs inhibited melanoma growth more than control iMSCs did. Immunofluorescence and histochemical analysis showed larger necrotic areas and cell nuclear aggregation in tumors with IL24-iMSCs than control iMSCs, indicating that IL24-iMSCs inhibited tumor growth by inducing apoptosis. These findings demonstrate efficient transformation of iPSCs through gene targeting with non-viral vectors into a rDNA locus. The ability of these genetically modified MSCs to inhibit in vivo melanoma growth is suggestive of the clinical potential of autologous cell therapy in cancer.

Targeting of the human F8 at the multicopy rDNA locus in Hemophilia A patient-derived iPSCs using TALENickases

Hemophilia A (HA) is a monogenic disease due to lack of the clotting factor VIII (FVIII). This deficiency may lead to spontaneous joint hemorrhages or life-threatening bleeding but there is no cure for HA until very recently. In this study, we derived induced pluripotent stem cells (iPSCs) from patients with severe HA and used transcription activator-like effector nickases (TALENickases) to target the factor VIII gene (F8) at the multicopy ribosomal DNA (rDNA) locus in HA-iPSCs, aiming to rescue the shortage of FVIII protein. The results revealed that more than one copy of the exogenous F8 could be integrated into the rDNA locus. Importantly, we detected exogenous F8 mRNA and FVIII protein in targeted HA-iPSCs. After they were differentiated into endothelial cells (ECs), the exogenous FVIII protein was still detectable. Thus, it is showed that the multicopy rDNA locus could be utilized as an effective target site in patient-derived iPSCs for gene therapy. This strategy provides a novel iPSCs-based therapeutic option for HA and other monogenic diseases.

In situ genetic correction of F8 intron 22 inversion in hemophilia A patient-specific iPSCs

Nearly half of severe Hemophilia A (HA) cases are caused by F8 intron 22 inversion (Inv22). This 0.6-Mb inversion splits the 186-kb F8 into two parts with opposite transcription directions. The inverted 5' part (141 kb) preserves the first 22 exons that are driven by the intrinsic F8 promoter, leading to a truncated F8 transcript due to the lack of the last 627 bp coding sequence of exons 23-26. Here we describe an in situ genetic correction of Inv22 in patient-specific induced pluripotent stem cells (iPSCs). By using TALENs, the 627 bp sequence plus a polyA signal was precisely targeted at the junction of exon 22 and intron 22 via homologous recombination (HR) with high targeting efficiencies of 62.5% and 52.9%. The gene-corrected iPSCs retained a normal karyotype following removal of drug selection cassette using a Cre-LoxP system. Importantly, both F8 transcription and FVIII secretion were rescued in the candidate cell types for HA gene therapy including endothelial cells (ECs) and mesenchymal stem cells (MSCs) derived from the gene-corrected iPSCs. This is the first report of an efficient in situ genetic correction of the large inversion mutation using a strategy of targeted gene addition.

Gene therapy for hemophilia

Hemophilia is an X-linked inherited bleeding disorder consisting of two classifications, hemophilia A and hemophilia B, depending on the underlying mutation. Although the disease is currently treatable with intravenous delivery of replacement recombinant clotting factor, this approach represents a significant cost both monetarily and in terms of quality of life. Gene therapy is an attractive alternative approach to the treatment of hemophilia that would ideally provide life-long correction of clotting activity with a single injection. In this review, we will discuss the multitude of approaches that have been explored for the treatment of both hemophilia A and B, including both in vivo and ex vivo approaches with viral and nonviral delivery vectors.

Nonviral gene targeting at rDNA locus of human mesenchymal stem cells

Background. Genetic modification, such as the addition of exogenous genes to the MSC genome, is crucial to their use as cellular vehicles. Due to the risks associated with viral vectors such as insertional mutagenesis, the safer nonviral vectors have drawn a great deal of attention. Methods. VEGF, bFGF, vitamin C, and insulin-transferrin-selenium-X were supplemented in the MSC culture medium. The cells' proliferation and survival capacity was measured by MTT, determination of the cumulative number of cells, and a colony-forming efficiency assay. The plasmid pHr2-NL was constructed and nucleofected into MSCs. The recombinants were selected using G418 and characterized using PCR and Southern blotting. Results. BFGF is critical to MSC growth and it acted synergistically with vitamin C, VEGF, and ITS-X, causing the cells to expand significantly. The neomycin gene was targeted to the rDNA locus of human MSCs using a nonviral human ribosomal targeting vector. The recombinant MSCs retained multipotential differentiation capacity, typical levels of hMSC surface marker expression, and a normal karyotype, and none were tumorigenic in nude mice. Conclusions. Exogenous genes can be targeted to the rDNA locus of human MSCs while maintaining the characteristics of MSCs. This is the first nonviral gene targeting of hMSCs.

A non-viral vector for potential DMD gene therapy study by targeting a minidystrophin-GFP fusion gene into the hrDNA locus

Gene therapy has emerged as a promising approach for the lethal disorder of Duchenne muscular dystrophy (DMD). Using a novel non-viral delivery system, the human ribosomal DNA (hrDNA) targeting vector, we targeted a minidystrophin-GFP fusion gene into the hrDNA locus of HT1080 cells with a high site-specific integrated efficiency of 10(-5), in which the transgene could express efficiently and continuously. The minidystrophin-GFP fusion protein was easily found to localize on the plasma membrane of HT1080 cells, indicating its possible physiologic performance. Our findings showed that the hrDNA-targeting vector might be highly useful for DMD gene therapy study.

Site-directed integration of transgenes: transposons revisited using DNA-binding-domain technologies

In the last 20 years, tools derived from DNA transposons have made major contributions to genetic studies from gene delivery to gene discovery. Various complementary and fairly ubiquitous DNA vehicles have been developed. Although many transposons are efficient DNA vehicles, they appear to have limited ability to target specific sequences, since all that is required at the integration locus is the presence of a short 2- to 4-bp sequence. Consequently, insertions mediated by transposon-based vectors occur somewhat randomly. In the past 5 years, strategies have emerged to enhance the site-specificity of transposon-based vectors, and to avoid random integrations. The first proposes that new target site specificity could be grafted onto a transposase by adding a new DNA-binding domain. Alternative strategies consist of indirectly targeting either the transposase or the transposon to a chosen genomic locus. The most important information available about each strategy are presented, and limitations and future prospects are discussed.