In situ generation of pseudotyped retroviral progeny by adenovirus-mediated transduction of tumor cells enhances the killing effect of HSV-tk suicide gene therapyin vitro andin vivo

Gene Therapy Applications of Viral Vectors

Viral vectors have frequently been applied in gene therapy with the final goal of treating various diseases in the areas of neurology, neurodegeneration, metabolic disease, and cancer. Vectors have been engineered based on AAV, adenoviruses, alphaviruses, herpes simplex viruses, lentiviruses, and retroviruses. Some vectors are suitable for short-term episomal transgene expression, whereas others are integrated into the host cell genome to provide long-term expression. Additionally, hybrid vectors with favorable features from different viruses have been developed. Therapeutic genes of choice have typically been toxic genes such as thymidine kinase, pro-apoptotic genes like Bax, and immunostimulatory genes (for instance, interleukin-12). A large number of animal studies have demonstrated proof of concept of viral gene therapy. Many types of viral vectors have been employed in more than 700 clinical trials that have been carried out or are currently in progress.

A vaccinia virus recombinant transcribing an alphavirus replicon and expressing alphavirus structural proteins leads to packaging of alphavirus infectious single cycle particles

Poxviruses and Alphaviruses constitute two promising viral vectors that have been used extensively as expression systems, or as vehicles for vaccine purposes. Poxviruses, like vaccinia virus (VV) are well-established vaccine vectors having large insertion capacity, excellent stability, and ease of administration. In turn, replicons derived from Alphaviruses like Semliki Forest virus (SFV) are potent protein expression and immunization vectors but stocks are difficult to produce and maintain. In an attempt to demonstrate the use of a Poxvirus as a means for the delivery of small vaccine vectors, we have constructed and characterized VV/SFV hybrid vectors. A SFV replicon cDNA was inserted in the VV genome and placed under the control of a VV early promoter. The replicon, transcribed from the VV genome as an early transcript, was functional, and thus capable of initiating its own replication and transcription. Further, we constructed a VV recombinant additionally expressing the SFV structural proteins under the control of a vaccinia synthetic early/late promoter. Infection with this recombinant produced concurrent transcription of the replicon and expression of SFV structural proteins, and led to the generation of replicon-containing SFV particles that were released to the medium and were able to infect additional cells. This combined VV/SFV system in a single virus allows the use of VV as a SFV delivery vehicle in vivo. The combination of two vectors, and the possibility of generating in vivo single-cycle, replicon containing alphavirus particles, may open new strategies in vaccine development or in the design of oncolytic viruses.

Specific inhibition of tumor cells by oncogenic EGFR specific silencing by RNA interference

Anticancer agents that have minimal effects on normal cells and tissues are ideal cancer drugs. Here, we show specific inhibition of human cancer cells carrying oncogenic mutations in the epidermal growth factor receptor (EGFR) gene by means of oncogenic allele-specific RNA interference (RNAi), both in vivo and in vitro. The allele-specific RNAi (ASP-RNAi) treatment did not affect normal cells or tissues that had no target oncogenic allele, whereas the suppression of a normal EGFR allele by a conventional in vivo RNAi caused adverse effects, i.e., normal EGFR is vital. Taken together, our current findings suggest that specific inhibition of oncogenic EGFR alleles without affecting the normal EGFR allele may provide a safe treatment approach for cancer patients and that ASP-RNAi treatment may be capable of becoming a safe and effective, anticancer treatment method.

Current Challenges and Future Directions in Recombinant AAV-Mediated Gene Therapy of Duchenne Muscular Dystrophy

Various characteristics of adeno-associated virus (AAV)-based vectors with long-term safe expression have made it an exciting transduction tool for clinical gene therapy of Duchenne muscular dystrophy (DMD). Although host immune reactions against the vector as well as transgene products were detected in some instances of the clinical studies, there have been promising observations. Methods of producing AAV vectors for considerable in vivo experimentation and clinical investigations have been developed and a number of studies with AAV vector-mediated muscle transduction were attempted. Notably, an intravenous limb perfusion transduction technique enables extensive transgene expression in the skeletal muscles without noticeable adverse events. Furthermore, cardiac transduction by the rAAV9-microdystrophin would be promising to prevent development of cardiac dysfunction. Recent achievements in transduction technology suggest that long-term transgene expression with therapeutic benefits in DMD treatment would be achieved by the rAAV-mediated transduction strategy with an adequate regimen to regulate host immune response.

[Gene therapy with vector-producing multipotent mesenchymal stromal cells]

Suicide gene therapy with retroviral vector-producing cells was feasible as an adjuvant to the surgical resection of recurrent glioblastoma, although any benefit appeared to be marginal. Further evaluation of the therapeutic strategy with the vector-producing cells must incorporate improved delivery of vectors and transgenes to the target cells. We have previously demonstrated the ability of vector-producing tumor cells engineered by the adenovirus-retrovirus hybrid vector to destroy satellite tumor cells, although therapeutic efficacy for aggressive tumor has to be further evaluated by the systemic delivery of the vector-producing cells. Mesenchymal stem cells (MSCs) should be an effective delivery vehicle to seek out tumor cells in vivo and transport cancer-killing gene or immune products with minimal rejection reaction by the host. We developed vector-producing tumor-tracking cells to improve suicide cancer gene therapy. Nucleofection was attempted to deliver retrovirus vector components into rodent MSCs. Athymic nude mice with subcutaneous 9L glioma were received vector-producing MSCs through the left ventricular cavity. Optical bioluminescence imaging in vivo revealed accumulation of the MSCs into the subcutaneous 9L tumors but not Rat-1 transplants. Consequently, the vector-producing MSCs significantly enhanced pro-drug killing of glioma cells compared to MSCs without ability to generate progeny virus. Our study demonstrated the effective MSCs-mediated tumor transduction with progeny vector production to improve suicide gene therapy. Although therapeutic benefit in the various orthotopic or metastatic tumor models has to be further validated, this transduction strategy would eradicate evasive tumors in situ.

Scalable purification of adeno-associated virus serotype 1 (AAV1) and AAV8 vectors, using dual ion-exchange adsorptive membranes

In vivo gene transduction with adeno-associated virus (AAV)-based vectors depends on laborious procedures for the production of high-titer vector stocks. Purification steps for efficient clearance of impurities such as host cell proteins and empty vector particles are required to meet end-product specifications. Therefore, the development of alternative, realistic methods to facilitate a scalable virus recovery procedure is critical to promote in vivo investigations. However, the conventional purification procedure with resin-based packed-bed chromatography suffers from a number of limitations, including variations in pressure, slow pore diffusion, and large bed volumes. Here we have employed disposable high-performance anion- and cation-exchange membrane adsorbers to effectively purify recombinant viruses. As a result of isoelectric focusing analysis, the isoelectric point of empty particles was found to be significantly higher than that of packaged virions. Therefore, AAV vector purification with the membrane adsorbers was successful and allowed higher levels of gene transfer in vivo without remarkable signs of toxicity or inflammation. Electron microscopy of the AAV vector stocks obtained revealed highly purified virions with as few as 0.8% empty particles. Furthermore, the membrane adsorbers enabled recovery of AAV vectors in the transduced culture supernatant. Also, the ion-exchange enrichment of retroviral vectors bearing the amphotropic envelope was successful. This rapid and scalable viral purification protocol using disposable membrane adsorbers is particularly promising for in vivo experimentation and clinical investigations.

Retroviral vector-producing mesenchymal stem cells for targeted suicide cancer gene therapy

BACKGROUND

Mesenchymal stem cells (MSCs) are a promising vehicle for targeted cancer gene therapy because of their potential of tumor tropism. For efficient therapeutic application, we developed retroviral vector-producing MSCs that enhance tumor transduction via progeny vector production.

METHODS

Rat bone marrow-derived MSCs were nucleofected with the proviral plasmids (vesicular stomatitis virus-G protein-pseudotyped retroviral vector components) (VP-MSCs) or pLTR plasmid alone (non-VP-MSCs). The luciferase-based in vivo imaging system was used to assess gene expression periodically. To evaluate the anticancer effects, we administered MSCs expressing herpes simplex virus-thymidine kinase (HSV-tk) into the left ventricular cavity of nude mice engrafted with 9L glioma cells subcutaneously.

RESULTS

In vivo imaging revealed that administration of luciferase-expressing non-VP-MSCs enhanced the bioluminescence signal at the inoculation sites of 9L cells, whereas no accumulation was observed in mice at the site of the control Rat-1 fibroblasts. Compared to non-VP-MSCs, the administration of VP-MSCs resulted in significant augmentation of the signal with an increase in transgene copy number. Immunohistochemical analysis showed marked luciferase expression at the tumor periphery in mice injected with VP-MSCs, whereas little expression was detected in those injected with non-VP-MSCs. Under the continuous infusion of ganciclovir, systemic administration of VP-MSCs expressing HSV-tk suppressed tumor growth more effectively than non-VP-MSC administration, whereas no anticancer effect was observed without ganciclovir treatment. Furthermore, VP-MSC administration caused no transgene transduction in the normal tissues and organs.

CONCLUSIONS

VP-MSCs accumulated at the site of tumors after intravascular injection in tumor-bearing mice, followed by in situ gene transfer to tumors without transduction of normal organs. When applied to the HSV-tk/ganciclovir suicide gene therapy, more efficient tumor growth suppression was observed using VP-MSCs compared to non-VP-MSCs. This VP-MSC-based system has great potential for improved cancer gene therapy.

The piggyBac transposon is an integrating non-viral gene transfer vector that enhances the efficiency of GDEPT

Gene-directed enzyme prodrug therapy (GDEPT) is a strategy developed to selectively target cancer cells. However, the clinical benefit is limited due to its poor gene transfer efficiency. To overcome this obstacle, we took advantage of piggyBac (PB) transposon, a natural non-viral gene vector that can induce stable chromosomal integration and persistent gene expression in vertebrate cells, including human cells. To determine whether the vector can also mediate stable gene expression in ovarian cancer cells, we constructed a PB transposon system that simultaneously expresses the Herpes simplex virus thymidine kinase (HSV-tk) gene and the monomeric red fluorescent protein (mRFP1) reporter gene. The recombinant plasmid, pPB/TK, was transfected into ovarian adenocarcinoma cells SKOV3 with FuGENE HD reagent, and the efficiency was given by the percentage of mRFP1-positive cells detected by flow cytometry and confocal microscopy. The specific expression of HSV-tk in transfected cells was confirmed by RT-PCR and western blotting. The sensitivity of transfected cells to pro-drug ganciclovir (GCV) was determined by methylthiazoletetrazolium (MTT) assay. A total of 56.4 +/- 8.4% cells transfected with pPB/TK were mRFP1 positive, compared to no measurable mRFP1 expression in pORF-HSVtk-transfected cells. The expression level of HSV-tk in pPB/TK-transfected cells was 10 times higher than in pORF-HSVtk-transfected cells. The results show that pPB/TK transfection increases the sensitivity of cells to GCV in a dose-dependent manner. Our data indicate that the PB transposon system could enhance the anti-tumor efficiency of GDEPT in ovarian cancer.

Phage phiC31 integrase-mediated genomic integration of the common cytokine receptor gamma chain in human T-cell lines

BACKGROUND

X-linked severe combined immunodeficiency (SCID-X1, X-SCID) is a life-threatening disease caused by a mutated common cytokine receptor gamma chain (gammac) gene. Although ex vivo gene therapy, i.e., transduction of the gammac gene into autologous CD34(+) cells, has been successful for treating SCID-X1, the retrovirus vector-mediated transfer allowed dysregulated integration, causing leukemias. Here, to explore an alternative gene transfer methodology that may offer less risk of insertional mutagenesis, we employed the phiC31 integrase-based integration system using human T-cell lines, including the gammac-deficient ED40515(-).

METHODS

A phiC31 integrase and a neo(r) gene expression plasmid containing the phiC31 attB sequence were co-delivered by electroporation into Jurkat cells. After G418 selection, integration site analyses were performed using linear amplification mediated-polymerase chain reaction (LAM-PCR). ED40515(-) cells were also transfected with a gammac expression plasmid containing attB, and the integration sites were determined. IL-2 stimulation was used to assess the functionality of the transduced gammac in an ED40515(-)-derived clone.

RESULTS

Following co-introduction of the phiC31 integrase expression plasmid and the plasmid carrying attB, the efficiency of integration into the unmodified human genome was assessed. Several integration sites were characterized, including new integration sites in intergenic regions on chromosomes 13 and 18 that may be preferred in hematopoietic cells. An ED40515(-) line bearing the integrated gammac gene exhibited stable expression of the gammac protein, with normal IL-2 signaling, as assessed by STAT5 activation.

CONCLUSIONS

This study supports the possible future use of this phiC31 integrase-mediated genomic integration strategy as an alternative gene therapy approach for treating SCID-X1.

Large-Scale Production of Recombinant Viruses by Use of a Large Culture Vessel with Active Gassing

Adenovirus and adeno-associated virus (AAV) vectors are increasingly used for gene transduction experiments. However, to produce a sufficient amount of these vectors for in vivo experiments requires large-capacity tissue culture facilities, which may not be practical in limited laboratory space. We describe here a large-scale method to produce adenovirus and AAV vectors with an active gassing system that uses large culture vessels to process labor- and cost-effective infection or transfection in a closed system. Development of this system was based on the infection or transfection of 293 cells on a large scale, using a large culture vessel with a surface area of 6320 cm2. A minipump was connected to the gas inlet of the large vessel, which was placed inside the incubator, so that the incubator atmosphere was circulated through the vessel. When active gassing was employed, the productivity of the adenovirus and AAV vectors significantly increased. This vector production system was achieved by improved CO2 and air exchange and maintenance of pH in the culture medium. Viral production with active gassing is particularly promising, as it can be used with existing incubators and the large culture vessel can readily be converted for use with the active gassing system.

Transcriptional targeting of RGD fiber-mutant adenovirus vectors can improve the safety of suicide gene therapy for murine melanoma

Since RGD fiber-mutant adenovirus vector (AdRGD), which contains an alphav-integrin tropism, is highly efficient in gene transduction to melanoma, the AdRGD-mediated herpes simplex virus thymidine kinase (HSVtk)/ganciclovir (GCV) system is an attractive approach for melanoma treatment. However, the intratumoral injection of AdRGD causes limited transgene expression in healthy normal tissue, due to unwanted vector spread. Herein, we describe our attempt to overcome this limitation related to the safety of HSVtk/GCV treatment by using AdRGD carrying either melanoma-specific tyrosinase (Tyr) promoter or tumor-specific telomerase reverse transcriptase (TERT) promoter instead of universal cytomegalovirus promoter. Our in vitro study revealed that Tyr promoter-regulated AdRGD exhibited high transgene expression specificity for melanoma cells, and that TERT promoter-regulated AdRGD could induce efficient gene expression in tumor cells, but was relatively quiescent in normal cells. Anti-B16BL6 melanoma effects in mice injected intratumorally with AdRGD-Tyr/HSVtk or AdRGD-TERT/HSVtk, after which GCV was injected intraperitoneally for 10 days, were comparable to those in mice injected with AdRGD-CMV/HSVtk at 10 times less vector dosage. On the other hand, AdRGD-Tyr/HSVtk and AdRGD-TERT/HSVtk did not induce severe adverse effects even when they were intravenously injected into mice at 10(9) plaque-forming units (PFU), whereas mice injected with AdRGD-CMV/HSVtk at 10(8) PFU exhibited body weight reduction and serum level increase of biochemical enzymes for hepatotoxicity. These results indicate that AdRGD combined with transcriptional regulation using Tyr or TERT promoter is a potentially useful and safe vector system for suicide gene therapy for melanoma.