Construction and characterization of retroviral vectors expressing biologically active human interleukin-12

Internal Ribosome Entry Site (IRES)-Mediated Translation and Its Potential for Novel mRNA-Based Therapy Development

Many conditions can benefit from RNA-based therapies, namely, those targeting internal ribosome entry sites (IRESs) and their regulatory proteins, the IRES trans-acting factors (ITAFs). IRES-mediated translation is an alternative mechanism of translation initiation, known for maintaining protein synthesis when canonical translation is impaired. During a stress response, it contributes to cell reprogramming and adaptation to the new environment. The relationship between IRESs and ITAFs with tumorigenesis and resistance to therapy has been studied in recent years, proposing new therapeutic targets and treatments. In addition, IRES-dependent translation initiation dysregulation is also related to neurological and cardiovascular diseases, muscular atrophies, or other syndromes. The participation of these structures in the development of such pathologies has been studied, yet to a far lesser extent than in cancer. Strategies involving the disruption of IRES–ITAF interactions or the modification of ITAF expression levels may be used with great impact in the development of new therapeutics. In this review, we aim to comprehend the current data on groups of human pathologies associated with IRES and/or ITAF dysregulation and their application in the designing of new therapeutic approaches using them as targets or tools. Thus, we wish to summarise the evidence in the field hoping to open new promising lines of investigation toward personalised treatments.

Adaptive Immunity and the Tumor Microenvironment

The adaptive immune response is a 500-million-year-old (the "Big Bang" of Immunology) collective set of rearranged and/or selected receptors capable of recognizing soluble and cell surface molecules or shape (B cells, antibody), endogenous and extracellular peptides presented by Major Histocompatibility (MHC) molecules including Class I and Class II (conventional αβ T cells), lipid in the context of MHC-like molecules of the CD1 family (NKT cells), metabolites and B7 family molecules/butyrophilins with stress factors (γδT cells), and stress ligands and absence of MHC molecules (natural killer, NK cells). What makes tumor immunogenic is the recruitment of initially innate immune cells to sites of stress or tissue damage with release of Damage-Associated Molecular Pattern (DAMP) molecules. Subsequent maintenance of a chronic inflammatory state, representing a balance between mature, normalized blood vessels, innate and adaptive immune cells and the tumor provides a complex tumor microenvironment serving as the backdrop for Darwinian selection, tumor elimination, tumor equilibrium, and ultimately tumor escape. Effective immunotherapies are still limited, given the complexities of this highly evolved and selected tumor microenvironment. Cytokine therapies and Immune Checkpoint Blockade (ICB) enable immune effector function and are largely dependent on the shape and size of the B and T cell repertoires (the "adaptome"), now accessible by Next-Generation Sequencing (NGS) and dimer-avoidance multiplexed PCR. How immune effectors access the tumor (infiltrated, immune sequestered, and immune desserts), egress and are organized within the tumor are of contemporary interest and substantial investigation.

Production and Application of Multicistronic Constructs for Various Human Disease Therapies

The development of multicistronic vectors has opened up new opportunities to address the fundamental issues of molecular and cellular biology related to the need for the simultaneous delivery and joint expression of several genes. To date, the examples of the successful use of multicistronic vectors have been described for the development of new methods of treatment of various human diseases, including cardiovascular, oncological, metabolic, autoimmune, and neurodegenerative disorders. The safety and effectiveness of the joint delivery of therapeutic genes in multicistronic vectors based on the internal ribosome entry site (IRES) and self-cleaving 2A peptides have been shown in both in vitro and in vivo experiments as well as in clinical trials. Co-expression of several genes in one vector has also been used to create animal models of various inherited diseases which are caused by mutations in several genes. Multicistronic vectors provide expression of all mutant genes, which allows the most complete mimicking disease pathogenesis. This review comprehensively discusses multicistronic vectors based on IRES nucleotide sequence and self-cleaving 2A peptides, including its features and possible application for the treatment and modeling of various human diseases.

Comparing the effects of different cell death programs in tumor progression and immunotherapy

Our conception of programmed cell death has expanded beyond apoptosis to encompass additional forms of cell suicide, including necroptosis and pyroptosis; these cell death modalities are notable for their diverse and emerging roles in engaging the immune system. Concurrently, treatments that activate the immune system to combat cancer have achieved remarkable success in the clinic. These two scientific narratives converge to provide new perspectives on the role of programmed cell death in cancer therapy. This review focuses on our current understanding of the relationship between apoptosis and antitumor immune responses and the emerging evidence that induction of alternate death pathways such as necroptosis could improve therapeutic outcomes.

Systematic comparison of 2A peptides for cloning multi-genes in a polycistronic vector

Cloning of multiple genes in a single vector has greatly facilitated both basic and translational studies that require co-expression of multiple factors or multi-units of complex protein. Many strategies have been adopted, among which 2A “self-cleaving” peptides have garnered increased interest for their polycistronic nature, small size and high “cleavage” efficiency. However, broad application of 2 A peptides is limited by the lack of systematic comparison of different 2As alone or in combination. Here we characterized the effect of varying gene position and 2As on the expression of proteins encoded in bi-, tri-, or quad-cistronic constructs. Using direct cardiac reprogramming as an example, we further determined the effect of varied 2As on the efficiency of fluorescent cell labeling and cell fate conversion. We found that the expression of fluorophores decreased as it was moved towards the end of the construct while reprogramming was most efficient with the fluorophore at the second position. Moreover, quad-cistronic TPE2A constructs resulted in more efficient reprogramming than 3P2A or PTE2A constructs. We expect that the bi-, tri-, and quad-cistronic vectors constructed here and our results on protein expression ratios from different 2A constructs could serve to guide future utilization of 2A peptides in basic research and clinical applications.

Engraftability of Murine Bone Marrow-Derived Multipotent Mesenchymal Stem Cell Subpopulations in the Tissues of Developing Mice following Systemic Transplantation

INTRODUCTION

Cell therapies for generalized musculoskeletal diseases would require distribution of cells to all the skeletal tissues; however, there are controversies regarding the transplantability of multipotent mesenchymal stems cells (MSCs). We generated single-cell subpopulations of MSCs from murine bone marrow and assessed them for differences in trafficking through the circulatory system and engraftment in bone and other tissues.

MATERIALS AND METHODS

Seven single-cell clonal subpopulations were generated by serial dilution of GFP-marked MSCs isolated from bone marrow. The subpopulations were examined for putative MSC surface marker expression, in vitro differentiation toward osteogenic and adipogenic lineages, migration and engraftment in different tissues following intravenous delivery in normal, sublethally irradiated neonatal mice.

RESULTS

The surface marker expression profile revealed notable differences among clonal cells, specifically CD44 and CD105. All the cell subpopulations differentiated toward osteogenic and adipogenic lineages, with some committed to only one or the other. Two clones enriched in CXCR4 expression were highly efficient in migrating and engrafting in skeletal tissue including bone; this confirmed the role of this chemokine in cell migration. Donor cells retrieved from various tissues displayed different morphologies and potential differentiation into tissue cell type of engraftment, suggesting modification by the tissues in which the donor cells engrafted.

CONCLUSION

We have reported that, within bone marrow, there are heterogeneous subpopulations of MSCs that may differ in their ability to migrate in the circulatory system and engraft in different tissues.

Targeting the tumor microenvironment to enhance antitumor immune responses

The identification of tumor-specific antigens and the immune responses directed against them has instigated the development of therapies to enhance antitumor immune responses. Most of these cancer immunotherapies are administered systemically rather than directly to tumors. Nonetheless, numerous studies have demonstrated that intratumoral therapy is an attractive approach, both for immunization and immunomodulation purposes. Injection, recruitment and/or activation of antigen-presenting cells in the tumor nest have been extensively studied as strategies to cross-prime immune responses. Moreover, delivery of stimulatory cytokines, blockade of inhibitory cytokines and immune checkpoint blockade have been explored to restore immunological fitness at the tumor site. These tumor-targeted therapies have the potential to induce systemic immunity without the toxicity that is often associated with systemic treatments. We review the most promising intratumoral immunotherapies, how these affect systemic antitumor immunity such that disseminated tumor cells are eliminated, and which approaches have been proven successful in animal models and patients.

Bioengineering heterodimeric cytokines: turning promiscuous proteins into therapeutic agents

The interleukin 12 (IL-12) family comprises a group of heterodimeric cytokines that can cope with a great variety of immune conditions as the microenvironment demands. By sharing cytokine and receptor subunits, IL-12 (comprised of p40/p35 subunits), IL-23 (p40/p19), IL-27 (p28/EBI3), and IL-35 (p35/EBI3) represent, as a whole, a highly versatile system participating in controlling the continuum from inflammation to tolerance. Promiscuity, a peculiar feature of those cytokines, is a powerful and economic means of producing individual factors with distinct activities via different combinations of a single set of subunits. Whereas IL-12 and IL-23 have a clearly dominant immunostimulatory functional profile and IL-35 is a potent immunosuppressive agent, IL-27 can exert both adjuvant and regulatory effects, depending on the cytokine milieu. Promiscuity itself, however, may significantly hamper the therapeutic use of heterodimeric cytokines. The subunits of a recombinant cytokine, when administered in its native form, will rapidly dissociate in vivo and reassociate with alternative partners, thus generating different heterodimeric or even homodimeric molecules (i.e., p40/p40) with unwanted effects. As in other areas, bioengineering has provided a formidable tool to overcome the constraints associated with the potential use of IL-12 family cytokines. The generation of several gene constructs expressing IL-12, IL-23, IL-27, IL-35, or even the homodimer p40/p40, in their monomerized, single-chain form has allowed us to unveil the efficacy of those molecules in several experimental settings, including neoplasia, viral infection, chronic inflammation, allergy and autoimmunity. Although work is still needed to obtain an overall picture of therapeutic vs. adverse effects of individual molecules before any use in humans, the new frontiers of bioengineering are now driving the production of completely new combinations of cytokine subunits that may further extend the potential clinical use of such eclectic proteins.

Bladder Cancer Immunotherapy: BCG and Beyond

Mycobacterium bovis bacillus Calmette-Guérin (BCG) has become the predominant conservative treatment for nonmuscle invasive bladder cancer. Its mechanism of action continues to be defined but has been shown to involve a T helper type 1 (Th1) immunomodulatory response. While BCG treatment is the current standard of care, a significant proportion of patients fails or do not tolerate treatment. Therefore, many efforts have been made to identify other intravesical and immunomodulating therapeutics to use alone or in conjunction with BCG. This paper reviews the progress of basic science and clinical experience with several immunotherapeutic agents including IFN-α, IL-2, IL-12, and IL-10.

Bone marrow stromal cells contribute to bone formation following infusion into femoral cavities of a mouse model of osteogenesis imperfecta

Currently, there are conflicting data in literature regarding contribution of bone marrow stromal cells (BMSCs) to bone formation when the cells are systemically delivered in recipient animals. To understand if BMSCs contribute to bone cell phenotype and bone formation in osteogenesis imperfecta bones (OI), MSCs marked with GFP were directly infused into the femurs of a mouse model of OI (oim). The contribution of the cells to the cell phenotype and bone formation was assessed by histology, immunohistochemistry and biomechanical loading of recipient bones. Two weeks following infusion of BMSCs, histological examination of the recipient femurs demonstrated presence of new bone when compared to femurs injected with saline which showed little or no bone formation. The new bone contained few donor cells as demonstrated by GFP fluorescence. At 6 weeks following cell injection, new bone was still detectable in the recipient femurs but was enhanced by injection of the cells suspended in pepsin solubilized type I collagen. Immunofluorescence and immunohistochemical staining showed that donor GFP positive cells in the new bone were localized with osteocalcin expressing cells suggesting that the cells differentiated into osteoblasts in vivo. Biomechanical loading to failure in three point bending, revealed that, femurs infused with BMSCs in PBS or in soluble type I collagen were biomechanically stronger than those injected with PBS or type I collagen alone. Taken together, the results indicate that transplanted cells differentiated into osteoblasts in vivo and contributed to bone formation in vivo; we also speculate that donor cells induced differentiation or recruitment of endogenous cells to initiate reparative process at early stages following transplantation.

Hypoxia targeting gene expression for breast cancer gene therapy

Gene therapy is a promising strategy to treat various inherited and acquired diseases. However, targeting gene expression to specific tissue is required to minimize side effects of gene therapy. Hypoxia is present in the microenvironment of solid tumors such as breast tumors. A hypoxic tumor targeting gene expression system has been developed for cancer gene therapy. In hypoxic tissues, hypoxia inducible factor (HIF)-1alpha is accumulated and stimulates transcription of the genes that have hypoxia response elements (HREs) in their promoters. Therefore, transcriptional regulation with a hypoxia inducible promoter is the most widely used strategy for hypoxic tumors targeting gene therapy. In breast cancer gene therapy, breast tumor specific promoters in combination with HREs have been used to induce gene expression in hypoxic breast tumors. Post-transcriptional regulation using an untranslated region (UTR) is also a useful strategy to increase gene expression in hypoxic tumor tissue. In addition, post-translational regulation with the oxygen-dependent degradation (ODD) domain is effective to eliminate therapeutic gene products and reduce side effects in normal tissue. In combination with the breast tumor specific promoters, hypoxic tumor targeting strategies will be useful for the development of a safe breast cancer gene therapy.

Respiratory Homeostasis and Exploitation of the Immune System for Lung Cancer Vaccines

Lung cancer is the leading cause of all cancer deaths in the US. The international scientific and clinical community has made significant advances toward understanding specific molecular mechanisms underlying lung carcinogenesis; however, despite these insights and advances in surgery and chemoradiotherapy, the prognosis for non-small-cell lung cancer (NSCLC) remains poor. Nonetheless, significant effort is being focused on advancing translational research evaluating the efficacy of novel targeted therapeutic strategies for lung cancer. Illustrative examples of this include antagonists of the epidermal growth factor receptor (EGFR), tyrosine kinase inhibitors (TKIs) such as gefitinib and erlotinib, and a diverse assortment of anti-angiogenic compounds targeting growth factors and/or their receptors that regulate tumor-associated angiogenic programs. In addition, with the increased awareness of the significant role chronically activated leukocytes play as potentiators of solid-tumor development, the role of innate and adaptive immune cells as regulators of lung carcinogenesis is being examined. While some of these studies are examining how novel therapeutic strategies may enhance the efficacy of lung cancer vaccines, others are evaluating the intrinsic characteristics of the immune response to lung cancer in order to identify rate-limiting molecular and/or cellular programs to target with novel anticancer therapeutics. In this article, we explore important aspects of the immune system and its role in regulating normal respiratory homeostasis compared with the immune response accompanying development of lung cancer. These hallmarks are then discussed in the context of recent efforts to develop lung cancer vaccines, where we have highlighted important concepts that must be taken into consideration for future development of novel therapeutic strategies and clinical trials assessing their efficacy.

Preclinical study of an ex vivo gene therapy protocol for hepatocarcinoma

Preclinical studies in several animal models as well as clinical trials have shown a reduction in tumor growth following immunotherapy with interleukin-12 (IL-12). This cytokine is appropriate to test in therapeutic clinical trials to treat hepatocarcinoma (HC), a pathology often associated with hepatitis B or C-induced cirrhosis. The local delivery into the liver would be achieved through ex vivo gene transfer using retroviral (rv) vectors in autologous fibroblast carriers. In support of this clinical trial, a rv vector has been constructed to express coordinately both chains p35 and p40 of human IL-12. Here, we have tested good manufacturing practices (GMP) clinical lots of viral vectors derived from the transfected packaging cell line, PG13rvIL-12. We have also devised methods to facilitate the isolation of fibroblasts from freshly harvested skin specimens, enhance their outgrowth in large-scale cultures and assay IL-12 production following transduction, without any selection and irradiation. Twenty-four human skin specimens were processed to obtain fibroblast suspensions that were typically maintained for up to 8 or 12 passages. The mean +/-s.d. overall time for obtaining the required number of transduced cells for the highest IL-12 need was 40 days. The procedure, in accordance with the French medical agency for gene therapy clinical trials, is now ready to begin a clinical trial.

Distribution of single-cell expanded marrow derived progenitors in a developing mouse model of osteogenesis imperfecta following systemic transplantation

We evaluated single-cell-expanded, marrow-derived progenitors for engraftment in a developing mouse model of osteogenesis imperfecta (OI) following systemic transplantation. The present study was initiated to evaluate the potential of mesenchymal stem cells to treat OI. Single-cell-derived progenitors were prepared from marrow stromal cells harvested from normal mice. Selected single-cell-expanded progenitors marked with green fluorescent protein were injected into the neonatal mouse model of OI, and the recipient mice were sacrificed at 2 and 4 weeks following cell transplantation. Examination of the tissues harvested from recipient mice at 2 and 4 weeks after cell transplantation demonstrated that the cells extravasated and engrafted in most of the bones as well as other tissues. Tissue sections made from the tibias and femurs of a selected recipient mouse showed that the cells were distributed in bone marrow, trabecular, and cortical bone as demonstrated by histology and confocal microscopy. The cells that engrafted in the bones of the recipient mouse synthesized and deposited type I collagen composed of alpha1(I) and alpha2(I) collagen heterotrimers. Genotyping and gene expression analysis of the cells retrieved from the bones of the recipient mouse at 2 and 4 weeks demonstrated that the cells expressed osteoblast-specific genes, suggesting that the donor cells differentiated into osteoblasts in vivo with no evidence of cell fusion. These data suggest that progenitors infused in developing mice will engraft in various tissues including bones, undergo differentiation, and deposit matrix and form bone in vivo. Disclosure of potential conflicts of interest is found at the end of this article.

Angiogenesis meets immunology: Cytokine gene therapy of cancer

Delivery of cytokine genes at the tumor site in pre-clinical models has been shown to recruit host inflammatory cells followed by inhibition of tumor growth. This local effect is often accompanied by systemic protection mediated by the immune system, mainly by CD8(+) T and NK cells. On this basis, cytokine gene-transduced tumor cells have widely been used as vaccines in clinical trials, which have shown good safety profiles and some local responses but substantial lack of systemic efficacy. Are these findings the end of the story? Possibly not, if major improvements will be attained in the coming years. These should be directed at the level of gene selection and delivery, in order to identify the optimal cytokine and achieve efficient and durable cytokine expression, and at the level of improving immune stimulation, i.e. by co-administration of co-stimulatory molecules including B7 and CD40, or boosting the expression of tumor antigens or MHC class I molecules. Interestingly, some of the cytokines which have shown encouraging anti-tumor activity, including IFNs, IL-4, IL-12 and TNF-alpha, are endowed with anti-angiogenic or vasculotoxic effects, which may significantly contribute to local tumor control. Therapeutic exploitation of this property may result in the design of novel approaches which, by maximizing immune-stimulating and anti-angiogenic effects, could possibly lead to starvation of established tumors in patients.

Picornavirus internal ribosome entry site elements can stimulate translation of upstream genes

Certain viral and cellular mRNAs initiate translation cap-independently at internal ribosome entry site (IRES) elements. Picornavirus IRES elements are widely used in dicistronic or multicistronic vectors in gene therapy, virus replicon systems, and analysis of IRES function. In such vectors, expression of the upstream gene often serves as internal control to standardize the readings of IRES-driven downstream reporter activity. Picornaviral IRES elements translate optimally at up to 120 mM K(+) concentration, whereas genes used as upstream reporters usually have lower salt optima when present in monocistronic mRNAs. However, here we show that such reporter genes are efficiently translated at higher K(+) concentrations when placed upstream of a functional picornavirus IRES. This translation enhancement occurs in cis, is independent of the nature of the first reporter and of second reporter translation, and is conferred by the IRESs of picornaviruses but not of hepatitis C virus. A defective picornavirus IRES with a deletion killing IRES activity but leaving the binding site for initiation factor eIF4G intact retains translation enhancement activity. Translation enhancement on a capped mRNA is disabled by m(7)GDP. In addition, the C-terminal fragment of eIF4G can confer translation enhancement also on uncapped mRNA. We conclude that whenever eIF4F has been captured to a dicistronic mRNA by binding to a picornavirus IRES via its eIF4G moiety, it can be provided in cis to the 5'-end of the RNA and there stimulate translation initiation, either by binding to the cap nucleotide using its eIF4E moiety or by binding to the RNA cap-independently using its eIF4G moiety.

Buffalo (Bubalus bubalis) interleukin-12: Analysis of expression profiles and functional cross-reactivity with bovine system

Interleukin-12, a heterodimeric pro-inflammatory cytokine, from water buffaloes (Bubalus bubalis) was analyzed for its for its tissue specific expression and functionality. Concanavalin A stimulated splenocytes displayed an up-regulation of the IL-12 p40 subunit 8-24h post-stimulation, whereas the p35 subunit did not show any quantitative variation at different time intervals. Basal level expressions of both the subunits were observed by RT-PCR in spleen. In addition p40 transcripts could be detected in liver and p35 in brain and muscle tissues as well in very low levels. Functional recombinant buffalo IL-12 was expressed in HEK 293T cells as a heterodimer using foot-and-mouth disease virus 2A polypeptide as a linker. Culture supernatants from transfected cells contained a hetero-dimeric p70 subunit as revealed in western blot of the proteins separated by native polyacrylamide gel electrophoresis (PAGE) using a monoclonal antibody against bovine IL-12 p40. IL-12 containing culture supernatant induced production of nitric oxide in cultured splenocytes of both buffalo and bovine origin. Our study reveals that buffalo IL-12, which shares a high-level sequence identity with bovine IL-12, also has functional cross-reactivity with the bovine immune cells.

Development of 2A peptide-based strategies in the design of multicistronic vectors

As science progresses in its understanding of diseases and their treatment, advances have been made in the biotechnology used in disease therapy. Most gene therapy approaches utilise viral vectors to deliver genes of interest. However, multiple proteins are often involved in disease processes and there is often a need to efficiently deliver more than one gene. Researchers have employed several strategies to accomplish this goal. When designing vectors to express multiple genes, there are several factors that need to be taken into account, including cell type, the activity of the protein of interest and subcellular protein localisation. In most cases, it is ideal for each protein to be expressed at comparable levels, a leading issue with traditional strategies for multigene expression. This review describes some of the techniques that have been used to express multiple genes, and will focus on the use of 2A peptides or 2A peptide-like sequences in the design of multicistronic vectors that may alleviate some of these issues.

A vector expressing feline mature IL-18 fused to IL-1beta antagonist protein signal sequence is an effective adjuvant to a DNA vaccine for feline leukaemia virus

DNA vaccination using vectors expressing the gag/pol and env genes of feline leukaemia virus (FeLV) and plasmids encoding feline interleukin-12 (IL-12) and IL-18 completely protected cats from viraemia following challenge [Hanlon L, Argyle D, Bain D, Nicolson L, Dunham S, Golder MC, et al. Feline leukaemia virus DNA vaccine efficacy is enhanced by coadministration with interleukin-12 (IL-12) and IL-18 expression vectors. J Virol 2001;75:8424-33]. However, the relative contribution of each cytokine gene towards protection is unknown. This study aimed to resolve this issue. IL-12 and IL-18 constructs were modified to ensure effective expression, and bioactivity was demonstrated using specific assays. Kittens were immunised intramuscularly with FeLV DNA and various cytokine constructs. Together with control kittens, these were challenged oronasally with FeLV and monitored for 15 weeks. All six kittens given FeLV, IL-12 and IL-18 were protected from the establishment of persistent viraemia and four from latent infection. Of six kittens immunised with FeLV DNA and IL-18, all were protected from viraemia and five from latent infection. In contrast, three of five kittens given FeLV DNA and IL-12 became persistently viraemic. Therefore, the adjuvant effect on the FeLV DNA vaccine appears to reside in the expression of IL-18.

The fate of mesenchymal stem cells transplanted into immunocompetent neonatal mice: implications for skeletal gene therapy via stem cells

To explore the feasibility of skeletal gene and cell therapies, we transduced murine bone marrow-derived mesenchymal stem cells (MSCs) with a retrovirus carrying the enhanced green fluorescent protein and zeocin-resistance genes prior to transplantation into 2-day-old immunocompetent neonatal mice. Whole-body imaging of the recipient mice at 7 days post-systemic cell injection demonstrated a wide distribution of the cells in vivo. Twenty-five days posttransplantation, most of the infused cells were present in the lung as assessed by examination of the cells cultured from the lungs of the recipient mice. The cells persisted in lung and maintained a high level of gene expression and could be recovered from the recipient mice at 150 days after cell transplantation. A significant number of GFP-positive cells were also present in the bones of the recipient mice at 35 days post-cell transplantation. Recycling of the cells recovered from femurs of the recipient mice at 25 days posttransplantation by repeated injections into different neonatal mice resulted in the isolation of a clone of cells that was detected in bone and cartilage, but not in lung and liver after systemic injection. These data demonstrate that MSCs persist in immunocompetent neonatal mice, maintain a high level of gene expression, and may participate in skeletal growth and development of the recipient animals.

Correction of multi-gene deficiency in vivo using a single 'self-cleaving' 2A peptide–based retroviral vector

Attempts to generate reliable and versatile vectors for gene therapy and biomedical research that express multiple genes have met with limited success. Here we used Picornavirus 'self-cleaving' 2A peptides, or 2A-like sequences from other viruses, to generate multicistronic retroviral vectors with efficient translation of four cistrons. Using the T-cell receptor:CD3 complex as a test system, we show that a single 2A peptide-linked retroviral vector can be used to generate all four CD3 proteins (CD3epsilon, gamma, delta, zeta), and restore T-cell development and function in CD3-deficient mice. We also show complete 2A peptide-mediated 'cleavage' and stoichiometric production of two fluorescent proteins using a fluorescence resonance energy transfer-based system in multiple cell types including blood, thymus, spleen, bone marrow and early stem cell progenitors.

Engineering the splice acceptor for improved gene expression and viral titer in an MLV-based retroviral vector

We have recently developed a retroviral vector that contains a splice acceptor from the human EF1-alpha gene and drives a significantly higher level of gene expression than other well known murine leukemia virus-based vectors. However, one downside of this vector is that viral titer significantly varies depending on the packaging lines used. Results from Northern blot analysis indicated that in certain cell lines the genomic transcript containing the packaging signal sequence was too efficiently spliced to the subgenomic RNA, resulting in low levels of genomic RNA and thus leading to a low viral titer. We tested the possibility of overcoming this problem by introducing mutations around the splice acceptor sequence in such a way that a delicate balance was maintained between the splicing efficiency (which determines the level of gene expression) and the amount of genomic transcript (which influences viral titer). After mutational analysis, one such mutant was found to meet this requirement. The newly constructed vector containing the engineered splice acceptor could indeed drive higher levels of expression in many therapeutic genes than other control vectors, without significantly compromising viral titer.

Delivery of IL-12 intranasally leads to reduced IL-12-mediated toxicity

Interleukin-12 (IL-12) is a heterodimeric cytokine that enhances immune responses to bacterial, parasitic, and viral pathogens, and leads to tumor regression in animal models. For this reason, the use of IL-12 as a vaccine adjuvant and as a therapeutic agent for the treatment of cancer is being investigated. Unfortunately, the extreme toxicity of this molecule observed during clinical trials has limited its use. This toxicity correlates with increased IFN-gamma expression, decreased glucose levels, and altered histological responses in the spleen and duodenum. In this study, we show that intranasal (i.n.) delivery of IL-12 is a less toxic route of inoculation compared to the commonly employed subcutaneous route. When delivered i.n., IL-12 induces less systemic IFN-gamma production and fewer pathological tissue changes, yet is efficacious, as indicated by enhanced CD3(+) T cell activation and increased production of Th1-associated immunoglobulins (i.e., serum IgG2a). Thus, IL-12 can be delivered safely and effectively by the i.n. route, a finding which may allow IL-12 to fulfill its clinical potential.

Gene therapy for human malignant brain tumors

PURPOSE

Brain tumors were the first human malignancy to be targeted by therapeutic transfer of nucleic acids into somatic cells, a process also known as gene therapy. Malignant brain tumor cells in the adult brain have some unique biologic features, such as high mitotic activity on an essentially postmitotic background and virtually no tumor spread outside of the central nervous system. Brain tumors seem therefore to offer major advantages in the design of tumor-selective gene therapy strategies, and the role of gene therapy in malignant glioma has been investigated since the late 1980s, initially in numerous laboratory studies and later on in clinical trials.

DESIGN

Retrovirus has been one of the earliest recombinant virus vectors used in brain tumors. Experiments in cell culture and in animal models have demonstrated the feasibility of retrovirus-mediated transduction and subsequent killing of glioma cells by toxic transgenes. Phase I and II clinical studies in patients with recurrent malignant glioma have shown a favorable safety profile and some efficacy of retrovirus-mediated gene therapy. However, the only prospective, randomized, phase III clinical study of retrovirus gene therapy in primary malignant glioma failed to demonstrate significant extension of progression-free or overall survival. Adenovirus- and herpes simplex virus type 1-based vectors have been actively investigated along with retrovirus, but their clinical use is still limited, mostly because of safety concerns. To increase efficacy, novel generations of therapeutic adenovirus and herpes simplex virus type 1 rely more on genetically engineered and tumor-selective lytic properties and less on the actual transfer of therapeutic genes.

CONCLUSIONS

The failure of most clinical gene therapy protocols to produce a significant and unequivocal benefitto brain tumor patients seems to be mainly due to the low tumor cell transduction rates observed in vivo, but it may also depend on the respective physical delivery strategy of the vector. Standard radiologic criteria for assessing the efficacy of clinical treatments may also not be fully applicable to the specific metabolic changes and blood-brain barrier permeability phenomena caused in brain tumors by virus-mediated gene therapy. Clinical trials in malignant glioma have nevertheless produced a substantial amount of data and have contributed to the continuous improvement of vector systems, delivery methods, and clinical protocols.

Inhibition of established subcutaneous and metastatic murine tumors by intramuscular electroporation of the interleukin-12 gene

In vivo electroporation (EP) of the murine interleukin-12 (IL-12) gene in an expression plasmid (pIL-12) was evaluated for antitumor activity. EP transfer of pIL-12 into mouse quadriceps muscles elicited significant levels of serum IL-12 and interferon-gamma. Intramuscular EP of pIL-12 resulted in complete regression or substantial inhibition of 38C13 B-cell lymphoma, whereas pIL-12 delivered by gene gun or intramuscular injection without EP showed little therapeutic effect. Impressive antitumor activity by intramuscular EP was also demonstrated in animals with advanced malignant disease. At day 14 after 38C13 tumor inoculation, all animals were found to carry large tumors and to have metastases; without treatment, most died within a week. A single intramuscular EP of pIL-12 resulted in regression of 50% of large subcutaneous tumors and significantly prolonged the lifespan of these animals. Moreover, animals that were previously cured of 38C13 tumors by in vivo EP treatment significantly suppressed tumor growth when challenged 60 days later. In vivo EP of the IL-12 gene was also effective in suppressing subcutaneous and lung metastatic tumors of CT-26 colon adenocarcinoma and B16F1 melanoma cells. Together, these results show that intramuscular electrotransfer of the IL-12 gene may represent a simple and effective strategy for cancer treatment.

In vivo selective expansion of gene-modified hematopoietic cells in a nonhuman primate model

A major problem limiting hematopoietic stem cell (HSC) gene therapy is the low efficiency of gene transfer into human HSCs using retroviral vectors. Strategies, which would allow in vivo expansion of gene-modified hematopoietic cells, could circumvent the problem. To this end, we developed a selective amplifier gene (SAG) consisting of a chimeric gene composed of the granulocyte colony-stimulating factor (G-CSF) receptor gene and the estrogen receptor gene hormone-binding domain. We have previously demonstrated that primary bone marrow progenitor cells transduced with the SAG could be expanded in response to estrogen in vitro. In the present study, we evaluated the efficacy of the SAG in the setting of a clinically applicable cynomolgus monkey transplantation protocol. Cynomolgus bone marrow CD34(+) cells were transduced with retroviral vectors encoding the SAG and reinfused into each myeloablated monkey. Three of the six monkeys that received SAG transduced HSCs showed an increase in the levels of circulating progeny containing the provirus in vivo following administration of estrogen or tamoxifen without any serious adverse effects. In one monkey examined in detail, transduced hematopoietic progenitor cells were increased by several-fold (from 5% to 30%). Retroviral integration site analysis revealed that this observed increase was polyclonal and no outgrowth of a dominant single clonal population was observed. These results demonstrate that the inclusion of our SAG in the retroviral construct allows selective in vivo expansion of genetically modified cells by a non-toxic hormone treatment.

Clinical-scale selection of anti-CD3/CD28-activated T cells after transduction with a retroviral vector expressing herpes simplex virus thymidine kinase and truncated nerve growth factor receptor

Activation of T cells is necessary for efficient retroviral-mediated gene transfer. In addition, if the population of infused cells is to be limited to transduced cells, a means of positive selection is required. We describe a clinical scale procedure for activation of donor T cells with anti-CD3/CD28 beads followed by transduction with a retroviral construct expressing the herpes simplex virus thymidine kinase (HSV-tk) and human nerve growth factor receptor (NGFR). Optimization of transduction parameters was performed, testing the timing of transduction, centrifugation, and the use of serum. In large-scale experiments, 3-5 x 10(8) peripheral blood mononuclear cells (PBMC) were activated with anti-CD3/CD28 beads and expanded to day 13. Transduction was accomplished using MFG-TKiNG supernatant produced from the PG13 packaging line 48 hr after T-cell activation. The mean transduction frequency was 37.5% based on NGFR expression, and the mean expansion observed was 42.6-fold (mean final cell number 1.85 x 10(10)). A comparison of the ability of the Baxter Isolex 300i and the Miltenyi CliniMACS to perform purification of NGFR+ cells suggests that greater purity can be achieved with the CliniMACS device (67.4% vs. 97.7%), while the yield of transduced cells appears higher with the Isolex 300i (41.3% vs. 23.5%). We conclude that a strategy based on activation of human T cells with anti-CD3/CD28 beads can result in sufficient transduction, expansion, and purification based on NGFR expression for clinical trials.

Enhancing antitumor by immunization with fusion of dendritic cells and engineered tumor cells

A novel approach for a dentritic cells (DCs)-based tumor vaccine was developed for the formation of hybrid-engineered J558 after fusion with DCs. To make the hybrid-tumor vaccine generate more efficient specific CTL cytotoxicity against wild-type tumor cells, we genetically engineered tumor cells with mIL-12 gene prior to the cell fusion. mIL-12 was detected at 870 +/- 60 pg/(10(5) cells/ml) in the culture supernatants and the fusion ratio was about 30% by the co-focal microscopic analysis. Vaccination of mice with DCs fused with engineered J558 induced more efficient tumor-specific CTL cytotoxicity against wild-type tumor cells in vitro and with efficient antitumor immunity in vivo. These results suggest that this approach of using DCs fused with engineered tumor cells could be applied in clinical settings of DCs-based cancer vaccines.

Production of biologically active equine interleukin 12 through expression of p35, p40 and single chain IL-12 in mammalian and baculovirus expression systems

Interleukin-12 (IL-12) is a key cytokine in the development of cell-mediated immune responses. Bioactive IL-12 is a heterodimeric cytokine composed of disulphide linked p35 and p40 subunits. The aim of this study was to verify biologically activity of the products expressed from equine interleukin-12 (IL-12) p35 and p40 cDNAs and to establish whether equine IL-12 could be expressed as a p35/p40 fusion polypeptide, as has been reported for IL-12a of several mammalian species. We report production of equine IL-12 through expression of p35 and p40 subunits in mammalian and insect cells and of a p35:p40 fusion polypeptide in mammalian cells. Conditioned medium recovered from cultures transiently transfected with constructs encoding equine p35 and p40 subunits or single chain IL-12 enhanced IFN-gamma production in cells derived from equine lymph nodes. Preincubation of IFN-gamma inducing preparations with anti-p40 monoclonal antibody resulted in a significant decrease in IFN-gamma induction capacity. Medium recovered from p35 and p40-expressing baculovirus infected cultures enhanced target cell IFN-gamma production and proliferation. Experimental studies in mice and other animals have revealed a therapeutic benefit of IL-12 in cancer, inflammatory and infectious disease and an adjuvant effect in prophylactic regimes. Production of a bioactive species-specific IL-12 is a first step towards an investigation of its potential application in equine species.

Composition and arrangement of genes define the strength of IRES-driven translation in bicistronic mRNAs

In addition to the cap-dependent mechanism, eukaryotic initiation of translation can occur by a cap-independent mechanism which directs ribosomes to defined start codons enabled by internal ribosome entry site (IRES) elements. IRES elements from poliovirus and encephalomyocarditis virus are often used to construct bi- or oligocistronic expression vectors to co-express various genes from one mRNA. We found that while cap-dependent translation initiation from bicistronic mRNAs remains comparable to monocistronic expression, internal initiation mediated by these viral IRESs is often very inefficient. Expression of bicistronic expression vectors containing the hepatitis B virus core antigen (HBcAg) together with various cytokines in the second cistron of bicistronic mRNAs gave rise to very low levels of the tested cytokines. On the other hand, the HBcAg was well expressed when positioned in the second cistron. This suggests that the arrangement of cistrons in a bicistronic setting is crucial for IRES-dependent translation of the second cistron. A systematic examination of expression of reporter cistrons from bicistronic mRNAs with respect to position was carried out. Using the dual luciferase assay system we show that the composition of reading frames on a bicistronic mRNA and the order in which they are arranged define the strength of IRES-dependent translation. Although the cellular environment and the nature of the IRES element influence translation strength the dominant determinant is the nature and the arrangement of cistrons on the mRNA.

In vivo electroporation-mediated transfer of interleukin-12 and interleukin-18 genes induces significant antitumor effects against melanoma in mice

Direct intratumoral transfection of cytokine genes was performed by means of the in vivo electroporation as a novel therapeutic strategy for cancer. Plasmid vectors carrying the firefly luciferase, interleukin (IL)-12 and IL-18 genes were injected into established subcutaneous B16-derived melanomas followed by electric pulsation. When plasmid vectors with Epstein--Barr virus (EBV) nuclear antigen 1 (EBNA1) gene were employed, the expression levels of the transgenes were significantly higher in comparison with those obtained with conventional plasmid vectors. In consequence of the transfection with IL-12 and IL-18 genes, serum concentrations of the cytokines were significantly elevated, while interferon (IFN)-gamma also increased in the sera of the animals. The IL-12 gene transfection resulted in significant suppression of tumor growth, while the therapeutic effect was further improved by co-transfection with IL-12 and IL-18 genes. Repetitive co-transfection with IL-12 and IL-18 genes resulted in significant prolongation of survival of the animals. Natural killer (NK) and cytotoxic T lymphocyte (CTL) activities were markedly enhanced in the mice transfected with the cytokine genes. The present data suggest that the cytokine gene transfer can be successfully achieved by in vivo electroporation, leading to both specific and nonspecific antitumoral immune responses and significant therapeutic outcome.

Tricistronic viral vectors co-expressing interleukin-12 (1L-12) and CD80 (B7-1) for the immunotherapy of cancer: preclinical studies in myeloma

Synergy between interleukin-12 (IL-12) and B7-1 (CD80) for cancer immunotherapy has previously been demonstrated in animal models of breast cancer, lymphoma, and multiple myeloma. With a view to human clinical application, tricistronic retroviral and adenovirus vectors co-expressing IL-12 (IL-12p40 plus IL-12p35) and CD80 were constructed by utilizing two internal ribosome entry site (IRES) sequences to link the three cDNAs. A murine stem cell virus (MSCV)-based retroviral vector (MSCV-hIL12.B7) utilized distinct IRES sequences from the encephalomyocarditis virus (EMCV) and the foot-and-mouth disease virus (FMCV), whereas Ad5-based adenovirus vectors contained transcriptional units with two EMCV IRES sequences under the control of murine (AdMh12.B7) or human (AdHh12.B7) cytomegalovirus promoters. AdMh12.B7 was found to consistently direct higher levels of IL-12 and CD80 expression than AdHh12.B7 following infection of a number of human tumor cell lines. In preclinical studies, the human myeloma cell line U266 was infected with MSCV-hIL12.B7 and a resulting clonal cell line, U/MSCV-h12.B7, was generated with stable expression of CD80 and secreting IL-12 at 1 ng/24 h/10(6) cells. By comparison, following AdMh12.B7 infection, 81% of infected U266 cells (U/AdMh12.B7) expressed CD80 and secreted IL-12 at 25-50 ng/24 h/10(6) cells. Both engineered myeloma cell lines stimulated enhanced allogeneic mixed lymphocyte proliferation and provoked increases in cytotoxic T-lymphocyte responses and gamma-interferon release from normal donor lymphocytes exposed to parental U266 cells. These results suggest potential clinical utility of AdMh12.B7 in immunotherapy strategies for the treatment of multiple myeloma and other cancers.

Retroviral vectors

Retroviral vectors are widely used for preclinical and clinical applications. Unlike many of the other types of vectors currently being developed for gene therapy, retroviral vectors are able to genetically modify cells stably without perturbing cell growth. Retroviral vectors based on murine retroviruses are well suited for ex vivo applications where the cells are rapidly dividing. In particular, retroviral viral vectors have been used for a variety of ex vivo gene therapy approaches for treating genetic diseases such as Gaucher and severe combined immunodeficiency (SCID) and for acquired diseases such as cancer and arthritis. However, recent advances in the production of retroviral vectors have allowed for their use in vivo such as for the treatment of cancer and human immunodeficiency virus. The ability to target retroviral vectors to specific cell types will also increase the utility of high titer retroviral vectors for in vivo applications. Clearly retroviral vectors have been extremely useful for both preclinical and clinical gene therapy studies, and it is likely that they will continue to be utilized for ex vivo and in vivo strategies in the future.

Interleukin 12 gene therapy of cancer by peritumoral injection of transduced autologous fibroblasts: outcome of a phase I study

A phase I dose-escalation clinical trial of peritumoral injections of interleukin 12 (IL-12)-transduced autologous fibroblasts was performed in patients with disseminated cancer for whom effective treatment does not exist. The goals of this study were to assess the safety and toxicities as well as the efficacy, and ancillarily the immunomodulatory effects, of peritumoral IL-12 gene transfer. Primary dermal fibroblasts cultured from the patients were transduced with retroviral vector carrying human IL-12 genes (p35 and p40) as well as the neomycin phosphotransferase gene (TFG-hIL-12-Neo). Patients received four injections at intervals of 7 days. Nine patients were enrolled in this dose-escalation study, with secreted IL-12 doses ranging from 300 ng/24 hr for the first three patients to 1000, 3000, and 5000 ng/24 hr for two patients in each subsequent dosage level. Although a definite statement cannot be made, there appears to be perturbation of systemic immunity. Also, the locoregional effects mediated by tumor necrosis factor alpha (TNF-alpha) and CD8+ T cells were observed with tumor regression. Treatment-related adverse events were limited to mild to moderate pain at the injection site; clinically significant toxicities were not encountered. Transient but clear reductions of tumor sizes were observed at the injected sites in four of nine cases, and at noninjected distant sites in one melanoma patient. Hemorrhagic necrosis of tumors was observed in two melanoma patients. These data indicate that gene therapy by peritumoral injection of IL-12-producing autologous fibroblasts is feasible, and promising in patients with advanced cancer.

Fusagene vectors: a novel strategy for the expression of multiple genes from a single cistron

Transduction of cells with multiple genes, allowing their stable and co-ordinated expression, is difficult with the available methodologies. A method has been developed for expression of multiple gene products, as fusion proteins, from a single cistron. The encoded proteins are post-synthetically cleaved and processed into each of their constituent proteins as individual, biologically active factors. Specifically, linkers encoding cleavage sites for the Golgi expressed endoprotease, furin, have been incorporated between in-frame cDNA sequences encoding different secreted or membrane bound proteins. With this strategy we have developed expression vectors encoding multiple proteins (IL-2 and B7.1, IL-4 and B7.1, IL-4 and IL-2, IL-12 p40 and p35, and IL-12 p40, p35 and IL-2 ). Transduction and analysis of over 100 individual clones, derived from murine and human tumour cell lines, demonstrate the efficient expression and biological activity of each of the encoded proteins. Fusagene vectors enable the co-ordinated expression of multiple gene products from a single, monocistronic, expression cassette.

Expression of a bioactive bovine interleukin-12 using baculovirus

Recombinant baculoviruses that express recombinant bovine interleukin-12 (rboIL-12) subunits, p35 and p40 subunits were constructed. A recombinant virus containing the p40 subunit gene expressed the p40 subunit as a 40kDa monomer and an 80kDa disulfide-linked homodimer in the infected insect cells and in the culture supernatant. The p35 subunit was expressed in a 30kDa monomer in the infected cells but not in the supernatant. Superinfection of both recombinant viruses into the cells in a spinner flask resulted in the formation of a 70kDa disulfide-bonded heterodimer detected in the supernatant by immunoblotting using anti-p40 and anti-p35 subunits antibodies. The superinfected culture supernatant showed induction of IFNgamma mRNA synthesis and IFNgamma production in bovine peripheral blood mononuclear cells. Thus, the bioactive rboIL-12 was produced in large scale using a baculovirus expression system.

Tricistronic and tetracistronic retroviral vectors for gene transfer

We have combined the picornavirus foot-and-mouth disease virus (FMDV) 2A sequence and the internal ribosome entry sites (IRESes) from encephalomyocarditis virus (ECMV) and avian reticuloendotheliosis virus type A (REV-A) to construct tricistronic and tetracistronic vectors. All the polycistronic constructs show high titers and expression of the genes inserted. Clones have been obtained in which cells simultaneously express the three or four genes carried by the polycistronic vectors.

Viral vectors for gene transfer: a review of their use in the treatment of human diseases

The efficient delivery of therapeutic genes and appropriate gene expression are the crucial issues for clinically relevant gene therapy. Viruses are naturally evolved vehicles which efficiently transfer their genes into host cells. This ability made them desirable for engineering virus vector systems for the delivery of therapeutic genes. The viral vectors recently in laboratory and clinical use are based on RNA and DNA viruses processing very different genomic structures and host ranges. Particular viruses have been selected as gene delivery vehicles because of their capacities to carry foreign genes and their ability to efficiently deliver these genes associated with efficient gene expression. These are the major reasons why viral vectors derived from retroviruses, adenovirus, adeno-associated virus, herpesvirus and poxvirus are employed in more than 70% of clinical gene therapy trials worldwide. Among these vector systems, retrovirus vectors represent the most prominent delivery system, since these vectors have high gene transfer efficiency and mediate high expression of therapeutic genes. Members of the DNA virus family such as adenovirus-, adeno-associated virus or herpesvirus have also become attractive for efficient gene delivery as reflected by the fast growing number of clinical trials using these vectors. The first clinical trials were designed to test the feasibility and safety of viral vectors. Numerous viral vector systems have been developed for ex vivo and in vivo applications. More recently, increasing efforts have been made to improve infectivity, viral targeting, cell type specific expression and the duration of expression. These features are essential for higher efficacy and safety of RNA- and DNA-virus vectors. From the beginning of development and utilisation of viral vectors it was apparent that they harbour risks such as toxicities, immunoresponses towards viral antigens or potential viral recombination, which limit their clinical use. However, many achievements have been made in vector safety, the retargeting of virus vectors and improving the expression properties by refining vector design and virus production. This review addresses important issues of the current status of viral vector design and discusses their key features as delivery systems in gene therapy of human inherited and acquired diseases at the level of laboratory developments and of clinical applications.

Long-term tracking of murine hematopoietic cells transduced with a bicistronic retrovirus containing CD24 and EGFP genes

Hematopoietic stem cells (HSCs) are attractive targets for gene therapy, but current gene transfer methodologies are inadequate for efficient HSC transduction and perpetual transgene expression. To improve gene transfer vectors and transduction protocols, it is vital to establish a system to evaluate transgene expression and the long-term behavior of transduced cells in vivo. For this purpose, we constructed a bicistronic retrovirus encoding the human CD24 (as the first cistron) and the enhanced green fluorescent protein (EGFP; as the second cistron). Murine bone marrow cells were transduced with this vector and the transgene expression was monitored along with hematopoietic reconstitution. Stable expression of CD24 and EGFP was demonstrated in the long-term repopulating cells for at least 6 months, and multi-parameter flow cytometry illustrated expression of both markers in all the lymphohematopoietic lineages examined (B and T lymphoid, erythroid and myeloid). Sustained expression was also shown in the secondary transplants for 6 months, suggesting that self-renewing HSCs were transduced by this vector. Overall, EGFP-tagged bicistronic retroviruses would provide powerful tools for detailed in vivo analysis of transduced hematopoietic cells, such as transgene expression in conjunction with lineage differentiation. Gene Therapy (2000) 7, 1193-1199.

Comparison of bicistronic retroviral vectors containing internal ribosome entry sites (IRES) using expression of human interleukin-12 (IL-12) as a readout

BACKGROUND

Many gene therapy applications require the co-ordinated delivery of more than one reading frame. We wished to systematically compare IRES in the context of a retroviral vector to determine which was the most effective for protein production and viral titre. To do this we monitored expression of IL-12, as co-ordinated expression of both p35 and p40 subunits is required for production of the active heterodimer.

METHODS

Retroviral vectors were constructed to express human IL-12 in which an IRES initiates translation of the p40 subunit, with the IRES optimally aligned to the initiation codon of p40. Vectors containing an IRES from either polio virus (PV), encephalomyocarditis virus (EMCV), foot and mouth disease virus (FMDV) or murine leukaemia virus (MLV) were compared with a vector expressing IL-12 as a single protein (Flexi-12; in which the two IL-12 subunits are linked by a peptide).

RESULTS

All vectors produced high titre virus and directed synthesis of IL-12 in target cells. The bicistronic vectors containing the IRES from EMCV and PV were the most effective in infected 3T3 cells, producing up to 40 ng IL-12/10(6) cells/48 h, similar to the 50 ng IL-12/10(6) cells/48 h obtained with Flexi-12. The IRES from PV was the most efficient in human melanoma cells.

CONCLUSIONS

Bicistronic retroviral vectors have been constructed that effectively transduce target cells and produce high levels of protein. Target cell specificity of IRES function was observed. The combination of Flexi-12 and the IRES from PV will be useful in the generation of vectors expressing IL-12 with a second protein such as IL-2 for transduction of melanoma cells.

Genetic immunotherapy of established tumours with adenoviral vectors transducing murine interleukin-12 (mIL12) subunits in a rat medullary thyroid carcinoma model

OBJECTIVE

Interleukin-12 (IL12) is a heterodimeric cytokine that plays an important role in the development of cellular immunity. Studies have demonstrated antitumour activity after systemic administration of recombinant IL12. As with other cytokines, with increasing dosage and longer exposure, systemic toxicity is observed. To reduce systemic toxicity and obtain local production of IL12, we developed a replication defective adenovirus transducing two subunits of the murine IL12 (AdCMVmIL12) gene.

DESIGN

Two separate cassettes, expressing the p35 or p40 subunit of mIL12, under the control of human cytomeglavirus immediate early promoter, were inserted into the early1 (E1) region of adenovirus 5. Biological activity of virally expressed mIL12 was demonstrated in vitro through its ability to induce proliferation of mouse ConA blast cells.

RESULTS

Rat medullary thyroid carcinoma (MTC) cells infected with AdCMVmIL12 lost their tumorigenicity in their syngenic WAG/Rij rat hosts. Efficient antitumour activity was found after direct injection of the AdCMVmIL12 vector into rMTC tumours. After intratumoural treatment with AdCMVmIL12, 86% of tumour bearing animals were apparently cured, and almost all remaining tumours were stabilized. Challenge studies showed that most animals cured after the first treatment remained tumour free after reinjection of wild type rMTC cells, indicating that long-term antitumour immunity developed.

CONCLUSIONS

This study demonstrates the construction of an adenoviral vector expressing a functional heterodimeric mIL12 and its efficient antitumour activity after in vivo delivery in an animal model of medullary thyroid carcinoma.

Engineered herpes simplex virus expressing IL-12 in the treatment of experimental murine brain tumors

Genetically engineered, neuroattenuated herpes simplex viruses (HSVs) expressing various cytokines can improve survival when used in the treatment of experimental brain tumors. These attenuated viruses have both copies of gamma(1)34.5 deleted. Recently, we demonstrated increased survival of C57BL/6 mice bearing syngeneic GL-261 gliomas when treated with an engineered HSV expressing IL-4, as compared with treatment with the parent construct (gamma(1)34. 5(-)) alone or with a virus expressing IL-10. Herein, we report construction of a conditionally replication-competent mutant expressing both subunits of mIL-12 (M002) and its evaluation in a syngeneic neuroblastoma murine model. IL-12 induces a helper T cell subset type 1 response, which may induce more durable antitumor effects. In vitro studies showed that, when infected with M002, both Vero cells and murine Neuro-2a neuroblastoma cells produced physiologically relevant levels of IL-12 heterodimers, as determined by ELISA. M002 was cytotoxic for Neuro-2a cells and human glioma cell lines U251MG and D54MG. Neurotoxicity studies, as defined by plaque-forming units/LD(50), performed in HSV-1-sensitive A/J strain mice found that M002 was not toxic even at high doses. When evaluated in an intracranial syngeneic neuroblastoma murine model, median survival of M002-treated animals was significantly longer than the median survival of animals treated with R3659, the parent gamma(1)34.5(-) mutant lacking any cytokine gene insert. Immunohistochemical analysis of M002-treated tumors identified a pronounced influx of CD4(+) T cells and macrophages as well as CD8(+) cells when compared with an analysis of R3659-treated tumors. We conclude that M002 produced a survival benefit via oncolytic effects combined with immunologic effects meditated by helper T cells of subset type 1.

Interleukin-12. Opportunities for the treatment of bladder cancer

Despite incomplete understanding of the human immune system, the rapid progress in tumor immunology provides a framework for more effective and safe interventions in the near future. Early approaches in patients with cancer that have focused on the nonspecific and broad stimulation of the immune system by interferons and IL-12 will be replaced by the highly specific stimulation of immune reactions targeting precisely defined tumor antigens. IL-12 has several biologic properties that seem useful in immune therapy for bladder cancer. The striking antitumor responses with IL-12 in preclinical animal models of bladder cancer provide optimism that future clinical trials involving this agent may impact on the risk and mortality associated with this disease.

Inhibition of apoptosis in human tumour cells by the tumour-associated serpin, SCC antigen-1

The squamous cell carcinoma antigen (SCC Ag) is a tumour-associated protein and a member of the serine protease inhibitor (serpin) family. The SCC Ag has been used as a serologic tumour marker for SCC progression, and its elevated serum levels are a risk factor for disease relapse. However, the biologic significance of this intracytoplasmic protein in cancer cells remains unknown. In this report, we demonstrated that apoptosis induced by 7-ethyl-10-hydroxycamptothecin, tumour necrosis factor-alpha (TNF-alpha) or interleukin (IL)-2-activated natural killer (NK) cells was significantly inhibited in tumour cells transduced with the SCC Ag-1 cDNA, as compared to control cells in vitro. Also, inhibition of the SCC Ag-1 expression in tumour cells by transfection of antisense SCC Ag-1 cDNA was accompanied by significantly increased sensitivity of these cells to apoptosis induced by etoposide or TNF-alpha. The mechanism of protection of tumour cells from apoptosis involved inhibition of caspase-3 activity and/or upstream proteases. In vivo, tumour cells overexpressing the SCC Ag-1 formed significantly larger tumours in nude mice than the SCC Ag-1-negative controls. Thus, overexpression of the SCC Ag-1, a member of the serpin family, in human cancer cells contributed to their survival by mediating protection from drug-, cytokine- or effector cell-induced apoptosis.