A system for efficient generation of adenovirus protein IX-producing helper cell lines

Adenoviral Gene Therapy Vectors in Clinical Use-Basic Aspects with a Special Reference to Replication-Competent Adenovirus Formation and Its Impact on Clinical Safety

Adenoviral vectors are commonly used in clinical gene therapy. Apart from oncolytic adenoviruses, vector replication is highly undesired as it may pose a safety risk for the treated patient. Thus, careful monitoring for the formation of replication-competent adenoviruses (RCA) during vector manufacturing is required. To render adenoviruses replication deficient, their genomic E1 region is deleted. However, it has been known for a long time that during their propagation, some viruses will regain their replication capability by recombination in production cells, most commonly HEK293. Recently developed RCA assays have revealed that many clinical batches contain more RCA than previously assumed and allowed by regulatory authorities. The clinical significance of the higher RCA content has yet to be thoroughly evaluated. In this review, we summarize the biology of adenovirus vectors, their manufacturing methods, and the origins of RCA formed during HEK293-based vector production. Lastly, we share our experience using minimally RCA-positive serotype 5 adenoviral vectors based on observations from our clinical cardiovascular gene therapy studies.

Reovirus Type 3 Dearing Variants Do Not Induce Necroptosis in RIPK3-Expressing Human Tumor Cell Lines

Reoviruses are used as oncolytic viruses to destroy tumor cells. The concomitant induction of anti-tumor immune responses enhances the efficacy of therapy in tumors with low amounts of immune infiltrates before treatment. The reoviruses should provoke immunogenic cell death (ICD) to stimulate a tumor cell-directed immune response. Necroptosis is considered a major form of ICD, and involves receptor-interacting protein kinase 1 (RIPK1), RIPK3 and phosphorylation of mixed-lineage kinase domain-like protein (MLKL). This leads to cell membrane disintegration and the release of damage-associated molecular patterns that can activate immune responses. Reovirus Type 3 Dearing (T3D) can induce necroptosis in mouse L929 fibroblast cells and mouse embryonic fibroblasts. Most human tumor cell lines have a defect in RIPK3 expression and consequently fail to induce necroptosis as measured by MLKL phosphorylation. We used the human colorectal adenocarcinoma HT29 cell line as a model to study necroptosis in human cells since this cell line has frequently been described in necroptosis-related studies. To stimulate MLKL phosphorylation and induce necroptosis, HT29 cells were treated with a cocktail consisting of TNFα, the SMAC mimetic BV6, and the caspase inhibitor Z-VAD-FMK. While this treatment induced necroptosis, three different reovirus T3D variants, i.e., the plasmid-based reverse genetics generated virus (T3D^K), the wild-type reovirus T3D isolate R124, and the junction adhesion molecule-A-independent reovirus mutant (jin-1) failed to induce necroptosis in HT29 cells. In contrast, these viruses induced MLKL phosphorylation in murine L929 cells, albeit with varying efficiencies. Our study shows that while reoviruses efficiently induce necroptosis in L929 cells, this is not a common phenotype in human cell lines. This study emphasizes the difficulties of translating the results of ICD studies from murine cells to human cells.

T-Box20 inhibits osteogenic differentiation in adipose-derived human mesenchymal stem cells: the role of T-Box20 on osteogenesis

Background

Skeletal development and its cellular function are regulated by various transcription factors. The T-box (Tbx) family of transcription factors have critical roles in cellular differentiation as well as heart and limbs organogenesis. These factors possess activator and/or repressor domains to modify the expression of target genes. Despite the obvious effects of Tbx20 on heart development, its impact on bone development is still unknown.

Methods

To investigate the consequence by forced Tbx20 expression in the osteogenic differentiation of human mesenchymal stem cells derived from adipose tissue (Ad-MSCs), these cells were transduced with a bicistronic lentiviral vector encoding Tbx20 and an enhanced green fluorescent protein.

Results

Tbx20 gene delivery system suppressed the osteogenic differentiation of Ad-MSCs, as indicated by reduction in alkaline phosphatase activity and Alizarin Red S staining. Consistently, reverse transcription-polymerase chain reaction analyses showed that Tbx20 gain-of-function reduced the expression levels of osteoblast marker genes in osteo-inductive Ad-MSCs cultures. Accordingly, Tbx20 negatively affected osteogenesis through modulating expression of key factors involved in this process.

Conclusion

The present study suggests that Tbx20 could inhibit osteogenic differentiation in adipose-derived human mesenchymal stem cells.

Cardiomyogenic differentiation of human adipose-derived mesenchymal stem cells transduced with Tbx20-encoding lentiviral vectors

Ischemic heart disease often results in myocardial infarction and is the leading cause of mortality and morbidity worldwide. Improvement in the function of infarcted myocardium is a main purpose of cardiac regenerative medicine. One possible way to reach this goal is via stem cell therapy. Mesenchymal stem cells (MSCs) are multipotent stromal cells that can differentiate into a variety of cell types but display limited cardiomyogenic differentiation potential. Members of the T-box family of transcription factors including Tbx20 play important roles in heart development and cardiomyocyte homeostasis. Therefore, in the current study, we investigated the potential of Tbx20 to enhance the cardiomyogenic differentiation of human adipose-derived MSCs (ADMSCs). Human ADMSCs were transduced with a bicistronic lentiviral vector encoding Tbx20 (murine) and the enhanced green fluorescent protein (eGFP) and analyzed 7 and 14 days post transduction. Transduction of human ADMSCs with this lentiviral vector increased the expression of the cardiomyogenic differentiation markers ACTN1, TNNI3, ACTC1, NKX2.5, TBX20 (human), and GATA4 as revealed by RT-qPCR. Consistently, immunocytological results showed elevated expression of α-actinin and cardiac troponin I in these cells in comparison to the cells transduced with control lentiviral particles coding for eGFP alone. Accordingly, forced expression of Tbx20 exerts cardiomyogenic effects on human ADMSCs by increasing the expression of cardiomyogenic differentiation markers at the RNA and protein level.

c-Myc is targeted to the proteasome for degradation in a SUMOylation-dependent manner, regulated by PIAS1, SENP7 and RNF4

c-Myc is the most frequently overexpressed oncogene in tumors, including breast cancer, colon cancer and lung cancer. Post-translational modifications comprising phosphorylation, acetylation and ubiquitylation regulate the activity of c-Myc. Recently, it was shown that c-Myc-driven tumors are strongly dependent on the SUMO pathway. Currently, the relevant SUMO target proteins in this pathway are unknown. Here we show that c-Myc is a target protein for SUMOylation, and that SUMOylated c-Myc is subsequently ubiquitylated and degraded by the proteasome. SUMO chains appeared to be dispensable for this process, polymerization-deficient SUMO mutants supported proteolysis of SUMOylated c-Myc. These results indicate that multiple SUMO monomers conjugated to c-Myc could be sufficient to direct SUMOylated c-Myc to the ubiquitin-proteasome pathway. Knocking down the SUMO-targeted ubiquitin ligase RNF4 enhanced the levels of SUMOylated c-Myc, indicating that RNF4 could recognize a multi-SUMOylated protein as a substrate in addition to poly-SUMOylated proteins. Knocking down the SUMO E3 ligase PIAS1 resulted in reduced c-Myc SUMOylation and increased c-Myc transcriptional activity, indicating that PIAS1 mediates c-Myc SUMOylation. Increased SUMOylation of c-Myc was noted upon knockdown of the SUMO protease SENP7, indicating that it also could regulate a multi-SUMOylated protein in addition to poly-SUMOylated proteins. C-Myc lacks KxE-type SUMOylation consensus motifs. We used mass spectrometry to identify 10 SUMO acceptor lysines: K52, K148, K157, K317, K323, K326, K389, K392, K398 and K430. Intriguingly, mutating all 10 SUMO acceptor lysines did not reduce c-Myc SUMOylation, suggesting that SUMO acceptor lysines in c-Myc act promiscuously. Our results provide novel insight into the complexity of c-Myc post-translational regulation.

System-wide identification of wild-type SUMO-2 conjugation sites

SUMOylation is a reversible post-translational modification (PTM) regulating all nuclear processes. Identification of SUMOylation sites by mass spectrometry (MS) has been hampered by bulky tryptic fragments, which thus far necessitated the use of mutated SUMO. Here we present a SUMO-specific protease-based methodology which circumvents this problem, dubbed Protease-Reliant Identification of SUMO Modification (PRISM). PRISM allows for detection of SUMOylated proteins as well as identification of specific sites of SUMOylation while using wild-type SUMO. The method is generic and could be widely applied to study lysine PTMs. We employ PRISM in combination with high-resolution MS to identify SUMOylation sites from HeLa cells under standard growth conditions and in response to heat shock. We identified 751 wild-type SUMOylation sites on endogenous proteins, including 200 dynamic SUMO sites in response to heat shock. Thus, we have developed a method capable of quantitatively studying wild-type mammalian SUMO at the site-specific and system-wide level.

Tryptic digestion of SUMOylated proteins generates large peptides, rendering proteomic characterisation of this post-translational modification particularly challenging unless mutant SUMO is used. Hendriks et al. present a method that allows the quantitative identification of wild-type SUMO sites.

Uncovering global SUMOylation signaling networks in a site-specific manner

SUMOylation is a reversible post-translational modification essential for genome stability. Using high-resolution mass spectrometry, we have studied global SUMOylation in human cells and in a site-specific manner, identifying a total of over 4,300 SUMOylation sites in over 1,600 proteins. Moreover, for the first time in excess of 1,000 SUMOylation sites were identified under standard growth conditions. SUMOylation dynamics were quantitatively studied in response to SUMO protease inhibition, proteasome inhibition and heat shock. A considerable amount of SUMOylated lysines have previously been reported to be ubiquitylated, acetylated or methylated, indicating crosstalk between SUMO and other post-translational modifications. We identified 70 phosphorylation and 4 acetylation events in close proximity to SUMOylation sites, and provide evidence for acetylation-dependent SUMOylation of endogenous histone H3. SUMOylation regulates target proteins involved in all nuclear processes including transcription, DNA repair, chromatin remodeling, pre-mRNA splicing and ribosome assembly.

Evaluation of viral interference with MHC class I-restricted antigen processing and presentation using a flow cytometry-based approach

The peptide content of MHC class I molecules present at the cell surface is monitored by surveilling CD8(+) cytotoxic T cells. In case of a viral infection, a proportion of the MHC class I molecules will carry peptides derived from viral proteins. This allows the CD8(+) T cells to recognize and eliminate virus-infected cells. This highly sensitive detection system of the host is counteracted by viruses, which have acquired functions to downregulate cell surface expression of MHC class I molecules. In this chapter, we describe a flow cytometry-based method to identify viral gene product(s) responsible for evasion from MHC class I-restricted antigen presentation. To this end, cells are transiently transfected using polyethylenimine (PEI) as a transfection reagent, followed by cell surface staining with MHC class I-specific monoclonal antibodies. Once viral proteins responsible for MHC class I downregulation have been identified, their mechanism of action can be characterized. Identification and characterization of virus-encoded MHC class I inhibitors augments our understanding of virus-host interactions and often provides new insights into antigen processing and presentation pathways, including related cellular processes such as protein trafficking and degradation.

EBV BILF1 evolved to downregulate cell surface display of a wide range of HLA class I molecules through their cytoplasmic tail

Coevolution of herpesviruses and their hosts has driven the development of both host antiviral mechanisms to detect and eliminate infected cells and viral ploys to escape immune surveillance. Among the immune-evasion strategies used by the lymphocryptovirus (γ(1)-herpesvirus) EBV is the downregulation of surface HLA class I expression by the virally encoded G protein-coupled receptor BILF1, thereby impeding presentation of viral Ags and cytotoxic T cell recognition of the infected cell. In this study, we show EBV BILF1 to be expressed early in the viral lytic cycle. BILF1 targets a broad range of HLA class I molecules, including multiple HLA-A and -B types and HLA-E. In contrast, HLA-C was only marginally affected. We advance the mechanistic understanding of the process by showing that the cytoplasmic C-terminal tail of EBV BILF1 is required for reducing surface HLA class I expression. Susceptibility to BILF1-mediated downregulation, in turn, is conferred by specific residues in the intracellular tail of the HLA class I H chain. Finally, we explore the evolution of BILF1 within the lymphocryptovirus genus. Although the homolog of BILF1 encoded by the lymphocryptovirus infecting Old World rhesus primates shares the ability of EBV to downregulate cell surface HLA class I expression, this function is not possessed by New World marmoset lymphocryptovirus BILF1. Therefore, this study furthers our knowledge of the evolution of immunoevasive functions by the lymphocryptovirus genus of herpesviruses.

A cathepsin-cleavage site between the adenovirus capsid protein IX and a tumor-targeting ligand improves targeted transduction

Human adenoviruses have a great potential as anticancer agents. One strategy to improve their tumor-cell specificity and anti-tumor efficacy is to include tumor-specific targeting ligands in the viral capsid. This can be achieved by fusion of polypeptide-targeting ligands with the minor capsid protein IX. Previous research suggested that protein IX-mediated targeting is limited by inefficient release of protein IX-fused ligands from their cognate receptors in the endosome. This thwarts endosomal escape of the virus particles. Here we describe that the targeted transduction of tumor cells is augmented by a cathepsin-cleavage site between the protein IX anchor and the HER2/neu-binding ZH Affibody molecule as ligand. The cathepsin-cleavage site did not interfere with virus production and incorporation of the Affibody molecules in the virus capsid. Virus particles harboring the cleavable protein IX-ligand fusion in their capsid transduced the HER2/neu-positive SKOV-3 ovarian carcinoma cells with increased efficiency in monolayer cultures, three-dimensional spheroid cultures and in SKOV-3 tumors grown on the chorioallantoic membrane of embryonated chicken eggs. These data show that inclusion of a cathepsin-cleavage sequence between protein IX and a high-affinity targeting ligand enhances targeted transduction. This modification further augments the applicability of protein IX as an anchor for coupling tumor-targeting ligands.

Epstein-Barr virus isolates retain their capacity to evade T cell immunity through BNLF2a despite extensive sequence variation

The Epstein-Barr virus (EBV)-encoded immune evasion protein BNLF2a inhibits the transporter associated with antigen processing (TAP), thereby downregulating HLA class I expression at the cell surface. As a consequence, recognition of EBV-infected cells by cytotoxic T cells is impaired. Here, we show that sequence polymorphism of the BNLF2a protein is observed with natural EBV isolates, with evidence for positive selection. Despite these mutations, the BNLF2a variants efficiently reduce cell surface HLA class I levels. This conservation of BNLF2a function during evolution of EBV implies an important role for the viral TAP inhibitor in preventing T cell recognition during viral infection.

EBV protein BNLF2a exploits host tail-anchored protein integration machinery to inhibit TAP

EBV, the prototypic human γ(1)-herpesvirus, persists for life in infected individuals, despite the presence of vigorous antiviral immunity. CTLs play an important role in the protection against viral infections, which they detect through recognition of virus-encoded peptides presented in the context of HLA class I molecules at the cell surface. The viral peptides are generated in the cytosol and are transported into the endoplasmic reticulum (ER) by TAP. The EBV-encoded lytic-phase protein BNLF2a acts as a powerful inhibitor of TAP. Consequently, loading of antigenic peptides onto HLA class I molecules is hampered, and recognition of BNLF2a-expressing cells by cytotoxic T cells is avoided. In this study, we characterize BNLF2a as a tail-anchored (TA) protein and elucidate its mode of action. Its hydrophilic N-terminal domain is located in the cytosol, whereas its hydrophobic C-terminal domain is inserted into membranes posttranslationally. TAP has no role in membrane insertion of BNLF2a. Instead, Asna1 (also named TRC40), a cellular protein involved in posttranslational membrane insertion of TA proteins, is responsible for integration of BNLF2a into the ER membrane. Asna1 is thereby required for efficient BNLF2a-mediated HLA class I downregulation. To optimally accomplish immune evasion, BNLF2a is composed of two specialized domains: its C-terminal tail anchor ensures membrane integration and ER retention, whereas its cytosolic N terminus accomplishes inhibition of TAP function. These results illustrate how EBV exploits a cellular pathway for TA protein biogenesis to achieve immune evasion, and they highlight the exquisite adaptation of this virus to its host.

Enhanced transduction of CAR-negative cells by protein IX-gene deleted adenovirus 5 vectors

In human adenoviruses (HAdV), 240 copies of the 14.3-kDa minor capsid protein IX stabilize the capsid. Three N-terminal domains of protein IX form triskelions between hexon capsomers. The C-terminal domains of four protein IX monomers associate near the facet periphery. The precise biological role of protein IX remains enigmatic. Here we show that deletion of the protein IX gene from a HAdV-5 vector enhanced the reporter gene delivery 5 to 25-fold, specifically to Coxsackie and Adenovirus Receptor (CAR)-negative cell lines. Deletion of the protein IX gene also resulted in enhanced activation of peripheral blood mononuclear cells. The mechanism for the enhanced transduction is obscure. No differences in fiber loading, integrin-dependency of transduction, or factor-X binding could be established between protein IX-containing and protein IX-deficient particles. Our data suggest that protein IX can affect the cell tropism of HAdV-5, and may function to dampen the innate immune responses against HAdV particles.

Adenovirus-derived vectors for prostate cancer gene therapy

Prostate cancer is a leading cause of death among men in Western countries. Whereas the survival rate approaches 100% for patients with localized cancer, the results of treatment in patients with metastasized prostate cancer at diagnosis are much less successful. The patients are usually presented with a variety of treatment options, but therapeutic interventions in prostate cancer are associated with frequent adverse side effects. Gene therapy and oncolytic virus therapy may constitute new strategies. Already a wide variety of preclinical studies has demonstrated the therapeutic potential of such approaches, with oncolytic prostate-specific adenoviruses as the most prominent vector. The state of the art and future prospects of gene therapy in prostate cancer are reviewed, with a focus on adenoviral vectors. We summarize advances in adenovirus technology for prostate cancer treatment and highlight areas where further developments are necessary.

Adenoviral producer cells

Adenovirus (Ad) vectors, in particular those of the serotype 5, are highly attractive for a wide range of gene therapy, vaccine and virotherapy applications (as discussed in further detail in this issue). Wild type Ad5 virus can replicate in numerous tissue types but to use Ad vectors for therapeutic purposes the viral genome requires modification. In particular, if the viral genome is modified in such a way that the viral life cycle is interfered with, a specific producer cell line is required to provide trans-complementation to overcome the modification and allow viral production. This can occur in two ways; use of a producer cell line that contains specific adenoviral sequences incorporated into the cell genome to trans-complement, or use of a producer cell line that naturally complements for the modified Ad vector genome. This review concentrates on producer cell lines that complement non-replicating adenoviral vectors, starting with the historical HEK293 cell line developed in 1977 for first generation Ad vectors. In addition the problem of replication-competent adenovirus (RCA) contamination in viral preparations from HEK293 cells is addressed leading to the development of alternate cell lines. Furthermore novel cell lines for more complex Ad vectors and alternate serotype Ad vectors are discussed.

RNF4 and VHL regulate the proteasomal degradation of SUMO-conjugated Hypoxia-Inducible Factor-2alpha

Hypoxia-inducible factors (HIFs) are critical transcription factors that mediate cell survival during reduced oxygen conditions (hypoxia). At regular oxygen conditions (normoxia), HIF-1alpha and HIF-2alpha are continuously synthesized in cells and degraded via the ubiquitin-proteasome pathway. During hypoxia, these proteins are stabilized and translocate to the nucleus to activate transcription of target genes that enable cell survival at reduced oxygen levels. HIF proteins are tightly regulated via post-translational modifications including phosphorylation, acetylation, prolyl-hydroxylation and ubiquitination. Here we show for the first time that exogenous and endogenous HIF-2alpha are also regulated via the ubiquitin-like modifier small ubiquitin-like modifiers (SUMO). Using mutational analysis, we found that K394, which is situated in the sumoylation consensus site LKEE, is the major SUMO acceptor site in HIF-2alpha. Functionally, sumoylation reduced the transcriptional activity of HIF-2alpha. Similar to HIF-1alpha, HIF-2alpha is regulated by the SUMO protease SENP1. The proteasome inhibitor MG132 strongly stabilized SUMO-2-conjugated HIF-2alpha during hypoxia but did not affect the total level of HIF-2alpha. The ubiquitin E3 ligases von Hippel-Lindau and RNF4 control the levels of sumoylated HIF-2alpha, indicating that sumoylated HIF-2alpha is degraded via SUMO-targeted ubiquitin ligases.

Targeting of adenovirus vectors to the LRP receptor family with the high-affinity ligand RAP via combined genetic and chemical modification of the pIX capsomere

Adenovirus (Ad) vector targeting requires presentation of specific ligands on the virion's surface. Geneti-chemical targeting is based on the genetic introduction of cysteine residues bearing reactive thiol groups into solvent-accessible capsomeres of the virion and subsequent chemical coupling of ligands. Here, we exploited this technology to modify the pIX capsomere with high-affinity ligands. Genetic introduction of C-terminal cysteines to pIX allowed for specific coupling of full-length proteins to the virion, while not affecting vector production. Direct comparison of the two high-affinity ligands receptor- associated protein (RAP) and transferrin (Tf) revealed that targeting after coupling of a high-affinity ligand to pIX presumably requires release of the ligand from its receptor after cell entry. In addition, data obtained by live cell imaging of labeled vector particles demonstrated that coupling of very large proteins to pIX can impair intracellular vector particle trafficking. Finally, we demonstrate that the geneti-chemical targeting technology is suitable for in vivo targeting to liver after intravenous injection. Our data provide significant insight into basic requirements for successful targeting of pIX-modified Ad vectors.

A strategy for genetic modification of the spike-encoding segment of human reovirus T3D for reovirus targeting

Human Orthoreovirus Type 3 Dearing is not pathogenic to humans and has been evaluated clinically as an oncolytic agent. Its transduction efficiency and the tumor cell selectivity may be enhanced by incorporating ligands for alternative receptors. However, the genetic modification of reoviruses has been difficult, and genetic targeting of reoviruses has not been reported so far. Here we describe a technique for generating genetically targeted reoviruses. The propagation of wild-type reoviruses on cells expressing a modified sigma 1-encoding segment embedded in a conventional RNA polymerase II transcript leads to substitution of the wild-type genome segment by the modified version. This technique was used for generating reoviruses that are genetically targeted to an artificial receptor expressed on U118MG cells. These cells lack the junction adhesion molecule-1 and therefore resist infection by wild-type reoviruses. The targeted reoviruses were engineered to carry the ligand for this receptor at the C terminus of the sigma 1 spike protein. This demonstrates that the C terminus of the sigma 1 protein is a suitable locale for the insertion of oligopeptide ligands and that targeting of reoviruses is feasible. The genetically targeted viruses can be propagated using the modified U118MG cells as helper cells. This technique may be applicable for the improvement of human reoviruses as oncolytic agents.

Expression of heterologous genes in oncolytic adenoviruses using picornaviral 2A sequences that trigger ribosome skipping

Insertion of picornaviral 2A sequences into mRNAs causes ribosomes to skip formation of a peptide bond at the junction of the 2A and downstream sequences, leading to the production of two proteins from a single open reading frame. Adenoviral protein IX is a minor capsid protein that has been used to display foreign peptides on the surface of the capsid. We have used 2A sequences from the foot-and-mouth disease virus (FMDV) and porcine teschovirus 1 (PTV-1) to express protein IX (pIX) and green fluorescent protein (GFP) from pIX-2A-GFP fusion genes in an oncolytic virus derived from human adenovirus 5. GFP was efficiently expressed by constructs containing either 2A sequence. Peptide bond skipping was more efficient with the 58 aa FMDV sequence than with the 22 aa PTV-1 2A sequence, but the virus with the FMDV 2A sequence showed a reduction in plaque size, cytopathic effect, viral burst size and capsid stability. We conclude that ribosome skipping induced by 2A sequences is an effective strategy to express heterologous genes in adenoviruses; however, careful selection or optimization of the 2A sequence may be required if protein IX is used as the fusion partner.

Adenovirus targeting to HLA-A1/MAGE-A1-positive tumor cells by fusing a single-chain T-cell receptor with minor capsid protein IX

Adenovirus vectors have great potential in cancer gene therapy. Targeting of cancer-testis (CT) antigens, which are specifically presented at the surface of tumor cells by human leukocyte antigen (HLA) class I molecules, is an attractive option. In this study, a single-chain T-cell receptor (scTCR) directed against the CT antigen melanoma-associated antigen (MAGE)-A1 in complex with the HLA class I molecule of haplotype HLA-A1 is fused with the C terminus of the adenovirus minor capsid protein IX. Propagation of a protein-IX (pIX)-gene-deleted human adenovirus 5 (HAdV-5) vector on cells that constitutively express the pIXscTCR fusion protein yielded viral particles with the pIXscTCR fusion protein incorporated in their capsid. Generated particles specifically transduced melanoma cell lines expressing the HLA-A1/MAGE-A1 target complex with at least 10-fold higher efficiency than control viruses. Whereas loading of HLA-A1-positive cells with MAGE-A1 peptides leads to enhanced transduction of the cells, the efficiency of virus transduction is strongly reduced if the HLA-A1 molecules are not accessible at the target cell. Taken together, these data provide proof of principle that pIXscTCR fusions can be used to target HAdV-5 vectors to tumor cells expressing intracellular CT antigens.

The microtubule-associated protein doublecortin-like regulates the transport of the glucocorticoid receptor in neuronal progenitor cells

In neuronal cells, activated glucocorticoid receptor (GR) translocates to the nucleus guided by the cytoskeleton. However, the detailed mechanisms underlying GR translocation remain unclear. Using gain and loss of function studies, we report here for the first time that the microtubule-associated protein doublecortin-like (DCL) controls GR translocation to the nucleus. DCL overexpression in COS-1 cells, neuroblastoma cells, and rat hippocampus organotypic slice cultures impaired GR translocation and decreased GR-dependent transcriptional activity, measured by a specific reporter gene assay, in COS-1 cells. Moreover, DCL and GR directly interact on microtubule bundles formed by DCL overexpression. A C-terminal truncated DCL with conserved microtubule-bundling activity did not influence GR translocation. In N1E-115 mouse neuroblastoma cells and neuronal progenitor cells in rat hippocampus organotypic slice cultures, laser-scanning confocal microscopy showed colabeling of endogenously expressed DCL and GR. In these systems, RNA-interference-mediated DCL knockdown hampered GR translocation. Thus, we conclude that DCL expression is tightly regulated to adequately control GR transport. Because DCL is primarily expressed in neuronal progenitor cells, our results introduce this microtubule-associated protein as a new modulator of GR signaling in this cell type and suggest the existence of cell-specific mechanisms regulating GR translocation to the nucleus.

Modification of pIX or hexon based on fiberless Ad vectors is not effective for targeted Ad vectors

Adenovirus (Ad) vector application in gene therapy is limited by its naïve tropism. We previously developed protein IX (pIX)-modified and hexon-modified Ad vectors in order to alter Ad vector tropism. However, these modified Ad vectors failed to infect cells with the foreign ligands displayed in the pIX or hexon. We hypothesized that steric hindrance by fiber proteins might have prevented the ligand-mediated transduction, as fibers are the outmost capsid proteins of Ad vectors. Therefore, we generated a series of fiberless Ad vectors and investigated their gene expression properties. Unexpectively, however, pIX- or hexon-modified fiberless Ad vector did not achieve any gene expression (the gene expression level by these vectors was similar to the background level). These results might be caused by the fact that the fiberless particles were weaker against physical burdens. To the best of our knowledge, this study is the first reported attempt to develop fiberless Ad vectors containing foreign ligands in the pIX or hexon region. The drawback of the lower stability of fiberless Ad vectors must be overcome to develop targeted Ad vectors based on such vectors. This study could provide basic information for the development of effective targeted Ad vectors.

Expression of pIX Gene Induced by Transgene Promoter: Possible Cause of Host Immune Response in First-Generation Adenoviral Vectors

First-generation (FG) adenoviral vectors (AdVs) have been widely used not only for gene therapy but also for basic studies. Because vectors of this type lack the E1A gene that is essential for the expression of other viral genes, their expression levels in target cells have been considered low. However, we found that the viral pIX gene, located immediately downstream of the inserted expression unit of the transgene, was significantly coexpressed with the transgene in cells infected with FG AdV. Whereas CAG and SRalpha promoters activated the pIX promoter considerably through their enhancer effects, the EF1alpha promoter hardly did. Moreover, when the expression unit was inserted in the rightward orientation, not only the pIX protein but also a fusion protein consisting of the N-terminal part of transgene product and pIX were sometimes coexpressed with the transgene product through an aberrant splicing mechanism. In in vivo experiments, a LacZ-expressing AdV bearing the CAG promoter caused an elevation of alanine aminotransferase, but an AdV bearing the EF1alpha promoter produced no detectable levels. Whereas the FG AdV expressing human growth hormone under the control of the CAG promoter maintained a high hormone level for less than 1 month, the FG AdV under the control of the EF1alpha promoter maintained a high level for at least 6 months. These results suggest that pIX coexpression may be one of the main causes of AdV-induced immune responses, and that the EF1alpha promoter is probably valuable for the long-term expression of FG AdV. Thus, the in vivo utility of FG AdV should be reevaluated.

Fibroblasts from human postmyocardial infarction scars acquire properties of cardiomyocytes after transduction with a recombinant myocardin gene

Myocardial scar formation impairs heart function by inducing cardiac remodeling, decreasing myocardial compliance, and compromising normal electrical conduction. Conversion of myocardial scar fibroblasts (MSFs) into (functional) cardiomyocytes may be an effective alternative treatment to limit loss of cardiac performance after myocardial injury. In this study, we investigated whether the phenotype of MSFs can be modified by gene transfer into cells with properties of cardiomyocytes. To this end, fibroblasts from postmyocardial infarction scars of human left ventricles were isolated and characterized by cell biological, immunological, and molecular biological assays. Cultured human MSFs express GATA4 and connexin 43 and display adipogenic differentiation potential. Infection of human MSFs with a lentivirus vector encoding the potent cardiogenic transcription factor myocardin renders them positive for a wide variety of cardiomyocyte-specific proteins, including sarcomeric components, transcription factors, and ion channels, and induces the expression of several smooth muscle marker genes. Forced myocardin expression also endowed human MSFs with the ability to transmit an action potential and to repair an artificially created conduction block in cardiomyocyte cultures. These finding indicate that in vivo myocardin gene transfer may potentially limit cardiomyocyte loss, myocardial fibrosis, and disturbances in electrical conduction caused by myocardial infarction.

Efficient incorporation of a functional hyper-stable single-chain antibody fragment protein-IX fusion in the adenovirus capsid

Recombinant adenoviruses are frequently used as gene transfer vehicles for therapeutic gene delivery. Strategies to amend their tropism include the incorporation of polypeptides with high affinity for cellular receptors. Single-chain antibodies have a great potential to achieve such cell type specificity. In this study, we evaluated the efficiency of incorporation of a single-chain antibody fused with the adenovirus minor capsid protein IX in the capsid of adenovirus type 5 vectors. To this end, the codons for the single-chain antibody fragments (scFv) 13R4 were fused with those encoding of pIX via a 75-Angstrom spacer sequence. The 13R4 is a hyper-stable single-chain antibody directed against beta-galactosidase, which was selected for its capacity to fold correctly in a reducing environment such as the cytoplasm. A lentiviral vector was used to stably express the pIX.flag.75.13R4.MYC.HIS fusion gene in 911 helper cells. Upon propagation of pIX-gene deleted human adenovirus-5 vectors on these cells, the pIX-fusion protein was efficiently incorporated in the capsid. Here, the 13R4 scFv was functional as was evident from its capacity to bind its ligand beta-galactosidase. These data demonstrate that the minor capsid protein IX can be used as an anchor for incorporation of single-chain antibodies in the capsids of adenovirus vectors.

Characterization of capsid-modified adenovirus vectors containing heterologous peptides in the fiber knob, protein IX, or hexon

Adenovirus (Ad) vectors are widely used in gene therapy and in vitro/in vivo gene transfer because of their high transduction efficiency. However, Ad vector application in the gene therapy field is limited by poor transduction into cells not expressing the primary receptor, coxsackievirus and adenovirus receptor. To overcome this problem, several types of capsid-modified Ad vectors have been developed. The HI loop or C-terminus of the fiber knob, the C-terminus of the protein IX (pIX) and the hypervariable region 5 of the hexon are promising candidate locations for displaying foreign peptide sequences. In the present study, we constructed Ad vectors in which each of the above region was modified by a simple in vitro ligation-based method, and examined the characterization of each Ad vector containing the FLAG tag (DYKDDDDK) or RGD (CDCRGDCFC) peptide. Enzyme-linked immunosorbent assay examining the surface expression of foreign peptides on the virus suggested that foreign peptides are exposed on virion surfaces in all types vectors and that the hexon was the most efficiently reacted, reflecting the copy number of the modification. However, in the case of the transduction efficiency of Ad vectors containing the RGD peptides, the modification of pIX and the hexon showed no effect. The modification of the HI loop of the fiber knob was the most efficient, followed by the modification of the C-terminus region of the fiber knob. These comparative analyses, together with a simple construction method for each modified Ad vector, could provide basic information for the generation of capsid-modified Ad vectors.