A rapid and easy method for production and selection of recombinant adenovirus genomes

Enhanced growth suppression of TERT-positive tumor cells by oncolytic adenovirus armed with CCL20 and CD40L

Conditionally replicating adenoviruses (CRAds) selectively replicate in cancer cells and induce cell lysis, which represents a potential platform for cancer immunotherapy. The chemokine CCL20 exerts antitumor activity via chemoattraction of immature dendritic cells (DCs) and lymphocytes. However, the activation and maturation status of DCs is a limiting factor in the DCs -based immunity response. CD40L induces the phenotypic maturation of DCs, mediates DCs cytokine secretion, and increases the expression of FasL, which mediates apoptosis. We constructed a CCL20/CD40L co-expression CRAds (Ad-CCL20-CD40L) based on the AdEasy system. Ad-CCL20-CD40L was constructed from three plasmids, pGTE-CD40L, pShuttle-CMV-CCL20 and AdEasy-1, and was homologously recombined and propagated in the Escherichia coli strain BJ5183 and the packaging cell line HEK-293, respectively. Ad-CCL20-CD40L selectively replicates in TERT-positive tumor cells because the pGTE-CD40L plasmid contains the telomerase reverse transcriptase promoter (TERTp). Our results showed that Ad-CCL20-CD40L induced oncolytic effects and tumor-specific cytotoxicity of cytotoxic T lymphocytes (CTLs) in vitro. This study suggests that Ad-CCL20-CD40L can induce the antitumor immune response and that this platform can be modified to generate novel CRAds with other transgenes.

A simplified system for generating recombinant E3-deleted canine adenovirus-2

Canine adenovirus type 2 (CAV-2) has been used extensively as a vector for studying gene therapy and vaccine applications. We describe a simple strategy for generating a replication-competent recombinant CAV-2 using a backbone vector and a shuttle vector. The backbone plasmid containing the full-length CAV-2 genome was constructed by homologous recombination in Escherichia coli strain BJ5183. The shuttle plasmid, which has a deletion of 1478 bp in the nonessential E3 viral genome region, was generated by subcloning a fusion fragment containing the flanking sequences of the CAV-2 E3 region and expression cassette sequences from pcDNA3.1(+) into modified pUC18. To determine system effectiveness, a gene for enhanced green fluorescent protein (EGFP) was inserted into the shuttle plasmid and cloned into the backbone plasmid using two unique NruI and SalI sites. Transfection of Madin-Darby canine kidney (MDCK) cells with the recombinant adenovirus genome containing the EGFP expression cassette resulted in infectious viral particles. This strategy provides a solid foundation for developing candidate vaccines using CAV-2 as a delivery vector.

Sstr2A: a relevant target for the delivery of genes into human glioblastoma cells using fiber-modified adenoviral vectors

Glioblastomas are the most aggressive of the brain tumors occurring in adults and children. Currently available chemotherapy prolongs the median survival time of patients by only 4 months. The low efficiency of current treatments is partly owing to the blood-brain barrier, which restricts the penetration of most drugs into the central nervous system. Locoregional treatment strategies thus become mandatory. In this context, viral tools are of great interest for the selective delivery of genes into tumoral cells. Gliomas express high levels of type 2 somatostatin receptors (sstr2A), pinpointing them as suitable targets for the improvement of transduction efficiency in these tumors. We designed a new adenoviral vector based on the introduction of the full-length somatostatin (SRIF (somatotropin release-inhibiting factor)) sequence into the HI loop of the HAdV fiber protein. We demonstrate that (i) HAdV-5-SRIF uptake into cells is mediated by sstr2A, (ii) our vector drives high levels of gene expression in cells expressing endogenous sstr2A, with up to 65-fold enhancement and (iii) low doses of HAdV-5-SRIF are sufficient to infect high-grade human primary glioblastoma cells. Adenoviral vectors targeting SRIF receptors might thus represent a promising therapeutic approach to brain tumors.

A fiber-modified adenoviral vector interacts with immunoevasion molecules of the B7 family at the surface of murine leukemia cells derived from dormant tumors

Tumor cells can escape the immune system by overexpressing molecules of the B7 family, e.g. B7-H1 (PD-L1 or CD86), which suppresses the anti-tumor T-cell responses through binding to the PD-1 receptor, and similarly for B7.1 (CD80), through binding to CTLA-4. Moreover, direct interactions between B7-H1 and B7.1 molecules are also likely to participate in the immunoevasion mechanism. In this study, we used a mouse model of tumor dormancy, DA1-3b leukemia cells. We previously showed that a minor population of DA1-3b cells persists in equilibrium with the immune system for long periods of time, and that the levels of surface expression of B7-H1 and B7.1 molecules correlates with the dormancy time. We found that leukemia cells DA1-3b/d365 cells, which derived from long-term dormant tumors and overexpressed B7-H1 and B7.1 molecules, were highly permissive to Ad5FB4, a human adenovirus serotype 5 (Ad5) vector pseudotyped with chimeric human-bovine fibers. Both B7-H1 and B7.1 were required for Ad5FB4-cell binding and entry, since (i) siRNA silencing of one or the other B7 gene transcript resulted in a net decrease in the cell binding and Ad5FB4-mediated transduction of DA1-3b/d365; and (ii) plasmid-directed expression of B7.1 and B7-H1 proteins conferred to Ad5FB4-refractory human cells a full permissiveness to this vector. Binding data and flow cytometry analysis suggested that B7.1 and B7-H1 molecules played different roles in Ad5FB4-mediated transduction of DA1-3b/d365, with B7.1 involved in cell attachment of Ad5FB4, and B7-H1 in Ad5FB4 internalization. BRET analysis showed that B7.1 and B7-H1 formed heterodimeric complexes at the cell surface, and that Ad5FB4 penton, the viral capsomere carrying the fiber projection, could negatively interfere with the formation of B7.1/B7-H1 heterodimers, or modify their conformation. As interactors of B7-H1/B7.1 molecules, Ad5FB4 particles and/or their penton capsomeres represent potential therapeutic agents targeting cancer cells that had developed immunoevasion mechanisms.

Intratumor RNA interference of cell cycle genes slows down tumor progression

Small interfering RNAs (siRNAs) are emerging as promising therapeutic tools. However, the widespread clinical application of such molecules as modulators of gene expression is still dependent on several aspects that limit their bioavailability. One of the most promising strategies to overcome the barriers faced by gene silencing molecules involves the use of lipid-based nanoparticles (LNPs) and viral vectors, such as adenoviruses (Ads). The primary obstacle for translating gene silencing technology from an effective research tool into a feasible therapeutic strategy remains its efficient delivery to the targeted cell type in vivo. In this study, we tested the capability of LNPs and Ad to transduce and treat locally tumors in vivo. Efficient knockdown of a surrogate reporter (luciferase) and therapeutic target genes such as the kinesin spindle protein (KIF11) and polo-like kinase 1 were observed. Most importantly, this activity led to a cell cycle block as a consequence and slowed down tumor progression in tumor-bearing animals. Our data indicate that it is possible to achieve tumor transduction with si/short hairpin RNAs and further improve the delivery strategy that likely in the future will lead to the ideal non-viral particle for targeted cancer gene silencing.

Influence of chimeric human-bovine fibers on adenoviral uptake by liver cells and the antiviral immune response

Human adenoviruses (HAdV) are widely used for in vitro and in vivo gene transfer. Viral hepatotropism, inflammatory responses and neutralization by pre-existing antibodies (NAbs) are obstacles for clinical applications of HAdV vectors. Although the multifactorial events leading to innate HAdV toxicity are far from being elucidated, there is a consensus that the majority of intravenously injected-HAdV vectors is sequestered by Kuppfer cells, probably independently of coagulation factors. In this study, we show that the adenoviral-associated humoral and innate cytokine immune responses are significantly reduced when HAdV-5 vector carrying human bovine chimeric fibers (HAdV-5-F2/BAdV-4) is intravenously injected into mice. Fiber pseudotyping modified its interaction with blood coagulation factors, as FIX and FX no longer mediate the infection of liver cells by HAdV-5-F2/BAdV-4. As a consequence, at early time points post-infection, several cytokines and chemokines (IFN-gamma, IL-6, IP-10, MCP-1, RANTES and MP1beta) were found to be present at lower levels in the plasma of mice that had been intravenously injected with HAdV-5-F2/BAdV-4 compared with mice injected with the parental vector HAdV-5. Moreover, genetic modification of the fiber allowed HAdV-5-F2/BAdV-4 to partially escape neutralization by NAbs.

Serotype 5 Adenovirus fiber (F7F41S) chimeric vectors incur packaging deficiencies when targeting peptides are inserted into Ad41 short fiber

Adenovirus is a well-established viral gene transfer model system that presents two major hurdles when being considered for cell-specific targeting applications. First is the need to detarget the vector from inherent host binding mechanisms, and second is the need to establish a productive and stable method to retarget the vector to a desired cell receptor. In previous studies we had generated an adenovirus vector platform that lacks the normal targeting attributes derived from the fiber and penton capsid proteins. In the current study we characterized our detargeted Ad5-based vectors (Ad5.F7F41S and Ad5.F7F41SDeltaRGD) as platforms for novel retargeted viruses. The experimental strategy relied on incorporating small peptide ligands into several sites of the Ad 41short fiber knob domain (AB, CD, HI, G and Cterm). Reengineering of Ad41 short fiber resulted either in a bypass to fiber 7 usage, or in a dominant negative packaging/production deficiency phenotype. Under specific growth conditions we could remedy some of the capsid deficiencies and generate high titer viruses. However when examined by Western blot analysis, the resulting viruses were still defective in capsid content. The tandem fiber F7F41S platform has revealed an unanticipated sensitivity of Adenovirus packaging to fiber 41short structural modifications. These studies indicate fiber assembly into an intact virion or fiber influenced capsid stability as a bottleneck to efficient particle production. We also demonstrate that virus particles characterized as mature virions following CsCl banding can vary significantly in capsid protein content. Considering the complexity of virus entry into a target cell, modified "mature virions" may be compromised at the level of transduction not only through the intended modification, but also by virtue of secondary structural packaging conflicts.

A simplified in vitro ligation approach to clone an E1B55k-deleted double-targeted conditionally-replicative adenovirus

BACKGROUND

Construction of conditionally-replicative Adenovirus (CRAd) is complex and time-consuming. While homologous recombination (HR) using a two-plasmid system in bacteria is commonly used to generate CRAds, alternative methods may be required when HR fails. Previously, in vitro ligation has been suggested to facilitate construction of E1/E3-deleted, replication-incompetent Ad vectors. However, in vitro ligation has only rarely been used to generate CRAds and may be a complex procedure for molecular biologists who are not experts in the field.

METHODS AND RESULTS

A modified in vitro ligation approach was developed to construct a double-targeted, E1B55k-deleted CRAd. The method allowed the incorporation of a tumor-specific promoter, e.g. the heat-shock protein 70 (hsp70) promoter, upstream of E1a, deletion of the E1B55k gene, and HR-free cloning of the recombined E1Delta55k gene into the Ad genome. The genetic structure of the CRAd was confirmed using restriction analysis and PCR. The replication rate of the hsp70E1Delta55k CRAd was 1.5-2% of Ad without E1Delta55k deletion.

CONCLUSION

A 3-step cloning approach can generate a double-targeted, E1B55k-deleted CRAd using a straight-forward, modified in vitro ligation procedure.

A novel adenovirus vector for easy cloning in the E3 region downstream of the CMV promoter

The construction of expression vectors derived from the human adenovirus type 5 (Ad5), usually based on homologous recombination, is time consuming as a shuttle plasmid has to be selected before recombination with the viral genome. Here, we describe a method allowing direct cloning of a transgene in the E3 region of the Ad5 genome already containing the immediate early CMV promoter upstream of three unique restriction sites. This allowed the construction of recombinant adenoviral genomes in just one step, reducing considerably the time of selection and, of course, production of the corresponding vectors. Using this vector, we produced recombinant adenoviruses, each giving high-level expression of the transgene in the transduced cells.

Intracellular trafficking of a fiber-modified adenovirus using lipid raft/caveolae endocytosis

Most adenoviral vectors (HAdvs) elaborated for gene therapy are derived from serotype 5 viruses that use clathrin-coated vesicle endocytosis for cell entry. However, it appears that adenoviral vectors are able to take advantage of lipid raft/caveolae endocytosis to infect cells. In vivo targeting of a therapeutic gene to specific cells by vector engineering has become a major focus of gene therapy research. Yet, modification of adenoviral tropism, especially fiber gene engineering, can induce deficient intracellular trafficking of the viral particle, with a shift in subcellular localization resulting in extensive exocytosis. In this study we demonstrate that uptake of a fiber-modified adenovirus using lipid raft/caveolae endocytosis leads to non-altered intracellular trafficking without endosomal retention. Moreover, activation of lipid raft structures by this vector leads to the formation of "mega-caveosomes". These results demonstrate that, by forcing adenoviruses to take advantage of a non-clathrin, non-classical endocytic pathway, it is possible to compensate for the deficiency in endosomolysis that is associated with the use of some of the fiber-modified adenoviral constructs. Moreover, it renders such vectors ideal candidates for infecting human coxsackie and adenoviruses receptor (hCAR) negative cells.

Immunogenicity and safety of a DNA prime/adenovirus boost vaccine against rhesus CEA in nonhuman primates

Scaling up experimental protocols from rodents to humans is often not a straightforward procedure, and this particularly applies to cancer vaccines, where vaccination technology must be especially effective to overcome a variety of immune suppressive mechanisms. DNA electroporation (DNA-EP) and adenoviral vectors (Ad) have shown high potency and therapeutic efficacy for different antigens in several pre-clinical models. To evaluate the ability of DNA-EP and Ad to break tolerance to a self-antigen in large animals, we have cloned the CEA homologue (rhCEA) from rhesus monkeys (Macaca mulatta) colon tissue samples. rhCEA is a 705 aa protein and shares 78.9% homology to human CEA protein. Immunogenicity of rhCEA expressing vectors was tested in mice and subsequently in rhesus monkeys. To further increase the immunogenic potency of these vectors, a synthetic codon optimized rhCEA cDNA (rhCEAopt) was constructed. Genetic vaccination of rhesus monkeys was effective in breaking immune tolerance to rhCEA in all immunized animals, maintaining over time the elicited immune response, and most importantly, neither autoimmunity nor other side-effects were observed upon treatment. Our data confirm the efficacy of genetic cancer vaccines in large animals such as nonhuman primates and show that development of modified expression cassettes that result in increased potency of plasmid DNA and adenovirus may have a significant impact on vaccine development against malignancies expressing tumor associated antigens in patients.

Improved gene delivery to B lymphocytes using a modified adenovirus vector targeting CD21

Gene transfer by adenoviruses, which are widely used for gene therapy, may provide an alternative approach to treatment of several hematopoietic malignancies. However, a major limitation of adenovirus 5-based gene therapy lies in the natural tropism of the virus for the widely expressed hCAR receptor. The efficacy of adenoviral vectors could be improved if viral vectors that exhibit tissue-specific gene delivery were developed. For efficient gene transfer it is essential that every step from binding of virus to target cells to transgene expression is successfully accomplished. We developed a specific vector targeting the CD21 receptor, by inserting a CD21 binding sequence, derived from the EBV GP350/220 protein, into the HI loop of the HAdV5 fiber protein. This vector, HAdV5-CD21HIloop, binds specifically to CD21-positive cells and results in enhanced expression of the transgene in these cells and reduced expression in CD21-negative cells. Viral infection is highly correlated with the presence of CD21 receptors. Taken together, these results demonstrate that HAdV5-CD21HIloop is able to transduce CD21-positive cells specifically with reduced infection of nontarget cells. This is the result of the maintenance of the intracellular trafficking of the genetically modified adenovirus without vesicular retention, leading to enhanced nuclear transfer.

Characterization of a permissive epitope insertion site in adenovirus hexon

A robust immune response is generated against components of the adenovirus capsid. In particular, a potent and long-lived humoral response is elicited against the hexon protein. This is due to the efficient presentation of adenovirus capsid proteins to CD4+ T cells by antigen-presenting cells, in addition to the highly repetitive structure of the adenovirus capsids, which can efficiently stimulate B-cell proliferation. In the present study, we take advantage of this immune response by inserting epitopes against which an antibody response is desired into the adenovirus hexon. We use a B-cell epitope from Bacillus anthracis protective antigen (PA) as a model antigen to characterize hypervariable region 5 (HVR5) of hexon as a site for peptide insertion. We demonstrate that HVR5 can accommodate a peptide of up to 36 amino acids without adversely affecting virus infectivity, growth, or stability. Viruses containing chimeric hexons elicited antibodies against PA in mice, with total immunoglobulin G (IgG) titers reaching approximately 1 x 10(3) after two injections. The antibody response contained both IgG1 and IgG2a subtypes, suggesting that Th1 and Th2 immunity had been stimulated. Coinjection of wild-type adenovirus and a synthetic peptide from PA produced no detectable antibodies, indicating that incorporation of the epitope into the capsid was crucial for immune stimulation. Together, these results indicate that the adenovirus capsid is an efficient vehicle for presenting B-cell epitopes to the immune system, making this a useful approach for the design of epitope-based vaccines.

Efficient species C HAdV infectivity in plasmocytic cell lines using a clathrin-independent lipid raft/caveola endocytic route

Hematopoietic cells are known to be refractory to species C human adenovirus (HAdV) infection; however, the reason for this has not been clearly established. We have previously demonstrated that this nonpermissivity is the consequence of inefficient HAdV particle uptake, notably in B lymphocytes. We noted that while the protein clathrin is observed in association with membranes in epithelial cells, it is found predominantly in the cytoplasm of hematopoietic cell lines. So it appears that altered clathrin-coated pit endocytosis could explain the weak HAdV uptake in B cells. In contrast, mature B cell plasmocytes are permissive to HAdV. However, this is not the result of clathrin-coated pit endocytosis since this process is also inefficient in these cells. Confocal microscopy showed colocalization between HAdV particles and caveolae/lipid rafts in plasmocytes. Moreover, inhibiting caveola endocytosis by depletion of cholesterol or expression of dominant negative caveolin-1 in these cells results in a 50-70% reduction in HAdV infectivity. It appears that caveola endocytosis and nonclathrin noncaveola endocytosis are used by HAdV to enter plasmocytes in response to a loss of the clathrin-dependent pathway. Thus targeting of caveolae by modifying the capsid of HAdV may represent an alternative approach to enhancing uptake in most hematopoietic cells for future gene therapy.

Abolition of hCAR-dependent cell tropism using fiber knobs of Atadenovirus serotypes

Most adenoviral vectors use in gene therapy protocols derive from species C. However, expression of the primary receptor (human Coxsackievirus and Adenovirus receptor, hCAR) for these AdV is variable on cancer cells. In vivo targeting of a therapeutic gene to specific cells has then become a major issue in gene therapy. The Ad fiber protein largely determines viral tropism through interaction with specific receptors. Hereto, we constructed a set of HAdV5 vectors carrying chimeric fibers with knob domains from nonhuman AdV, namely from the FAdV-1 (Aviadenovirus), DAdV-1, and BAdV-4 (Atadenovirus). Correspondents viruses were produced using an established new HEK293 cell line, which express the HAdV2 fiber. Recombinant HAdV harboring chimeric fibers constituted of the N-terminal domain of HAdV2, and knob domain of bovine adenovirus type 4 (BAdV-4) demonstrated the greatest reduction in fiber-mediated gene transfer into human cells expressing the hCAR. Moreover, this vector infects with a better efficiency than vector with wild-type fiber, the Chinese Hamster Ovarian (CHO) and SKOV3 cell lines, both from ovarian origin, hamster and human, respectively. These studies support the concept that changing the fiber knob domain to ablate hCAR interaction should result in a de- or retargeted adenoviral vector. The adenoviral vector with the chimeric HAdV2/BAdV-4 fiber lacking hCAR interaction and with an ovarian cell tropism could be a nice candidate to elaborate vectors for ovarian tumor therapy.

Factors involved in the sensitivity of different hematopoietic cell lines to infection by subgroup C adenovirus: implication for gene therapy of human lymphocytic malignancies

Gene transfer approaches using viruses such human adenovirus (HAdV) may provide an alternative treatment for diseases involving hematopoietic cells. Better understanding of the cellular mechanisms by which the HAdV introduces DNA into these cells should help in vector design. We examined HAdV intracellular delivery in several cell lines including B and T lymphocytes. We demonstrated that HAdV resistance in most B lymphocytes is the result of moderate HAdV uptake. In contrast, high levels of coxsackie and HAdV receptor (hCAR) are expressed on the surface of HSB2 (T cells), allowing efficient binding and uptake but no transgene expression, probably because of deficient endosomolysis and subsequent exocytose. This work demonstrates the existence of hCAR-dependent and -independent endocytic route in hematopoietic cells. Moreover, it precises the intracellular barriers to be overcome by HAdV in such cells to be infectious and gives previous information's to design new vectors for gene transfer.