Philip Boehme

A Novel Adenoviral Hybrid-vector System Carrying a Plasmid Replicon for Safe and Efficient Cell and Gene Therapeutic Applications

In dividing cells, the two aims a gene therapeutic approach should accomplish are efficient nuclear delivery and retention of therapeutic DNA. For stable transgene expression, therapeutic DNA can either be maintained by somatic integration or episomal persistence of which the latter approach would diminish the risk of insertional mutagenesis. As most monosystems fail to fulfill both tasks with equal efficiency, hybrid-vector systems represent promising alternatives. Our hybrid-vector system synergizes high-capacity adenoviral vectors (HCAdV) for efficient delivery and the scaffold/matrix attachment region (S/MAR)–based pEPito plasmid replicon for episomal persistence. After proving that this plasmid replicon can be excised from adenovirus in vitro, colony forming assays were performed. We found an increased number of colonies of up to sevenfold in cells that received the functional plasmid replicon proving that the hybrid-vector system is functional. Transgene expression could be maintained for 6 weeks and the extrachromosomal plasmid replicon was rescued. To show efficacy in vivo, the adenoviral hybrid-vector system was injected into C57Bl/6 mice. We found that the plasmid replicon can be released from adenoviral DNA in murine liver resulting in long-term transgene expression. In conclusion, we demonstrate the efficacy of our novel HCAdV-pEPito hybrid-vector system in vitro and in vivo.

An Engineered Virus Library as a Resource for the Spectrum-wide Exploration of Virus and Vector Diversity

Adenoviruses (Ads) are large human-pathogenic double-stranded DNA (dsDNA) viruses presenting an enormous natural diversity associated with a broad variety of diseases. However, only a small fraction of adenoviruses has been explored in basic virology and biomedical research, highlighting the need to develop robust and adaptable methodologies and resources. We developed a method for high-throughput direct cloning and engineering of adenoviral genomes from different sources utilizing advanced linear-linear homologous recombination (LLHR) and linear-circular homologous recombination (LCHR). We describe 34 cloned adenoviral genomes originating from clinical samples, which were characterized by next-generation sequencing (NGS). We anticipate that this recombineering strategy and the engineered adenovirus library will provide an approach to study basic and clinical virology. High-throughput screening (HTS) of the reporter-tagged Ad library in a panel of cell lines including osteosarcoma disease-specific cell lines revealed alternative virus types with enhanced transduction and oncolysis efficiencies. This highlights the usefulness of this resource.

A High-Capacity Adenoviral Hybrid Vector System Utilizing the Hyperactive Sleeping Beauty Transposase SB100X for Enhanced Integration

For efficient delivery of required genetic elements we utilized high-capacity adenoviral vectors in the past allowing high transgene capacities of up to 36 kb. Previously we explored the hyperactive Sleeping Beauty (SB) transposase (HSB5) for somatic integration from the high-capacity adenoviral vectors genome. To further improve this hybrid vector system we hypothesized that the previously described hyperactive SB transposase SB100X will result in significantly improved efficacies after transduction of target cells. Plasmid based delivery of the SB100X system revealed significantly increased integration efficiencies compared with the previously published hyperactive SB transposase HSB5. After optimizing experimental setups for high-capacity adenoviral vectors-based delivery of the SB100X system we observed up to eightfold and 100-fold increased integration efficiencies compared with the previously published hyperactive SB transposase HSB5 and the inactive transposase mSB, respectively. Furthermore, transposon copy numbers per cell were doubled with SB100X compared with HSB5 when using the identical multiplicity of infection. We believe that this improved hybrid vector system represents a valuable tool for achieving stabilized transgene expression in cycling cells and for treatment of numerous genetic disorders. Especially for in vivo approaches this improved adenoviral hybrid vector system will be advantageous because it may potentially allow reduction of the applied viral dose.For efficient delivery of required genetic elements we utilized high-capacity adenoviral vectors in the past allowing high transgene capacities of up to 36 kb. Previously we explored the hyperactive Sleeping Beauty (SB) transposase (HSB5) for somatic integration from the high-capacity adenoviral vectors genome. To further improve this hybrid vector system we hypothesized that the previously described hyperactive SB transposase SB100X will result in significantly improved efficacies after transduction of target cells. Plasmid based delivery of the SB100X system revealed significantly increased integration efficiencies compared with the previously published hyperactive SB transposase HSB5. After optimizing experimental setups for high-capacity adenoviral vectors-based delivery of the SB100X system we observed up to eightfold and 100-fold increased integration efficiencies compared with the previously published hyperactive SB transposase HSB5 and the inactive transposase mSB, respectively. Furthermore, transposon copy numbers per cell were doubled with SB100X compared with HSB5 when using the identical multiplicity of infection. We believe that this improved hybrid vector system represents a valuable tool for achieving stabilized transgene expression in cycling cells and for treatment of numerous genetic disorders. Especially for in vivo approaches this improved adenoviral hybrid vector system will be advantageous because it may potentially allow reduction of the applied viral dose.

Standard Free Droplet Digital Polymerase Chain Reaction as a New Tool for the Quality Control of High-Capacity Adenoviral Vectors in Small-Scale Preparations

High-capacity adenoviral vectors (HCAdVs) are promising tools for gene therapy as well as for genetic engineering. However, one limitation of the HCAdV vector system is the complex, time-consuming, and labor-intensive production process and the following quality control procedure. Since HCAdVs are deleted for all viral coding sequences, a helper virus (HV) is needed in the production process to provide the sequences for all viral proteins in trans. For the purification procedure of HCAdV, cesium chloride density gradient centrifugation is usually performed followed by buffer exchange using dialysis or comparable methods. However, performing these steps is technically difficult, potentially error-prone, and not scalable. Here, we establish a new protocol for small-scale production of HCAdV based on commercially available adenovirus purification systems and a standard method for the quality control of final HCAdV preparations. For titration of final vector preparations, we established a droplet digital polymerase chain reaction (ddPCR) that uses a standard free-end-point PCR in small droplets of defined volume. By using different probes, this method is capable of detecting and quantifying HCAdV and HV in one reaction independent of reference material, rendering this method attractive for accurately comparing viral titers between different laboratories. In summary, we demonstrate that it is possible to produce HCAdV in a small scale of sufficient quality and quantity to perform experiments in cell culture, and we established a reliable protocol for vector titration based on ddPCR. Our method significantly reduces time and required equipment to perform HCAdV production. In the future the ddPCR technology could be advantageous for titration of other viral vectors commonly used in gene therapy.

Cloning and Large-Scale Production of High-Capacity Adenoviral Vectors Based on the Human Adenovirus Type 5.

High-capacity adenoviral vectors (HCAdV) devoid of all viral coding sequences represent one of the most advanced gene delivery vectors due to their high packaging capacity (up to 35 kb), low immunogenicity and low toxicity. However, for many laboratories the use of HCAdV is hampered by the complicated procedure for vector genome construction and virus production. Here, a detailed protocol for efficient cloning and production of HCAdV based on the plasmid pAdFTC containing the HCAdV genome is described. The construction of HCAdV genomes is based on a cloning vector system utilizing homing endonucleases (I-CeuI and PI-SceI). Any gene of interest of up to 14 kb can be subcloned into the shuttle vector pHM5, which contains a multiple cloning site flanked by I-CeuI and PI-SceI. After I-CeuI and PI-SceI-mediated release of the transgene from the shuttle vector the transgene can be inserted into the HCAdV cloning vector pAdFTC. Because of the large size of the pAdFTC plasmid and the long recognition sites of the used enzymes associated with strong DNA binding, careful handling of the cloning fragments is needed. For virus production, the HCAdV genome is released by NotI digest and transfected into a HEK293 based producer cell line stably expressing Cre recombinase. To provide all adenoviral genes for adenovirus amplification, co-infection with a helper virus containing a packing signal flanked by loxP sites is required. Pre-amplification of the vector is performed in producer cells grown on surfaces and large-scale amplification of the vector is conducted in spinner flasks with producer cells grown in suspension. For virus purification, two ultracentrifugation steps based on cesium chloride gradients are performed followed by dialysis. Here tips, tricks and shortcuts developed over the past years working with this HCAdV vector system are presented.

Human adenovirus type 17 from species D transduces endothelial cells and human CD46 is involved in cell entry

More than 70 human adenoviruses with type-dependent pathogenicity have been identified but biological information about the majority of these virus types is scarce. Here we employed multiple sequence alignments and structural information to predict receptor usage for the development of an adenoviral vector with novel biological features. We report the generation of a cloned adenovirus based on human adenovirus type 17 (HAdV17) with high sequence homology to the well characterized human adenovirus type 37 (HAdV37) that causes epidemic keratoconjunctivitis (EKC). Our study revealed that human CD46 (CD46) is involved in cell entry of HAdV17. Moreover, we found that HAdV17 infects endothelial cells (EC) in vitro including primary cells at higher efficiencies compared to the commonly used human adenovirus type 5 (HAdV5). Using a human CD46 transgenic mouse model, we observed that HAdV17 displays a broad tropism in vivo after systemic injection and that it transduces ECs in this mouse model. We conclude that the HAdV17-based vector may provide a novel platform for gene therapy.

105. Enhanced Oncolytic Activity Mediated by a Novel Human Adenovirus Type 6 Based Vector

Most existing oncolytic adenoviruses (AdV) are based on human AdV type 5 (hAdV-5). Clinical efficacy of hAdV-5 based oncolytic viruses is limited by variable expression levels of coxsackie- and adenovirus receptor (CAR) in different tumor cells and insufficient replication rates. Additionally, high prevalence of neutralizing antibodies against hAdV-5 resulting in lower efficiency makes hAdV-5 a less suitable candidate for systemic application. Recent studies have highlighted human adenovirus type 6 (hAdV-6) as a promising candidate for oncolytic and vaccine vectors. Thus, development of novel oncolytic AdV based on hAdV-6 may help overcoming these limitations. We further hypothesised that oncolytic efficacy of the candidate virus can be augmented by expression of RNAi suppressor protein P19 (Lecellier et al., Nature 2005) as has been shown previously for hAdV-5 (Rauschhuber et al, Sci. Rep. 2013). Here we aim at evaluating a novel hAdV-6-based, p19-containing oncolytic AdV as novel candidate for oncolytic applications in different tumour cell lines. We cloned a P19-containing hAdV-6 based virus (hAdV-6FP19) by a novel seamless recombineering technique (Zhang et al, unpublished). In order to allow P19 expression from the adenoviral vector genome, the P19 cDNA was fused via an internal ribosome entry site (IRES) to the late fiber gene. After release of the respective recombinant adenoviral genomes from plasmids containing the complete DNA molecule, linearized viral DNA was transfected into HEK293 cells for virus reconstitution. After initial amplification steps which were monitored by virus specific PCRs upscaling and virus purification using cesium-chloride density-gradient ultracentrifugation was performed. Rescue and amplification efficiencies were comparable to commonly used hAdV-5 based vectors. Various cancer cell lines from different origin were used to perform oncolysis assays. This included A549 (lung carcinoma), HCT 116 (colon carcinoma), Hela (cervical carcinoma) and Huh7 (hepatocellular carcinoma) cells which were infected with hAdV-6FP19, hAdV-6 and hAdV-5 at various multiplicities of infection (MOI). 2-3 days after infection cells were fixed and stained with methylene blue. We observed significantly higher cell lysis (up to 100-fold) for hAdV-6FP19 infected cells as compared to hAdV-5 and 6 at identical MOIs. Higher cell lysis rates for hAdV-6FP19 compared to wildtype virus were present in all evaluated cell lines, suggesting significantly enhanced oncolytic potential for hAdV-6FP19. In total we believe that hAdV6-based vectors hold great promise for oncolytic applications and that their oncolytic effectiveness can be further improved by RNAi-suppression.

14. Engineering and Characterization of a Cloned Adenoviral-Library to Explore Natural Virus Diversity

Large double-stranded DNA (dsDNA) viruses such as adenovirus (Ad), herpesvirus, poxvirus and their recombinant counterparts were well explored in basic virology and biomedical research. Especially for the development of novel vaccines and gene therapies, Ad gained special attention and represents the most widely explored vector worldwide. Although ~70 types of human Ad and numerous nonhuman Ad (>200) have been identified so far a system for efficient Ad genome cloning and manipulation was lacking and therefore the majority of recombinant adenoviral vectors (AdVs) are based on a small fraction of Ad types. Here we report the generation and characterization of an engineered human adenoviral-library allowing exploration and system studies of the natural Ad diversity. Towards that end we first established that adenoviral genomes can be cloned and tagged in a high-throughput manner utilizing advanced homologous recombination techniques. Wild type Ads from clinical isolates including around half of the currently known adenovirus types that represent all seven human adenovirus species were propagated and direct high-throughput cloning (HTC) applied. The integrity of cloned Ad genomes was confirmed by DNA restriction enzyme pattern and virus reconstitution was conducted using optimized conditions. Most importantly next-generation sequencing (NGS) and phylogenetic analysis was performed. As a further step, half of all cloned adenoviruses representing each species were tagged with a 2A peptide-mediated multicistronic expression cassette providing a Turbo Green fluorescent protein as in vitro marker, a NanoLuc luciferase for in vivo studies and kanamycin/neomycin as selection marker. For HTC of tagged viruses the reporter cassette was inserted into the adenovirus E3 region using different orientations because the orientation of the transgene was essential for reconstitution efficiencies. After successful reconstitution these double reporters-labeled AdVs were evaluated in cultured cell lines and mouse models. In vitro characterization revealed distinct tropisms for tested viruses. Among the currently evaluated cell lines, specie B viruses demonstrated high transduction efficiencies in epithelial (Hela- and A549 cells) and endothelial cells, while Ad5 still displayed highest transduction rates in other human and murine cell types (hepatocytes, lymphocytes, neuroblastoma cells and myoblasts). For the further characterization of unknown receptor usage, we injected recombinant viruses into DSG2 or CD46 transgenic mice for in vivo bio-distribution analyses on genome level by quantitative PCR and on protein level by immunohistology analyses. We anticipate that our engineered adenoviral-library will provide a spacious novel view to the adenovirus field. As a broader perspective it will bring AdV and also other large dsDNA viruses from mono- to multi-types and enables broader applications in molecular medicine including gene therapy and vaccination studies, as well as basic virology.

17. Human Adenovirus D17 Has Tropism for Endothelium Cells and Can Use Both hCAR and CD46 as Receptors

Human adenovirus type 5-derived vectors (HAdV5) from species C were broadly explored for gene therapeutic approaches and vaccination. However, disadvantages associated with this vector type are the strong liver tropism in vivo in mice, preexisting immunity and induction of robust immune responses. There is growing interest in exploring other adenovirus types of which >69 were identified. Here we constructed a new first generation adenovirus labelled with green fluorescent protein marker based on human adenovirus D17 which was first isolated from conjunctival scrapings in 1955 and aimed at characterizing the vector in vitro and in vivo. We applied a new homologous recombineering technology to construct GFP labelled early E1 gene deleted HAdV17 and HAdV5, rescued viruses in complementary stable cell lines, and then screened a panel of different cell lines by FACS analyses and quantitative PCR. Competition assays based on soluble recombinant fiber knob blocking reagents (5knob, 17knob, JO4, Augmab) were used to characterize the receptor interaction in vitro. In vivo biodistribution analyses were performed after intravenous injection of recombinant viruses into normal and CD46 transgenic mice. We observed that HAdV17 has tropism for endothelium cells which are normally refractory to HAdV5 infection. This finding was further verified using primary human umbilical vein endothelial cells (HUVEC). Moreover, after performing competition assays we found that HAdV17 can utilize both CD46 (a membrane cofactor protein which is expressed on all nucleated cells) and CAR (coxsackievirus and adenovirus receptor) as cell attachment receptors. The endothelium tropism was CD46-dependent and could be blocked by the CD46 blocking reagent Ad35K++/Augmab. In vivo biodistribution studies showed significantly increased vector genome copies (VCN) in various organs of human CD46 transgenic mice compared to normal mice indicating involvement of CD46 as a receptor. Immunohistological analyses using cell-specific marker are ongoing. Neutralizing antibody assays revealed that there was less seroprevalence with HAdV17 compared to HAdV5. In total, we believe that HAdV17-based vectors, which can use both hCAR and CD46 as receptors, hold great promise for gene therapy in endothelial disease. The understanding of the molecular interaction between virus and host will be beneficial for vaccination and drug development.

Presentation of Gastric Adenocarcinoma with Acute Arterial Occlusive Disease, Nonbacterial Thrombotic Endocarditis and Pyogenic Liver Abscess

Fatal outcome at early presentation of cancer is rare. Here, a case is discussed of a 53 year old female that presented with an acute onset of left lower extremity pain with paleness, pulselessness, abdominal cramps and vomiting that had been present for several weeks. Rapid evaluation led to the initial diagnosis of metastasized gastric cancer that had evolved to hepatic abscedation and aortic valve endocarditis. The patient rapidly developed severe sepsis with multiple organ failure and died 48 hours after presentation.