Methods for the production of helper-dependent adenoviral vectors

Advances of Recombinant Adenoviral Vectors in Preclinical and Clinical Applications

Adenoviruses (Ad) have the potential to induce severe infections in vulnerable patient groups. Therefore, understanding Ad biology and antiviral processes is important to comprehend the signaling cascades during an infection and to initiate appropriate diagnostic and therapeutic interventions. In addition, Ad vector-based vaccines have revealed significant potential in generating robust immune protection and recombinant Ad vectors facilitate efficient gene transfer to treat genetic diseases and are used as oncolytic viruses to treat cancer. Continuous improvements in gene delivery capacity, coupled with advancements in production methods, have enabled widespread application in cancer therapy, vaccine development, and gene therapy on a large scale. This review provides a comprehensive overview of the virus biology, and several aspects of recombinant Ad vectors, as well as the development of Ad vector, are discussed. Moreover, we focus on those Ads that were used in preclinical and clinical applications including regenerative medicine, vaccine development, genome engineering, treatment of genetic diseases, and virotherapy in tumor treatment.

Intranasal HD-Ad vaccine protects the upper and lower respiratory tracts of hACE2 mice against SARS-CoV-2

Background

The ongoing COVID-19 pandemic has resulted in 185 million recorded cases and over 4 million deaths worldwide. Several COVID-19 vaccines have been approved for emergency use in humans and are being used in many countries. However, all the approved vaccines are administered by intramuscular injection and this may not prevent upper airway infection or viral transmission.

Results

Here, we describe a novel, intranasally delivered COVID-19 vaccine based on a helper-dependent adenoviral (HD-Ad) vector. The vaccine (HD-Ad_RBD) produces a soluble secreted form of the receptor binding domain (RBD) of the SARS-CoV-2 spike protein and we show it induced robust mucosal and systemic immunity. Moreover, intranasal immunization of K18-hACE2 mice with HD-Ad_RBD using a prime-boost regimen, resulted in complete protection of the upper respiratory tract against SARS-CoV-2 infection.

Conclusion

Our approaches provide a powerful platform for constructing highly effective vaccines targeting SARS-CoV-2 and its emerging variants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00723-0.

A helper-dependent adenoviral vector rescues CFTR to wild-type functional levels in cystic fibrosis epithelial cells harbouring class I mutations

Cystic fibrosis (CF) is a genetic disorder affecting multiple organs, including the pancreas, hepatobiliary system and reproductive organs; however, lung disease is responsible for the majority of morbidity and mortality. Management of CF involves CF transmembrane conductance regulator (CFTR) modulator agents including corrector drugs to augment cellular trafficking of mutant CFTR as well as potentiators that open defective CFTR channels. These therapies are poised to help most individuals with CF, with the notable exception of individuals with class I mutations where full-length CFTR protein is not produced. For these mutations, gene replacement has been suggested as a potential solution.In this work, we used a helper-dependent adenoviral vector (HD-CFTR) to express CFTR in nasal epithelial cell cultures derived from CF subjects with class I CFTR mutations.CFTR function was significantly restored in CF cells by HD-CFTR and reached healthy control functional levels as detected by Ussing chamber and membrane potential (FLIPR) assay. A dose-response relationship was observed between the amount of vector used and subsequent functional outcomes; small amounts of HD-CFTR were sufficient to correct CFTR function. At higher doses, HD-CFTR did not increase CFTR function in healthy control cells above baseline values. This latter observation allowed us to use this vector to benchmark in vitro efficacy testing of CFTR-modulator drugs.In summary, we demonstrate the potential for HD-CFTR to inform in vitro testing and to restore CFTR function to healthy control levels in airway cells with class I or CFTR nonsense mutations.

Overcoming Immunological Challenges to Helper-Dependent Adenoviral Vector-Mediated Long-Term CFTR Expression in Mouse Airways

Cystic Fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, and CF patients require life-long treatment. Although CFTR modulators show a great potential for treating most CF patients, some individuals may not tolerate the treatment. In addition, there is no effective therapy for patients with some rare CFTR mutations, such as class I CF mutations, which lead to a lack of CFTR protein production. Therefore, other therapeutic strategies, such as gene therapy, have to be investigated. Currently, immune responses to gene therapy vectors and transgene products are a major obstacle to applying CF gene therapy to clinical applications. In this study, we examined the effects of cyclophosphamide on the modulation of host immune responses and for the improvement of the CFTR transgene expression in the repeated delivery of helper-dependent adenoviral (HD-Ad) vectors to mouse lungs. We have found that cyclophosphamide significantly decreased the expression of T cell genes, such as CD3 (cluster of differentiation 3) and CD4, and reduced their infiltration into mouse lung tissues. We have also found that the levels of the anti-adenoviral antibody and neutralizing activity as well as B-cell infiltration into the mouse lung tissues were significantly reduced with this treatment. Correspondingly, the expression of the human CFTR transgene has been significantly improved with cyclophosphamide administration compared to the group with no treatment. These data suggest that the sustained expression of the human CFTR transgene in mouse lungs through repeated vector delivery can be achieved by transient immunosuppression.

Bi-allelic Homology-Directed Repair with Helper-Dependent Adenoviruses

We describe a strategy to achieve footprintless bi-allelic homology-directed repair (HDR) using helper-dependent adenoviruses (HDAds). This approach utilizes two HDAds to deliver the donor DNA. These two HDAds are identical except for their selectable marker. One expresses the puromycin N-acetyltransferase-herpes simplex virus I thymidine kinase fusion gene (PACTk), while the other expresses the hygromycin phosphotransferase-herpes simplex virus I thymidine kinase fusion gene (HyTk). Therefore, puromycin and hygromycin double resistance can be used to select for targeted HDAd integration into both alleles. Subsequently, piggyBac-mediated excision of both PACTk and HyTk will confer resistance to gancyclovir, resulting in footprintless HDR at both alleles. However, gene-targeting frequency was not high enough to achieve simultaneous targeting at both alleles. Instead, sequential targeting, whereby the two alleles were targeted one at a time, was required in order to achieve bi-allelic HDR with HDAd.

TALEN-Mediated Gene Targeting for Cystic Fibrosis-Gene Therapy

Cystic fibrosis (CF) is an inherited monogenic disorder, amenable to gene-based therapies. Because CF lung disease is currently the major cause of mortality and morbidity, and the lung airway is readily accessible to gene delivery, the major CF gene therapy effort at present is directed to the lung. Although airway epithelial cells are renewed slowly, permanent gene correction through gene editing or targeting in airway stem cells is needed to perpetuate the therapeutic effect. Transcription activator-like effector nuclease (TALEN) has been utilized widely for a variety of gene editing applications. The stringent requirement for nuclease binding target sites allows for gene editing with precision. In this study, we engineered helper-dependent adenoviral (HD-Ad) vectors to deliver a pair of TALENs together with donor DNA targeting the human AAVS1 locus. With homology arms of 4 kb in length, we demonstrated precise insertion of either a LacZ reporter gene or a human cystic fibrosis transmembrane conductance regulator (CFTR) minigene (cDNA) into the target site. Using the LacZ reporter, we determined the efficiency of gene integration to be about 5%. In the CFTR vector transduced cells, we were able to detect CFTR mRNA expression using qPCR and function correction using fluorometric image plate reader (FLIPR) and iodide efflux assays. Taken together, these findings suggest a new direction for future in vitro and in vivo studies in CF gene editing.

Properties of LINE-1 proteins and repeat element expression in the context of amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease involving loss of motor neurons and having no known cure and uncertain etiology. Several studies have drawn connections between altered retrotransposon expression and ALS. Certain features of the LINE-1 (L1) retrotransposon-encoded ORF1 protein (ORF1p) are analogous to those of neurodegeneration-associated RNA-binding proteins, including formation of cytoplasmic aggregates. In this study we explore these features and consider possible links between L1 expression and ALS.

RESULTS

We first considered factors that modulate aggregation and subcellular distribution of LINE-1 ORF1p, including nuclear localization. Changes to some ORF1p amino acid residues alter both retrotransposition efficiency and protein aggregation dynamics, and we found that one such polymorphism is present in endogenous L1s abundant in the human genome. We failed, however, to identify CRM1-mediated nuclear export signals in ORF1p nor strict involvement of cell cycle in endogenous ORF1p nuclear localization in human 2102Ep germline teratocarcinoma cells. Some proteins linked with ALS bind and colocalize with L1 ORF1p ribonucleoprotein particles in cytoplasmic RNA granules. Increased expression of several ALS-associated proteins, including TAR DNA Binding Protein (TDP-43), strongly limits cell culture retrotransposition, while some disease-related mutations modify these effects. Using quantitative reverse transcription PCR (RT-qPCR) of ALS tissues and reanalysis of publicly available RNA-Seq datasets, we asked if changes in expression of retrotransposons are associated with ALS. We found minimal altered expression in sporadic ALS tissues but confirmed a previous report of differential expression of many repeat subfamilies in C9orf72 gene-mutated ALS patients.

CONCLUSIONS

Here we extended understanding of the subcellular localization dynamics of the aggregation-prone LINE-1 ORF1p RNA-binding protein. However, we failed to find compelling evidence for misregulation of LINE-1 retrotransposons in sporadic ALS nor a clear effect of ALS-associated TDP-43 protein on L1 expression. In sum, our study reveals that the interplay of active retrotransposons and the molecular features of ALS are more complex than anticipated. Thus, the potential consequences of altered retrotransposon activity for ALS and other neurodegenerative disorders are worthy of continued investigation.

Conditional disruption of hepatic carbamoyl phosphate synthetase 1 in mice results in hyperammonemia without orotic aciduria and can be corrected by liver-directed gene therapy

Carbamoyl phosphate synthetase 1 (CPS1) is a urea cycle enzyme that forms carbamoyl phosphate from bicarbonate, ammonia and ATP. Bi-allelic mutations of the CPS1 gene result in a urea cycle disorder presenting with hyperammonemia, often with reduced citrulline, and without orotic aciduria. CPS1 deficiency is particularly challenging to treat and lack of early recognition typically results in early neonatal death. Therapeutic interventions have limited efficacy and most patients develop long-term neurologic sequelae. Using transgenic techniques, we generated a conditional Cps1 knockout mouse. By loxP/Cre recombinase technology, deletion of the Cps1 locus was achieved in adult transgenic animals using a Cre recombinase-expressing adeno-associated viral vector. Within four weeks from vector injection, all animals developed hyperammonemia without orotic aciduria and died. Minimal CPS1 protein was detectable in livers. To investigate the efficacy of gene therapy for CPS deficiency following knock-down of hepatic endogenous CPS1 expression, we injected these mice with a helper-dependent adenoviral vector (HDAd) expressing the large murine CPS1 cDNA under control of the phosphoenolpyruvate carboxykinase promoter. Liver-directed HDAd-mediated gene therapy resulted in survival, normalization of plasma ammonia and glutamine, and 13% of normal Cps1 expression. A gender difference in survival suggests that female mice may require higher hepatic CPS1 expression. We conclude that this conditional murine model recapitulates the clinical and biochemical phenotype detected in human patients with CPS1 deficiency and will be useful to investigate ammonia-mediated neurotoxicity and for the development of cell- and gene-based therapeutic approaches.

Synaptotagmin-7 controls the size of the reserve and resting pools of synaptic vesicles in hippocampal neurons

Continuous neurotransmitter release is subjected to synaptic vesicle availability, which in turn depends on vesicle recycling and the traffic of vesicles between pools. We studied the role of Synaptotagmin-7 (Syt-7) in synaptic vesicle accessibility for release in hippocampal neurons in culture. Synaptic boutons from Syt-7 knockout (KO) mice displayed normal basal secretion with no alteration in the RRP size or the probability of release. However, stronger stimuli revealed an increase in the size of the reserve and resting vesicle pools in Syt-7 KO boutons compared with WT. These data suggest that Syt-7 plays a significant role in the vesicle pool homeostasis and, consequently, in the availability of vesicles for synaptic transmission during strong stimulation, probably, by facilitating advancing synaptic vesicles to the readily releasable pool.

Sustained secretion of anti-tumor necrosis factor α monoclonal antibody from ex vivo genetically engineered dermal tissue demonstrates therapeutic activity in mouse model of rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a symmetric inflammatory polyarthritis associated with high concentrations of pro-inflammatory, cytokines including tumor necrosis factor (TNF)-α. Adalimumab is a monoclonal antibody (mAb) that binds TNF-α, and is widely used to treat RA. Despite its proven clinical efficacy, adalimumab and other therapeutic mAbs have disadvantages, including the requirement for repeated bolus injections and the appearance of treatment limiting anti-drug antibodies. To address these issues, we have developed an innovative ex vivo gene therapy approach, termed transduced autologous restorative gene therapy (TARGT), to produce and secrete adalimumab for the treatment of RA.

METHODS

Helper-dependent (HD) adenovirus vector containing adalimumab light and heavy chain coding sequences was used to transduce microdermal tissues and cells of human and mouse origin ex vivo, rendering sustained secretion of active adalimumab. The genetically engineered tissues were subsequently implanted in a mouse model of RA.

RESULTS

Transduced human microdermal tissues implanted in SCID mice demonstrated 49 days of secretion of active adalimumab in the blood, at levels of tens of microgram per milliliter. In addition, transduced autologous dermal cells were implanted in the RA mouse model and demonstrated statistically significant amelioration in RA symptoms compared to naïve cell implantation and were similar to recombinant adalimumab bolus injections.

CONCLUSIONS

The results of the present study report microdermal tissues engineered to secrete active adalimumab as a proof of concept for sustained secretion of antibody from the novel ex vivo gene therapy TARGT platform. This technology may now be applied to a range of antibodies for the therapy of other diseases.

Orphan receptor GPR158 controls stress-induced depression

Stress can be a motivational force for decisive action and adapting to novel environment; whereas, exposure to chronic stress contributes to the development of depression and anxiety. However, the molecular mechanisms underlying stress-responsive behaviors are not fully understood. Here, we identified the orphan receptor GPR158 as a novel regulator operating in the prefrontal cortex (PFC) that links chronic stress to depression. GPR158 is highly upregulated in the PFC of human subjects with major depressive disorder. Exposure of mice to chronic stress also increased GPR158 protein levels in the PFC in a glucocorticoid-dependent manner. Viral overexpression of GPR158 in the PFC induced depressive-like behaviors. In contrast GPR158 ablation, led to a prominent antidepressant-like phenotype and stress resiliency. We found that GPR158 exerts its effects via modulating synaptic strength altering AMPA receptor activity. Taken together, our findings identify a new player in mood regulation and introduce a pharmacological target for managing depression.

Gene Editing with Helper-Dependent Adenovirus Can Efficiently Introduce Multiple Changes Simultaneously over a Large Genomic Region

Helper-dependent adenoviral vectors (HDAds) possess long homology arms that mediate high-efficiency gene editing. These long homology arms may permit simultaneous introduction of multiple modifications into a large genomic region or may permit a single HDAd to correct many different individual mutations spread widely across a gene. We investigated this important potential using an HDAd bearing 13 genetic markers in the region of homology to the target CFTR locus in human iPSCs and found that all markers can be simultaneously introduced into the target locus, with the two farthest markers being 22.2 kb apart. We found that genetic markers closer to the HDAd’s selectable marker are more efficiency introduced into the target locus; a marker located 208 bp from the selectable marker was introduced with 100% efficiency. However, even markers 11 kb from the selectable marker were introduced at a relatively high frequency of 21.7%. Our study also revealed extensive heteroduplex DNA formation of up to 10 kb with no bias toward vector or chromosomal repair. However, mismatches escape repair at a frequency of up to 15%, leading to a genetically mixed colony and emphasizing the need for caution, especially if the donor and target sequences are not 100% homologous.

Engineered LINE-1 retrotransposition in nondividing human neurons

Half the human genome is made of transposable elements (TEs), whose ongoing activity continues to impact our genome. LINE-1 (or L1) is an autonomous non-LTR retrotransposon in the human genome, comprising 17% of its genomic mass and containing an average of 80-100 active L1s per average genome that provide a source of inter-individual variation. New LINE-1 insertions are thought to accumulate mostly during human embryogenesis. Surprisingly, the activity of L1s can further impact the somatic human brain genome. However, it is currently unknown whether L1 can retrotranspose in other somatic healthy tissues or if L1 mobilization is restricted to neuronal precursor cells (NPCs) in the human brain. Here, we took advantage of an engineered L1 retrotransposition assay to analyze L1 mobilization rates in human mesenchymal (MSCs) and hematopoietic (HSCs) somatic stem cells. Notably, we have observed that L1 expression and engineered retrotransposition is much lower in both MSCs and HSCs when compared to NPCs. Remarkably, we have further demonstrated for the first time that engineered L1s can retrotranspose efficiently in mature nondividing neuronal cells. Thus, these findings suggest that the degree of somatic mosaicism and the impact of L1 retrotransposition in the human brain is likely much higher than previously thought.

Homology Requirements for Efficient, Footprintless Gene Editing at the CFTR Locus in Human iPSCs with Helper-dependent Adenoviral Vectors

Helper-dependent adenoviral vectors mediate high efficiency gene editing in induced pluripotent stem cells without needing a designer nuclease thereby avoiding off-target cleavage. Because of their large cloning capacity of 37 kb, helper-dependent adenoviral vectors with long homology arms are used for gene editing. However, this makes vector construction and recombinant analysis difficult. Conversely, insufficient homology may compromise targeting efficiency. Thus, we investigated the effect of homology length on helper-dependent adenoviral vector targeting efficiency at the cystic fibrosis transmembrane conductance regulator locus in induced pluripotent stem cells and found a positive correlation. With 23.8 and 21.4 kb of homology, the frequencies of targeted recombinants were 50–64.6% after positive selection for vector integration, and 97.4–100% after negative selection against random integrations. With 14.8 kb, the frequencies were 26.9–57.1% after positive selection and 87.5–100% after negative selection. With 9.6 kb, the frequencies were 21.4 and 75% after positive and negative selection, respectively. With only 5.6 kb, the frequencies were 5.6–16.7% after positive selection and 50% after negative selection, but these were more than high enough for efficient identification and isolation of targeted clones. Furthermore, we demonstrate helper-dependent adenoviral vector-mediated footprintless correction of cystic fibrosis transmembrane conductance regulator mutations through piggyBac excision of the selectable marker. However, low frequencies (≤ 1 × 10⁻³) necessitated negative selection for piggyBac-excision product isolation.

Preclinical and Preliminary Clinical Evaluation of Genetically Transduced Dermal Tissue Implants for the Sustained Secretion of Erythropoietin and Interferon α

Protein drugs are currently delivered by bolus injection and although treatment frequently is successful, these methods also have major drawbacks, which call for the development of alternative technologies allowing prolonged delivery of these drugs. We developed a new ex vivo gene therapy platform called Transduced Autologous Restorative Gene Therapy (TARGT) for sustained long term production and secretion of autologous therapeutic proteins. A biopsy of dermal tissue taken from the patient is transduced ex vivo with a viral vector encoding the required gene under a constitutive promoter. Following measurement of protein secretion ex vivo, the transduced dermal tissue is implanted back into the patient, where it secretes the therapeutic protein into the circulation for several months or longer. A major hurdle to this approach is potential immunogenicity of the transduced tissue following implantation. In this paper we describe the preclinical and early clinical development of this technology, which allowed for overcoming these hurdles. To that end, we have used the helper dependent (HD) adenoviral vector with newly designed expression cassette containing genetic elements to optimize transgene expression. Moreover, we have developed procedures for TARGT tissue implantation, with measures to improve engraftment and reduce inflammation and rejection. Implantation of human TARGT to severe combined immune deficient (SCID) mice indicated long-term production of active proteins in the blood. Preliminary results of a clinical trial from two anemic end-stage renal disease patients, implanted with TARGTs expressing the human erythropoietin (EPO) gene, demonstrated prolonged secretion with physiologic blood level of the hormone and hemoglobin maintenance in the desired range, for a period of at least 5 months without exogenous EPO administration. We believe that the TARGT technology has the potential to become a platform for the sustained delivery of therapeutic proteins in various clinical indications.

Helper virus-mediated downregulation of transgene expression permits production of recalcitrant helper-dependent adenoviral vector

Helper-dependent adenoviral vectors (HDAd) that express certain transgene products are impossible to produce because the transgene product is toxic to the producer cells, especially when made in large amounts during vector production. Downregulating transgene expression from the HDAd during vector production is a way to solve this problem. In this report, we show that this can be accomplished by inserting the target sequence for the adenoviral VA RNAI into the 3’ untranslated region of the expression cassette in the HDAd. Thus during vector production, when the producer cells are coinfected with both the helper virus (HV) and the HDAd, the VA RNAI produced by the HV will target the transgene mRNA from the HDAd via the endogenous cellular RNAi pathway. Once the HDAd is produced and purified, transduction of the target cells results in unimpeded transgene expression because of the absence of HV. This simple and universal strategy permits for the robust production of otherwise recalcitrant HDAds.

Down-regulation of Risa improves insulin sensitivity by enhancing autophagy

It has been reported that some small noncoding RNAs are involved in the regulation of insulin sensitivity. However, whether long noncoding RNAs also participate in the regulation of insulin sensitivity is still largely unknown. We identified and characterized a long noncoding RNA, regulator of insulin sensitivity and autophagy (Risa), which is a poly(A)(+) cytoplasmic RNA. Overexpression of Risa in mouse primary hepatocytes or C2C12 myotubes attenuated insulin-stimulated phosphorylation of insulin receptor, Akt, and Gsk3β, and knockdown of Risa alleviated insulin resistance. Further studies showed that overexpression of Risa in hepatocytes or myotubes decreased autophagy, and knockdown of Risa up-regulated autophagy. Moreover, knockdown of Atg7 or -5 significantly inhibited the effect of knockdown of Risa on insulin resistance, suggesting that knockdown of Risa alleviated insulin resistance via enhancing autophagy. In addition, tail vein injection of adenovirus to knock down Risa enhanced insulin sensitivity and hepatic autophagy in both C57BL/6 and ob/ob mice. Taken together, the data demonstrate that Risa regulates insulin sensitivity by affecting autophagy and suggest that Risa is a potential target for treating insulin-resistance-related diseases.-Wang, Y., Hu, Y., Sun, C., Zhuo, S., He, Z., Wang, H., Yan, M., Liu, J., Luan, Y., Dai, C., Yang, Y., Huang, R., Zhou, B., Zhang, F., Zhai, Q. Down-regulation of Risa improves insulin sensitivity by enhancing autophagy.

Preclinical Efficacy and Safety Profile of Allometrically Scaled Doses of Doxycycline Used to Turn "On" Therapeutic Transgene Expression from High-Capacity Adenoviral Vectors in a Glioma Model

Glioblastoma multiforme (GBM) is the most commonly occurring primary brain cancer in adults, in whom its highly infiltrative cells prevent total surgical resection, often leading to tumor recurrence and patient death. Our group has discovered a gene therapy approach for GBM that utilizes high-capacity "gutless" adenoviral vectors encoding regulatable therapeutic transgenes. The herpes simplex type 1-thymidine kinase (TK) actively kills dividing tumor cells in the brain when in the presence of the prodrug, ganciclovir (GCV), whereas the FMS-like tyrosine kinase 3 ligand (Flt3L) is an immune-stimulatory molecule under tight regulation by a tetracycline-inducible "Tet-On" activation system that induces anti-GBM immunity. As a prelude to a phase I clinical trial, we evaluated the safety and efficacy of Food and Drug Administration (FDA)-approved doses of the tetracycline doxycycline (DOX) allometrically scaled for rats. DOX initiates the expression of Flt3L, which has been shown to recruit dendritic cells to the brain tumor microenvironment-an integral first step in the development of antitumor immunity. The data revealed a highly safe profile surrounding these human-equivalent doses of DOX under an identical therapeutic window as proposed in the clinical trial. This was confirmed through a neuropathological analysis, liver and kidney histopathology, detection of neutralizing antibodies, and systemic toxicities in the blood. Interestingly, we observed a significant survival advantage in rats with GBM receiving the 300 mg/day equivalent dosage of DOX versus the 200 mg/day equivalent. Additionally, rats rejected "recurrent" brain tumor threats implanted 90 days after their primary brain tumors. We also show that DOX detection within the plasma can be an indicator of optimal dosing of DOX to attain therapeutic levels. This work has significant clinical relevance for an ongoing phase I clinical trial in humans with primary GBM and for other therapeutic approaches using Tet-On transactivation system in humans.

Adenovirus-Vectored Broadly Neutralizing Antibodies Directed Against gp120 Prevent Human Immunodeficiency Virus Type 1 Acquisition in Humanized Mice

Despite nearly three decades of research, a safe and effective vaccine against human immunodeficiency virus type 1 (HIV-1) has yet to be achieved. More recently, the discovery of highly potent anti-gp160 broadly neutralizing antibodies (bNAbs) has garnered renewed interest in using antibody-based prophylactic and therapeutic approaches. Here, we encoded bNAbs in first-generation adenoviral (ADV) vectors, which have the distinctive features of a large coding capacity and ease of propagation. A single intramuscular injection of ADV-vectorized bNAbs in humanized mice generated high serum levels of bNAbs that provided protection against multiple repeated challenges with a high dose of HIV-1, prevented depletion of peripheral CD4(+) T cells, and reduced plasma viral loads to below detection limits. Our results suggest that ADV vectors may be a viable option for the prophylactic and perhaps therapeutic use of bNAbs in humans.

Transient blocking of NK cell function with small molecule inhibitors for helper dependant adenoviral vector-mediated gene delivery

One major challenge in gene therapy is the host immune responses against viral vectors. Previous studies indicate the involvement of NK cells in stunted gene expression in viral vector mediated gene therapy. To understand the problem of the immune responses, we have developed an in-vitro co-culture system with human NK cell line, macrophages and airway epithelial cells. We showed that small molecule blockers, CAPE and ruxolitinib, for NF-κB and JAK-STAT pathways, respectively, significantly inhibited cytokine secretion by macrophages. When NK cells are co-cultured with helper-dependent adenoviral (HD-Ad) vector activated macrophages, IFN-γ cytokine expression by NK cells increased significantly, which was inhibited effectively by ruxolitinib and CAPE, and there was an additive effect when both inhibitors were used. We demonstrated that NK cells activated by cytokines produced by HD-Ad-activated macrophages kill HD-Ad vector transduced bronchial epithelial cells. This cell killing activity was significantly reduced by CAPE and ruxolitinib. Combination of these two inhibitors had an additive effect on inhibiting NK cell mediate killing of gene transduced cells. Transient inhibition of NK cell response at its peak may enhance sustained gene expression. Our data suggest that combination of CAPE and ruxolitinib may help in protecting gene transduced airway epithelial cells to prolong transgene expression.

Pancreatic transduction by helper-dependent adenoviral vectors via intraductal delivery

Pancreatic gene transfer could be useful to treat several diseases, such as diabetes mellitus, cystic fibrosis, chronic pancreatitis, or pancreatic cancer. Helper-dependent adenoviral vectors (HDAds) are promising tools for gene therapy because of their large cloning capacity, high levels of transgene expression, and long-term persistence in immunocompetent animals. Nevertheless, the ability of HDAds to transduce the pancreas in vivo has not been investigated yet. Here, we have generated HDAds carrying pancreas-specific expression cassettes, that is, driven either by the elastase or insulin promoter, using a novel and convenient plasmid family and homologous recombination in bacteria. These HDAds were delivered to the pancreas of immunocompetent mice via intrapancreatic duct injection. HDAds, encoding a CMV-GFP reporter cassette, were able to transduce acinar and islet cells, but transgene expression was lost 15 days postinjection in correlation with severe lymphocytic infiltration. When HDAds encoding GFP under the control of the specific elastase promoter were used, expression was detected in acinar cells, but similarly, the expression almost disappeared 30 days postinjection and lymphocytic infiltration was also observed. In contrast, long-term transgene expression (>8 months) was achieved with HDAds carrying the insulin promoter and the secretable alkaline phosphatase as the reporter gene. Notably, transduction of the liver, the preferred target for adenovirus, was minimal by this route of delivery. These data indicate that HDAds could be used for pancreatic gene therapy but that selection of the expression cassette is of critical importance to achieve long-term expression of the transgene in this tissue.

High-level production of replication-defective human immunodeficiency type 1 virus vector particles using helper-dependent adenovirus vectors

Gene transfer vectors based upon human immunodeficiency virus type 1 (HIV) are widely used in bench research applications and increasingly in clinical investigations, both to introduce novel genes but also to reduce expression of unwanted genes of the host and pathogen. At present, the vast majority of HIV-based vector supernatants are produced in 293T cells by cotransfection of up to five DNA plasmids, which is subject to variability and difficult to scale. Here we report the development of a HIV-based vector production system that utilizes helper-dependent adenovirus (HDAd). All necessary HIV vector components were inserted into one or more HDAds, which were then amplified to very high titers of ~10¹³ vp/ml. These were then used to transduce 293-based cells to produce HIV-based vector supernatants, and resultant VSV G-pseudotyped lentiviral vector (LV) titers and total IU were 10- to 30-fold higher, compared to plasmid transfection. Optimization of HIV-based vector production depended upon maximizing expression of all HIV vector components from HDAd. Supernatants contained trace amounts of HDAd but were free of replication-competent lentivirus. This production method should be applicable to other retroviral vector systems. Scalable production of HIV-based vectors using this two-step procedure should facilitate their clinical advancement.

Challenges and Prospects for Helper-Dependent Adenoviral Vector-Mediated Gene Therapy

Helper-dependent adenoviral (HDAd) vectors that are devoid of all viral coding sequences are promising non-integrating vectors for gene therapy because they efficiently transduce a variety of cell types in vivo, have a large cloning capacity, and drive long-term transgene expression without chronic toxicity. The main obstacle preventing clinical applications of HDAd vectors is the host innate inflammatory response against the vector capsid proteins that occurs shortly after intravascular vector administration and result in acute toxicity, the severity of which is dose dependent. Intense efforts have been focused on elucidating adenoviral vector-host interactions and the factors involved in the acute toxicity. This review focuses on the recent acquisition of data on such interactions and on strategies investigated to improve the therapeutic index of HDAd vectors.

Safety profile, efficacy, and biodistribution of a bicistronic high-capacity adenovirus vector encoding a combined immunostimulation and cytotoxic gene therapy as a prelude to a phase I clinical trial for glioblastoma

Adenoviral vectors (Ads) are promising gene delivery vehicles due to their high transduction efficiency; however, their clinical usefulness has been hampered by their immunogenicity and the presence of anti-Ad immunity in humans. We reported the efficacy of a gene therapy approach for glioma consisting of intratumoral injection of Ads encoding conditionally cytotoxic herpes simplex type 1 thymidine kinase (Ad-TK) and the immunostimulatory cytokine fms-like tyrosine kinase ligand 3 (Ad-Flt3L). Herein, we report the biodistribution, efficacy, and neurological and systemic effects of a bicistronic high-capacity Ad, i.e., HC-Ad-TK/TetOn-Flt3L. HC-Ads elicit sustained transgene expression, even in the presence of anti-Ad immunity, and can encode large therapeutic cassettes, including regulatory elements to enable turning gene expression "on" or "off" according to clinical need. The inclusion of two therapeutic transgenes within a single vector enables a reduction of the total vector load without adversely impacting efficacy. Because clinically the vectors will be delivered into the surgical cavity, normal regions of the brain parenchyma are likely to be transduced. Thus, we assessed any potential toxicities elicited by escalating doses of HC-Ad-TK/TetOn-Flt3L (1×10(8), 1×10(9), or 1×10(10) viral particles [vp]) delivered into the rat brain parenchyma. We assessed neuropathology, biodistribution, transgene expression, systemic toxicity, and behavioral impact at acute and chronic time points. The results indicate that doses up to 1×10(9) vp of HC-Ad-TK/TetOn-Flt3L can be safely delivered into the normal rat brain and underpin further developments for its implementation in a phase I clinical trial for glioma.

Linearized oncolytic adenoviral plasmid DNA delivered by bioreducible polymers

As an effort to overcome limits of adenovirus (Ad) as a systemic delivery vector for cancer therapy, we developed a novel system using oncolytic Ad plasmid DNA with two bioreducible polymers: arginine-grafted bioreducible poly(disulfide amine)polymer (ABP) and PEG5k-conjugated ABP (ABP5k) in expectation of oncolytic effect caused by progeny viral production followed by replication. The linearized Ad DNAs for active viral replication polyplexed with each polymer were able to replicate only in human cancer cells and produce progeny viruses. The non-immunogenic polymers delivering the DNAs markedly elicited to evade the innate and adaptive immune response. The biodistribution ratio of the polyplexes administered systemically was approximately 99% decreased in liver when compared with naked Ad. Moreover, tumor-to-liver ratio of the Ad DNA delivered by ABP or ABP5k was significantly elevated at 229- or 419-fold greater than that of naked Ad, respectively. The ABP5k improved the chance of the DNA to localize within tumor versus liver with 1.8-fold increased ratio. In conclusion, the innovative and simple system for delivering oncolytic Ad plasmid DNA with the bioreducible polymers, skipping time-consuming steps such as generation and characterization of oncolytic Ad vectors, can be utilized as an alternative approach for cancer therapy.

Altering the Ad5 packaging domain affects the maturation of the Ad particles

We have previously described a new family of mutant adenoviruses carrying different combinations of attB/attP sequences from bacteriophage PhiC31 flanking the Ad5 packaging domain. These novel helper viruses have a significantly delayed viral life cycle and a severe packaging impairment, regardless of the presence of PhiC31 recombinase. Their infectious viral titers are significantly lower (100–1000 fold) than those of control adenovirus at 36 hours post-infection, but allow for efficient packaging of helper-dependent adenovirus. In the present work, we have analyzed which steps of the adenovirus life cycle are altered in attB-helper adenoviruses and investigated whether these viruses can provide the necessary viral proteins in trans. The entry of attB-adenoviral genomes into the cell nucleus early at early timepoints post-infection was not impaired and viral protein expression levels were found to be similar to those of control adenovirus. However, electron microscopy and capsid protein composition analyses revealed that attB-adenoviruses remain at an intermediate state of maturation 36 hours post-infection in comparison to control adenovirus which were fully mature and infective at this time point. Therefore, an additional 20–24 hours were found to be required for the appearance of mature attB-adenovirus. Interestingly, attB-adenovirus assembly and infectivity was restored by inserting a second packaging signal close to the right-end ITR, thus discarding the possibility that the attB-adenovirus genome was retained in a nuclear compartment deleterious for virus assembly. The present study may have substantive implications for helper-dependent adenovirus technology since helper attB-adenovirus allows for preferential packaging of helper-dependent adenovirus genomes.

Development of an inflammation-inducible gene expression system using helper-dependent adenoviral vectors

BACKGROUND

Clinical studies have shown that gene therapy is a promising approach for treating such genetic diseases as the eye disease, Leber's congenital amaurosis. Development of gene therapy approaches for treating chronic inflammatory diseases is, however, more challenging because it requires the production of anti-inflammatory molecules at the diseased tissues only when they are needed.

METHODS

We designed such a system by modifying the human interleukin (IL)-6 gene promoter to direct transgene expression and delivered the system into cultured cells as well as mouse lungs using a helper-dependent adenoviral vector.

RESULTS

We have demonstrated both in vitro and in vivo that the reporter LacZ or human IL-10 gene can be induced by inflammatory stimuli.

CONCLUSIONS

The results obtained indicate that the inflammation inducible gene expression system based on the modified human IL-6 gene promoter has the potential to be used for developing gene therapy for treating inflammatory diseases.

Helper-Dependent Adenoviral Vectors

Helper-dependent adenoviral vectors are devoid of all viral coding sequences, possess a large cloning capacity, and can efficiently transduce a wide variety of cell types from various species independent of the cell cycle to mediate long-term transgene expression without chronic toxicity. These non-integrating vectors hold tremendous potential for a variety of gene transfer and gene therapy applications. Here, we review the production technologies, applications, obstacles to clinical translation and their potential resolutions, and the future challenges and unanswered questions regarding this promising gene transfer technology.

Modifications of adenovirus hexon allow for either hepatocyte detargeting or targeting with potential evasion from Kupffer cells

In vivo gene transfer with adenovirus vectors would significantly benefit from a tight control of the adenovirus-inherent liver tropism. For efficient hepatocyte transduction, adenovirus vectors need to evade from Kupffer cell scavenging while delivery to peripheral tissues or tumors could be improved if both scavenging by Kupffer cells and uptake by hepatocytes were blocked. Here, we provide evidence that a single point mutation in the hexon capsomere designed to enable defined chemical capsid modifications may permit both detargeting from and targeting to hepatocytes with evasion from Kupffer cell scavenging. Vector particles modified with small polyethylene glycol (PEG) moieties specifically on hexon exhibited decreased transduction of hepatocytes by shielding from blood coagulation factor binding. Vector particles modified with transferrin or, surprisingly, 5,000 Da PEG or dextran increased hepatocyte transduction up to 18-fold independent of the presence of Kupffer cells. We further show that our strategy can be used to target high-capacity adenovirus vectors to hepatocytes emphasizing the potential for therapeutic liver-directed gene transfer. Our approach may lead to a detailed understanding of the interactions between adenovirus vectors and Kupffer cells, one of the most important barriers for adenovirus-mediated gene delivery.

Adenovirus-retrovirus hybrid vectors achieve highly enhanced tumor transduction and antitumor efficacy in vivo

Murine leukemia virus (MLV)-based replication-competent retrovirus (RCR) vectors have been shown to mediate efficient, selective, and persistent tumor transduction, thereby achieving significant therapeutic benefit in a wide variety of cancer models. To further augment the efficiency of this strategy, we have developed a delivery method employing a gutted adenovirus encoding an RCR vector (AdRCR); thus, tumor cells transduced with the adenoviral vector transiently become RCR vector producer cells in situ. As expected, high-titer AdRCR achieved significantly higher initial transduction levels in human cancer cells both in vitro and in vivo, as compared to the original RCR vector itself. Notably, even at equivalent initial transduction levels, more secondary RCR progeny were produced from AdRCR-transduced cells as compared to RCR-transduced cells, resulting in further acceleration of subsequent RCR replication kinetics. In pre-established tumor models in vivo, prodrug activator gene therapy with high-titer AdRCR could achieve enhanced efficacy compared to RCR alone, in a dose-dependent manner. Thus, AdRCR hybrid vectors offer the advantages of high production titers characteristic of adenovirus and secondary production of RCR in situ, which not only accelerates subsequent vector spread and progressive tumor transduction, but can also significantly enhance the therapeutic efficacy of RCR-mediated prodrug activator gene therapy.

A novel bicistronic high-capacity gutless adenovirus vector that drives constitutive expression of herpes simplex virus type 1 thymidine kinase and tet-inducible expression of Flt3L for glioma therapeutics

Glioblastoma multiforme (GBM) is a deadly primary brain tumor. Conditional cytotoxic/immune-stimulatory gene therapy (Ad-TK and Ad-Flt3L) elicits tumor regression and immunological memory in rodent GBM models. Since the majority of patients enrolled in clinical trials would exhibit adenovirus immunity, which could curtail transgene expression and therapeutic efficacy, we used high-capacity adenovirus vectors (HC-Ads) as a gene delivery platform. Herein, we describe for the first time a novel bicistronic HC-Ad driving constitutive expression of herpes simplex virus type 1 thymidine kinase (HSV1-TK) and inducible Tet-mediated expression of Flt3L within a single-vector platform. We achieved anti-GBM therapeutic efficacy with no overt toxicities using this bicistronic HC-Ad even in the presence of systemic Ad immunity. The bicistronic HC-Ad-TK/TetOn-Flt3L was delivered into intracranial gliomas in rats. Survival, vector biodistribution, neuropathology, systemic toxicity, and neurobehavioral deficits were assessed for up to 1 year posttreatment. Therapeutic efficacy was also assessed in animals preimmunized against Ads. We demonstrate therapeutic efficacy, with vector genomes being restricted to the brain injection site and an absence of overt toxicities. Importantly, antiadenoviral immunity did not inhibit therapeutic efficacy. These data represent the first report of a bicistronic vector platform driving the expression of two therapeutic transgenes, i.e., constitutive HSV1-TK and inducible Flt3L genes. Further, our data demonstrate no promoter interference and optimum gene delivery and expression from within this single-vector platform. Analysis of the efficacy, safety, and toxicity of this bicistronic HC-Ad vector in an animal model of GBM strongly supports further preclinical testing and downstream process development of HC-Ad-TK/TetOn-Flt3L for a future phase I clinical trial for GBM.

Large-scale production of high-quality helper-dependent adenoviral vectors using adherent cells in cell factories

The most efficient and widely used system for generating helper-dependent adenoviral vectors (HDAds) is the Cre/loxP system developed by Graham and co-workers (Parks, R.J., Chen, L., Anton, M., Sankar, U., Rudnicki, M.A., and Graham, F.L. [ 1996 ]. Proc. Natl. Acad. Sci. U. S. A. 93, 13565-13570). Alternative systems have been developed for HDAd production, but all are limited by the technical complexity of a three-component vector production system for reproducibly generating large quantities of adenovirus with high infectivity and low helper virus (HV) contamination. Recently, these problems were addressed by Ng and co-workers (Palmer, D., and Ng, P. [ 2003 ]. Mol Ther. 8, 846-852), who developed an improved system that combines the use of a suspension-adapted producer cell line expressing high levels of Cre recombinase, a HV resistant to mutation, and a refined purification protocol. With this system, >1 x 10(13) highly infectious vector particles are easily produced without vector genome rearrangements and having very low HV contamination levels. However, the Ng system incorporates a spinner flask culture system that involves considerable time, effort, and tissue culture medium to produce HDAds. We have an alternative system to obtain comparable quantities with equivalent quality to the spinner flask approach but requiring reduced labor and lower volumes of medium. This method utilizes a 10-chamber cell factory with adherent cells to produce high infectivity of HDAds with minimal HV contamination while improving yield and reducing technical complexity, effort, and medium requirements. This system is easily translatable to the production of clinical-grade HDAds for human trials.