Establishment and validation of new complementing cells for production of E1-deleted adenovirus vectors in serum-free suspension culture

Development of oncolytic and gene therapy vectors based on adenovirus serotype 4 as an alternative to adenovirus serotype 5

BACKGROUND

Adenoviral vectors are among the most frequently used vectors for gene therapy and cancer treatment. Most vectors are derived from human adenovirus (Ad) serotype 5 despite limited applicability caused by pre-existing immunity and unfavorable liver tropism, whereas the other more than 100 known human serotypes remain largely unused. Here, we screened a library of human Ad types and identified Ad4 as a promising candidate vector.

METHODS

Reporter-gene-expressing viruses representative of the natural human Ad diversity were used to transduce an array of muscle cell lines and two- or three-dimensional tumor cultures. The time-course of transgene expression was monitored by fluorescence or luminescence measurements. To generate replication-deficient Ad4 vector genomes, successive homologous recombination was applied.

RESULTS

Ad4, 17 and 50 transduced human cardiomyocytes more efficiently than Ad5, whereas Ad37 was found to be superior in rhabdomyocytes. Despite its moderate transduction efficiency, Ad4 showed efficient and long-lasting gene expression in papillomavirus (HPV) positive tumor organoids. Therefore, we aimed to harness the potential of Ad4 for improved muscle transduction or oncolytic virotherapy of HPV-positive tumors. We deleted the E1 and E3 transcription units to produce first generation Ad vectors for gene therapy. The E1- and E1/E3-deleted vectors were replication-competent in HEK293 cells stably expressing E1 but not in the other cell lines tested. Furthermore, we show that the Ad5 E1 transcription unit can complement the replication of E1-deleted Ad4 vectors.

CONCLUSIONS

Our Ad4-based gene therapy vector platform contributes to the development of improved Ad vectors based on non-canonical serotypes for a broad range of applications.

A Method to Generate and Rescue Recombinant Adenovirus Devoid of Replication-Competent Particles in Animal-Origin-Free Culture Medium

Adenoviruses are promising vectors for vaccine production and gene therapy. Despite all the efforts in removing animal-derived components such as fetal bovine serum (FBS) during the production of adenovirus vector (AdV), FBS is still frequently employed in the early stages of production. Conventionally, first-generation AdVs (E1 deleted) are generated in different variants of adherent HEK293 cells, and plaque purification (if needed) is performed in adherent cell lines in the presence of FBS. In this study, we generated an AdV stock in SF-BMAdR (A549 cells adapted to suspension culture in serum-free medium). We also developed a limiting dilution method using the same cell line to replace the plaque purification assay. By combining these two technologies, we were able to completely remove the need for FBS from the process of generating and producing AdVs. In addition, we demonstrated that the purified AdV stock is free of any replication-competent adenovirus (RCA). Furthermore, we demonstrated that our limiting dilution method could effectively rescue an AdV from a stock that is highly contaminated with RCA.

BCG administration promotes the long-term protection afforded by a single-dose intranasal adenovirus-based SARS-CoV-2 vaccine

Recent publications have explored intranasal (i.n.) adenovirus-based (Ad) vaccines as an effective strategy for SARS-CoV-2 in pre-clinical models. However, the effects of prior immunizations and infections have yet to be considered. Here, we investigate the immunomodulatory effects of Mycobacterium bovis BCG pre-immunization followed by vaccination with an S-protein-expressing i.n. Ad, termed Ad(Spike). While i.n. Ad(Spike) retains some protective effect after 6 months, a single administration of BCG-Danish prior to Ad(Spike) potentiates its ability to control viral replication of the B.1.351 SARS-CoV-2 variant within the respiratory tract. Though BCG-Danish did not affect Ad(Spike)-generated humoral immunity, it promoted the generation of cytotoxic/Th1 responses over suppressive FoxP3+ TREG cells in the lungs of infected mice. Thus, this vaccination strategy may prove useful in limiting future pandemics by potentiating the long-term efficacy of mucosal vaccines within the context of the widely distributed BCG vaccine.

Protease-deleted adenovirus as an alternative for replication-competent adenovirus vector

For cancer therapy and vaccination an amplified expression of the therapeutic gene is desired. Previously, we have developed a single-cycle adenovirus vector (SC-AdV) by deleting the adenovirus protease (PS) gene. In order to keep the E1 region intact within the PS-deleted adenoviruses, we examined the insertion of two transgenes under the control of a constitutive or inducible promoters. These were inserted between E4 and the right inverted terminal repeat in a wide variety of backbones with various combinations of PS, E3 and E4 deletion. Our data showed that PS-deleted adenoviruses, expressed transgenes as strongly as replication-competent AdVs in HEK293A and a variant of HeLa cells. In a head-to-head comparison in four human cell lines, we demonstrated that SC-AdV, was comparable for transgene expression efficacy with its replication-competent counterpart. However, the SC-AdV expresses its transgene 10 to 16,000 times higher than its replication-defective counterpart.

Preclinical Development and Characterization of Novel Adeno-Associated Viral Vectors for the Treatment of Lipoprotein Lipase Deficiency

Lipoprotein lipase deficiency (LPLD) results from mutations within the lipoprotein lipase (LPL) gene that lead to a complete lack of catalytically active LPL protein. Glybera was one of the first adeno-associated virus (AAV) gene replacement therapy to receive European Medicines Agency regulatory approval for the treatment of LPLD. However, Glybera is no longer marketed potentially due to a combination of economical, manufacturing, and vector-related issues. The aim of this study was to develop a more efficacious AAV gene therapy vector for LPLD. Following preclinical biodistribution, efficacy and non-Good Laboratory Practice toxicity studies with novel AAV1 and AAV8-based vectors in mice, we identified AAV8 pVR59. AAV8 pVR59 delivered a codon-optimized, human gain-of-function hLPLS447X transgene driven by a CAG promoter in an AAV8 capsid. AAV8 pVR59 was significantly more efficacious, at 10- to 100-fold lower doses, compared with an AAV1 vector based on Glybera, when delivered intramuscularly or intravenously, respectively, in mice with LPLD. Efficient gene transfer was observed within the injected skeletal muscle and liver following delivery of AAV8 pVR59, with long-term correction of LPLD phenotypes, including normalization of plasma triglycerides and lipid tolerance, for up to 6 months post-treatment. While intramuscular delivery of AAV8 pVR59 was well tolerated, intravenous administration augmented liver pathology. These results highlight the feasibility of developing a superior AAV vector for the treatment of LPLD and provide critical insight for initiating studies in larger animal models. The identification of an AAV gene therapy vector that is more efficacious at lower doses, when paired with recent advances in production and manufacturing technologies, will ultimately translate to increased safety and accessibility for patients.

Packaging cells for lentiviral vectors generated using the cumate and coumermycin gene induction systems and nanowell single-cell cloning

Lentiviral vectors (LVs) are important for cell therapy because of their capacity to stably modify the genome after integration. This study describes a novel and relatively simple approach to generate packaging cells and producer clones for self-inactivating (SIN) LVs pseudotyped with the vesicular stomatitis virus glycoprotein (VSV-G). A novel gene regulation system, based on the combination of the cumate and coumermycin induction systems, was developed to ensure tight control for the expression of cytotoxic packaging elements. To accelerate clone isolation and ensure monoclonality, the packaging genes were transfected simultaneously into human embryonic kidney cells (293SF-3F6) previously engineered with the induction system, and clones were isolated after limiting dilution into nanowell arrays using a robotic cell picking instrument with scanning capability. The method's effectiveness to isolate colonies derived from single cells was demonstrated using mixed populations of cells labeled with two different fluorescent markers. Because the recipient cell line grew in suspension culture, and all the procedures were performed without serum, the resulting clones were readily adaptable to serum-free suspension culture. The best producer clone produced LVs expressing GFP at a titer of 2.3 × 10⁸ transduction units (TU)/mL in the culture medium under batch mode without concentration.

Complementary Cell Lines for Protease Gene-Deleted Single-Cycle Adenovirus Vectors

To increase the safety of adenovirus vector (AdV)-based therapy without reducing its efficacy, a single-cycle adenovirus vector (SC-AdV) with a deletion in the protease gene (PS) was developed in order to be used as a substitute for the replication-competent adenovirus (RC-AdV). Since no infectious viral particles are assembled, there is no risk of viral shedding. The complementary cell lines for this developed AdV proved to be suboptimal for the production of viral particles and require the presence of fetal bovine serum (FBS) to grow. In the current study, we produced both stable pools and clones using adherent and suspension cells expressing the PS gene. The best adherent cell pool can be used in the early stages for the generation of protease-deleted adenovirus, plaque purification, and titration. Using this, we produced over 3400 infectious viral particles per cell. Additionally, the best suspension subclone that was cultured in the absence of FBS yielded over 4000 infectious viral particles per cell. Harvesting time, culture media, and concentration of the inducer for the best suspension subclone were further characterized. With these two types of stable cells (pool and subclone), we successfully improved the titer of protease-deleted adenovirus in adherent and suspension cultures and eliminated the need for FBS during the scale-up production. Eight lots of SC-AdV were produced in the best suspension subclone at a scale of 2 to 8.2 L. The viral and infectious particle titers were influenced by the virus backbone and expressed transgene.

A low dose adenovirus vectored vaccine expressing Schistosoma mansoni Cathepsin B protects from intestinal schistosomiasis in mice

BACKGROUND

Schistosomiasis is an underestimated neglected tropical disease which affects over 236.6 million people worldwide. According to the CDC, the impact of this disease is second to only malaria as the most devastating parasitic infection. Affected individuals manifest chronic pathology due to egg granuloma formation, destroying the liver over time. The only FDA approved drug, praziquantel, does not protect individuals from reinfection, highlighting the need for a prophylactic vaccine. Schistosoma mansoni Cathepsin B (SmCB) is a parasitic gut peptidase necessary for helminth growth and maturation and confers protection as a vaccine target for intestinal schistosomiasis.

METHODS

An SmCB expressing human adenovirus serotype 5 (AdSmCB) was constructed and delivered intramuscularly to female C57BL/6 mice in a heterologous prime and boost vaccine with recombinant protein. Vaccine induced immunity was described and subsequent protection from parasite infection was assessed by analysing parasite burden and liver pathology.

FINDINGS

Substantially higher humoral and cell-mediated immune responses, consisting of IgG2c, Th1 effectors, and polyfunctional CD4+ T cells, were induced by the heterologous administration of AdSmCB when compared to the other regimens. Though immune responses favoured Th1 immunity, Th2 responses provided by SmCB protein boosts were maintained. This mixed Th1/Th2 immune response resulted in significant protection from S. mansoni infection comparable to other vaccine formulations which are in clinical trials. Schistosomiasis associated liver pathology was also prevented in a murine model.

INTERPRETATION

Our study provides missing preclinical data supporting the use of adenoviral vectoring in vaccines for S. mansoni infection. Our vaccination method significantly reduces parasite burden and its associated liver pathology - both of which are critical considerations for this helminth vaccine.

FUNDING

This work was supported by the Canadian Institutes of Health Research, R. Howard Webster Foundation, and the Foundation of the McGill University Health Centre.

A rapid Focus-Forming Assay for quantification of infectious adenoviral vectors

Currently available methods to titrate adenoviral vectors (AdV) in the absence of a gene reporter such as GFP, are either time-consuming or not very reproducible. A Focus-Forming Assay (FFA) for quantification of infectious AdV particles followed by automated focus counting was developed using new monoclonal antibodies (mAbs) against the human adenovirus type 5. Briefly, in this method, 96-well plates of HEK293A cells were infected with 2-fold dilutions of AdV at seeding time. Forty eight hours post-infection, the cells were fixed with methanol. The cells were then incubated with each mAb followed by a FITC conjugated anti-mouse antibody. The plates were scanned and positive cells counted using an automated fluorescence microscopy system. The results of the FFA were compared with the plaque assay and the TCID₅₀ assay. The titer of six different recombinant AdV were compared using the FFA along with a commercial kit. The results were similar, but in contrast to the commercial kit for which the stained cells are counted manually, the software automatically counts the positives cells in the FFA. The automatic counting of positive cells makes the FFA a more precise and reliable assay compared to the commercial kit for titration of AdV.

Establishing Suspension Cell Cultures for Improved Manufacturing of Oncolytic Adenovirus

Recent clinical trials have shown the potential of oncolytic adenoviruses as a cancer immunotherapy. A successful transition of oncolytic adenovirus to clinical applications requires efficient and good manufacturing practice compatible production and purification bioprocesses. Suspension cultures are preferable for virus production as they can reduce process costs and increase product quality and consistency. This work describes the adaptation of the A549 cell line to suspension culture in serum-reduced medium validated by oncolytic adenovirus production in stirred tank bioreactor. Cell concentrations up to 3 × 10⁶ cells mL^-1 are obtained during the production process. At harvest 1.4 × 10¹⁰ infectious particles mL^-1 and 6.9 ± 1.1 × 10¹⁰ viral genome mL^-1 are obtained corresponding to a viral genome: infectious particles ratio of 5.2 (± 1.9): 1 confirming the virus quality. Overall, the suspension characteristics of these A549 cells support an easily scalable, less time-consuming, and more cost-effective process for expanded success in the use of oncolytic viruses for cancer therapy.

Optimization of production of vesicular stomatitis virus (VSV) in suspension serum-free culture medium at high cell density

During the last decade, oncolytic viruses such as vesicular stomatitis virus (VSV) have gained tremendous popularity as efficient vaccines for infectious diseases as well as for the treatment of cancer. Our laboratory has developed two stable cell lines, 293SF-3F6 (derived from HEK293A cells) and SF-BMAdR cells (a variant of A549 that expresses the E1 region of human adenovirus). These two cell lines were adapted to grow efficiently in suspension culture and in serum-free medium. In this report we evaluated the production of a recombinant VSV expressing the green fluorescent protein (VSV-GFP) in these two stable cell lines. At a relatively low cell density of 500,000 cells per ml, 293SF-3F6 produced 4.6 times more infectious particles than SF-BMAdR cells. There was a positive correlation between volumetric virus titer and cell density up to 2.E + 07 cells/ml. A fed-batch process using an in-house medium and feed was developed to support the growth of 293SF-3F6 cells up to a concentration of 1.E + 07 cells/ml for infection at higher cell density and VSV production at high titer. Shifting the temperature from 37 °C to 34 °C at infection time improved VSV titer up to 3.3 fold. After scaling up the optimal condition from small scale (3 ml) to larger volumes (50 & 200 ml), the maximal volumetric titer obtained using the 293SF-3F6 cells was in average 2.9E + 10 extracellular infectious particles/ml. In conclusion, our data demonstrated that 293SF-3F6 cells, for which a cGMP master cell bank is available, is a performant cell line to scale up VSV production in suspension culture using serum-free medium.

Development of a recombinant murine tumour model using hepatoma cells expressing hepatitis C virus nonstructural antigens

Hepatitis C virus (HCV) chronically infects 2%-3% of the world's population, causing liver disease and cancer with prolonged infection. The narrow host range of the virus, being restricted largely to human hepatocytes, has made the development of relevant models to evaluate the efficacy of vaccines a challenge. We have developed a novel approach to accomplish this by generating a murine hepatoma cell line stably expressing nonstructural HCV antigens which can be used in vitro or in vivo to test HCV vaccine efficacies. These HCV-recombinant hepatoma cells formed large solid-mass tumours when implanted into syngeneic mice, allowing us to test candidate HCV vaccines to demonstrate the development of an HCV-specific immune response that limited tumour growth. Using this model, we tested the therapeutic potential of recombinant anti-HCV-specific vaccines based on two fundamentally different attenuated pathogen vaccine systems-attenuated Salmonella and recombinant adenoviral vector based vaccine. While attenuated Salmonella that secreted HCV antigens limited growth of the HCV-recombinant tumours when used in a therapeutic vaccination trial, replication-competent but noninfectious adenovirus expressing nonstructural HCV antigens showed overall greater survival and reduced weight loss compared to non-replicating nondisseminating adenovirus. Our results demonstrate a model with anti-tumour responses to HCV nonstructural (NS) protein antigens and suggest that recombinant vaccine vectors should be explored as a therapeutic strategy for controlling HCV and HCV-associated cancers.

A Role for DLK in Microtubule Reorganization to the Cell Periphery and in the Maintenance of Desmosomal and Tight Junction Integrity

Dual leucine zipper-bearing kinase (DLK) is an inducer of keratinocyte differentiation, a complex process also involving microtubule reorganization to the cell periphery. However, signaling mechanisms involved in this process remain to be elucidated. Here, we demonstrate that DLK enhances and is required for microtubule reorganization to the cell periphery in human cell culture models and in Dlk knockout mouse embryos. In tissue-engineered skins with reduced DLK expression, cortical distribution of two microtubule regulators, LIS1 and HSP27, is impaired as well as desmosomal and tight junction integrity. Altered cortical distribution of desmosomal and tight junction proteins was also confirmed in Dlk knockout mouse embryos. Finally, desmosomal and tight junction defects were also observed after microtubule disruption in nocodazole-treated tissue-engineered skins, thus confirming a role for microtubules in the maintenance of these types of cell junctions. Globally, this study demonstrates that DLK is a key regulator of microtubule reorganization to the cell periphery during keratinocyte differentiation and that this process is required for the maintenance of desmosomal and tight junction integrity.

A Single Dose Respiratory Recombinant Adenovirus-Based Vaccine Provides Long-Term Protection for Non-Human Primates from Lethal Ebola Infection

As the Ebola outbreak in West Africa continues and cases appear in the United States and other countries, the need for long-lasting vaccines to preserve global health is imminent. Here, we evaluate the long-term efficacy of a respiratory and sublingual (SL) adenovirus-based vaccine in non-human primates in two phases. In the first, a single respiratory dose of 1.4 × 10⁹ infectious virus particles (ivp)/kg of Ad-CAGoptZGP induced strong Ebola glycoprotein (GP) specific CD8⁺ and CD4⁺ T cell responses and Ebola GP-specific antibodies in systemic and mucosal compartments and was partially (67%) protective from challenge 62 days after immunization. The same dose given by the SL route induced Ebola GP-specific CD8⁺ T cell responses similar to that of intramuscular (IM) injection, however, the Ebola GP-specific antibody response was low. All primates succumbed to infection. Three primates were then given the vaccine in a formulation that improved the immune response to Ebola in rodents. Three primates were immunized with 2.0 × 10¹⁰ ivp/kg of vaccine by the SL route. Diverse populations of polyfunctional Ebola GP-specific CD4⁺ and CD8⁺ T cells and significant anti-Ebola GP antibodies were present in samples collected 150 days after respiratory immunization. The formulated vaccine was fully protective against challenge 21 weeks after immunization. While diverse populations of Ebola GP-specific CD4⁺ T cells were produced after SL immunization, antibodies were not neutralizing and the vaccine was unprotective. To our knowledge, this is the first time that durable protection from a single dose respiratory adenovirus-based Ebola vaccine has been demonstrated in primates.