The adenovirus E1A and E1B19K genes provide a helper function for transfection-based adeno-associated virus vector production

Generalization of neoantigen-based tumor vaccine by delivering peptide-MHC complex via oncolytic virus

Neoantigen vaccine is a promising breakthrough in tumor immunotherapy. However, the application of this highly personalized strategy in the treatment of solid tumors is hindered by several obstacles, including very costly and time-consuming preparation steps, uncertainty in prediction algorithms and tumor heterogeneity. Universalization of neoantigen vaccine is an ideal yet currently unattainable solution to such limitations. To overcome these limitations, we engineered oncolytic viruses co-expressing neoantigens and neoantigen-binding major histocompatibility complex (MHC) molecules to force ectopic delivery of peptide-MHC ligands to T cell receptors (TCRs), enabling specific targeting by neoantigen vaccine-primed host immunity. When integrated with neoantigen vaccination, the engineered viruses exhibited potent cytolytic activity in a variety of tumor models irrespective of the neoantigen expression profiles, eliciting robust systemic antitumor immunity to reject tumor rechallenge and inhibit abscopal tumor growth with a favorable safety profile. Thus, this study provides a powerful approach to enhance the universality and efficacy of neoantigen vaccines, meeting the urgent need for universal neoantigen vaccines in the clinic to facilitate the further development of tumor immunotherapy.

Unravelling the essential elements for recombinant adeno-associated virus (rAAV) production in animal cell-based platforms

Recombinant adeno-associated viruses (rAAVs) stand at the forefront of gene therapy applications, holding immense significance for their safe and efficient gene delivery capabilities. The constantly increasing and unmet demand for rAAVs underscores the need for a more comprehensive understanding of AAV biology and its impact on rAAV production. In this literature review, we delved into AAV biology and rAAV manufacturing bioprocesses, unravelling the functions and essentiality of proteins involved in rAAV production. We discuss the interconnections between these proteins and how they affect the choice of rAAV production platform. By addressing existing inconsistencies, literature gaps and limitations, this review aims to define a minimal set of genes that are essential for rAAV production, providing the potential to advance rAAV biomanufacturing, with a focus on minimizing the genetic load within rAAV-producing cells.

Calcium-binding protein 7 expressed in muscle negatively regulates age-related degeneration of neuromuscular junctions in mice

The neuromuscular junction (NMJ) forms centrally in myotubes and, as the only synapse between motor neuron and myotube, are indispensable for motor activity. The midmuscle formation of NMJs, including midmuscle-restricted expression of NMJ-related genes, is governed by the muscle-specific kinase (MuSK). However, mechanisms underlying MuSK-mediated signaling are unclear. Here, we find that the Calcium-binding protein 7 (Cabp7) gene shows midmuscle-restricted expression, and muscle-specific depletion of Cabp7 in mice accelerated age-related NMJ degeneration, muscle weakness/atrophy, and motor dysfunction. Surprisingly, forced expression in muscle of CIP, an inhibitory peptide of the negative regulator of NMJ formation cyclin-dependent kinase 5 (Cdk5), restored NMJ integrity and muscle strength, and healed muscle atrophy in muscle-specific Cabp7-deficient mice, which showed increased muscle expression of the Cdk5 activator p25. These findings together demonstrate that MuSK-mediated signaling induces muscle expression of Cabp7, which suppresses age-related NMJ degeneration likely by attenuating p25 expression, providing insights into prophylactic/therapeutic intervention against age-related motor dysfunction.

Engineering a highly durable adeno-associated virus receptor for analytical applications

Adeno-associated virus (AAV) is a major viral vector used in gene therapy. There are multiple AAV serotypes, and many engineered AAV serotypes are developed to alter their tissue tropisms with capsid modification. The universal AAV receptor (AAVR) is an essential receptor for multiple AAV serotypes. Since most AAV serotypes used in gene therapy infect cells via interaction with AAVR, the quantification of the vector-binding ability of AAV to AAVR could be an important quality check for therapeutic AAV vectors. To enable a steady evaluation of the AAV-AAVR interaction, we created an engineered AAVR through mutagenesis. Engineered AAVR showed high durability against acid while retaining its AAV-binding activity. An affinity chromatography column with the engineered AAVR was also developed. This column enabled repeated binding and acid dissociation measurements of AAVR with various AAV serotypes. Our data showed that the binding affinities of AAV2 to AAVR were diverse among serotypes, providing insight into the relationship with the infection efficiency of AAV vectors. Thus, this affinity column can be used in process development for quality checks, quantitating capsid titers, and affinity purification of AAV vectors. Furthermore, this column may serve as a useful tool in novel AAV vector capsid engineering.

Critical challenges and advances in recombinant adeno-associated virus (rAAV) biomanufacturing

Gene therapy is a promising therapeutic approach for genetic and acquired diseases nowadays. Among DNA delivery vectors, recombinant adeno-associated virus (rAAV) is one of the most effective and safest vectors used in commercial drugs and clinical trials. However, the current yield of rAAV biomanufacturing lags behind the necessary dosages for clinical and commercial use, which embodies a concentrated reflection of low productivity of rAAV from host cells, difficult scalability of the rAAV-producing bioprocess, and high levels of impurities materialized during production. Those issues directly impact the price of gene therapy medicine in the market, limiting most patients' access to gene therapy. In this context, the current practices and several critical challenges associated with rAAV gene therapy bioprocesses are reviewed, followed by a discussion of recent advances in rAAV-mediated gene therapy and other therapeutic biological fields that could improve biomanufacturing if these advances are integrated effectively into the current systems. This review aims to provide the current state-of-the-art technology and perspectives to enhance the productivity of rAAV while reducing impurities during production of rAAV.

Large-scale purification of functional AAV particles packaging the full genome using short-term ultracentrifugation with a zonal rotor

Adeno-associated virus (AAV) vector-based gene therapy is potentially curative for various genetic diseases; however, the development of a scalable purification method for full-genome AAV vectors remains crucial to increase productivity and reduce cost of GMP production. In this study, we developed a large-scale short-term purification method for functional full-genome AAV particles by using 2-step cesium chloride (CsCl) density-gradient ultracentrifugation with a zonal rotor. The 2-step CsCl method with a zonal rotor improves separation between empty and full-genome AAV particles, reducing the ultracentrifugation time (4-5 h) and increasing the AAV volume for purification. The highly purified full-genome AAV particles were confirmed by analytical ultracentrifugation (AUC), droplet digital PCR (ddPCR) in the whole region of the AAV vector genome, transduction efficiency in target cells, and transmission electronic microscopy (TEM). The high-purity AAV9 particles were obtained using culture supernatant during vector preparation rather than cell lysate. CsCl could be simply removed by a hydroxyapatite column. Interestingly, ddPCR analysis revealed that "empty" AAV particles contain small fragments of the inverted terminal repeat (ITR), probably due to unexpected packaging of Rep-mediated ITR fragments. This large-scale functional AAV vector purification with ultracentrifugation would be effective for gene therapy.

Adeno-associated virus-mediated expression of an inactive CaMKIIβ mutant enhances muscle mass and strength in mice

A concurrent reduction in muscle mass and strength is frequently observed in numerous conditions, including neuromuscular disease, ageing, and muscle inactivity due to limb immobilization or prolonged bed rest. Thus, identifying the molecular mechanisms that control skeletal muscle mass and strength is fundamental for developing interventions aimed at counteracting muscle loss (muscle atrophy). It was recently reported that muscle atrophy induced by denervation of motor nerves was associated with increased expression of Ca2+/calmodulin-dependent protein serine/threonine kinase II β (CaMKIIβ) in muscle. In addition, treatment with KN-93 phosphate, which inhibits CaMKII-family kinases, partly suppressed denervation-induced muscle atrophy. Therefore, to test a possible role for CaMKIIβ in muscle mass regulation, we generated and injected recombinant adeno-associated virus (AAV) vectors encoding wild-type (AAV-WT), inactive (AAV-K43 M), or constitutively active (AAV-T287D) CaMKIIβ into the left hindlimb tibialis anterior muscle of mice at three months of age. Although AAV-WT infection induced expression of exogenous CaMKIIβ in the hindlimb muscle, no significant changes in muscle mass and strength were observed. By contrast, AAV-K43 M or AAV-T287D infection induced exogenous expression of the corresponding mutants and significantly increased or decreased the muscle mass and strength of the infected hind limb, respectively. Together, these findings demonstrate the potential of CaMKIIβ as a novel therapeutic target for enhancing muscle mass and strength.

A PCR-amplified transgene fragment flanked by a single copy of a truncated inverted terminal repeat for recombinant adeno-associated virus production prevents unnecessary plasmid DNA packaging

The application of recombinant adeno-associated viruses (rAAVs) for gene therapy faces certain challenges, including genome packaging of non-vector sequences. Inverted terminal repeats (ITRs) flanking the rAAV genome, comprising three inverted repeat regions (A, B, and C) and a non-inverted repeat region (D), contribute to non-vector genome packaging. We aimed to circumvent this issue by comparing the properties of rAAV containing DNA plasmids and PCR-amplified transgenes, including a single copy of the AD sequence (rAAV-pAD/L-AD, respectively), which is a truncated form of ITR, with those of wild-type ITR genome (single-stranded and self-complementary AAV; ssAAV and scAAV). The packaging efficiency of rAAV-pAD/L-AD was found to be comparable to that of scAAV, whereas the transduction efficiency of rAAV-pAD/L-AD was lower than that of ss/scAAV. Remarkably, rAAV-L-AD reduced the plasmid backbone packaging contamination compared to ss/scAAV. Furthermore, to confirm the functionality of this system, we generated a rAAV-L-AD harboring a short hairpin RNA targeting ATP5B (rAAV-L-AD-shATP5B) and found that it caused a significant decrease in ATP5B mRNA levels when transduced into HEK293EB cells, suggesting that it was functional. Thus, our system successfully packaged L-AD into capsids with minimal contamination of plasmid DNA, offering a novel functional packaging platform without causing plasmid backbone encapsidation.

Transplantation of a Novel Recombinant Adeno-Associated Virus (pAAV-HE1B19K-TE1A) Demonstrates Higher Anti-Tumor Effects in Tumor Cells

BACKGROUND Oncolytic viruses (OVs) can specifically infect and kill tumor cells. Adeno-associated virus (AAV) is a widely-studied OV. This study aimed to construct a tumor-targeted recombinant AAV using genetic engineering technology. MATERIAL AND METHODS The transgene plasmid pAAV-HE1B19K-TE1A was constructed with 4 genes (hTERT, E1A, HKII, and E1B19K) and co-transfected with pAAV-RC and pHelper to tumor cells (HepG2, A549, BGC-803) and normal cells (HUVEC). rAAV was verified with fluorescence microscopy. Quantitative PCR (qPCR) assay was used to test the titer of rAAV in each cell line. Apoptosis was analyzed using qPCR and Western blot assay. MTT was used to detect the effect of rAAV on cell viability. RESULTS The pAAV-HE1B19K-TE1A transgene plasmid was successfully structured. pAAV-HE1B19K-TE1A was highly expressed in all tumor cells. The titers of pAAV-HE1B19K-TE1A in HepG2, A549, and BGC-803 were 7.4×10⁷, 1.4×10⁸, and 1.1×10⁸ gc/μl, respectively. pAAV-HE1B19K-TE1A significantly decreased cell viability of tumor cells compared to that in HUVEC (p<0.05). pAAV-HE1B19K-TE1A remarkably triggered cleaved caspase 3 (C-caspase 3) activity in tumor cells compared to that in untransfected tumor cells (p<0.05). pAAV-HE1B19K-TE1A significantly induced release of cytochrome C (Cyto C) in tumor cells compared to that in untransfected tumor cells (p<0.05). pAAV-HE1B19K-TE1A demonstrated no toxicity to vital tissues of animals. CONCLUSIONS Tumor-targeted rAAV was successfully produced using the Helper-free system with recombinant plasmid, demonstrating high efficacy in decreasing viability of tumor cells without adverse effects on normal cells.

The Interplay between Adeno-Associated Virus and its Helper Viruses

The adeno-associated virus (AAV) is a small, nonpathogenic parvovirus, which depends on helper factors to replicate. Those helper factors can be provided by coinfecting helper viruses such as adenoviruses, herpesviruses, or papillomaviruses. We review the basic biology of AAV and its most-studied helper viruses, adenovirus type 5 (AdV5) and herpes simplex virus type 1 (HSV-1). We further outline the direct and indirect interactions of AAV with those and additional helper viruses.

DOK7 gene therapy enhances motor activity and life span in ALS model mice

Amyotrophic lateral sclerosis (ALS) is a progressive, multifactorial motor neurodegenerative disease with severe muscle atrophy. The glutamate release inhibitor riluzole is the only medication approved by the FDA, and prolongs patient life span by a few months, testifying to a strong need for new treatment strategies. In ALS, motor neuron degeneration first becomes evident at the motor nerve terminals in neuromuscular junctions (NMJs), the cholinergic synapse between motor neuron and skeletal muscle; degeneration then progresses proximally, implicating the NMJ as a therapeutic target. We previously demonstrated that activation of muscle‐specific kinase MuSK by the cytoplasmic protein Dok‐7 is essential for NMJ formation, and forced expression of Dok‐7 in muscle activates MuSK and enlarges NMJs. Here, we show that therapeutic administration of an adeno‐associated virus vector encoding the human DOK7 gene suppressed motor nerve terminal degeneration at NMJs together with muscle atrophy in the SOD1‐G93A ALS mouse model. Ultimately, we show that DOK7 gene therapy enhanced motor activity and life span in ALS model mice.

Postnatal knockdown of dok-7 gene expression in mice causes structural defects in neuromuscular synapses and myasthenic pathology

The neuromuscular junction (NMJ) is a synapse between a motor neuron and skeletal muscle and is required for muscle contraction. The formation and maintenance of NMJs are governed by the muscle-specific receptor tyrosine kinase MuSK. We previously showed that the muscle cytoplasmic protein Dok-7 is an essential activator of MuSK. Indeed, mice lacking either Dok-7 or MuSK form no NMJs, and defects in the human DOK7 gene underlie a congenital myasthenic syndrome (an NMJ disorder). However, it remains unproven whether Dok-7 is required for the postnatal maintenance of NMJs. In this study, we generated recombinant adeno-associated virus (AAV) vectors encoding short hairpin RNAs targeting the mouse dok-7 gene (AAV-shD7). Systemic administration of AAV-shD7 into 2-week-old mice down-regulated dok-7 expression in muscle and induced myasthenic symptoms including reduction in body weight and motor function. Moreover, AAV-shD7 treatment suppressed MuSK-dependent gene expression of NMJ components and reduced the size of NMJs. These results demonstrate that correct, physiological levels of dok-7 expression are required for the postnatal maintenance of NMJs.

Dissecting the roles of E1A and E1B in adenoviral replication and RCAd-enhanced RDAd transduction efficacy on tumor cells

Oncolytic viruses have recently received widespread attention for their potential in innovative cancer therapy. Many telomerase promoter-regulated oncolytic adenoviral vectors retain E1A and E1B. However, the functions of E1A and E1B proteins in the oncolytic role of replication-competent adenovirus (RCAd) and RCAd enhanced transduction of replication defective adenoviruses (RDAd) have not been addressed well. In this study, we constructed viruses expressing E1A alone, E1A plus E1B-19 kDa, and E1A plus E1B-19 kDa/55 kDa. We then tested their roles in oncolysis and replication of RCAd as well as their roles in RCAd enhanced transfection rate and transgene expression of RDAd in various cancer cells in vitro and in xenografted human NCI-H460 tumors in nude mice. We demonstrated that RCAds expressing E1A alone and plus E1B-19 kDa exhibited an obvious ability in replication and oncolytic effects as well as enhanced RDAd replication and transgene expression, with the former showed more effective oncolysis, while the latter exhibited superior viral replication and transgene promotion activity. However, RCAd expressing both E1A and E1B-19 kDa/55 kDa was clearly worst in all these abilities. The effects of E1A and E1B observed through using RCAd were further validated by using plasmids expressing E1A alone, E1A plus E1B-19 kDa, and E1A plus E1B-19 kDa/55 kDa proteins. Our study provided evidence that E1A was essential for inducing replication and oncolytic effects of RCAd as well as RCAd enhanced RDAd transduction, and expression of E1B-19 kDa other than E1B-55 kDa could promote these effects. E1B-55 kDa is not necessary for the oncolytic effects of adenoviruses and somehow inhibits RCAd-mediated RDAd replication and transgene expression.

Combination of oncolytic adenovirus and endostatin inhibits human retinoblastoma in an in vivo mouse model

There is a critical need for new paradigms in retinoblastoma (RB) treatment that would more efficiently inhibit tumor growth while sparing the vision of patients. Oncolytic adenoviruses with the ability to selectively replicate and kill tumor cells are a promising strategy for cancer gene therapy. Exploration of a novel targeting strategy for RB utilizing combined oncolytic adenovirus and anti-angiogenesis therapy was applied over the course of the current study with positive results. The oncolytic adenoviruses Ad-E2F1 p-E1A and Ad-TERT p-E1 were constructed. The E1 region was regulated by the E2F-1 promoter or the human telomerase reverse transcriptase (hTERT) promoter, respectively. Effects on both replication and promotion of enhanced green fluorescent protein (EGFP) expression were observed in the replication-defective adenovirus Ad-EGFP in diverse cancer cell lines, HXO-RB44, Y79, Hep3B, NCIH460, MCF-7 and HLF. The cancer cell death induced by these agents was also explored. The in situ RB model demonstrated that mice with tumors treated with the oncolytic adenovirus and replication-defective adenovirus Ad-endostatin exhibited notable cancer cell death. This anticancer effect was further examined by stereo microscope, and the survival rate of experimental mice was determined. Both Ad-E2F1 p-E1A and Ad-TERT p-E1 replicated specifically in cancer cells in vitro and promoted EGFP expression in Ad-EGFP, although Ad-E2F1 p-E1A demonstrated superior EGFP promotion activity than Ad-TERT p-E1. In Hep3B, NCIH460 and MCF-7 cells, the number of Ad-TERT p-E1 copies was observed to exceed of the number of Ad-E2F1 p-E1A copies by a minimum of 10-fold. Furthermore, Ad-TERT p-E1 demonstrated significantly superior oncolytic effects in the RB mouse model, and Ad-endostatin effectively suppressed tumor growth and extended the overall lifespan of subjects; however, the Ad-E2F1 p-E1A was clearly less effective in attaining these goals. Most notably, the antitumor effect and survival rate of subjects in the combined Ad-TERT p-E1 + Ad-endostatin group were higher than those treated with either single Ad-TERT p-E1 (p=0.097, p=0.022, respectively) or Ad-endostatin (p=0.037, p=0.006, respectively). In conclusion, application of transcription factor E2F-1 and human telomerase reverse transcriptase (hTERT) promoters to control E1 offer some guarantee that not only is RB gene therapy effective, but it is also safe. Combination therapy using the oncolytic adenovirus Ad-TERT p-E1 and replication-defective adenovirus Ad-endostatin demonstrates desirable oncolysis in the in situ RB mouse model. Additionally, E1B19K is important in the RB tumor suppression effect of oncolytic adenoviruses.

Latest developments in the large-scale production of adeno-associated virus vectors in insect cells toward the treatment of neuromuscular diseases

Adeno-associated viral (AAV) vectors are gene vectors of choice for the development of gene therapy treatments for many rare diseases affecting various tissues including retina, central nervous system, liver, and muscle. The AAV based gene therapy approach became conceivable only after the development of easily scalable production systems including the Sf9 cell/baculovirus expression system. Since the establishment of the production of AAV in the Sf9/baculovirus system by the group of Rob Kotin, this new production system has largely been developed for optimizing the large scale production of different serotypes of AAV for preclinical and clinical purposes. Today this manufacturing system allows for the production of purified vector genome (vg) quantities of up to 2 × 10(15) for AAV1 using a 50L reactor and the scale up to larger reactor volumes is paralleled by a corresponding increase in the vector yield. This review presents the principles and achievements of the Sf9/baculovirus system for the production of AAV in comparison to other expression systems based on mammalian cells. In addition, new developments and improvements, which have not yet been implemented at a large scale, and perspectives for further optimization of this production system will be discussed. All of these achievements as well as further process intensifications are urgently needed for the production of clinical doses for the treatment of neuromuscular diseases for which estimated doses of up to 10(14)vg/kg body mass are required.

Manufacturing recombinant adeno-associated viral vectors from producer cell clones

A commercial rAAV manufacturing process needs to provide a safe product at high yield, be easily scalable, regulatory-compliant, and have reasonable cost of goods. Considerations for process development include not only product quantity and quality, but also ease of obtaining equipment, performing validation, and demonstrating control. In these regards, it is usually efficient to make use of proven technologies for more established areas of manufacturing, such as cell culture and purification methods used by the recombinant protein/monoclonal antibody industry. We have focused on stable mammalian producer cell lines with adenovirus type 5 helper virus as a means of achieving these goals. This review describes our current approach for generating producer cell clones and designing a scalable, regulatory-compliant vector production and purification process that addresses any product safety concerns relating to helper virus. To date, a producer cell line-based manufacturing process has been implemented at the 250-liter production scale, with no foreseeable impediments to scaling up to commercial vector manufacturing in 2000-liter bioreactors or larger.

Cellular apoptosis induced by replication of hepatitis B virus: possible link between viral genotype and clinical outcome

HBV remains one of the major pathogens of liver diseases but the outcomes as inflammation, cirrhosis and cancer of the liver are greatly related to different viral genotypes. The aim of this study was to assess the pro-apoptotic effect of HBSP from three HBV genotypes on liver derived cells. HepG2 cells were applied in our system and transfected by HBV genotype A, B, and C. Cells were observed under phase contrast microscope, stained by apoptosis marker and analyzed by flow cytometre. HBSP expression was detected by western blot assay. BH3 sequences were aligned and analyzed by Vector NTI. HBV genotypes A, B, and C transfected cells displayed evidence of cell death which was further proved as apoptosis. Natural expression of a pro-apoptotic protein HBSP was detected during genomes transfection. The different apoptotic effects were correlated to the HBSP expression from each genome. Alignment and analysis of the BH3 domains from the three genomes revealed slight variance which might also contribute to the result. Our results suggested that variant HBSP expression and BH3 sequence of HBV genotypes may be involved in differential apoptotic effect in transfected cells. Detailed analysis of the role of HBV genotypes in cellular apoptotic process should provide molecular information on the reported clinical outcome of infection by different HBV genotypes.

Transfection of mammalian cells using linear polyethylenimine is a simple and effective means of producing recombinant adeno-associated virus vectors

We have developed a simple protocol to transfect mammalian cells using linear polyethylenimine (PEI). Our linear PEI protocol is as effective as commercial reagents in the transfection of HeLa cells and XDC293 cells, a derivative of HEK293 cells, but at a fraction of the cost. Greater than 90% of XDC293 cells and 98% of HeLa cells transfected using our method were positive for EGFP expression as determined by flow cytometery. Our protocol should be useful for many different applications such as large-scale production of recombinant protein and viruses, which requires transient transfection of mammalian cells in large batches. We have used this protocol to produce recombinant adeno-associated virus (AAV) in XDC293 cells and in HeLa cells. This requires transient expression of three adenovirus gene-products (E2A, E4orf6, and VA RNAs) as well as the AAV replication (Rep78, Rep68, Rep52, and Rep40) and capsid (VP1, VP2, and VP3) proteins. Production of a recombinant AAV that expresses green fluorescent protein was assessed by quantitative PCR and by transduction of HeLa cells. Linear PEI is a better transfection reagent than calcium phosphate for the production of recombinant AAV in both HEK293 and HeLa cells. In addition, when both HeLa and XDC293 cells were by our method, HeLa cells in the absence of E1A generated three-fold more recombinant AAV than XDC293 cells, which constitutively express E1A.