Scaleable chromatographic purification process for recombinant adeno-associated virus (rAAV)

IGF2 prevents dopaminergic neuronal loss and decreases intracellular alpha-synuclein accumulation in Parkinson's disease models

Parkinson's disease (PD) is the second most common late-onset neurodegenerative disease and the predominant cause of movement problems. PD is characterized by motor control impairment by extensive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). This selective dopaminergic neuronal loss is in part triggered by intracellular protein inclusions called Lewy bodies, which are composed mainly of misfolded alpha-synuclein (α-syn) protein. We previously reported insulin-like growth factor 2 (IGF2) as a key protein downregulated in PD patients. Here we demonstrated that IGF2 treatment or IGF2 overexpression reduced the α-syn aggregates and their toxicity by IGF2 receptor (IGF2R) activation in cellular PD models. Also, we observed IGF2 and its interaction with IGF2R enhance the α-syn secretion. To determine the possible IGF2 neuroprotective effect in vivo we used a gene therapy approach in an idiopathic PD model based on α-syn preformed fibrils intracerebral injection. IGF2 gene therapy revealed a significantly preventing of motor impairment in idiopathic PD model. Moreover, IGF2 expression prevents dopaminergic neuronal loss in the SN together with a decrease in α-syn accumulation (phospho-α-syn levels) in the striatum and SN brain region. Furthermore, the IGF2 neuroprotective effect was associated with the prevention of synaptic spines loss in dopaminergic neurons in vivo. The possible mechanism of IGF2 in cell survival effect could be associated with the decrease of the intracellular accumulation of α-syn and the improvement of dopaminergic synaptic function. Our results identify to IGF2 as a relevant factor for the prevention of α-syn toxicity in both in vitro and preclinical PD models.

The downstream bioprocess toolbox for therapeutic viral vectors

Viral vectors are poised to acquire a prominent position in modern medicine and biotechnology owing to their role as delivery agents for gene therapies, oncolytic agents, vaccine platforms, and a gateway to engineer cell therapies as well as plants and animals for sustainable agriculture. The success of viral vectors will critically depend on the availability of flexible and affordable biomanufacturing strategies that can meet the growing demand by clinics and biotech companies worldwide. In this context, a key role will be played by downstream process technology: while initially adapted from protein purification media, the purification toolbox for viral vectors is currently undergoing a rapid expansion to fit the unique biomolecular characteristics of these products. Innovation efforts are articulated on two fronts, namely (i) the discovery of affinity ligands that target adeno-associated virus, lentivirus, adenovirus, etc.; (ii) the development of adsorbents with innovative morphologies, such as membranes and 3D printed monoliths, that fit the size of viral vectors. Complementing these efforts are the design of novel process layouts that capitalize on novel ligands and adsorbents to ensure high yield and purity of the product while safeguarding its therapeutic efficacy and safety; and a growing panel of analytical methods that monitor the complex array of critical quality attributes of viral vectors and correlate them to the purification strategies. To help explore this complex and evolving environment, this study presents a comprehensive overview of the downstream bioprocess toolbox for viral vectors established in the last decade, and discusses present efforts and future directions contributing to the success of this promising class of biological medicines.

Best of most possible worlds: Hybrid gene therapy vectors based on parvoviruses and heterologous viruses

Parvoviruses and especially the adeno-associated virus (AAV) species provide an exciting and versatile platform for the rational design or molecular evolution of human gene-therapy vectors, documented by literature from over half a century, hundreds of clinical trials, and the recent commercialization of multiple AAV gene therapeutics. For the last three decades, the power of these vectors has been further potentiated through various types of hybrid vectors created by intra- or inter-genus juxtaposition of viral DNA and protein cis elements or by synergistic complementation of parvoviral features with those of heterologous, prokaryotic, or eukaryotic viruses. Here, we provide an overview of the history and promise of this rapidly expanding field of hybrid parvoviral gene-therapy vectors, starting with early generations of chimeric particles composed of a recombinant AAV genome encapsidated in shells of synthetic AAVs or of adeno-, herpes-, baculo-, or protoparvoviruses. We then dedicate our attention to two newer, highly promising types of hybrid vectors created via (1) pseudotyping of AAV genomes with bocaviral serotypes and capsid mutants or (2) packaging of AAV DNA into, or tethering of entire vector particles to, bacteriophages. Finally, we conclude with an outlook summarizing critical requirements and improvements toward clinical translation of these original concepts.

AAV Production Everywhere: A Simple, Fast, and Reliable Protocol for In-house AAV Vector Production Based on Chloroform Extraction

Recombinant adeno-associated virus (rAAV) is a mammalian virus that has been altered to be used as a gene delivery vehicle. Several changes to the viral genome have made them replication deficient so that this aspect of the viral infection cycle is under full control of the experimenter, while maintaining gene expression machinery. Over the last decades, rAAVs have become the gold standard for studying in vivo gene function and are especially favorable for gene transfer in the central nervous system. AAVs have been proven safe and provide stable gene expression over a long period of time. They are extensively used in preclinical experiments and show great potential for clinical applications. However, the use of AAVs in preclinical settings are often held back due to availability. Waiting lines are long at commercial production facilities, and in-lab production is hindered due to lack of specific laboratory equipment needed. Here we present a novel production method that can be carried out in any molecular biology laboratory using standard laboratory equipment. We provide a simple, fast, and streamlined protocol for production that can result in titers comparable with the more time-consuming iodixanol gradient ultracentrifugation method. The yield using this protocol is high enough for any type of study where AAV is the vector of choice. © 2020 The Authors.

Enforced dimerization between XBP1s and ATF6f enhances the protective effects of the UPR in models of neurodegeneration

Alteration to endoplasmic reticulum (ER) proteostasis is observed in a variety of neurodegenerative diseases associated with abnormal protein aggregation. Activation of the unfolded protein response (UPR) enables an adaptive reaction to recover ER proteostasis and cell function. The UPR is initiated by specialized stress sensors that engage gene expression programs through the concerted action of the transcription factors ATF4, ATF6f, and XBP1s. Although UPR signaling is generally studied as unique linear signaling branches, correlative evidence suggests that ATF6f and XBP1s may physically interact to regulate a subset of UPR target genes. In this study, we designed an ATF6f/XBP1s fusion protein termed UPRplus that behaves as a heterodimer in terms of its selective transcriptional activity. Cell-based studies demonstrated that UPRplus has a stronger effect in reducing the abnormal aggregation of mutant huntingtin and α-synuclein when compared to XBP1s or ATF6 alone. We developed a gene transfer approach to deliver UPRplus into the brain using adeno-associated viruses (AAVs) and demonstrated potent neuroprotection in vivo in preclinical models of Parkinson's disease and Huntington's disease. These results support the concept in which directing UPR-mediated gene expression toward specific adaptive programs may serve as a possible strategy to optimize the beneficial effects of the pathway in different disease conditions.

Removal of empty capsids from adeno-associated virus preparations by multimodal metal affinity chromatography

Separation of empty and full adeno-associated virus capsids by multimodal metal affinity chromatography was investigated using a positively charged metal affinity ligand. A subpopulation of empty capsids eluted first, followed by full capsids, and later by more empty capsids and debris. Empty and full capsid composition of chromatography fractions was evaluated by cesium chloride density gradient centrifugation followed by stratigraphic flow analysis of the centrifuge tube contents, monitored by intrinsic fluorescence. Columns charged with barium, calcium, magnesium, zinc, manganese, and ferric ions gave similar results with respect to capsid separation. Charging with cupric ions maintained resolution between early-eluting empty capsids and full capsids but caused them to elute at lower conductivity. Empty and full capsids were fractionated with Tris-borate gradients, sodium chloride gradients, and magnesium chloride gradients. Recovery of full serotype 9 capsids was 100% with complete elimination of empty capsids. All metal ions bound contaminant subsets that required sodium hydroxide for removal. Columns charged with ferric iron and manganese bound more contaminants than all other metals. Columns charged with calcium, magnesium, barium, and copper bound the least. Contaminant binding on zinc-charged columns was intermediate between the two groups.

Development of a scalable and robust AEX method for enriched rAAV preparations in genome-containing VCs of serotypes 5, 6, 8, and 9

Removal of empty capsids from adeno-associated virus (AAV) manufacturing lots remains a critical step in the downstream processing of AAV clinical-grade batches. Because of similar physico-chemical characteristics, the AAV capsid populations totally lacking or containing partial viral DNA are difficult to separate from the desired vector capsid populations. Based on minute differences in density, ultracentrifugation remains the most effective separation method and has been extensively used at small scale but has limitations associated with availabilities and operational complexities in large-scale processing. In this paper, we report a scalable, robust, and versatile anion-exchange chromatography (AEX) method for removing empty capsids and subsequent enrichment of vectors of AAV serotypes 5, 6, 8, and 9. On average, AEX resulted in about 9-fold enrichment of AAV5 in a single step containing 80% ± 5% genome-containing vector capsids, as verified and quantified by analytical ultracentrifugation. The optimized process was further validated using AAV6, AAV8, and AAV9, resulting in over 90% vector enrichment. The AEX process showed comparable results not only for vectors with different transgenes of different sizes but also for AEX runs under different geometries of chromatographic media. The herein-reported sulfate-salt-based AEX process can be adapted to different AAV serotypes by appropriately adjusting elution conditions to achieve enriched vector preparations.

Insulin-like growth factor 2 (IGF2) protects against Huntington's disease through the extracellular disposal of protein aggregates

Impaired neuronal proteostasis is a salient feature of many neurodegenerative diseases, highlighting alterations in the function of the endoplasmic reticulum (ER). We previously reported that targeting the transcription factor XBP1, a key mediator of the ER stress response, delays disease progression and reduces protein aggregation in various models of neurodegeneration. To identify disease modifier genes that may explain the neuroprotective effects of XBP1 deficiency, we performed gene expression profiling of brain cortex and striatum of these animals and uncovered insulin-like growth factor 2 (Igf2) as the major upregulated gene. Here, we studied the impact of IGF2 signaling on protein aggregation in models of Huntington's disease (HD) as proof of concept. Cell culture studies revealed that IGF2 treatment decreases the load of intracellular aggregates of mutant huntingtin and a polyglutamine peptide. These results were validated using induced pluripotent stem cells (iPSC)-derived medium spiny neurons from HD patients and spinocerebellar ataxia cases. The reduction in the levels of mutant huntingtin was associated with a decrease in the half-life of the intracellular protein. The decrease in the levels of abnormal protein aggregation triggered by IGF2 was independent of the activity of autophagy and the proteasome pathways, the two main routes for mutant huntingtin clearance. Conversely, IGF2 signaling enhanced the secretion of soluble mutant huntingtin species through exosomes and microvesicles involving changes in actin dynamics. Administration of IGF2 into the brain of HD mice using gene therapy led to a significant decrease in the levels of mutant huntingtin in three different animal models. Moreover, analysis of human postmortem brain tissue and blood samples from HD patients showed a reduction in IGF2 level. This study identifies IGF2 as a relevant factor deregulated in HD, operating as a disease modifier that buffers the accumulation of abnormal protein species.

Production, Processing, and Characterization of Synthetic AAV Gene Therapy Vectors

Over the last two decades, gene therapy vectors based on wild-type Adeno-associated viruses (AAV) are safe and efficacious in numerous clinical trials and are translated into three approved gene therapy products. Concomitantly, a large body of preclinical work has illustrated the power and potential of engineered synthetic AAV capsids that often excel in terms of an organ or cell specificity, the efficiency of in vitro or in vivo gene transfer, and/or reactivity with anti-AAV immune responses. In turn, this has created a demand for new, scalable, easy-to-implement, and plug-and-play platform processes that are compatible with the rapidly increasing range of AAV capsid variants. Here, the focus is on recent advances in methodologies for downstream processing and characterization of natural or synthetic AAV vectors, comprising different chromatography techniques and thermostability measurements. To illustrate the breadth of this portfolio, two chimeric capsids are used as representative examples that are derived through forward- or backwards-directed molecular evolution, namely, AAV-DJ and Anc80. Collectively, this ever-expanding arsenal of technologies promises to facilitate the development of the next AAV vector generation derived from synthetic capsids and to accelerate their manufacturing, and to thus boost the field of human gene therapy.

Sequential two-step chromatographic purification of infectious poliovirus using ceramic fluoroapatite and ceramic hydroxyapatite columns

Infectious virus purification techniques are important for vaccine development and gene therapy applications. However, the standardized one-step purification technique using ceramic hydroxyapatite (CHAp) has proven unsuitable for poliovirus. Therefore, we designed a sequential two-step chromatographic technique for purification of the infectious Sabin type 2 vaccine strain of poliovirus from the cell culture supernatant. In the first step, we removed protein contaminants from the Sabin type 2 virus fraction by pH gradient elution on a ceramic fluoroapatite column. In the second step, we removed double-stranded DNA derived from host cells by diluting the virus fraction, directly loading it on a CHAp column, and purifying it using a phosphate gradient with 1 M sodium chloride. This process achieved removal rates of more than 99.95% and 99.99% for proteins and double-stranded DNA, respectively, and was highly reproducible and scalable. Furthermore, it is likely that it will be applicable to other virus species.

Adeno-Associated Virus Production, Purification, and Titering

Adeno-associated virus (AAV) vectors are exemplary tools for studying gene function in vivo and are particularly favorable for transferring genes of interest into brain tissues. They have shown great promise as a gene therapy vector for preclinical and clinical applications. However, the ability to use this tool is often hampered because the viruses themselves are not readily available. Many methods have been developed for AAV production. Here, we describe a simple method for small- to medium-scale (10¹² -10¹³ viral particles) production of AAV based on Polyethylenimine Max (PEI Max)-mediated triple transfection of HEK 293 cells and purification with iodixanol gradient ultracentrifugation. These methods will provide users with ample material of sufficient quality for performing in vivo gene transfer. © 2018 by John Wiley & Sons, Inc.

Universal Method for the Purification of Recombinant AAV Vectors of Differing Serotypes

The generation of clinical good manufacturing practices (GMP)-grade adeno-associated virus (AAV) vectors requires purification strategies that support the generation of vectors of high purity, and that exhibit a good safety and efficacy profile. To date, most reported purification schemas are serotype dependent, requiring method development for each AAV gene therapy product. Here, we describe a platform purification process that is compatible with the purification of multiple AAV serotypes. The method generates vector preparations of high purity that are enriched for capsids with full vector genomes, and that minimizes the fractional content of empty capsids. The two-column purification method, a combination of affinity and ion exchange chromatographies, is compatible with a range of AAV serotypes generated by either the transient triple transfection method or the more scalable producer cell line platform. In summary, the adaptable purification method described can be used for the production of a variety of high-quality AAV vectors suitable for preclinical testing in animal models of diseases.

Identification of an adeno-associated virus binding epitope for AVB sepharose affinity resin

Recent successes of adeno-associated virus (AAV)-based gene therapy have created a demand for large-scale AAV vector manufacturing and purification techniques for use in clinical trials and beyond. During the development of purification protocols for rh.10, hu.37, AAV8, rh.64R1, AAV3B, and AAV9 vectors, based on a widely used affinity resin, AVB sepharose (GE), we found that, under the same conditions, different serotypes have different affinities to the resin, with AAV3B binding the best and AAV9 the poorest. Further analysis revealed a surface-exposed residue (amino acid number 665 in AAV8 VP1 numbering) differs between the high-affinity AAV serotypes (serine in AAV3B, rh.10, and hu.37) and the low-affinity ones (asparagine in AAV8, rh.64R1, and AAV9). The residue locates within a surface-exposed, variable epitope flanked by highly conserved residues. The substitution of the epitope in AAV8, rh.64R1, and AAV9 with the corresponding epitope of AAV3B (SPAKFA) resulted in greatly increased affinity to AVB sepharose with no reduction in the vectors' in vitro potency. The presence of the newly identified AVB-binding epitope will be useful for affinity resin selection for the purification of novel AAV serotypes. It also suggests the possibility of vector engineering to yield a universal affinity chromatography purification method for multiple AAV serotypes.

Scalable downstream strategies for purification of recombinant adeno- associated virus vectors in light of the properties

Recombinant adeno-associated virus (rAAV) vector is one of the promising delivery tools for gene therapy. Currently, hundreds of clinical trials are performed but the major barrier for clinical application is the absence of any ideal large scale production technique to obtain sufficient and highly pure rAAV vector. The large scale production technique includes upstream and downstream processing. The upstream processing is a vector package step and the downstream processing is a vector purification step. For large scale downstream processing, the scientists need to recover rAAV from dozens of liters of cell lysate or medium, and a variety of purification strategies have been developed but not comprehensively compared till now. Consequently, this review will evaluate the scalable downstream purification strategies systematically, especially those based on the physicochemical properties of AAV virus, and attempt to find better scalable downstream strategies for rAAV vectors.

Control of dopaminergic neuron survival by the unfolded protein response transcription factor XBP1

Parkinson disease (PD) is characterized by the selective loss of dopaminergic neurons of the substantia nigra pars compacta (SNpc). Although growing evidence indicates that endoplasmic reticulum (ER) stress is a hallmark of PD, its exact contribution to the disease process is not well understood. Here we report that developmental ablation of X-Box binding protein 1 (XBP1) in the nervous system, a key regulator of the unfolded protein response (UPR), protects dopaminergic neurons against a PD-inducing neurotoxin. This survival effect was associated with a preconditioning condition that resulted from induction of an adaptive ER stress response in dopaminergic neurons of the SNpc, but not in other brain regions. In contrast, silencing XBP1 in adult animals triggered chronic ER stress and dopaminergic neuron degeneration. Supporting this finding, gene therapy to deliver an active form of XBP1 provided neuroprotection and reduced striatal denervation in animals injected with 6-hydroxydopamine. Our results reveal a physiological role of the UPR in the maintenance of protein homeostasis in dopaminergic neurons that may help explain the differential neuronal vulnerability observed in PD.

Activation of the unfolded protein response enhances motor recovery after spinal cord injury

Spinal cord injury (SCI) is a major cause of paralysis, and involves multiple cellular and tissular responses including demyelination, inflammation, cell death and axonal degeneration. Recent evidence suggests that perturbation on the homeostasis of the endoplasmic reticulum (ER) is observed in different SCI models; however, the functional contribution of this pathway to this pathology is not known. Here we demonstrate that SCI triggers a fast ER stress reaction (1–3 h) involving the upregulation of key components of the unfolded protein response (UPR), a process that propagates through the spinal cord. Ablation of X-box-binding protein 1 (XBP1) or activating transcription factor 4 (ATF4) expression, two major UPR transcription factors, leads to a reduced locomotor recovery after experimental SCI. The effects of UPR inactivation were associated with a significant increase in the number of damaged axons and reduced amount of oligodendrocytes surrounding the injury zone. In addition, altered microglial activation and pro-inflammatory cytokine expression were observed in ATF4 deficient mice after SCI. Local expression of active XBP1 into the spinal cord using adeno-associated viruses enhanced locomotor recovery after SCI, and was associated with an increased number of oligodendrocytes. Altogether, our results demonstrate a functional role of the UPR in SCI, offering novel therapeutic targets to treat this invalidating condition.

Simultaneous gene transduction and silencing using stimuli-responsive viral/nonviral chimeric nanoparticles

Despite viral vectors' predominant use in clinical trials, due to higher gene delivery efficiency than nonviral counterparts, intrinsic immunogenicity and limited tunability for multi-modal effects are major concerns for their usage in gene therapy. An adeno-associated viral (AAV) particle was shielded with acid-degradable, siRNA-encapsulating polyketal (PK) shell, resulting in core-shell viral/nonviral chimeric nanoparticles (ChNPs). The AAV core of a ChNP is protected from immune responses by the PK shell which also facilitates the intracellular trafficking of the AAV core and efficiently releases the encapsulated siRNA into the cytoplasm. ChNPs led to significantly enhanced gene transduction, compared to unmodified free AAVs, and simultaneous silencing of a target gene, while avoiding inactivation by recognition from the immune system. Furthermore, conjugation of sialic acid (SA) on the surface of ChNPs enabled receptor-mediated targeted gene delivery to CD22-expressing cells. The ChNPs developed in this study combine the advantages of both viral and nonviral vectors and are a promising platform for targeted co-delivery of DNA and siRNA in inducing synergistic therapeutic effects by simultaneous expression and silencing of multiple genes.

Production and purification of recombinant adeno-associated vectors

The use of recombinant adeno-associated virus (rAAV) vectors in gene therapy for preclinical studies in animal models and human clinical trials is increasing, as these vectors have been shown to be safe and to mediate persistent transgene expression in vivo. Constant improvement in rAAV manufacturing processes (upstream production and downstream purification) has paralleled this evolution to meet the needs for larger vector batches, higher vector titer, and improved vector quality and safety. This chapter provides an overview of existing production and purification systems used for adeno-associated virus (AAV) vectors, and the advantages and disadvantages of each system are outlined. Regulatory guidelines that apply to the use of these systems for clinical trials are also presented. The methods described are examples of protocols that have been utilized for establishing rAAV packaging cell lines, production of rAAV vectors using recombinant HSV infection, and for chromatographic purification of various AAV vector serotypes. A protocol for the production of clinical-grade rAAV type 2 vectors using transient transfection and centrifugation-based purification is also described.

Downstream processing of cell culture-derived virus particles

Manufacturing of cell culture-derived virus particles for vaccination and gene therapy is a rapidly growing field in the biopharmaceutical industry. The process involves a number of complex tasks and unit operations ranging from selection of host cells and virus strains for the cultivation in bioreactors to the purification and formulation of the final product. For the majority of cell culture-derived products, efforts focused on maximization of bioreactor yields, whereas design and optimization of downstream processes were often neglected. Owing to this biased focus, downstream procedures today often constitute a bottleneck in various manufacturing processes and account for the majority of the overall production costs. For efficient production methods, particularly in sight of constantly increasing economic pressure within human healthcare systems, highly productive downstream schemes have to be developed. Here, we discuss unit operations and downstream trains to purify virus particles for use as vaccines and vectors for gene therapy.

Large-scale recombinant adeno-associated virus production

Since recombinant adeno-associated virus (rAAV) was first described as a potential mammalian cell transducing system, frequent reports purportedly solving the problems of scalable production have appeared. Yet few of these processes have enabled the development of robust and economical rAAV production. Two production platforms have emerged that have gained broad support for producing both research and clinical grade vectors. These processes differ fundamentally in several aspects. One approach is based on adherent mammalian cells and uses optimized chemical transient transfection for introducing the essential genetic components into the cells. The other approach utilizes suspension cultures of invertebrate cells. Baculovirus expression vectors are used for introducing the AAV genes into the cells. In addition, the baculovirus provides the helper functions necessary for efficient AAV DNA replication. The use of suspension cell culture provides an intrinsically more scalable platform system than using adherent cells. The upstream processes for suspension cultures are amenable for automation and are easily monitored and regulated to maintain optimum conditions that produce consistent yields of rAAV. Issues relating to developing new and improving existing rAAV production methods are discussed.

PEG-modulated column chromatography for purification of recombinant adeno-associated virus serotype 9

Column chromatography has been described for purification of recombinant adeno-associated viral vectors (rAAV) serotypes 1, 2, 5, 6 and 8. Some of these purification processes have been used in manufacturing pre-clinical grade and clinical grade rAAV vectors. Recently, recombinant AAV9 has been reported to be highly efficient in transducing cardiac muscle in animal models. Systemic or cardiac gene delivery and other applications may require large quantities of rAAV9 vectors, thus a scalable method supporting large scale purification of rAAV9 is needed for clinical development. However, column chromatography-based purification has not been reported to date for rAAV9. This study reports a polyethylene glycol (PEG) modulated chromatography process for purification of AAV9 vectors. Inclusion of PEG in chromatography buffers modulated rAAV9 elution profiles in a manner that resulted in significantly improved resin binding capacity, vector purity and yield. PEG-modulated methods were developed and optimized for hydroxyapatite and ion exchange chromatography, and shown to result in vectors of high purity and functional activity.

Overview of current scalable methods for purification of viral vectors

As a result of the growing interest in the use of viruses for gene therapy and vaccines, many virus-based products are being developed. The manufacturing of viruses poses new challenges for process developers and regulating authorities that need to be addressed to ensure quality, efficacy, and safety of the final product. The design of suitable purification strategies will depend on a multitude of variables including the vector production system and the nature of the virus. In this chapter, we provide an overview of the most commonly used purification methods for viral gene therapy vectors. Current chromatography options available for large-scale purification of γ-retrovirus, lentivirus, adenovirus, adeno-associated virus, herpes simplex virus, baculovirus, and poxvirus vectors are presented.

Influence of peptide ligand surface density and ethylene oxide spacer arm on the capture of porcine parvovirus

In previous work, we identified two trimeric peptide ligands (designated WRW and KYY), which bound specifically to porcine parvovirus (PPV) and demonstrated their ability to capture and remove the virus from solutions containing 7.5% human blood plasma. This article examines the influences of peptide density and the presence of an ethylene oxide spacer arm on the efficiency of virus capture using these two ligands. The WRW peptide bound the most virus from plasma solutions at the lowest peptide density tested (0.008 mmol/g dry resin), and binding was enhanced by the presence of the spacer arm. On the other hand, the KYY peptide bound the most viruses at the same low peptide density, but it performed better in the absence of the spacer arm. Of the two, the binding efficiency of the WRW peptide was more sensitive to peptide density and spacer arm presence. These results indicate that low peptide densities enhance binding selectivity, facilitating specific peptide-virus binding even in the presence of plasma proteins which can theoretically bind nonspecifically.

A simplified baculovirus-AAV expression vector system coupled with one-step affinity purification yields high-titer rAAV stocks from insect cells

Scalable methods of recombinant adeno-associated virus (rAAV) production have gained much recent interest as the field of rAAV-mediated gene therapy approaches the clinic. In particular, the production of rAAV vectors in insect cells via the use of recombinant baculovirus technology has proven to be an efficient and scalable means of rAAV production. Here, we describe a method for the production of rAAV serotypes 1 and 2 in insect cells using a simplified baculovirus-AAV expression vector system coupled with particle purification via affinity chromatography. The number of separate baculovirus constructs required for rAAV production was reduced by genetically modifying the AAV rep gene to allow expression of the AAV-encoded replication enzymes, Rep78 and Rep52, from a single mRNA species and combining the modified rep gene with an AAV cap gene expression cassette in a single baculovirus construct. Additionally, we describe lysis, binding, and elution conditions compatible with a commercially available affinity medium (AVB Sepharose High Performance) used to purify rAAV particles to near homogeneity in a single chromatography step. Using the described method, we obtained an average yield of 7 x 10(4) purified rAAV particles per cell (range: 3.7 x 10(4) to 9.6 x 10(4)) from suspension cultures of recombinant baculovirus-infected insect cells.

Cytotoxic T lymphocyte responses to transgene product, not adeno-associated viral capsid protein, limit transgene expression in mice

The use of adeno-associated viral (AAV) vectors for gene replacement therapy is currently being explored in several clinical indications. However, reports have suggested that input capsid proteins from AAV-2 vector particles may result in the stimulation of cytotoxic T lymphocyte (CTL) responses that can result in a loss of transduced cells. To explore the impact of anti-AAV CTLs on AAV-mediated transgene expression, both immunocompetent C57BL=6 mice and B cell-deficient muMT mice were immunized against the AAV2 capsid protein (Cap) and were injected intravenously with an AAV-2 vector encoding alpha-galactosidase (alpha-Gal). C57BL=6 mice, which developed both CTL and neutralizing antibody responses against Cap, failed to show any detectable alpha-Gal expression. In contrast, serum alpha-Gal levels comparable to those of naive mice were observed in muMT mice despite the presence of robust CTL activity against Cap, indicating that preexisting Cap-specific CTLs did not have any effect on the magnitude and duration of transgene expression. The same strategy was used to assess the impact of CTLs against the alpha-Gal transgene product on AAV-mediated gene delivery and persistence of transgene expression. Preimmunization of muMT mice with an Ad=alpha-Gal vector induced a robust CTL response to alpha-Gal. When these mice were injected with AAV2=alpha-Gal vector, initial levels of alpha-Gal expression were reduced by more than 1 log and became undetectable by 2 weeks postinjection. Overall, our results indicate that CTLs against the transgene product as opposed to AAV capsid protein are more likely to interfere with AAV transgene expression.

Chromatography-based purification of adeno-associated virus

Virus-mediated gene transfer shows great potential as a therapeutic strategy for the management of various inherited and acquired human diseases. Among the current viral vectors, adeno-associated virus (AAV) has become the vector of choice for numerous gene therapy applications. As AAV-based vectors approach the clinic, the need for scalable methods of production and purification is steadily increasing. In this chapter, we present a column chromatography-based protocol for the purification of recombinant AAV type 1 (AAV-1) to near homogeneity. The protocol, which can be completed within one working day, employs three major purification steps: (1) polyethylene glycol-mediated vector precipitation, (2) anion-exchange chromatography, and (3) gel filtration chromatography. This method provides a basic strategy, or "platform," that can be adapted to the purification of other recombinant AAV vector serotypes.

PEGylated adenovirus for targeted gene therapy

Bifunctional polyethylene glycol (PEG) molecules provide a novel approach to retargeting viral vectors without the need to genetically modify the vector. Modification of the surface of adenovirus with heterofunctional PEG allows further modification of the capsid with ligands. In addition, heterofunctional PEG modification ablates the normal tropism of the virus and reduces transduction of non-target tissues in vivo. Moreover, the addition of PEG chains to the surface of the virus shields antigen-binding sites, significantly reducing the susceptibility of the virus to antibody neutralization. Finally, T cell subsets from mice exposed to the PEGylated vector demonstrate a marked decrease in Th1 and Th2 responses, suggesting that PEG modification may help reduce the immune response to the vector.

Timing of therapeutic intervention determines functional and survival outcomes in a mouse model of late infantile batten disease

Classical late infantile neuronal ceroid lipofuscinosis (cLINCL) is a monogenic disorder caused by the loss of tripeptidyl peptidase 1 (TPP1) activity as a result of mutations in CLN2. Absence of TPP1 results in lysosomal storage with an accompanying axonal degeneration throughout the central nervous system (CNS), which leads to progressive neurodegeneration and early death. In this study, we compared the efficacies of pre- and post-symptomatic injections of recombinant adeno-associated virus (AAV) for treating the cellular and functional abnormalities of CLN2 mutant mice. Intracranial injection of AAV1-hCLN2 resulted in widespread human TPP1 (hTPP1) activity in the brain that was 10-100-fold above wild-type levels. Injections before disease onset prevented storage and spared neurons from axonal degeneration, reflected by the preservation of motor function. Furthermore, the majority of CLN2 mutant mice treated pre-symptomatically lived for at least 330 days, compared with a median survival of 151 days in untreated CLN2 mutant controls. In contrast, although injection after disease onset ameliorated lysosomal storage, there was evidence of axonal degeneration, motor function showed limited recovery, and the animals had a median lifespan of 216 days. These data illustrate the importance of early intervention for enhanced therapeutic benefit, which may provide guidance in designing novel treatment strategies for cLINCL patients.

Combination brain and systemic injections of AAV provide maximal functional and survival benefits in the Niemann-Pick mouse

Niemann-Pick disease (NPD) is caused by the loss of acid sphingomyelinase (ASM) activity, which results in widespread accumulation of undegraded lipids in cells of the viscera and CNS. In this study, we tested the effect of combination brain and systemic injections of recombinant adeno-associated viral vectors encoding human ASM (hASM) in a mouse model of NPD. Animals treated by combination therapy exhibited high levels of hASM in the viscera and brain, which resulted in near-complete correction of storage throughout the body. This global reversal of pathology translated to normal weight gain and superior recovery of motor and cognitive functions compared to animals treated by either brain or systemic injection alone. Furthermore, animals in the combination group did not generate antibodies to hASM, demonstrating the first application of systemic-mediated tolerization to improve the efficacy of brain injections. All of the animals treated by combination therapy survived in good health to an investigator-selected 54 weeks, whereas the median lifespans of the systemic-alone, brain-alone, or untreated ASM knockout groups were 47, 48, and 34 weeks, respectively. These data demonstrate that combination therapy is a promising therapeutic modality for treating NPD and suggest a potential strategy for treating disease indications that cause both visceral and CNS pathologies.

The use of recombinant adeno-associated virus for skeletal gene therapy

OBJECTIVES

To provide a comprehensive literature review describing recent developments of the recombinant adeno-associated virus (rAAV) vector and exploring the therapeutic application of rAAV for bone defects, cartilage lesions and rheumatoid arthritis.

DESIGN

Narrative review.

RESULT

The review outlines the serotypes and genome of AAV, integration and life cycle of the rAAV vectors, the immune response and regulating system for AAV gene therapy. Furthermore, the advancements of rAAV gene therapy for bone growth together with cartilage repair are summarized.

CONCLUSION

Recombinant adeno-associated virus vector is perceived to be one of the most promising vector systems for bone and cartilage gene therapy approaches and further investigations need to be carried out for craniofacial research.

Primary recovery and chromatographic purification of adeno-associated virus type 2 produced by baculovirus/insect cell system

Adeno-associated virus (AAV) is making its place in gene therapy applications; however, the industry is still facing obstacles in producing a large quantity of highly purified material for clinical studies. Insect cell technology can be used to produce AAV to meet the current demand. During the purification process it was observed that there was a reduced recovery of AAV produced in insect cells, Spodoptera frugiperda (Sf9). It was assumed that the formation of AAV agglomerates and the interaction of AAV with other cellular components were major contributors to this loss. After studying different systems of extraction a sequence of treatment for primary recovery of AAV from cell paste was developed. This sequence was necessary to reduce the AAV losses and to increase the recovery. The purification method avoided the use of ultracentrifugation and adopted chromatographic methods for the purification of AAV. Primary recovery, ion exchange chromatography and hydrophobic interaction chromatography gave an overall yield of 75% from the extracted AAV. The purification process was based on chromatographic methods; therefore, it can be scaled up. Although this method was developed for AAV type 2, it is believed that this method could be modified easily to purify other AAV serotypes.

Effective gene therapy in an authentic model of Tay-Sachs-related diseases

Tay-Sachs disease is a prototypic neurodegenerative disease. Lysosomal storage of GM2 ganglioside in Tay-Sachs and the related disorder, Sandhoff disease, is caused by deficiency of beta-hexosaminidase A, a heterodimeric protein. Tay-Sachs-related diseases (GM2 gangliosidoses) are incurable, but gene therapy has the potential for widespread correction of the underlying lysosomal defect by means of the secretion-recapture cellular pathway for enzymatic complementation. Sandhoff mice, lacking the beta-subunit of hexosaminidase, manifest many signs of classical human Tay-Sachs disease and, with an acute course, die before 20 weeks of age. We treated Sandhoff mice by stereotaxic intracranial inoculation of recombinant adeno-associated viral vectors encoding the complementing human beta-hexosaminidase alpha and beta subunit genes and elements, including an HIV tat sequence, to enhance protein expression and distribution. Animals survived for >1 year with sustained, widespread, and abundant enzyme delivery in the nervous system. Onset of the disease was delayed with preservation of motor function; inflammation and GM2 ganglioside storage in the brain and spinal cord was reduced. Gene delivery of beta-hexosaminidase A by using adeno-associated viral vectors has realistic potential for treating the human Tay-Sachs-related diseases.

Identification of Novel Biomarkers for Niemann–Pick Disease Using Gene Expression Analysis of Acid Sphingomyelinase Knockout Mice

Although several therapies are available or being developed for lysosomal storage disorders (LSDs), assessment of therapeutic efficacy is challenged by the lack of markers to assess disease progression and severity. This is particularly true for rare diseases such as LSDs, since natural history data from human populations are often lacking. Herein we describe the use of gene expression analysis in the acid sphingomyelinase-deficient mouse model (ASMKO) of Types A and B Niemann-Pick disease (NPD) to identify novel serum biomarkers. We used microarray and real-time PCR analyses to compare mRNA expression in ASMKO and normal mice in two important sites of pathology, lung and brain, and from these data identified and validated several potential biomarkers. The cytokine MIP-1alpha was markedly elevated in ASMKO mouse serum, and following enzyme replacement therapy (ERT) it was reduced to normal levels. Total iron levels were similarly elevated in ASMKO mice, reflective of the elevated ferritin light chain transcript, and decreased to normal after ERT. Serum growth hormone levels were also elevated in ASMKO mice and were reduced to normal after brain-directed gene therapy, but not ERT. These studies illustrate the value of gene expression analysis for the identification of biomarkers, and provide new insight into the pathobiology of NPD.

Chromatographic purification of recombinant adenoviral and adeno-associated viral vectors: methods and implications

In recent years, recombinant adenoviral and adeno-associated viral (AAV) vectors have been exploited in a number of gene delivery approaches. The use of these vectors in clinical gene transfer has increased the demand for their characterization, production and purification. Although the classical method of adenovirus or AAV purification by density gradient centrifugation is effective on a small scale, chromatographic separation is the most versatile and powerful method for large-scale production of recombinant adenovirus or AAV. This review describes different chromatographic modes for adenovirus or AAV purification and process development, as well as the utility of different purification steps for virus production. Advances in the development of viral vectors for gene therapy, such as the discovery of new AAV serotypes, adenoviral and AAV retargeting and improved production of helper-dependent adenoviral vectors, require further development of efficient purification methods.

Downstream processing of viral vectors and vaccines

Viral vectors and viral vaccines more and more play an important role in current medical approaches. Gene vectors like adenoviruses, adeno-associated viruses or retroviruses are the vehicles being developed for delivering genetic material to the target cell in gene therapy. Viral vaccines, like attenuated or inactivated rabies virus, influenza virus or hepatitis virus vaccines, are powerful tools to limit the number of serious viral infections and pandemics. Higher safety demands, that is, reduction of side effects, by regulatory authorities like Food and Drug Administration (FDA) and European Agency for the Evaluation of Medicinal Products (EMEA), nowadays force developers as well as manufacturers to improve their production and purification processes for viral vectors and vaccines. Like for influenza viral vaccines, manufacturers begin to switch from egg cultivation to mammalian cell culture systems. Also within the purification procedure, a clear trend from classical purification methods like sucrose gradient centrifugation towards more sophisticated techniques like tangential flow filtration and liquid chromatography can be observed.

Hydroxyapatite chromatography of phage-display virions

Hydroxyapatite column chromatography can be used to purify filamentous bacteriophage—the phage most commonly used for phage display. Virions that have been partially purified from culture supernatant by two cycles of precipitation in 2% polyethylene glycol are adsorbed onto the matrix at a density of at least 7.6 × 1013 virions (about 3 mg) per milliliter of packed bed volume in phosphate-buffered saline (PBS; 0.15 M NaCl, 5 mM NaH2PO4, pH-adjusted to 7.0 with NaOH). The matrix is washed successively with wash buffer I (150 mM NaCl, 125 mM phosphate, pH 7.0), wash buffer II (2.55 M NaCl, 125 mM phosphate, pH 7.0), and wash buffer I; after which virions are desorbed in desorption buffer (150 mM NaCl, 200 mM phosphate, pH 7.0), and the matrix is stripped with stripping buffer (150 mM NaCl, 1 M phosphate, pH 7.0). About half of the applied virions are recovered in desorption buffer. Western blot analysis shows that they have undetectable levels of host-derived protein contaminants that are present in the input virions and in virions purified by CsCl equilibrium density gradient centrifugation—the method most commonly used to prepare virions in high purity. Hydroxyapatite chromatography is thus an attractive alternative method for purifying filamentous virions, particularly when the scale is too large for ultracentrifugation to be practical.

Gene transfer of human acid sphingomyelinase corrects neuropathology and motor deficits in a mouse model of Niemann-Pick type A disease

Niemann-Pick type A disease is a lysosomal storage disorder caused by a deficiency in acid sphingomyelinase (ASM) activity. Previously we showed that storage pathology in the ASM knockout (ASMKO) mouse brain can be corrected by adeno-associated virus serotype 2 (AAV2)-mediated gene transfer. The present experiment compared the relative therapeutic efficacy of different recombinant AAV serotype vectors (1, 2, 5, 7, and 8) using histological, biochemical, and behavioral endpoints. In addition, we evaluated the use of the deep cerebellar nuclei (DCN) as a site for injection to facilitate global distribution of the viral vector and enzyme. Seven-week-old ASM knockout mice were injected within the DCN with different AAV serotype vectors encoding human ASM (hASM) and then killed at either 14 or 20 weeks of age. Results showed that AAV1 was superior to serotypes 2, 5, 7, and 8 in its relative ability to express hASM, alleviate storage accumulation, and correct behavioral deficits. Expression of hASM was found not only within the DCN, but also throughout the cerebellum, brainstem, midbrain, and spinal cord. This finding demonstrates that targeting the DCN is an effective approach for achieving widespread enzyme distribution throughout the CNS. Our results support the continued development of AAV based vectors for gene therapy of the CNS manifestations in Niemann-Pick type A disease.

AAV8-Mediated Hepatic Expression of Acid Sphingomyelinase Corrects the Metabolic Defect in the Visceral Organs of a Mouse Model of Niemann–Pick Disease

Acid sphingomyelinase deficiency is a lysosomal storage disorder in which the defective lysosomal hydrolase fails to degrade sphingomyelin. The resulting accumulation of substrate in the lysosomes of histiocytic cells leads to hepatosplenomegaly and severe pulmonary inflammation. Administration of a recombinant AAV1 vector encoding human acid sphingomyelinase to acid sphingomyelinase knockout (ASMKO) mice effectively reduced the accumulated substrate in all of the affected visceral organs. However, more complete and rapid clearance of sphingomyelin was observed when an AAV8-based serotype vector was used in lieu of AAV1. Importantly, AAV8-mediated hepatic expression of higher and sustained levels of the enzyme also corrected the abnormal cellularity, cell differentials, and levels of the chemokine MIP-1alpha in the bronchoalveolar lavage fluids of the ASMKO mice. Treatment also reversed the morphological aberrations associated with the alveolar macrophages of ASMKO mice and restored their phagocytic activity. No antibodies to the expressed enzyme were detected when the viral vectors were used in conjunction with a transcription cassette harboring a liver-restricted enhancer/promoter. Together, these data support the continued development of AAV8-mediated hepatic gene transfer as an approach to treat the visceral manifestations observed in individuals with acid sphingomyelinase deficiency.

AAV vector-mediated correction of brain pathology in a mouse model of Niemann-Pick A disease

Niemann-Pick A disease (NPA) is a fatal lysosomal storage disorder caused by a deficiency in acid sphingomyelinase (ASM) activity. The lack of functional ASM results in cellular accumulation of sphingomyelin and cholesterol within distended lysosomes throughout the brain. In this study, we investigated the potential of AAV-mediated expression of ASM to correct the brain pathology in an ASM knockout (ASMKO) mouse model of NPA. An AAV serotype 2 vector encoding human ASM (AAV2-hASM) was injected directly into the adult ASMKO hippocampus of one hemisphere. This resulted in expression of human ASM in all major cell layers of the ipsilateral hippocampus for at least 15 weeks postinjection. Transduced cells were also present in the entorhinal cortex, medial septum, and contralateral hippocampus in a pattern consistent with retrograde axonal transport of AAV2. There was a substantial reduction of distended lysosomes and an almost complete reversal of cholesterol accumulation in all areas of the brain that were targeted by AAV2-hASM. These findings show that the ASMKO brain is responsive to ASM replacement and that retrograde transport of AAV2 functions as a platform for widespread gene delivery and reversal of pathology in affected brain.

Correction of glycogen storage disease type II by an adeno-associated virus vector containing a muscle-specific promoter

Glycogen storage disease type II (Pompe disease) causes death in infancy from cardiorespiratory failure due to acid alpha-glucosidase (GAA; acid maltase) deficiency. An AAV2 vector pseudotyped as AAV6 (AAV2/6 vector) transiently expressed high-level human GAA in GAA-knockout (GAA-KO) mice without reducing glycogen storage; however, in immunodeficient GAA-KO/SCID mice the AAV2/6 vector expressed high-level GAA and reduced the glycogen content of the injected muscle for 24 weeks. A CD4+/CD8+ lymphocytic infiltrate was observed in response to the AAV2/6 vector in immunocompetent GAA-KO mice. When a muscle-specific creatine kinase promoter was substituted for the CB promoter (AAV-MCKhGAApA), that AAV2/6 vector expressed high-level GAA and reduced glycogen content in immunocompetent GAA-KO mice. Muscle-restricted expression of hGAA provoked only a humoral (not cellular) immune response. Intravenous administration of a high number of particles of AAV-MCKhGAApA as AAV2/7 reduced the glycogen content of the heart and skeletal muscle and corrected individual myofibers in immunocompetent GAA-KO mice 24 weeks postinjection. In summary, persistent correction of muscle glycogen content was achieved with an AAV vector containing a muscle-specific promoter in GAA-KO mice, and this approach should be considered for muscle-targeted gene therapy in Pompe disease.

Large-scale production, purification and crystallization of wild-type adeno-associated virus-2

Adeno-associated virus-2 (AAV-2) has long been recognized as a potential vector for human gene therapy. Although much progress has been made in the molecular virology of AAV-2, structural studies of AAV-2 have been hampered by the low efficiency of virus production in culture, the low purity of preparations, and the low solubility of pure virus particles in solution. Methods of larger scale AAV-2 production have been developed through adaptation to suspension culture and re-optimization of the times of infection and transfection with respect to particle production. The methods allow the purification of 10mg ( approximately 10(15) particles) of AAV-2 per preparation at approximately 99% purity as judged by SDS-PAGE. This was sufficient for the screening of conditions for the formation of diffraction-grade crystals, ultimately leading to an atomic structure for AAV-2.

Recombinant adeno-associated viral (rAAV) vectors as therapeutic tools for Duchenne muscular dystrophy (DMD)

Duchenne muscular dystrophy (DMD) is a lethal genetic muscle disorder caused by recessive mutations in the dystrophin gene. The size of the gene (2.4 Mb) and mRNA (14 kb) in addition to immunogenicity problems and inefficient transduction of mature myofibres by currently available vector systems are formidable obstacles to the development of efficient gene therapy approaches. Adeno-associated viral (AAV) vectors overcome many of the problems associated with other vector systems (nonpathogenicity and minimal immunogenicity, extensive cell and tissue tropism) but accommodate limited transgene capacity (<5 kb). As a result of these observations, a number of laboratories worldwide have engineered a series of microdystrophin cDNAs based on genotype-phenotype relationship in Duchenne (DMD) and Becker (BMD) dystrophic patients, and transgenic studies in mdx mice. Recent progress in characterization of AAV serotypes from various species has demonstrated that alternative AAV serotypes are far more efficient in transducing muscle than the traditionally used AAV2. This article summarizes the current progress in the field of recombinant adeno-associated viral (rAAV) delivery for DMD, including optimization of recombinant AAV-microdystrophin vector systems/cassettes targeting the skeletal and cardiac musculature.

Immobilized cobalt affinity chromatography provides a novel, efficient method for herpes simplex virus type 1 gene vector purification

Herpes simplex virus type 1 (HSV-1) is a promising vector for gene therapy applications, particularly at peripheral nerves, the natural site of virus latency. Many gene vectors require large particle numbers for even early-phase clinical trials, emphasizing the need for high-yield, scalable manufacturing processes that result in virus preparations that are nearly free of cellular DNA and protein contaminants. HSV-1 is an enveloped virus that requires the development of gentle purification methods. Ideally, such methods should avoid centrifugation and may employ selective purification processes that rely on the recognition of a unique envelope surface chemistry. Here we describe a novel method that fulfills these criteria. An immobilized metal affinity chromatography (IMAC) method was developed for the selective purification of vectors engineered to display a high-affinity binding peptide. Feasibility studies involving various transition metal ions (Cu2+, Zn2+, Ni2+, and Co2+) showed that cobalt had the most desirable features, which include a low level of interaction with either the normal virus envelope or contaminating DNA and proteins. The introduction of a cobalt-specific recognition element into the virus envelope may provide a suitable target for cobalt-dependent purification. To test this possibility, we engineered a peptide with affinity for immobilized cobalt in frame in the heparan sulfate binding domain of HSV-1 glycoprotein B, which is known to be exposed on the surface of the virion particle and recombined into the viral genome. By optimizing the IMAC loading conditions and reducing cobalt ion leakage, we recovered 78% of the tagged HSV-1 recombinant virus, with a >96% reduction in contaminating proteins and DNA.