Serotype specificity of adenovirus purification using anion-exchange chromatography

Development of indirect ELISA for the detection of canine adenovirus type 2 antibodies in dog sera

Background

Canine adenovirus type 2 (CAV-2) induces infectious laryngotracheitis in members of the family Canidae, including dogs. To date, no ELISA kits specific for CAV-2 antibody have been commercialized for dogs in Korea.

Objectives

We aimed to develop new indirect enzyme-linked immunosorbent assay (I-ELISA) to perform rapid, accurate serological surveys of CAV-2 in dog serum samples.

Methods

In total, 165 serum samples were collected from dogs residing in Chungbuk and Gyeongbuk provinces between 2016 and 2018. The Korean CAV-2, named the APQA1701-40P strain, was propagated in Madin–Darby canine kidney cells and purified in an anion-exchange chromatography column for use as an antigen for I-ELISA. The virus-neutralizing antibody titers of CAV-2 in the dog sera were measured by virus neutralization (VN) test.

Results

We compared the results obtained between the VN and new I-ELISA tests. The sensitivity, specificity, and accuracy of new I-ELISA were 98.6%, 86.4% and 97.0% compared with VN test, respectively. New I-ELISA was significantly correlated with VN (r = 0.91).

Conclusions

These results indicate that new I-ELISA is useful for sero-surveillance of CAV-2 in dog serum.

A Flow-Through Chromatographic Strategy for Hepatitis C Virus-Like Particles Purification

Biopharmaceuticals are currently becoming one of the fastest growing segments of the global pharmaceutical industry, being used in practically all branches of medicine from disease treatment to prevention. Virus-like particles (VLP) hold tremendous potential as a vaccine candidate due to their anticipated immunogenicity and safety profile when compared to inactivated or live attenuated viral vaccines. Nevertheless, there are several challenges yet to be solved in the development and manufacturing of these products, which ultimately can increase time to market. Suchlike virus-based products, the development of a platform approach is often hindered due to diversity and inherent variability of physicochemical properties of the product. In the present work, a flow-through chromatographic purification strategy for hepatitis C VLP expressed using the baculovirus-insect cell expression system was developed. The impact of operational parameters, such as residence time and ionic strength were studied using scaled-down models and their influence on the purification performance was described. The flow-through strategy herein reported made use of radial-flow chromatography columns packed with an anion exchanger and was compared with a bind and elute approach using the same chromatography media. Overall, by selecting the optimal operational setpoints, we were able to achieve higher VLP recoveries in the flow-through process (66% versus 37%) with higher removal of DNA, baculovirus and host-cell protein (92%, 99% and 50% respectively).

A novel method to purify adenovirus based on increasing salt concentrations in buffer

With the rapid development of gene therapy, gene-based medicine with adenovirus as vectors has become a new method for disease treatment. However, there are still enormous challenges in the large-scale production of adenoviruses for clinical use. Recent reports show that ion-exchange chromatography (IEC) is an effective tool for the isolation and purification of adenovirus. However, during the separation and purification, host cell protein and DNA, as well as serum from the culture medium, can non-specifically occupy numerous binding sites of the chromatography packings, thereby reducing the binding between the adenovirus and packing media. We here report a novel method for highly efficient purification of adenoviruses by increasing the salt concentrations of the samples to be ultrafiltrated by tangential flow filtration, the diafiltration buffer, and the samples for IEC purification. This method could significantly remove a large amount of serum proteins and host cell proteins, increase the amount of sample loaded on the IEC column, and improve the binding of the adenovirus samples to the packing media. A purity of > 95% could be obtained after one chromatography operation, and the number of purification steps and the amount of used packing media were reduced. The method is simple, economical, and efficient, and has excellent applications.

Simian adenovirus vector production for early-phase clinical trials: A simple method applicable to multiple serotypes and using entirely disposable product-contact components

A variety of Good Manufacturing Practice (GMP) compliant processes have been reported for production of non-replicating adenovirus vectors, but important challenges remain. Most clinical development of adenovirus vectors now uses simian adenoviruses or rare human serotypes, whereas reported manufacturing processes mainly use serotypes such as AdHu5 which are of questionable relevance for clinical vaccine development. Many clinically relevant vaccine transgenes interfere with adenovirus replication, whereas most reported process development uses selected antigens or even model transgenes such as fluorescent proteins which cause little such interference. Processes are typically developed for a single adenovirus serotype - transgene combination, requiring extensive further optimization for each new vaccine. There is a need for rapid production platforms for small GMP batches of non-replicating adenovirus vectors for early-phase vaccine trials, particularly in preparation for response to emerging pathogen outbreaks. Such platforms must be robust to variation in the transgene, and ideally also capable of producing adenoviruses of more than one serotype. It is also highly desirable for such processes to be readily implemented in new facilities using commercially available single-use materials, avoiding the need for development of bespoke tools or cleaning validation, and for them to be readily scalable for later-stage studies. Here we report the development of such a process, using single-use stirred-tank bioreactors, a transgene-repressing HEK293 cell - promoter combination, and fully single-use filtration and ion exchange components. We demonstrate applicability of the process to candidate vaccines against rabies, malaria and Rift Valley fever, each based on a different adenovirus serotype. We compare performance of a range of commercially available ion exchange media, including what we believe to be the first published use of a novel media for adenovirus purification (NatriFlo® HD-Q, Merck). We demonstrate the need for minimal process individualization for each vaccine, and that the product fulfils regulatory quality expectations. Cell-specific yields are at the upper end of those previously reported in the literature, and volumetric yields are in the range 1 × 10¹³ - 5 × 10¹³ purified virus particles per litre of culture, such that a 2-4 L process is comfortably adequate to produce vaccine for early-phase trials. The process is readily transferable to any GMP facility with the capability for mammalian cell culture and aseptic filling of sterile products.

Designer Oncolytic Adenovirus: Coming of Age

The licensing of talimogene laherparepvec (T-Vec) represented a landmark moment for oncolytic virotherapy, since it provided unequivocal evidence for the long-touted potential of genetically modified replicating viruses as anti-cancer agents. Whilst T-Vec is promising as a locally delivered virotherapy, especially in combination with immune-checkpoint inhibitors, the quest continues for a virus capable of specific tumour cell killing via systemic administration. One candidate is oncolytic adenovirus (Ad); it’s double stranded DNA genome is easily manipulated and a wide range of strategies and technologies have been employed to empower the vector with improved pharmacokinetics and tumour targeting ability. As well characterised clinical and experimental agents, we have detailed knowledge of adenoviruses’ mechanisms of pathogenicity, supported by detailed virological studies and in vivo interactions. In this review we highlight the strides made in the engineering of bespoke adenoviral vectors to specifically infect, replicate within, and destroy tumour cells. We discuss how mutations in genes regulating adenoviral replication after cell entry can be used to restrict replication to the tumour, and summarise how detailed knowledge of viral capsid interactions enable rational modification to eliminate native tropisms, and simultaneously promote active uptake by cancerous tissues. We argue that these designer-viruses, exploiting the viruses natural mechanisms and regulated at every level of replication, represent the ideal platforms for local overexpression of therapeutic transgenes such as immunomodulatory agents. Where T-Vec has paved the way, Ad-based vectors now follow. The era of designer oncolytic virotherapies looks decidedly as though it will soon become a reality.

Substitution of blood coagulation factor X-binding to Ad5 by position-specific PEGylation: Preventing vector clearance and preserving infectivity

The biodistribution of adenovirus type 5 (Ad5) vector particles is heavily influenced by interaction of the particles with plasma proteins, including coagulation factor X (FX), which binds specifically to the major Ad5 capsid protein hexon. FX mediates hepatocyte transduction by intravenously-injected Ad5 vectors and shields vector particles from neutralization by natural antibodies and complement. In mice, mutant Ad5 vectors that are ablated for FX-binding become detargeted from hepatocytes, which is desirable for certain applications, but unfortunately such FX-nonbinding vectors also become sensitive to neutralization by mouse plasma proteins. To improve the properties of Ad5 vectors for systemic delivery, we developed a strategy to replace the natural FX shield by a site-specific chemical polyethylene glycol shield. Coupling of polyethylene glycol to a specific site in hexon hypervariable region 1 yielded vector particles that were protected from neutralization by natural antibodies and complement although they were unable to bind FX. These vector particles evaded macrophages in vitro and showed significantly improved pharmacokinetics and hepatocyte transduction in vivo. Thus, site-specific shielding of Ad5 vectors with polyethylene glycol rendered vectors FX-independent and greatly improved their properties for systemic gene therapy.

Evaluation of novel large cut-off ultrafiltration membranes for adenovirus serotype 5 (Ad5) concentration

The purification of virus particles and viral vectors for vaccine and gene therapy applications is gaining increasing importance in order to deliver a fast, efficient, and reliable production process. Ultrafiltration (UF) is a widely employed unit operation in bioprocessing and its use is present in several steps of the downstream purification train of biopharmaceuticals. However, to date few studies have thoroughly investigated the performance of several membrane materials and cut-offs for virus concentration/diafiltration. The present study aimed at developing a novel class of UF cassettes for virus concentration/diafiltration. A detailed study was conducted to evaluate the effects of (i) membrane materials, namely polyethersulfone (PES), regenerated cellulose (RC), and highly cross-linked RC (xRC), (ii) nominal cut-off, and (iii) UF device geometry at different production scales. The results indicate that the xRC cassettes with a cut-off of approximately 500 kDa are able to achieve a 10-fold concentration factor with 100% recovery of particles with a process time twice as fast as that of a commercially available hollow fiber. DNA and host cell protein clearances, as well as hydraulic permeability and fouling behavior, were also assessed.

Adenovirus purification by two-column, size-exclusion, simulated countercurrent chromatography

Adenovirus serotype 5 (Ad5) was successfully separated by size-exclusion chromatography (SEC) using a simple, yet efficient, two-column, quasi-continuous, simulated moving-bed process operated in an open-loop configuration. The operating cycle is divided into two identical half-cycles, each of them consisting of the following sequence of sub-steps: (i) elution of the upstream column and direction of the effluent of the downstream column to waste; (ii) elution of the upstream column and redirection of its effluent to waste while the downstream column is fed with the clarified bioreaction bulk and its effluent collected as purified product; (iii) operation of the system as in step (i) but collecting the effluent of the downstream column as product; (iv) elution of the upstream column and direction of its effluent to waste while the flow through the downstream column is temporarily halted. Clearance of impurities, namely DNA and host cell protein (HCP), were experimentally assessed. The pilot-scale run yielded a virus recovery of 86%, and a clearance of 90% and 89% for DNA and HCP, respectively, without any fine tunning of the predetermined operating parameters. These figures compare very favorably against single-column batch chromatography for the same volume of size-exclusion resin. However, and most importantly, the virus yield was increased from 57% for the batch system to 86% for the two-column SEC process because of internal recycling of the mixed fractions of contaminated Ad5, even though the two-column process was operated strictly in an open-loop configuration. And last, but not least, the productivity was increased by 6-fold with the two-column process. In conclusion, the main drawbacks of size-exclusion chromatography, namely low productivity and low product titer, were overcome to a considerable extent by an innovative two-column configuration that keeps the mixed fractions inside the system at all times.

SR-A and SREC-I are Kupffer and endothelial cell receptors for helper-dependent adenoviral vectors

Helper-dependent adenoviral (HDAd) vectors can mediate long-term, high-level transgene expression from transduced hepatocytes with no chronic toxicity. However, a toxic acute response with potentially lethal consequences has hindered their clinical applications. Liver sinusoidal endothelial cells (LSECs) and Kupffer cells are major barriers to efficient hepatocyte transduction. Understanding the mechanisms of adenoviral vector uptake by non-parenchymal cells may allow the development of strategies aimed at overcoming these important barriers and to achieve preferential hepatocyte gene transfer with reduced toxicity. Scavenger receptors on Kupffer cells bind adenoviral particles and remove them from the circulation, thus preventing hepatocyte transduction. In the present study, we show that HDAd particles interact in vitro and in vivo with scavenger receptor-A (SR-A) and with scavenger receptor expressed on endothelial cells-I (SREC-I) and we exploited this knowledge to increase the efficiency of hepatocyte transduction by HDAd vectors in vivo through blocking of SR-A and SREC-I with specific fragments antigen-binding (Fabs).

Avian influenza vaccination in chickens and pigs with replication-competent adenovirus-free human recombinant adenovirus 5

Protective immunity to avian influenza (AI) virus can be elicited in chickens by in ovo or intramuscular vaccination with replication-competent adenovirus (RCA)-free human recombinant adenovirus serotype 5 (Ad5) encoding AI virus H5 (AdTW68.H5) or H7 (AdCN94.H7) hemagglutinins. We evaluated bivalent in ovo vaccination with AdTW68.H5 and AdCN94.H7 and determined that vaccinated chickens developed robust hemagglutination inhibition (HI) antibody levels to both H5 and H7 AI strains. Additionally, we evaluated immune responses of 1-day-old chickens vaccinated via spray with AdCN94.H7. These birds showed increased immunoglobulin A responses in lachrymal fluids and increased interleukin-6 expression in Harderian gland-derived lymphocytes. However, specific HI antibodies were not detected in the sera of these birds. Because pigs might play a role as a "mixing vessel" for the generation of pandemic influenza viruses we explored the use of RCA-free adenovirus technology to immunize pigs against AI virus. Weanling piglets vaccinated intramuscularly with a single dose of RCA-free AdTW68.H5 developed strong systemic antibody responses 3 wk postvaccination. Intranasal application of AdTW68.H5 in piglets resulted in reduced vaccine coverage, i.e., 33% of pigs (2/6) developed an antibody response, but serum antibody levels in those successfully immunized animals were similar to intramuscularly vaccinated animals.

Insight into the mechanisms of adenovirus capsid disassembly from studies of defensin neutralization

Defensins are effectors of the innate immune response with potent antibacterial activity. Their role in antiviral immunity, particularly for non-enveloped viruses, is poorly understood. We recently found that human alpha-defensins inhibit human adenovirus (HAdV) by preventing virus uncoating and release of the endosomalytic protein VI during cell entry. Consequently, AdV remains trapped in the endosomal/lysosomal pathway rather than trafficking to the nucleus. To gain insight into the mechanism of defensin-mediated neutralization, we analyzed the specificity of the AdV-defensin interaction. Sensitivity to alpha-defensin neutralization is a common feature of HAdV species A, B1, B2, C, and E, whereas species D and F are resistant. Thousands of defensin molecules bind with low micromolar affinity to a sensitive serotype, but only a low level of binding is observed to resistant serotypes. Neutralization is dependent upon a correctly folded defensin molecule, suggesting that specific molecular interactions occur with the virion. CryoEM structural studies and protein sequence analysis led to a hypothesis that neutralization determinants are located in a region spanning the fiber and penton base proteins. This model was supported by infectivity studies using virus chimeras comprised of capsid proteins from sensitive and resistant serotypes. These findings suggest a mechanism in which defensin binding to critical sites on the AdV capsid prevents vertex removal and thereby blocks subsequent steps in uncoating that are required for release of protein VI and endosomalysis during infection. In addition to informing the mechanism of defensin-mediated neutralization of a non-enveloped virus, these studies provide insight into the mechanism of AdV uncoating and suggest new strategies to disrupt this process and inhibit infection.

Flow-dependent entrapment of large bioparticles in porous process media

The need for purification of biomolecules extends to larger bioparticles as well. For example, virus purification is required for production of many vaccines and gene delivery vectors, and understanding virus removal in porous media is also important in downstream processing of therapeutic proteins and in purification of water in soils. A convective entrapment mechanism for retention of large bioparticles is discussed here based on retention of such bioparticles in pore constrictions at high enough flow rates, even under non-binding conditions. A simple equation to predict whether such entrapment is expected to occur in a given system is derived based on a Péclet number that is proportional to the flow rate and to the cube of the bioparticle diameter. To test the theory, adenovirus was spiked onto chromatographic beds. As expected from the theory, under non-interacting conditions a progressively larger amount of virus becomes trapped with increasing flow rate. The entrapment is reversible upon flow rate reduction, which, within the proposed model, is based on the possibility of diffusive escape from pore constrictions. This mechanism can be exploited for virus purification or removal, and the theory is also consistent with the anecdotal evidence that monoliths and membranes are more difficult to clean than conventional chromatographic beds, especially at high flow rates.

Protection of chickens against avian influenza with nonreplicating adenovirus-vectored vaccine

Protective immunity against avian influenza (AI) virus has been elicited in chickens by single-dose in ovo or i.m. vaccination with a replication-competent adenovirus (Ad)-free human Ad vector encoding the AI virus A/Turkey/Wisconsin/68 H5 (AdTW68. H5) or the A/Chicken/New York/94 H7 (AdChNY94. H7) hemagglutinin (HA). The AdTW68.H5-vaccinated chickens were protected against both H5N1 and H5N2 highly pathogenic AI virus challenges. The AdChNY94. H7-vaccinated chickens were protected against an H7N3 highly pathogenic avian influenza virus challenge. Chickens vaccinated in ovo with AdTW68.H5 followed by posthatch i.m. vaccination with AdChNY94.H7 responded to both vaccinations, with robust antibody titers against both the H5 and H7 AI proteins. The use of a synthetic AI H5 HA gene codon optimized to match the tRNA pool found in chicken cells is more potent than the cognate H5 HA gene. Mass administration of this AI vaccine can be streamlined with available robotic in ovo injectors. In addition, Ad5-vectored vaccines can be produced rapidly and the safety margin of the nonreplicating vector is superior to that of a replicating counterpart. Furthermore, this mode of vaccination will not interfere with epidemiological surveys of natural AI infections. Finally, the demonstration that Ad-vectored vaccines can be administered repeatedly without appreciably losing potency highlights the commercial potential of this new class of vaccine in poultry.

Rapid high-performance liquid chromatographic analysis of adenovirus type 5 particles with a prototype anion-exchange analytical monolith column

To support effective process development there is a requirement for rapid analytical methods that can identify and quantitate adenoviral particles throughout the manufacturing process, from cellular lysate through to purified adenovirus. An anion-exchange high-performance liquid chromatography method for the analysis of adenovirus type 5 (Ad5) particles has been developed using a novel quaternary amine monolithic column (Bio-Monolith QA, Agilent). The developed method separates intact Ad5 from contaminating proteins and DNA, thus allowing analysis of non-purified samples during process development. Regeneration conditions were incorporated to extend the functional life of the column. Once developed, the method was qualified according to performance criteria of repeatability, intermediate precision and linearity. The linear working range of analysis was established between 7.5 x 10(8) to at least 2.4 x 10(10) viral particles (3 x 10(10) to 9.6 x 10(11) viral particles/mL), with a correlation coefficient of 0.9992. Relative standard deviations (RSDs) for intra- and inter-day repeatability and precision for retention time and peak area were less than 1 and 2.5%, respectively.

Clearance of adenovirus by Kupffer cells is mediated by scavenger receptors, natural antibodies, and complement

Kupffer cells (KCs) rapidly remove intravenously injected adenovirus (Ad) vectors from the circulation. A better understanding of the mechanisms involved could suggest strategies to improve Ad gene delivery by suppressing or evading KC uptake. We recently showed that clearance of Ad type 5 vectors by KCs does not involve the interaction of Ad with the well-established Ad receptors, namely, integrins or the coxsackievirus and Ad receptor (J. S. Smith, Z. Xu, J. Tian, S. C. Stevenson, and A. P. Byrnes, Hum. Gene Ther. 19:547-554, 2008). In the current study, we systematically quantified the contributions of various receptors and plasma proteins to the clearance of Ad by KCs. We found that scavenger receptors are a predominant mechanism for the clearance of Ad by KCs. In addition, we found that Ad is opsonized by natural immunoglobulin M antibodies and complement and that these opsonins play a contributory role in the clearance of Ad by KCs. We also examined additional mechanisms that have been postulated to be involved in the clearance of Ad, including the binding of Ad to platelets and vitamin K-dependent coagulation factors, but we found that neither of these were required for the clearance of Ad by KCs.

Scaleable purification of adenovirus vectors

Adenovirus vectors currently are being evaluated in gene delivery studies ranging from prophylactic vaccination to therapeutic gene therapy. The quantity of purified virus required for these studies necessitate that purification methods must shift from classical density gradient ultracentrifugation to scaleable approaches. A methodology is described herein using batch centrifugation, tangential flow ultrafiltration, and chromatography to purify adenovirus particles at a scale of approximately 10(13) viral particles. This method has been demonstrated to easily scale an additional 40-fold. While purification of human adenovirus type 5 is exemplified, modifications are suggested for the purification of other serotypes.

Protection of chickens against avian influenza with non-replicating adenovirus-vectored vaccine

Protective immunity against avian influenza (AI) virus was elicited in chickens by single-dose vaccination with a replication competent adenovirus (RCA)-free human adenovirus (Ad) vector encoding an H7 AI hemagglutinin (AdChNY94.H7). Chickens vaccinated in ovo with an Ad vector encoding an AI H5 (AdTW68.H5) previously described, which were subsequently vaccinated intramuscularly with AdChNY94.H7 post-hatch, responded with robust antibody titers against both the H5 and H7 AI proteins. Antibody responses to Ad vector in ovo vaccination follow a dose-response kinetic. The use of a synthetic AI H5 gene codon optimized to match the chicken cell tRNA pool was more potent than the cognate H5 gene. The use of Ad-vectored vaccines to increase resistance of chicken populations against multiple AI strains could reduce the risk of an avian-originating influenza pandemic in humans.

Sorption processes in ion-exchange chromatography of viruses

Purified viruses are used in gene therapy and vaccine production. Ion-exchange chromatography (IEC) is the most common method for large-scale downstream purification of viruses and proteins. Published IEC protocols provide details for specific separations but not general methods for selecting operating parameters. To make the selection more systematic, we study adenovirus type 5 (Ad5) as a model virus and develop batch uptake and light scattering methods for optimizing the ionic strength and pH of adsorption, as well as providing heuristics for resin geometry. The static capacity for Ad5 was found to go through a maximum with increasing ionic strength. Comparison to a protein-resin system shows that resin capacity for the virus is at least an order of magnitude lower, even on a wide-pore resin. Virus penetration into the wide-pore resin is only partial and the uptake rate is an order of magnitude slower than the uptake onto a narrow-pore resin.

Protective avian influenza in ovo vaccination with non-replicating human adenovirus vector

Protective immunity against avian influenza virus was elicited in chickens by single-dose in ovo vaccination with a non-replicating human adenovirus vector encoding an H5N9 avian influenza virus hemagglutinin. Vaccinated chickens were protected against both H5N1 (89% hemagglutinin homology; 68% protection) and H5N2 (94% hemagglutinin homology; 100% protection) highly pathogenic avian influenza virus challenges. This vaccine can be mass-administered using available robotic in ovo injectors which provide a major advantage over current vaccination regimens. In addition, this class of adenovirus-vectored vaccines can be produced rapidly with improved safety since they do not contain any replication-competent adenoviruses. Furthermore, this mode of vaccination is compatible with epidemiological surveys of natural avian influenza virus infections.