Clarification of vaccines: An overview of filter based technology trends and best practices

Role of Microfiltration Membrane Morphology on Nanoparticle Purification to Enhance Downstream Purification of Viral Vectors

In the rapidly advancing realms of gene therapy and biotechnology, the efficient purification of viral vectors is pivotal for ensuring the safety and efficacy of gene therapies. This study focuses on optimizing membrane selection for viral vector purification by evaluating key properties, including porosity, thickness, pore structure, and hydrophilicity. Notably, we employed adeno-associated virus (AAV)-sized nanoparticles (20 nm), 200 nm particles, and bovine serum albumin (BSA) to model viral vector harvesting. Experimental data from constant pressure normal flow filtration (NFF) at 1 and 2 bar using four commercial flat sheet membranes revealed distinct fouling behaviors. Symmetric membranes predominantly showed internal and external pore blockage, while asymmetric membranes formed a cake layer on the surface. Hydrophilicity exhibited a positive correlation with recovery, demonstrating an enhanced recovery with increased hydrophilicity. Membranes with higher porosity and interpore connectivity showcased superior throughput, reduced operating time, and increased recovery. Asymmetric polyether sulfone (PES) membranes emerged as the optimal choice, achieving ∼100% recovery of AAV-sized particles, an ∼44% reduction in model cell debris (200 nm particles), an ∼35% decrease in BSA, and the fastest operating time of all membranes tested. This systematic investigation into fouling behaviors and membrane properties not only informs optimal conditions for viral vector recovery but also lays the groundwork for advancing membrane-based strategies in bioprocessing.

Efficient and scalable clarification of Orf virus from HEK suspension for vaccine development

The Orf virus (ORFV) is a promising vector platform for the generation of vaccines against infectious diseases and cancer, highlighted by its progression to clinical testing phases. One of the critical steps during GMP manufacturing is the clarification of crude harvest because of the enveloped nature and large size of ORFV. This study presents the first description of ORFV clarification process from a HEK suspension batch process. We examined various filter materials, membrane pore sizes, harvest timings, and nuclease treatments. Employing the Ambr® crossflow system for high-throughput, small-volume experiments, we identified polypropylene-based Sartopure® PP3 filters as ideal. These filters, used in two consecutive stages with reducing pore sizes, significantly enhanced ORFV recovery and addressed scalability challenges. Moreover, we demonstrated that the time of harvest and the use of a nuclease play a decisive role to increase ORFV yields. With these findings, we were able to establish an efficient and scalable clarification process of ORFV derived from a suspension production process, essential for advancing ORFV vaccine manufacturing.

Immunoadsorption as a method of antibody donation during the COVID-19 pandemic

BACKGROUND AND OBJECTIVES

Initial therapeutic efforts to treat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) included the use of plasma from convalescent donors containing anti-SARS-CoV-2 antibodies. High-neutralizing antibody titres are required for therapeutic efficacy. This study aims to show that immunoadsorption followed by tangential flow filtration can be used to obtain antibody concentrates with high-neutralizing capacities.

MATERIALS AND METHODS

Eligible donors (n = 10, five males and three females) underwent immunoadsorption using adsorber columns specific for human antibodies. Glycine-washed out eluates of 1.5 L volume were further concentrated by tangential flow filtration using 30 kDa ultrafiltration membranes. The same membranes were applied for diafiltrations to exchange residual glycine for 0.9% normal saline.

RESULTS

Antibody concentrates were obtained within 8 h from the start of donation and had 4.58 ± 1.95, 3.28 ± 1.28 and 2.02 ± 0.92 times higher total IgG, IgA and IgM concentrations, 3.29 ± 1.62 and 3.74 ± 0.6 times higher SARS-CoV-2 N and S antibody concentrations and 3.85 ± 1.71 times higher SARS-CoV-2 S-specific IgG concentrations compared to the donors' peripheral blood. The specific SARS-CoV-2 virus neutralization capacities increased in all but one concentrate. All antibody concentrates (50-70 mL final volume) passed microbiological tests, were free of hazardous glycine levels and could be stored at -80°C and 4°C for 1 year with 20 ± 3% antibody loss.

CONCLUSION

Immunoadsorption followed by tangential flow filtration is a feasible procedure to collect IgG, IgA and IgM as well as SARS-CoV-2 N- and S-specific antibody concentrates of low volume, free of albumin and coagulation factors. Whether these concentrates can be used as passive immunisation in infected patients remains to be elucidated.

Vaccine process technology-A decade of progress

In the past decade, new approaches to the discovery and development of vaccines have transformed the field. Advances during the COVID-19 pandemic allowed the production of billions of vaccine doses per year using novel platforms such as messenger RNA and viral vectors. Improvements in the analytical toolbox, equipment, and bioprocess technology have made it possible to achieve both unprecedented speed in vaccine development and scale of vaccine manufacturing. Macromolecular structure-function characterization technologies, combined with improved modeling and data analysis, enable quantitative evaluation of vaccine formulations at single-particle resolution and guided design of vaccine drug substances and drug products. These advances play a major role in precise assessment of critical quality attributes of vaccines delivered by newer platforms. Innovations in label-free and immunoassay technologies aid in the characterization of antigenic sites and the development of robust in vitro potency assays. These methods, along with molecular techniques such as next-generation sequencing, will accelerate characterization and release of vaccines delivered by all platforms. Process analytical technologies for real-time monitoring and optimization of process steps enable the implementation of quality-by-design principles and faster release of vaccine products. In the next decade, the field of vaccine discovery and development will continue to advance, bringing together new technologies, methods, and platforms to improve human health.

Adaptation of an rVSV Ebola vaccine purification process for rapid development of a viral vaccine candidate for SARS-CoV-2

During the COVID-19 pandemic, long development timelines typically associated with vaccines were challenged. The urgent need for a vaccine provided a strong driver to reevaluate existing vaccine development approaches. Innovative approaches to regulatory approval were realized, including the use of platform-based technology. In collaboration with the International AIDS Vaccine Initiative, Inc. (IAVI), Merck & Co., Inc., Rahway, NJ, USA rapidly advanced an investigational SARS-CoV-2 vaccine based on the recombinant vesicular stomatitis virus (rVSV) platform used for the Ebola vaccine ERVEBO (rVSV∆G-ZEBOV-GP). An rVSV∆G-SARS-CoV-2 vaccine candidate was generated using the SARS-CoV-2 spike protein to replace the VSV G protein. The purification process development for this vaccine candidate was detailed in this paper. Areas were highlighted where the ERVEBO platform process was successfully adopted and where additional measures were needed for the SARS-CoV-2 vaccine candidate. These included: (i) endonuclease addition directly into the bioreactor prior to harvest, (ii) inclusion of a core-shell chromatography step for improved purification, and (iii) incorporation of a terminal, sterile filtration step to eliminate the need for aseptic, closed processing. High infectious virus titers were achieved in Phase 3 clinical drug substance (>108 PFU mL-1 ), and process consistency was demonstrated across four large scale batches that were completed in 6 months from clone selection.

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.

Downstream process design for Gag HIV-1 based virus-like particles

Virus-like particles-based vaccines have been gaining interest in recent years. The manufacturing of these particles includes their production by cell culture followed by their purification to meet the requirements of its final use. The presence of host cell extracellular vesicles represents a challenge for better virus-like particles purification, because both share similar characteristics which hinders their separation. The present study aims to compare some of the most used downstream processing technologies for capture and purification of virus-like particles. Four steps of the purification process were studied, including a clarification step by depth filtration and filtration, an intermediate step by tangential flow filtration or multimodal chromatography, a capture step by ion exchange, heparin affinity and hydrophobic interaction chromatography and finally, a polishing step by size exclusion chromatography. In each step, the yields were evaluated by percentage of recovery of the particles of interest, purity, and elimination of main contaminants. Finally, a complete purification train was implemented using the best results obtained in each step. A final concentration of 1.40 × 1010 virus-like particles (VLPs)/mL with a purity of 64% after the polishing step was achieved, with host cell DNA and protein levels complaining with regulatory standards, and an overall recovery of 38%. This work has resulted in the development of a purification process for HIV-1 Gag-eGFP virus-like particles suitable for scale-up.

A robust and efficient alluvial filtration method for the clarification of adeno-associated viruses from crude cell lysates

Adeno-associated virus (AAV) based vectors have recently been gaining importance as DNA delivery systems. Efficient downstream processing of AAV remains a major challenge as serotypes differ in physicochemical properties, making it difficult to design uniform purification processes. Clarification of AAV is an especially critical step. Harvesting of AAV, like other viruses, often requires cell lysis, resulting in a difficult-to-filter cell lysate. In this study, we evaluated the applicability of diatomaceous earth (DE) as a filter aid for clarification of AAV crude cell lysates. DE filtration proved to be a viable clarification method for AAV2, AAV5 and AAV8. Based on a design of experiment approach, the DE concentration was identified as the main factor influencing AAV particle loss. The loss of AAV during DE filtration was limited to <2% by maintaining the DE quantity below 0.181mg DE/10¹⁰ AAV. Use of DE reduced manual handling time 3-fold and increased the filter capacity 3.5-fold compared to filtration combined with a prior centrifugation step. Moreover, we showed that the DE type had only a minor influence on the filtration performance. This study demonstrated that filtration with DE as a filter aid is an efficient clarification method for different AAV serotypes.

Incubation Temperature and Period During Denarase Treatment and Microfiltration Affect the Yield of Recombinant Adenoviral Vectors During Downstream Processing

Adenoviral vectors (AV) are commonly used as vaccine and gene therapy vehicles because of their ease of construction, ability to grow to high titers in the large-scale production process, and safety for human applications. However, the efficiency rate of downstream processes for adenoviral vectors still varies greatly. In the current study, we aimed to investigate the effect of the downstream treatment protocol and microfiltration of the harvested upstream material on viral vector yield. We compared the performance of the repeated freeze-thaw (RFT) and the Tween-20 detergent lysis (DLT) methods. In addition, the effects of the cell lysis method, incubation temperature, and time on viral yield were investigated. The samples were incubated at either room temperature or 37 °C for 1-, 2-, and 4-h periods. Samples were filtered with PES and SFCA membrane. Virus yield and infectivity were assayed by qPCR and immuno-titration. In conclusion, our results suggest that 2-h incubation gives the best results when incubated at 37 °C for denarase activity when Tween-20 is used for virus recovery. If the room temperature is preferred, 4-h incubation could be preferred. A phase 1 clinical trial (NCT05526183, January 21, 2022) was started with the recombinant adenovirus used in the study.

Evaluation of parameters for efficient purification and long-term storage of herpes simplex virus-based vectors

Replication competent oncolytic herpes simplex virus (HSV) vectors have been used extensively to treat solid tumors with promising results. However, highly defective HSV vectors will be needed for applications that require sustained therapeutic gene expression in the absence of vector-related toxicity or inflammation. These vectors require complementing cell lines for their manufacture, creating significant challenges to achieve high yields of infectious virus particles. We recently described an improved upstream process for the production of a non-cytotoxic HSV vector for gene therapy applications. Here, we sought to optimize the downstream conditions for purification and long-term storage of the same vector, JΔNI5. We compared different methods to remove cellular impurities and concentrate the vector by monitoring both physical and biological titers, resulting in the establishment of optimal conditions for vector production. To optimize the long-term storage parameters for non-cytotoxic HSV vectors, we evaluated vector stability at low temperature and sensitivity to freeze-thaw cycles. We report that suboptimal purification and storage methods resulted in loss of vector viability. Our results describe effective and reproducible protocols for purification and storage of HSV vectors for pre-clinical studies.

Asymmetric depth-filtration: A versatile and scalable method for high-yield isolation of extracellular vesicles with low contamination

We developed a novel asymmetric depth filtration (DF) approach to isolate extracellular vesicles (EVs) from biological fluids that outperforms ultracentrifugation and size‐exclusion chromatography in purity and yield of isolated EVs. By these metrics, a single‐step DF matches or exceeds the performance of multistep protocols with dedicated purification procedures in the isolation of plasma EVs. We demonstrate the selective transit and capture of biological nanoparticles in asymmetric pores by size and elasticity, low surface binding to the filtration medium, and the ability to cleanse EVs held by the filter before their recovery with the reversed flow all contribute to the achieved purity and yield of preparations. We further demonstrate the method's versatility by applying it to isolate EVs from different biofluids (plasma, urine, and cell culture growth medium). The DF workflow is simple, fast, and inexpensive. Only standard laboratory equipment is required for its implementation, making DF suitable for low‐resource and point‐of‐use locations. The method may be used for EV isolation from small biological samples in diagnostic and treatment guidance applications. It can also be scaled up to harvest therapeutic EVs from large volumes of cell culture medium.

Evaluation of Host Cell Impurity Effects on the Performance of Sterile Filtration Processes for Therapeutic Viruses

Efficient downstream processing represents a significant challenge in the rapidly developing field of therapeutic viruses. While it is known that the terminal sterile filtration step can be a major cause of product loss, there is little known about the effect of host cell impurities (DNA and protein) on filtration performance. In this study, fractions of relatively pure Vero host cell protein and DNA were spiked into a highly pure preparation of vesicular stomatitis virus (VSV). Then, the resulting solutions were sterile filtered using two commercially available 0.22 µm rated microfiltration membranes. A combination of transmembrane pressure measurements, virus recovery measurements, and post-filtration microscopy images of the microfiltration membranes was used to evaluate the sterile filtration performance. It was found that increasing the amount of host cell protein from approximately 1 µg/mL (in the un-spiked VSV preparation) to 25 µg/mL resulted in a greater extent of membrane fouling, causing the VSV recovery to decrease from 89% to 65% in experiments conducted with the highly asymmetric Express PLUS PES membrane and to go as low as 48% in experiments conducted with the symmetric Durapore PVDF membrane. Similar effects were not seen when bovine serum albumin, a common model protein used in filtration studies, was spiked into the VSV preparation, which indicates that the sterile filtration performance is critically dependent on the complex composition of the mixture of host cell proteins rather than the presence of any protein. The results presented in this work provide important insights into the role of host cell impurities on the performance of sterile filtration processes for therapeutic viruses.

Production- and Purification-Relevant Properties of Human and Murine Cytomegalovirus

There is a large unmet need for a prophylactic vaccine against human cytomegalovirus (HCMV) to combat the ubiquitous infection that is ongoing with this pathogen. A vaccination against HCMV could protect immunocompromised patients and prevent birth defects caused by congenital HCMV infections. Moreover, cytomegalovirus (CMV) has a number of features that make it a very interesting vector platform for gene therapy. In both cases, preparation of a highly purified virus is a prerequisite for safe and effective application. Murine CMV (MCMV) is by far the most studied model for HCMV infections with regard to the principles that govern the immune surveillance of CMVs. Knowledge transfer from MCMV and mice to HCMV and humans could be facilitated by better understanding and characterization of the biological and biophysical properties of both viruses. We carried out a detailed investigation of HCMV and MCMV growth kinetics as well as stability under the influence of clarification and different storage conditions. Further, we investigated the possibilities to concentrate and purify both viruses by ultracentrifugation and ion-exchange chromatography. Defective enveloped particles were not separately analyzed; however, the behavior of exosomes was examined during all experiments. The effectiveness of procedures was monitored using CCID₅₀ assay, Nanoparticle tracking analysis, ELISA for host cell proteins, and quantitative PCR for host cell DNA. MCMV generally proved to be more robust in handling. Despite its greater sensitivity, HCMV was efficiently (100% recovery) purified and concentrated by anion-exchange chromatography using QA monolithic support. The majority of the host genomic DNA as well as most of the host cell proteins were removed by this procedure.

Evaluation of a downstream process for the recovery and concentration of a Cell-Culture-Derived rVSV-Spike COVID-19 vaccine candidate

rVSV-Spike (rVSV-S) is a recombinant viral vaccine candidate under development to control the COVID-19 pandemic and is currently in phase II clinical trials. rVSV-S induces neutralizing antibodies and protects against SARS-CoV-2 infection in animal models. Bringing rVSV-S to clinical trials required the development of a scalable downstream process for the production of rVSV-S that can meet regulatory guidelines. The objective of this study was the development of the first downstream unit operations for cell-culture-derived rVSV-S, namely, the removal of nucleic acid contamination, the clarification and concentration of viral harvested supernatant, and buffer exchange. Retaining the infectivity of the rVSV-S during the downstream process was challenged by the shear sensitivity of the enveloped rVSV-S and its membrane protruding spike protein. Through a series of screening experiments, we evaluated and established the required endonuclease treatment conditions, filter train composition, and hollow fiber-tangential flow filtration parameters to remove large particles, reduce the load of impurities, and concentrate and exchange the buffer while retaining rVSV-S infectivity. The combined effect of the first unit operations on viral recovery and the removal of critical impurities was examined during scale-up experiments. Overall, approximately 40% of viral recovery was obtained and the regulatory requirements of less than 10 ng host cell DNA per dose were met. However, while 86–97% of the host cell proteins were removed, the regulatory acceptable HCP levels were not achieved, requiring subsequent purification and polishing steps. The results we obtained during the scale-up experiments were similar to those obtained during the screening experiments, indicating the scalability of the process. The findings of this study set the foundation for the development of a complete downstream manufacturing process, requiring subsequent purification and polishing unit operations for clinical preparations of rVSV-S.

A Four-Step Purification Process for Gag VLPs: From Culture Supernatant to High-Purity Lyophilized Particles

Gag-based virus-like particles (VLPs) have high potential as scaffolds for the development of chimeric vaccines and delivery strategies. The production of purified preparations that can be preserved independently from cold chains is highly desirable to facilitate distribution and access worldwide. In this work, a nimble purification has been developed, facilitating the production of Gag VLPs. Suspension-adapted HEK 293 cells cultured in chemically defined cell culture media were used to produce the VLPs. A four-step downstream process (DSP) consisting of membrane filtration, ion-exchange chromatography, polishing, and lyophilization was developed. The purification of VLPs from other contaminants such as host cell proteins (HCP), double-stranded DNA, or extracellular vesicles (EVs) was confirmed after their DSP. A concentration of 2.2 ± 0.8 × 10⁹ VLPs/mL in the lyophilized samples was obtained after its storage at room temperature for two months. Morphology and structural integrity of purified VLPs was assessed by cryo-TEM and NTA. Likewise, the purification methodologies proposed here could be easily scaled up and applied to purify similar enveloped viruses and vesicles.

A high cell density perfusion process for Modified Vaccinia virus Ankara production: Process integration with inline DNA digestion and cost analysis

By integrating continuous cell cultures with continuous purification methods, process yields and product quality attributes have been improved over the last 10 years for recombinant protein production. However, for the production of viral vectors such as Modified Vaccinia virus Ankara (MVA), no such studies have been reported although there is an increasing need to meet the requirements for a rising number of clinical trials against infectious or neoplastic diseases. Here, we present for the first time a scalable suspension cell (AGE1.CR.pIX cells) culture-based perfusion process in bioreactors integrating continuous virus harvesting through an acoustic settler with semi-continuous chromatographic purification. This allowed obtaining purified MVA particles with a space-time yield more than 600% higher for the integrated perfusion process (1.05 × 10¹¹ TCID₅₀ /L_bioreactor /day) compared to the integrated batch process. Without further optimization, purification by membrane-based steric exclusion chromatography resulted in an overall product recovery of 50.5%. To decrease the level of host cell DNA before chromatography, a novel inline continuous DNA digestion step was integrated into the process train. A detailed cost analysis comparing integrated production in batch versus production in perfusion mode showed that the cost per dose for MVA was reduced by nearly one-third using this intensified small-scale process.

Critical Assessment of Purification and Analytical Technologies for Enveloped Viral Vector and Vaccine Processing and Their Current Limitations in Resolving Co-Expressed Extracellular Vesicles

Viral vectors and viral vaccines are invaluable tools in prevention and treatment of diseases. Many infectious diseases are controlled using vaccines designed from subunits or whole viral structures, whereas other genetic diseases and cancers are being treated by viruses used as vehicles for delivering genetic material in gene therapy or as therapeutic agents in virotherapy protocols. Viral vectors and vaccines are produced in different platforms, from traditional embryonated chicken eggs to more advanced cell cultures. All these expression systems, like most cells and cellular tissues, are known to spontaneously release extracellular vesicles (EVs). EVs share similar sizes, biophysical characteristics and even biogenesis pathways with enveloped viruses, which are currently used as key ingredients in a number of viral vectors and licensed vaccine products. Herein, we review distinctive features and similarities between EVs and enveloped viruses as we revisit the downstream processing steps and analytical technologies currently implemented to produce and document viral vector and vaccine products. Within a context of well-established viral vector and vaccine safety profiles, this review provides insights on the likely presence of EVs in the final formulation of enveloped virus products and discusses the potential to further resolve and document these components.

Glycoconjugation of Shigella flexneri type 2a O-polysaccharide with CRM197 as a potential vaccine candidate for shigellosis

Shigellosis, a diarrheal disorder caused by an entero-invasive bacterium Shigella, is a major concern among children often leading to mortality. As most of these strains have developed universal antibiotic resistance, the development of a vaccine is crucial in combating the infection. The O-specific polysaccharide (O-PSs) from S. flexneri type 2a is considered to be the major disease-causing antigen in shigellosis. Therefore, the O-PSs conjugated with carrier proteins, can serve as a potential high molecular weight vaccine candidate. Accordingly, in the present study, O-PS extracted from S. flexneri 2a is conjugated with Cross-Reactive Material (CRM₁₉₇), a non-toxic mutant of diphtheria toxin. We derivatized CRM₁₉₇ and O-PS separately with adipic acid dihydrazide (ADH) and reacted with their counterparts to probe the conjugation efficacy. Among the two strategies, the CRM₁₉₇-ADH treated with O-PS has yielded a stable glycoconjugate of 311 kDa. The conjugation efficiency has been probed by estimating the free protein, free O-PS and O-PS:CRM₁₉₇ ratio using slot-blot, size exclusion and high-performance anion exchange chromatography techniques. The conjugate exhibited enhanced shelf-life of three months. The cytotoxicity studies with Vero/MRC-5 cells have confirmed the non-toxicity of the conjugate, which makes the glycoconjugate a potential vaccine candidate for shigellosis.

Cell-based influenza vaccine: current production, halal status assessment, and recommendations towards Islamic-compliant manufacturing

Influenza virus is a life-threatening pathogen that infects millions of people every year, with annual mortality in the hundreds of thousands. The scenario for controlling infection has worsened with increasing numbers of vaccine hesitancy cases reported worldwide due to objections on safety, religious and other grounds. Uses of haram (impermissible) and mashbooh (doubtful) ingredients in vaccine production has raised doubts among Muslim consumers and consequently stimulated serious vaccine hesitancy. To address this major problem, we have reviewed and recommended some alternatives appropriate for manufacturing cell-based influenza vaccine which comply with Islamic laws and consumers' needs. Intensive assessments of current influenza vaccine production in both scientific and Islamic views have led to the identification of four main ingredients deemed impermissible in novel sharia-compliant (approved by Islamic laws) vaccine manufacturing. Only some of these impermissible components could be replaced with halal (permissible) alternatives, while others remain impermissible due to unavailability and unsuitability.

Osmolyte enhanced aqueous two-phase system for virus purification

Due to the high variation in viral surface properties, a platform method for virus purification is still lacking. A potential alternative to the high-cost conventional methods is aqueous two-phase systems (ATPSs). However, optimizing virus purification in ATPS requires a large experimental design space, and the optimized systems are generally found to operate at high ATPS component concentrations. The high concentrations capitalize on hydrophobic and electrostatic interactions to obtain high viral particle yields. This study investigated using osmolytes as driving force enhancers to reduce the high concentration of ATPS components while maintaining high yields. The partitioning behavior of porcine parvovirus (PPV), a nonenveloped mammalian virus, and human immunodeficiency virus-like particle (HIV-VLP), a yeast-expressed enveloped VLP, were studied in a polyethylene glycol (PEG) 12 kDa-citrate system. The partitioning of the virus modalities was enhanced by osmoprotectants glycine and betaine, while trimethylamine N-oxide was ineffective for PPV. The increased partitioning to the PEG-rich phase pertained only to viruses, resulting in high virus purification. Recoveries were 100% for infectious PPV and 92% for the HIV-VLP, with high removal of the contaminant proteins and more than 60% DNA removal when glycine was added. The osmolyte-induced ATPS demonstrated a versatile method for virus purification, irrespective of the expression system.

Prefiltration enhances performance of sterile filtration for glycoconjugate vaccines

Recent studies have reported very low capacity during sterile filtration of glycoconjugate vaccines due to rapid fouling of the sterile filter. The objective of this study was to explore the potential for significantly increasing the capacity of the sterile filter through the use of an appropriate prefilter. Data were obtained using prefilters with different pore size and chemistry, with the sterile filtration performed at constant filtrate flux using 0.22 μm nominal pore size Durapore® polyvinylidene difluoride membranes. Prefiltration through 5 μm pore size Durapore® or Nylon prefilters nearly eliminated the fouling of the sterile filter, leading to more than a 100-fold reduction in the rate of pressure increase for the sterile filter. This dramatic improvement in sterile filter performance was due to the removal of large components (greater than 1 μm in size) as confirmed by dynamic light scattering. These results demonstrate the potential of using large pore size prefilters to significantly enhance the performance of the sterile filtration process for the production of important glycoconjugate vaccines.

Protein Adsorption on Core-shell Particles: Comparison of Capto™ Core 400 and 700 Resins

Structural and functional characteristics of the two core-shell resins Capto™ Core 400 and 700, which are useful for the flow-through purification of bioparticles such as viruses, viral vectors, and vaccines, are compared using bovine serum albumin (BSA) and thyroglobulin (Tg) as models for small and large protein contaminants. Both resins are agarose-based and contain an adsorbing core surrounded by an inert shell. Although shell thicknesses are comparable (3.6 and 4.2 µm for Capto Core 400 and 700, respectively), the two resins differ substantially in pore size (pore radii of 19 and 50 nm, respectively). Because of the smaller pores and higher surface area, the BSA binding capacity of Capto Core 400 is approximately double that of Capto Core 700. However, for the much larger Tg, the attainable capacity is substantially larger for Capto Core 700. Mass transfer in both resins is affected by diffusional resistances through the shell and within the adsorbing core. For BSA, core and shell effective pore diffusivities are about 0.25 × 10^-7 and 0.6 × 10^-7 cm²/s, respectively, for Capto Core 400, and about 1.6 × 10^-7 and 2.6 × 10^-7 cm²/s, respectively, for Capto Core 700. These values decrease dramatically for Tg to 0.022 × 10^-7 and 0.088 × 10^-7 cm²/s and to 0.13 × 10^-7 and 0.59 × 10^-7 cm²/s for Capto Core 400 and 700, respectively. Adsorbed Tg further hinders diffusion of BSA in both resins. Column measurements show that, despite the higher static capacity of Capto Core 400 for BSA, the dynamic binding capacity is greater for Capto Core 700 as a result of its faster kinetics. However, some of this advantage is lost if the feed is a mixture of BSA and Tg since, in this case, Tg binding leads to greater diffusional hindrance for BSA.

Downstream processing for influenza vaccines and candidates: An update

Seasonal and pandemic influenza outbreaks present severe health and economic burdens. To overcome limitations on influenza vaccines' availability and effectiveness, researchers chase universal vaccines providing broad, long-lasting protection against multiple influenza subtypes, and including pandemic ones. Novel influenza vaccine designs are under development, in clinical trials, or reaching the market, namely inactivated, or live-attenuated virus, virus-like particles, or recombinant antigens, searching for improved effectiveness; all these bring downstream processing (DSP) new challenges. Having to deal with new influenza strains, including pandemics, requires shorter development time, driving the development of faster bioprocesses. To cope with better upstream processes, new regulatory demands for quality and safety, and cost reduction requirements, new unit operations and integrated processes are increasing DSP efficiency for novel vaccine formats. This review covers recent advances in DSP strategies of different influenza vaccine formats. Focus is given to the improvements on relevant state-of-the-art unit operations, from harvest and clarification to purification steps, ending with sterile filtration and formulation. The development of more efficient unit operations to cope with biophysical properties of the new candidates is discussed: emphasis is given to the design of new stationary phases, 3D printing approaches, and continuous processing tools, such as continuous chromatography. The impact of the production platforms and vaccine designs on the downstream operations for the different influenza vaccine formats approved for this season are highlighted.

Sterilization methods of liposomes: Drawbacks of conventional methods and perspectives

Liposomes are targeted drug delivery systems that are of great pharmaceutical and therapeutic interest. Parenteral route is the main way used for liposome administration. In this case, their sterility is a requirement. However, due to the particular sensitivity of liposomes and their tendency to physicochemical alterations, their sterilization remains a real challenge. Conventional sterilization methods such as heat, ethylene oxide, ultraviolet and gamma irradiations are considered as unsuitable for liposome sterilization and the recommended methods for obtaining sterility of liposomes are filtration and aseptic manufacturing. Unfortunately, these recommended methods are not without limitations. This review outlines the difficulties associated with the use of these different classical methods for obtaining liposome sterility. The effects on liposome physicochemical and biopharmaceutical characteristics as well as efficacy, toxicity and practical problems of these sterilization techniques have been discussed. The search for an alternative method being therefore necessary, the applicability of supercritical carbon dioxide (ScCO₂) technology, which is nowadays a promising strategy for the sterilization of sensitive products such as liposomes, is also examined. It appears from this analysis that ScCO₂ could effectively be an interesting alternative to achieve sterility of liposomes, but for this, sterilization assays including challenge tests and optimization studies are needed.

A new simplified clarification approach for lentiviral vectors using diatomaceous earth improves throughput and safe handling

Lentiviral vectors have proven their great potential to serve as a DNA delivery tool for gene modified cell therapy and gene therapy applications. The downstream processing of these vectors is however still a great challenge, particularly because of the low stability of the virus. Harvesting and clarification are critical and until now insufficiently characterized steps for lentivirus processing. To address this bottleneck, we analyzed whether lentiviral vectors produced by transient transfection of HEK293 T/17 SF suspension cells can be efficiently clarified with a lab-scale method with the filter aid diatomaceous earth (DE) and bioburden reducing membrane filters achieving high lentivirus recoveries. Using a design of experiment approach we found that higher DE concentrations are advantageous for a higher turbidity reduction and shorter filtration times, but at the same time LV titer decreases with increasing DE concentration. A DE concentration of 9 g/L was identified with a DoE as a robust set-point. Clarification with DE was compared with for lab-scale traditionally employed centrifugation and subsequent bioburden reduction filtration of viral vectors. The use of DE allows to perform a harvest and clarification process, which does not only facilitate faster and safer virus handling, but enables a lower material consumption due to the extremely increased filter capacity, thus representing an efficient and robust lab-scale clarification process.

Virus recovery by tangential flow filtration: A model to guide the design of a sample concentration process

A simple model is developed to describe the instantaneous (r_v ) and cumulative (R_v ) recovery of viruses from water during sample concentration by tangential flow filtration in the regime of constant water recovery, r. A figure of merit, M = r_v r, is proposed as an aggregate performance metric that captures both the efficiency of virus recovery and the speed of sample concentration. We derive an expression for virus concentration in the sample as a function of filtration time with the rate-normalized virus loss, η = 1 - r v r , as a parameter. A practically relevant case is considered when the rate of virus loss is proportional to the permeation-driven mass flux of viruses to the membrane: d m ad dt ∼ Q p C f ≫ Q p C p . In this scenario, the instantaneous recovery is constant, the cumulative recovery is decreasing as a power function of time, R v = 1 - Q p V 0 t η , η mediates the trade-off between r and r_v , and M is maximized at r = r opt = 1 2 η . The proposed model can guide the design of the sample concentration process and serve as a framework for quantification and interlaboratory comparison of experimental data on virus recovery.

Evaluation of a sterile filtration process for viral vaccines using a model nanoparticle suspension

There is growing interest in the development of new vaccines based on live-attenuated viruses (LAVs) and virus-like particles. The large size of these vaccines, typically 100-400 nm, significantly complicates the use of sterile filtration. The objectives of this study are to examine the performance of several commercial sterile filters for filtration of a cytomegalovirus vaccine candidate (referred to as the LAV) and to develop and evaluate the use of a model nanoparticle suspension to perform a more quantitative assessment. Data obtained with a mixture of 200- and 300-nm fluorescent particles provided yield and pressure profiles that captured the behavior of the viral vaccine. This included the excellent performance of the Sartorius Sartobran P filter, which provided greater than 80% yield of both the vaccine and model particles even though the average particle size was more than 250 nm. The particle yield for the Sartobran P was independent of filtrate flux above 200 L/m² /h, but increased with increasing particle concentration, varying from less than 10% at concentrations around 10⁷  particles/ml to more than 80% at concentrations above 10¹⁰  particles/ml due to saturation of particle capture/binding sites within the filter. These results provide important insights into the factors controlling transmission and fouling during sterile filtration of large vaccine products.

Purification Methods and the Presence of RNA in Virus Particles and Extracellular Vesicles

The fields of extracellular vesicles (EV) and virus infections are marred in a debate on whether a particular mRNA or non-coding RNA (i.e., miRNA) is packaged into a virus particle or copurifying EV and similarly, whether a particular mRNA or non-coding RNA is contained in meaningful numbers within an EV. Key in settling this debate, is whether the purification methods are adequate to separate virus particles, EV and contaminant soluble RNA and RNA:protein complexes. Differential centrifugation/ultracentrifugation and precipitating agents like polyethylene glycol are widely utilized for both EV and virus purifications. EV are known to co-sediment with virions and other particulates, such as defective interfering particles and protein aggregates. Here, we discuss how encased RNAs from a heterogeneous mixture of particles can be distinguished by different purification methods. This is particularly important for subsequent interpretation of whether the RNA associated phenotype is contributed solely by virus or EV particles or a mixture of both. We also discuss the discrepancy of miRNA abundance in EV from different input material.

Safety Profile of a Multi-Antigenic DNA Vaccine Against Hepatitis C Virus

Despite direct acting antivirals (DAAs) curing >95% of individuals infected with hepatitis C (HCV), in order to achieve the World Health Organization HCV Global Elimination Goals by 2030 there are still major challenges that need to be overcome. DAAs alone are unlikely to eliminate HCV in the absence of a vaccine that can limit viral transmission. Consequently, a prophylactic HCV vaccine is necessary to relieve the worldwide burden of HCV disease. DNA vaccines are a promising vaccine platform due to their commercial viability and ability to elicit robust T-cell-mediated immunity (CMI). We have developed a novel cytolytic DNA vaccine that encodes non-structural HCV proteins and a truncated mouse perforin (PRF), which is more immunogenic than the respective canonical DNA vaccine lacking PRF. Initially we assessed the ability of the HCV pNS3-PRF and pNS4/5-PRF DNA vaccines to elicit robust long-term CMI without any adverse side-effects in mice. Interferon-γ (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) assay was used to evaluate CMI against NS3, NS4 and NS5B in a dose-dependent manner. This analysis showed a dose-dependent bell-curve of HCV-specific responses in vaccinated animals. We then thoroughly examined the effects associated with reactogenicity of cytolytic DNA vaccination with the multi-antigenic HCV DNA vaccine (pNS3/4/5B). Hematological, biochemical and histological studies were performed in male Sprague Dawley rats with a relative vaccine dose 10–20-fold higher than the proposed dose in Phase I clinical studies. The vaccine was well tolerated, and no toxicity was observed. Thus, the cytolytic multi-antigenic DNA vaccine is safe and elicits broad memory CMI.

Opportunities to debottleneck the downstream processing of the oncolytic measles virus

Oncolytic viruses (including measles virus) offer an alternative approach to reduce the high mortality rate of late-stage cancer. Several measles virus strains infect and lyse cancer cells efficiently, but the broad application of this therapeutic concept is hindered by the large number of infectious particles required (10⁸-10¹² TCID₅₀ per dose). The manufacturing process must, therefore, achieve high titers of oncolytic measles virus (OMV) during upstream production and ensure that the virus product is not damaged during purification by applying appropriate downstream processing (DSP) unit operations. DSP is currently a production bottleneck because there are no specific platforms for OMV. Infectious OMV must be recovered as intact, enveloped particles, and host cell proteins and DNA must be reduced to acceptable levels to meet regulatory guidelines that were developed for virus-based vaccines and gene therapy vectors. Handling such high viral titers and process volumes is technologically challenging and expensive. This review considers the state of the art in OMV purification and looks at promising DSP technologies. We discuss here the purification of other enveloped viruses where such technologies could also be applied to OMV. The development of DSP technologies tailored for enveloped viruses is necessary to produce sufficient titers for virotherapy, which could offer hope to millions of patients suffering from incurable cancer.

Recent Developments in Bioprocessing of Recombinant Proteins: Expression Hosts and Process Development

Infectious diseases, along with cancers, are among the main causes of death among humans worldwide. The production of therapeutic proteins for treating diseases at large scale for millions of individuals is one of the essential needs of mankind. Recent progress in the area of recombinant DNA technologies has paved the way to producing recombinant proteins that can be used as therapeutics, vaccines, and diagnostic reagents. Recombinant proteins for these applications are mainly produced using prokaryotic and eukaryotic expression host systems such as mammalian cells, bacteria, yeast, insect cells, and transgenic plants at laboratory scale as well as in large-scale settings. The development of efficient bioprocessing strategies is crucial for industrial production of recombinant proteins of therapeutic and prophylactic importance. Recently, advances have been made in the various areas of bioprocessing and are being utilized to develop effective processes for producing recombinant proteins. These include the use of high-throughput devices for effective bioprocess optimization and of disposable systems, continuous upstream processing, continuous chromatography, integrated continuous bioprocessing, Quality by Design, and process analytical technologies to achieve quality product with higher yield. This review summarizes recent developments in the bioprocessing of recombinant proteins, including in various expression systems, bioprocess development, and the upstream and downstream processing of recombinant proteins.

Current challenges in biotherapeutic particles manufacturing

Introduction: The development of novel complex biotherapeutics led to new challenges in biopharmaceutical industry. The potential of these particles has been demonstrated by the approval of several products, in the different fields of gene therapy, oncolytic therapy, and tumor vaccines. However, their manufacturing still presents challenges related to the high dosages and purity required.Areas covered: The main challenges that biopharmaceutical industry faces today and the most recent developments in the manufacturing of different biotherapeutic particles are reported here. Several unit operations and downstream trains to purify virus, virus-like particles and extracellular vesicles are described. Innovations on the different purification steps are also highlighted with an eye on the implementation of continuous and integrated processes.Expert opinion: Manufacturing platforms that consist of a low number of unit operations, with higher-yielding processes and reduced costs will be highly appreciated by the industry. The pipeline of complex therapeutic particles is expanding and there is a clear need for advanced tools and manufacturing capacity. The use of single-use technologies, as well as continuous integrated operations, are gaining ground in the biopharmaceutical industry and should be supported by more accurate and faster analytical methods.

An efficient large-scale refolding technique for recovering biologically active recombinant human FGF-21 from inclusion bodies

Fibroblast growth factor 21 (FGF-21) is an important regulator in glycolipid metabolism that is a promising drug candidate for treatment of diabetes and obesity. However, the productivity of recombinant hFGF-21 (rhFGF-21) in Escherichia coli (E. coli) is relatively low, which limits its clinical application. To meet the clinical demand and control the production cost, rhFGF-21 proteins were expressed in inclusion bodies (IBs) form in Rosetta (DE3) by high cell density fermentation in 50-L scale. Hollow fiber membrane filtration technology was used to enrich the bacteria, wash, denature and refold the IBs in the current report. The renatured proteins were purified by two-step affinity chromatography. Authenticity of the purified rhFGF-21 was confirmed by the N-and C-terminal sequence, disulfide bond composition and molecular weight analyses. Results showed that the average target protein and recovery of rhFGF-21 expressed in IBs form of three batches were more than those of the soluble form. Both the rhFGF-21 proteins from the two forms showed equal potency in improving the glucose uptake in HepG2 cells and anti-diabetic effect in db/db mice. In this study, an efficient method for preparation of FGF-21 was established. This novel process provides an important technical basis for the large-scale production of rhFGF-21.

An effective, simple and low-cost pretreatment for culture clarification in tetanus toxoid production

Chemically inactivated tetanus toxin (tetanus toxoid, TT), purified from cultures of a virulent Clostridium tetani strain, is the active pharmaceutical ingredient of anti-tetanus vaccines. Culture clarification for TT production and is usually performed by filtration-based techniques. Final clarification of the culture supernatant is achieved by passage through 0.2 µm pore size filtering membranes. Large particles removal (primary clarification) before final filtration (secondary clarification) reduces costs of the overall clarification process. With this aim, chitosan-induced particle aggregation was assessed as an alternative for primary clarification. Three chitosan variants were tested with similar results. Optimal clarification of culture supernatant was achieved by the addition of 8 mg chitosan per l of culture. Extrapolation analysis of filter sizing results indicate that 100 l of chitosan-treated supernatant can be finally filtered with a 0.6 m2 normal filtration cartridge of 0.45 + 0.2 µm pore size. The clarified material is compatible with current standard downstream processing techniques for TT purification. Thus, chitosan-induced particle aggregation is a suitable operation for primary clarification.

A Simplified and Efficient Process for Insulin Production in Pichia pastoris

A significant barrier to insulin is affordability. In this manuscript we describe improvements to key steps in the insulin production process in Pichia pastoris that reduce cost and time. The strategy for recovery and processing of human insulin precursor has been streamlined to two steps from bioreactor to the transpeptidation reaction. In the first step the insulin precursor secreted during the methanol induction phase is recovered directly from the culture broth using Tangential Flow Filtration with a Prostak^™ module eliminating the laborious and time-consuming multi-step clarification, including centrifugation. In the second step the protein is applied at very high loadings on a cation exchange resin and eluted in a mixture of water and ethanol to obtain a concentrated insulin precursor, suitable for use directly in the transpeptidation reaction. Overall the yield from insulin precursor to human insulin was 51% and consisted of three purification chromatography steps. In addition we describe a method for recovery of the excess of H-Thr(tBu)-OtBu from the transpeptidation reaction mixture, one of the more costly reagents in the process, along with its successful reuse.

Integrated molecular and bioprocess engineering for bacterially produced immunogenic modular virus-like particle vaccine displaying 18 kDa rotavirus antigen

A high global burden of rotavirus disease and the unresolved challenges with the marketed rotavirus vaccines, particularly in the developing world, have ignited efforts to develop virus-like particle (VLP) vaccines for rotavirus. While rotavirus-like particles comprising multiple viral proteins can be difficult to process, modular VLPs presenting rotavirus antigenic modules are promising alternatives in reducing process complexity and cost. In this study, integrated molecular and bioprocess engineering approaches were used to simplify the production of modular murine polyomavirus capsomeres and VLPs presenting a rotavirus 18 kDa VP8* antigen. A single construct was generated for dual expression of non-tagged murine polyomavirus capsid protein VP1 and modular VP1 inserted with VP8*, for co-expression in Escherichia coli. Co-expressed proteins assembled into pentameric capsomeres in E. coli. A selective salting-out precipitation and a polishing size exclusion chromatography step allowed the recovery of stable modular capsomeres from cell lysates at high purity, and modular capsomeres were successfully translated into modular VLPs when assembled in vitro. Immunogenicity study in mice showed that modular capsomeres and VLPs induced high levels of VP8*-specific antibodies. Our results demonstrate that a multipronged synthetic biology approach combining molecular and bioprocess engineering enabled simple and low-cost production of highly immunogenic modular capsomeres and VLPs presenting conformational VP8* antigenic modules. This strategy potentially provides a cost-effective production route for modular capsomere and VLP vaccines against rotavirus, highly suitable to manufacturing economics for the developing world. Biotechnol. Bioeng. 2017;114: 397-406. © 2016 Wiley Periodicals, Inc.