Hybrid modeling of an ultracentrifugation process for separation of full and empty adeno-associated virus particles.

Ultracentrifugation is an attractive method for separating full and empty capsids, exploiting their density difference. Changes of the serotype/capsid, density of loading material, or the genetic information contained in the adeno-associated viruses (AAVs) require the adaptation of the harvesting parameters and the density gradient loaded onto the centrifuge. To streamline these adaptations, a mathematical model could support the design and testing of operating conditions.Here, hybrid models, which combine empirical functions with artificial neural networks, are proposed to describe the separation of full and empty capsids as a function of material and operational parameters, i.e., the harvest model. In addition, critical quality attributes are estimated by a quality model which is operating on top of the harvest model. The performance of these models was evaluated using test data and two additional blind runs. Also, a "what-if" analysis was conducted to investigate whether the models' predictions align with expectations.It is concluded that the models are sufficiently accurate to support the design of operating conditions, though the accuracy and applicability of the models can further be increased by training them on more specific data with higher variability.

Truly continuous low pH viral inactivation for biopharmaceutical process integration.

Continuous virus inactivation (VI) has received little attention in the efforts to realize fully continuous biomanufacturing in the future. Implementation of continuous VI must assure a specific minimum incubation time, typically 60 min. To guarantee the minimum incubation time, we implemented a packed bed continuous viral inactivation reactor (CVIR) with narrow residence time distribution (RTD) for low pH incubation. We show that the RTD does not broaden significantly over a wide range of linear flow velocities-which highlights the flexibility and robustness of the design. Prolonged exposure to acidic pH has no impact on bed stability, assuring constant RTD throughout long term operation. The suitability of the packed bed CVIR for low pH inactivation is shown with two industry-standard model viruses, that is xenotropic murine leukemia virus and pseudorabies virus. Controls at neutral pH showed no system-induced VI. At low pH, significant VI is observed, even after only 15 min. Based on the low pH inactivation kinetics, the continuous process is equivalent to traditional batch operation. This study establishes a concept for continuous low pH inactivation and, together with previous reports, highlights the versatility of the packed bed reactor for continuous VI, regardless of the inactivation method.

A narrow residence time incubation reactor for continuous virus inactivation based on packed beds.

A narrow residence time distribution (RTD) is highly desirable for continuous processes where a strict incubation time must be ensured, such as continuous virus inactivation. A narrow RTD also results in faster startup and shut down phases and limits the broadening of potential disturbances in continuous processes. A packed bed reactor with non-porous inert beads was developed to achieve narrow RTDs. The performance was defined as the ratio between the onset of the cumulative RTD and the median residence time (tx%/t50%). Laboratory-scale packed columns were used to study the influence of the column parameters on the RTD. A larger column with a void volume of 0.65 L and a length of 89 cm, packed with beads in a size range of 125 to 250 µm, achieved t0.5%/t50% >0.93 across flow rates from 0.1 to 9.8 mL/min. The RTD was significantly narrower than the RTDs of other reactor designs, such as the Coiled Flow Inverter and Jig in a Box. The pressure drop remained under 3 kPa for all tested flow rates. Fluorescent nanoparticles (30 and 200 nm) were used to mimic viruses. These two sizes showed less than 2% difference in terms of t1%/t50% and t0.01%/t50% scores. These results indicated that viruses travelled through the column at rates independent of size. This proposal of packed beds as incubation chambers for continuous virus inactivation is simple, scalable, and can be realized as single-use devices. Due to the low pressure drop, the system can be easily integrated into a fully continuous process.

Continuous Solvent/Detergent Virus Inactivation Using a Packed-Bed Reactor.

Continuous virus inactivation (VI) remains one of the missing pieces while the biopharma industry moves toward continuous manufacturing. The challenges of adapting VI to the continuous operation are two-fold: 1) achieving fluid homogeneity and 2) a narrow residence time distribution (RTD) for fluid incubation. To address these challenges, a dynamic active in-line mixer and a packed-bed continuous virus inactivation reactor (CVIR) are implemented, which act as a narrow RTD incubation chamber. The developed concept is applied using solvent/detergent (S/D) treatment for inactivation of two commonly used model viruses. The in-line mixer is characterized and enables mixing of the viscous S/D chemicals to ±1.0% of the target concentration in a small dead volume. The reactor's RTD is characterized and additional control experiments confirm that the VI is due to the S/D action and not induced by system components. The CVIR setup achieves steady state rapidly before two reactor volumes and the logarithmic reduction values of the continuous inactivation process are identical to those obtained by the traditional batch operation. The packed-bed reactor for continuous VI unites fully continuous processing with very low-pressure drop and scalability.

Biobased monoliths for adenovirus purification.

Adenoviruses are important platforms for vaccine development and vectors for gene therapy, increasing the demand for high titers of purified viral preparations. Monoliths are macroporous supports regarded as ideal for the purification of macromolecular complexes, including viral particles. Although common monoliths are based on synthetic polymers as methacrylates, we explored the potential of biopolymers processed by clean technologies to produce monoliths for adenovirus purification. Such an approach enables the development of disposable and biodegradable matrices for bioprocessing. A total of 20 monoliths were produced from different biopolymers (chitosan, agarose, and dextran), employing two distinct temperatures during the freezing process (-20 °C and -80 °C). The morphological and physical properties of the structures were thoroughly characterized. The monoliths presenting higher robustness and permeability rates were further analyzed for the nonspecific binding of Adenovirus serotype 5 (Ad5) preparations. The matrices presenting lower nonspecific Ad5 binding were further functionalized with quaternary amine anion-exchange ligand glycidyltrimethylammonium chloride hydrochloride by two distinct methods, and their performance toward Ad5 purification was assessed. The monolith composed of chitosan and poly(vinyl) alcohol (50:50) prepared at -80 °C allowed 100% recovery of Ad5 particles bound to the support. This is the first report of the successful purification of adenovirus using monoliths obtained from biopolymers processed by clean technologies.

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.

Impact of grafting on the design of new membrane adsorbers for adenovirus purification.

The impacts of quaternary amine ligand density and matrix structure, namely hydrogel grafted and directly grafted, on state-of-the-art chromatographic membranes operated in bind-and-elute mode were evaluated for the purification of adenovirus serotype 5. The experiments were performed on a 96-well plate membrane holder, which is a convenient high-throughput screening tool for obtaining the best operating conditions for a process yield optimization. The results show that the hydrogel-grafted membranes are more suitable for virus purification than the directly grafted ones. By reducing the number of grafted ligands to low (1.7µmol/cm(2)) or medium (2.4µmol/cm(2)) density, it is possible to increase the recovery of purified virus by 60% compared to a highly charged membrane (3.3µmol/cm(2)) that yielded a recovery rate lower than 30%. In the reported experiments, Sartobind(®) Q, chosen as benchmark comparison, provides a better compromise between high recovery and large dynamic binding capacity. Overall, this work contributes to the understanding and development of new membrane adsorbers specifically designed for virus purification.