Plasmid DNA processing for gene therapy and vaccination: Studies on the membrane sterilisation filtration step

Membrane technology for the purification of RNA and DNA therapeutics

Nucleic acid therapeutics have the potential to revolutionize the biopharmaceutical industry, providing highly effective vaccines and novel treatments for cancers and genetic disorders. The successful commercialization of these therapeutics will require development of manufacturing strategies specifically tailored to the purification of nucleic acids. Membrane technologies already play a critical role in the downstream processing of nucleic acid therapeutics, ranging from clarification to concentration to selective purification. This review provides an overview of how membrane systems are currently used for nucleic acid purification, while highlighting areas of future need and opportunity, including adoption of membranes in continuous bioprocessing.

Culturing of SARS-CoV-2 from patient samples: Protocol for optimal virus recovery and assessment of infectious viral load

Optimal sampling, preservation, and culturing of SARS-CoV-2 from COVID-19 patients are critical for successful recovery of virus isolates and to accurately estimate contagiousness of the patient. In this study, we investigated the influence of the type of sampling media, storage time, freezing conditions, sterile filtration, and combinations of these to determine the optimal pre-analytic conditions for virus recovery and estimation of infectious viral load in COVID-19 patients. Further, we investigated the viral shedding kinetics and mucosal antibody response in 38 COVID-19 hospitalized patients. We found Universal Transport Medium (Copan) to be the most optimal medium for preservation of SARS-CoV-2 infectivity. Our data showed that the probability of a positive viral culture was strongly correlated to Ct values, however some samples did not follow the general trend. We found a significant correlation between plaque forming units and levels of mucosal antibodies and found that high levels of mucosal antibodies correlated with reduced chance of isolating the virus. Our data reveals essential parameters to consider from specimen collection over storage to culturing technique for optimal chance of isolating SARS-CoV-2 and accurately estimating patient contagiousness.

The water droplet with huge charge density excited by triboelectric nanogenerator for water sterilization

Water is one of the most essential resources for the survival of human beings and all other living things. For the point of daily use, water sterilization has enormous social and economic significance, especially for remote and undeveloped areas. Here, we developed a self-powered water sterilization device, which consists of a rotating-disk freestanding triboelectric-layer mode triboelectric nanogenerator (RF-TENG), a voltage-multiplying circuit, and a water droplet control system. The output voltage of the RF-TENG is boosted by a voltage-multiplying circuit and then utilized to charge water droplet. When the rotation rate of the RF-TENG is 300 rpm, the output voltage of a six-fold voltage-multiplying circuit can reach 9319 V, and a 62.50μl water droplet can be positively charged to 6320 nC at the flow rate of 0.31 ml min^-1. The charge density and electric filed of the water droplet can reach 101.12 nCμl^-1and 11.28 kV cm^-1, respectively. The charged water droplet can killE. coliandS. aureusquickly and efficiently through electroporation mechanism. With the advantages of low cost, simple in fabrication and usage, portability, and etc, the self-powered water sterilization device has wide application prospects in remote and undeveloped areas.

Scale-Up of Plasmid DNA Downstream Process Based on Chromatographic Monoliths

Purification of high-quality plasmid DNA in large quantities is a crucial step in its production for therapeutic use and is usually conducted by different chromatographic techniques. Large-scale preparations require the optimization of yield and homogeneity, while maximizing removal of contaminants and preserving molecular integrity. The advantages of Convective Interaction Media^® (CIM^®) monolith stationary phases, including low backpressure, fast separation of macromolecules, and flow-rate-independent resolution qualified them to be used effectively in separation of plasmid DNA on laboratory as well as on large scale. A development and scale-up of plasmid DNA downstream process based on chromatographic monoliths is described and discussed below. Special emphasis is put on the introduction of process analytical technology principles and tools for optimization and control of a downstream process.

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.

Enhanced purification of plasmid DNA isoforms by exploiting ionic strength effects during ultrafiltration

The solution structure of plasmid DNA is known to be a strong function of solution conditions due to intramolecular electrostatic interactions between the charged phosphate groups along the DNA backbone. The objective of this work was to determine whether it was possible to enhance the use of ultrafiltration for separation of different plasmid isoforms by proper selection of the solution ionic strength and ion type. Experiments were performed with a 3.0 kbp plasmid using composite regenerated cellulose ultrafiltration membranes. The transmission of the linear isoform was nearly independent of solution ionic strength, but increased significantly with increasing filtrate flux due to the elongation of the highly flexible plasmid in the converging flow field into the membrane pores. In contrast, the transmission of the open-circular and supercoiled plasmids both increased with increasing NaCl or MgCl2 concentration due to the change in plasmid size and conformational flexibility. The effect of ionic strength was greatest for the supercoiled plasmid, providing opportunities for enhanced purification of this therapeutically active isoform. This behavior was confirmed using experiments performed with binary mixtures of the different isoforms. These results clearly demonstrate the potential for enhancing the performance of membrane systems for plasmid DNA separations by proper selection of the ionic conditions.

Detoxification and fermentation of pyrolytic sugar for ethanol production

The sugars present in bio-oil produced by fast pyrolysis can potentially be fermented by microbial organisms to produce cellulosic ethanol. This study shows the potential for microbial digestion of the aqueous fraction of bio-oil in an enrichment medium to consume glucose and produce ethanol. In addition to glucose, inhibitors such as furans and phenols are present in the bio-oil. A pure glucose enrichment medium of 20 g/l was used as a standard to compare with glucose and aqueous fraction mixtures for digestion. Thirty percent by volume of aqueous fraction in media was the maximum additive amount that could be consumed and converted to ethanol. Inhibitors were removed by extraction, activated carbon, air stripping, and microbial methods. After economic analysis, the cost of ethanol using an inexpensive fermentation medium in a large scale plant is approximately $14 per gallon.

Degradation of supercoiled plasmid DNA within a capillary device

Supercoiled plasmid DNA is susceptible to fluid stress in large-scale manufacturing processes. A capillary device was used to generate controlled shear conditions and the effects of different stresses on plasmid DNA structure were investigated. Computational fluid dynamics (CFD) analysis was employed to characterize the flow environment in the capillary device and different analytical techniques were used to quantify the DNA breakage. It was found that the degradation of plasmid DNA occurred at the entrance of the capillary and that the shear stress within the capillary did not affect the DNA structure. The degradation rate of plasmids was well correlated with the average elongational strain rate or the pressure drop at the entrance region. The conclusion may also be drawn that laminar shear stress does not play a significant role in plasmid DNA degradation.

Salt-induced changes in plasmid DNA transmission through ultrafiltration membranes

Recent studies have demonstrated the feasibility of using ultrafiltration for the purification of plasmid DNA, but there is still little understanding of the factors governing DNA transmission. Experimental data were obtained for the transmission of a 3.0 kbp supercoiled plasmid DNA through composite regenerated cellulose ultrafiltration membranes as a function of solution ionic environment in a stirred ultrafiltration cell. The dependence on salt concentration was quite dramatic, with the sieving coefficient increasing by more than 80-fold as the NaCl concentration increased from 1 to 150 mM at a fixed filtrate flux. At the same total ionic strength, the sieving coefficient in an MgCl2 solution was significantly larger than that evaluated in NaCl. The sieving results are consistent with independent studies showing a reduction in the effective plasmid size due to salt specific shielding of intramolecular electrostatic interactions. DNA transmission was also a strong function of the filtrate flux, with negligible transmission below a critical value of the flux. The predicted values of the critical filtrate flux determined using a modified elongational flow model were in excellent agreement with the experimental data. These results clearly demonstrate that salt-induced changes in plasmid DNA structure have a significant effect on plasmid DNA transmission through ultrafiltration membranes.

Studies on aerosol delivery of plasmid DNA using a mesh nebulizer

Aerosol delivery of plasmid DNA therapeutic solutions is promising for the treatment of respiratory diseases. However, it poses challenges, most significantly the need to protect the delicate supercoiled (sc) structure of plasmid during aerosolization. Nebulizers for liquid aerosolization using meshes appear a better method for delivery than conventional jet and ultrasonic nebulizers. This paper explores their application to the delivery of plasmid DNA. A computational fluid dynamics model of the dynamics of fluid flow through the nozzle of the MicroAIR mesh nebulizer indicated high strain rates (>10(5) s(-1)) near the nozzle exit capable of causing damage to the shear-sensitive plasmid DNA. Knowledge of the strain rates predicted using CFD and molecule size determined using atomic force microscopy (AFM) enabled estimation of the hydrodynamic force and whether damage of shear-sensitive therapeutics was likely. Plasmids of size 5.7 and 20 kb were aerosolized in the mesh nebulizer. The sc structure of the 5.7-kb plasmid was successfully delivered without damage, while aerosolization of the 20-kb plasmid led to disintegration of the pDNA sc structure as observed in AFM. Subsequent formulation of the sc 20-kb plasmid with PEI resulted in successful aerosol delivery. The maximum hydrodynamic forces computed for the aerosolization of structures of the size of 5.7-kb and PEI formulated 20-kb plasmids were less than the forces reported to damage the structure of double-stranded DNA. A combination of CFD analysis and structure analysis may be used to predict successful aerosol delivery in such a mesh nebulizer.