Downstream processing of plasmid DNA for gene therapy and DNA vaccine applications

Analytical separation of plasmid DNA isoforms using anion exchanging chromatographic monoliths with 6 µm channels

High-performance liquid chromatography (HPLC)-based analytical assays are used to effectively monitor purity and quantity of plasmid DNA (pDNA) throughout the purification process. However, the phenomenon of physical entrapment of open circular (OC) isoforms pDNA inside narrow channels of chromatographic support decreases its accuracy and precision and the effect increases with pDNA size. The purpose of the study was to develop a chromatographic method for accurate analytical separation between isoforms of <16 kbp pDNA using weak anion exchanging monolithic column with large (6 µm) convective channels. Purified samples of 4.7 and 15.4 kbp large pDNA with known isoform composition were prepared and their isoforms separated in ascending salt gradient. Both OC and supercoiled (SC) isoforms were baseline separated at a flow rate below 0.5 mL min-1 in a guanidinium chloride (GdnCl) gradient with a ≥95% OC pDNA elution recovery. However, these chromatographic conditions increased 2 times the peak width for linear (LIN) pDNA isoform compared to the results using monoliths with 1.4 µm channel size. If other chaotropic agents, such as urea or thiocyanate (SCN), were added to Gdn ions, the elution volume for LIN isoform decreased. Optimization of combined GdnCl/GdnSCN gradient for pDNA elution resulted in a simple and robust chromatographic method, where OC-LIN and LIN-SC pDNA (up to 15 kbp size) were separated with resolution above 1.0 and above 2.0, respectively. The accessibility and general acceptance of anion exchange chromatography for pDNA analytics give the newly developed method a great potential for in-process control monitoring of pDNA production processes.

Identification of plasmids in avian-associated Escherichia coli using nanopore and illumina sequencing

BACKGROUND

Avian pathogenic Escherichia coli (APEC) are the causative agents of colibacillosis in chickens, a disease which has significant economic impact on the poultry industry. Large plasmids detected in APEC are known to contribute to strain diversity for pathogenicity and antimicrobial resistance, but there could be other plasmids that are missed in standard analysis. In this study, we determined the impact of sequencing and assembly factors for the detection of plasmids in an E. coli whole genome sequencing project.

RESULTS

Hybrid assembly (Illumina and Nanopore) combined with plasmid DNA extractions allowed for detection of the greatest number of plasmids in E. coli, as detected by MOB-suite software. In total, 79 plasmids were identified in 19 E. coli isolates. Hybrid assemblies were robust and consistent in quality regardless of sequencing kit used or if long reads were filtered or not. In contrast, long read only assemblies were more variable and influenced by sequencing and assembly parameters. Plasmid DNA extractions allowed for the detection of physically smaller plasmids, but when averaged over 19 isolates did not significantly change the overall number of plasmids detected.

CONCLUSIONS

Hybrid assembly can be reliably used to detect plasmids in E. coli, especially if researchers are focused on large plasmids containing antimicrobial resistance genes and virulence factors. If the goal is comprehensive detection of all plasmids, particularly if smaller sized vectors are desired for biotechnology applications, the addition of plasmid DNA extractions to hybrid assemblies is prudent. Long read sequencing is sufficient to detect many plasmids in E. coli, however, it is more prone to errors when expanded to analyze a large number of isolates.

Nucleic acid-based vaccine platforms against the coronavirus disease 19 (COVID-19)

The coronavirus disease 2019 (COVID-19) pandemic has infected 673,010,496 patients and caused the death of 6,854,959 cases globally until today. Enormous efforts have been made to develop fundamentally different COVID-19 vaccine platforms. Nucleic acid-based vaccines consisting of mRNA and DNA vaccines (third-generation vaccines) have been promising in terms of rapid and convenient production and efficient provocation of immune responses against the COVID-19. Several DNA-based (ZyCoV-D, INO-4800, AG0302-COVID19, and GX-19N) and mRNA-based (BNT162b2, mRNA-1273, and ARCoV) approved vaccine platforms have been utilized for the COVID-19 prevention. mRNA vaccines are at the forefront of all platforms for COVID-19 prevention. However, these vaccines have lower stability, while DNA vaccines are needed with higher doses to stimulate the immune responses. Intracellular delivery of nucleic acid-based vaccines and their adverse events needs further research. Considering re-emergence of the COVID-19 variants of concern, vaccine reassessment and the development of polyvalent vaccines, or pan-coronavirus strategies, is essential for effective infection prevention.

Ionic-liquid-based approaches to improve biopharmaceuticals downstream processing and formulation

The emergence of biopharmaceuticals, including proteins, nucleic acids, peptides, and vaccines, revolutionized the medical field, contributing to significant advances in the prophylaxis and treatment of chronic and life-threatening diseases. However, biopharmaceuticals manufacturing involves a set of complex upstream and downstream processes, which considerably impact their cost. In particular, despite the efforts made in the last decades to improve the existing technologies, downstream processing still accounts for more than 80% of the total biopharmaceutical production cost. On the other hand, the formulation of biological products must ensure they maintain their therapeutic performance and long-term stability, while preserving their physical and chemical structure. Ionic-liquid (IL)-based approaches arose as a promise alternative, showing the potential to be used in downstream processing to provide increased purity and recovery yield, as well as excipients for the development of stable biopharmaceutical formulations. This manuscript reviews the most important progress achieved in both fields. The work developed is critically discussed and complemented with a SWOT analysis.

Recent advances in gene therapy: genetic bullets to the root of the problem

Genetics and molecular genetic techniques have changed many perspectives and paradigms in medicine. Using genetic methods, many diseases have been cured or alleviated. Gene therapy, in its simplest definition, is application of genetic materials and related techniques to treat various human diseases. Evaluation of the trends in the field of medicine and therapeutics clarifies that gene therapy has attracted a lot of attention due to its powerful potential to treat a number of diseases. There are various genetic materials that can be used in gene therapy such as DNA, single- and double-stranded RNA, siRNA and shRNA. The main gene editing techniques used for in vitro and in vivo gene modification are ZNF, TALEN and CRISPR-Cas9. The latter has increased hopes for more precise and efficient gene targeting as it requires two separate recognition sites which makes it more specific and can also cause rapid and sufficient cleavage within the target sequence. There must be carriers for delivering genes to the target tissue. The most commonly used carriers for this purpose are viral vectors such as adenoviruses, adeno-associated viruses and lentiviruses. Non-viral vectors consist of bacterial vectors, liposomes, dendrimers and nanoparticles.

Efficient Isolation of Bacterial RNAs Using Silica-Based Materials Modified with Ionic Liquids

High quality nucleic acids (with high integrity, purity, and biological activity) have become indispensable products of modern society, both in molecular diagnosis and to be used as biopharmaceuticals. As the current methods available for the extraction and purification of nucleic acids are laborious, time-consuming, and usually rely on the use of hazardous chemicals, there is an unmet need towards the development of more sustainable and cost-effective technologies for nucleic acids purification. Accordingly, this study addresses the preparation and evaluation of silica-based materials chemically modified with chloride-based ionic liquids (supported ionic liquids, SILs) as potential materials to effectively isolate RNAs. The investigated chloride-based SILs comprise the following cations: 1-methyl-3-propylimidazolium, triethylpropylammonium, dimethylbutylpropylammonium, and trioctylpropylammonium. All SILs were synthesized by us and characterized by solid-state ¹³C Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM), elemental analysis, and zeta potential measurements, confirming the successful covalent attachment of each IL cation with no relevant changes in the morphology of materials. Their innovative application as chromatographic supports for the isolation of recombinant RNA was then evaluated. Adsorption kinetics of transfer RNA (tRNA) on the modified silica-based materials were investigated at 25 °C. Irrespective to the immobilized IL, the adsorption experimental data are better described by a pseudo first-order model, and maximum tRNA binding capacities of circa 16 µmol of tRNA/g of material were achieved with silica modified with 1-methyl-3-propylimidazolium chloride and dimethylbutylpropylammonium chloride. Furthermore, the multimodal character displayed by SILs was explored towards the purification of tRNA from Escherichia coli lysates, which in addition to tRNA contain ribosomal RNA and genomic DNA. The best performance on the tRNA isolation was achieved with SILs comprising 1-methyl-3-propylimidazolium chloride and dimethylbutylpropylammonium chloride. Overall, the IL modified silica-based materials represent a more efficient, sustainable, and cost-effective technology for the purification of bacterial RNAs, paving the way for their use in the purification of distinct biomolecules or nucleic acids from other sources.

Two Dimensional Anion Exchange-Size Exclusion Chromatography Combined with Mathematical Modeling for Downstream Processing of Foot and Mouth Disease Vaccine

The production of high-quality purified virus particles in high quantities for vaccine preparation requires a scalable purification procedure in the downstream step. A purification scheme based on combined strong anion-exchange and size exclusion chromatography (2D-AEC-SEC) was developed for the production of non-structural protein-free foot and mouth disease vaccine, and the whole procedure was accomplished with 77.9% virus yield. Additionally, a mathematical modeling and a simulation approach based on a plate model of chromatography were developed and matched with the experimental chromatography data to improve prediction of retention behavior and save time in the development of the downstream scale-up method. The purified pooled virus fraction obtained from the final polishing step had a purity higher than 85% based on analytical size exclusion analysis. Moreover, more than 90.1% of residual DNA (rDNA) was removed from the purified vaccine. The analysis of purified virus particles by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), dynamic light scattering (DLS), high performance size exclusion chromatography (HP-SEC), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and transmission electron microscopy (TEM) provided clear evidence of purity and demonstrated that the final product is structurally spherical, intact particles qualified for formulation as a vaccine product.

Advances in gene-based vaccine platforms to address the COVID-19 pandemic

The novel betacoronavirus, SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), has spread across the globe at an unprecedented rate since its first emergence in Wuhan City, China in December 2019. Scientific communities around the world have been rigorously working to develop a potent vaccine to combat COVID-19 (coronavirus disease 2019), employing conventional and novel vaccine strategies. Gene-based vaccine platforms based on viral vectors, DNA, and RNA, have shown promising results encompassing both humoral and cell-mediated immune responses in previous studies, supporting their implementation for COVID-19 vaccine development. In fact, the U.S. Food and Drug Administration (FDA) recently authorized the emergency use of two RNA-based COVID-19 vaccines. We review current gene-based vaccine candidates proceeding through clinical trials, including their antigenic targets, delivery vehicles, and route of administration. Important features of previous gene-based vaccine developments against other infectious diseases are discussed in guiding the design and development of effective vaccines against COVID-19 and future derivatives.

Minicircle Biopharmaceuticals–An Overview of Purification Strategies

Minicircles are non-viral delivery vectors with promising features for biopharmaceutical applications. These vectors are plasmid-derived circular DNA molecules that are obtained in vivo in Escherichia coli by the intramolecular recombination of a parental plasmid, which generates a minicircle containing the eukaryotic therapeutic cassette of interest and a miniplasmid containing the prokaryotic backbone. The production process results thus in a complex mixture, which hinders the isolation of minicircle molecules from other DNA molecules. Several strategies have been proposed over the years to meet the challenge of purifying and obtaining high quality minicircles in compliance with the regulatory guidelines for therapeutic use. In minicircle purification, the characteristics of the strain and parental plasmid used have a high impact and strongly affect the purification strategy that can be applied. This review summarizes the different methods developed so far, focusing not only on the purification method itself but also on its dependence on the upstream production strategy used.

Dilemma on plasmid DNA purification: binding capacity vs selectivity

Plasmid DNA chromatography is a powerful field in constant development and evolution. The use of this technique is considered mandatory in the production of an efficient and safe formulation to be applied for plasmid-mediated gene therapy. Concerning this, the search for an ideal chromatographic support/ligand combination motivated scientist to pursue a continuous improvement on the plasmid chromatography performance, looking for a progression on the ligands and supports used. The present review explores the different approaches used over time to purify plasmid DNA, ambitioning both high recovery and high purity levels. Overall, it is presented a critical discussion relying on the relevance of the binding capacity versus selectivity of the supports.

Enhancement of a biotechnological platform for the purification and delivery of a human papillomavirus supercoiled plasmid DNA vaccine

New biotechnological strategies are being explored, aimed at rapid and economic manufacture of large quantities of DNA vaccines with the required purity for therapeutic applications, as well as their correct delivery as biopharmaceuticals to target cells. This report describes the purification of supercoiled (sc) HPV-16 E6/E7 plasmid DNA (pDNA) vaccine from a bacterial lysate, using an arginine-based monolith, presenting a spacer arm in its configuration. To enhance the performance of the purification process, monolith modification with the spacer arm can improve accessibility of the arginine ligand. By using a low NaCl concentration at pH 7.0, a condition to eliminate the RNA impurity directly in the flow through was established. The pH increase to 7.5 allowed the elimination of non-functional pDNA isoforms, the sc pDNA being recovered by increasing the ionic strength. As well as a binding capacity of 2.53 mg/mL obtained with a pre-purified sc pDNA sample, the column also purified sc pDNA from high lysate loading, with capacities above 1 mg/mL. Due to the sample displacement phenomena, non-functional pDNA isoforms were eliminated throughout column loading, favoring the degree of purity of final sc pDNA of 93.3%-98.5%. Thereafter, purified sc pDNA was successfully encapsulated into CaCO₃-gelatin nano-complexes. Delivery of the pDNA-carriers to THP-1 cells was assessed through pDNA cellular uptake evaluation and correct E6 expression was verified by mRNA and protein detection. A biotechnological platform was established for sc pDNA purification and delivery to dendritic cells, stimulating further in vivo studies.

GMP-Compliant Adenoviral Vectors for Gene Therapy

Recently, gene therapy as one of the most promising treatments can apply genes for incurable diseases treatment. In this context, vectors as gene delivery systems play a pivotal role in gene therapy procedure. Hereupon, viral vectors have been increasingly introduced as a hyper-efficient tools for gene therapy. Adenoviral vectors as one of the most common groups which are used in gene therapy have a high ability for humans. Indeed, they are not integrated into host genome. In other words, they can be adapted for direct transduction of recombinant proteins into targeted cells. Moreover, they have large packaging capacity and high levels of efficiency and expression. In accordance with translational pathways from the basic to the clinic, recombinant adenoviral vectors packaging must be managed under good manufacturing practice (GMP) principles before applying in clinical trials. Therein, in this chapter standard methods for manufacturing of GMP-compliant Adenoviral vectors for gene therapy have been introduced.

Interpolyelectrolyte complexes: advances and prospects of application

Advances in the development of water-soluble nonstoichiometric polyelectrolyte complexes, which are characterized by high stability and can be involved in competitive interpolyelectrolyte reactions, are summarized and analyzed. The complexes remain stable over a wide range of external conditions (pH, ionic strength, temperature), but show a rapid, reversible and highly sensitive response to environmental changes outside this range by changing the phase state. The review considers methods of preparation and properties of nonstoichiometric polyelectrolyte complexes formed by interactions between oppositely charged polyelectrolytes. These reagents can be used for controlled modification of various surfaces, the preparation of soluble complexes functionalized by different molecules, the suppression and prevention of protein aggregation. The review briefly summarizes new types of soluble polyelectrolytes and polyelectrolyte complexes of different nature and with different structures, including biopolymers and dendrimers, suitable for solving problems in medicine and agricultural biotechnology. In order to evaluate the results achieved, there is a need to integrate and analyze the data on interpolyelectrolyte reactions, which are of most interest for a wide range of researchers.

The bibliography includes 118 references.

Application of Plasmid Engineering to Enhance Yield and Quality of Plasmid for Vaccine and Gene Therapy

There is an increased interest in plasmid DNA as therapeutics. This is evident in the number of ongoing clinical trials involving the use of plasmid DNA. In order to be an effective therapeutic, high yield and high level of supercoiling are required. From the bioprocessing point of view, the supercoiling level potentially has an impact on the ease of downstream processing. We approached meeting these requirements through plasmid engineering. A 7.2 kb plasmid was developed by the insertion of a bacteriophage Mu strong gyrase-binding sequence (Mu-SGS) to a 6.8 kb pSVβ-Gal and it was used to transform four different E. coli strains, and cultured in order to investigate the Mu-SGS effect and dependence on strain. There was an increase of over 20% in the total plasmid yield with pSVβ-Gal398 in two of the strains. The supercoiled topoisomer content was increased by 5% in both strains leading to a 27% increase in the overall yield. The extent of supercoiling was examined using superhelical density (σ) quantification with pSVβ-Gal398 maintaining a superhelical density of −0.022, and pSVβ-Gal −0.019, in both strains. This study has shown that plasmid modification with the Mu-phage SGS sequence has a beneficial effect on improving not only the yield of total plasmid but also the supercoiled topoisomer content of therapeutic plasmid DNA during bioprocessing.

Synthesis, Functionalization, and Characterization of Fusogenic Porous Silicon Nanoparticles for Oligonucleotide Delivery

With the advent of gene therapy, the development of an effective in vivo nucleotide-payload delivery system has become of parallel import. Fusogenic porous silicon nanoparticles (F-pSiNPs) have recently demonstrated high in vivo gene silencing efficacy due to its high oligonucleotide loading capacity and unique cellular uptake pathway that avoids endocytosis. The synthesis of F-pSiNPs is a multi-step process that includes: (1) loading and sealing of oligonucleotide payloads in the silicon pores; (2) simultaneous coating and sizing of fusogenic lipids around the porous silicon cores; and (3) conjugation of targeting peptides and washing to remove excess oligonucleotide, silicon debris, and peptide. The particle's size uniformity is characterized by dynamic light scattering, and its core-shell structure may be verified by transmission electron microscopy. The fusogenic uptake is validated by loading a lipophilic dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), into the fusogenic lipid bilayer and treating it to cells in vitro to observe for plasma membrane staining versus endocytic localizations. The targeting and in vivo gene silencing efficacies were previously quantified in a mouse model of Staphylococcus aureus pneumonia, in which the targeting peptide is expected to help the F-pSiNPs to home to the site of infection. Beyond its application in S. aureus infection, the F-pSiNP system may be used to deliver any oligonucleotide for gene therapy of a wide range of diseases, including viral infections, cancer, and autoimmune diseases.

Engineering DNA vaccines against infectious diseases

Engineering vaccine-based therapeutics for infectious diseases is highly challenging, as trial formulations are often found to be nonspecific, ineffective, thermally or hydrolytically unstable, and/or toxic. Vaccines have greatly improved the therapeutic landscape for treating infectious diseases and have significantly reduced the threat by therapeutic and preventative approaches. Furthermore, the advent of recombinant technologies has greatly facilitated growth within the vaccine realm by mitigating risks such as virulence reversion despite making the production processes more cumbersome. In addition, seroconversion can also be enhanced by recombinant technology through kinetic and nonkinetic approaches, which are discussed herein. Recombinant technologies have greatly improved both amino acid-based vaccines and DNA-based vaccines. A plateau of interest has been reached between 2001 and 2010 for the scientific community with regard to DNA vaccine endeavors. The decrease in interest may likely be attributed to difficulties in improving immunogenic properties associated with DNA vaccines, although there has been research demonstrating improvement and optimization to this end. Despite improvement, to the extent of our knowledge, there are currently no regulatory body-approved DNA vaccines for human use (four vaccines approved for animal use). This article discusses engineering DNA vaccines against infectious diseases while discussing advantages and disadvantages of each, with an emphasis on applications of these DNA vaccines.

Statement of Significance

This review paper summarizes the state of the engineered/recombinant DNA vaccine field, with a scope entailing “Engineering DNA vaccines against infectious diseases”. We endeavor to emphasize recent advances, recapitulating the current state of the field. In addition to discussing DNA therapeutics that have already been clinically translated, this review also examines current research developments, and the challenges thwarting further progression. Our review covers: recombinant DNA-based subunit vaccines; internalization and processing; enhancing immune protection via adjuvants; manufacturing and engineering DNA; the safety, stability and delivery of DNA vaccines or plasmids; controlling gene expression using plasmid engineering and gene circuits; overcoming immunogenic issues; and commercial successes. We hope that this review will inspire further research in DNA vaccine development.

Recent advances in chromatographic purification of plasmid DNA for gene therapy and DNA vaccines: A review

The wide spread of infectious diseases have provoked the scientists to develop new types of vaccines. Among the different types of vaccines, the recently discovered plasmid DNA vaccines, have gained tremendous attentions in the last few decades as a modern approach of vaccination. The scientific interest in plasmid DNA vaccines is attributed to their prominent efficacy as they trigger not only the cellular immune response but also the humoral immune responses. Moreover, pDNA vaccines are easily to be stored, shipped and produced. However, the purification of the pDNA vaccines is a crucial step in their production and administration, which is usually conducted by different chromatographic techniques. This review summarizes the most recent chromatographic purification methods provided in the literature during the last five years following our last review in 2013, including affinity chromatography, hydrophobic interaction chromatography, ion exchange chromatography, multimodal chromatography, sample displacement chromatography and miscellaneous chromatographic methods.

Microscale disruption of microorganisms for parallelized process development

Escherichia coli, Saccharomyces cerevisiae, and Pichia pastoris are the standard platforms for biopharmaceutical production with 40% of all between 2010 to 2014 approved protein drugs produced in those microbial hosts. Typically, products overexpressed E. coli and S. cerevisiae remain in the cytosol or are secreted into the periplasm. Consequently, efficient cell disruption is essential for high product recovery during microbial production. Process development platforms at microscale are essential to shorten time to market. While high-pressure homogenization is the industry standard for cell disruption at large scale this method is not practicable for experiments in microscale. This review describes microscale methods for cell disruption at scales as low as 200 µL. Strategies for automation, parallelization and miniaturization, as well as comparability of the results at this scale to high pressure homogenization are considered as those criteria decide which methods are most suited for scale down. Those aspects are discussed in detail for protein overexpression in E. coli and yeast but also the relevance for alternative products and host such as microalgae are taken into account. The authors conclude that bead milling is the best comparable microscale method to large scale high-pressure homogenization and therefore the most suitable technique for automated process development of microbial hosts with the exception of pDNA production.

Current progress on microRNAs-based therapeutics in neurodegenerative diseases

MicroRNAs (miRNAs)-based therapy has recently emerged as a promising strategy in the treatments of neurodegenerative diseases. Thus, in this review, the most recent and important challenges and advances on the development of miRNA therapeutics for brain targeting are discussed. In particular, this review highlights current knowledge and progress in the field of manufacturing, recovery, isolation, purification, and analysis of these therapeutic oligonucleotides. Finally, the available miRNA delivery systems are reviewed and an analysis is presented in what concerns to the current challenges that have to be addressed to ensure their specificity and efficacy. Overall, it is intended to provide a perspective on the future of miRNA-based therapeutics, focusing the biotechnological approach to obtain miRNAs. WIREs RNA 2017, 8:e1409. doi: 10.1002/wrna.1409 For further resources related to this article, please visit the WIREs website.

Microbial ribonucleases (RNases): production and application potential

Ribonuclease (RNase) is hydrolytic enzyme that catalyzes the cleavage of phosphodiester bonds in RNA. RNases play an important role in the metabolism of cellular RNAs, such as mRNA and rRNA or tRNA maturation. Besides their cellular roles, RNases possess biological activity, cell stimulating properties, cytotoxicity and genotoxicity. Cytotoxic effect of particular microbial RNases was comparable to that of animal derived counterparts. In this respect, microbial RNases have a therapeutic potential as anti-tumor drugs. The significant development of DNA vaccines and the progress of gene therapy trials increased the need for RNases in downstream processes. In addition, RNases are used in different fields, such as food industry for single cell protein preparations, and in some molecular biological studies for the synthesis of specific nucleotides, identifying RNA metabolism and the relationship between protein structure and function. In some cases, the use of bovine or other animal-derived RNases have increased the difficulties due to the safety and regulatory issues. Microbial RNases have promising potential mainly for pharmaceutical purposes as well as downstream processing. Therefore, an effort has been given to determination of optimum fermentation conditions to maximize RNase production from different bacterial and fungal producers. Also immobilization or strain development experiments have been carried out.

HIV Tat protein: Is Tat-C much trickier than Tat-B?

Out of various subtypes of human immunodeficiency virus type 1 (HIV-1), subtype B and C cause most of the infections worldwide. Clade specific differences have been reported in differences in clinical picture of HIV pathogenesis. Transcription of the HIV-1 genome is regulated by the interaction of HIV Tat protein to the trans-activation response (TAR) element. The differential binding of clade B and C Tat proteins to TAR and differences in activation of NF-κB cascade leading to differential transactivation capacity and cytokine expression has been examined in this study. More stable Tat-TAR complex formation by Tat-C revealed by EMSA and higher TNF-α expression shown by Tat-C compared to Tat-B leads to higher NF-κB activation, which may be plausible cause for higher transactivation by Tat-C as obtained by FACS analysis. This comparative study would be helpful in understanding the basic mechanism of clade specific Tat protein differences and their functional relationships.

IRES-incorporated lactococcal bicistronic vector for target gene expression in a eukaryotic system

Plasmid DNAs isolated from lactic acid bacteria (LAB) such as Lactococcus lactis (L. lactis) has been gaining more interests for its positive prospects in genetic engineering-related applications. In this study, the lactococcal plasmid, pNZ8048 was modified so as to be able to express multiple genes in the eukaryotic system. Therefore, a cassette containing an internal ribosome entry site (IRES) was cloned between VP2 gene of a very virulent infectious bursal disease (vvIBDV) UPM 04190 of Malaysian local isolates and the reporter gene, green fluorescent protein (GFP) into pNZ:CA, a newly constructed derivative of pNZ8048 harboring the cytomegalovirus promoter (Pcmv) and polyadenylation signal. The new bicistronic vector, denoted as pNZ:vig was subjected to in vitro transcription/translation system followed by SDS-PAGE and Western blot analysis to rapidly verify its functionality. Immunoblotting profiles showed the presence of 49 and 29kDa bands that corresponds to the sizes of the VP2 and GFP proteins respectively. This preliminary result shows that the newly constructed lactococcal bicistronic vector can co-express multiple genes in a eukaryotic system via the IRES element thus suggesting its feasibility to be used for transfection of in vitro cell cultures and vaccine delivery.

Gene therapy and DNA delivery systems

Gene therapy is a promising new technique for treating many serious incurable diseases, such as cancer and genetic disorders. The main problem limiting the application of this strategy in vivo is the difficulty of transporting large, fragile and negatively charged molecules like DNA into the nucleus of the cell without degradation. The key to success of gene therapy is to create safe and efficient gene delivery vehicles. Ideally, the vehicle must be able to remain in the bloodstream for a long time and avoid uptake by the mononuclear phagocyte system, in order to ensure its arrival at the desired targets. Moreover, this carrier must also be able to transport the DNA efficiently into the cell cytoplasm, avoiding lysosomal degradation. Viral vehicles are the most commonly used carriers for delivering DNA and have long been used for their high efficiency. However, these vehicles can trigger dangerous immunological responses. Scientists need to find safer and cheaper alternatives. Consequently, the non-viral carriers are being prepared and developed until techniques for encapsulating DNA can be found. This review highlights gene therapy as a new promising technique used to treat many incurable diseases and the different strategies used to transfer DNA, taking into account that introducing DNA into the cell nucleus without degradation is essential for the success of this therapeutic technique.

Purification of human papillomavirus 16 E6/E7 plasmid deoxyribonucleic acid-based vaccine using an arginine modified monolithic support

The development of efficient plasmid DNA (pDNA) purification processes has fostered therapeutic applications like gene therapy and DNA vaccination. In fact, monolithic supports have emerged as interesting approaches to purify pDNA due to their excellent mass transfer properties and high binding capacity for large biomolecules. The present study describes a method that combines the high selectivity of arginine affinity ligands with the versatility of monoliths to efficiently purify the supercoiled (sc) plasmid HPV-16 E6/E7. Quality control tests indicated that the level of impurities (proteins, endotoxins, gDNA and RNA) in the final plasmid sample was in accordance with the guidelines proposed by regulatory agencies. Breakthrough experiments were designed to compare the dynamic binding capacity of pDNA in the conventional arginine-agarose matrix with the modified monolithic support. The arginine monolith capacity was substantially higher than the conventional arginine-agarose matrix at 10% of breakthrough under the flow rate and pDNA concentration used. Overall, given that the pDNA final product complies with regulatory specifications, this combined support can be the key to obtain an adequate non-viral vaccine against a HPV infection.

Multilayer dual-polymer-coated upconversion nanoparticles for multimodal imaging and serum-enhanced gene delivery

Upconversion nanoparticles (UCNPs) have been widely explored for various bioapplications because of their unique optical properties, easy surface functionalization, and low cytotoxicity. Herein, we synthesize gadolinium (Gd3+)-doped UCNPs, which are modified first with poly(ethylene glycol) (PEG) and then with two layers of poly(ethylenimine) (PEI) via covalent conjugation and layer-by-layer assembly, respectively. Compared with UCNP-PEG@1×PEI with only one layer of PEI coating, the final complex, UCNP-PEG@2×PEI, with two PEI layers exhibits reduced cytotoxicity and enhanced gene transfection efficiency. It is interesting to find that while free PEI polymer is only effective in gene transfection in a serum-free medium and shows drastically reduced transfection ability if serum is added, UCNP-PEG@2×PEI is able to transfect cells in both serum-free and -containing media and, surprisingly, offers even higher gene transfection efficiency if serum is added. This is likely due to the formation of protein corona on the nanoparticle surface, which triggers the receptor-mediated endocytosis of our UCNP vectors. Considering the upconversion luminescence and magnetic resonance imaging contrasting ability of UCNPs, our novel nanovector could serve as a "trackable" gene-delivery carrier promising for theranostic applications.