Rapid titration of adenoviral infectivity by flow cytometry in batch culture of infected HEK293 cells

Tutorial: design, production and testing of oncolytic viruses for cancer immunotherapy

Oncolytic viruses (OVs) represent a novel class of cancer immunotherapy agents that preferentially infect and kill cancer cells and promote protective antitumor immunity. Furthermore, OVs can be used in combination with established or upcoming immunotherapeutic agents, especially immune checkpoint inhibitors, to efficiently target a wide range of malignancies. The development of OV-based therapy involves three major steps before clinical evaluation: design, production and preclinical testing. OVs can be designed as natural or engineered strains and subsequently selected for their ability to kill a broad spectrum of cancer cells rather than normal, healthy cells. OV selection is further influenced by multiple factors, such as the availability of a specific viral platform, cancer cell permissivity, the need for genetic engineering to render the virus non-pathogenic and/or more effective and logistical considerations around the use of OVs within the laboratory or clinical setting. Selected OVs are then produced and tested for their anticancer potential by using syngeneic, xenograft or humanized preclinical models wherein immunocompromised and immunocompetent setups are used to elucidate their direct oncolytic ability as well as indirect immunotherapeutic potential in vivo. Finally, OVs demonstrating the desired anticancer potential progress toward translation in patients with cancer. This tutorial provides guidelines for the design, production and preclinical testing of OVs, emphasizing considerations specific to OV technology that determine their clinical utility as cancer immunotherapy agents.

Experimental Infection Models and Their Usefulness for White Spot Syndrome Virus (WSSV) Research in Shrimp

White spot syndrome virus (WSSV) is marked as one of the most economically devastating pathogens in shrimp aquaculture worldwide. Infection of cultured shrimp can lead to mass mortality (up to 100%). Although progress has been made, our understanding of WSSV's infection process and the virus-host-environment interaction is far from complete. This in turn hinders the development of effective mitigation strategies against WSSV. Infection models occupy a crucial first step in the research flow that tries to elucidate the infectious disease process to develop new antiviral treatments. Moreover, since the establishment of continuous shrimp cell lines is a work in progress, the development and use of standardized in vivo infection models that reflect the host-pathogen interaction in shrimp is a necessity. This review critically examines key aspects of in vivo WSSV infection model development that are often overlooked, such as standardization, (post)larval quality, inoculum type and choice of inoculation procedure, housing conditions, and shrimp welfare considerations. Furthermore, the usefulness of experimental infection models for different lines of WSSV research will be discussed with the aim to aid researchers when choosing a suitable model for their research needs.

Development of a Rapid Immuno-Based Screening Assay for the Detection of Adenovirus in Eye Infections

Despite progress in fighting infectious diseases, human pathogenesis and death caused by infectious diseases remain relatively high worldwide exceeding that of cancer and cardiovascular diseases. Human adenovirus (HAdV) infects cells of the upper respiratory tract causing flu-like symptoms that are accompanied by pain and inflammation. Diagnosis of HAdV is commonly achieved by conventional methods such as viral cultures, immunoassays, and polymerase chain reaction (PCR) techniques. However, there are a variety of problems with conventional methods including slow isolation and propagation, inhibition by neutralizing antibodies, low sensitivity of immunoassays, and the diversity of HAdV strains for the PCR technique. Herein, we report the development and evaluation of a novel, simple, and reliable nanobased immunosensing technique for the rapid detection of human adenoviruses (HAdVs) that cause eye infections. This rapid and low-cost assay can be used for screening and quantitative tests with a detection limit of 10² pfu/mL in less than 2 min. The sensing platform is based on a sandwich assay that can detect HAdVs visually by a color change. Sensor specificity was demonstrated using other common viral antigens, including Flu A, Flu B, coronavirus (COV), and Middle East respiratory syndrome coronavirus (MERS COV). This cotton-based testing device potentially exhibits many of the desired characteristics of a suitable point-of-care and portable test, which can be carried out by nurses or clinicians especially for low-resource settings.

Determination of lentiviral titer by surface enhanced Raman scattering

Lentiviruses are commonly used to deliver genetic code into host cells for biomedical applications, such as gene therapy, pharmaceuticals, and vaccine development. Knowing the infectious titer of these virus particles is critical for development in these areas. Current methods of determining viral titer often require cell culture, where a cell is infected and the inserted genetic code is expressed in a known number of cells, which can require days or weeks to prepare and analyze samples. To provide a more rapid method of determining viral titer, the use of surface enhanced Raman spectroscopy (SERS) was explored. SERS provides both chemical and structural information by using plasmonic metallic nanostructures to amplify the Raman signal. Two different lentiviruses, one with a vector encoding a GFP gene and the same virus without the GFP gene included, were analyzed by SERS in viral production media at various concentrations. The SERS response was demonstrated to be sensitive to the incorporation of the GFP gene into the viral vector. Chemometric analysis using multivariate curve resolution (MCR) was able to identify a component in the observed SERS spectra that correlated with the concentration of GFP containing virus particles. Using the MCR model and the SERS response, the viral titer of lentivirus encoding for GFP was determined. The viral titer determined by SERS agreed well with expression of the GFP in infected cells. The SERS response using different metals and excitation wavelengths was also explored. Overall, this work demonstrates the utility of SERS for rapid determination of lentiviral titer.

Heterologous Expression and Purification of GPCRs

G protein-coupled receptors (GPCRs) are involved in a variety of human physiological processes and are attractive targets for treating various diseases. Yet, despite the importance as therapeutic targets, only 97 unique GPCR structures have been determined to date. A key challenge in their structural biology study is to obtain adequate protein samples because GPCRs usually have the low expression in native tissues. The in vitro recombinant expression provides the possibility to obtain large quantities of high-quality proteins suitable for three-dimensional structure determination by crystallography or single particle cryo-EM methods. For GPCR protein production, eukaryotic expression systems, such as baculovirus system and mammalian system, are the most widely used. In this chapter, we provide an overview of the methodological approaches on GPCRs expression and purification optimization using insect cells and mammalian cells, which is the prerequisite conditions for structural biology studies.

Modifying gap junction communication in cancer therapy

AIM

Drug delivery is crucial for therapeutic efficacy and gap junction communication channels (GJIC) facilitate movement within the tumour. Pro-drug activation, a modality of cancer therapy leads to Ganciclovir triphosphate (GCV-TP) incorporation into newly synthesized DNA resulting in cell death. The objective was to enhance, with Histone deacetylase inhibitors (HDACi) and All Trans Retinoic Acid (ATRA), GJIC, crucial for drug delivery, and with combination, abrogate the observed detrimental effect of Dexamethasone (DXM).

METHODS

Cell lines (NT8E, and HeLa) were pre-treated with Valproic Acid (VPA) (1 mM), 4 Phenyl Butyrate (4PB) (2 mM), ATRA (10 μM) and Dexamethasone (1 μM). Protein quantitated with the Bicinchoninic (BCA) assay for cell lysates, membrane and soluble fractions was assessed with Western blotting for Connexins (43, 26 and 32) and E-Cadherin. A qRT-PCR was done for CX 43-GJA1, CX 26-GJB2, CX 32-GJB1 and E-Cadherin, and normalized with Glyceraldehyde Phosphate dehydrogenase (GAPDH). Further, localization of Connexins (CX) and E-Cadherin, GJIC competence, pre-clinical in-vitro studies and the mechanism of cell death were evaluated.

RESULTS

There was no toxicity or change in growth patterns observed with the drugs. In both the cell lines CX 43 localized to the membrane whereas CX 32 and CX 26 were present but not membrane bound. E-Cadherin was present on the membrane in NT8E and completely absent in HeLa cells. Effects of HDACi, DXM and ATRA were seen on the expression of Connexins and E-Cadherin in both the cell lines. NT8E and HeLa cell lines showed enhanced GJIC with 4PB [30 %], VPA [36 %] and ATRA [54 %] with a 60 % increase in cytotoxicity and an abrogation of Dexamethasone inhibition on combination with VPA or ATRA.

CONCLUSION

An enhancement of GJIC function by HDACi and ATRA increased cytotoxicity and could be effective in the presence of Dexamethasone, when combined with ATRA or VPA.

Integration of Fluorescence Detection and Image-Based Automated Counting Increases Speed, Sensitivity, and Robustness of Plaque Assays

Plaque assays are used to measure the infectious titer of viral samples. These assays are multi-day and low-throughput and may be subject to analyst variability from biased or subjective manual plaque counting. Typically, on day 1, cells are adhered to plates overnight. On day 2, cells are infected with virus. After 3 additional days, plaques are fixed, stained with a horseradish peroxidase (HRP)-conjugated antibody and a HRP substrate, and counted by eye. Manual-based visual counting of plaques is time-consuming and laborious and may be subject to variability between analysts. Also, the assay must proceed for several days to allow the plaques to increase to sufficiently large sizes for manual identification. Here, we integrate fluorescent detection and automated plaque counting to increase the sensitivity and speed of the assay. First, we stain plaques with a fluorescent-labeled antibody. Second, we implement a plate-based cell imager to perform non-biased, non-subjective plaque counting. The integration of these two technologies decreases the assay length by 40%, from 5 days to 3 days, because plaque size, plaque signal to noise, and manual visualization are no longer limiting. This optimized plaque assay is sensitive, fast, and robust and expands the throughput and usage of this method for measuring plaque formation.

New Insights to Adenovirus-Directed Innate Immunity in Respiratory Epithelial Cells

The nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) family of transcription factors is a key component of the host innate immune response to infectious adenoviruses and adenovirus vectors. In this review, we will discuss a regulatory adenoviral protein encoded by early region 3 (E3) called E3-RIDα, which targets NFκB through subversion of novel host cell pathways. E3-RIDα down-regulates an EGF receptor signaling pathway, which overrides NFκB negative feedback control in the nucleus, and is induced by cell stress associated with viral infection and exposure to the pro-inflammatory cytokine TNF-α. E3-RIDα also modulates NFκB signaling downstream of the lipopolysaccharide receptor, Toll-like receptor 4, through formation of membrane contact sites controlling cholesterol levels in endosomes. These innate immune evasion tactics have yielded unique perspectives regarding the potential physiological functions of host cell pathways with important roles in infectious disease.

Detection and Quantification of Label-Free Infectious Adenovirus Using a Switch-On Cell-Based Fluorescent Biosensor

Reliable and fast viral detection and quantification protocols are a requirement for the advance of basic research and clinical approaches with wild type or recombinant viruses. However, available cell-based assays are either time-consuming or require labeled viral particles, which may alter virus biology or pose safety issues in clinical applications. Since adenoviruses constitute a major healthcare burden but also, when engineered, widely used vectors in vaccination and gene and oncolytic therapies, herein we developed a genetically encoded switch-on fluorescent biosensor consisting of a cyclized Green fluorescent protein-cVisensor-with an adenoviral protease cleavable site as a switch. After initial sensor optimization (35% increase in performance), whole-cell biosensors were established-by stably expressing cVisensor in mammalian cells-and used for live-cell monitoring of adenovirus infection as the intracellular biosensor is specifically activated by the viral protease. A rapid flow cytometry-based bioassay using cVisensor cells was established 48 h postinfection, showing an estimated limit of detection of 10⁵ infectious particles/mL, in-line with previously reported flow cytometry assays requiring labeled virus, and significantly faster than standard plaque-forming assays requiring up to 14 days. cVisensor was also successfully applied in the detection of HIV-1 protease activity, validating its wider potential for the detection of other viruses. Overall, this work presents a fast and easy method for detection and quantification of label-free infectious virus, allowing the establishment of new biosensing platforms for basic research in virology and biotechnological applications of recombinant virus biopharmaceuticals.

A Flow Cytometry-Based Method to Determine the Titer of Adenoviruses Expressing an Extraneous Gene

In recent times, oncolytic viruses expressing an extraneous gene have attracted great interest; in fact, they have been engaged in multiple applications, such as medicine for cancer. Our group made an oncolytic adenovirus, namely, OBP-301, for use in treating solid cancers and press clinical trial to get approval for a pharmaceutical product. In this study, we applied a flow cytometry-based method to determine the titer of adenoviruses expressing an extraneous gene as well as assess their quality. We considered using the green fluorescent protein (GFP)₅₀ titer as a measure of viral quality. The GFP₅₀ titer (GFP₅₀/mL) is the viral load required to render the HeLa S3 cell line 50% GFP-positive by analysing flow cytometry data. We measured the GFP₅₀ titers for three types of recombinant adenoviruses (OBP-401, OBP-1101, and OBP-1106). We compared GFP₅₀/mL and tissue culture infectious dose (TCID₅₀/mL), a conventional titration index, and found that these titers showed a linear correlation, with a correlation coefficient of >0.9. Moreover, GFP₅₀/mL showed high repetitive accuracy. We expect this flow cytometry-based method to be useful in case of clinically relevant viruses expressing an extraneous gene, in particular, to control viral quality.

Complex Dynamics of Virus Spread from Low Infection Multiplicities: Implications for the Spread of Oncolytic Viruses

While virus growth dynamics have been well-characterized in several infections, data are typically collected once the virus population becomes easily detectable. Earlier dynamics, however, remain less understood. We recently reported unusual early dynamics in an experimental system using adenovirus infection of human embryonic kidney (293) cells. Under identical experimental conditions, inoculation at low infection multiplicities resulted in either robust spread, or in limited spread that eventually stalled, with both outcomes occurring with approximately equal frequencies. The reasons underlying these observations have not been understood. Here, we present further experimental data showing that inhibition of interferon-induced antiviral states in cells results in a significant increase in the percentage of robust infections that are observed, implicating a race between virus replication and the spread of the anti-viral state as a central mechanism. Analysis of a variety of computational models, however, reveals that this alone cannot explain the simultaneous occurrence of both viral growth outcomes under identical conditions, and that additional biological mechanisms have to be invoked to explain the data. One such mechanism is the ability of the virus to overcome the antiviral state through multiple infection of cells. If this is included in the model, two outcomes of viral spread are found to be simultaneously stable, depending on initial conditions. In stochastic versions of such models, the system can go by chance to either state from identical initial conditions, with the relative frequency of the outcomes depending on the strength of the interferon-based anti-viral response, consistent with the experiments. This demonstrates considerable complexity during the early phase of the infection that can influence the ability of a virus to become successfully established. Implications for the initial dynamics of oncolytic virus spread through tumors are discussed.

We investigate in vitro adenovirus spread starting from the lowest infection multiplicities. This phase of virus dynamics remains poorly understood and is likely critical for ensuring that engineered oncolytic viruses successfully spread and destroy tumors. We find unexpectedly complex dynamics, which are analyzed with a combination of experiments and mathematical models. The experiments indicate that the induction of an interferon-based anti-viral state is a crucial underlying mechanism. The mathematical models demonstrate that this mechanism alone cannot explain the experiments, and that additional mechanisms must be invoked to account for the data. The models suggest that the ability of the virus to overcome the anti-viral state through multiple infection of cells might be one such mechanism.

Neuronal cholesterol metabolism increases dendritic outgrowth and synaptic markers via a concerted action of GGTase-I and Trk

Cholesterol 24-hydroxylase (CYP46A1) is responsible for brain cholesterol elimination and therefore plays a crucial role in the control of brain cholesterol homeostasis. Altered CYP46A1 expression has been associated with several neurodegenerative diseases and changes in cognition. Since CYP46A1 activates small guanosine triphosphate-binding proteins (sGTPases), we hypothesized that CYP46A1 might be affecting neuronal development and function by activating tropomyosin-related kinase (Trk) receptors and promoting geranylgeranyl transferase-I (GGTase-I) prenylation activity. Our results show that CYP46A1 triggers an increase in neuronal dendritic outgrowth and dendritic protrusion density, and elicits an increase of synaptic proteins in the crude synaptosomal fraction. Strikingly, all of these effects are abolished by pharmacological inhibition of GGTase-I activity. Furthermore, CYP46A1 increases Trk phosphorylation, its interaction with GGTase-I, and the activity of GGTase-I, which is crucial for the enhanced dendritic outgrowth. Cholesterol supplementation studies indicate that cholesterol reduction by CYP46A1 is the necessary trigger for these effects. These results were confirmed in vivo, with a significant increase of p-Trk, pre- and postsynaptic proteins, Rac1, and decreased cholesterol levels, in crude synaptosomal fractions prepared from CYP46A1 transgenic mouse cortex. This work describes the molecular mechanisms by which neuronal cholesterol metabolism effectively modulates neuronal outgrowth and synaptic markers.

VEGF dose regulates vascular stabilization through Semaphorin3A and the Neuropilin-1+ monocyte/TGF-β1 paracrine axis

VEGF is widely investigated for therapeutic angiogenesis, but while short-term delivery is desirable for safety, it is insufficient for new vessel persistence, jeopardizing efficacy. Here, we investigated whether and how VEGF dose regulates nascent vessel stabilization, to identify novel therapeutic targets. Monoclonal populations of transduced myoblasts were used to homogeneously express specific VEGF doses in SCID mouse muscles. VEGF was abrogated after 10 and 17 days by Aflibercept treatment. Vascular stabilization was fastest with low VEGF, but delayed or prevented by higher doses, without affecting pericyte coverage. Rather, VEGF dose-dependently inhibited endothelial Semaphorin3A expression, thereby impairing recruitment of Neuropilin-1-expressing monocytes (NEM), TGF-β1 production and endothelial SMAD2/3 activation. TGF-β1 further initiated a feedback loop stimulating endothelial Semaphorin3A expression, thereby amplifying the stabilizing signals. Blocking experiments showed that NEM recruitment required endogenous Semaphorin3A and that TGF-β1 was necessary to start the Semaphorin3A/NEM axis. Conversely, Semaphorin3A treatment promoted NEM recruitment and vessel stabilization despite high VEGF doses or transient adenoviral delivery. Therefore, VEGF inhibits the endothelial Semaphorin3A/NEM/TGF-β1 paracrine axis and Semaphorin3A treatment accelerates stabilization of VEGF-induced angiogenesis.

The Evaluation of Nerve Growth Factor Over Expression on Neural Lineage Specific Genes in Human Mesenchymal Stem Cells

Objective

Treatment and repair of neurodegenerative diseases such as brain tumors, spinal cord injuries, and functional disorders, including Alzheimer’s disease, are challenging problems. A common treatment approach for such disorders involves the use of mesenchymal stem cells (MSCs) as an alternative cell source to replace injured cells. However, use of these cells in hosts may potentially cause adverse outcomes such as tumorigenesis and uncontrolled differentiation. In attempt to generate mesenchymal derived neural cells, we have infected MSCs with recombinant lentiviruses that expressed nerve growth factor (NGF) and assessed their neural lineage genes.

Materials and Methods

In this experimental study, we cloned the NGF gene sequence into a helper dependent lentiviral vector that contained the green fluorescent protein (GFP) gene. The recombinant vector was amplified in DH5 bacterial cells. Recombinant viruses were generated in the human embryonic kidney 293 (HEK-293) packaging cell line with the helper vectors and analyzed under fluorescent microscopy. Bone marrow mesenchymal cells were infected by recombinant viruses for three days followed by assessment of neural differentiation. We evaluated expression of NGF through measurement of the NGF protein in culture medium by ELISA; neural specific genes were quantified by real-time polymerase chain reaction (PCR).

Results

We observed neural morphological changes after three days. Quantitative PCR showed that expressions of NESTIN, glial derived neurotrophic factor (GDNF), glial fibrillary acidic protein (GFAP) and Microtubule-associated protein 2 (MAP2) genes increased following induction of NGF overexpression, whereas expressions of endogenous NGF and brain derived neural growth factor (BDNF) genes reduced.

Conclusion

Ectopic expression of NGF can induce neurogenesis in MSCs. Direct injection of MSCs may cause tumorigenesis and an undesirable outcome. Therefore an alternative choice to overcome this obstacle may be the utilization of differentiated neural stem cells.

Production of Chemokine/Chemokine Receptor Complexes for Structural Biophysical Studies

The development of methods for expression and purification of seven-transmembrane receptors has led to an increase in structural and biophysical data and greatly improved the understanding of receptor structure and function. For chemokine receptors, this has been highlighted by the determination of crystal structures of CXCR4 and CCR5 in complex with small-molecule antagonists, followed recently by two receptor/chemokine complexes; CXCR4 in complex with vMIP-II and US28 in complex with the CX3CL1. However, these studies cover only a few of the many chemokines and chemokine receptors and production of stable receptor/chemokine complexes remains a challenging task. Here, we present a method for producing purified complexes between chemokine receptors and chemokines by coexpression in Sf9 cells. Using the complex between atypical chemokine receptor 3 and its native chemokine CXCL12 as an example, we describe the virus production, protein expression, and purification process as well as reconstitution into different membrane mimics. This method provides an efficient way of producing pure receptor/chemokine complexes and has been used to successfully produce receptor/chemokine complexes for CXC as well as CC receptors.

Linear correlation between average fluorescence intensity of green fluorescent protein and the multiplicity of infection of recombinant adenovirus

Background

Adenoviral vector is an efficient tool for gene transfer. Protein expression is regulated by a number of factors, but the regulation by gene copy number remains to be investigated further.

Results

Assessed by flow cytometry, we demonstrated a significant linear correlation between average fluorescence intensity of green fluorescent protein (GFP) and a wide range of multiplicity of infection (MOI), spanning from 0.01 to 200. Average GFP intensity was calculated by mean fluorescence intensity (MFI) × percentage of infection (POI) (MFI × POI) and the correlation was observed in cells transduced with GFP-expressing adenoviral vector driven either by a cytomegalovirus (CMV) promoter for 3 to 6 h or by a human phosphoglycerate kinase (PGK) promoter for 18 to 24 h. Factors impacting this linear correlation include MOI of viral vector, strength of promoter driving GFP expression, cell type transduced and incubation time after gene transfer. We also found that weak GFP signals could be interfered by background signals, whereas strong GFP signals could overshot the detection limitation of the flow cytometer and resulted in a deviation from linearity which was prevented by adjusting the setting in flow cytometer. Moreover, we compared promoter strength as measured by MFI × POI and found that the relative activity of CMV promoter to PGK promoter was 20 to 47 folds in A549 cells and 32 to > 100 folds in H1299 cells.

Conclusions

The linear correlation between MFI × POI and a wide range of adenoviral MOI provides an efficient method to investigate factors regulating protein expression and to estimate virus titers.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-015-0137-z) contains supplementary material, which is available to authorized users.

Effect of UV light on the inactivation of recombinant human adenovirus and murine norovirus seeded in seawater in shellfish depuration tanks

Shellfish depuration is a process that aims to eliminate pathogens from mollusk tissues. Seawater disinfection during the depuration process is important and ultraviolet (UV) light treatment is the most used method worldwide. Viral models are usually employed as surrogates of fastidious viruses in viability studies. The aim of this study was to employ methods based on green fluorescent protein (GFP) fluorescence and plaque forming units to detect, respectively, recombinant adenovirus (rAdV-GFP) and murine norovirus (MNV) artificially seeded in environmental matrices. These assays were applied to assess the inactivation of rAdV-GFP and MNV in seawater in recirculation shellfish depuration tanks with and without UV light treatment. Kinetics of rAdV GFP-expression was previously measured by UV-spectrophotometer. Flow cytometry (FC), fluorescence microscopy (FM), and plaque assay were used to determine virus titer and detection limits. The influence of the environmental matrix on the performance of the methods was prior determined using either drinking water or filtered seawater seeded with rAdV-GFP. Disinfection of seeded seawater was evaluated with and without UV treatment. The time of 24-h post-infection was established as ideal for fluorescence detection on rAdV-GFP infected cells. FC showed lower sensitivity, when compared to FM, which was similar to plaque assay. Seawater disinfection on depuration tanks was promising and rAdV-GFP declined 99.99 % after 24 and 48 h with and without UV treatment, respectively. MNV was completely inactivated after 24 h in both treatments. As conclusion, the depuration tanks were effective to inactivate rAdV-GFP and MNV and the UV disinfection treatment accelerated the process.

Application of statistical techniques for elucidating flow cytometric data of batch and fed-batch cultures

The objective of this work is to develop structured, segregated stochastic models for bioprocesses using time-series flow cytometric (FC) data. To this end, mammalian CHO cells were grown in both batch and fed-batch cultures, and their viable cell numbers (VCDs), monoclonal antibody (MAb), cell cycle phases, mitochondria membrane potential/mitochondria mass, Golgi apparatus, and endoplasmic reticulum (ER) were analyzed. For the fed-batch mode, soy hydrolysate was introduced at 24-H intervals. The cytometric data were analyzed for early indicators of growth and productivity by multiple linear regression analysis, which involved taking into account multicollinearity diagnostics, Durbin-Watson statistics, and Houston tests to determine and refine statistically significant correlations between categorical variables (FC parameters) and response variables (yield parameters). The results indicate that the percentage of G1 cells and ER was significantly correlated with VCD and MAb in the case of batch culture, whereas for fed-batch culture, the percentage of G2 cells and ER was correlated significantly. There was a significant difference between cells in the batch and fed-batch cultures in their ER content, suggesting that the increase in protein synthesis as reflected by the ER content and consequent increase in growth rate and MAb productivity both can be monitored at the cellular level by FC analysis of ER content.

A rapid Q-PCR titration protocol for adenovirus and helper-dependent adenovirus vectors that produces biologically relevant results

Adenoviruses are employed in the study of cellular processes and as expression vectors used in gene therapy. The success and reproducibility of these studies is dependent in part on having accurate and meaningful titers of replication competent and helper-dependent adenovirus stocks, which is problematic due to the use of varied and divergent titration protocols. Physical titration methods, which quantify the total number of viral particles, are used by many, but are poor at estimating activity. Biological titration methods, such as plaque assays, are more biologically relevant, but are time consuming and not applicable to helper-dependent gene therapy vectors. To address this, a protocol was developed called "infectious genome titration" in which viral DNA is isolated from the nuclei of cells ~3 h post-infection, and then quantified by Q-PCR. This approach ensures that only biologically active virions are counted as part of the titer determination. This approach is rapid, robust, sensitive, reproducible, and applicable to all forms of adenovirus. Unlike other Q-PCR-based methods, titers determined by this protocol are well correlated with biological activity.

Therapeutic angiogenesis due to balanced single-vector delivery of VEGF and PDGF-BB

Therapeutic angiogenesis by delivery of vascular growth factors is an attractive strategy for treating debilitating occlusive vascular diseases, yet clinical trials have thus far failed to show efficacy. As a result, limb amputation remains a common outcome for muscle ischemia due to severe atherosclerotic disease, with an overall incidence of 100 per million people in the United States per year. A challenge has been that the angiogenic master regulator vascular endothelial growth factor (VEGF) induces dysfunctional vessels, if expressed outside of a narrow dosage window. We tested the hypothesis that codelivery of platelet-derived growth factor-BB (PDGF-BB), which recruits pericytes, could induce normal angiogenesis in skeletal muscle irrespective of VEGF levels. Coexpression of VEGF and PDGF-BB encoded by separate vectors in different cells or in the same cells only partially corrected aberrant angiogenesis. In marked contrast, coexpression of both factors in every cell at a fixed relative level via a single bicistronic vector led to robust, uniformly normal angiogenesis, even when VEGF expression was high and heterogeneous. Notably, in an ischemic hindlimb model, single-vector expression led to efficient growth of collateral arteries, revascularization, increased blood flow, and reduced tissue damage. Furthermore, these results were confirmed in a clinically applicable gene therapy approach by adenoviral-mediated delivery of the bicistronic vector. We conclude that coordinated expression of VEGF and PDGF-BB via a single vector constitutes a novel strategy for harnessing the potency of VEGF to induce safe and efficacious angiogenesis.

Cholesterol-rich microdomains as docking platforms for respiratory syncytial virus in normal human bronchial epithelial cells

Respiratory syncytial virus (RSV) is one of the major causes of respiratory infections in children, and it is the main pathogen causing bronchiolitis in infants. The binding and entry mechanism by which RSV infects respiratory epithelial cells has not yet been determined. In this study, the earliest stages of RSV infection in normal human bronchial epithelial cells were probed by tracking virions with fluorescent lipophilic dyes in their membranes. Virions colocalized with cholesterol-containing plasma membrane microdomains, identified by their ability to bind cholera toxin subunit B. Consistent with an important role for cholesterol in RSV infection, cholesterol depletion profoundly inhibited RSV infection, while cholesterol repletion reversed this inhibition. Merger of the outer leaflets of the viral envelope and the cell membrane appeared to be triggered at these sites. Using small-molecule inhibitors, RSV infection was found to be sensitive to Pak1 inhibition, suggesting the requirement of a subsequent step of cytoskeletal reorganization that could involve plasma membrane rearrangements or endocytosis. It appears that RSV entry depends on its ability to dock to cholesterol-rich microdomains (lipid rafts) in the plasma membrane where hemifusion events begin, assisted by a Pak1-dependent process.

Rapid titration of viruses by flow cytometry

Traditionally, the most common methods used to titrate virus stocks are the plaque assay and the hemagglutination assay. The protocol presented here is based on the detection of viral-expressed proteins in infected cells by flow cytometry. It is simpler and more rapid than the traditional plaque-forming assay and it enables high-throughput analyses.

Rapid titration of measles and other viruses: optimization with determination of replication cycle length

Background

Measles virus (MV) is a member of the Paramyxoviridae family and an important human pathogen causing strong immunosuppression in affected individuals and a considerable number of deaths worldwide. Currently, measles is a re-emerging disease in developed countries. MV is usually quantified in infectious units as determined by limiting dilution and counting of plaque forming unit either directly (PFU method) or indirectly from random distribution in microwells (TCID50 method). Both methods are time-consuming (up to several days), cumbersome and, in the case of the PFU assay, possibly operator dependent.

Methods/Findings

A rapid, optimized, accurate, and reliable technique for titration of measles virus was developed based on the detection of virus infected cells by flow cytometry, single round of infection and titer calculation according to the Poisson's law. The kinetics follow up of the number of infected cells after infection with serial dilutions of a virus allowed estimation of the duration of the replication cycle, and consequently, the optimal infection time. The assay was set up to quantify measles virus, vesicular stomatitis virus (VSV), and human immunodeficiency virus type 1 (HIV-1) using antibody labeling of viral glycoprotein, virus encoded fluorescent reporter protein and an inducible fluorescent-reporter cell line, respectively.

Conclusion

Overall, performing the assay takes only 24–30 hours for MV strains, 12 hours for VSV, and 52 hours for HIV-1. The step-by-step procedure we have set up can be, in principle, applicable to accurately quantify any virus including lentiviral vectors, provided that a virus encoded gene product can be detected by flow cytometry.

A flow cytometry-based immuno-titration assay for rapid and accurate titer determination of modified vaccinia Ankara virus vectors

A flow cytometry-based immuno-titration titer assay was established to determine infectious unit (IU) and transducing unit (TU) of modified vaccinia Ankara (MVA) virus vectors. This titration method enumerates infected cells by measuring the expression of viral protein for IU and transgene protein for TU in individual cells after staining with fluorophore-conjugated antibodies. It presents many advantages over standard virus titration approaches, such as TCID(50) or plaque assay, for its convenience, rapidity and accuracy as illustrated by excellent assay linearity and reproducibility. Importantly, the IU and the TCID(50) assays generated similar batch-specific titer values when testing varied MVA-derived virus preparations. Assay development revealed that the post-infection time at which viral protein expression is evaluated, host cell type, and blocking the formation and release of progeny virion with nocodazole, an anti-microtubule agent or rifampin, a specific vaccinia virus assembly inhibitor, are critical parameters for the precision, robustness, and accuracy of IU titer determination. An added advantage of this assay is that it enables the concurrent determination of IU and transducing units (TU) by measuring the expression of a transgene product when testing recombinant viruses. The latter was demonstrated using a MVA vector carrying a human HER-2 gene fragment as model. Hence, this assay is very versatile in that it can be used to determine IU as well as multiple TU titers simultaneously. Furthermore, it can readily be adapted to other poxvirus vectors.

HDAC inhibitor valproic acid enhances tumor cell kill in adenovirus-HSVtk mediated suicide gene therapy in HNSCC xenograft mouse model

Safety, efficacy and enhanced transgene expression are the primary concerns while using any vector for gene therapy. One of the widely used vectors in clinical trials is adenovirus which provides a safe way to deliver the therapeutic gene. However, adenovirus has poor transduction efficiency in vivo since most tumor cells express low coxsackie and adenovirus receptors. Similarly transgene expression remains low, possibly because of the chromatization of adenoviral genome upon infection in eukaryotic cells, an effect mediated by histone deacetylases (HDACs). Using a recombinant adenovirus (Ad-HSVtk) carrying the herpes simplex thymidine kinase (HSVtk) and GFP genes we demonstrate that HDAC inhibitor valproic acid can bring about an increase in CAR expression on host cells and thereby enhanced Ad-HSVtk infectivity. It also resulted in an increase in transgene (HSVtk and GFP) expression. This, in turn, resulted in increased cell kill of HNSCC cells, following ganciclovir treatment in vitro as well as in vivo in a xenograft nude mouse model.

HPLC purification of adenoviral vectors

Adenoviruses are attractive vectors for gene therapy where short-term transgene expression is required. In order to meet the clinical requirements of adenovirus for use beyond the laboratory, advanced methods are required for the purification and quantitation of recombinant adenoviral vectors (rAd). Chromatographic systems offer the advantages of linear scalability and reproducibility, and this method describes a laboratory-scale process based on liquid chromatography, which can be technically transferred and readily scaled-up according to the demands of the laboratory or clinic in which it will be used.

From the first to the third generation adenoviral vector: what parameters are governing the production yield?

Human adenoviral viral vector serotype 5 (AdV) is presently the primary viral vector used in gene therapy trials. Advancements in AdV process development directly contribute to the clinical application and commercialization of the AdV gene delivery technology. Notably, the development of AdV production in suspension culture has driven the increase in AdV volumetric and specific productivity, therefore providing large quantities of AdV required for clinical studies. This review focuses on detailing the viral, cell and cell culture parameters governing the productivity of the three generations of AdV vectors.

Expanding the spectrum of genetic elements transferable by retroviral vectors

Retroviral vectors are powerful tools to study gene function. However, conventional methods require a cellular transcription step to generate the genomic RNA for viral production. This limits the scope of genetic elements that may be transferred by these vectors, excluding many key gene regulatory signals, including RNA editing motifs, alternative splicing, and various promoter/enhancer constellations, as well as cytotoxic genes. To address this problem, we devised a simple approach where in vitro-synthesized vector genomic RNA is transfected into the cytoplasm of a packaging cell, allowing immediate viral particle assembly. We demonstrate that high-titer retroviruses that efficiently transduce mammalian cell lines and primary cells are readily generated. Importantly, we show that an intron-containing expression cassette can be transferred by this method, leading to increased expression levels in the target cell. Further, we demonstrate that the cap structure is not required for retroviral packaging, thus avoiding translation of vector-encoded genes in the packaging cell. This allows the retroviral transfer of cytotoxic genes or proteins that otherwise inhibit viral production.

Prediction of recombinant protein production in an insect cell–baculovirus system using a flow cytometric technique

The baculovirus expression vector system (BEVS) utilising the Autographa californica nucleopolyhedrovirus (AcMNPV) is widely becoming the system of choice for the production of many recombinant protein products due to the high yields obtained. However, there is a need to develop a simple reliable on-line method to monitor the production of recombinant proteins that have no intrinsic reporter properties. Here we utilise flow cytometry to measure cell size, granularity and DNA content in a single step analysis and correlate these parameters with the production of the recombinant protein beta-galactosidase. Clear correlations between these parameters and productivity are made with forward and side scatter signals showing the highest correlation coefficients. Measuring these parameters does not require any processing of the cells from culture to analysis. These parameters can therefore be used successfully to predict the amount of recombinant protein product in a BEVS system on-line.

Population kinetics during simultaneous infection of insect cells with two different recombinant baculoviruses for the production of rotavirus-like particles

Background

The simultaneous production of various recombinant proteins in every cell of a culture is often needed for the production of virus-like particles (VLP) or vectors for gene therapy. A common approach for such a purpose is the coinfection of insect cell cultures with different recombinant baculoviruses, each containing one or more recombinant genes. However, scarce information exists regarding kinetics during multiple infections, and to our knowledge, no studies are available on the behavior of the different populations that arise during coinfections. Such information is useful for designing infection strategies that maximize VLP or vector yield. In this work, kinetics of cell populations expressing rotavirus GFPVP2 (infected with bacGFPVP2), VP6 (infected with bacVP6), or both proteins simultaneously (coinfected with both baculoviruses) were followed by flow cytometry.

Results

In single infections, the population infected with any of the recombinant baculoviruses followed the Poisson distribution, as the population expressing a recombinant protein exhibited a hyperbolic-type function with respect to the multiplicity of infection (MOI) up to 5 pfu/cell. In coinfections, the population fraction expressing each recombinant protein could not be anticipated from results of single infections, as in some cases interference and synergistic effects were found. Only cultures with a total MOI below 5 pfu/cell followed the Poisson distribution. For cultures with a MOI of bacGFPVP2 above that of bacVP6 (overall MOI above 5 pfu/cell), the total population expressing one or both recombinant proteins was as low as 50% below that predicted by Poisson. In contrast, the population fraction expressing VP6 increased in coinfections, compared to that in single infections. The largest population fraction simultaneously expressing both recombinant proteins was 58%, and corresponded to cultures infected at a MOI of 5 and 1 pfu/cell of bacGFPVP2 and bacVP6, respectively.

Conclusion

The infection conditions that maximize the cell population simultaneously expressing two recombinant proteins were determined. Such conditions could not have been anticipated from population kinetics in individual infections. This information should be taken into account for improved simultaneous production of various recombinant proteins in any work dealing with coinfections.

Using QPCR to assign infectious potencies to adenovirus based vaccines and vectors for gene therapy: toward a universal method for the facile quantitation of virus and vector potency

The assignment of infectious potency to test articles of adenovirus has been conducted mainly using classical end-point dilution methods, which rely on virus induced cytopathology to reveal the presence of infectious virus. These assays suffer the disadvantages of labor intensity, duration, throughput restriction and variability. In the course of our development of an Ad5 based HIV vaccine for clinical evaluation, we sought a facile method for the assignment of potency to the numerous test articles generated during the development of bioprocesses for bulk manufacture, downstream purification and formulation. In this paper we describe a quantitative PCR based potency assay (QPA) which uses QPCR to quantitate adenovirus genomes replicated 24h after the inoculation of a test article on 293 cell monolayers, and then relates that mass to potency by interpolation to a standard curve of replicated adenovirus genomes constructed with a reference adenovirus standard to which infectious potency has been previously assigned in the classical end-point dilution assay. The QPA assay for adenovirus is simple and rapid, with a throughput capacity adequate to the potency assay demands of bioprocess development, and with a precision expressed as a root variability of 16.8% R.S.D., allowing for close discriminations of the products of alternative process configurations. The adenovirus QPA principle can be applied to the quantitation of infectious potency of both RNA and DNA viruses and we report briefly on the development of QPA assays for measles and mumps. QPA assays owing to their simplicity and easy automation, rapidity, capacity and precision hold promise to become widely practiced methods for the quantitation of the potency of live virus vaccines and other recombinant virus vectors.