Antibody-mediated uncoating of adenovirus in vitro

Significance of Preexisting Vector Immunity and Activation of Innate Responses for Adenoviral Vector-Based Therapy

An adenoviral (AdV)-based vector system is a promising platform for vaccine development and gene therapy applications. Administration of an AdV vector elicits robust innate immunity, leading to the development of humoral and cellular immune responses against the vector and the transgene antigen, if applicable. The use of high doses (10¹¹-10¹³ virus particles) of an AdV vector, especially for gene therapy applications, could lead to vector toxicity due to excessive levels of innate immune responses, vector interactions with blood factors, or high levels of vector transduction in the liver and spleen. Additionally, the high prevalence of AdV infections in humans or the first inoculation with the AdV vector result in the development of vector-specific immune responses, popularly known as preexisting vector immunity. It significantly reduces the vector efficiency following the use of an AdV vector that is prone to preexisting vector immunity. Several approaches have been developed to overcome this problem. The utilization of rare human AdV types or nonhuman AdVs is the primary strategy to evade preexisting vector immunity. The use of heterologous viral vectors, capsid modification, and vector encapsulation are alternative methods to evade vector immunity. The vectors can be optimized for clinical applications with comprehensive knowledge of AdV vector immunity, toxicity, and circumvention strategies.

The Effect of Residual Triton X-100 on Structural Stability and Infection Activity of Adenovirus Particles

To ensure the high purity and biological activity of the adenovirus vector to be used for clinical applications, a stable and linearly scalable preparation method is highly imperative. During the adenovirus-harvesting process, the Triton X-100-based lysis method possesses the advantages of higher efficiency as well as easier linearization and amplification. Most Triton X-100 can be removed from the adenovirus sample by chromatographic purification. However, there is no report that a small amount of residual Triton X-100, present in adenovirus sample, can affect the particle integrity, infectivity, and structure of adenoviruses. Here, we found that although residual Triton X-100 affected the short-term stability, purity, infectivity, and structure of adenoviruses at 37°C, it did not hamper these properties of adenoviruses at 4°C. This study suggests that although the Triton X-100-based lysis method is a simple, efficient, and easy-to-scale process for lysing host cells to release the adenovirus, the storage conditions of adenovirus products must be taken into consideration.

Virion glycosylation governs integrity and infectivity of infectious pancreatic necrosis virus

The possible importance of the O-linked glycosylation in virion stability and infectivity of infectious pancreatic necrosis virus (IPNV) was analysed. Enzymatic treatment with O-glycosidase of radiolabelled virions under different ionic conditions, to allow for possible alternative exposure of glycosidic enzyme cleavage sites, did not alter the specific infectivity of virions re-isolated after rate-zonal centrifugation in glycerol gradients. As an alternative method to assess the significance of carbohydrates in IPNV integrity, periodate oxidation in the presence of an aldehyde quencher was chosen. Following re-isolation of viruses, a 3-5 (10)log-unit reduction in specific infectivity was revealed and, at higher concentrations, a total disruption or virion aggregation was observed. The loss of infectivity of intact virions was not because of a lack of attachment to cells. Additionally, re-evaluation of reading values from UV-spectra of purified IPNV yielded a specific infectivity of 3 × 10(11) TCID(50)-units mg(-1) of protein and a ratio of 40 virions per TCID(50)-unit in the CHSE-214 cell system.

Adenovirus

Of the 53 different human adenovirus (HAdV) serotypes belonging to species A-G, a significant number are associated with acute respiratory, gastrointestinal and ocular infections. Replication-defective HAdV-5-based vectors also continue to play a significant role in gene transfer trials and in vaccine delivery efforts in the clinic. Although significant progress has been made from studies of AdV biology, we still have an incomplete understanding of AdV's structure as well as its multifactorial interactions with the host. Continuing efforts to improve knowledge in these areas, as discussed in this chapter, will be crucial for revealing the mechanisms of AdV pathogenesis and for allowing optimal use of AdV vectors for biomedical applications.

Classification of single-projection reconstructions for cryo-electron microscopy data of icosahedral viruses

We present a novel strategy for classification of heterogeneous electron microscopy data of icosahedral virus particles. The effectiveness of the procedure, which is based on classification of single-projection reconstructions (SPRs), is first investigated using simulated data. Of several reconstruction approaches examined, best results were obtained with algebraic reconstruction techniques (ART) when providing prior information about the reconstruction in the form of a starting volume. The results presented indicate that SPR-classification is sufficiently sensitive to classify assemblies with differences of only a few percent of the total mass. The usefulness of this procedure is illustrated by application to a heterogeneous cryo-electron microscopy dataset of adenovirus mutant dl313, lacking minor coat protein IX. These data were successfully divided into two distinct classes, in agreement with gel analysis and immuno-electron microscopy results. The classes yielded a wildtype-like reconstruction and a reconstruction representing the polypeptide IX-deficient dl313 virion. As the largest difference between these volumes is found at the location previously assigned to the external portion of minor coat protein polypeptide IIIa, questions arise concerning the current adenovirus model.

Capturing ion exchanger-bound infectious pancreatic necrosis virus--design and application for large volume water samples

A method was designed for rapid and reliable demonstration of the presence of infectious pancreatic necrosis virus retrieved from 5 l water samples. Viruses together with an added carrier protein were adsorbed to a resin of an added anion exchanger. Then the resin was collected rapidly and quantitatively through a specific device which we designed. The resin was transferred to a column from which the viruses were eluted, and subsequently further concentrated by acid precipitation, followed by SDS-polyacrylamide gel electrophoresis and Western blot analysis. Serological results were obtained within 24 h after the water sample was introduced into the laboratory. Proteins were recovered at an efficiency between 70 and 80% and the total concentration factor ranged between 150000 and 250000 times, depending on the requirements and the methods of choice.

Adenovirus uncoating and nuclear establishment are not affected by weak base amines

We have used four established lysosomotropic agents, ammonium chloride, amantadine, chloroquine, and methylamine, to monitor the possible interference with an early low-pH-dependent step during adenovirus replication. Two concentrations of each of the different agents were selected; one was essentially nontoxic to uninfected HeLa cells, and the other resulted in some toxicity as measured by trypan blue staining and by interference with cell monolayer establishment, cell proliferation, and radioisotope labelling. It was separately determined that these concentrations displayed pH-raising effects of the same magnitude as higher concentrations previously used in similar studies. Adenovirus uncoating in vivo, normally reaching its maximum within 1 h after infection, was not affected by any of the agents. The subsequent levels of successful nuclear entry events by the parental genomes were monitored by measuring the extent of transcription of an mRNA species coding for the early 72-kDa DNA-binding protein at 10 to 12 h postinfection. In HeLa, KB, HEp-2, and A549 cells, none of the agents were able to affect the levels of early transcription after administration at the point of infection or at 3 h after infection. The cumulative synthesis of the hexon antigen was assessed late in infection, and inhibitory effects were revealed upon administration of 10, 20, and 40 mM ammonium chloride, 10 mM methylamine, and 0.5 mM amantadine, irrespective of the time point of addition. Ammonium chloride at 5 mM reduced the hexon yield by 20% at the most when added within 50 min after infection. Chloroquine at concentrations of 2.5 and 5 microM specifically reduced the hexon yields by 30 to 40% when administered within the first 50 min of infection. On the basis of the lack of effects of nontoxic concentrations of the four agents on the early virus-cell interactive event of uncoating and the early virus-specified transcription, we conclude that a low-pH-dependent step early in the adenovirus replication cycle is not mandatory for a successful infection.

Purification of infectious pancreatic necrosis virus by anion exchange chromatography increases the specific infectivity

An improved method for the isolation and purification of infectious pancreatic necrosis virus (IPNV) is described. Virions released into the clarified growth medium are adsorbed to an anion exchange resin of diethylaminoethyl cellulose at pH 8.1. IPNV together with the likewise released and accumulated excess pool of the precursor to the major capsid protein, ICP62, are eluted at a salt concentration between 100 and 125 mM NaCl. The bovine serum albumin content of the growth medium supplement also elutes close to this position. Upon one step of combined sucrose- and CsCl-gradient centrifugation the recovered viruses display lower levels of aggregation, higher specific nucleic acid contents and an approximately 350% higher specific infectivity as compared with pools of viruses processed in parallel and isolated according to the established method relying on precipitation with poly(ethylene glycol).