Various types of viral vectors are being employed extensively as gene therapeutics to treat cancer and genetic diseases. Among the viruses that have been produced for human clinical trials (i.e. retrovirus, adenovirus, poxvirus, adeno-associated virus, and herpesvirus vectors) adenoviruses exhibit the lowest pathogenicity yet still infect an extensive range of cell types with high efficiency. These key characteristics make recombinant adenoviruses efficient gene-delivery vehicles and excellent research tools. However, the time-consuming and complex processes of generation, amplification, purification, and quality testing associated with production of recombinant adenoviruses make it difficult for many researchers to utilize these vectors. This is particularly true with respect to cell culture optimization and the virus propagation protocols employed in vector production. In this regard, the development of innovative cell culture techniques has become vital for optimizing vector production for gene therapy…
Category: <span>Viral Vectors</span>
The use of virus-based vectors for gene transfer has become an important delivery method for both in vitro applications and in vivo experimental clinical therapies. In small-scale experimental applications, most vectors can easily be concentrated and purified by simple methods (for example, ultracentrifugation.) However, it is challenging to scale up centrifugation-based vector purification methods for the large-scale production required for clinical use. In particular, when considering production of vector for human use, additional steps such as final sterilization by filtration must be taken to ensure the purity and safety of the vector preparation. Because the vector aggregates when pelleted by centrifugation, sterile filtration will eliminate vector particles from the solution. An efficient vector purification process that maintains vector potency is an important step in vector production for gene therapy…
The first HIV-based lentiviral vector to be used in humans, VRX496, is currently being tested in Phase I clinical trials (initiated in January 2003). With each new therapeutic comes the need to establish quality control (QC) testing designed specifically for that product. The QC testing for VRX496 was developed in accordance with the Code of Federal Regulations (CFR) 21 for pharmaceutical and bulk chemical GMPs, Points to Consider in the Characterization of Cell Lines Used to Produce Biologicals (1993) from the Center for Biologics Evaluation and Research (CBER) at FDA, and the United States Pharmacopeia (USP) 1046 for Cell and Gene Therapy Products. This report describes the QC testing of lot VRX496V02-009 of our clinical grade vector, which is being used in an ongoing clinical trial evaluating the first lentiviral gene therapy vector in humans. All assays are performed according to established standard operating procedures (SOPs) and in accordance with the principles of cGMP regulations…
With the continued progress of adenoviral vectors in gene therapy studies it is increasingly evident that a more formalized approach to the characterization and analysis of these viral vectors is urgently needed. Today, adenoviral vectors are beginning to be considered “well characterized biologics,” as shown by numerous publications describing sophisticated analytical approaches for recombinant adenovirus product candidates. Because the analytical definitions of adenoviral vectors currently lack comparison to a common standard, the problem for regulatory agencies is how to objectively evaluate safety in relation to the administered dose. This well-recognized need for an adenovirus standard has been addressed by a consortium of representatives from regulatory agencies, industry, and academic organizations — the Adenoviral Reference Material (ARM) Working Group. Its work has come to fruition in the recent public availability of the ARM, a purified wild type 5 adenovirus. Many aspects of the history, production, and characterization of the ARM have been published in detail…
An astonishing range of viruses has provided building blocks for gene delivery systems, from the simple adeno-associated virus with a 5 kb genome to the complex poxviruses with 300 kb. This review focuses on non-replicating viral vectors that infect host cells just once, without producing infections virus. Viral vectors are generally characterized by several criteria, including their ability to integrate into the host genome, coding capacity, titer, toxicity, immunogenicity, host range, duration of gene expression, and transient or stable production systems. These are precisely the features that need to be carefully studied in the context of the application when deciding which vector to use…
Recombinant adenovirus are attractive as vectors for gene therapy because: they exhibit wide tissue tropism and high transduction efficiency; adenovirus cultures can reach high specific titers (10^10 VP/mL), and; their use in the treatment of cancer and other serious diseases is valuable. A primary mode of adenovirus purification continues to be CsCl density gradient centrifugation…
In the past, researchers developing gene therapy applications used replication-defective human Adenovirus 5 (Ad5) as a vector for delivering DNA sequences, almost exclusively. Ad5 vectors are typically rendered replication defective by the deletion of E1a gene sequences. A complementing cell line containing the E1a gene makes it possible to produce Ad5 vectors in large scale. Of the various cell lines that have been constructed for the purpose of high-titer Ad5 production, HEK293 cells and PER.C6 cells are the most widely used…
Production of non-enveloped viruses generally requires a cell lysis procedure to liberate mature particles trapped within their host cells. The standard bench-scale practice of using freeze/thaw cycles is simple and effective, but heat transfer limitations restrict the technique to relatively small applications. Here we show that a ten-minute treatment with a dilute mixture of polysorbate-80 and tri-butyl phosphate effectively liberates adenovirus from host cells…
Recombinant adeno-associated viral (rAAV) vectors are known to be efficient vehicles for gene transfer in animal models. The attractive feature of this vector system consists primarily of long-term gene expression with little or no associated toxicities following administration to a variety of tissues. Previous and ongoing clinical trials in humans demonstrate a very good overall safety profile, but problems persist due to the lack of any systematic method for normalizing doses administered to animals and humans. To date, most of the work involves AAV serotype 2 vectors, but vector systems based on other AAV serotypes continue to develop rapidly. Administered doses are usually based on titer, but the defective nature of AAV makes determining vector infectious units difficult. Titering methods based on vector genomes (using hybridization, real-time PCR, or spectrophotometry) are more reliable, but give no information as to the infectivity of the vector. Determining infectious titer is critical, as the ratio of infectious virions to vector genome-containing virions helps to determine the dose, potency, and strength of the vector preparation…
The development of reference testing reagents has been used successfully in the past to standardize measurements among laboratories, particularly for biological products such as recombinant cytokines. This approach was recommended by many parties with a stake in adenovirus vector delivery in order to address the fact that particle units and infectious units are not standardized in the field. This has made interpretation of preclinical and clinical data, as it relates to the amount of adenovirus vector administered, difficult to compare across the field. An Adenovirus Reference Material is being developed to define the particle unit and infectious unit for adenovirus gene vectors, and create a commonality for comparisons, especially for data related to vector safety…