Replication defective vectors derived from simple retroviruses or the more complex genomes of lentiviruses continue to offer the advantages of long-term expression, cell and tissue specific tropism, and large packaging capacity for the delivery of therapeutic genes. The occurrence of adverse events caused by insertional mutagenesis in three patients in a gene therapy trial for X-linked SCID emphasizes the potential for problems in translating this approach to the clinic. Several genome-wide studies of retroviral integration are now providing novel insights into the integration site preferences of different vector classes. We review recent developments in vector design, integration, biosafety, and production.

Gene Therapy Progress and Prospects: Development of improved lentiviral and retroviral vectors – design, biosafety, and production

Lentiviral vectors (LV) have seen considerably increase in use as gene therapy vectors for the treatment of acquired and inherited diseases. This review presents the state of the art of the production of these vectors with particular emphasis on their large-scale production for clinical purposes. In contrast to oncoretroviral vectors, which are produced using stable producer cell lines, clinical-grade LV are in most of the cases produced by transient transfection of 293 or 293T cells grown in cell factories. However, more recent developments, also, tend to use hollow fiber reactor, suspension culture processes, and the implementation of stable producer cell lines. As is customary for the biotech industry, rather sophisticated downstream processing protocols have been established to remove any undesirable process-derived contaminant, such as plasmid or host cell DNA or host cell proteins. This review compares published large-scale production and purification processes of LV and presents their process performances. Furthermore, developments in the domain of stable cell lines and their way to the use of production vehicles of clinical material will be presented.

Production of lentiviral vectors

Promising results in several clinical studies have emphasized the potential of gene therapy to address important medical needs and initiated a surge of investments in drug development and commercialization. This enthusiasm is driven by positive data in clinical trials including gene replacement for Hemophilia B, X-linked Severe Combined Immunodeficiency, Leber's Congenital Amaurosis Type 2 and in cancer immunotherapy trials for hematological malignancies using chimeric antigen receptor T cells. These results build on the recent licensure of the European gene therapy product Glybera for the treatment of lipoprotein lipase deficiency. The progress from clinical development towards product licensure of several programs presents challenges to gene therapy product manufacturing. These include challenges in viral vector-manufacturing capacity, where an estimated 1-2 orders of magnitude increase will likely be needed to support eventual commercial supply requirements for many of the promising disease indications. In addition, the expanding potential commercial product pipeline and the continuously advancing development of recombinant viral vectors for gene therapy require that products are well characterized and consistently manufactured to rigorous tolerances of purity, potency and safety. Finally, there is an increase in regulatory scrutiny that affects manufacturers of investigational drugs for early-phase clinical trials engaged in industry partnerships. Along with the recent increase in biopharmaceutical funding in gene therapy, industry partners are requiring their academic counterparts to meet higher levels of GMP compliance at earlier stages of clinical development. This chapter provides a brief overview of current progress in the field and discusses challenges in vector manufacturing.

Progress and challenges in viral vector manufacturing.

From the perspective of a pilot clinical gene therapy trial for Wiskott–Aldrich syndrome (WAS), we implemented a process to produce a lentiviral vector under good manufacturing practices (GMP). The process is based on the transient transfection of 293T cells in Cell Factory stacks, scaled up to harvest 50 liters of viral stock per batch, followed by purification of the vesicular stomatitis virus glycoprotein-pseudotyped particles through several membrane-based and chromatographic steps. The process leads to a 200-fold volume concentration and an approximately 3-log reduction in protein and DNA contaminants. An average yield of 13% of infectious particles was obtained in six full-scale preparations. The final product contained low levels of contaminants such as simian virus 40 large T antigen or E1A sequences originating from producer cells. Titers as high as 2 × 109 infectious particles per milliliter were obtained, generating up to 6 × 1011 infectious particles per batch. The purified WAS vector...

Large-Scale Manufacture and Characterization of a Lentiviral Vector Produced for Clinical Ex Vivo Gene Therapy Application

This review is intended to exemplify the roles and responsibilities of the two agencies under the Department of Health and Human Services, the National Institutes of Health and the Food and Drug Administration, that have oversight for human gene transfer clinical protocols, as seen through our experience of bringing a first-in-its-class lentiviral vector to clinical trials. In response to the changing circumstances in gene therapy research between 1999 and 2002, the concerns of these agencies regarding gene therapy have been evolving. This review provides an overview of the major safety concerns regarding insertional oncogenesis, the generation of a replication- competent lentivirus (RCL), and vector mobilization thought to be related to lentiviral vectors, which had to be addressed during the regulatory review process before initiating the clinical trial. Specific monitoring assays to address these concerns were established to test for RCL generation, vector mobilization, persistence of vector-modified cells, and abnormal clonal expansion of modified cells. We hope to provide a basic understanding and appreciation of the regulatory process and major safety concerns, toward providing useful insight to those presently embarking on the development of clinical application of lentiviral vectors.

Regulatory considerations for novel gene therapy products: a review of the process leading to the first clinical lentiviral vector.

Large-scale Purification of a Lentiviral Vector by Size Exclusion Chromatography or Mustang Q Ion Exchange Capsule

QC Release Testing of an HIV-1 Based Lentiviral Vector Lot and Transduced Cellular Product

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Large-scale Purification of a Lentiviral Vector by Size Exclusion Chromatography or Mustang Q Ion Exchange Capsule

QC Release Testing of an HIV-1 Based Lentiviral Vector Lot and Transduced Cellular Product