Current Gene Therapy - Volume 10, Issue 6, 2010

As the successes of Gene Therapy trials become ever more frequent so does the need to develop production processes allowing faster transfer into the clinical development phases. The Gene Therapy field is significantly pulverised, with many different vectors being currently available. Furthermore, new developments on vector design and safety as well as in vector production and purification technologies raise new challenges for the GMP production of Gene Therapy products. This issue of Current Gene Therapy gathers the expertise of a number of partners from the CliniGene European Network of Excellence. Indeed, benefitting from the common ground gained as the CliniGene network strongly impacted the practise in the field, it became clear that such knowledge as created in CliniGene should be made available to the Gene Therapy community. In this issue the production of the most commonly used vectors - adeno-associated virus, adenovirus, gamma-retrovirus, lentivirus and non-viral vectors - is thoroughly addressed. The focus is on the current need for larger scale production and purification to ensure safety and efficacy of the most advanced technologies available. The vector production core of this special issue is flanked by two very important contributions. One introductory paper led by CliniGene's Network of Excellence Coordinator, Prof. Odile Cohen-Haguenauer, on how production facilities in Europe should be made to cooperate in a common infrastructure ensuring the progress of this therapy and a final paper on the design and operation of GMP facilities for Advanced Therapy Medicinal Products. As more innovative treatment solutions are proposed, improved technological innovations arise and thus more clinical trials guarantee more and better products, this issue attempts to depict the current state-of-the-art on the production of vectors for Gene Therapy clinical applications. Hopefully, this integrated volume will ensure a fast spread and harmonization of production processes, reducing the barriers to make Gene Therapy a successful deliverer of Advanced Therapy Medicinal Products (ATMP's).

In the past 5 years, European investigators have played a major role in the development of clinical gene therapy. The provision of substantial funds by some individual member states to construct GMP facilities makes it an opportune time to network available gene therapy GMP facilities at an EU level. The integrated coordination of GMP production facilities and human skills for advanced gene and genetically-modified (GM) cell therapy, can dramatically enhance academic-led “First-in-man” gene therapy trials. Once proof of efficacy is gathered, technology can be transferred to the private sector which will take over further development taking advantage of knowledge and know-how. Complex technical challenges require existing production facilities to adapt to emerging technologies in a coordinated manner. These include a mandatory requirement for the highest quality of production translating gene-transfer technologies with pharmaceutical-grade GMP processes to the clinic. A consensus has emerged on the directions and priorities to adopt, applying to advanced technologies with improved efficacy and safety profiles, in particular AAV, lentivirus-based and oncolytic vectors. Translating cutting-edge research into “First-in-man” trials require that pre-normative research is conducted which aims to develop standard assays, processes and candidate reference materials. This research will help harmonise practices and quality in the production of GMP vector lots and GM-cells. In gathering critical expertise in Europe and establish conditions for interoperability, the PEVI infrastructure will contribute to the demands of the advanced therapy medicinal products* regulation and to both health and quality of life of EU-citizens.

The use of recombinant adeno-associated viral vectors (rAAVs) as gene transfer tools has increased dramatically during the past several years, establishing AAV as the vector of choice for many therapeutic applications. With the steady advance of the field toward clinical studies, and the isolation and engineering of several novel AAV serotypes, efficient, scalable, and versatile production and purification methods are continuously under development. Here, we review the current state of the art in the various production and purification methods for rAAVs. Classical parameters and methodologies to characterize rAAV stocks will be also discussed.

Replication deficient adenovirus vectors are frequently used tools for the delivery of transgenes in vitro and in vivo. In addition, several therapeutic products based on adenovirus are under clinical development. This review outlines adenovirus vector production discussing different vector types, available production cell lines and state of the art of production process development and purification.

Retroviral vectors are presently amongst the most widely used vectors in gene therapy clinical trials to target pathologies of different origins, such as cancers, genetic diseases or neurological disorders. This review provides an overview on the evolution of retroviral vector design and production for gene therapy applications, including state of the art developments in flexible producer cells and safe vectors. In addition, production and purification processes will be addressed, with a particular focus on the improvements undertaken to increase vector productivity and to reduce the rapid loss of infectivity, which presently represent the main challenges in retroviral vectors production for gene therapy.

Lentiviral vectors become more and more famous for the use as gene vector for gene therapy purposes for the treatment of acquired or inherited diseases. In this review, the present state of the art of the production of lentiviral vectors is presented with particular emphasis on the large scale production of these vectors for preclinical and clinical purposes. In contrast to oncoretroviral vectors which are produced using stable producer cell lines, clinical grade lentiviral vectors are essentially produced by transient transfection of 293 or 293T cells grown in Cell Factories. The main reason is that these production processes have been developed when good and safe LV producer cell lines were not available. With respect to the purification of lentiviral and in agreement with actual developments in the biotech industry, rather sophisticated downstream processing protocols have been established in order to remove any potentially dangerous process derived contaminant, such as plasmid or host cell DNA or host cell proteins. This review presents large scale production means for LV vectors, the different downstream processing steps as used for the purification of LV vectors as well as LV specific safety issues. Published large scale production and purification processes of lentiviral vectors and their process performances are compared.

After some decades of research, development and first clinical approaches to use DNA vectors in gene therapy, cell therapy and DNA vaccination, the requirements for the pharmaceutical manufacturing of gene vectors has improved significantly step by step. Even the expression level and specificity of non viral DNA vectors were significantly modified and followed the success of viral vectors. The strict separation of “viral” and “non-viral” gene transfer are historic borders for scientists and we will show that both fields together are able to allow the next step towards successful prevention and therapy. Here we summarize the features of producing and modifying these non-viral gene vectors to ensure the required quality to modify cells and to treat human and animals.

To be able to produce advanced therapy medicinal products, compliance with regulatory standards while maintaining flexibility is mandatory. For this purpose, careful planning is vital in the design or upgrade of a facility. Similarly, extensive foresight is elemental to anticipate upcoming needs and requirements. Failing this may lead to the facility's inability to meet the demands. In this chapter we aim to outline the current issues with regards to the European Union Directives (EUD) on advanced therapies, which impact gene and cell therapy facilities in Europe. This chapter is an attempt to elucidate what the minimum requirements for GMP facilities for gene and cell therapy products are and what is considered necessary to comply with the regulations in Europe.