Preface [Hot Topic: Biosafety of Virus-Derived Vectors (Guest Editor: William Moens)]

Biosafety of viral vectors was first conceived as a set of guidelines for the risk assessment and management of viral vectors under various research and development situations. People from academia or industrial area concerned with basic research, gene therapy and vaccine technologies, were demanding ways to improve their daily research practices or production activities, their in vivo experiments and their clinical trials with appropriate safeguards. Such a need was originating either from safety concerns or from the necessity of compliance of pharmaceuticals and therapeutic development to international regulatory standards. Our idea was then not to evaluate conceptual risks -that nobody is able to assess anyway- but to build an coherent scientific image of the current biosafety of each type of viral vectors from the puzzle of published data and spread experiences. The project was set-up by a multidisciplinary group of experts organized by the secretariat of the Belgian Biosafety Advisory Council. Virologists, geneticists, vectors engineers, medical and veterinean users, experts familiar with clinical trials, registration of medicinal products, and post-marketing surveillance could be gathered. Most of the experts were members of safety advisory bodies in the European Union or at the level of the European Commission. “Viral vectors” are mainly engineered derivatives from eukaryotic viruses or attenuated variants thereof such as adenovirus, retrovirus, parvovirus, herpes viruses and poxviridae. Depending on the viewpoint, viral vectors are also conceptually transgenic viruses, chimerical transgenes, gene therapy vectors, vaccine vectors, or seen in innovative biotechnology as a source of future medicinal products. But viral vectors already have a long story. It started with the golden years of bacteriophages and with genetic engineering. How many students and biotechnologists today, still know the brilliant science of phage lambda, a bacterial virus, underlying the commercial packaging kits sold for the building of genomic libraries? As an example, do they know that the phage DNA sequences used in those packaging kits are restricted to the phage terminal repeats as carriers of “insert”, substrates for the encapsidation, and, in certain cases, as promoters for gene expression? Some readers may perhaps recognize or discover the amazing similarities between the classic recombinant lambda phages and some of the viral vectors described here. Whereas gene therapy vectors are intended for use with diseased animals and later on patients, life recombinant vaccines are intended for treatment of healthy people and animals. The corresponding scientific and medical literatures have few overlaps: somehow lessons from the design and use of vaccine vectors could be exploited for the design or assay of gene therapy vectors and vice-versa. Therefore, gathering “vaccine” and “gene therapy” people in a single review of risk assessment should certainly enrich both of them. Assessment of viral vectors is usually carried out after assessment of their components: the biology and ecology of gene donors and acceptors. The components of the expression cassette, the functional genetics of the construct, the natural spectrum of hosts of the construct acceptor are the main elements illustrated by the authors. The present review is the first but modest attempt to globally illustrate the various strategies of assessment at various steps of vector development and testing. One ambition of the review is to show that the risk assessment exercise may lead to unfamiliar conclusions and perhaps also show how to identify key knowledge that is missing and -in fact- should be known or demonstrated to justify claims of vector “safety”. In that sense the authors felt that biosafety assessment is not a way to block research and development but rather a responsible and qualitative way to frame it professionally. We do not know everything about the in vivo biology of viral vectors, these extra-ordinary chimerical genetic entities wherein huge amounts of human smartness and scientific culture are concentrated in an apparently innocent puzzle of DNA sequences. If the DNA sequence is indeed a program, safety can certainly be integrated in the engineered constructs. But this has limitations defined by our lack of knowledge of virus-host(s) interactions in vitro, and most certainly in vivo. However, these tools are the necessary probes to make Knowledge advance. Nowadays, industrial scales of vector production are rather impressive; The last fifteen years, the uses of virus derived genetic constructs, viral vectors, virosomes moved from academia to industries and even to production centers working under good manufacturing practices. The scale of production of these “products” evolved from titers of 10 3-10 5 pfu(particle forming units) up to those titers of 10 10 - 10 13 pfu necessary for relevant in vivo experiments. Such a suspension spread on the floor is not exactly the planned outcome of viral vectors. How do you estimate what to do as a clinician or a lab scientist should such a black day once occur? Containing the design and uses of these vectors in appropriate facilities seems obvious to everybody. Elaborating good laboratory or husbandry practices and quality procedures sounds also as logical. However, what do we do in the real world when designing a new construct, with not fully characterized or understood promoters, spacers, enhancers, terminators? What are the related precautions and decisions, what are the preventive measures, what are the training needs, how is the key art of “educated guessing” applied to viral vectors and transmitted to young scientists? The examples of assessment gathered in the present review might bring some rationale in the handling of such questions. The publication of “biosafety of viral vectors” is not just an academic exercise. Hopefully, it could trigger the appropriate criticisms, amendments and most probably a need for permanent improvements