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Environmental risk assessment of replication competent viral vectors in gene therapy trials

Leidraad voor de milieurisicobeoordeling van genetisch gemodificeerde replicatiecompetente virussen in gentherapiestudies


The National Institute for Public Health and the Environment (RIVM) has developed a method to estimate the risks for man and the environment of the application of replication competent viral vectors in cancer therapy. Since such a method did not exist, this report will be a significant aid in the risk assessment of replication competent viruses and in guiding applications for a gene therapy license involving the use of these viruses through the regulatory process in the Netherlands. Dutch scientists are planning to initiate clinical trials in which genetically modified replication competent viruses will be applied. These viruses are able to specifically replicate in cancer cells leading to their destruction. Potential adverse effects of viral therapies are related to the exposure of man and the environment to the virus. In the Netherlands, exclusively clinical studies making use of replication deficient viruses have been permitted thus far. These 'crippled' viruses can only infect a limited amount of cells and are thereby able to repair the effects of a genetic defect, for instance in a patient with a metabolic disease. Using risk assessment it has been concluded that in most cases the environmental risks of this type of application are negligible. Replication competent viruses, however, retain characteristics that make them able to multiply within a cancer patient and therefore a basic principle in the risk assessment of these viruses should be that there is a chance of spreading of the virus from the patient into the environment. The report gives points to consider for the environmental risk assessment of replication competent viruses taking into account the viral characteristics, the effects of the genetic modifications on the virus, the current clinical applications and future developments. The report is expected to provide guidance to risk assessors and regulatory officers as well as to applicants for a gene therapy license.

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