Replication-competent non-human viruses for use in clinical gene therapy: an inventory study

All living organisms are exposed to viruses. In general, viruses infect only a single
host species or a restricted set of host species. In very rare cases productive infection
may occur outside the natural host(s) species. This may be manifested by a distinct
disease in the new host. Although very rare, this could lead to establishment and
persistence of the virus in the new host. In view of the knowledge that virus
adaptation can occur, the intensive use of non‐human viruses and their genetically
modified variants as therapeutic agents in clinical therapy may be cause for concern.
The administration of non‐human viruses (either systemically or intratumoral) to
humans may have an associated risk of adapting the virus to increase replication in
humans. Theoretically this could result in horizontal transfer of adapted viruses to
the recipient’s relatives or medical personnel. This is evidently undesirable.
The risks associated with spread of the administered therapeutic virus from patients
are unknown. Therefore the Commission on Genetic Modification (COGEM)
commissioned a study.