On the stability of sequences inserted into viral genomes

Willemsen, Anouk; Zwart, Mark P

Engineered alphabaculoviruses (infecting arthropods) are widely used as vectors for the expression of heterologous genes in insect cells. Nonetheless, during serial passaging defective interfering (DI) baculoviruses that lack large portions of the genome are rapidly produced, in what appears to be an intrinsic property of baculovirus infection (Pijlman et al. 2001) . As a result of having a smaller genome size, these DIs most likely have a replicative advantage (higher fitness). Especially in bioreactor configurations where the cellular multiplicity of infection (MOI, the number of virus particles infecting a cell) is high, fasterreplicating DIs can rapidly reach high frequencies (Kool et al. 1991) . The rapid generation of DIs involves several recombination steps and prevents the development of stable baculovirus expression vectors, as inserted sequences are then also rapidly lost (Pijlman et al. 2001) .