van der Heijden et al.
reported 12.85% of an HPV pDNA vaccine plasmid contained an IS2 although none had been detected in their master cell bank. They calculated that “it would have to be at a frequency below 1 in 10,000” to be undetectable. This study shows that massive expansion of IS elements from a very low starting level can be catastrophic. The authors conclude that the only way to avoid the problem is to use an IS-free host. Learn More