 In experiments designed to introduce or propagate DNA from non-viral or other low risk agents in animal cells, only low risk animal DNA could be used as vectors and the manipulations were to be confined to moderate risk containment facilities.With eukaryotes, attempts to clone segments of DNA using recombinant DNA technology from warm-blooded vertebrates genomes were to be performed only with vector-host systems that had demonstrably restricted growth capabilities outside the laboratory and in a moderate risk containment facility.This was because they potentially contained cryptic viral genomes that were potentially pathogenic to humans.