Table 1.

The safety concerns and possible solutions for plasmid DNA vaccines and their production hosts. A priori each safety concern should be addressed as early in development as possible.

	Safety concern	Possible solution
Genetic elements	Transfer of plasmid to host flora	Narrow host-range replication region Non-antibiotic plasmid marker
	Germline integration	Avoidance of mammalian replication region
	Insertional mutagenesis and oncogenesis	Artificial DNA for promoter, intron, and signal sequence Avoidance of human-homologous DNA
	Adverse effects of encoded peptide(s)	Artificial signal sequences Avoidance of mammalian replication region Evaluation of vaccine peptide case-by-case
	Induction of autoimmune reactions	Minimized plasmids
Production host	Endotoxins and biogenic amines	Use of gram-positive organism
	Transferable antibiotic resistance genes	Determination of minimal inhibitory concentrations (MIC's) Screening for transferability
	Genetic instability	Analysis of plasmid population by sequencing and mass spectrometry
	Pathogenicity	Use of food-grade organism