Table 1.

Methods for delivering the reprogramming factors.

	reprogramming factor delivery	considerations	references
integrative	retrovirus (ssRNA)	high efficiency integrates into genome: activation of proto-oncogenes/ disruption of tumour suppressor genes possible only infects dividing cells reactivation of viral genes possible	[22]
	lentivirus (ssRNA)	high efficiency infects also non-dividing cells integrates into genome: activation of proto-oncogenes/disruption of tumour suppressor genes possible reactivation of viral genes possible	[23]
not integrative	adenovirus (dsDNA)	low efficiency several rounds of infection necessary	[24]
	sendai virus (ssRNA)	high efficiency replicating virus has to be removed from iPSCs by negative selection	[25]
	pSin plasmid	low efficiency several transfections necessary integrates occasionally	[26]
	minicircle DNA	low efficiency several transfections necessary integrates occasionally does not contain any bacterial genes	[27]
	piggyBac transposon	traceless excision possible integrates into genome at specific integration sites: some effect transcription units excision may affect endogenous piggyBac elements reintegration possible	[28,29]
	sleepingbeauty transposon	traceless excision possible transposase allows efficient removal of transposon integrates into genome at specific integration sites: some effect transcription units reintegration possible	[30]
	oriP/EBNA1 based episomal plasmids	low efficiency self-replicative	[31]
	synthetic modified mRNA	increasing efficiency with more elaborate mRNA synthesis methods repeated transfections necessary because of rapid mRNA degradation	[32]
	VEE RF-RNA	self-replicating RNA that can be easily eliminated	[33]
	miRNA	very low efficiency repeated transfections necessary because of rapid miRNA degradation	[34]
	cell penetrating peptide-coupled protein	very low efficiency repeated transfections necessary because of rapid mRNA degradation	[35]