Table 1.

Comparison of various reprogramming methods

Virus	Method	Advantages	Disadvantages
Yes	Conventional	High efficiency	Risk of insertional mutagenesis transgene reactivation and residual expression
	Retrovirus
			Risk of presence of proviral genome
			Can only be used in divided cells
Yes	Lentivirus	High efficiency	Risk of insertional mutagenesis transgene reactivation and residual expression
		Can be used in both dividing and nondividing cells
			Risk of presence of proviral genome
Yes	Adenovirus	No/small risk of integration	Moderate efficiency
			Need for repeated transductions
			Risk of presence of viral particles
Yes	Sendai virus	High efficiency	Risk of presence of viral particles
		No viral integration
No	Conventional and episomal plasmids	No integration	Very low efficiency
		No viral particles	Need for repeated transfections
No	Minicircle	Efficiency higher than conventional plasmids	Low efficiency (lower than viral methods)
			Need for repeated transfections
		No integration
		No viral particles
		No bacterial backbone
No	piggyBac transposon	No viral particles	Low efficiency
		Possibility to excise transgenes after reprogramming	Extra excision step
			Not imprint-free
			Risk of insertional mutagenesis transgene reactivation and residual expression
			Possible interactions between piggyBac system and endogenous transposon systems
No	mRNA	Very high efficiency	Need for repeated transfections
		Nontransgene, no integration	Requires specified reprogramming media
		No viral particles
No	Protein	Nontransgene, no integration, no exogenous nucleic acids	Very low efficiency
		No viral particles
No	Small molecule compounds	Nontransgene, no integration, no exogenous nucleic acids	Extremely low efficiency
		No viral particles
		Moderate efficiency
No	Direct transfection of mature miRNA	Nontransgene, no integration,	Low and inconsistent efficiency
		No viral particles