Table 1.

iPS induction methods in human fibroblasts.

type of vector	method	genomic integration	factorsd	reprogramming efficiency in human fibroblasts e	reference
virus	retrovirus	+	OSKM	++++	[13]
	lentivirus	+	OSNL	+++	[14]
	adenovirus	−a	OSKM	+	[19]
	Sendai virus	−b	OSKM	++++	[20]
DNA	episomal plasmid	−a	OSKMNLT	+	[24]
	transposon	−a,c	OSKM	++	[21,22]
	minicircle	−a	OSNL	+	[23]
RNA	RNA	–	OSKM	+++	[25]
protein	cell transparent protein	–	OSKM	+	[26]

^aAbsence of genomic integration should be experimentally examined.

^bAbsence of virus RNA genome should be experimentally examined.

^cTransposon vector is integrated into genome, but it can be removed.

^dO, OCT3/4; S, SOX2; K, KLF4; M, C-MYC; N, NANOG; L, LIN28; T, SV40-large T antigen.

^e+, <0.001%; ++, <0.01%; +++, <0.1%; ++++, >0.1%.