Table 1. Comparison of the characteristics of different stem cells.

	Embryonic stem cells	Induced pluripotent stem cells	Somatic or adult stem cells
Source	Inner cell mass of the blastocyst	Reprogrammed somatic cells	Tissue-specific protocols from different tissues
Differentiation potential	Can differentiate into cell types of all three germ lineages	Can differentiate into cell types of all three germ lineages	Can only differentiate into limited cell types
Self-renewal	Complete	Complete	Limited
Proliferative capacity	Strongest	Powerful	Weak and cannot be maintained for a long periods
Tumorigenicity	Yes	Yes	No
Ethical controversy	Yes	No	No