Table 2.

Terms, Definitions, Experimental Tests, and Examples of Cells with Different Degrees of Potency

Term	Definition	Experimental test	Examples
Totipotent	An isolated cell that is able to produce a fertile adult individual.	An isolated cell is transferred to a uterus (after inserting into an empty zona pellucida or after developing to the blastocyst stage in culture) and it gives rise to a fertile adult.	Zygotes Some early cleavage-stage blastomeres
Plenipotent	An isolated cell that is able to produce all or most of the derivatives of the ICM and some or all of the TE- and PE-derived cells, but is unable to organize these cells into an integrated body plan.	The cell produces all the structures of the mature body (including germ line) with substantial contributions to TE- and/or PE-derived structures in a complementation assay. The cell makes substantial contributions to all three germ layers and to TE- and/or PE-derived structures in a chimeric embryo/animal. The cell is able to form type I yolk-sac-containing teratomas after injection into an immune-compromised mouse, including tissues with gene expression patterns and histology characteristic of the derivatives of all three germ layers plus TE- and/or PE-derived cells. The cell is able to differentiate in culture into cells with gene expression patterns and physiology characteristic of the derivatives of all three germ layers as well as TE- and/or PE-derived structures.	ICM cells in normal embryos, prior to segregation into epiblast and PE Late morula-stage blastomeres in normal embryos prior to commitment to TE or ICM Mouse and human embryonal carcinoma cellsa Most hESCs and human induced pluripotent stem cellsa Primordial germ cells and some germ cell linesb
Pluripotent	An isolated cell that is able to produce all or most of the derivatives of the epiblast, but is unable to organize these cells into an integrated body plan or to produce derivatives of TE and/or PE.	The cell produces all of the structures of the mature body (including germ line), with minimal contribution to the TE- and/or PE-derived structures in a complementation assay. The cell makes substantial contributions to all three germ layers with minimal contribution to TE- and/or PE-derived structures in a chimeric embryo/animal. The cell is able to form type I non-yolk-sac-containing teratomas, including derivatives of all three germ layers, with minimal representation of TE- and/or PE-derived cells. The cell is able to differentiate in culture into cells with gene expression patterns and physiology characteristic of the derivatives of all three germ layers.	Epiblast cells in normal embryos mESCs and mouse induced pluripotent cells under standard culture conditionsc

Cell types that have met some or all of the experimental tests listed are given as examples, with cases in which there is some debate over the evidence being given in italics. The tests are listed in rough order of stringency, with the first test being the only definitive proof for the specified level of potency. Teratoma classification follows the designation of Cunningham et al. [193]. Note: These terms apply only to individual cells, not to groups of cells.

^aTesting the developmental potency of human cells is limited by ethical constraints. hESCs, iPSCs, and embryonal carcinomas are plenipotent based primarily on the last two tests and on limited data from chimeric mice.

^bPrimordial germ cells are plenipotent based primarily on yolk-sac tumor/teratoma formation.

^cSome mESCs and iPSCs are able to form PE-derived cells under some culture conditions and can make limited contributes to both TE- and PE-derived structures in chimeric mice, suggesting that they may be plenipotent.

hESCs, human embryonic stem cells; iPSCs, induced pluripotent stem cells; mESCs, mouse embryonic stem cells.