Table 4.

Proposed Criteria for the Validation of hPSC-Derived Kidney Cells

Assay		Comments	References
Phenotypic characterization   Expression of embryonic and/or   adult kidney markers		Specificity of antibodies and   probes should be shown using   positive and negative controls	27,29,30,31,34,37,41,42,43,44,45,46,47,48,49,50,56,57,59,63
		Co-localization of multiple markers   within the same cells and in   neighboring segments should   be shown
		Quantification of kidney marker   expression and absence of   expression of nonkidney   markers should be performed
		Gene and protein expression   levels should be interpreted   cautiously in heterogeneous   differentiated cell populations
		Marker expression should be   consistent with a specific cell   identity
Kidney epithelial structures		Insufficient without accompanying   marker analysis because PSCs   are epithelial cells and are   capable of differentiating into   diverse epithelia	27,30,31,36,42,48,59,63
		Ultrastructural analysis (presence   of brush border) could provide   more supportive evidence of   kidney phenotype
		Evidence of hollow lumens   surrounded by polarized   epithelia should be presented
Functional analysis   In vitro	Biochemical assays of epithelial   cell function	Epithelial functions should be   compared with primary kidney   cells as positive controls and   nonkidney epithelial cells as   negative controls	59
	Integration into embryonic kidney   explant cultures	Results should be compared with   stochastically differentiated   PSCs as negative controls and   primary fetal kidney cells as   positive controls	27,28,29,30,37,41,44,48,57,59,63
In vivo	Formation of glomeruli   and nephron structures	Should be accompanied by   marker analysis, ideally showing   nephron segments in serial   sections	31
	Urine production	Requires PSC-derived kidney   tissue to be vascularized	Not shown
	Functional rescue after kidney   injury	Requires strategy to deliver cells   to the kidney effectively	Not shown