Brief report: benchmarking human pluripotent stem cell markers during differentiation into the three germ layers unveils a striking heterogeneity: all markers are not equal.

Pluripotent stem cells (PSC) are functionally characterized by their capacity to differentiate into all the cell types from the three germ layers. A wide range of markers, the expression of which is associated with pluripotency, has been used as surrogate evidence of PSC pluripotency, but their respective relevance is poorly documented. Here, we compared by polychromatic flow cytometry the kinetics of loss of expression of eight widely used pluripotency markers (SSEA3, SSEA4, TRA-1-60, TRA-1-81, CD24, OCT4, NANOG, and alkaline phosphatase [AP]) at days 0, 5, 7, and 9 after induction of PSC differentiation into cells representative of the three germ layers. Strikingly, each marker showed a different and specific kinetics of disappearance that was similar in all the PSC lines used and for all the induced differentiation pathways. OCT4, SSEA3, and TRA-1-60 were repeatedly the first markers to be downregulated, and their expression was completely lost at day 9. By contrast, AP activity, CD24, and NANOG proteins were still detectable at day 9. In addition, we show that differentiation markers are coexpressed with pluripotency markers before the latter begin to disappear. These results suggest that OCT4, SSEA3, and TRA-1-60 might be better to trace in vitro the emergence of pluripotent cells during reprogramming.