Alternative induced pluripotent stem cell characterization criteria for in vitro applications.

We also wish to point out that Maherali and Hochedlinger propose that human iPSCs should be derived using morphological or live cell staining procedures that require “a considerable degree of ESC expertise” and that “selection methods were unnecessary and actually counterproductive.” For iPSC technology to have its most profound impact, it is important to simplify the entrance requirements to recruit more laboratories to contribute new disease-specific lines and in vitro applications to the field. While we agree that iPSC lines can readily be isolated by morphological criteria and live cell staining, we contend that well-designed reporters containing fluorescent or selectable markers can facilitate isolation and expansion of reprogrammed colonies and would be critical for new investigators in the field. They also have utility for optimization of novel reprogramming methods and can monitor the presence of undifferentiated cells during directed differentiation protocols. Furthermore, looking into future therapeutic applications of iPSCs, reporter constructs could be engineered to encode a suicide gene to destroy residual undifferentiated iPSCs ex vivo prior to transplantation, or to track and ablate any misbehaving cells that appear in vivo in the patient.In summary, we welcome a discussion to establish a globally acceptable set of fundamental criteria that define iPSCs for in vitro applications. These criteria should be compatible with rapid characterization of the isolated iPSCs. In addition, development of reagents that facilitate entry into the field and that genetically modify iPSCs for safe future transplantations should be encouraged.