A call to adopt a "fit for purpose" approach to antibody validation for flow cytometry analyses of stem cell models and beyond.

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) can be exploited as models for a wide range of research applications and numerous protocols for generating hPSC-CMs have been described. However, it is currently not possible to direct differentiation to a single, homogeneous end point, and the resulting heterogeneity may be variable among laboratories, cell lines, and protocols. Consequently, the ability to assess phenotypic heterogeneity of the cell population is critical to the interpretation, repeatability, and reproduction of hPSC-CM studies. While flow cytometry is well suited for this purpose, a review of published literature reveals there is currently no consensus regarding which marker, antibody, or protocol is best suited to enable comparisons of hPSC-CM culture heterogeneity. Moreover, the lack of available experimental detail, combined with the variability in the approaches used for hPSC-CM evaluation, makes it challenging to reproduce, interpret, and compare published data. Consequently, this article calls for an alignment of the way researchers approach the routine use and documentation of the antibodies and controls used during flow cytometry-based assessment of hPSC-CM cultures. We advocate for the adoption of a "fit for purpose" validation mindset, whereby antibodies and experimental conditions are demonstrated as specific within a defined experimental design and biological context. Overall, we expect that by adhering to rigorous standards for antibody validation and use, reporting of experimental details, and presentation of data, the concepts emphasized here will promote enhanced utility and dialogue regarding hPSC-CM for a variety of research and translational applications by enabling more accurate comparisons of results among studies.