Abstract
As stem cell products are increasingly entering early stage clinical trials, we are learning from experience about how cell products may be best assessed for safety and efficacy. In two papers published in this issue of Stem Cell Reports, a human neural stem cell product, HuCNS-SC, failed to demonstrate efficacy in central nervous system repair in two different animal models (Anderson et al., 2017; Marsh et al., 2017), although closely related research-grade cell products showed evidence of efficacy. This indicates the need for increased cell characterization to determine comparability of lots proposed for pre-clinical and clinical use. Without such improvements, pre-clinical data supporting a clinical study might not adequately reflect the performance of subsequent batches of cells intended for use in patients.