their phenotypic heterogeneity, and our limited understanding of their natural histories and prognoses. Indeed, as exciting as these new strategies of cell therapy might be, and as strong as the preclinical animal data may be in suggesting their potential efficacy, we will be unable to establish which treatments indeed provide significant benefit, whether that benefit might outweigh the risks inherent in cell therapy, and whether the durability of their benefits justifies the effort, until we can claim a better understanding of the heterogeneity and genotype-dependent natural histories of these disorders, and design our clinical trials accordingly.
