Currently cellular therapies, such as hematopoietic stem cell transplantation (HSCT), are produced at a small scale on a case-by-case basis, usually in a clinical or near-clinical setting. Meeting the demand for future cellular therapies will require a robust and scalable manufacturing process that is either designed around or controls the variation associated with biological starting materials. Understanding variation requires both a measure of the allowable variation (that does not negatively affect patient outcome) and the achievable variation (with current technology). The prevalence of HSCT makes it an ideal case study to prepare for more complex biological manufacturing with more challenging regulatory classifications.