Probing hematopoietic stem cell function using serial transplantation: Seeding characteristics and the impact of stem cell purification

Appropriate regulation of hematopoietic stem cell (HSC) numbers and function is a requisite for life-long blood cell replenishment. Knowledge of factors that regulate HSC activity is derived largely from murine model systems, with serial transplantation often considered a "gold standard" to assess longevity and self-renewal of HSCs. In the literature, we noted inconsistencies in how serial transplantations are conducted and decided to assess a set of parameters at play in such experiments. We found that HSCs distribute and expand unevenly among individual bones following transplantation, suggesting that isolation of a limited number of bone marrow cells for serial transplantation and/or analysis can influence experimental outcomes. Comparing donor cell output from transplanted unfractionated bone marrow cells, as opposed to fluorescence-activated cell-sorted HSCs, revealed distinct differences in the output of mature blood cells. Specifically, we found that long-lived progenitor and/or mature co-transplanted cells can severely affect the interpretation of ongoing HSC activity in secondary hosts. The implications of these data for the design and execution of serial transplantation experiments are discussed. Copyright (C) 2015 ISEH - International Society for Experimental Hematology. Published by Elsevier Inc.