Left or right? Directions to stem cell engraftment

A tri-phasic model of HSC engraftment. The top circle graphs demonstrate HSC distribution across different anatomical locations in several phases after transplantation. The bottom bar graphs show the resulting clonal complexity. (A) Early after transplantation, HSC distribution is characterized by marked asymmetry intrinsic to single-cell engraftment. (B) Subsequently, HSC proliferation produces clonal offspring, which are initially largely confined to their initial site of production. Only few clones (for as yet unknown reasons) have the capacity to mobilize, which is clone-size independent. (C) Only months to years after transplant, HSC composition equilibrates across different sites. In the example given, at each time point, several clones is found in blood that is not present in any of the sampled bone marrow sites, suggestive of their production in other, nonsampled locations.