The heterogeneity of life spans in the HSC compartment is derived from HSC clones with preprogrammed self-renewal capacity. (A) Single donor type HSCs were transplanted into individual hosts. Daughter HSCs were serially transplanted into multiple secondary, tertiary and, if possible, quaternary host to follow the HSC clones over extended periods.3 All HSCs have a limited life span, although the life span varies. (B) Representation of the serial transplants of an individual HSC demonstrating the synchronicity of HSCs within a clone. Note the similarities of the repopulation kinetics in the secondary hosts and the simultaneous extinction of all daughter HSCs in all tertiary hosts. Additional examples can be found in Sieburg et al.41 The behavior of daughter HSC contrasts with the extensive heterogeneity of secondary repopulation kinetics after a multiclonal graft (C). This representation exemplifies a multiclonal graft (2 × 105 BM cells) originally injected into a single ablated host. Blue line represents donor type cells in blood after the primary graft; and different colored lines, donor type cells in blood in secondary and tertiary hosts. This research was originally published in Blood.3,4
