Paul H. Miller

Analysis of the clonal growth and differentiation dynamics of primitive barcoded human cord blood cells in NSG mice

Human cord blood (CB) offers an attractive source of cells for clinical transplants because of its rich content of cells with sustained repopulating ability in spite of an apparent deficiency of cells with rapid reconstituting ability. Nevertheless, the clonal dynamics of nonlimiting CB transplants remain poorly understood. To begin to address this question, we exposed CD34+ CB cells to a library of barcoded lentiviruses and used massively parallel sequencing to quantify the clonal distributions of lymphoid and myeloid cells subsequently detected in sequential marrow aspirates obtained from 2 primary NOD/SCID-IL2Rγ(-/-) mice, each transplanted with ∼10(5) of these cells, and for another 6 months in 2 secondary recipients. Of the 196 clones identified, 68 were detected at 4 weeks posttransplant and were often lympho-myeloid. The rest were detected later, after variable periods up to 13 months posttransplant, but with generally increasing stability throughout time, and they included clones in which different lineages were detected. However, definitive evidence of individual cells capable of generating T-, B-, and myeloid cells, for over a year, and self-renewal of this potential was also obtained. These findings highlight the caveats and utility of this model to analyze human hematopoietic stem cell control in vivo.

Heterogeneity in hematopoietic stem cell populations: implications for transplantation.

Purpose of reviewTransplantation of hematopoietic cells is now a well established clinical procedure, although optimal outcomes are not always obtained. This reflects insufficient knowledge of the different subsets of primitive cells required to achieve a rapid and permanent recovery of mature blood cell production. Here we review recent findings that extend our understanding of these cells and their regulation, and implications for the ex-vivo expansion of these cells. Recent findingsSeparate subsets of platelet and neutrophil lineage-restricted human hematopoietic cells with rapid but transient repopulating activities have been identified, thus adding to previous evidence of short-term repopulating cells that generate both of these lineages. New studies also suggest intrinsically determined heterogeneity in differentiation potentialities that are sustained at the stem cell level, and have revealed new ways their self-renewal can be influenced. SummaryHematopoietic repopulation posttransplant is highly complex both in terms of the differing numbers and types of cells required for optimal hematopoietic recoveries and the factors that will determine the composition and behavior of a given inoculum. Successful ex-vivo expansion protocols will, thus, need to incorporate conditions that will produce adequate numbers of all cell types required with retention of their full functionality.