title: Estimating human hematopoietic stem cell kinetics using granulocyte telomere lengths.
abstract: OBJECTIVE
  To study in vivo behavior of hematopoietic stem cells (HSC).
  
  
  METHODS
  Behavior of HSC is difficult to study because one cannot observe and track cells within the marrow microenvironment. Therefore, information must be obtained from indirect means, such as competitive repopulation assays or surrogate studies, such as observations of telomere shortening in granulocytes. In this article, we use granulocyte telomere length data and a novel approach, stochastic simulation, to derive replication rates of HSC. The approach is first applied to cats and then to humans.
  
  
  RESULTS
  Human HSC replicate infrequently, on average once per 45 weeks (range: once per 23 to once per 67 weeks).
  
  
  CONCLUSIONS
  This rate is substantially slower than the average replication rates estimated for murine (once per 2.5 weeks) and feline (once per 8.3-10 weeks) HSC in vivo.
authors.affiliation: Department of Biostatistics, University of Washington, Seattle, WA, USA.
authors.forename: Bryan E
authors.initials: BE
authors.lastname: Shepherd
authors.forename: Peter
authors.initials: P
authors.lastname: Guttorp
authors.forename: Peter M
authors.initials: PM
authors.lastname: Lansdorp
authors.forename: Janis L
authors.initials: JL
authors.lastname: Abkowitz
mesh_terms: D000367:Age Factors; D000818:Animals; D002415:Cats; D002453:Cell Cycle; D006098:Granulocytes / Q000648:ultrastructure*; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D006801:Humans; D007700:Kinetics; D008962:Models, Theoretical; D016615:Telomere / Q000648:ultrastructure*