Marrow or Peripheral Blood for Hematopoietic Engraftment

To the Editor: Implicit in the suggestion of Storb et al.1 that normal human peripheral blood may be used as a supplementary source of cells for hematopoietic engraftment is the belief that true hematopoietic stem cells circulate. This is a view with which we concur,2 and it has the support of circumstantial evidence derived from clinical experience.3 4 5 In this regard it should be noted that the demonstrable presence, in human blood, of progenitor cells committed to differentiation along established pathways6 7 8 9 10 is irrelevant to the goal of successful engraftment, since these cells have a limited capacity for self-replication.11 Using an.