Side population cells in highly enriched CD34-positive cells from peripheral blood progenitor cells identify an immature subtype of hematopoietic progenitor cells but do not predict time to engraftment in patients treated with high-dose therapy.

Objective: A Hoechst 33342 dye efflux assay can be used to define a population of immature hematopoietic progenitor cells (HPC) that are called side population (SP) cells. Previously, SP cells examined from bone marrow (BM) and peripheral blood progenitor cells (PBPC) were found to be predominantly CD34 negative.