RhG-CSF-mobilized CD34+ peripheral blood progenitors are myeloperoxidase-negative and noncycling irrespective of CD33 or CD13 coexpression

Cycling status, myeloperoxidase expression, informative surface markers, and proliferative potential of peripheral blood hemopoietic progenitors (PBHP) were evaluated by flow cytometry in 10 patients affected by resistant lymphoma, and submitted to stem cell mobilization with combination chemotherapy (MiCMA) followed by recombinant human granulocyte colony-stimulating factor (rhG-CSF, 5 micrograms/kg/day). CD34+ PBHP coexpressed myeloid-associated and activation antigens, i.e., CD33 (96%, range 85-99), CD13 (99.5%, range 99.4-99.8), HLA-DR (99%, range 96.5-99.8), and CD38 (98%, range 90-100), lacked intracytoplasmic myeloperoxidase (MPO, < 3%), and resided in the Gzero/G1 phase of the cell cycle (96.5%, range 81-99.5, compared with 70%, range 49-78 bone marrow HP; p = 0.0007), independently of surface membrane phenotype; S-phase percentages of sorted CD34+ CD33(+)/-, CD34+CD38(+)/-, CD34+HLA-DR(+)/-, CD34+CD45RA(+)/-, CD34+CD45RO(+)/-, and CD34+CD41a(+)/- subpopulations were always negligible. In colony assays, 5-week-old long-term cultures seeded with CD34+CD33- cells yielded as many colonies as did CD34+CD33+ cells. In conclusion, rhG-CSF-mobilized CD34+ PBHPs contain noncycling, highly immature progenitors in which the expression of myeloid-associated antigens, i.e., CD33 or CD13, might not be indicative of myeloid commitment.