Biological characterization of CD34+ cells mobilized into peripheral blood.
We review here the functional and kinetic characteristics of highly purified hematopoietic CD34+ mobilized into peripheral blood (PB) by granulocyte colony-stimulating factor (G-CSF) with or without chemotherapy for autologous or allogeneic transplantation. Circulating CD34+ cells were evaluated for their colony-forming capacity and trilineage proliferative response to selected recombinant human (rh) CSF in vitro, and the content of very primitive long-term culture initiating cells (LTC-IC). In addition, the cycling status of PB CD34+ cells, including committed clonogenic progenitor cells and the more immature LTC-IC, was determined by the cytosine arabinoside (Ara-C) suicide test and the acridine orange (AO) flow cytometric technique. By comparison, bone marrow (BM) CD34+ cells from the same individuals were studied under steady-state conditions and during G-CSF administration. Clonogenic assays in methylcellulose showed the same frequency of colony-forming unit cells (CFU-C) when PB primed-CD34+ cells and BM cells were stimulated with phytohemagglutinin-lymphocyte-conditioned medium (PHA-LCM). However, mobilized CD34+ cells were significantly more responsive than their steady-state BM counterparts to interleukin-3 (IL-3) and stem cell factor (SCF) combined with G-CSF or IL-3 in the presence of erythropoietin (Epo). Conversely, circulating and BM megakaryocyte precursors (CFU-MK) showed the same clonogenic efficiency in response to IL-3, GM-CSF and IL-3, IL-6 and Epo. Interestingly, very few CD34+ cells expressed the Mpl receptor and this finding resulted in the lower proliferative response of mobilized CFU-MK to the Mpl-ligand (megakaryocyte growth and development factor; MGDF), as compared to BM cells. After 5 weeks of liquid culture supported by the engineered murine stromal cell line M2-10B4 to produce G-CSF and IL-3, we reported a similar frequency of LTC-IC in PB and steady-state BM. Kinetic studies on PB and BM CD34+ cells, including LTC-IC, showed the low number of circulating progenitor cells in S and G2M phase whereas simultaneous DNA/RNA analysis and the Ara-C suicide assay demonstrated that the majority of PB CD34+ cells and LTC-IC are not quiescent (ie in G0 phase) being in G1 phase. Moreover, G-CSF administration prevented apoptosis in a small but significant proportion of mobilized CD34+ cells. Thus, our results indicate that mobilized and BM CD34+ cells can be considered equivalent for the frequency of both committed and more immature hematopoietic progenitor cells, although they show different kinetic and functional profiles. A further set of experiments indicated that G-CSF treatment did not alter the alloantigen presenting function of CD34+ cells which was mainly mediated by the upregulation of costimulatory molecules upon coincubation with allogeneic T cells. Taken together, these findings should allow a better understanding of PBSC transplantation.
Lemoli
R M
RM
Institute of Hematology, L & A Seràgnoli, University of Bologna, Italy.
Tafuri
A
A
Fortuna
A
A
Catani
L
L
Rondelli
D
D
Ratta
M
M
Tura
S
S
D000328:Adult; D017951:Antigen Presentation / Q000502:physiology; D018952:Antigens, CD34 / Q000032:analysis; D001854:Bone Marrow Cells / Q000166:cytology / Q000276:immunology; D002452:Cell Count / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay; D003115:Colony-Stimulating Factors / Q000494:pharmacology; D003561:Cytarabine / Q000494:pharmacology; D005434:Flow Cytometry; D019650:Hematopoietic Stem Cell Mobilization; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D006801:Humans; D011994:Recombinant Proteins / Q000494:pharmacology; D013997:Time Factors