Author:

Keywords:

Antigens, CD34, Bone Marrow Cells, Cell Culture Techniques, Granulocyte Colony-Stimulating Factor, HLA-DR Antigens, Hematopoiesis, Hematopoietic Stem Cells, Humans, Time Factors, Science & Technology, Life Sciences & Biomedicine, Hematology, HEMATOPOIETIC STEM-CELLS, CD34+ CELLS, LIMITING DILUTION, EXVIVO EXPANSION, IN-VITRO, TRANSPLANTATION, LEUKEMIA, INVITRO, STROMA, PROLIFERATION, 1102 Cardiorespiratory Medicine and Haematology, 1103 Clinical Sciences, 1114 Paediatrics and Reproductive Medicine, Immunology, 3101 Biochemistry and cell biology, 3201 Cardiovascular medicine and haematology, 3213 Paediatrics

Abstract:

We have recently shown that more than 90% of long-term culture initiating cells (LTC-IC) mobilized in the peripheral blood (PB) of normal individuals express HLA-DR and CD38 antigens and can sustain hematopoiesis for only 5 weeks. However, 10% of LTC-IC in mobilized PB are CD34+ HLA-DR- and CD34+ CD38- and can sustain hematopoiesis for at least 8 weeks. We now examine the ex vivo expansion potential of CD34+ HLA-DR+ cells (rich in mature LTC-IC) and CD34+ HLA-DR- cells (rich in primitive LTC-IC) in granulocyte colony-stimulating factor (G-CSF) mobilized PB progenitor cells (PBPC). Cells were cultured in contact with M2-10B4 cells (contact) or in transwells above M2-10B4 (noncontact) without and with interleukin-3 (IL-3) and macrophage inflammatory protein (MIP-1alpha) for 2 and 5 weeks. Progeny were evaluated for the presence of colony-forming cells (CFC) and LTC-IC. When CD34+ HLA-DR+ PB cells were cultured in contact cultures without cytokines, a threefold expansion of CFC was seen at 2 weeks, but an 80% decrease in CFC was seen at week 5. Further, the recovery of LTC-IC at week 2 was only 17% and 1% at week 5. This confirms our previous observation that although CD34+ HLA-DR+ mobilized PB cells can initiate long-term cultures, they are relatively mature and cannot sustain long-term hematopoiesis. In contrast, when CD34+ HLA-DR- mobilized PB cells were cultured in contact cultures without cytokines, CFC expansion persisted until week 5 and 49% and 11% of LTC-IC were recovered at week 2 and 5, respectively. As we have shown for steady state bone marrow (BM) progenitors, recovery of LTC-IC was threefold higher when CD34+ HLA-DR- PBPC were cultured in noncontact rather than contact cultures, and improved further when IL-3 and MIP-1alpha were added to noncontact cultures (96 +/- 2% maintained at week 5). We conclude that although G-CSF mobilizes a large population of "mature" CD34+ HLA-DR+ LTC-IC with a limited proliferative capacity, primitive CD34+ HLA-DR- LTC-IC present in mobilized PB have similar characteristics as LTC-IC from steady state BM: (1) they can be maintained in noncontact cultures containing IL-3 and MIP-1alpha for at least 5 weeks; (2) they are subject to the same proliferation inhibitory influences of contact with stroma. Since the absolute number of primitive LTC-IC (week 8 LTC-IC) per mL of G-CSF mobilized PB is similar to that per mL of steady state BM, these studies further confirm that G-CSF mobilized PBPC may have similar long-term repopulating abilities as steady state BM.