Frequency and differentiation capacity of circulating LTC-IC mobilized by G-CSF or GM-CSF following chemotherapy: A comparison with steady-state bone marrow and peripheral blood

Objective The present study was designed to compare directly the frequency of circulating LTC-IC and E-LTC-IC mobilized in peripheral blood (PB) after chemotherapy supported by either G-CSF (PB-G) or GM-CSF (PB-GM) in comparison to steady-state bone marrow (BM) and PB (PB-ST) values in the same patients. Materials and Methods Long-term cultures (LTC) were performed from 20 patients with malignant lymphoma at saturating cell concentrations to assess bulk progenitor cell production and by limiting dilution assay (LDA) to measure both frequency of LTC-IC and their proliferative and differentiation capacities. Results While CFC production in bulk LTC was higher at weeks 3–5 with PB-G than with PB-GM samples, week-5 LTC-IC and week-10 LTC-IC (E-LTC-IC) frequencies were not different using a LDA. However, the number of CFC derived from a single LTC-IC was higher in PB-G patients than in PB-GM patients (p = 0.01). Interestingly, the frequency of LTC-IC per 1 × 105 MNC in mobilized PB positively correlated with one-year marrow progenitor cell recovery, in contrast to the number of autografted CD34+ cells and CFU-GM per kg. Conclusion Both G-CSF and GM-CSF resulted in similar increases in LTC-IC and E-LTC-IC in PB at comparable levels to those present in BM. However, the differentiation capacity of LTC-IC was higher after mobilization with G-CSF than with GM-CSF, suggesting qualitative differences in LTC-IC mobilized with these growth factors.