Background: Classically bone marrow(BM) is the maior source of hsmatopoietic stem cells for the transplantation. Recently, hematopoietic stem cells circulating in peripheral
nlood and umbilical cord stem cells have been widely accepted for use in high doss chmotherapy requiring hematopoietic stem cells support. Number if CFU-GM and
CD34+ cells ars routinely used to assess the engraftment potential of BM aspirates and leukapherssls harvests. However, these parameters predominantly reflect
clonogenic cell activity which might only be relevant to short-term hematopoeitic reconstitution, and not necessarily reflect the hsmatopoeitic stem cell activity capable of sustained engraftment. Long-term culture system is regarded as a quantitative method of estimating hsmatopoietic stem cell activity in clinical samples.
Methods: We enumerated CFU-GM and CD34+ cells in G-CSF mobilized peripheral blood (MPB), BM and umbilical cord blood(UCB). Ws obtained the number of LTC-IC from each of tress hematopoietic stem cell sourcss using the long-term culture system. These parameters have compared between the stem cell sources.
Results: CD34+ calls were detected in MPB, BM, and UCB at incidences of 2.27±1.58%, 0.7과土0.55%, 1.24土0.24% of total mononuclear calls. The highest number
of CD34+ cells were seen in UCB. The colony counts higher in UCB than in MPB and BM. Direct comparison of LTC-IC was made between three sources based on CD34+ cell counts. The total numbers of LTC-IC per 10 5CD34+ cell were 713 for UCB, 263 for BM, 104 for MPB. Thess UCB was superior to BM and MPB by cell all three parameters; CFU-GM, CD34+
LTC-IC.
Conclusion: We speculate that UCB should be better source of hematopoletic stem cell transplanation as well as gene thrapy if it could be expanded.

Keywords: LTC-IC, Umbilical cord blood, Bone marrow, Perlpheral blood