Objective: Even though much progress has been made in defining primitive hematologic cell phenotypes by using flow cytometry and clonogenic methods, the direct method for study of marrow repopulating cells still remains to be elusive. Long Term Culture-Initiating Cells (LTC-IC) are known as the most primitive human hematopoietic cells detectable by in vitro functional assays. Materials and Methods: In this study, LTC-IC with limiting dilution assay was used to evaluate repopulating potential of

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... cord blood stem cells. Results: CD34 selections from cord blood were completed succesfully with magnetic beads (73,64%±9,12). The average incidence of week 5 LTC-IC was 1: 1966 CD34+ cells (range 1261-2906). Conclusion: We found that number of LTC-IC obtained from CD34+ cord blood cells were relatively low in numbers when compared to previously reported bone marrow CD34+ cells. This may be due to the lack of some transcription and growth factors along with some cytokines and chemokines released by accessory cells which are necessary for proliferation of cord blood progenitor/stem cells and it presents an area of interest for further studies. (Turk J Hematol 2010; 27: 234-41) Özet Amaç: Ak m hücre ölçer ve klonojenik yöntemler kullan m ile öncül hematolojik hücre fenotiplerinin tan mlanmas nda çok a ama kaydedilmi olmas na ra men, kemik ili ini yenileyen hücrelerin do rudan bir yöntemle tan mlanmas henüz mümkün olmamaktad r. Uzun Dönemli Kültür-Ba latan Hücreler (UDK-BH) in vitro fonksiyonel yöntemlerle saptanabilen en öncül insan hematopoietik hücreleridir. Yöntem ve Gereçler: Bu ara t rmada, kordon kan kök hücrelerinin kemik ili ini yenileyen hücre yetene ini ölçümlemek üzere k s tl dilüsyon ile UDK-BH yöntemi uygulanm t r. Bulgular: Kordon kan ndan CD34+ hücrelerin seleksiyonu manyetik boncuklarla ba ar ile gerçekle tirilmi tir (%73,64±9,12) . UDK-BH'lerin 5. haftada ortalama görülme s kl 1: 1966 CD34+ hücredir (aral k: 1261-2906).