CLONAL HETEROGENEITY IN GROWTH KINETICS OF CD34⁺CD38^- HUMAN CORD BLOOD CELLS IN VITRO IS CORRELATED WITH GENE EXPRESSION PATTERN AND TELOMERE LENGTH

Kerol Bartolovi ¹, Stefan Balabanov ¹, Birgit Berner ¹, Hans-Jörg Bühring ¹, Martina Komor ², Sven Becker ³, Dieter Hoelzer ², Lothar Kanz ¹, Wolf-Karsten Hofmann ², Tim H. Brümmendorf ^1*

¹ Department of Hematology/Oncology, University Medical Center, Tübingen, Germany
² Department of Hematology/Oncology, University Medical Center, Frankfurt/Main, Germany
³ Department of Obstetrics/Gynecology, University Medical Center, Tübingen, Germany

^* To whom correspondence should be addressed. E-mail: t.bruemmendorf{at}uke.uni-hamburg.de.

	Abstract

Human hematopoietic stem cells (HSC) are characterized by an extensive proliferative capacity which decreases from fetal liver to cord blood to adult bone marrow. In previous studies, it was demonstrated that the proliferative capacity of individual CD34⁺CD38^- HSC clones is correlated with their growth kinetics in vitro and that HSC turnover in vivo can be estimated by telomere length measurements.

The present study was aimed at the characterization of the clonal composition of CD34⁺CD38^- human umbilical cord blood (CB) cells in terms of growth kinetics, telomere length and gene expression profile. For this purpose, individual CD34⁺CD38^- CB cells were sorted into 96-well plates containing serum-free medium supplemented with six growth factors. During expansion, cell numbers in each individual well were scored in 3-day intervals. Once sufficient cell numbers were achieved, telomere length was measured by flow FISH. In a second set of experiments, gene expression and colony forming capacity was analyzed in slowly as compared to fast growing clones using linear amplification and oligonucleotide microarrays (HG-U133A, Affymetrix). Individual CD34⁺CD38^- cells from CB displayed an extensive functional heterogeneity in growth kinetics. Among highly proliferative clones, the most slowly growing clones were characterized by the longest telomeres. Furthermore, significant differences in gene expression were detected between slow and fast growing clones, whereas no significant difference in colony-forming capacity was observed. These data provide further evidence for a functional hierarchy in the human HSC compartment and suggest a link between telomere length and proliferation capacity of individual HSC clones.