Submitted July 13, 2006
Accepted December 8, 2006
Chromatin modifying agents permit human hematopoietic stem cells to undergo multiple cell divisions while retaining their repopulating potential
Hiroto Araki, Kazumi Yoshinaga, Piernicola Boccuni, Yan Zhao, Ronald Hoffman, and Nadim Mahmud*
Section of Hematology/Oncology, Dept of Medicine, University of Illinois at Chicago, Chicago, IL
* Corresponding author; email: nadim{at}uic.edu.
Human hematopoietic stem cells (HSCs) exposed to cytokines in vitro rapidly divide and lose their characteristic functional properties presumably due to the alteration of a genetic program which determines the properties of an HSC. We have attempted to reverse the silencing of this HSC genetic program by the sequential treatment of human cord blood CD34+ cells with the chromatin modifying agents, 5-aza-2'f-deoxycytidine (5azaD) and trichostatin A (TSA). We determined that all CD34+CD90+ cells treated with 5azaD/TSA and cytokines after 9 days of incubation divide, but to a lesser degree than cells exposed to only cytokines. When CD34+CD90+ cells that have undergone extensive number (5-10) of cell divisions in the presence of cytokines alone were transplanted into immunodeficient mice, donor cell chimerism was not detectable. By contrast, 5azaD/TSA treated cells that have undergone similar numbers of cell divisions retained their marrow repopulating potential. The expression of several genes and their products previously implicated in HSC self-renewal were up-regulated in the cells treated with 5azaD/TSA as compared to cells exposed to cytokines alone. These data indicate that HSC treated with chromatin modifying agents are capable of undergoing repeated cell divisions in vitro while retaining their marrow repopulation potential.
