Leukemia-Induced Alterations of Bone Marrow Microenvironment Contribute to Leukemogenesis.

Abstract 2597

The impact of microenvironment on the regulation of normal hematopoietic process is being unveiled, but their role during leukemogenesis have been poorly understood. In this study, to characterize the leukemic microenvironment, we have analyzed mesenchymal stromal cells (MSC) of bone marrows from 55 cases of acute myelogenous leukemia (AML), and 17 of AML in the remission. When the colonogenic activity of MSCs were compared, 43% of AML-derived BM exhibited defect in colony (CFU-F) formation, where no colony formation or premature growth arrest of colonies were observed, whereas only 11% of normal BM exhibited growth arrest of colonies. In the AML subtypes, M3 type (FAB classification) exhibited most profound loss of CFU-Fs, where none of them (n=9) exhibited normal growth of colonies. In addition, numbers of colony (CFU-F) in AML was significantly lower than normal BM (52 vs. 155 per each ml of BM, respectively for AML and normal, p<0.05). In contrast, BMs of AML in remission did not exhibit significant difference in the number of CFU-F compared to numbers of normal BM (88 vs. 71.4 per 5×10⁶ MNCs, respectively for normal and remission), indicating that the quantitative loss of CFU-F is correlated to disease activity of AML.

We next examined the qualitative changes of MSCs in AML, i.e., 83% of MSCs in AML (5/6) exhibited poor osteogenic differentiation, and all examined AML MSCs (6/6) exhibited lower adipogenic differentiaton compared to normal MSCs. During in-vitro culture, MSCs from AML showed accelerated loss of colonogenic activity during passage cultures compared to normal MSCs and lower intensity levels of CD146 in the cell surface. Moreover, MSCs from AML showed significantly higher levels of senescence-associated beta-galactosidase without changes in telomere length, indicating that the MSC has undergone qualitative change during leukemogenesis. When co-cultured with umbilical cord blood-derived CD34+ cells, AML-derived MSCs inhibited proliferation of CD34+ cells and caused significantly lower levels of hematopoietic cell expansion compared to the levels from co-culture with normal BM-derived MSCs or stroma-free cultures, indicating that leukemic MSCs should contribute to the loss of normal hematopoietic cells in leukemia.

Taken together, our study shows that microenvironment of BM undergoes quantitative and qualitative alteration during leukemogenesis and that such leukemic microenvironment contributes to the pathology of leukemia.