Heterogeneous Interactions of Leukemic and Control Bone Marrow Stroma Cells with an AML Cell Line and AML Leukemic Blasts.

Abstract 1047

Tumor-stroma interaction plays a pivotal role for malignant cell survival, proliferation, immune escape, and drug resistance. We had previously shown that bone marrow (BM) stroma from leukemia patients had different gene expression patterns and support of normal CD34+ cells compared to controls (Ctr). Aim of this study was to evaluate growth, survival, and colony-forming potential issues of M-07e AML cells and AML blasts as indicator cells (IC) upon contact with non-leukemic and leukemic stroma. Plastic-adherent BM cells from leukemic or Ctr non-leukemic donors were cultured for several weeks. Polyclonal as well as isolated single fibroblast colony (F-CFU) cultures were set up. Short-term and long-term co-cultures of BM stroma used M-07e AML cells and AML blasts as IC. After long-term co-culture colony forming units (CFU) were determined in the adherent and non-adherent fraction of the IC. Proliferation of IC was determined by cell counting and 3H-TdR incorporation assays. The human HS-5 stroma cell line was used in selected experiments. The F-CFU frequency was determined from 39 Ctr samples, 6 MDS samples, 59 leukemic samples, and 12 lymphoma samples with BM infiltration. Succession of F-CFU numbers in respective samples was AML / MDS < Ctr < MM / FL II << 2°AML. Polyclonal stroma cells from AML BM supported M-07e IC survival slightly but not significantly better than Ctr stroma. No noteworthy support for primary AML blasts was observed with either stroma. Stroma from both AML and Ctr donors stimulated colony formation of M-07e IC without marked differences in the frequency of compact and diffuse colonies. In 3H-TdR assays M-07e IC were stimulated by IL-3 and certain but not all stroma samples tested. Notably, IL-3-induced proliferation of M-07e IC was decreased in the presence of stroma and almost completely suppressed by HS-5 cells. When single F-CFU were isolated, expanded, and tested for their capacity to support M-07e IC stimulating as well as non-stimulating F-CFU were found. Support competence of stroma cells decreased with passage number. Primary BM polyclonal stroma cells and single F-CFU from leukemic and non-leukemic donors showed a broad heterogeneity with respect to support of cell growth or colony-forming potential in favour of the AML M-07e IC line. Thus, the interaction of stroma and normal or leukemic hematopoietic cells seems to be a complex system awaiting further investigations.