HUMAN BONE-MARROW STROMAL CELL CONTACT AND SOLUBLE FACTORS HAVE DIFFERENT EFFECTS ON THE SURVIVAL AND PROLIFERATION OF PEDIATRIC B-LINEAGE ACUTE LYMPHOBLASTIC LEUKEMIC BLASTS

Recent studies have confirmed that in vitro viability and proliferatio n of precursor B-cell leukaemia (ALL) cells are linked to the presence of bone marrow derived stromal cells. To investigate whether this eff ect is mediated by direct contact or through the action of soluble fac tors, using a method we have recently described, the growth parameters of ALL bone marrow blast cells from eight newly diagnosed patients we re determined with the lipophilic fluorescent probe PKH 26 GL. The via bility of ALL cells and the rate of cell division in cultures containi ng either medium alone; stromal cell conditioned medium; stromal cell layers allowing direct contact, or in 0.4 mu m microporous membrane cu ltures suspended above stromal cell layers were examined. In all eight samples an improved maintenance of ALL cells in a viable state in cul tures containing bone marrow stromal cells was observed. The survival of leukaemic cells was equivalent in 0.4 mu m microporous membrane cul tures suspended above stromal cell layers and in cultures of leukaemic cells in direct contact with stromal cell layers. It was thus demonst rated that this effect was mediated by the action of soluble factor(s) present in these cultures. However, the improved maintenance of ALL c ells in a viable state was observed in only one of the eight cases whe n ALL cells were cultured in stromal cell conditioned medium alone. Th e highest rate of cell division of leukaemic cells was observed in ALL cells in direct contact with bone marrow stromal cells. The activitie s of stromal cell derived soluble factors could not be reproduced by r ecombinant forms of likely candidate factors including IL-1 beta P, IL -4, IL-6, IL-7, SCF, TNF alpha, TGF beta, LIF, NGF or a mixture of the se factors when examined in cultures of the same patient samples. This study implicates the existence of a novel bone marrow derived factor( s) that improves survival of ALL cells in vitro.