A NOVEL HEMATOPOIETIC MULTILINEAGE CLONE, MYL-D-7, IS STROMAL CELL-DEPENDENT AND SUPPORTED BY AN ALTERNATIVE MECHANISM(S) INDEPENDENT OF STEM-CELL FACTOR C-KIT INTERACTION

A strictly stroma-dependent hematopoietic clone, Myl-D-7, with lympho- myeloid potential has been isolated. A subset of cells expresses myelo id-macrophage (Mac-1 and Gr-1), erythroid (TER119), and lymphoid (Thy- 1 and B220) lineage markers. Spontaneous differentiation to the myeloi d-macrophage, erythroid, or lymphoid pathway can be seen by morphologi c criteria, detection of beta major globin synthesis, or expression of the early lymphoid specific transcription factor, Ikaros. By sorting lineage marker (Mac-1, Gr-1, B220, and TER119)-negative (LIN(-)) cells , we showed that the LIN(-) population actively self-renews on top of MS-5 stromal cells, and differentiates to LIN(+) cells. Removal of str oma induces apoptosis and none of the growth factors tested can preven t apoptosis. Granulocyte-macrophage colony-stimulating factor accelera tes the differentiation towards the myeloid-macrophage lineage. Using this clone, we show that (1) contact with stroma induces expression of bcl-2, (2) stromal cells derived from Sl/Sl homozygous fetuses can su pport long-term growth, and (3) conditioned media of specific stromal cells contains an activity that supports proliferation and self-renewa l of the clone. Myl-D-7 can thus be used as an indicator cell for unkn own factors that may provide stromal cell support. (C) 1996 by The Ame rican Society of Hematology.