Reversible switching of expression of c-kit and Pax-5 in immature hematopoietic progenitor cells by stromal cells

Objective. Bone marrow stromal cells provide the microenvironment for self-renewal and differentiation of hematopoietic stem/progenitor cells through complex cell-cell interaction. To elucidate the regulatory mechanisms of hematopoiesis by stromal cells, we established a novel stroma-dependent hematopoietic cell line and explored the phenotypic changes regulated by the two stromal cells. Materials and Methods. DFC-28 cells clonally established from long-term bone marrow culture of C57BL/6 mice were sustained by coculture on MSS62 cells (mouse spleen stromal cell line). When DFC-28 cells were transferred to TBR31-1 cells (mouse bone marrow stromal cell line), their phenotypic changes were analyzed by flow cytometry and reverse transcriptase polymerase chain reaction. Results. DFC-28 cells on MSS62 cells exhibited surface phenotypes of the immature hematopoietic progenitor cells (Lin(-)AA4.1(+)c-kit(+)Sca-1(-)). By stroma-replacement from MSS62 cells to TBR31-1 cells, DFC-28 cells were differentiated into very early B-lymphoid stage characterized by c-kit down-regulation and induction of BP-1 and B-lymphoid-associated genes (Pax-5, CD19, TdT, Rag-1, and Rag-2). In addition, the differentiation phenotypes reverted to the immature state characterized by c-kit induction and down-regulation of BP-1 and B-lymphoid-associated genes by replacing stroma back to MSS62 from TBR31-1. Interleukin-7 stimulation and conditioned medium of TBR31-1 cells were ineffective in converting the differentiation phenotypes of DFC-28 cells. Conclusion. The results demonstrate that the differentiation phenotypes and growth potential of stroma-dependent hematopoietic progenitor cells we established could be reversibly controlled via direct contact with stromal cells in the microenvironment. (C) 2002 International Society for Experimental Hematology. Published by Elsevier Science Inc.