BASIC FIBROBLAST GROWTH-FACTOR AND EPIDERMAL GROWTH-FACTOR DOWN-MODULATE THE GROWTH OF HEMATOPOIETIC-CELLS IN LONG-TERM STROMAL CULTURES

The bone marrow microenvironment consists of stromal cells and extrace llular matrix components which act in concert to regulate the growth a nd differentiation of hematopoietic stem cells. There is little unders tanding of the mechanisms which modulate the regulatory role of stroma l cells. This study examined the hypothesis that mesenchymal growth fa ctors such as basic Fibroblast growth factor (bFCF) and epidermal grow th factor (ECF) modulate stromal cell activities and thereby influence the course of hematopoiesis. Both bFGF and EGF were potent mitogens f or marrow stroma. However, both factors proved to be inhibitory to hem atopoiesis in primary long-term marrow cultures. Inhibition was also o bserved when hematopoietic cells and bFGF or EGF were added to subconf luent irradiated stromal layers, demonstrating that the decline of hem atopoiesis was not due to overgrowth of the stromal layer. Loss of hem atopoietic support in bFGF and ECF was dose-dependent. Removal of bFGF and EGF permitted stromal layers to regain their normal capacity to s upport hematopoiesis. In stroma-free long-term cultures, neither facto r affected CFU-CM expansion. Basic FGF slightly enhanced granulocyte-m acrophage colony forming unit (CFU-SM) cloning efficiency in short-ter m agarose culture. Basic FGF did not reduce the levels of interleukin- 6 (IL-6), CM-CSF, or C-CSF released by steady state or IL-1-stimulated stroma. Similarly, the constitutive levels of steel factor (SF) mRNA and protein were not affected by bFGF. Basic FGF did not alter the lev el of TGF-beta 1 in stromal cultures. We conclude that bFGF and EGF ca n act as indirect negative modulators of hematopoietic growth in strom al cultures. The actual mediators of regulation, whether bound or solu ble, remain to be identified. (C) 1995 Wiley-Liss, Inc.