Negative regulators of hemopoiesis and stroma function in patients with myelodysplastic syndrome

The mechanism that leads to hemopoietic failure in patients with myelodyspl astic syndrome (MDS) is not well understood. There is evidence, however, th at regulatory molecules such as tumor necrosis factor (TNF)-alpha, Fas (CD9 5), and Fas-ligand, which negatively affect hemopoiesis by way of apoptosis are upregulated. Here we analyzed marrow samples from 80 patients with MDS in regard to TNF-alpha and Fas-ligand levels and a possible correlation wi th various disease parameters and risk factors. TNF-alpha levels were eleva ted in comparison to samples from normal marrow donors, however, no signifi cant correlation with FAB subtype, cytogenetic risk group or score by the I nternational Prognostic Scoring System (IPSS) was observed. However, there was an inverse correlation between the cytogenetic risk category (low, inte rmediate, high) and levels of soluble Fas-ligand. The major source of TNF-a lpha were mononuclear (non-stromal) cells which appeared to produce TNF-alp ha at maximum levels. Limiting dilution analysis of CD34(+) precursor cells showed that individually assayed cells, removed from companion cells that presumably provided negative signals such as TNF-alpha or Fas-ligand, were able to generate progressively increasing numbers of colonies. Stromal laye rs derived from MDS marrow did not have an inhibitory effect. In fact, high er colony numbers were obtained from both normal and MDS marrow derived hem opoietic precursors propagated on irradiated stromal layers from MDS marrow than on stromal layers from normal marrow. These results show that substan tial numbers of normal hemopoietic precursors persist in MDS marrow. Howeve r, differentiation into mature cells is inhibited by negative signals origi nating from accessory or abnormal hemopoietic precursors in the non-adheren t marrow fraction.