Assessment of stromal function, and its potential contribution to deregulation of hematopoiesis in the myelodysplastic syndromes.

BACKGROUND AND OBJECTIVES The regulation of hematopoiesis by marrow stroma in vitro, has been shown to be abnormal in some patients with myelodysplastic syndromes (MDS). This study was performed to assess whether a range of mechanisms may be altered within the MDS microenvironment. DESIGN AND METHODS The effects of diffusible factors produced by normal or MDS stromal layers on hematopoietic cells were studied by comparing the ability of media conditioned (CM) by normal or MDS stroma to regulate migration of target normal marrow CD34+ cells across 5 microm transmembranes. The ability of CM to stimulate hematopoietic cells was also assessed: changes in membrane polarity of KG-1a cells on exposure to stroma CM were compared. Subsequently, contact-mediated interactions between normal marrow CD34+ cells and normal and MDS stroma were studied: survival of allogeneic normal marrow CD34+ cells on live and glutaraldehyde-fixed normal and myelodysplastic stroma after 24h of co-culture was measured using 7-aminoactinomycin D staining. To determine whether hematopoietic cell survival on normal and MDS stroma was related to oxidative stress within the stromal microenvironment, intracellular superoxide levels, both constitutively and induced by tumor necrosis factor-a were measured within live stromal cells by FACScan analysis of ethidium bromide stained cells. RESULTS The ability of CM from normal and MDS stroma to regulate short-term migration and activation of hematopoietic cells was similar. The mean percentage of apoptotic CD34+ cells (13+/-11%) adherent to glutaraldehyde-fixed myelodysplastic stroma was higher than on paired fixed normal stroma (11+/-10%) (n=6, p=0.056). Constitutive mean levels of superoxide in myelodysplastic cultures (9.5+/-2.1) were greater than in normal stromal cultures (4.9+/-0.6; n=6). However, following treatment with tumor necrosis factor-a, the mean value for superoxide in myelodysplastic stromal cultures was unchanged (fractional change=0.99+/-0.56), compared with an increase in normal stroma (fractional change=1.6+/-0.1, p<0.05). No correlation was observed between superoxide levels, proportion of apoptotic CD34+ cells and percentage of CD14+ stromal cells [mean 8%, range 0-37% (myelodysplastic); mean 1.3%, range 0-5% (normal)]. INTERPRETATION AND CONCLUSIONS Abnormalities of stromal function in myelodysplastic syndromes are likely to be heterogeneous in origin: altered matrix molecules and changes in superoxide within stromal cells may contribute to abnormal survival and development of hematopoietic cells within the myelodysplastic marrow microenvironment