Measurement of secondary colony formation after 5 weeks in long-term cultures in patients with myelodysplastic syndrome.

Pancytopenia is a frequent manifestation of myelodysplastic syndromes (MDS). In the presence of an empty bone marrow, clinical distinction from aplastic anemia may be difficult. The hypoplastic marrow morphology seen in some cases of MDS raises questions about etiologic and pathophysiologic relationships between aplastic anemia and MDS. The goal of our study was to compare the degree of the hematopoietic failure in these diseases at the level of the most immature progenitor and stem cells that can be measured in vitro. In a systemic, prospective fashion, we have studied bone marrow (n = 45) and peripheral blood (n = 33) of patients with MDS for the number of long-term culture initiating cells (LTC-IC) in comparison to 17 normal controls and patients with new, untreated aplastic anemia (46 marrow; 62 blood samples). Due to the low numbers of cells available for the analysis, formal limiting dilution analysis could not be performed, instead secondary colony-forming cells (CFC) after 5 weeks of LTBMC were measured. As the number of these cells is proportional to the input number of LTC-IC, the number of secondary CFC per 10(6) mononuclear cells (MNC) initiating the LTBMC can be used as a measure of the content of immature stem cells in bone marrow and peripheral blood. The MDS group consisted of 34 RA, three RARS, eight RAEB and two RAEB-T patients with mean absolute neutrophil values of 1992, 1413, 1441, and 380 per mm3, respectively. The diagnosis was established based on bone marrow morphology and results of cytogenetic studies. In comparison to controls (147 +/- 38/10(6) MNC), significantly decreased numbers of bone marrow secondary CFC were found in MDS: in patients with RA and RARS, 21 +/- 7 secondary CFC per 10(6) bone marrow MNC (P < 0.001); patients with RAEB and RAEB-T: 39 +/- 12 CFC per 10(6) marrow MNC (P < 0.001). In all groups tested, the decrease in peripheral blood secondary CFC numbers was consistently less pronounced. In MDS patients with hypocellular bone marrow, secondary CFC were lower but not significantly different in comparison to MDS with hypercellular marrow (18 +/- 6 vs 35 +/- 11; NS; hypoplastic bone marrow also was not associated with significantly lower neutrophil counts). However, in 24% of patients with MDS, bone marrow secondary CFC were within the normal range, while in the aplastic anemia group only one of the patients showed secondary CFC number within normal range. Bone marrow and blood secondary CFC numbers in hypoplastic RA were significantly higher than those in severe aplastic anemia 919 +/- 5 in bone marrow, P < 0.01; 7 +/- 2 in blood, P < 0.05). This trend was even more pronounced in hypoplastic RA with chromosomal abnormalities. However, no significant differences were found between the secondary CFC numbers in hypoplastic RA and moderate aplastic anemia. We concluded that, although the deficiency in the stem cell compartment is less severe in MDS than in aplastic anemia, depletion of early hematopoietic cells is an essential part of the pathophysiology in both diseases.