Isolation and characterization of hematopoietic progenitor/stem cells in 5q-deleted myelodysplastic syndromes: evidence for involvement at the hematopoietic stem cell level

Abstract

Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal disorders characterized by ineffective hematopoiesis and frequent progression to acute myeloid leukemia. Within MDS, 5q− syndrome constitutes a distinct clinical entity characterized by an isolated deletion of the long arm of chromosome 5 (5q−), a relatively good prognosis, and infrequent transformation to acute leukemia. The cell of origin in 5q− syndrome as well as in other 5q-deleted MDS patients has not been established, but evidence for involvement of multiple myeloid (but not lymphoid) lineages has suggested that a myeloid-restricted progenitor rather than a pluripotent (lympho-myeloid) stem cell might be the primary target in most patients. Although in 9 patients no evidence of peripheral blood T-cell and only 1 case of B-cell involvement was found, the data herein support that 5q deletions occur in hematopoietic stem cells (HSCs) with a combined lympho-myeloid potential. First, in all investigated patients a minimum of 94% of cells in the minor CD34+CD38− HSC compartment were 5q deleted as determined by fluorescence in situ hybridization. Second, in 3 of 5 patients 5q aberrations were detected in a large fraction (25% to 90%) of purified CD34+CD19+ pro-B cells. Furthermore, extensive functional characterization with regard to responsiveness to early-acting cytokines, long-term culture-initiating cells, and nonobese diabetic/severe combined immunodeficiency repopulating cells supported that MDS HSCs in 5q-deleted patients are CD34+CD38−, but inefficient at reconstituting hematopoiesis.

Promoter hypermethylation of p15INK4B, HIC1, CDH1, and ER is frequent in myelodysplastic syndrome and predicts poor prognosis in early‐stage patients

“…Hypermethylation of promoter CpG islands could be detected in both immunoseparated CD34 + precursor cells and total BM‐MNC, and the methylation band patterns in these sample types were similar. Together with a previous study showing that p15 INK 4 B hypermethylation is not restricted to blast cells but to cells from the MDS clone in general (23), these observations suggest that promoter hypermethylation encompasses both immature and end‐stage hematopoietic cells and provide independent support for the contention that MDS is essentially a stem cell disorder (24). As hypomethylating agents are being increasingly used in clinical trials of treatment for MDS (25, 26), it may be helpful to know that clinical monitoring of promoter methylation status can be reliably accomplished directly on unseparated BM‐MNC with no need for purification of CD34 + precursor cells.…”

Molecular pathways in myelodysplastic syndromes and acute myeloid leukemia: relationships and distinctions–a review

“…In both disorders cytogenetic and FISH studies aimed at establishing whether mesenchymal stromal cells (MSC) harbour the same cytogenetic abnormalities of the neoplastic clone have provided conflicting results (Soenen‐Cornu et al , 2005; Blau et al , 2007). In contrast to leukemic cells, propagation of MDS‐derived clones in vitro or in vivo has proven difficult (Nilsson et al , 2000; Benito et al, 2003). In vitro studies have revealed difficulties in establishing stromal layers from MDS bone marrow mononuclear cells (BMNC) (Manakova et al , 2000; Tennant et al , 2000) and these adherent stromal layers show an abnormal interleukin (IL) 1β expression (Tennant et al , 2000).…”

The myelodysplastic syndromes: the era of understanding

“…MDS is a disease of the stem cells. It was already shown two decades ago that cytogenetic abnormalities found in mature myeloid cells are also found in stem cells . Recent work has shown that different mutations can also be found within the stem cell compartment .…”