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Characterization (eg, phenotyping) of blasts present at low percentages in clinical samples is often required for decisions regarding the approach to therapy. However, the available methods for cell characterization do not yield reliable data when the target cells are scant, and the existing methods for blast enrichment, such as cell sorting by flow cytometry (FCM), cannot enrich blasts of unknown immunophenotype. Blastretriever is a newly developed density centrifugation reagent for retrieving blasts. We examined the utility of Blastretriever in clinical practice. When normal bone marrow (BM) cells were separated with this reagent, myeloblasts and B-cell precursors were enriched and detected as clusters on the FCM cytogram. Compared with a conventional reagent for mononuclear cell preparation, the Blastretriever reagent markedly enriched leukemic myeloblasts, leukemic lymphoblasts, and blastoid lymphoma cells from 36 test samples (BM cells and peripheral blood). We then applied the Blastretriever reagent to samples from 11 consecutive patients who had been referred to us because they exhibited low percentages of blasts (1 patient had only 0.2% blasts). Characterization was needed but impossible with conventional analyses. Blast enrichment was achieved for all 11 samples, allowing reliable blast characterization by FCM, fluorescence in situ hybridization, and/or G-banding determinations. The revealed blast characteristics were valuable for choosing appropriate therapy for the patients.

CD45 is a hematopoietic lineage-restricted antigen that is expressed on all hematopoietic cells except for some mature cell types. Cells expressing CD45 and CD34 but lacking CD38 and lineage antigens (CD45+CD34+CD38−Lin− cells) are well-documented hematopoietic stem cells (HSCs), and CD45+CD34−CD38−Lin− cells are probably less mature HSCs. In myelodysplastic syndromes (MDS), the malignant transformation site was reported to be committed myeloid progenitors and, more recently, the CD45+CD34+CD38−Lin− HSCs. In this study, we detected CD45−CD34−CD38−Lin− cells in the peripheral blood and bone marrow of MDS patients. Fluorescence in situ hybridization showed that CD45−CD34−CD38−Lin− cells had the same chromosomal aberration as the myeloblasts. In addition to CD45- and CD34-negativity, they lacked CD117 and CD133 expressions. Generally, MDS cells have extremely reduced hematopoietic potential compared with normal hematopoietic cells, but we documented the following in some cases. Freshly-isolated CD45−CD34−CD38−Lin− cells did not form any hematopoietic colonies but had long-term culture-initiating cell activity. When these cells were co-cultured with stroma cells, CD45−CD34−CD38−Lin− cells showed only weak potential for proliferation/differentiation, yet differentiated to CD34+ cells and then mature myeloid cells. This newly-identified cell population represents the most immature immunophenotype so far identified in the hematopoietic lineage and is involved in the malignant clone in MDS.

A 52-year-old Japanese woman who presented with gastrointestinal (GI) bleeding underwent a proximal gastrectomy for a gastrointestinal stromal tumor (GIST) with a foveolar hyperplasia at the apex of the tumor, 4.5 cm in size, located in the upper body of the stomach. Although GIST are often asymptomatic and are found only incidentally, clinical symptoms such as bleeding, abdominal pain, or obstruction, occasionally lead to a premorbid diagnosis. When submucosal tumors present GI bleeding, the source of the bleeding usually is an ulceration of the mucosa over the tumor. However, in the present study, it was thought that the bleeding originated from the region of foveolar hyperplasia.