Congenital leukaemia with a mixed phenotype of megakaryoblasts and erythroblasts: a case report and characterization of the blasts.

We present a congenital leukaemia with a mixed phenotype of megakaryoblasts and erythroblasts. A newborn male with exopthalmus and multiple skin nodules, had bone marrow blasts which expressed CD41b, CD42b, glycophorin-A and haemoglobin, but monocyte or lymphoid markers were negative. The patient achieved a complete remission with chemotherapy. Blasts cultured for a few months expressed erythroid markers but lost the megakaryocytic phenotype, although addition of phorbol ester induced the latter phenotype. Spontaneous colony formation was observed in semi-solid culture and the number of colonies was increased by erythropoietin. Detailed studies further indicated the heterogeneity of congenital leukaemia.

Molecular interactions between human B-cell progenitors and the bone marrow microenvironment.

Apoptosis of normal and leukemic immature B-cells in vitro is suppressed when either cell type is grown in direct contact with a feeder layer of bone marrow-derived stromal cells, including fibroblasts, macrophages, endothelial cells, and adipocytes. In this study, our objective was to identify a stromal cell type which is essential for lymphoblast survival and to characterize the molecules involved in lymphoblast adhesion to these cells. In experiments with B-lineage acute lymphoblastic leukemia (ALL) cells (n = 28) and purified CD19(+) cells from normal bone marrow (n = 6) we found that homogeneous populations of bone marrow fibroblasts could sustain survival of normal and leukemic immature B-cells as efficiently as composite bone marrow stromal layers. Electron microscopic studies showed that leukemic lymphoblasts associate with fibroblasts and with the extracellular matrix (ECM) primarily via their specialized cell surface structures. Immunogold labelingsoliduselectron microscopy analysis revealed that the areas of contact between lymphoblasts and fibroblasts contained beta1 integrins (VLA-4 and VLA-5), fibronectin, vascular cell adhesion molecule (VCAM-1), and a cartilage-link protein, CD44. Double immunogold labeling studies disclosed a direct in situ relationship between fibronectin and VLA-4, VLA-5, and CD44. We hypothesize that these molecular interactions either bring lymphoblasts into close physical proximity with other fibroblast-bound or ECM-bound survival factors or provide survival signals themselves.

Growth requirements of normal and leukemic human B cell progenitors.

Leukemic lymphoblasts in B-lineage acute lymphoblastic leukemia (ALL) express morphologic, phenotypic and genotypic features which resemble those of B lymphocyte progenitors in normal bone marrow. Normal immature B cells and cells from most cases of B-lineage ALL rapidly die in vitro unless they are supported by bone marrow-derived stromal feeder layers. Techniques suitable for maintaining normal and leukemic immature B cells in culture have been developed. Thus, the stromal cell types and growth factors that generate a milieu suitable for immature B-cell development can now be elucidated. In addition, the similarities and discrepancies in survival requirements of normal and leukemic B cell precursors can be studied. We postulate that leukemic B cell precursors can survive and expand in microenvironments incapable of supporting their normal counterparts, and that the study of the survival requirements of ALL cells will provide indications about the aggressivity of the disease in vivo. In this review, we discuss the culture conditions that support in vitro survival of human immature B cells, some of the factors that influence their expansion, and the putative molecular basis for the prolonged life-span of leukemic lymphoblasts.