Homing on Track: Rare cell detection methods to study homing of leukemic and normal hematopoietic stem cells

Hematopoiesis is the process of blood cell formation. A relatively small number of pluripotent hematopoietic stem cells lies at the basis of the entire cascade of progressively more mature progenitor cells of the different hematopoietic lineages, culminating in the formation of mature, functional blood cells (Figure 1.1). The regulation of hematopoiesis relies on complex interactions between hematopoietic cells and stromal cells, growth factors and their receptors, extracellular matrix molecules and cellcell interactions through specialized cell adhesion molecules. The sites where hematopoietic stem cens can find just the right mixture of these regulatory interactions are refcncd to as niches. During mammalian embryogenesis the hematopoietic system originates from mcsodermally derived cells localized in the yolk-sac. At a later stage in the development of the fetus totipotent hematopoietic stem cells are predominantly found in the liver. Still later, hematopoiesis shifts to the spleen and the bone marrow. The spleen then gradually becomes a less important hematopoietic organ, so that at birth hematopoiesis in humans is almost exclusively situatcd in the bone marrow

Differential suppression of background mammalian lysosomal β-galactosidase increases the detection sensitivity of LacZ-marked leukemic cells

A method is described for the detection of Escherichia coli β-galactosidase-expressing leukemic cells in ex vivo bone marrow samples. 4-Methylumbelliferyl-β-D-galactopyranoside is used as a substrate in a kinetic assay. D-Galactose is used to suppress endogenous lysosomal β-galactosidase activity, yielding a sixfold increase in sensitivity. With this assay, the detection limit is one leukemic cell per 104 normal bone marrow cells