Normal human bone marrow cells were mixed with
neuroblastoma cells from four different human cell lines, and the cell mixtures were separated by differential agglutination with
soybean agglutinin (SBA). The unagglutinated cell fraction, previously shown to be highly enriched for the hematopoietic pluripotential stem cells and capable of reconstituting lethally irradiated adult patients with acute
leukemia, was further fractionated by affinity chromatography on the
lectin conjugated to
Sepharose 6MB beads. Two independent assays, one using radiolabeling of the
tumor cells and the other based on cloning of the
neuroblastoma cells on
agar, showed that the agglutination step alone removes 64-76% of the radiolabeled
neuroblastoma cells and 85-98% of the clonogenic cells from the
tumor/bone marrow cell mixture. Passage of the unagglutinated radiolabeled cells through SBA-
Sepharose columns results in further purging of 28-53% of the
neuroblastoma cells. Thus a combination of the two methods affords only one-log depletion for the
neuroblastoma cells, compared to a three-log depletion achieved for a
T-cell leukemia line CEM tested in parallel. It seems therefore that the agglutination technique, or the use of SBA-
Sepharose columns, can be used only as a preliminary step for the purging of
neuroblastoma cells from involved human bone marrow preparations. Staining with
fluorescein isothiocyanate-conjugated SBA of nine different
neuroblastoma cell lines, including the four tested in the fractionation studies, showed that more than 98% of the cells, of all the cell lines tested, specifically bind to the
lectin, whereas no specific binding can be detected on the stem cell-enriched bone marrow cell fraction. However, the total number of receptors on the
neuroblastoma cells is small compared to that of line CEM or normal granulocytes, which are strongly agglutinated by SBA. It seems therefore that the quantitative difference in the total number of SBA receptors is a crucial factor for purging by the agglutination technique or by affinity chromatography. Although these results show limitations to the use of both methods, this study establishes that all
neuroblastoma cell lines tested express receptors for the
lectin. Improved purging of
neuroblastoma cells may possibly be achieved by targeting SBA-bound toxins or magnetic spheres to these receptors.