Non-specific cell binding characteristics of para-magnetic polystyrene microspheres used for antibody-mediated cell...

The binding of cells to paramagnetic polystyrene microbeads in the absence of coupling antibodies was measured. Cells from normal bone marrow, from an acute lymphoblastic leukemia (ALL) cell line or from a neuroblastoma cell line, were labeled with the fluorochrome Hoechst 33342 and incubated with microbeads by rotation at 4 degrees C. Following this incubation, the microbeads with all attached cells were collected using an externally applied magnetic field and visualized by microscopic examination under ultraviolet illumination. The incubation variables included the protein content of the medium, and the period of rotation. Normal bone marrow was found to adhere sparingly to the microbeads; less than 1.0% of the total nucleated cell population was recovered with the beads, whereas greater than 5% of the ALL cells and greater than 30% of the neuroblastoma cells were found to bind non-specifically to the microspheres. Neither changes in the protein concentration of the medium or in the incubation period significantly altered the non-specific binding of the cell types examined. It is thus apparent that the use of these microspheres for positive selection of cells, such as the collection of hematopoietic stem cells for transplantation, would be compromised by a sizeable non-specific interaction. Modification of the surface of the microspheres to substantially reduce this interaction will be necessary before efforts at positive selection using the magnetic microspheres can be fruitful.