Magnetic sorting of leukocytes.

Magnetic filtration of surface-labeled cells has been applied to the fractionation of leukocytes in a model system, using a colloidal magnetite reagent to label mouse spleen cells. This reagent was completely free from problems of aggregation or settling. Since the individual submicron particles were invisible under the microscope, cells were not visibly altered by labeling. Viability also was unaffected by either labeling or magnetic filtration. Using a 10-kG magnet and a 5-ml filter column, 50 million cells were fractionated in less than 10 min, with 99% removal of labeled T lymphocytes. The efficiency of the magnetic method is limited at present by the fact that cells that do not have the surface target antigen of interest, and so are not antibody coated, may adsorb a small amount of label nonspecifically. These then have a nonzero chance of being captured in the filter along with the labeled cells.