High purity, recovery, and selection of human blood cells with a novel high gradient magnetic separator

The selective isolation of cell subpopulations from previously cryopreserved human blood mononuclear cells was achieved magnetically using a novel, well-characterized conical funnel filter containing a variety of ordered wire arrays. Tetrameric antibody complexes targeted against the CD8 antigen were used to bind colloidal superparamagnetic dextran-iron particles to the desired cells with very low nonspecific binding. The novel design of the filter was such that the retention of cells at zero magnetic field was on average 0.9%. After two successive magnetic separations, an average purity of 98% was obtained for the desired labeled cells. A third separation gave > 99% purity. Purity was affected by the unlabeled cells, which expressed high intercellular adhesion (0.5% of the total cells). The ultimate recovery of the labeled cells was limited by the degree of nonmagnetic labeling of the cells expressing very low levels of targeted antigen. Recoveries could be as low as 78%, depending on the donor. The separation system described was believed suitable for difficult large-scale separations, that is, cells expressing the CD34 antigen.