Magnetic albumin/protein A immunomicrospheres. II. Specificity, reproducibility, and resolution of the magnetic cell separation technique.

Magnetically responsive albumin/protein A immunomicrospheres (MIMS) were prepared by reacting a mixture of albumin, iron oxide, and protein A in a two-phase emulsion coagulation procedure. The protein A ligand permits strong affinity binding of the monoclonal anti-HLA BW6 antibody to the 500-nm MIMS in a one-step process. HLA BW6+ and BW4+ human peripheral blood lymphocytes and mixtures of both were incubated with these MIMS. The findings obtained after only one run in a magnetic field were as follows: depletion of 98.6 +/- 0.9% of the target cells when 2 mg MIMS/10(6) cells were used, unspecific trapping of 5.9 +/- 2.5% of the nontarget cells from cell mixtures, and effective separation of cell populations as small as 1-0.1%. Thus, using albumin/protein A MIMS, the magnetic cell separation technique is simple, rapid, and highly sensitive.