The efficacy of a novel monosized and magnetizable
polymer bead, denoted
M-280, in immunomagnetic removal of Rael B-
lymphoma cells was compared with that of M-450 beads, previously used in
bone marrow purging. The
M-280 beads which are smaller (diameter 2.8 microns) and contain less
iron than the M-450 beads were coated with polyclonal
IgG sheep antimouse (SAM) antibody. The two types of immunobeads were equally efficacious when used together with the mouse monoclonal
IgG antibodies HH1 or FN1, giving
tumor cell depletions of about 3 logs in one cycle of operation. However, when used together with the primary
IgM monoclonal antibodies (MoAbs) AB1 or HH2, the new immunobeads were significantly more efficacious than the M-450 immunobeads. To elucidate the underlying mechanism flow cytometric studies and measurements of the binding of the labeled primary MoAbs to the cellular
antigens as well as to the immunobeads were carried out. Competition experiments showed that in the case of
IgG MoAbs, the SAM beads bind predominantly to the Fc portion, whereas in the case of the
IgM MoAbs, the Fab part plays a relatively greater role in the binding. The results indicate that if
M-280 immunobeads are used,
IgM MoAbs may profitably be included in antibody cocktails together with
IgG antibodies in immunomagnetic purging of B-
lymphoma cells. They suggest that in the case of cell bound MoAbs, the
epitopes on
IgG are more accessible to SAM beads than those of surface bound
IgM molecules.(ABSTRACT TRUNCATED AT 250 WORDS)