Purging of small cell lung cancer-contaminated bone marrow by monoclonal antibodies and magnetic beads.
At diagnosis, most patients with small cell lung cancer (SCLC) have bone marrow involvement detected by immunological techniques. As preparative regimens become more effective in the elimination of systemic disease, bone marrow purging may become a significant intervention, even more so with the trend toward use of greater numbers of stem cells for reconstitution (such as peripheral blood stem cells). The optimal conditions for removal of SCLC cell lines from bone marrow mixtures with magnetic bead immunoconjugates are described. Metabolically labelled SCLC cells (SW2, OC2, NCI-H82) were incubated with mouse monoclonal antibodies reactive with SCLC membrane antigens (SM1, LAM2, LS1) alone or in combination. Magnetic beads conjugated with secondary goat anti-mouse-IgG or IgM antibody were added and the unpurged cells decanted off. Tumor removal was evaluated by residual radioactive counts in the decanted cell mixture as well as by clonogenic assay. The log removal was compared to controls performed without primary or secondary antibody. All assays were performed in triplicate. Bone marrow toxicity was similarly evaluated. In a simulation of bone marrow purging, a bead to total cell ratio of greater than or equal to 10:1 provided maximal tumor removal regardless of the degree of contamination. However, when the bead to total cell ratio dropped lower than 10:1, purging efficiency lessened despite maintenance of bead: tumor cell ratio of 100:1. A concentration of primary antibody ten-fold greater than saturation by indirect immunofluorescence provided optimal elimination. Using single exposures of antibody and beads, a mixture of all 3 MoAbs resulted in 2.4-2.6 log removal for SW2 and OC2. However, with NCI-H82, a cell line with low expression of these antibodies on the cell surface, maximal elimination was only 1.6 logs. Double bead exposure for 30 minutes each was more effective than single treatments for 30-60 minutes. No significant toxicity to bone marrow function was observed in parallel studies. Magnetic bead separation appears to be an efficient and nontoxic method to purge bone marrow of tumor contamination with SCLC.
Elias
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Department of Medicine, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115.
Pap
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Bernal
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D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D001853:Bone Marrow / Q000276:immunology; D001854:Bone Marrow Cells; D018288:Carcinoma, Small Cell / Q000628:therapy*; D002478:Cells, Cultured; D002999:Clone Cells; D006801:Humans; D008175:Lung Neoplasms / Q000628:therapy*; D008280:Magnetics; D051379:Mice; D008863:Microspheres; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal