Isolation of circulating cancer cells from whole blood by immunomagnetic cell enrichment and unenriched immunocytochemistry in vitro.

Abstract

We improved tumor cell detection compared with currently available immunocytochemical methods by immunomagnetic cell enrichment. Two methods of immunomagnetic enrichment using antibody coated magnetic beads were tested and compared with unenriched immunocytochemistry, including positive selection of epithelial cells with the antiepithelial antibody BER-EP4 and depletion of mononuclear cells with the anti-leukocyte antibody CD45. Various numbers of tumor cells from the 4 tissue culture cell lines DU 145, RT-4, KTCTL-2 and KTCTL-30 obtained from urological tumors were added to whole blood and mononuclear cells were isolated by density centrifugation. After incubation of the cell suspensions with beads cell separation was done in a magnetic field. After centrifugation on glass slides immunocytochemical staining for cytokeratin was performed. A total of 96 experiments were completed and negative controls were obtained. The number of tumor cells detected by positive selection and depletion was significantly higher compared with immunocytochemistry (Wilcoxon test p <0.01). Mean enrichment factor and tumor cell recovery rates were 12.9% and 43.5% for positive selection, and 9.4% and 32.6% for depletion, respectively (p <0.05). With 1 tumor cell suspended in up to 30 ml. full blood unenriched immunocytochemistry failed to detect cancer cells, whereas positive selection revealed epithelial cells in 12 of 14 cases (85.5%) and depletion in all 14 (p <0.05). No false-positive results were observed. Compared with unenriched immunocytochemistry immunomagnetic enrichment significantly improves the detection of epithelial cells added to blood. A significant advantage was observed for positive selection. Immunomagnetic enrichment may be important for clinical practice in the future.