Cell sorting. Schematic diagram of QMS. Magnetically labeled cells migrate toward the outer walls, leading to a separate outlet. (Adapted from Biotechnol. Prog. 2001, 17 (6), 1145–1155.)

In a recent paper (Biotechnol. Prog. 2001, 17 (6), 1145–1155), Masayuki Nakamura and colleagues at The Ohio State University (Columbus) and The Cleveland Clinic Foundation reported on the development of a new magnetic technique “to facilitate high-throughput binary cell separation”, using what they have termed a quadrupole magnetic flow sorter (QMS). Their test case involved the separation of a breast cancer cell line from human blood cells.

The QMS as designed has a potential throughput of up to 10⁷ cells/s. Cells are fed by a syringe pump through an inlet into an annular flow channel that contains a magnetic energy gradient (see figure). Cells from the breast carcinoma line HCC1954 that overexpresses the HER-2/neu gene were mixed with isolated normal peripheral blood leukocytes (PBLs). The breast carcinoma cells were differentially labeled using antibodies to the HER-2/neu gene product that were conjugated to colloidal magnetic beads. These magnetically labeled cells migrated preferentially to the outer wall of the extraction chamber and were thus easily separable from the PBLs. Twin outlets fed off the cancer cell-enriched and the cancer cell-depleted fractions. Using a mixture of 1% HCC1954 cells and 99% unlabeled PBLs, recoveries of up to 89% of the added cancer cells were demonstrated.

Although unlabeled cell crossover was still a problem, the researchers stated that they were working to improve the design of the QMS to increase both yield and purity. No data were presented on the effectiveness of the technique on naturally occurring cancer-contaminated blood samples.