No abstract

We have developed a quadrupole magnetic flow sorter (QMS) to facilitate high-throughput binary cell separation. Optimized QMS operation requires the adjustment of three flow parameters based on the immunomagnetic characteristics of the target cell sample. To overcome the inefficiency of semiempirical operation/optimization of QMS flow parameters, a theoretical model of the QMS sorting process was developed. Application of this model requires measurement of the magnetophoretic mobility distribution of the cell sample by the cell tracking velocimetry (CTV) technique developed in our laboratory. In this work, the theoretical model was experimentally tested using breast carcinoma cells (HCC1954) overexpressing the HER-2/neu gene, and peripheral blood leukocytes (PBLs). The magnetophoretic mobility distribution of immunomagnetically labeled HCC1954 cells was measured using the CTV technique, and then theoretical predictions of sorting recoveries were calculated. Mean magnetophoretic mobilities of (1-3) x 10(-4) mm(3)/(T A s) were obtained depending on the labeling conditions. Labeled HCC1954 cells were mixed with unlabeled PBLs to form a "spiked" sample to be separated by the QMS. Fractional recoveries of cells for different flow parameters were examined and compared with theoretical predictions. Experimental results showed that the theoretical model accurately predicted fractional recoveries of HCC1954 cells. High-throughput (3.29 x 10(5) cells/s) separations with high recovery (0.89) of HCC1954 cells were achieved.

Background:The magnetic separation of a cell population based on cell surface markers is a critical step in many biological and clinical laboratories. In this study, the effect of antibody concentration on the separation of human natural killer cells in a commercial, immunomagnetic cell separation system was investigated. Methods: Specifically, the degree of saturation of antibody binding sites using a two-step antibody sandwich was quantified. The quantification of the first step, a primary anti-CD56-PE antibody, was achieved through fluorescence intensity measurements using a flow cytometer. The quantification of the second step, an anti-PE-microbeads antibody reagent, was achieved through magnetophoretic mobility measurements using cell tracking velocimetry. Results: From the results of these studies, two different labeling protocols were used to separate CD56ϩ cells from human, peripheral blood by a Miltenyi Biotech Mini-MACS cell separation system. The first of these two labeling protocols was based on company recommendations, whereas the second was based on the results of the saturation studies. The results from these studies demonstrate that the magnetophoretic mobility is a function of both primary and secondary antibody concentrations and that mobility does have an effect on the performance of the separation system. Conclusions: As the mobility increased due to an increase in bound antibodies, the positive cells were almost completely eliminated from the negative eluent. However, with an increase in bound antibodies, and thus mobility, the total amount of positive cells recovered decreases. It is speculated that these cells are irreversibly retained in the column. These results demonstrate the complexity of immunomagnetic cell separation and the need to further optimize the cell separation process. Cytometry 45: 285-293, 2001.

Three strains of Bacillus: Bacillus atrophaeus (formally Bacillus globigii), Bacillus thuringiensis, and Bacillus cereus were tested for their intrinsic magnetic susceptibility. All three strains when sporulated demonstrated significant magnetic susceptibility using an instrument referred to as Cell Tracking Velocimetry. Energy dispersive spectroscopy also confirmed the presence of paramagnetic elements, Fe and Mn, in the spore form of the bacteria. It was demonstrated that this magnetic susceptibility is sufficient to separate and deposit these spores on glass slides in a magnetic deposition system. These results indicate the potential to separate spores with intrinsic magnetic susceptibility directly out of water or air samples.