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Posted on Thu, Jul 28, 2016

Magnetic bead cell separation for the detection of circulating tumor cells

Circulating tumor cells (CTCs) are responsible for the spread of cancer from a primary tumor site to other locations in a patient’s body (metastasis). The cells break off from the primary tumor and circulate through the system until they attach to another site in the body and begin to grow a secondary tumor. It is critical to identify the presence of these cells in the bloodstream as soon as possible. However, detecting CTCs is challenging because they are rare events in metastatic patients (1 in 10 million white blood cells and 1 in 5 billion red blood cells). Although these events are rare, it is possible to isolate and enrich the population of CTCs by using magnetic beads and bulk magnetic bead cell separation techniques. This is the gold standard method in clinical use today.

Magnetic beads are functionalized to specifically bind to CTCs

Circulating tumor cells express epithelial cell adhesion molecule (EpCAM) on their surfaces. Normal cells in the bloodstream do not express this molecule, and epithelial cells are not typically found in circulation. Therefore, EpCAM is the most obvious target when functionalizing magnetic beads. The magnetic particles have an iron oxide core and are coated with a biocompatible coating prior to decoration with antibodies. The most common magnetic beads used for CTC detection are coated with anti-EpCAM antibodies. After functionalization the beads are ready to be used for cell separation and enrichment of CTCs from a clinical sample. The beads are incubated with the clinical sample. The anti-EPCAM on the surface of the magnetic beads binds with the EpCAM expressed on the surface of CTCs to form bead-cell conjugates. The bead-cell conjugates are isolated from the sample by bulk magnetic separation.

Bulk magnetic bead cell separation of bead-cell conjugates

During the separation process the sample is placed into a magnetic field gradient set up by an external magnet. The bead-cell conjugates move along the gradient toward the edges of the container while the unbound cells remain in solution. Following sufficient separation time the bead-cell conjugates are held in place by the magnetic field while the unbound cells are washed away. The bead-cell conjugates are then recovered by removing the magnet. What remains is an enriched population of CTCs that can then be identified by downstream methods such as PCR or immunohistochemistry. 

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FREE Download: Basic guide to magnetic bead cell separation

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