Rare cell separation and analysis by magnetic sorting

Magnetic separation and antibiotics selection enable enrichment of cells with ZFN/TALEN-induced mutations

The ability to enrich cells with targeted mutations greatly facilitates the process of using engineered nucleases, including zinc-finger nucleases and transcription activator-like effector nucleases, to construct such cells. We previously used surrogate reporters to enrich cells containing nuclease-induced mutations via flow cytometry. This method is, however, limited by the availability of flow cytometers. Furthermore, sorted cells occasionally fail to form colonies after exposure to a strong laser and hydrostatic pressure. Here we describe two different types of novel reporters that enable mutant cell enrichment without the use of flow cytometers. We designed reporters that express H-2K^k, a surface antigen, and the hygromycin resistance protein (Hygro^R), respectively, when insertions or deletions are generated at the target sequences by the activity of engineered nucleases. After cotransfection of these reporters and the engineered nuclease-encoding plasmids, H-2K^k- and Hygro^R-expressing cells were isolated using magnetic separation and hygromycin treatment, respectively. We found that mutant cells were drastically enriched in the isolated cells, suggesting that these two reporters enable efficient enrichment of mutants. We propose that these two reporters will greatly facilitate the use of engineered nucleases in a wider range of biomedical research.

Monitoring the endocytosis of magnetic nanoparticles by cells using permanent micro-flux sources

Trapping of cells is essential to perform basic handling operations in cell-based microsystems, such as media exchange, concentration, cell isolation and cell sorting. Cell trapping by magnetophoresis typically requires cell labeling with magnetic nanoparticles. Here we report on endocytotic uptake of 100 nm magnetic nanoparticles by Human Embryonic Kidney 293 cells. The attraction of labeled cells by micro-magnet arrays characterised by very high magnetic field gradients (≤10⁶ T/m) was studied as a function of labeling conditions (nanoparticle concentration in the extracellular medium, incubation time). The threshold incubation conditions for effective magnetophoretic trapping were established. This simple technique may be exploited to minimise the quantity of magnetic nanoparticles needed for efficient cell trapping, thus reducing stress or nanoparticle-mediated toxicity. Nanoparticle internalization into cells was confirmed using both confocal and Transmission Electron Microscopy (TEM).

On-chip magnetophoretic isolation of CD4 + T cells from blood

This paper presents the design, fabrication, and testing of a magnetophoretic bioseparation chip for the rapid isolation and concentration of CD4 + T cells from the peripheral blood. In a departure from conventional magnetic separation techniques, this microfluidic-based bioseperation device has several unique features, including locally engineered magnetic field gradients and a continuous flow with a buffer switching scheme to improve the performance of the separation process. Additionally, the chip is capable of processing significantly smaller sample volumes than conventional methods and sample losses are eliminated due to decreased handling. Furthermore, the possibility of sample-to-sample contamination is reduced with the disposable format. The overall dimensions of the device were 22 mm by 60 mm by 1 mm, approximately the size of a standard microscope slide. The results indicate a cell purity of greater than 95% at a sample flow rate of 50 ml/h and a cell recovery of 81% at a sample flow rate of 10 ml/h. The cell purity was found to increase with increasing the sample flow rate. However, the cell recovery decreases with an increase in the flow rate. A parametric study was also performed to investigate the effects of channel height, substrate thickness, magnetic bead size, and number of beads per cell on the cell separation performance.

Cell adhesion and migration on nanopatterned substrates and their effects on cell-capture yield

With scanning electron microscopy analysis, we investigated the role of nanoscale topography on cellular activities; e.g. cell adhesion and spreading by culturing A549 cells (human lung carcinoma cell line cells) for 1-48 h on three sets of nanostructures; quartz nanopillars (QNPs), silicon nanopillars and silicon nanowire (SiNW) arrays, along with planar glass substrates. We found that cells on QNP arrays developed a longer shape than those on SiNW arrays. In addition, we studied how cell morphologies influence the cell-capture yield on the three sets of nanostructures. This research showed that the filopodial formations were directing the cell-capture yield on nanostructured substrates. This finding implies the possibility of using nanoscale topography features to control the filopodial formation including extension and migration from the cells. Using streptavidin-functionalized SiNW substrate, we further demonstrated a substantially higher yield (~91.8 ± 5.9%) than the planar glass wafers (~24.1 ± 7.5%) in the range of 200-3000 cells.

Genetically programmed superparamagnetic behavior of mammalian cells

Although magnetic fields and paramagnetic inorganic materials were abundant on planet earth during the entire evolution of living species the interaction of organisms with these physical forces remains a little-understood phenomenon. Interestingly, rather than being genetically encoded, organisms seem to accumulate and take advantage of inorganic nanoparticles to sense or react to magnetic fields. Using a synthetic biology-inspired approach we have genetically programmed mammalian cells to show superparamagnetic behavior. The combination of ectopic production of the human ferritin heavy chain 1 (hFTH1), engineering the cells for expression of an iron importer, the divalent metal ion transferase 1 (DMT1) and the design of an iron-loading culture medium to maximize cellular iron uptake enabled efficient iron mineralization in intracellular ferritin particles and conferred superparamagnetic behavior to the entire cell. When captured by a magnetic field the superparamagnetic cells reached attraction velocities of up to 30 μm/s and could be efficiently separated from complex cell mixtures using standard magnetic cell separation equipment. Technology that enables magnetic separation of genetically programmed superparamagnetic cells in the absence of inorganic particles could foster novel opportunities in diagnostics and cell-based therapies.

Multiparameter analysis, including EMT markers, on negatively enriched blood samples from patients with squamous cell carcinoma of the head and neck

Epithelial to mesenchymal transition (EMT) has been hypothesized as a mechanism by which cells change phenotype during carcinogenesis, as well as tumor metastasis. Whether EMT is involved in cancer metastasis has a specific, practical impact on the field of circulating tumor cells (CTCs). Since the generally accepted definition of a CTC includes the expression of epithelial surface markers, such as EpCAM, if a cancer cell loses its epithelial surface markers (which is suggested in EMT), it will not be separated and/or identified as a CTC. We have developed, and previously reported on the use of, a purely negative enrichment technology enriching for CTCs in the blood of squamous cell carcinoma of the head and neck (SCCHN). This methodology does not depend on the expression of surface epithelial markers. Using this technology, our initial data on SCCHN patient blood indicates that the presence of CTCs correlates with worse disease-free survival. Since our enrichment is not dependent on epithelial markers, we have initiated investigation of the presence of mesenchymal markers in these CTC cells to include analysis of: vimentin, epidermal growth factor receptor, N-cadherin, and CD44. With the aid of confocal microscopy, we have demonstrated not only presumed CTCs that express and/or contain: a nucleus, cytokeratins, vimentin, and either EGFR, CD44, or N-cadherin, but also cells that contain all of the aforementioned proteins except cytokeratins, suggesting that the cells have undergone the EMT process. We suggest that our negative depletion enrichment methodology provides a more objective approach in identifying and evaluating CTCs, as opposed to positive selection approaches, as it is not subjective to a selection bias and can be tailored to accommodate a variety of cytoplasmic and surface markers which can be evaluated to identify a multitude of phenotypic patterns within CTCs from individual patients, including so-called EMT as presented here.

Breast tumor cell detection at single cell resolution using an electrochemical impedance technique

Gold micro-electrodes with various diameters (25, 50, 75, 100 and 250 μm) were manufactured using standard micro-fabrication techniques and optimized for counting of MCF-7 cells (breast tumor cells) with single cell resolution. For specific cell capture, anti-EpCAM was immobilized on 11-mercaptoundecanoic acid (11-MUA)-3-mercaptopropionic acid (3-MPA) mixed self-assembled monolayer (SAM) modified gold surface of micro-electrodes. Electrodes were characterized using optical, cyclic voltammetry and electrochemical impedance spectroscopic (EIS) techniques. Cell capture response recorded using EIS suggested that optimum electrode dimensions should be analogous to desired cell size. For MCF-7 cells with an average diameter of 18 ± 2 μm, an electrode with 25 μm diameter was established as the optimum electrode size for precise single cell recognition and enumeration. In EIS investigation, the 25 μm electrode exhibited an impedance change of ~2.2 × 10(7) Ω in response to a single tumor cell captured on its surface. On the other hand other electrodes (250, 100, 75 and 50 μm) showed much less response for a single tumor cell. In future, the use of high density arrays of such electrodes with surface modifications will result in miniaturized lab on a chip devices for precise counting of MCF-7 cells with single cell resolution.

Computational analysis of microfluidic immunomagnetic rare cell separation from a particulate blood flow

We describe a computational analysis method to evaluate the efficacy of immunomagnetic rare cell separation from non-Newtonian particulate blood flow. The core procedure proposed here is calculation of local viscosity distributions induced by red blood cell (RBC) sedimentation. Numerical calculation methods have previously been introduced to simulate particulate behavior of individual RBCs. However, due to the limitation of the computational power, those studies are typically capable of calculating only a very small number (less than 100) of RBCs and are not suitable to analyze many practical separation methods for rare cells such as circulating tumor cells (CTCs). We introduce a sedimentation and viscosity model based on our experimental measurements. The computational field is divided into small unit control volumes, where the local viscosity distribution is dynamically calculated based on the experimentally found sedimentation model. For analysis of rare cell separation, the local viscosity distribution is calculated as a function of the volume RBC rate. The direction of gravity has an important role in such a sedimentation-involved cell separation system. We evaluated the separation efficacy with multiple design parameters including the channel design, channel operational orientations (inverted and upright), and flow rates. The results showed excellent agreement with real experiments to demonstrate the effectiveness of our computational analytical method. We demonstrated higher capture efficiency with the inverted microchannel configuration.We conclude that proper direction of blood sedimentation significantly enhances separation efficiency in microfluidic devices.

Iron transport in cancer cell culture suspensions measured by cell magnetophoresis

Cell motion in a magnetic field reveals the presence of intracellular paramagnetic elements, such as iron or manganese. Under controlled field and liquid media composition, such motion previously allowed us to compare the paramagnetic contribution to cell magnetic susceptibility in erythrocytes differing in the spin state of heme associated with hemoglobin. The method is now tested on cells with less obvious paramagnetic properties: cell cultures derived from human cancers to determine if the magnetophoretic mobility (MM) measurement is sufficiently sensitive to the dysregulation of the intracellular iron metabolism as suggested by reports on loss of iron homeostasis in cancer. The cell lines included hepatocellular carcinoma (Hep 3B 2.1-7 and Hep G2), promyelocytic (HL-60) and chronic myelogenous (K-562) leukemias, histiocytic lymphoma (U-937), tongue (CAL 27) and pharyngeal (Detroit 562) carcinomas, and epitheloid carcinoma (HeLa), whose MM was measured in complete media with standard and elevated soluble iron (ferric nitrate and ferric ammonium citrate), against oxy- and met-hemoglobin erythrocytes used as controls. Different cell lines responded differently to the magnetic field and the soluble iron concentrations in culture media establishing the possibility of single cell elemental analysis by magnetophoresis and magnetic cell separation based upon differences in intracellular iron concentration.

Microfluidic approaches for cancer cell detection, characterization, and separation

This article reviews the recent developments in microfluidic technologies for in vitro cancer diagnosis. We summarize the working principles and experimental results of key microfluidic platforms for cancer cell detection, characterization, and separation based on cell-affinity micro-chromatography, magnetic activated micro-sorting, and cellular biophysics (e.g., cell size and mechanical and electrical properties). We examine the advantages and limitations of each technique and discuss future research opportunities for improving device throughput and purity, and for enabling on-chip analysis of captured cancer cells.

Multifunctional plasmonic shell-magnetic core nanoparticles for targeted diagnostics, isolation, and photothermal destruction of tumor cells

Cancer is the greatest challenge in human healthcare today. Cancer causes 7.6 million deaths and economic losses of around 1 trillion dollars every year. Early diagnosis and effective treatment of cancer are crucial for saving lives. Driven by these needs, we report the development of a multifunctional plasmonic shell-magnetic core nanotechnology-driven approach for the targeted diagnosis, isolation, and photothermal destruction of cancer cells. Experimental data show that aptamer-conjugated plasmonic/magnetic nanoparticles can be used for targeted imaging and magnetic separation of a particular kind of cell from a mixture of different cancer cells. A targeted photothermal experiment using 670 nm light at 2.5 W/cm(2) for 10 min resulted selective irreparable cellular damage to most of the cancer cells. We also showed that the aptamer-conjugated magnetic/plasmonic nanoparticle-based photothermal destruction of cancer cells is highly selective. We discuss the possible mechanism and operating principle for the targeted imaging, separation, and photothermal destruction using magnetic/plasmonic nanotechnology.

Clinically relevant microfluidic magnetophoretic isolation of rare-cell populations for diagnostic and therapeutic monitoring applications

Cells of biomedical interest are, despite their functional significance, often present in very small numbers. Therefore the analysis and isolation of previously inaccessible rare cells, such as peripheral hematopoietic stem cells, endothelial progenitor cells, or circulating tumor cells, require efficient, sensitive, and specific procedures that do not compromise the viability of the cells. The current study builds on previous work on a rationally designed microfluidic magnetophoretic cell separation platform capable of throughputs of 240 μL min(-1). Proof-of-concept was first conducted using MCF-7 (1-1000 total cells) as the target rare cell spiked into high concentrations of Raji B-lymphocyte nontarget cells (~10(6) total cells). These experiments lead to the establishment of a magnet-based separation for the isolation of 50 MCF-7 cells directly from whole blood. Results show an efficiency of collection greater than 85%, with a purity of over 90%. Next, resident endothelial progenitor cells and hematopoietic stem cells are directly isolated from whole human blood in a rapid and efficient fashion (>96%). Both cell populations could be simultaneously isolated and, via immunofluorescent staining, individually identified and enumerated. Overall, the presented device illustrates a viable separation platform for high purity, efficient, and rapid collection of rare cell populations directly from whole blood samples.