Isolation of monocytes from human peripheral blood using immuno-affinity expanded-bed adsorption

Past, Present, and Future of Affinity-based Cell Separation Technologies

Progress in cell purification technology is critical to increase the availability of viable cells for therapeutic, diagnostic, and research applications. A variety of techniques are now available for cell separation, ranging from non-affinity methods such as density gradient centrifugation, dielectrophoresis, and filtration, to affinity methods such as chromatography, two-phase partitioning, and magnetic-/fluorescence-assisted cell sorting. For clinical and analytical procedures that require highly purified cells, the choice of cell purification method is crucial, since every method offers a different balance between yield, purity, and bioactivity of the cell product. For most applications, the requisite purity is only achievable through affinity methods, owing to the high target specificity that they grant. In this review, we discuss past and current methods for developing cell-targeting affinity ligands and their application in cell purification, along with the benefits and challenges associated with different purification formats. We further present new technologies, like stimuli-responsive ligands and parallelized microfluidic devices, towards improving the viability and throughput of cell products for tissue engineering and regenerative medicine. Our comparative analysis provides guidance in the multifarious landscape of cell separation techniques and highlights new technologies that are poised to play a key role in the future of cell purification in clinical settings and the biotech industry. STATEMENT OF SIGNIFICANCE: Technologies for cell purification have served science, medicine, and industrial biotechnology and biomanufacturing for decades. This review presents a comprehensive survey of this field by highlighting the scope and relevance of all known methods for cell isolation, old and new alike. The first section covers the main classes of target cells and compares traditional non-affinity and affinity-based purification techniques, focusing on established ligands and chromatographic formats. The second section presents an excursus of affinity-based pseudo-chromatographic and non-chromatographic technologies, especially focusing on magnetic-activated cell sorting (MACS) and fluorescence-activated cell sorting (FACS). Finally, the third section presents an overview of new technologies and emerging trends, highlighting how the progress in chemical, material, and microfluidic sciences has opened new exciting avenues towards high-throughput and high-purity cell isolation processes. This review is designed to guide scientists and engineers in their choice of suitable cell purification techniques for research or bioprocessing needs.

Non-magnetic chromatographic separation of colloidally metastable superparamagnetic iron oxide nanoparticles and suspension cells

For magnetic control of cells for biomedical applications such as targeting of immune cells to tumors, cells must be magnetizable. For that, cells are incubated with superparamagnetic iron oxide nanoparticles (SPIONs) to take them up and thus become magnetizable. When using adherent cells, non-ingested SPIONs can be easily removed by rinsing of the particles regardless of their colloidal stability in cell culture medium. However, if suspension cells such as T cells are to be loaded with SPIONs, established methods to separate excess nanoparticles from cells are based on physicochemical parameters such as density, size or magnetizability. Thus, colloidal stability of the particles is of great importance, since only colloidally stable SPIONs can be completely separated from the cells due to their physicochemical differences. Aggregates of colloidally meta- or unstable particles cannot, however, be separated from cells due to their overlapping sizes and densities. Thus, development of an alternative method for the separation of nanoparticle aggregates from suspension cells is urgently needed. Here, we present an affinity chromatographic separation method based on immunohistochemical properties of the respective cells. A desthiobiotinylated antibody against a cellular surface antigen (here CD90.2 receptor on EL4 T cells) is immobilized on a streptavidin agarose column optimized for cell purification. Subsequently the column is loaded with the particle/cell suspension so that the cells bind to the column. After removing the particles by washing, the cells can be gently eluted with biotin solution under physiological conditions. This allows >95% of the excess iron concentration to be removed while maintaining cell viability.

Efficient release of immunocaptured cells using coiled-coils in a microfluidic device

Label-free and affinity-based cell separation allows highly specific cell capture through simple procedures, but it remains a major challenge to efficiently release the captured cells without changing their structure, phenotype, and function. We report a microfluidic platform for label-free immunocapture of target cells and efficient release of the cells with minimal biochemical and biophysical perturbations. The method capitalizes on self-assembly of a pair of heterodimerizing coiled-coils, A and B. Target cells are captured in microchannels functionalized with an antibody and A and efficiently released by a liquid flow containing B-PEG (a conjugate of B and polyethylene glycol) at a controlled, low shear stress. The released cells have no antibodies attached or endogenous surface molecules cleaved. In a model system, human umbilical vein endothelial cells (HUVECs) were isolated from a mixture of HUVECs and human ovarian carcinoma cells. The capture selectivity, capture capacity, and release efficiency were 96.3% ± 1.8%, 10 735 ± 1897 cells per cm², and 92.5% ± 3.8%, respectively, when the flow was operated at a shear stress of 1 dyn cm⁻². The method can be readily adapted for isolation of any cells that are recognizable by a commercially available antibody, and B-PEG is a universal cell-releasing trigger.

We report a microfluidic platform capable of isolating target cells from heterogeneous cell populations through highly specific immunocapture and efficiently releasing the captured cells with minimal biochemical and biophysical perturbations.

Sensitive and Specific Biomimetic Lipid Coated Microfluidics to Isolate Viable Circulating Tumor Cells and Microemboli for Cancer Detection

Here we presented a simple and effective membrane mimetic microfluidic device with antibody conjugated supported lipid bilayer (SLB) "smart coating" to capture viable circulating tumor cells (CTCs) and circulating tumor microemboli (CTM) directly from whole blood of all stage clinical cancer patients. The non-covalently bound SLB was able to promote dynamic clustering of lipid-tethered antibodies to CTC antigens and minimized non-specific blood cells retention through its non-fouling nature. A gentle flow further flushed away loosely-bound blood cells to achieve high purity of CTCs, and a stream of air foam injected disintegrate the SLB assemblies to release intact and viable CTCs from the chip. Human blood spiked cancer cell line test showed the ~95% overall efficiency to recover both CTCs and CTMs. Live/dead assay showed that at least 86% of recovered cells maintain viability. By using 2 mL of peripheral blood, the CTCs and CTMs counts of 63 healthy and colorectal cancer donors were positively correlated with the cancer progression. In summary, a simple and effective strategy utilizing biomimetic principle was developed to retrieve viable CTCs for enumeration, molecular analysis, as well as ex vivo culture over weeks. Due to the high sensitivity and specificity, it is the first time to show the high detection rates and quantity of CTCs in non-metastatic cancer patients. This work offers the values in both early cancer detection and prognosis of CTC and provides an accurate non-invasive strategy for routine clinical investigation on CTCs.

Improving washing strategies of human mesenchymal stem cells using negative mode expanded bed chromatography

The use of human mesenchymal stem cells (hMSC) in clinical applications has been increasing over the last decade. However, to be applied in a clinical setting hMSC need to comply with specific requirements in terms of identity, potency and purity. This study reports the improvement of established tangential flow filtration (TFF)-based washing strategies, further increasing hMSC purity, using negative mode expanded bed adsorption (EBA) chromatography with a new multimodal prototype matrix based on core-shell bead technology. The matrix was characterized and a stable, expanded bed could be obtained using standard equipment adapted from what is used for conventional packed bed chromatography processes. The effect of different expansion rates on cell recovery yield and protein removal capacity was assessed. The best trade-off between cell recovery (89%) and protein clearance (67%) was achieved using an intermediate expansion bed rate (1.4). Furthermore, we also showed that EBA chromatography can be efficiently integrated on the already established process for the downstream processing (DSP) of hMSC, where it improved the washing efficiency more than 10-fold, recovering approximately 70% of cells after global processing. This strategy showed not to impact cell viability (>95%), neither hMSC's characteristics in terms of morphology, immunophenotype, proliferation, adhesion capacity and multipotent differentiation potential.

Efficient elusion of viable adhesive cells from a microfluidic system by air foam

We developed a new method for releasing viable cells from affinity-based microfluidic devices. The lumen of a microchannel with a U-shape and user-designed microstructures was coated with supported lipid bilayers functionalized by epithelial cell adhesion molecule antibodies to capture circulating epithelial cells of influx solution. After the capturing process, air foam was introduced into channels for releasing target cells and then carrying them to a small area of membrane. The results show that when the air foam is driven at linear velocity of 4.2 mm/s for more than 20 min or at linear velocity of 8.4 mm/s for more than 10 min, the cell releasing efficiency approaches 100%. This flow-induced shear stress is much less than the physiological level (15 dyn/cm(2)), which is necessary to maintain the intactness of released cells. Combining the design of microstructures of the microfluidic system, the cell recovery on the membrane exceeds 90%. Importantly, we demonstrate that the cells released by air foam are viable and could be cultured in vitro. This novel method for releasing cells could power the microfluidic platform for isolating and identifying circulating tumor cells.

Selective individual primary cell capture using locally bio-functionalized micropores

Background

Solid-state micropores have been widely employed for 6 decades to recognize and size flowing unlabeled cells. However, the resistive-pulse technique presents limitations when the cells to be differentiated have overlapping dimension ranges such as B and T lymphocytes. An alternative approach would be to specifically capture cells by solid-state micropores. Here, the inner wall of 15-µm pores made in 10 µm-thick silicon membranes was covered with antibodies specific to cell surface proteins of B or T lymphocytes. The selective trapping of individual unlabeled cells in a bio-functionalized micropore makes them recognizable just using optical microscopy.

Methodology/Principal Findings

We locally deposited oligodeoxynucleotide (ODN) and ODN-conjugated antibody probes on the inner wall of the micropores by forming thin films of polypyrrole-ODN copolymers using contactless electro-functionalization. The trapping capabilities of the bio-functionalized micropores were validated using optical microscopy and the resistive-pulse technique by selectively capturing polystyrene microbeads coated with complementary ODN. B or T lymphocytes from a mouse splenocyte suspension were specifically immobilized on micropore walls functionalized with complementary ODN-conjugated antibodies targeting cell surface proteins.

Conclusions/Significance

The results showed that locally bio-functionalized micropores can isolate target cells from a suspension during their translocation throughout the pore, including among cells of similar dimensions in complex mixtures.

Evaluation of a novel non-destructive catch and release technology for harvesting autologous adult stem cells

BACKGROUND

Cell based therapies are required now to meet the critical care needs of paediatrics and healthy ageing in an increasingly long-lived human population. Repair of compromised tissue by supporting autologous regeneration is a life changing objective uniting the fields of medical science and engineering. Adipose stem cells (adSCs) are a compelling candidate for use in cell based medicine due to their plasticity and residence in numerous tissues. Adipose found in all animals contains a relatively high concentration of stem cells and is easily isolated by a minimally invasive clinical intervention; such as liposuction.

METHODS

This study utilised primary rat adipose to validate a novel strategy for selecting adult stem cells. Experiments explored the use of large, very dense cell-specific antibody loaded isolation beads (diameter 5x-10x greater than target cells) which overcome the problem of endocytosis and have proved to be very effective in cell isolation from minimally processed primary tissue. The technique also benefited from pH mediated release, which enabled elution of captured cells using a simple pH shift.

RESULTS

Large beads successfully captured and released adSCs from rat adipose, which were characterised using a combination of microscopy, flow cytometry and PCR. The resultant purified cell population retains minimal capture artefact facilitating autologous reperfusion or application in in vitro models.

CONCLUSION

Although evidenced here for adSCs, this approach provides a technological advance at a platform level; whereby it can be applied to isolate any cell population for which there is a characterised surface antigen.

Cell separation using cryogel-based affinity chromatography

In cell affinity chromatography, type-specific cell separation is based on the interaction between cell-surface receptors and an immobilized ligand on a stationary matrix. This protocol describes the preparation of monolithic polyacrylamide and polydimethylacrylamide cryogel affinity matrices that can be used as a generic type-specific cell separation approach. The supermacroporous monolithic cryogel has highly interconnected large pores (up to 100 μm) for convective migration of large particles such as mammalian cells. In this protocol, they are functionalized to immobilize a protein A ligand by a two-step derivatization of epoxy-containing cryogel monolith (reaction with ethylenediamine and glutaraldehyde). Target cells were labeled with specific antibodies and then they were captured in the cryogel through affinity with protein A. These specifically captured cells were recovered in high yields while retaining their viability by mechanical squeezing of the spongy and elastic cryogel matrices. The suggested cell separation protocol takes < 30 min for complete separation on a preprepared protein A-immobilized cryogel column.

Chromatography of living cells using supermacroporous hydrogels, cryogels

The preparative cell separation is an intrinsic requirement of various diagnostic, biotechnological and biomedical applications. Affinity chromatography is a promising technique for cell separation and is based on the interaction between a cell surface receptor and an immobilised ligand. Most of the currently available matrices have pore size smaller than the size of the cells and are not suitable for cell chromatography due to column clogging. Another problem encountered in chromatographic separation of cells is a difficulty to elute bound cells from affinity surfaces. Application of novel adsorbents, supermacroporous monolithic cryogels, allows overcoming these problems. Cryogels are characterised by highly interconnected large (10-100 microm) pores, sponge-like morphology and high elasticity. They are easily derivatised with any ligand of choice. Convective migration can be used to transport the cells through the matrix. Target cells bind to affinity ligands, while other cells pass through the cryogel column non-retained and are removed during a washing step. Because of the spongy and elastic nature of the cryogel matrices, the cells are efficiently desorbed by mechanical compression of cryogels, which provides high cell viability and yields. The release of affinity bound cells by mechanical compression of a cryogel monolithic adsorbent is a unique and efficient way of cell detachment. This detachment strategy and the continuous macroporous structure make cryogels very attractive for application in cell separation chromatography.

Affinity adsorption of cells to surfaces and strategies for cell detachment

The use of bio-specific interactions for the separation and recovery of bio-molecules is now widely established and in many cases the technique has successfully crossed the divide between bench and process scale operation. Although the major specificity advantage of affinity-based separations also applies to systems intended for cell fractionation, developments in this area have been slower. Many of the problems encountered result from attempts to take techniques developed for molecular systems and, with only minor modification to the conditions used, apply them for the separation of cells. This approach tends to ignore or at least trivialise the problems, which arise from the heterogeneous nature of a cell suspension and the multivalent nature of the cell/surface interaction. To develop viable separation processes on a larger scale, effective contacting strategies are required in separators that also allow detachment or recovery protocols that overcome the enhanced binding strength generated by multivalent interactions. The effects of interaction valency on interaction strength needs to be assessed and approaches developed to allow effective detachment and recovery of adsorbed cells without compromising cell viability. This article considers the influence of operating conditions on cell attachment and the extent to which multivalent interactions determine the strength of cell binding and subsequent detachment.

Cellular separations: A review of new challenges in analytical chemistry

The ability to generate a sample of cells of a given phenotype is a prerequisite for many cellular assays. In response to this growing need, numerous methods for cell separation have been developed in recent years. This Review covers recent progress in the field of cell separations and cell chromatography. Cell separation principles-such as size and affinity capture-are discussed, as well as conventional methods such as fluorescence-activated cell sorting and magnetic sorting. Planar flow cell arrays, dielectrophoresis, field-flow methods, and column separation devices are reviewed, as well as applications of these methods to medicine and biotechnology. Cell attachment and adhesion strategies and a comparison of techniques are also presented.

Micro- and nanotechnology in cell separation

This review describes recent work in cell separation using micro- and nanoscale technologies. These devices offer several advantages over conventional, macroscale separation systems in terms of sample volumes, low cost, portability, and potential for integration with other analytical techniques. More importantly, and in the context of modern medicine, these technologies provide tools for point-of-care diagnostics, drug discovery, and chemical or biological agent detection. This review describes work in five broad categories of cell separation based on (1) size, (2) magnetic attraction, (3) fluorescence, (4) adhesion to surfaces, and (5) new emerging technologies. The examples in each category were selected to illustrate separation principles and technical solutions as well as challenges facing this rapidly emerging field.

Separation and enrichment of neural stem cells using segregation in an expanded bed

An expanded bed system has been developed for a novel application in which the separation and enrichment of neural stem cells from a sample containing a mixture of stem and progenitor cells is achieved based on the difference in the sizes of the aggregates of these types of cells. Inert Sephadex beads and flocculated yeast cells were used as experimental controls and references. The characteristics of the separation of neural stem cell aggregates based on size are similar to those achieved with flocculated yeast where cell-to-cell aggregation controls the pattern of size separation different from those of inert Sephadex beads.

Affinity cryogel monoliths for screening for optimal separation conditions and chromatographic separation of cells

Suitable conditions for separating cells using a chromatographic procedure were evaluated in parallel chromatography on minicolumns. A 96-hole minicolumn plate filled with cryogel monoliths (18.8 mm x 7.1 mm Ø) with immobilized concanavalin A was used. Chromatographic columns (113 mm x 7.1 mm Ø) were used for chromatographic resolution of a mixture of Saccharomyces cerevisiae and Escherichia coli cells. Separation of a cell mixture containing equal amounts of cells of both types performed in a column format under the determined optimal conditions, resulted in a quantitative capture of applied S. cerevisiae cells, while E. coli passed through the column. Bound S. cerevisiae cells were released by flow-induced detachment and by compression of the adsorbent in the presence of 0.3 M methyl alpha-D-manno-pyranoside. The flowthrough and the eluted fractions were analyzed by plate counting and by registering metabolic activity of S. cerevisiae cells in the eluted fractions after capturing on ConA-cryogel monoliths in a 96-minicolumn plate format. The flowthrough fraction contained E. coli cells with nearly 100% purity, whereas the fraction eluted by compression of the adsorbent contained viable S. cerevisiae cells with 95% purity. Thus, an efficient chromatographic separation of cells was achieved using affinity cryogel column.

Expanded bed adsorption/desorption of proteins with Streamline Direct CST I adsorbent

Streamline Direct CST I is a new type of ion exchanger with multi-modal functional groups, specially designed for an expanded bed adsorption (EBA) process, which can capture directly the proteins from the high ionic strength feedstocks with a high binding capacity. In this study, an experimental study is carried out for two-component proteins (BSA and myoglobin) competitive adsorption and desorption in an expanded bed packed with Streamline Direct CST I. Based on the measurements of the single- and two-component bovine serum albumin (BSA)/myoglobin adsorption isotherm on Streamline Direct CST I, the binding and elution conditions for the whole EBA process are selected; and then frontal analysis for a longer timescale and column displacement experiments in a fixed bed (XK16/20 column) are carried out to evaluate the two-component proteins (BSA and myoglobin) competitive adsorption and displacement on Streamline Direct CST I. Finally, the feasibility of capturing both BSA and myoglobin by an expanded bed packed with Streamline Direct CST I is addressed in a Streamline 50 column packed with 300 mL Streamline Direct CST I.

Enrichment using antibody-coated microfluidic chambers in shear flow: model mixtures of human lymphocytes

Isolation of phenotypically-pure cell subpopulations from heterogeneous cell mixtures such as blood is a difficult yet fundamentally important task. Current techniques such as fluorescent activated cell sorting (FACS) and magnetic-activated cell sorting (MACS) require pre-incubation with antibodies which lead to processing times of at least 15-60 min. In this study, we explored the use of antibody-coated microfluidic chambers to negative deplete undesired cell types, thus obtaining an enriched cell subpopulation at the outlet. We used human lymphocyte cell lines, MOLT-3 and Raji, as a model system to examine the dynamic cell binding behavior on antibody coated surfaces under shear flow. Shear stress ranging between 0.75 and 1.0 dyn/cm2 was found to provide most efficient separation. Cell adhesion was shown to follow pseudo-first order kinetics, and an anti-CD19 coated (Raji-depletion) device with approximately 2.6 min residence time was demonstrated to produce 100% pure MOLT-3 cells from 50-50 MOLT-3/Raji mixture. We have developed a mathematical model of the separation device based on the experimentally determined kinetic parameters that can be extended to design future separation modules for other cell mixtures. We conclude that we can design microfluidic devices that exploits the kinetics of dynamic cell adhesion to antibody coated surfaces to provide enriched cell subpopulations within minutes of total processing time.

Affinity binding of cells to cryogel adsorbents with immobilized specific ligands: effect of ligand coupling and matrix architecture

The capture of human acute myeloid leukemia KG-1 cells expressing the CD34 surface antigen and the fractionation of human blood lymphocytes were evaluated on polyvinyl alcohol (PVA)-cryogel beads and dimethyl acrylamide (DMAAm) monolithic cryogel with immobilized protein A. The affinity ligand (protein A) was chemically coupled to the reactive PVA-cryogel beads and epoxy-derivatized monolithic cryogels through different immobilization techniques and the binding efficiency of the cell surface receptors specific antibody-labeled cells to the gels/beads was determined. The binding of cells to monolithic cryogel was higher (90-95%) compared with cryogel beads (76%). B-lymphocytes, which bound to the protein A-cryogel beads, were separated from T-lymphocytes with yields for the two cell types 74 and 85%, respectively. About 91% of the bound B-cells could be recovered without significantly impairing their viability. Our results show differences in the percentage of cell-binding to the immunosorbents caused by ligand density, flow shear forces and bond strength between the cells and the affinity surface once distinct chemical coupling of protein A, size of beads, sequence of antibody binding to protein A adsorbents, morphology and geometry of surface matrices were compared.

Affinity fractionation of lymphocytes using a monolithic cryogel

A new type of continuous, supermacroporous, monolithic, cryogel affinity adsorbent was developed, allowing specific fractionation and separation of human peripheral blood lymphocytes in a chromatographic format. The affinity adsorbent was used to design a novel cell separation strategy, which was based on the interaction of protein A from Staphylococcus aureus with cells bearing IgG antibodies on the surface. After treating lymphocytes with goat anti-human IgG(H+L), the IgG-positive B-lymphocytes were efficiently separated from T-lymphocytes. Protein A covalently coupled to epoxy activated dimethylacrylamide (DMAA) cryogel matrix specifically bound IgG-bearing B-lymphocytes through the Fc region, while non-bound T-lymphocytes passed through the column. More than 90% of the B-lymphocytes were retained in the column while the cells in the breakthrough fraction were enriched in T-lymphocytes (81%). The viability of the T-lymphocytes isolated was greater than 90%. The bound lymphocytes released by human or dog IgG recovered 60-70% of the B-cells without significantly impairing the cell viability. The technique can be applied in general to cell separation systems where IgG antibodies against specific cell surface markers are available.