Hollow-fibre affinity cell separation system for CD34+ cell enrichment

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.

Open-tubular capillary cell affinity chromatography: single and tandem blood cell separation

In this paper, an open-tubular capillary cell affinity chromatography (OT-CAC) method to enrich and separate target cells is described. Open tubular capillaries coated with anti-CD4, anti-CD14, or anti-CD19 antibodies were used as affinity chromatography columns to separate target blood cells. Cells were eluted using either shear force or bubbles. Bubbles were used to elute the captured cells without diluting the captured cells appreciably, while maintaining viability (the viability of the recovered cells was 85.83 +/- 7.34%; the viability of the cells was 90.41 +/- 3.49% before separation). Several aspects of the OT-CAC method were studied, such as the affinity of one antibody between two different cell lines, the effect of shear force, and the recovery of captured cells. Single- and multicell type separations were demonstrated by isolating CD4+ cells with antiCD4 coated capillary and isolating CD4+ and CD19+ cells with two capillaries in tandem from blood samples. In the one cell type isolation test, an average of 87.7% of the recovered cells from antiCD4 capillary were lymphocytes and an average of 97.7% of those lymphocytes were CD4+ cells. In the original blood sample, only 14.2% of the leukocytes were CD4+ cells. Two capillary columns were also run in tandem, separating two blood cell types from a single sample with high purity. The use of different elution shear forces was demonstrated to selectively elute one cell type. This method is an inexpensive, rapid, and effective method to separate target cells from blood samples.

Hollow-fibre affinity cell separation

The developing fields of cell and tissue engineering will require cost-effective technologies for delivery of cells to patients. Hollow-fibre affinity cell separation is a monoclonal antibody-based cell separation process whereby monoclonal antibody (ligand) is immobilised onto a stationary substrate, the luminal surface of a parallel array of hollow fibres. Deposited cells are fractionated on the basis of adhesion strength using hollow fibre geometry that generates a well-defined shear stress for cell recovery. In this chapter we present the biophysical basis for the process of ligand-mediated cell adhesion and relate this to the performance of affinity cell separation. We also discuss the hydrodynamics of hollow fibre arrays and the various approaches for modifying polymer substrates with protein ligands. One of the major limiting factors for large-scale epitope selective cell separation will be the prohibitive cost of these affinity processes. Hollow fibre systems offer the promise of providing flexibility and scalability for many of these applications.

Chimeric protein for selective cell attachment onto cellulosic substrates

We have developed a fusion protein (CBD-LG) incorporating a cellulose-binding domain and an antibody binding domain, protein LG, to provide an adaptor molecule for cell separation with regenerated cellulose hollow fiber arrays. A single hollow fiber cell adhesion assay utilizing a CD34+ cell line, KG1a, was used to investigate whether ligand affinity interactions were strong enough for cell attachment and separation. CBD-LG efficiently captured CD34+ cells labeled with the mouse IgG2a monoclonal antibody MHCD3400. However, it was not possible to bind CD34+ cells labeled with an IgG1 antibody (HPCA-2). The low affinity of HPCA-2 for LG was overcome by secondary antibodies: KG1a cells that were dual labeled with HPCA-2 followed by rat anti-mouse IgG1 adhered inside hollow fibers coated with CBD-LG. Alternatively, immobilized rabbit polyclonal anti-mouse IgG1 captured cells labeled with HPCA-2. The development of an adaptor molecule to display recombinant domains at the surface of hollow fibers will be an effective tool to investigate cellular ligand-receptor interactions, a necessary step in the development of hollow fiber bioreactors for manufacture of human cellular products.

Hollow-fiber assay for ligand-mediated cell adhesion

BACKGROUND

The investigation of receptor-ligand interactions in the cellular context presents significant technical challenges, first, to immobilize the ligand in a manner that preserves functional properties and, second, to relate ligand properties to cell adhesion and other cellular processes.

METHODS

Ligand-mediated cell adhesion was characterized by the development of a cellulose hollow-fiber adhesion assay in which ligand (protein A) was immobilized onto the cellulose membrane as a recombinant fusion protein containing a cellulose-binding domain affinity tag. Modules containing single cellulose hollow fibers were connected to a micro-flow system for cell deposition and detachment with fluid shear stress. The cell adhesion process that occurred inside a segment of hollow fiber was observed in real time by using an inverted microscope equipped with a CCD camera and digital frame grabber. Image analysis software was developed to count cells and record digital images.

RESULTS

Cell adhesion strength was characterized by counting the number of cells that were detached by application of fluid shear stress with values that ranged from 2.3 to 185 dyne/cm2. The median shear stress of detachment of KG1a cells was directly related to the duration of membrane contact and the amount of immobilized monoclonal antibody (anti-CD34).

CONCLUSIONS

The hollow-fiber assay provides a general method to determine functional properties of molecular domains that interact with cell surface receptors and markers.

Human leukocyte differentiation antigens as therapeutic targets: the CD molecules and CD antibodies

The cell membrane presents an attractive target in a number of different disease situations. Most obviously, malignant cells may be killed by damaging their cell membranes. There are also more subtle, though effective, ways of rendering cells harmless by engaging proteins at the cell surface. The cells of the immune system may be targeted, for example to stop a damaging immune reaction, such as acute inflammation or rejection of a transplanted organ. If we are to make the best use of the opportunities to modulate disease by targeting the cell membrane, we need a detailed understanding of the many proteins, glycoproteins and glycolipids that are attached to or inserted in the cell membrane. The CD (cluster of differentiation) Workshops, more properly known as the HLDA (Human Leukocyte Differentiation Antigens) Workshops have, since 1982, focussed on the study of the membrane molecules of leukocytes, including the major cells of the immune system and malignant cells derived from them. The scope has extended to molecules on endothelium which are important in interaction with leukocytes. Many of the molecules characterised as leukocyte antigens are also expressed on other tissue. The approaches developed by the HLDA Workshops are useful in the study of the molecular composition and function of cells of other organ systems. Some of the antibodies produced in order to study the CD molecules have proved useful as therapeutic agents. This review describes the CD system, how it has developed and what it means and introduces the field of therapy based on antibodies against CD or similar molecules. The author is responsible for organising the next (8th) HLDA Workshop and invites readers to suggest ways in which the therapeutic relevance of the Workshop may be enhanced.

Cell separation mediated by differential rolling adhesion

Recently, we showed a correlation between the maturity of hematopoietic stem and progenitor cells during development and rolling efficiency on selectins. These findings motivated us to explore a novel separation that exploits differences in selectin-mediated rolling adhesion between populations of cells. We extend the use of a previously developed cell-free system to study the separation of populations of sialyl Lewis x (sLe(x))-coated microspheres designed to roll with different average velocities on L-selectin chimeric substrates under well-defined flow. Results show that a separation that exploits differences in average rolling velocities between cell or microsphere populations is attainable. Excellent recovery and purity values for the slower rolling, or more desirable, populations are obtained and can be estimated from rolling velocity measurements. We also assess the feasibility of a selectin-mediated separation of adult bone marrow cell populations using previously obtained rolling velocity and rolling flux data for CD34+ and CD34- adult bone marrow cells on L-selectin substrates. We believe that a cell separation mediated by differential rolling adhesion can be used to enrich populations of hematopoietic stem and progenitor cells from an adult bone marrow cell preparation and that this method possesses several major advantages over existing antibody-mediated cell-affinity chromatography technologies.

Design of hollow fiber modules for uniform shear elution affinity cell separation

Large-scale monoclonal antibody based systems for the selection of cell subsets will play a prominent role in the development of hematotherapy and graft engineering. Hollow fiber systems for affinity cell separation rely on the generation of uniform fluid shear stress at the lumenal attachment interface. Potential mechanisms for nonuniformity of lumenal wall shear stress are fiber wall permeation fluxes driven by the pressure gradient along individual fibers and the influence of inlet header dynamic pressure on the radial distribution of axial flow within the fiber module. Dimensional analysis and numerical solution of the flow field within the lumen of a hollow fiber module illustrate the main physical criteria for design of hollow fiber modules. There will be a nearly uniform distribution of flow within the fiber bundle provided that the dynamic inlet pressure is small in comparison with the pressure drop along fibers. Fiber wall permeation fluxes will have a negligible effect on axial flow rate for nonporous membranes such as Cuprophan.