Immuno-affinity partition of cells in aqueous polymer two-phase systems

Enhancing the Sensitivity of the Virus BioResistor by Overoxidation: Detecting IgG Antibodies

The Virus BioResistor (VBR) is a biosensor capable of rapid and sensitive detection of small protein disease markers using a simple dip-and-read modality. For example, the bladder cancer-associated protein DJ-1 (22 kDa) can be detected in human urine within 1.0 min with a limit of detection (LOD) of 10 pM. The VBR uses engineered virus particles as receptors to recognize and selectively bind the protein of interest. These virus particles are entrained in a conductive poly(3,4-ethylenedioxythiophene) or PEDOT channel. The electrical impedance of the channel increases when the target protein is bound by the virus particles. But VBRs exhibit a sensitivity that is inversely related to the molecular weight of the protein target. Thus, large proteins, such as IgG antibodies (150 kDa), can be undetectable even at high concentrations. We demonstrate that the electrochemical overoxidation of the VBR's PEDOT channel increases its electrical impedance, conferring enhanced sensitivity for both small and large proteins. Overoxidation makes possible the detection of two antibodies, undetectable at a normal VBR, with a limit of detection of 40 ng/mL (250 pM), and a dynamic range for quantitation extending to 600 ng/mL.

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.

Virus Bioresistor (VBR) for Detection of Bladder Cancer Marker DJ-1 in Urine at 10 pM in One Minute

DJ-1, a 20.7 kDa protein, is overexpressed in people who have bladder cancer (BC). Its elevated concentration in urine allows it to serve as a marker for BC. However, no biosensor for the detection of DJ-1 has been demonstrated. Here, we describe a virus bioresistor (VBR) capable of detecting DJ-1 in urine at a concentration of 10 pM in 1 min. The VBR consists of a pair of millimeter-scale gold electrodes that measure the electrical impedance of an ultrathin (≈ 150-200 nm), two-layer polymeric channel. The top layer of this channel (90-105 nm in thickness) consists of an electrodeposited virus-PEDOT (PEDOT is poly(3,4-ethylenedioxythiophene)) composite containing embedded M13 virus particles that are engineered to recognize and bind to the target protein of interest, DJ-1. The bottom layer consists of spin-coated PEDOT-PSS (poly(styrenesulfonate)). Together, these two layers constitute a current divider. We demonstrate here that reducing the thickness of the bottom PEDOT-PSS layer increases its resistance and concentrates the resistance drop of the channel in the top virus-PEDOT layer, thereby increasing the sensitivity of the VBR and enabling the detection of DJ-1. Large signal amplitudes coupled with the inherent simplicity of the VBR sensor design result in high signal-to-noise (S/N > 100) and excellent sensor-to-sensor reproducibility characterized by coefficients of variation in the range of 3-7% across the DJ-1 binding curve down to a concentration of 30 pM, near the 10 pM limit of detection (LOD), encompassing four orders of magnitude in concentration.

Perspectives, Tendencies, and Guidelines in Affinity-Based Strategies for the Recovery and Purification of PEGylated Proteins

In recent years, the effective purification of PEGylated therapeutic proteins from reaction media has received particular attention. Although several techniques have been used, affinity-based strategies have been scarcely explored despite the fact that, after PEGylation, marked changes in the molecular affinity parameters of the modified molecules are observed. With this in mind, future contributions in the bioseparation of these polymer-protein conjugates are expected to exploit affinity in chromatographic and nonchromatographic techniques which will surely derive in the integration of different operations. However, this will only occur as novel ligands which are simultaneously found. As it will be mentioned, these novel ligands may be screened or designed. In both cases, computer-aided tools will support their identification or development. Additionally, ligand discovery by high-throughput screening (HTS) is believed to become a fast, economic, and informative technology that will aid in the mass production of ligands along with genetic engineering and related technologies. Therefore, besides analyzing the state of the art in affinity separation strategies for PEGylated molecules, this review proposes a basic guideline for the selection of adequate ligands to provide information and prospective on the future of affinity operations in solving this particular bioengineering problem.

Liquid Biphasic System: A Recent Bioseparation Technology

A well-known bioseparation technique namely liquid biphasic system (LBS) has attracted many researchers’ interest for being an alternative bioseparation technology for various kinds of biomolecules. The present review begins with an in-depth discussion on the fundamental principle of LBS and this is followed by the discussion on further development of various phase-forming components in LBS. Additionally, the implementation of various advance technologies to the LBS that is beneficial towards the efficiency of LBS for the extraction, separation, and purification of biomolecules was discussed. The key parameters affecting the LBS were presented and evaluated. Moreover, future prospect and challenges were highlighted to be a useful guide for future development of LBS. The efforts presented in this review will provide an insight for future researches in liquid-liquid separation techniques.

Effects of Polyethylene Glycol Substitution on Enzyme Activity

The effects of polyethylene-glycol (PEG) substitution on protein activity, us ing alkaline phosphatase as a model, have been studied. Such variables as PEG molecular weight, degree of substitution, and PEG mono- and di-functionality have been examined. Modification with the monomethyl ether of PEG 1900 (M- PEG-1900) does not alter enzyme activity until greater than 40% of the protein lysine groups are substituted, at which point increasing the degree of modifica tion gives increasing deactivation. Substitution with M-PEG-5000 gives more deactivation than does substitution with M-PEG-1900. Interestingly, modifica tion with PEG itself gives active protein conjugates in which there is little de pendence on molecular weight or degree of substitution.

Effects of Coupling Chemistry on the Activity of Poly(ethylene glycol)-Modified Alkaline Phosphatase

Proteins modified by covalent coupling to poly(ethylene glycol) are of interest for several biotechnical applications. In the present work we compare the effects of four commonly used coupling methods on alkaline phosphatase activi ty ; the four methods use the PEG tresylate, succinimidyl succinate, cyanuric chloride derivative, or carbonyl diimidazole derivative. All routes give active enzyme, with only the cyanuric chloride route giving significant deactivation; none the less the cyanuric chloride derivative is useful at lower degrees of modification. Examination of the Michaelis-Menten parameters for the cy anuric chloride coupling suggests that the loss of activity from this route results from intramolecular crosslinking of the protein, which in turn leads to loss of protein conformational flexibility.

Assessment of the Effects of Attaching an Enzyme to Glass by a Poly(ethylene glycol) Tether

Modification of surfaces and proteins by attaching poly(ethylene glycol) (PEG) is an important technique for controlling the properties of these materials. Our goal is to examine the possible combination of these effects by linking proteins to surfaces via a PEG spacer or tether. In the present work we have coupled alkaline phosphatase (as a model protein) to porous glass by means of PEG spacers, and we have compared the activity and operational sta bility of the PEG-bound enzyme to free enzyme and to enzyme immobilized by a conventional, short urea linkage. Significantly, the PEG-bound enzyme differs little in its catalytic properties from free enzyme, indicating that the bound enzyme extends into solution and is in essence free of the surface.

Development of separation technique for stem cells

In recent years, human embryonic stem cells have been established, and somatic stem cells derived from various adult organs have been identified and characterized to differentiate into various kinds of functional cells. There have been attempts to use functional cells induced from such stem cells for tissue regeneration and cell therapy. The method is expected to become an important treatment for intractable diseases in the near future. Since tissues and organs generally contain only a small quantity of somatic stem cells, and since it is necessary to separate functional cells generated from stem cells for use in therapy, an effective method for specific cell separation is crucial to the practical application of regenerative medicine. For the specific separation of cells, a fluorescence activated cell sorter using specific antibodies is a powerful tool, but the method is not suitable for large-scale processing and a special device is required. Although a magnetic cell separation system using immuno-magnetic fine particles is also commercially available, the system still needs special apparatus for large-scale processing. We developed a novel method for the separation of specific cells in an aqueous two-phase system using antibodies modified with a temperature-responsive polymer. The method enables the processing of a large quantity of cells without the requirement of a special device.

Type-specific separation of animal cells in aqueous two-phase systems using antibody conjugates with temperature-sensitive polymers

A new type of aqueous two-phase system (ATPS) has been developed in which a temperature-sensitive polymer, poly-N-isopropylacrylamide [poly (NIPAM)] was used as a ligand carrier for the specific separation of animal cells. Monoclonal antibodies were modified with itaconic anhydride and copolymerized with N-isopropylacrylamide, and the ligand-conjugated carriers were added to the polyethylene glycol 8000-dextran T500 aqueous two-phase systems. The antibody-polymer conjugates were partitioned to the top phase in the absence or presence of 0.15 M NaCl. When ligand-conjugated carriers were used, more than 80% of the cells were specifically partitioned to the top phase in the presence of NaCl up to 0.1 M. The cells were partitioned almost completely to the bottom phase at 0.1 M NaCl or above, when no antibody-conjugate was added in the ATPS. As a model system, CD34-positive human acute myeloid leukemia cells (KG-1) were specifically separated from human T lymphoma cells (Jurkat) by applying anti-CD34 conjugated with poly-N-isopropylacrylamide in the aqueous two-phase system. By the temperature-induced precipitation of the polymer, about 90% of the antibody-polymer conjugates were recovered from the top phase, which gave approximately 75% cell separating efficiency in the next cycle of reuse.

Effects of specific binding reactions on the partitioning behavior of biomaterials

Affinity partitioning is a special branch of biomaterials separations using aqueous two-phase systems. It combines the capability of diverse biomolecules to partition in aqueous two-phase systems using the principle of biorecognition. As a result, the macromolecule exhibiting affinity for a certain ligand is transferred to that phase where the ligand is present. This chapter describes the present status of the theoretical background of this approach and the properties of various natural and artificial compounds which act as affinity ligands in liquid-liquid systems. The affinity partitioning of proteins (enzymes and plasma proteins), cell membranes, cells, and nucleic acids are described as typical examples. The results are discussed in terms of theoretical understanding and practical application.

Aqueous two-phase affinity partitioning of biotinylated liposomes using neutral avidin as affinity ligand

Biotinylated small unilamellar liposomes were affinity partitioned in an aqueous poly(ethylene glycol)-dextran two-phase system using avidin coupled to dextran as affinity ligand. In the absence of affinity ligand more than 90% of the liposomes partitioned in the poly(ethylene glycol)-rich top phase, whereas in its presence more than 95% partitioned in the dextran-rich bottom phase. For this redistribution to occur 10 mM and above of lithium sulphate, or other appropriate salts, had to be added to the two-phase system. Without added salt the liposomes with complexed avidin-dextran instead partitioned in the top phase. An extended mixing time for the system was required for maximum redistribution. Less than two biotin residues per liposome, coupled via a C6 spacer arm, was required to redistribute the liposomes to the bottom phase.

A chemical modification of myeloperoxidase and lactoperoxidase with 2-(O-methoxypolyethylene glycol)-4, 6-dichloro-s-triazine (activated PEG1)

The modification of myeloperoxidase and lactoperoxidase with 2-(O-methoxypolethylene glycol)-4, 6-dichloro-s-triazine, an activated polyethylene glycol (PEG1), was investigated. The modification caused a shift of the Soret band in the light absorption spectrum, from 430 nm to 418 nm in the case of myeloperoxidase (native ferric form), and from 412 nm to 406 nm in the case of lactoperoxidase (native ferric form). PEG1-modified myeloperoxidase and PEG1-modified lactoperoxidase both failed to bind with antiserum to the respective native enzyme, but both retained respectively 4.5 +/- 0.3 per cent (mean +/- SE, n = 5) and 0.6 +/- 0.2 per cent (mean +/- SE, n = 5) of the activities of peroxidation of the hydrogen donor o-methoxyphenol in comparison with the native enzyme, and 1.5 +/- 0.2 per cent (mean +/- SE, n = 5) and 1.2 +/- 0.2 per cent (mean +/- SE, n = 5) of the activities of destruction of fuchsin basic in the presence of hydrogen peroxide and a halide, bromide. The pH dependencies of the peroxidating activities were almost the same as those of the corresponding native enzymes, but both the optimal pHs of the reactions involving the destruction of fuchsin basic were shifted by approximately 1.0 pH unit toward neutral pH compared with the respective native enzymes.

Analytical partitioning of poly(ethylene glycol)-modified proteins

Covalently grafting proteins with varying numbers (n) of poly(ethylene glycol) molecules (PEGs) often enhances their biomedical and industrial usefulness. Partition between the phases in aqueous polymer two-phase systems can be used to rapidly characterize polymer-protein conjugates in a manner related to various enhancements. The logarithm of the partition coefficient (K) approximates linearity over the range O<n<x. However, x varies with the nature of the conjugate (e.g., protein molecular mass) and such data analysis does not facilitate the comparison of varied conjugates. The known behavior of surface localized PEGs suggests a better correlation should exist between log K and the weight fraction of polymer in PEG-protein conjugates. Data from four independent studies involving three proteins (granulocyte-macrophage colony stimulation factor, bovine serum albumin and immunoglobulin G) has been found to support this hypothesis. Although somewhat simplistic, 'weight fraction' based analysis of partition data appears robust enough to accommodate laboratory to laboratory variation in protein, polymer and phase system type. It also facilitates comparisons between partition data involving disparate polymer-protein conjugates.

Affinity adsorption of Saccharomyces cerevisiae on concanavalin A perflurocarbon emulsions

Perfluorocarbon affinity emulsions have been generated by immobilizing concanavalin A onto the surface of triazine-activated perfluorocarbon droplets. Immobilized concanavalin A densities of 0.1, 0.7 and 2.1 mg/ml were obtained by varying the concentration of cyanuric chloride used for activation. The affinity emulsions were found to adsorb Saccharomyces cerevisiae cells from solution with adsorption capacities of 1 x 10(9) cells, 4.6 x 10(9) and 6 x 10(9) cell/ml, respectively. Optimal conditions for the elution of bound cells were obtained by studying inhibition curves of concanavalin A-mannan precipitation using simple sugars. Methyl alpha-D-mannopyranoside showed the greatest inhibitory power with 50 per cent inhibition displayed at a concentration of 0.05 mM. Experiments carried out examining the concentrations of methyl alpha-D-mannopyranoside necessary to dissociate a concanavalin A-mannan precipitate demonstrated that at least a seven-fold higher concentration of methyl alpha-D-mannopyranoside was required for dissociation than that required for inhibition of its formation. The efficiency of elution of bound yeast cells was found to be dependent on the concentration of methyl alpha-D-mannopyranoside used, the time of elution and the immobilized ligand density. Thus, 100 per cent elution was obtained with a concanavalin A affinity emulsion (0.1 mg/ml) by incubation with 500 mM methyl alpha-D-mannopyranoside for 1 h.

Polyethylene glycol-modified avidin: a novel agent for the selective extraction of biotinylated immune-complex in an aqueous two-phase system

Chicken avidin was chemically modified with 2,4-bis[O-methoxypoly(ethylene glycol)]-6-chloro-s-triazine (activated PEG2) to form PEG-avidin. The PEG-avidin, in which 78% of the amino groups were modified, retained 49% of the active biotin-binding sites. The modified avidin was partitioned preferentially into the PEG-phase in an aqueous two-phase system (PEG/dextran). Using PEG-avidin, the immune-complex formed between biotinylated anti-mouse IgG and its antigen IgG (mouse) molecules, was successfully transferred into the PEG-phase in an aqueous two-phase system. This finding leads to the effective isolation of a specific antigen among various kinds of antigens by partitioning with a two-phase system using PEG-avidin.

Ligand-receptor interactions in affinity cell partitioning. Studies with transferrin covalently linked to monomethoxypoly(ethylene glycol) and rat reticulocytes

The partitioning of rat reticulocytes in poly(ethylene glycol) (PEG)-dextran two-phase systems increases into the PEG-rich top phase when the cells are incubated with transferrin covalently modified with monomethoxy-PEG (MPEG-transferrin) prior to partitioning. Two observations support the suggestion that such an increase in top-phase partitioning is due to the specific interaction of the MPEG-transferrin conjugate with the transferrin receptor on the surface of the reticulocyte: first, the MPEG-transferrin conjugate competes with [125I]transferrin for the transferrin receptor on reticulocytes (Ka = 6.28 x 10(6) l mol-1); and second, the MPEG-modified transferrin is unable to change the partitioning of rat erythrocytes, cells lacking the transferrin receptor. This example illustrates the feasibility of manipulating the partitioning of a selected cell population when ligand-receptor interactions are exploited. The increase in the partitioning of the reticulocytes takes place within a narrow range of MPEG-transferrin bound per cell, viz., 10.2-11.3 fg per cell. The latter range corresponds to ca. 80,000-89,000 molecules of MPEG-transferrin bound per cell.

Affinity-mediated modification of electrical charge on a cell surface: a new approach to the affinity partitioning of biological particles

Polylysine has been covalently bound to human transferrin in a 1:1 molar ratio over a disulfide bond that can be easily split by reducing agents such as dithiothreitol. The association constant for the binding of the transferrin-polylysine derivative to transferrin receptors present on rat erythroblasts and the number of binding sites were identical to the corresponding values found for native transferrin. The incubation of the cells with transferrin-polylysine affected the partitioning of erythroblasts in a charge-sensitive aqueous two-phase system containing Dextran and polyethylene glycol. The polylysine part introduced a nonspecific influence on the partitioning that could be eliminated by preincubation of the cells with an excess of sialic acid. The partition ratio, G, of the erythroblasts changed with a factor of 1.9 for each set of 100,000 polylysine chains attached per cell.

Immobilized metal ion affinity partitioning of cells in aqueous two-phase systems: erythrocytes as a model

Immobilized metal ion affinity partitioning of erythrocytes from different species is described. We have explored the affinity between transition metal chelates and metal-binding sites situated on the cell surface by partitioning in aqueous two-phase system composed of poly(ethylene glycol) and dextran. Soluble metal-chelate-poly(ethylene glycol) was prepared by fixing metal ions to poly(ethylene glycol) via the covalently bonded chelator, iminodiacetic acid. The partitioning behaviour of erythrocytes in systems at different concentrations of the ligand was tested. The copper-chelate-poly(ethylene glycol) was quite effective in the affinity extraction of human and rabbit erythrocytes, while the zinc-chelate-poly(ethylene glycol) displayed significant affinity only to the rabbit cells. Furthermore, the influence of various effectors such as imidazole, sialic acid on immobilized metal ion affinity partitioning of erythrocytes was examined.

A method for the purification of DNA/protein complexes applied to DNA topoisomerase II cleavage sites

The object of this study was to devise a purification method for DNA/topoisomerase II complexes, with which to examine the enzyme's cleavage site specificity in cellular differentiation. Retinoic acid-induced differentiation involves topoisomerase II-mediated transient changes in DNA supercoiling, but it is not known whether this occurs at specific sites in the genome. Topoisomerase II forms a covalent DNA enzyme complex as it acts, which can be recovered by the sodium dodecyl sulfate (SDS)/KCl precipitation method, but this method fails to recover significantly more DNA from cells induced to differentiate. This may in part reflect the low numbers of retinoic acid-induced protein-linked breaks in DNA and also the method's relative inefficiency for DNA with few attached topoisomerase molecules. This suggested that an additional purification method would be required to enrich sufficiently for cleavage site DNA to address the issue of site specificity. The principle of our method is to couple poly(ethylene glycol) (PEG) to topoisomerase while it is covalently attached to DNA and then to use phase partitioning in an aqueous two-phase system of PEG and phosphate to separate free DNA from DNA bound to PEG-modified topoisomerases (which have high affinities for the phosphate-rich and PEG-rich phases, respectively). The method can be used in conjunction with DNase protection and, unlike the SDS/KCl method, can fractionate short fragments of DNA to which single protein molecules are attached. Using the SDS/KCl precipitation and new method in series, we have recovered protein-linked DNA from HL60 cells induced to differentiate to the granulocyte lineage (by retinoic acid) or to the monocyte/macrophage lineage (by phorbol myristate acetate) and have demonstrated that specific sequences become protein linked, probably to topoisomerase II, during induced differentiation.

Separation of cell mixtures by immunoaffinity cell partitioning: strategies for low abundance cells

The partitioning of cells in aqueous two-phase systems formed by poly(ethylene glycol) (PEG) and dextran can be changed by incubating the cells with a PEG-modified antibody directed specifically against its surface. We have developed a new approach for immunoaffinity cell partitioning (IACP) in which the antibodies are first reacted with tresylated monomethoxy PEG (TMPEG) in sodium phosphate buffer, pH 7.5, the excess TMPEG is quenched by reaction with bovine serum albumin, and the resulting preparation is used directly for incubation with the cells without any isolation of the monomethoxyPEG (MPEG)-antibody conjugates. We have demonstrated the specificity of this IACP method by showing that MPEG-modified anti-human red blood cell antibody increases the partition of human erythrocytes from the interface to the PEG-rich top phase (up to 100%) but not the partitioning of either neutrophils or HL60 cells. Irrelevant antibodies do not affect the partitioning of red blood cells. The partitioning behaviors of erythrocytes and HL60 cells in mixtures varying from 75 to 10% red blood cells subjected to IACP are similar to those of the pure cell population, i.e., erythrocytes ca. 100% and HL60 cells 3% in top phase. Thus, the population of erythrocytes can be almost completely extracted into the top phase in a single step. The contaminant cells represent only a small percentage (less than 5% in most of the cases) of the cell mixture recovered in top phase. Both cell populations can be completely separated by countercurrent distribution (CCD).(ABSTRACT TRUNCATED AT 250 WORDS)

Development of a general ligand for immunoaffinity partitioning in two phase aqueous polymer systems

The effect on the partition of erythrocytes in a two phase aqueous polymer system based on dextran T500 and polyethylene glycol (PEG) 8000 of a combination of immunoaffinity ligands, namely, rabbit immunoglobulin G (IgG) and PEG 1900-modified monoclonal IgG, was examined as a potential cell separation technique. Several hybridoma lines secreting mouse monoclonal IgG specific for the Fc receptor of rabbit IgG were raised. The monoclonal IgG was modified by cyanuric chloride attachment of PEG 1900, causing the modified antibody to partition predominantly into the PEG-rich upper phase of the systems. The PEG-modified monoclonal IgG was used as an affinity ligand in the two phase polymer system to specifically increase the partition of rabbit anti-NN glycophorin IgG. The rabbit IgG was applied together with the PEG-modified monoclonal IgG to increase the partition of human erythrocytes. The same system had no effect on the partition of rabbit erythrocytes. These experiments demonstrate that a monoclonal antibody can be modified and used as a general reagent with which to alter cell partition in two phase aqueous polymer systems in an immunologically specific manner.

Cell separation by immunoaffinity partitioning with polyethylene glycol-modified protein A in aqueous polymer two-phase systems

Previous work has shown that polyethylene glycol (PEG)-bound antibodies can be used as affinity ligands in PEG-dextran two-phase systems to provide selective partitioning of cells to the PEG-rich phase. In the present work we show that immunoaffinity partitioning can be simplified by use of PEG-modified Protein A which complexes with unmodified antibody and cells and shifts their partitioning into the PEG-rich phase, thus eliminating the need to prepare a PEG-modified antibody for each cell type. In addition, we provide a more rigorous test of the original technique with PEG-bound antibodies by showing that it is effective at shifting the partitioning of either cell type of a mixture of two cell populations.

Specific deposition of complement protein C3b on abnormal PNH erythrocytes permits their separation by partitioning. Possible general approach for isolation of specific cell populations

The deposition of complement proteins on a cell surface has previously been shown to reduce the cell's partition ratio in a two-polymer aqueous phase system. This phenomenon has now been extended to segregate, by partitioning, subpopulations of erythrocytes from patients with paroxysmal nocturnal hemoglobinuria (PNH). Purified components of the complement system were employed to deposit the protein C3b specifically on abnormal erythrocytes which lacked the membrane-associated complement regulatory protein DAF. As few as 2100 C3b/cell reduced the partition ratio and 24,000 C3b/cell resulted in resolution of the C3b-bearing and non-bearing human red cells. It was found that the proportion of cells separated did not equal the proportion of cells lysed by complement in the acidified serum lysis test when blood from three of the five patients was examined. The results indicate that the defect giving rise to DAF- cells may be, but is not necessarily, coexpressed with defects affecting other membrane-associated regulatory factors. A broader application of the method using monoclonal antibodies to direct purified complement components to specific cell populations should permit their isolation in large quantities.

Phase partitioning in space and on earth

In aqueous solution at low concentrations, the neutral polymers dextran and poly(ethylene glycol) (PEG) rapidly form a two-phase system consisting of a PEG-rich phase floating on top of a dextran-rich phase. Biological particles and macromolecules tend to partition differentially between the phases and the liquid-liquid phase interface in these systems. Bioparticle partitioning has been shown to be related to physiologically important surface properties such as membrane charge or lipid composition. Affinity partitioning into the PEG-rich phase can be accomplished by coupling PEG to a ligand having affinity for specific cells or macromolecules. Subpopulations can be identified or separated using multi-step countercurrent distribution (CCD). Incomplete understanding of the influence of gravity on the efficiency and quality of the impressive separations achievable by partitioning, and appreciation for the versatility of this efficient technique, have led to its study for low-gravity biomaterials processing. On Earth, two-phase systems rapidly demix because of density differences between the phases. In low-gravity, demixing has been shown to occur primarily by coalescence. Polymer surface coatings, developed to control localization of demixed phases in low-g, have been found to control electroosmosis which adversely affects electrophoretic separation processes on Earth and in space. In addition PEG-derivatized antibodies have been synthesized for use in immunoaffinity cell partitioning.

Differential partition of virulent Aeromonas salmonicida and attenuated derivatives possessing specific cell surface alterations in polymer aqueous-phase systems

Two-polymer aqueous-phase systems were used to compare via partitioning the surface properties of strains of the fish pathogen Aeromonas salmonicida which differed in their ability to produce the surface protein array known as the A layer and in their ability to produce smooth lipopolysaccharide. In these two-phase systems, biological particles are known to partition between the phases in a manner related to a variety of surface properties, including hydrophobicity, charge, and lipid composition. Both the presence of the superficial protein layer and the O polysaccharide chains of lipopolysaccharide were shown to play an important role in the partitioning behavior of A. salmonicida cells. The presence of the A layer, which is crucial to the virulence of A. salmonicida, appeared to decrease the surface hydrophilicity of this pathogen and to increase, in a somewhat specific manner, its surface affinity for fatty acid esters of polyethylene glycol. The ability of two-polymer aqueous-phase systems to differentially partition A. salmonicida cells on the basis of differences in surface architecture suggests their general usefulness for the analysis of surface properties important in bacterial virulence and should permit their use in the selection of strains and mutants exhibiting specific surface characteristics.