Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
  • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
  • G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
  • G01N33/543—Immunoassay; Biospecific binding assay; Materials therefor with an insoluble carrier for immobilising immunochemicals
  • G01N33/54393—Improving reaction conditions or stability, e.g. by coating or irradiation of surface, by reduction of non-specific binding, by promotion of specific binding
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
  • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
  • G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
  • G01N33/5306—Improving reaction conditions, e.g. reduction of non-specific binding, promotion of specific binding
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
  • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
  • G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
  • G01N33/536—Immunoassay; Biospecific binding assay; Materials therefor with immune complex formed in liquid phase
  • G01N33/537—Immunoassay; Biospecific binding assay; Materials therefor with immune complex formed in liquid phase with separation of immune complex from unbound antigen or antibody
  • G01N33/5375—Immunoassay; Biospecific binding assay; Materials therefor with immune complex formed in liquid phase with separation of immune complex from unbound antigen or antibody by changing the physical or chemical properties of the medium or immunochemicals, e.g. temperature, density, pH, partitioning
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2333/00—Assays involving biological materials from specific organisms or of a specific nature
  • G01N2333/195—Assays involving biological materials from specific organisms or of a specific nature from bacteria

Definitions

• the present invention relates to the determination of total concentration of analyte in fluid samples wherein the analyte may at least partially be in complex form, typically as an immune complex. More particularly, the invention relates to an assay method where preformed analyte complexes are dissociated prior to determining the analyte, as well as a kit for performing the method. Background of the invention
• proteins may form homo-multimers, e.g. fibrillating proteins, where critical epitopes essential for assaying will not be fully accessible in protein aggregates. If the monomer has a limited number of epitopes this might contribute to underestimation of the monomer protein concentration when multimerization is prone to occur (1).
• protein complexes may be formed between active enzymes and their inhibitors in a pre-determined ratio complicating accurate determination of the enzyme. This may lead to certain epitopes being inaccessible in immunoassays and hence an immunoassay may generate inaccurate concentration estimates (2).
• Intermittent release of intracellular proteins over longer periods of time due to cell damage of e.g. cardiac cells (3) or tumour cells (4) may generate immune responses against intracellular proteins. These may in a later stage contribute to the formation of immune complexes composed of target molecules and auto-antibodies. Given the amplification properties of the immune system, antibodies may be formed at much higher relative concentrations compared to the target protein leading to formation of immune complexes complicating accurate quantification of target protein.
• the ligand used for purification may leach from the resin during the process and end up as an impurity in the purified material. Leaching may occur as a consequence of the dissociation conditions used, for example, proteolytic cleavage of ligand by components from the cell culture, but also the property of resins used, the immobilization chemistry and other aspects related to manufacturing of the affinity resin, as well as the forces involved in the bio-specific interaction between the interactants, may all contribute to ligand leaching to some degree. Irrespective of which specific mechanism is involved, the ligand may contaminate the product being purified on the affinity resin.
• therapeutic proteins purified according to these principles may induce non- desired side effects, e.g. allergic shock or complement activation, increasing the risk-profile of the treatment.
• Native protein A produced by staphylococci, interacts with immunoglobulins in two principally different manners: ⁇ The classical interaction involving the Fc portion of human IgG (7).
• immunoglobulin class (8) that belongs to the VHIII (9) group of the variable domain of the heavy chains.
• Native protein A has five immunoglobulin binding domains (10), each of which can interact independently with IgG portions Fey and Fab, respectively. This creates a multitude of interaction possibilities between IgG and protein A, even forming precipitates at equimolar proportions (7). However, it is likely that also under conditions when the proportions of interactants are very dissimilar, heterogeneous complexes will be formed engaging several of the potential interactions in complex formation.
• Native protein A has been modified using recombinant technologies (1 1).
• recombinant technologies 1 1).
• One example is when native, staphylococcal protein A or recombinant versions of the same molecule, Fragment Z in multimer version (11), or MabSelect SuReTM ligand (GE Healthcare Life Sciences, Uppsala, Sweden), a protein A-derived molecule and modified with respect to alkaline tolerance (12) (immobilized on agarose in chromatography medium MabSelect SuReTM) to improve stability upon repeated cleaning-in-place procedures, are used as ligand in the purification process.
• alkaline tolerance (12)
• MabSelect SuReTM MabSelect SuReTM
• the selected pH should, on the one hand, quantitatively dissociate complexes between protein A and IgG (i.e. dissociate protein A from the Fc and/or Fab regions) while, on the other hand, the assay is still functional, a combination that has proven difficult to fulfill.
• WO 2008/033073 Al discloses a method of determining the total concentration of an analyte in a fluid sample, wherein at least part of the analyte is present as a complex with an analyte-binding species.
• the method comprises the steps of: a) subjecting the sample to conditions that reduce the binding affinity between analyte and analyte-binding species sufficiently to dissociate substantially any analyte complex and provide substantially all analyte in free form, b) subjecting the sample to conditions that restore the binding affinity between analyte and analyte-binding species, and c) immediately after the binding affinity has been restored, and before any substantial re-complexing of the analyte has taken place, determining the concentration of free analyte in the sample.
• the method is performed in a flow system using label-free detection, such as surface plasmon resonance (SPR).
• SPR surface plasmon resonance
• WO 2009/022001 Al discloses a method based on surface plasmon resonance for detection of anti-drug antibodies (ADAs) against a therapeutic drug. Drug interference in the presence of drug in the patient sample to be analysed is overcome by acidifying the sample (pH 2.5 or 3), and then neutralizing the sample before analysis.
• the above-mentioned object is achieved by an improved method wherein separate acidic pH's are used for, on the one hand, dissociating preformed complexes (e.g. protein A-IgG complexes) in fluid samples and, on the other hand, performing the immunoassay, viz. at a pH where reformation of complexes is largely prevented, and at which the capture molecule, typically antibody, is sufficiently active to generate a dose response for the analyte, even in presence of large amounts of complexing component.
• preformed complexes e.g. protein A-IgG complexes
• the present invention therefore provides a method of quantitatively determining an analyte in a fluid sample by an immunoassay comprising binding of the analyte to a ligand capable of specifically binding to the analyte, wherein at least part of the analyte is present as an analyte complex, and wherein the method comprises the steps of: a) subjecting the sample to a first acidic pH to at least substantially dissociate any analyte complex present and provide substantially all analyte in free form,
• analyte complex includes complexes with specifically as well as non-specifically binding species, and also includes multimers, such as dimers or trimers, of the analyte.
• the ligand may, for example, be an antibody.
• antibody as used herein is to be interpreted in a broad sense and refers to an immunoglobulin which may be natural or partly or wholly synthetically produced and also includes active fragments, including Fab antigen-binding fragments, univalent fragments and bivalent fragments. The term also covers any protein having a binding domain which is homologous to an immunoglobulin binding domain. Such proteins can be derived from natural sources, or partly or wholly synthetically produced. Exemplary antibodies are the immunoglobulin isotypes and the Fab, Fab', F(ab')2, scFv, Fv, dAb, and Fd fragments.
• the ligand is immobilized to a solid support.
• the analyte is selected from protein A, protein G, protein A/G, protein L or derivatives thereof (including native variants and recombinantly produced proteins or polypeptides), and the sample contains IgG.
• the first acidic pH is selected in the range from about 1.5 to about 3.2 (especially 1.5 to 3.2)
• the second acidic pH is selected in the range from about 2.7 to about 4.5 (especially 2.7 to 4.5), more preferably from about 2.8 to about 4.5 (especially 2.8 to 4.5).
• the second acidic pH may, for example, be selected in the range of from about 3.0 to about 4.5 (especially 3.0 to 4.5).
• the first acidic pH is selected in the range from about 2.3 to about 2.5 (especially 2.3 to 2.5) and/or the second acidic pH is selected in the range from about 2.8 to about 3.2 (especially 2.8 to 3.2).
• the second acidic pH is selected in the range from about 3.3 to about 3.5 (especially 3.3 to 3.5) or from about 3.0 to about 3.2 (especially 3.0 to 3.2).
• the method may conveniently be performed in a microfluidic system.
• kits for performing an immunoassay of an analyte which is present in a fluid sample at least partially in complex form comprising:
• a first acidic buffer preferably having a pH in the range from about 1.5 to about 3.2
• a second acidic buffer having a higher pH than the first acidic buffer, preferably a pH in the range from about 2.7 to about 4.5.
• the analyte is capable of binding to a ligand immobilized to a solid phase
• the kit further comprises a capture reagent for the analyte, wherein the capture reagent is capable of binding to the solid phase.
• the capture reagent is biotinylated and the ligand is avidin or
• Figure 1 is a plan view of a microstructure for performing an embodiment of the method of the present invention.
• Figure 2 is an illustration of pH intervals for protein A/IgG complex dissociation and analysis of released protein A, respectively.
• Figure 3 is an illustration of a method for automated acid dissociation and analysis of MabSelect SuReTM ligand in the presence of IgG at 5 mg/ ml.
• Figure 4 is a diagram showing in overlay format dose response relationship of assaying standard curves for (1) MabSelect SuRe in buffer only; (2) Mabselect SuRe + hlgG at 5 mg/ml after processing at pH 2.5 and 3.5; (3) (control) MabSelect SuRe + 5 mg/ml hlgG, dissociation at pH 2.5 and assay at pH 8.0; and (4) (control) MabSelect SuRe at 5 mg/ml of hlgG, no dissociation and assay at pH 7.4.
• Figure 5 is a diagram showing a standard curve of MabSelect SuRe in the presence of hlgG at 5 mg/ml.
• Figure 6 is a diagram showing a standard curve for MabSelect SuRe in the presence of hlgG at 5 mg/ml.
• Figure 7 is a diagram showing a standard curve for native protein A in the presence of polyclonal, human IgG at 5 mg/ml (pH for dissociation of complexes 2.3, and pH for analysis 3.3).
• Figure 8 is a diagram showing overlayed standard curves for two different molecular forms of protein A [native (1) and MabSelect SuRe (2)] in the presence of human polyclonal IgG (OctagamTM) at a concentration of 5 mg/ml.
• Figure 9 is a diagram showing in overlay format standard curves for MabSelect SuRe in the presence of different concentrations of HumiraTM (a therapeutic monoclonal antibody).
• HumiraTM a therapeutic monoclonal antibody.
• (1) is MabSelect SuRe in buffer only; (2) is MabSelect SuRe in 10 mg per ml HumiraTM; (3) is MabSelect SuRe in 5 mg per ml HumiraTM; and (4) is MabSelect SuRe in 2 mg per ml HumiraTM.
• Figure 10 is a diagram showing in overlay format standard curves for residual MabSelect SuRe (1) in buffer only; (2) in the presence of 5 mg per ml HerceptinTM (a therapeutic monoclonal antibody); and (3) in the presence of 5 mg per ml HumiraTM.
• Figure 11 is a diagram showing a standard curve for MabSelect SuRe in the presence of HumiraTM at 5 mg/ml.
• the present invention is based on the principle of using separate acidic pH's for the dissociation of preformed complexes in a sample and for performing the immunoassay, and more specifically by first using a relatively low pH for efficient complex dissociation, and subsequently performing the assay at a higher acidic pH where restoration of complexes is largely prevented, while the capture agent (typically antibody) is sufficiently active for efficient capture of the analyte to be quantified.
• the method may be performed using a wide variety of assay systems and assay formats.
• a heterogeneous assay system comprising a solid support surface with an immobilized analyte-specific ligand is used for measuring analyte concentration by detecting directly or indirectly the amount of binding to the solid support surface, either of the analyte (direct assay, including sandwich assay; or
• the solid support surface may have a variety of shapes as is per se known in the art and may, for example, be particles in a packed bed, typically provided in a microfluidic channel or cavity; or may be a surface area of a cuvette or well, such as a micro- well or a flow cell or channel, or the like.
• the method of the invention is generally applicable to a wide variety of analytes and analyte complexes, it will in the following be described primarily with regard to the quantification of protein A and protein A derivatives in the presence of IgG in a liquid sample, and with regard to performing the assay in a microfluidic system specifically the above-mentioned GyrolabTM platform.
• Examples of other analytes when present at least partially in complex form that may be contemplated for determination by the method of the invention include:
• immunochemical methodology e.g. dissociation of metalloproteases/TIMP inhibition.
• the selected pH for immunoassay is efficient for preventing the formation of complexes, e.g. when IgG and protein A solutions are acidified before being mixed, a situation which of course is quite far from the real analytical situation.
• this observation fits with basic biochemical principles demonstrating "hysteresis effects" on the conditions required for, on the one hand, dissociating pre-formed complexes and, on the other hand, the conditions required for preventing complex re-formation (17). Thus it takes more energy to dissociate preformed complexes than preventing the formation of new complexes.
• the present invention is based on transferring the above observations into practice, i.e. that it would be attractive to quantitatively dissociate complexes at a first low pH, and perform the assay at a second higher acidic pH, which is compatible with functional properties of the antibodies used, but selected such that re-formation of complexes is prevented (at least to a substantial degree). It should be emphasized that performing immunoassays at a mildly acidic pH, such as 3.5, is still very demanding on most antibodies.
• the present invention takes advantage of the hysteresis seen in interactions between molecules displaying natural affinity and of which at least one of the counterparts is subject to quantification using
• the method of the invention will now be described in the context of being used with a GyrolabTM immunoassay platform (Gyros AB, Uppsala, Sweden).
• the GyrolabTM system, or workstation uses compact discs (CD) with a plurality of microfluidic structures.
• CD compact discs
• this type of microfluidic analytical technology it may be referred to, for example, WO 99/058245, WO 02/074438 A2, WO 02/075312 Al , WO 03/018198 Al , WO 2004/083108 Al and WO
• Figure 1 illustrates one of the microstructures of GyrolabTM CD, CDMX1 , containing two liquid inlets (1), two volume definition units (2), an overflow channel (3), a mixing chamber (4), an enforced finger valve (5), and a capture column (6) where reactions take place and which contains beads coupled with ligand, here typically streptavidin to be coupled to biotinylated capture antibody (the streptavidin-biotin interaction is stable in the acid pH conditions used in the present method).
• a hydrophobic barrier (not shown) separates the mixing chamber (4) from the capture column (6).
• Reagents and buffers for performing the immunoassay are introduced in the left inlet (1), and samples and reagents for sample pre-treatment are introduced in the right inlet (1).
• the mixing chamber (4) is located upstream of the capture column (6), i.e. spinning of the CD will cause liquid to flow from the mixing chamber (4) to the capture column (6).
• Aliquots of sample and buffers aimed for pre-treatment of sample can sequentially be added in portions of, typically, 200 nl after volume definition within the CD into the mixing chamber (4).
• any type of liquid compatible with the microfluidic principles can be added.
• buffers aimed for efficient dissociation will generate a resulting pH of 1.5 to 3.2, whereas buffers intended to prepare samples for analysis will generate a resulting pH of 2.7 to 4.5, or more specifically 2.8 to 4.5, e.g.
• the dissociating effect of acid buffer addition is usually very rapid. In the protein A- IgG system, it seems that the dissociation is quantitative after 1-5 min generating a resulting pH of 2.5. The next step of adjusting the pH of the sample to running conditions for the assay is also very rapid.
• the analysis step is initiated by increasing the spinning speed of the CD to overcome the resistance of the hydrophobic barrier separating the mixing chamber (4) from the capture column (6) (Fig. 1).
• the capture column is functionalized with an appropriate capture antibody and the capture column may have to be
• a polyclonal chicken anti-Protein A antibody was purchased from Cygnus
• a biotinylated mouse monoclonal antibody directed against protein A was purchased from Sigma-Aldrich, St. Louis, MO, U.S.A. (eta no B3150;
• HumiraTM (a therapeutic antibody, marketed by Abbott Laboratories, Abbott Park, Illinois, USA) was purchased from the pharmacy on prescription.
• HerceptinTM (a therapeutic antibody, marketed by F. Hoffmann-La Roche Ltd, Basel, Switzerland) was purchased from the pharmacy on prescription. Buffers
• Buffers were prepared from solid chemicals at appropriate buffer capacity and pH.
• Protein A (native, 17-0872-05) and derivatives thereof (MabSelect SuReTM ligand, 28-4018-60) were purchased from GE Healthcare Life Sciences, Uppsala, Sweden (www.gelifesciences.com).
• CDMXl (P0020026), also called “Gyrolab ADA CD", was from Gyros AB, Uppsala, Sweden (www.gyros.com).
• Column packing was (15 ⁇ ) streptavidin-derivatised DynospheresTM (Invitrogen Dynal A.S., Oslo, Norway).
• Standard curves were prepared by dilution of protein A in 5 mg/ml of polyclonal IgG in PBS, pH 7.4, allowing complexes between protein A and IgG to be formed.
• Quality control (QC) samples were prepared in separate dilutions with known concentrations of protein A in the presence of polyclonal or monoclonal IgG at 5 mg/ml.
• MabSelect SuRe can be determined at sub-ppm levels in concentrations of IgG at 5 mg/ml.
• the assay used for MabSelect SuRe spans from approximately 1 ng/ml and upwards generating a sensitivity of approximately 0.2 ppm (w/w).
• Figure 4 illustrates the dose response relationship of assaying standard curves containing MabSelect SuReTM ligand only (1), and Mabselect SuRe + hlgG at 5 mg/ml after processing at pH 2.5 and 3.5 (2) as described for the method.
• Figure 5 shows a standard curve of MabSelect SuRe in the presence of hlgG at 5 mg/ml.
• the capture column was washed prior to the capture step using a glycine- citrate buffer, pH 3.5, and further washed twice before the column was neutralized using PBS before the analytical process was finalized.
• Table 1 shows the average bias of QC samples when using the standard curve in Figure 5.
• Figure 6 shows a dose response curve for MabSelect SuRe in presence of hlgG at 5 mg/ml.
• the capture column was kept in PBS, pH 7.4, during the entire process.
• Table 2 shows the average bias of QC samples when using the standard curve in Figure 6.
• Mouse monoclonal anti-Protein A antibody as capture antibody and chicken polyclonal anti-Protein A antibody as detection antibody (dissociation at pH 2.3 and capture at pH 3.3)
• Figure 7 shows a dose response curve for native protein A in the presence of polyclonal, human IgG at 5 mg/ml.
• the pH selected for dissociation of protein A-IgG complexes was 2.3 and the pH selected for analysis was 3.3.
• Table 3 shows analysis of QC samples containing different concentrations of native protein A in the presence of polyclonal human IgG at 5 mg/ ml employing
• Proprietary polyclonal anti-Protein A antibody as capture and detection antibodies (dissociation at pH 2.5 and capture at pH 2.8)
• Figure 8 shows an overlay chart of standard curves for (1) protein A and (2)
• MabSelect SuRe in the presence of human polyclonal IgG (OctagamTM) at a concentration of 5 mg/ ml.
• Figure 9 shows an overlay chart of standard curves for (1) MabSelect SuRe in buffer only, (2) MabSelect SuRe in 10 mg/ml HumiraTM (a therapeutic monoclonal antibody), (3) MabSelect SuRe in 5 mg/ml HumiraTM, and (4) MabSelect SuRe in 2 mg/ml HumiraTM.
• HumiraTM were analyzed for concentration of MabSelect SuRe in CDMX1. The average bias in relation to the expected concentration was determined. The results are illustrated in Table 4 below. Table 4
• Figure 10 shows an overlay chart of standard curves for residual MabSelect SuRe (1) in buffer only, (2) in the presence of 5 mg per ml HerceptinTM, and (3) in the presence of 5 mg per ml HumiraTM.
• IgG containing (HumiraTM) samples contaminated with residual MabSelect SuRe were provided. Samples were first normalized by diluting them to a concentration of 5 g/L. Samples were then analyzed for protein A using the above outlined procedure involving acid dissociation at pH 2.5 and capture at pH 2.8. A standard curve for dose-response vs concentration of MabSelect SuRe was prepared as shown in Figure 1 1. The concentration of residual MabSelect SuRe in the original samples were then determined using the standard curve and calculated by compensating for the dilution factor. The precision (CV%) of duplicate determinations is reported. The results are shown in Table 6 below.
• immunoglobulins can be accurately quantified in the presence of large
• the procedure can be performed in a CD containing microfluidic structures, each having a mixing chamber upstream the capture column in which pretreatment of sample with different buffers at different pH can be performed in a standardized manner.
• the procedure takes, depending on the specific set up, on average approximately one hour.
• the relative concentration of MabSelect SuReTM ligand that can be detected is in the range of 0.2-0.5 ppm at 5 mg/ml of IgG (w/w), a relative concentration that is far below the regulatory accepted level of impurity (13).
• the principal dissociation and analysis procedure is also compatible with native protein A in polyclonal, human IgG at 5 mg/ml. Kit composition - Assay for residual protein A
• An exemplary kit for performing analysis of residual protein A (or MabSelect SuRe) in the presence of IgG comprises the following reagents A to I.
• Reagents A, B and C are provided as stock solutions intended to be diluted with diluent reagents G, H and I, respectively.
• the entire kit is composed of nine different types of liquids sufficient for 5 GyrolabTM ADA CDs (Gyros AB) generating 240 data points (48/CD).
• Reagent A Capture reagent, biotinylated anti-protein A antibody, 625 ⁇ g/ml.
• Reagent B Detection reagent, fluorophore labelled anti-protein A antibody, 200 nM.
• Reagent C Native Protein A, 1000 ⁇ g/L.
• Reagent D Acid Dissociation Buffer 1 , 0.25 M Glycine-HCl, pH 2.5.
• Reagent E Acid Dissociation Buffer 2, 0.1 M Citrate buffer, pH 3.4.
• Reagent F Acidic Wash buffer, one part Reagent D mixed with one part Reagent E.
• Reagent G (2 vials) : Neutral wash buffer and for diluting capture reagent A.
• Reagent H (2 vials): Sample Dilution Buffer, RexxipTM ADA (P0020027, Gyros AB) for diluting samples.
• Reagent I Detecting Antibody Buffer, RexxipTM F (P0004825, Gyros AB) for diluting detecting reagent B (0.5 ml)
• Inganas M Comparison of mechanisms of interaction between protein A from Staphylococcus aureus and human monoclonal IgG, IgA and IgM in relation to the classical Fey and alternative F(ab ' )2 protein A interactions. Scand. J. Immunol. 13(4), 343-52, 1981.

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