WO2003044533A2

WO2003044533A2 - Capture and detection phase of a target biological material for elisa tests

Info

Publication number: WO2003044533A2
Application number: PCT/FR2002/003999
Authority: WO
Inventors: François Mallet; Thierry Delair; Valérie CHEYNET; Guy Oriol; Laurent Veron; Marie-Hélène Charles; Laure Allard
Original assignee: Biomerieux
Priority date: 2001-11-21
Filing date: 2002-11-21
Publication date: 2003-05-30
Also published as: AU2002356260A1; FR2832508A1; WO2003044533A3; AU2002356260A8

Abstract

The invention concerns a method for obtaining a capture phase of a target biological material, comprising a modified protein of interest, capable of binding with said target biological material and immobilized on an immobilization phase which consists in providing at least two different peptide sequences, including the peptide sequence of the protein of interest, and a succession of at least six lysine residues and a succession of at least six histidine residues at their N- and C- termini, immobilizing each of the two peptide sequences obtained on the immobilization phase, determining the efficacy of the coupling between each of the two sequences and the immobilization phase, selecting as capture phase, the peptide sequence more efficiently coupled to the immobilization phase. The invention also concerns a method for obtaining a detection phase of a target biological material, comprising a modified protein of interest capable of binding with said target biological material and coupled to a hapten, which consists in providing at least two different peptide sequences, including the peptide sequence of the protein of interest, and a succession of at least six lysine residues and a succession of at least six histidine residues at their N- and C- termini, coupling each of the two peptide sequences obtained to the hapten, determining the efficacy of the coupling between each of the two sequences to the hapten, selecting as detection phase, the peptide sequence more efficiently coupled to the hapten, and the use of the capture and detection phases obtained for detecting a target biological material, in ELISA.

Description

METHOD FOR OBTAINING A CAPTURE PHASE AND A DETECTION PHASE OF TARGET BIOLOGICAL MATERIAL AND USE IN ELISA TESTS

The invention relates to phases of capture and detection of a target biological material to be detected in a biological sample, and to their implementation in an ELISA test.

The capture and detection phases according to the invention comprise a protein modified to optimize this detection technique, by increasing its specificity and sensitivity.

A modified protein according to the invention is a protein, said to be of interest, that is to say a protein, or a part of this protein, which will interact with the target biological material which it is desired to detect, isolate , quantify, especially in diagnosis. The modification consists in adding to said sequence, by intercalation and / or addition, at least two successions of amino acid residues: a succession of at least six histidine residues and a succession of at least six histidine residues, one at the N-terminal end and the other at the C-terminal end. In the following description, the terms succession and tag will be used interchangeably to represent a group of amino acid residues.

According to document WO-A-98/59241, the authors of the present invention have demonstrated that the modification of the peptide sequence of the p24 capsid protein of HIV-1, by insertion of a tag of six lysine residues, makes it possible to considerably increase the protein coupling yield on the AMVE67 copolymer. This yield is a ratio expressed as a percentage of the amount of protein coupled to a polymer to the amount of protein initially introduced before the addition of the polymer. This resulted in the immobilization of 50 molecules of modified protein per copolymer chain. According to this document, we sought to obtain the fixation of the largest amount of protein on an immobilization phase. However, this high coupling or binding yield is obtained by the interaction of the protein and lysine tag sites, with the reaction groups of the immobilization phase. As a result, a high coupling yield can be detrimental to the integrity of the protein and therefore to its biological activity. In detection techniques such as ELISA, it is essential that the capture and detection phases retain the biological activity of the immobilized or coupled protein, after purification and immobilization or coupling. Also, the challenge of the invention resided in obtaining a capture phase and a detection phase each comprising a modified protein which has at least all the biological properties of the native protein, for which the protein modified is used, especially in diagnostics. Thus, the first objects of the invention are the following:

a method for obtaining a phase for capturing a target biological material, comprising a modified protein of interest, capable of specifically, directly or indirectly binding to said target biological material and immobilized on an immobilization phase comprising reactive groups, said method comprising the following steps: at least two different peptide sequences are available, comprising the peptide sequence of the protein of interest, and one comprising a succession of at least six lysine residues at its end N-terminal and a succession of at least six histidine residues at its C-terminal end, the other comprising a succession of at least six histidine residues at its N-terminal end and a succession of at least six lysine residues at at its C-terminal end, each of the two peptide sequences obtained is immobilized on the immobilization phase, by covalent reaction between the amino groups primary peptide sequences and the reactive groups of the support, the efficiency of the coupling between each of the two sequences and the immobilization phase is determined, the peptide sequence most effectively coupled to the immobilization phase is chosen as the capture phase ;

According to the invention, the determination of the coupling efficiency between each of the two sequences and the immobilization phase is carried out by quantification of the free primary amine groups of the immobilized peptide sequence and of the free primary amine groups of the same non-peptide sequence. immobilized, and deduction of the amino groups having interacted with the immobilization phase, being it is understood that the efficiency of the coupling is all the higher the higher the number of primary amine groups belonging to the protein of interest and which remain after coupling. This makes it possible not to prejudice the integrity of the protein and therefore its biological activity. The quantification of said groups is advantageously carried out by reaction of said groups with fluorescamine.

a method for obtaining a phase of detection of a target biological material, comprising a modified protein of interest, capable of specifically, directly or indirectly binding to said target biological material and coupled to a hapten, said method comprising the following steps: at least two different peptide sequences are available, comprising the peptide sequence of the protein of interest, one comprising a succession of at least six lysine residues at its N-terminal end and a succession of at least six histidine residues at its C-terminal end, the other comprising a succession of at least six histidine residues at its N-terminal end and a succession of at least six lysine residues at its C-terminal end, we couple each of the two peptide sequences obtained with hapten, the efficiency of the coupling of each of the two sequences with hapten is determined, and the detection phase is chosen peptide equation most efficiently coupled to hapten. The coupling efficiency is determined by the number of primary amine groups left free in the protein of interest, after immobilization or coupling.

According to the invention, the determination of the coupling efficiency between each of the two sequences and the hapten is carried out by quantification of the free primary amine groups of the coupled peptide sequence and of the free primary amine groups of the same uncoupled peptide sequence, and deduction of the amino groups having interacted with the hapten, it being understood that the coupling efficiency is higher the higher the number of primary amine groups belonging to the protein of interest and remaining after coupling. This makes it possible not to prejudice the integrity of the protein and therefore its biological activity. The quantification of said groups is advantageously carried out by mass spectrometry.

Before exposing the other objects of the invention and describing their characteristics and advantages in detail, a definition of certain terms used in the description and the claims is given below so that the invention and therefore the scope of protection are clearly delimited.

A succession or tag of amino acid residues is a short sequence of amino acids which is reported in the peptide sequence of the native or original protein, in a privileged place, to allow this succession or tag to be exposed in a way relevant, while retaining or even improving the biological properties of the native or original protein. In particular according to the invention, the presentation of the histidine residue tag must be favorable with respect to an affinity of this tag for metal ions, as used in the purification technique known as IMAC (affinity chromatography for immobilized metal ions) , that of the tag of lysine residues must be favorable compared to its fixation on an immobilization phase via a covalent interaction between the tag and reactive functions present on or in said phase. By intercalation or insertion of a tag, it is understood that the tag is introduced inside the peptide sequence of the protein of interest, between two amino acids. By adding a tag, it is understood that the tag means that the tag is "butted" to the peptide sequence of the protein of interest, at the N- or C-terminal end of said sequence. In practice, the proteins modified according to the invention will often contain amino acids which will be inserted between the tags, and / or between the tags and the peptide sequence of the native or original protein, without having any effect on the specificity of the tags and on the biological activity of the protein. The amino acid residues belonging to a tag according to the invention are chosen from natural amino acids and chemically modified amino acids. The chemical modification made to the natural amino acid must preserve, or even develop, the specificity of the tag with respect to its role in fixation. By way of example, mention may be made of the replacement of an amino acid L by the corresponding amino acid D and vice versa; a modification of the amino acid side chain: in in the case of lysine, it may be an acetylation of the amino group of the side chain; a modification of the peptide bonds of the tag, such as carba, retro, inverso, retro-inverso, reduced, methylene-oxy bonds.

The immobilization phase on which the binding of the modified protein is favored via the lysine residue tag can be a polymer, particulate or linear, and in particular chosen from homopolymers such as polylysine, polytyrosine; among the copolymers such as maleic anhydride copolymers, N-vinyl-pyrrolidone copolymers, natural or synthetic polysaccharides, polynucleotides and copolymers of amino acids such as enzymes. Advantageous polymers are the N-vinyl-pyrrolidone / N-acryloxysuccinimide copolymer, poly-6-aminoglucose, horseradish peroxidase (HRP) and alkaline phosphatase.

The immobilization phase includes reactive functions which will interact covalently with the lysine tag. These reactive functions are advantageously chosen from the ester, acid, halocarbonyl, sulfhydrile, disulfide, epoxide, halocarbonyl and aldehyde functions.

The immobilization phase can be fixed, directly or indirectly, on a solid support, by passive adsorption or by covalence.

This solid support can be in any suitable form such as a plate, a cone, a ball, the ball possibly being radioactive, fluorescent, magnetic and / or conductive, a bar, a glass tube, a well, a sheet, a chip or the like. The support material is preferably chosen from polystyrenes, styrene-butadiene copolymers, styrene-butadiene copolymers in admixture with polystyrenes, polypropylenes, polycarbonates, polystyrene-acrylonitrile copolymers, styrene-methyl methacrylate copolymers, from synthetic and natural fibers, among polysaccharides and cellulose derivatives, glass, silicon and their derivatives.

The immobilization phase of the capture phase is preferably a polymer having, at least on the surface, reaction groups, and in particular a maleic anhydride copolymer such as those chosen from poly (methyl vinyl ether anhydride). maleic), poly (ethylene- maleic anhydride), poly (styrene- maleic anhydride) and poly (N-vinylpyrrolidone- maleic anhydride). As the examples will show, poly (methyl vinyl ether-maleic anhydride) is preferred. During the immobilization step, the reaction groups of the polymer or of any other phase used, will interact with the amino groups present in the peptide sequence of the modified protein, to form a covalent bond.

In order to limit the number of reactive groups in the immobilization phase, the latter can be treated to inactivate, at least in part, but not all, of its reactive groups. This treatment can be carried out before the immobilization step, during the immobilization step, or even before and during immobilization. Thus, this treatment is advantageously carried out, when the immobilization step is carried out, in a medium allowing the partial, and not total, hydrolysis, of the reactive groups of said immobilization phase. These conditions provide a faculty for controlling the content of reaction groups in said phase. In fact, certain commercially available polymers contain an excessive content of reaction groups which can adversely affect the regioselectivity of the interaction between the modified protein and the immobilization phase pro To obtain a capture phase or a phase of detection according to the invention, the two peptide sequences at least comprise a succession of six lysine residues and a succession of at least six histidine residues, a succession of at least six lysine residues and a succession of six histidine residues or alternatively a succession of six lysine residues and one succession of six histidine residues. Preferably, the at least two peptide sequences comprise a succession of six lysine residues and a succession of six histidine residues. As the examples will demonstrate, a very sensitive capture phase, which can be implemented in an ELISA test, for the detection of anti-HIV-1 antibodies, is obtained with a protein of interest which is the protein p24 of the capsid of HIV-1, comprising the sequence SEQ ID NO: 2, and modified by addition in the peptide sequence, of a succession of 6 lysine residues at its N-terminus terminal and a succession of 6 histidine residues at its C-terminal end.

To obtain a detection phase according to the invention, the hapten is chosen from hormones, vitamins and drugs. In the main application according to the invention, namely detection, the hapten is preferably biotin.

The efficiency of the coupling between the peptide sequences and the hapten is advantageously carried out by mass spectrometry.

As the examples will demonstrate, a very sensitive detection phase, which can be implemented in an ELISA test, for the detection of anti-HIV-1 antibodies, in particular in combination with a capture phase described above, is obtained with a protein of interest which is the p24 protein of the HIV-1 capsid, comprising the sequence SEQ ID NO: 2, and modified by adding a sequence of 6 histidine residues to its N-terminus in the peptide sequence terminal and a succession of 6 lysine residues at its C-terminal end.

Another object of the invention is a kit for the detection by ELISA of a target biological material, comprising a capture phase and a detection phase as obtained according to the invention.

The capture and detection phases of the invention, such as in a kit defined above, find a very interesting application in a method of detection, and possibly quantification, of a target biological material, in a sample of biological fluid. , in ELISA, which comprises the following stages: there is a capture phase and a detection phase mentioned above, the sample is brought into contact with the capture phase and then the detection phase, the phase complex is detected capture - target biological material - detection phase.

In particular, when the hapten of the detection phase is biotin, the complex capture phase - target biological material - detection phase is detected by the addition of streptavidin - peroxidase and then orthophenylene diamine. The characteristics and advantages of the various objects of the invention are illustrated below, in support of Examples 1 to 6 and Figures 1 to 6, according to which:

Figure 1 illustrates the native protein p24 and the various modified proteins, as obtained and used according to the present invention.

FIG. 2 illustrates the comparison of the physicochemical characteristics and of the reactivity between the proteins described in FIG. 1, and the protein-polymer conjugates obtained by immobilization of said proteins on an AMVE67 support.

FIG. 3 represents histograms illustrating the ELISA reactivity at 492 nm of a capture phase consisting of the RH24 protein or the conjugate obtained by coupling RK24H to the AMVE67 support hydrolysed 48 hours in DMSO 10% H2O, with respect to 104 HIV negative sera and 105 HIV positive sera.

FIG. 4 illustrates, by the representation in a box plot, the distribution of the optical density signals obtained by ELISA as a function of the nature of the protein immobilized on a support (RH24 alone, noted "24"; RK24H coupled to the AMVE67 hydrolysis 48 copolymer hours in DMSO 10% H ₂ O noted "24Po") and according to clinical status (104 negative HIV sera noted "N", 105 positive HIV sera noted "P").

FIG. 5 represents histograms showing the reactivity in ELISA at 492 nm of a capture phase consisting of the protein RH24 or the conjugate RK24H - AMVE67 hydrolyzed 48 hours in DMSO 10% H ₂ O, opposite, on the one hand , sera from 7 HIV-positive patients, using a high or low titer (Figure 5A), on the other hand, with sera from 2 HIV-positive patients, collected sequentially during the seroconversion period (Figure 5B ). Figure 6 illustrates the comparison of the physicochemical characteristics and the biological reactivity of protein conjugates modified by a tag of six lysine-biotin residues, with respect to the reference protein RH24. Example 1: Set of Constructions for Obtaining Doubly Tagged Proteins

Schematically, the vectors allowing the expression of the tagged recombinant proteins were generated from the expression vector pMR24 obtained by ligation of the Ncol-Xbal fragment of pMH24 (Cheynet et al, 1 993) containing the p24 gene with the fragment Ncol-Xbal of pMR-T7 (WO-98/45449, Arnaud et al, 1 997) containing all the sequences regulating the replication of the plasmid as well as the elements allowing the expression of the inserted gene. Adequate oligonucleotide adapters bringing the coding information relating to the lysine and / or histidine tags were inserted between Clal and Ncol in 5 ′ and Smal and Xbal in 3 ′, in order to obtain a nucleotide sequence according to the invention. The portion of the p24 gene coding for the polypeptide starting at amino acid 3 (valine) and ending at amino acid 224 (proline) is conserved in all the constructs.

Competent bacteria E. coli strain XL1 were transformed by the seven plasmids obtained in Example 1, and the induction of protein expression is carried out by addition of isopropyl-β-D-thiogalactopyranoside (IPTG), as previously described (Cheynet et al, 1 993, Arnaud et al, 1 997). The proteins are extracted, after sonication of the bacterial pellet, in a 50 mM Tris buffer pH 8.0, 1 mM EDTA, 10 mM MgCI ₂ , 100 mM NaCI in the presence of anti-proteases (leupeptin 10 μg / μl and aprotinin 1, 25 μg / μl), then purified by IMAC. The purifications were carried out on a Sepharose gel activated with zinc ions. Recombinant proteins comprising a tag of 6 histidine residues are chelated by metal ions. The chromatographic system used is an FPLC (Àkta Explorer, Pharmacia Biotech). The loading loop is 2 ml. The purifications are carried out by injection of protein diluted 1/2 in the washing buffer which is a 67 mM phosphate buffer - 0.5 M NaCl pH7.8. The proteins of interest are specifically eluted at approximately pH 4.7 by developing a pH gradient using ammonium acetate buffers pH 6.0 and pH 3.0. The different purification fractions are collected. 10 μl of each of these fractions are deposited on Whatman 3MM Chr paper and then stained with Coomassie blue. The fractions (proteins not retained - purified protein) are then put to migrate on 12% acrylamide gels after reduction with β-Me and heating for 10 minutes at 95 ° C, then stained with Coomassie blue. The fractions most concentrated in protein of interest are then combined and then dialyzed in a Slide-A-Lyzer MWCO 10000 PIERCE dialysis cassette for 1 hour then 1 night at + 4 ° C. against a 50 mM Phosphate buffer pH 7.8. The protein concentrations are then defined by a Bradford Coomassie Plus Assay (PIERCE) colorimetric assay.

The purified proteins are then characterized by mass spectrometry coupled with liquid chromatography

(LC / ESI / MS). The analyzes were carried out on an API 100 simple quadrupole mass spectrometer, 140B pumps and a 785A detector (Perkin

Elmer). The reverse phase liquid chromatographies were carried out on a C4 column (Vydac Ref 214PT51 1 5, particle size 5 μm).

The elution buffers are for solvent A: formic acid in water

0.1% (v / v) and for solvent B: formic acid in a water / acetonitrile solution (5: 95 v / v). A gradient of 40 to 60% of B was used.

Figure 1A depicts the peptide sequence of the native p24 capsid protein of HIV-1, isolated from the HXB2 strain. The peptide fragment 3-224 represents the sequence conserved in all the recombinant proteins. Figure 1B illustrates the structure of the three recombinant proteins obtained in accordance with the above protocol, the conserved peptide sequence being represented by a white box, the tag of 6 histidine residues being represented by a gray box, the tag of 6 lysine residues being represented by a black box; the amino acid residues precisely indicated are specific amino acids, outside the three preceding boxes, which can vary from one recombinant protein to another.

The recombinant modified proteins obtained are the following: - RH24 coded by the plasmid pRH24, has a tag of 6 histidine residues in N-terminal position, illustrated by SEQ ID NO: 3;

RH24K, coded by the plasmid pRH24K, has a tag of 6 histidine residues in the N-terminal position and a tag of 6 lysine residues in the C-terminal position, illustrated by

SEQ ID NO: 4; RK24H, coded by the plasmid pRK24H, has a tag of 6 histidine residues in the C-terminal position and a tag of 6 lysine residues in the N-terminal position, illustrated by SEQ ID NO: 5; For each recombinant protein, are indicated, on the Figure

1 B, the number of amino acids, the theoretical molecular masses (MM) ( ^a ) determined using Mac Vector Version 6.5.3 software and the experimental molecular masses ( ^b ) determined by mass spectrometry coupled to a liquid chromatography (LC / ESI / MS). The results show that the molecular weights determined by mass spectrometry are in accordance with those expected for the proteins RH24, RH24K and RK24H, and that therefore the proteins used correspond to those deduced from the translation of the modified gene.

In addition, the proteins are recognized by polyclonal and monoclonal anti-p24 antibodies in western blot and in ELISA.

Example 2: Obtaining protein-polymer conjugates

The covalent immobilization of proteins on polymers is done by the establishment of a covalent amide bond between the anhydride groups of the polymer and the primary amines present on the side chains of the lysine residues as illustrated in the diagram (A) below . As the polymer is not water-soluble, it is necessary to dissolve it in anhydrous DMSO (dimethylsulfoxide) before the coupling reaction carried out in 95% aqueous medium. In this aqueous medium, the anhydride functions of the polymer undergo a hydrolysis reaction, illustrated in diagram (B) below, which, by consuming the reactive groups of the polymer, is in competition with the covalent coupling reaction.

This hydrolysis reaction is used to modulate the reactivity of the polymer, by predetermining the content of reactive groups which will interact with the protein. Partial hydrolysis of the polymers is thus carried out for certain experiments. Scheme A: covalent coupling

- -CH ₂ - CH-CH-CH

H, CO OHO NH-Protein

Scheme B: hydrolysis

H

Operating conditions: Coupling buffers: Phosphate 50 mM pH 7.8,

Polymer: weigh 2 mg of AMVE67 000 copolymer

(Polysciences INC lot N ° 427393) and gently dissolve in 2 ml of

DMSO anhydrous. The partially hydrolyzed polymers are dissolved in DMSO 10% H ₂ O and stored for 48 hours in an oven at 37 ° C before the coupling reaction.

Protein: thaw gently in ice, the amount required for coupling

Coupling protocol: 36 μg of proteins (1, 3.10 ^"9 moles) 5 μl of polymer at 1 g / l in DMSO (7.46.10 ^{" 11} moles) qs 105 μl phosphate buffer 1 x

The covalent coupling reaction is carried out spontaneously by incubation for 3 hours at 37 ° C. on a thermal stirrer.

In order to study the influence of the hydrolysis of the polymer on the reactivity of the conjugate, the polymer is dissolved 48 hours before the coupling reaction, in anhydrous DMSO supplemented with 10% water and then kept under study at 37 ° C.

The conjugates are then characterized as follows.

The samples are filtered in Ultrafree Millex HV 0.45 μm tubes (Millipore) and then analyzed by steric exclusion chromatography on a Shodex Protein KW 803 column. The chromatographic system is a Kontron HPLC comprising a pump 422, an automatic injector 465 and a DAD (Diode Array Detector). The elution is carried out in 0.1 M phosphate buffer pH 6.8 + 0.5% SDS (m / m) with a flow of 0.5 ml / min. Detection is carried out by measuring the absorbance at 280 (at the concentration used, the polymer does not absorb).

The ratio of the air in the peak corresponding to the protein coupled to the polymer versus the sum of the two peaks corresponding to the coupled and uncoupled proteins (i.e. the total amount of proteins involved in the reaction) gives the value of coupling efficiency (Y).

(Area of protein / polymer conjugate peak) „ ₀ „ x 100

(Area of protein / polymer conjugate peak) _{280 nm} + (Area of free protein peak> _{280 nm}

The number of proteins per polymer chain is defined by the following relationship: N = n.Y / n 'or n and n' represent respectively the number of moles of protein and the number of polymer chains in the reaction medium.

The results in terms of protein coupling yield on the polymer are as follows:

100% for RH24K immobilized on the AMVE67 polymer which is not hydrolyzed and hydrolyzed, and

100 and 94% for RK24H immobilized on the AMVE67 polymer which is not hydrolyzed and hydrolyzed respectively.

Such coupling yields demonstrate that only a very small proportion of free proteins (uncoupled) remain, and that it is therefore possible to be free from any process of purification of the protein-polymer conjugate. EXAMPLE 3 Comparison of the Physico-Chemical Characteristics and of the Biological Reactivity of Protein-Polymer Conjugates Compared to the Same Uncoupled Proteins, as a Function of the Position of the Tag on the Protein and of the Reactivity of the Polymer , as described in Example 2, are analyzed.

The position of the tag in the protein and the reactivity of the polymer linked to the number of reactive groups which it has and therefore of its hydrolysis character or not are the main variables which can influence the reactivity of the conjugates.

We have shown that the recognition by homogeneous phase monoclonal antibodies of protein-polymer conjugates can be altered in two essentially configurations:

- when the tag is in a region too close to the active site (epitope), or when the polymer is too reactive (non-hydrolysis versus hydrolysis)

Two tests made it possible to select the conjugate for which (i) the protein is in a configuration as close as possible to the native protein, that is to say a configuration according to which the position of the tag is such that no alteration of recognition is not observed and (ii) the reactivity of the conjugate is maximum.

In order to objectify which conjugate has the closest physico-chemical characteristics in solution to the uncoupled protein counterpart, the rate of modification of the primary amines by fluorescamine was evaluated, according to the following protocol.

The rate of modification of the primary amines is evaluated by using fluorescamine (Arcos Ref. 1 9167-5000 - FW 278.26) as described previously (Ganachaud F et al., 1 995). A molar excess of fluorescamine is used relative to the amount of primary amines. At 90 μl of a protein solution at 0.34 g / l (i.e. 1 95 mmol / ml of primary amines represented by 10 internal p24 lysines and 6 tag lysines) in 50 mM phosphate buffer pH7.8, are added 30 μl of fluorescamine at 0.4 g / l in anhydrous DMSO (or in 90 μl of a protein solution at 0.095 g / l are added 30 μl of fluorescamine at 0.4 g / l in anhydrous DMSO). The reaction scheme between fluorescamine and a primary amine is illustrated below.

Fluorescent non-fluorescent fluorescent

The reaction takes place for 20 minutes in the dark and the fluorescence is measured on an LS 50 fluorimeter (Perkin Elmer). The fluorescence intensity was determined at an excitation wavelength of 416 nm and an emission wavelength of 477 nm.

As described above, fluorescamine reacts with primary amines leading to the formation of fluorescent compounds. Consequently, the more primary amines initially available on the protein, the greater the fluorescence signal.

This technique therefore makes it possible to compare the level of primary amines available on proteins before and after immobilization on polymers. By deduction, the percentage of primary amine groups of the protein immobilized on the polymer, having reacted, is determined relative to the same free protein. This percentage is called percentage modification, it is 0% for the free protein. This percentage change is given by the following formula: 100 - [fluorescence of the test protein x 100] reference fluorescence

In order to objectify which conjugate exhibits, after adsorption on a solid phase, the biological reactivity closest to the protein counterpart or to the RH24 reference system (Janvier et al., 1 993), we have performed an ELISA test in rabbit polyclonal antigen / antibody coating. The protocol was carried out as follows:

100 μl / well of p24 protein or protein-polymer conjugate diluted to 0.25 μg / ml in PBS buffer are immobilized at the bottom of a 96-well microplate (Nunc Immuno ™ Plate Maxisorp ™ surface) by overnight incubation at room temperature . The non-specific sites are then saturated for 2 hours at 37 ° C. with 200 μl / well of a PBS-1% Régilait ™ solution (w / v). The wells are then washed 3 times in 0.05% PBS-tween. The rabbit polyclonal antibody (bioMérieux lot 970304BLL01 at 8.93 g / l) diluted to the appropriate dilution in PBS-tween 0.05% -0.2% Regilait ™ buffer are then incubated for 1 hour at 37 ° C. After 3 washes in 0.05% PBS-tween, the peroxidase-labeled anti-rabbit conjugate (Jackson ImmunoResearch) diluted to 1/2000 in 0.05% PBS-Tween -1% Régilait ™ is incubated for 1 hour at 37 ° C. Three washes in 0.05% PBS-Tween are carried out before the revelation during which 100 μl of a solution containing a 30 mg OPD tablet diluted in 10 ml of 0.03% H ₂ O ₂ substrate buffer ( Sanofi) are incubated for 10 min in the dark at room temperature. The reaction is then blocked by adding 100 μl / well of H ₂ SO ₄ 1 N, then the absorbance values are read with a spectrophotometer at 492 nm.

The data in FIG. 2 illustrate the rate of modification of the primary amines by fluorescamine and the OD observed in ELISA, as follows:

(a) Lys6- (RH24) proteins and Lys -l- (RH24K and RK24H) proteins not coupled and coupled to the copolymer

AMVE67 non hydrolysed (non hyd.) And hydrolyzed 48 hours in DMSO 10% H2O (hyd.)

(b) Measurement of the presence of free amino groups by emission of fluorescence generated by the chemical reaction between fluorescamine and the primary amines

(c) The percentage modification of the coupled protein is calculated from the signal of the same uncoupled reference protein, using the following formula:

100 - [fluorescence of uncoupled protein x 1 00] fluorescence of coupled protein (a) The detection in ELISA was carried out using a polyclonal rabbit antibody

(b) Ratio determined from the OD of the conjugate tested (DOET) and the OD obtained with the RH24 protein conventionally used in immunoassays (DORH24) - NA means Not Applicable

Analysis of the measurement of the presence of free amino groups for the various protein-polymer conjugates shows that the RK24H immobilized on the hydrolysed AMVE67 polymer has the physicochemical characteristics closest to those of its uncoupled counterpart.

Likewise, the most important ELISA signal is that obtained with the conjugate in which the RK24H is immobilized on the hydrolysed polymer.

Example 4: Evaluation of a protein-polymer bioconjugate in the antibody capture phase with respect to human sera.

The conjugate evaluated is the one exhibiting the best performance, in the homogeneous phase on the one hand and in the capture phase in an ELISA test on the other hand, namely the hydrolyzed RK24H / AMVE67 conjugate. Its performance as an antibody capture phase for human sera was tested and compared to that of the reference protein RH24 not coupled to the polymer, according to the following protocol: 100 μl / well of p24 protein or of conjugate protein-polymers diluted to 1 μg / ml in PBS buffer are immobilized at the bottom of a 96-well microplate (Nunc Immuno ™ Plate Maxisorp ™ surface) by overnight incubation at room temperature. The non-specific sites are then saturated for 2 hours at 37 ° C. with 200 μl / well of a solution of PBS-10% goat serum (v / v) - 0.2% Régilait ™ (w / v) - 1 50 mM NaCI. The wells are then washed 3 times in 0.05% PBS-Tween. The sera (HIV positive or negative controls) are then diluted to the appropriate dilution in PBS buffer - 10% goat serum (v / v) - 0.2% Régilait ™ (w / v) - 0.1% Tween 20 - 300 mM NaCl and then 100 μl per well are incubated for one hour at 37 ° C. The plates are then washed 3 times in 0.05% PBS-Tween. 100 μl of anti-human goat conjugate (anti Fc) diluted in PBS-goat serum 10% - 0.2% Régilait ™ - 0.1% Tween - 1 50 mM NaCl at 1 / 10,000 ^èmβ are incubated for 1 hour at 37 ° C. Three washes in 0.05% PBS-tween are carried out before the revelation during which 100 μl of a solution containing a 30 mg OPD tablet diluted in 10 ml of 0.03% H2O2 sustrate buffer (Sanofi) are incubated 10 min in the dark at room temperature. The reaction is then blocked by adding 100 μl / well of 1 N H2SO4, then the absorbance values are read with a spectrophotometer at 492 nm.

The ELISA signals at 492 nm from 105 HIV positive sera and 104 HIV negative sera on a capture phase consisting of RH24 (reference system, gray bars) or RK24H-AMVE67 hydrolysis (test system, black bars ) are shown in Figure 3. A comparative analysis of the diagnostic value of the reference system and of the test was carried out according to the so-called "Receiver-Operating Characteristic" (ROC) methodology (Greiner M et al., 2000). According to the ROC protocol, each of the samples tested is represented by its absorbance value in ELISA for the reference and for the test. From this value, the numbers of true and false positive are deduced, allowing thereafter a calculation of sensitivity and specificity for each of these points.

The sensitivity of the two test formats was evaluated for specificity values between 99 and 100%. For the reference RH24, sensitivities of 84.8 and 68.6% are found, respectively associated with the specificities of 99 and 100%. For the RK24H-AMVE67 hydrolysis test, sensitivities of 86.7 and 81.9% are found, respectively associated with the specificities of 99 and 100%. The sensitivities observed for the test are therefore higher than those observed for the reference, with comparable specificity. It is observed that the interval situated between the limits 99 and 100% specificity contains 20 samples for the reference and only 7 for the test.

These results lead to a more detailed analysis of the distribution of the signals obtained for each of the 2 systems. A box plot analysis was performed and the graphs obtained are represented in Figure 4, as follows:

Distribution of optical density signals obtained by ELISA as a function of the nature of the protein immobilized on the solid phase (RH24 alone denoted "24" or RK24H coupled with the AMVE67 copolymer hydrolysis 48 hours in DMSO 10% H2O noted "24Po"), and depending on clinical status (negative HIV noted "N" or positive HIV noted "P").

In Figure 4A, the box plots determined using StatView ™ II software indicate, for each group, the distribution and the median signal. The five horizontal lines in the boxes are expressed in percentiles expressing the 10 ^th , 25 ^th , 50 ^th , 75 ^th and 90 ^th percentiles. The values above and below the I 0 ^th and 90 ^th percentiles are represented in the form of points (empty circles). 104 HIV negative sera and 105 HIV positive sera were tested for this study. In FIG. 4B, the low OD values (between 0 and 0.5) have been amplified in order to better visualize the distribution of the negative samples as well as the sera of positive patients with low reactivity.

We see on these graphs a displacement of the signals towards the saturated values when the capture phase is a protein tagged with 6 lysines in N-terminal position RK24H immobilized on the hydrolysed polymer AMVE67. Indeed, with the reference system, the median (OD value for which 50% of the signals are above and 50% are below) is close to 1 with the reference system while it is saturated (beyond 4) with the test. Thus, the protein-polymer conjugate tested makes it possible to detect lower concentrations of antibodies in the sera than the reference system.

Example 5 Evaluation of a Protein-Polymer Bioconjugate in the Antibody Capture Phase Against Human Serums Containing Very Low Levels of Antibodies

The results described in Example 4 led the authors to study the two capture systems on sera having variable antibody titers (high or low), using either diluted sera or sera from patients in phase seroconversion. The results are shown in Figure 5 as follows:

Optical densities determined by ELISA as a function of the nature of the detection phase and of the concentration of anti-p24 antibody in the sera. In FIG. 5A, the ELISA detection was carried out on sera from 7 HIV-positive HIV patients (s58 to slV), using a high serological titer (dilution to ^1/500 ^{è β} striped bars) or low titer (dilutions from ^{1/1000 èmβ} to 1 / 200,000 ^th , solid bars). The capture phases are RH24 used as reference (striped and solid gray bars) and RK24H immobilized on IΑMVE67 hydrolyzes 48 hours in DMSO 10% H2O (striped and solid black bars). The black and gray horizontal lines represent an eut off set at "mean plus three standard deviations" and determined from the high titer conditions obtained with the 104 negative controls in the panel of FIG. 3 for respectively, the RH24 and the coupled RK24H to the hydrolyzed polymer. In FIG. 5B, the ELISA detection was carried out with sera diluted 1/20 from HIV-positive HIV patients, collected sequentially during the seroconversion period (panel No. 1, days 1 to 28 after the ^1st sample and panel N ° 2, days 32 to 1 45 after the 1 ^st sample). The capture phases are RH24 used as reference (gray bars) and RK24H immobilized on IΑMVE67 hydrolyzes 48 hours in DMSO 10% H2O (black bars). The black and gray horizontal lines represent the eut off determined from 7 sera of negative HIV controls diluted to 1/20, for RH24 and R 24H coupled to the hydrolysed polymer. The results of FIG. 5A show us that at low dilutions ( ^{1/500 èmβ} ), whatever the capture system, the signals obtained in ELISA are saturating, except for the sample s58 for which a weak signal is obtained when the capture phase is a RH24 protein alone. On the contrary, at strong (1/1000 ^th ) or even very strong

(1 / 200,000 ^em ) dilutions, that is to say when the antibody levels are low, the signal obtained with the reference system is weak or zero, while it remains very high or saturated with the protein-polymer test. The eut off calculated for the 104 negative HIV sera diluted to ^{1/500 èmβ} previously tested, can be applied to these more highly diluted samples. For the reference RH24, with an eut off set at 0.2387, one serum is positive (s7, with a signal to cut-off ratio of 4.53), 3 sera are slightly or very slightly higher than the eut off (s58, s27 and s28, with signal to cut-off ratios of 1.51, 1.05 and 1.14, respectively) and 3 sera are negative (sll, slll and slV). For the RK24H-AMVE67 hydrolysis trial, for an eut off set at 0.381 8, the 7 HIV positive sera tested are very much above this threshold, with signal to cut-off ratios varying from 4.98 (sll) to 10.32 (s27 and s28).

This ability of the protein-polymer system to detect very small quantities of antibodies in sera has led the authors to experiment on seroconversion panels. The results presented in the graph in FIG. 5B are those obtained for 2 seroconversion panels whose sera have been diluted to ^{1/20 èmβ} . Meanwhile, 7 negative HIV sera diluted also 1 / ^20th were tested on two systems to determine the cut-off corresponding to the mean of the negative controls 3 standard deviation. They are 0.6 for the RH24 reference and 0.69 for the RK24H-AMVE67 hydrolysis test. The seroconversion phase, determined using second generation commercial tests, is located between samples J3 and J 1 7 for panel 1 and J47 and J84 for panel 2. With regard to panel N ° 1, only the protein-polymer conjugate system is capable of detecting the first positive sample at D 17, with a very strong signal close to saturation, and therefore very above the cut-off value. On the contrary, panel N ° 2 does not show significant differences between the two test formats. This is probably due to the time difference between the 2 samples around seroconversion, close to 40 days (whereas this same interval is 14 days in panel 1), the sera then having concentrations of strong antibodies easily detectable by both systems. The protein-polymer conjugate therefore makes it possible, unlike the reference protein, to detect very low levels of antibodies in the sera of patients and therefore to confirm seropositivity earlier.

EXAMPLE 6 Evaluation of a Recombinant Protein-Biotin Bioconjugate in the Antibody Detection Phase in an Antigen Sandwich ELISA Test

The immobilization of biotin on the proteins was carried out according to the protocol described below: the p24 proteins (RH24, RH24K and RK24H) were previously dialyzed against a 100 mM carbonate buffer pH8.3. Five moles of biotin (long chain biotin NHS, Roche Ref 1008-960,

10 mg / ml in DMSO) were incubated with 1 mole of p24 protein, 1 hour with stirring at 18-25 ° C. The reaction was blocked with 5 moles of a 10 mM lysine solution. The reaction medium was then dialyzed against a phosphate buffered saline (PBS) containing NaN3. The conjugates were then quantified by the BCA technique (PIERCE). Finally, the number of biotins per p24 molecule was evaluated by MALDI TOF mass spectrometry.

The use of these conjugates in the antibody detection phase was carried out in an antigen sandwich test according to the following protocol: 100 μl / well of the RH24 protein diluted in PBS to 0.25 μg / ml were deposited at the bottom of 96-well microtiter plate (Nunc Immuno ™ Plate Maxisorp ™ surface) by overnight incubation at room temperature. The plate is then washed 3 times in 0.05% PBS-Tween, then passivated for 1 hour at 37 ° C. with 200 μl / well in passivation buffer (Tris 200 mM - NaCl 1 50 mM - Maleic acid 200 mM - NaOH 1 50 mM - Tween 20 0.05% - pH 6, 1). 3 washes with 0.05% PBS-Tween are carried out before incubation with rabbit polyclonal antibodies at the dilution chosen in Ac incubation buffer (100 mM Tris - 300 mM NaCl - 5% Tween - Regulated 0.2 % - BSA 2% - Adjust pH 7.0 with HCI) - 100 μl / well for 2 hours at 37 ° C. 3 washes with 0.05% PBS-T make it possible to remove the unreacted antibodies, then 100 μl / well of p24-biotinylated protein diluted to 1 μg / ml in PBS-Milk buffer 2.5 g / l Tween 0.05% (RH24-biotin, RH24K-biotin or RK24H-biotin) are incubated for 1 hour at 37 ° C. Three new washes with PBS-T 0.05% are carried out before addition of streptavidin-peroxidase (Jackson Immunoresearch) diluted to 1/5000 ^th in PBS- Milk 2.5 g / l Tween 0.05%, 100 μl / well for 1 hour at 37 ° C. After 3 last washes with 0.05% PBS-Tween, 100 μl / well of the peroxidase OPD substrate (1 30 mg tablet diluted in 10 ml 0.03% H2O2 substrate buffer (Sanofi)) are incubated for 10 minutes in the dark. The colored reaction is neutralized by addition of 1 N H2SO4 after 10 minutes - 100 μl / well and the OD values are read with a spectrophotometer at 492 nm.

The characteristics of the protein-biotin conjugates and their reactivity in ELISA are illustrated in Figure 6 as follows:

(a) Biotinylated Lys6 - (RH24) and Lys6 + (RH24K and RK24H) proteins (b) Determination of the number of biotins per protein by analysis by mass spectrometry (MALDI TOF)

(c) Detection by ELISA was carried out using a dilution range of polyclonal antibodies. Two extreme concentration points have been selected 1 and 0.125 μg / ml

(d) Ratio determined from the OD of the conjugate tested (DOET) and the OD obtained with the biotinylated reference protein RH24 (DθRH24-biot> - The presence of a 6 lysine tag makes it possible to immobilize a greater amount of biotin on proteins. In fact, on average, 4 biotins are coupled on an RH24, 7 on an RH24K and 5 on an RK24H. The evaluation of these 3 p24-biotin conjugates in the detection phase shows that the signals obtained with the biotinylated tagged proteins are superior to those of the untagged RH24 biotinylated protein, the most effective in detection phase being biotinylated RH24K. This allows, at low polyclonal antibody concentration, to improve the signal by 66% by compared to the biotinylated reference protein RH24 The biotinylated protein RK24H makes it possible to improve the signal by 22% for the same dilution of the monoclonal antibody and compared to the reference protein.

BIBLIOGRAPHY

Ladavière C, T. Delair, A. Domard, A. Novelli-Rousseau, B. Mandrand and F. Mallet. 1 998, Covalent immobilization of proteins onto (maleic anhydride-alt-methyl vinyl ether) copolymers: enhanced immobilization of recombinant proteins. Bioconjug Chem 9 (6): 655-661.

Cheynet, V., B. Verrier, and F. Mallet. 1 993. Overexpression of HIV-1 proteins in Escherichia coli by a modified expression vector and their one-step purification. Prot Express Purif 4: 367-372. Berthet-Colominas C, S. Monaco, A.Novelli, G. Siba ", F. Mallet and S. Cusack. 1,999. Head-to-tail dimers and interdomain flexibility revealed by the crystal structure of HIV-1 capsid protein (p24) complexed with a monoclonal antibody Fab. EMBO 1 8 (5): 1 1 24-1 1 36.

Arnaud N., V. Cheynet, G. Oriol, B. Mandrand and F. Mallet. 1 997. Construction and expression of a modular gene encoding bacteriophage T7 RNA polymerase. Gene 1 99 (1 -2): 149-1 56.

Ganachaud F., Mouterde G, Delair T, Elaïssari A. and Pichot C. 1 995 Preparation and characterization of cationic polystyrene latex particles of different aminated surface charges. Polymers for Advanced Technologies 6: 480-488.

Janvier, B., F. Mallet, V. Cheynet, P. Dalbon, G. Vernet, J. M.

Besnier, P. Choutet, A. Goudeau, B. Mandrand, and F. Barin. 1,993.

Prevalence and persistence of antibody titers to recombinant HIV-1 core and matrix proteins in HIV-1 infection. J. Acquir. Immune Defic. Syndr. 6 (8): 898-903.

Greiner M, Pfeiffer D, Smith RD. 2000. Principles and practical application of the receiver-operating characteristic analysis for diagnostic tests. Prev Vet Med. 45 (1 -2): 23-41. Review.

Claims

1. Method for obtaining a phase for capturing a target biological material, comprising a modified protein of interest, capable of specifically, directly or indirectly binding to said target biological material and immobilized on an immobilization phase comprising groups reagents, characterized in that it comprises the following stages: at least two different peptide sequences are available, comprising the peptide sequence of the protein of interest, and one comprising a succession of at least six lysine residues to its N-terminal end and a succession of at least six histidine residues at its C-terminal end, the other comprising a succession of at least six histidine residues at its N-terminal end and a succession of at least six residues lysine at its C-terminal end, each of the two peptide sequences obtained is immobilized on the immobilization phase, by covalent reaction between the am groups primary sequence of the peptide sequences and the reactive groups of the support, the efficiency of the coupling between each of the two sequences and the immobilization phase is determined, by quantification of the free primary amino groups of the immobilized peptide sequence and of the primary amino groups free of the same non-immobilized peptide sequence, and deduction of the amino groups having interacted with the immobilization phase, the peptide sequence most effectively coupled to the immobilization phase is chosen as the capture phase.

2. Method according to claim 1, characterized in that the free primary amine groups are quantified by reaction of said groups with fluorescamine.

3. Method according to claim 1 or 2, characterized in that the immobilization phase is a maleic anhydride copolymer chosen from poly (methylvinyl ether-maleic anhydride), poly (ethylene-maleic anhydride), poly (styrene - maleic anhydride) and poly (N-vinylpyrrolidone- maleic anhydride).

4. Method according to claim 3, characterized in that the copolymer is poly (methylvinylether-maleic anhydride).

5. Method according to any one of claims 1 to 4, characterized in that the immobilization of the two peptide sequences is carried out in a reaction medium inactivating at least part, but not all, of said reactive groups of the support.

6. Method according to claim 5, characterized in that the immobilization is carried out in a hydrolyzing medium at least part, but not all, of said reactive groups of the support.

7. Method according to any one of claims 1 to 6, characterized in that, before immobilization of the peptide sequences, the support is treated to inactivate at least part, but not all, of said reactive groups of the support.

8. Method according to claim 1, characterized in that the at least two peptide sequences comprise a succession of six lysine residues and a succession of at least six histidine residues, a succession of at least six lysine residues and a succession of six histidine residues or a succession of six lysine residues and a succession of six histidine residues.

9. Method according to claim 8, characterized in that the two peptide sequences at least comprise a succession of six lysine residues and a succession of six histidine residues.

10. Method according to claims 1 and 4, characterized in that the protein of interest is the p24 protein of the capsid of HIV-1, and in that the peptide sequence of the modified protein of interest comprises the sequence SEQ ID NO: 2, a succession of 6 lysine residues at its N-terminal end and a succession of 6 histidine residues at its C-terminal end.

1 1. Method for obtaining a phase for detecting a target biological material, comprising a modified protein of interest, capable of specifically, directly or indirectly binding to said target biological material and coupled to a hapten, characterized in that it comprises the following stages: at least two different peptide sequences are available, comprising the peptide sequence of the protein of interest, one comprising a succession of at least six lysine residues at its end N-terminal and a succession of at least six histidine residues at its C-terminal end, the other comprising a succession of at least six histidine residues at its N-terminal end and a succession of at least six lysine residues at its C-terminal end, each of the two peptide sequences obtained with hapten is coupled, by covalent reaction between the primary amine groups of the peptide sequences and the reactive groups of biotin, the coupling efficiency of each of the two sequences is determined with hapten, by quantification of the free primary amine groups of the coupled peptide sequence and of the free primary amine groups of the same uncoupled peptide sequence, and deduction of the amine groups having interacted with the hapten, the detection phase is chosen, the peptide sequence most efficiently coupled to the hapten.

1 2. Process according to claim 1 1, characterized in that the efficiency of the coupling between the peptide sequences and the hapten is determined by mass spectrometry.

1 3. Method according to claim 1 1 or 1 2, characterized in that the hapten is biotin.

14. Method according to claim 1 1, characterized in that the two peptide sequences at least comprise a succession of six lysine residues and a succession of at least six histidine residues, a succession of at least six lysine residues and a succession of six histidine residues, or a succession of six lysine residues and a succession of six histidine residues.

1 5. Method according to claim 14, characterized in that the two peptide sequences at least comprise a succession of six lysine residues and a succession of six histidine residues.

16. Method according to claims 1 1 and 1 3, characterized in that the protein of interest is the p24 protein of the capsid of HIV-1, and in that the peptide sequence of the modified protein of interest comprises the sequence SEQ ID NO: 2, a succession of 6 histidiine residues at its N-terminal end and a succession of 6 lysine residues at its C-terminal end.

1 7. Kit for the detection by ELISA of a target biological material, comprising a capture phase obtained according to any one of claims 1 to 10, and a detection phase obtained according to any one of claims 1 1 to 1 6.

1 8. Method for detecting, and possibly quantifying, a target biological material, in a sample of biological liquid, in ELISA, characterized in that it comprises the following steps: there is a capture phase obtained according to l 'any one of claims 1 to 10, and a detection phase obtained according to any one of claims 1 1 to 16, the sample is brought into contact with the capture phase and then the detection phase, the complex capture phase - target biological material - detection phase.

1 9. Method according to claim 1 8, characterized in the capture phase is obtained by the method according to claim 10, the detection phase is obtained by the method according to claim 16, and the complex capture phase - material is detected biological target - detection phase by addition of streptavidin - peroxidase then orthophenylene diamine.