EP2038296A2 - Method for the extraction of one or several proteins present in milk - Google Patents

Abstract

This invention concerns a method for extracting at least one protein present in milk, the said protein showing an affinity for calcium ions in complexes or free, in the said milk. It comprises the following steps: a) freeing the protein by precipitating the calcium compounds obtained by contact of the milk with a soluble salt, whose anion is chosen for its capacity to form the said insoluble calcium compounds in such a medium, in order to thus obtain a liquid phases that is enriched with the protein, b) separation of the enriched liquid phase into the protein precipitate with the calcium compound, the said liquid phase being moreover separated into a lipid phase and a non-lipid aqueous phase comprising the protein and c) collection of the aqueous non-lipid phase comprising the protein.

Description

Process for extracting one or more proteins present in milk

The present invention relates to a method for extracting one or more proteins present in milk, said proteins having an affinity for calcium ions complexed or not with said milk.

In the context of the invention, the term complexed or non-complexed calcium ions is the phosphocalcic salts bound to caseins to form a colloidal micellar structure of caseins, or such salts not related to caseins and mistletoe are therefore free. Such ions are also the various salts and / or organic and / or inorganic calcium complexes other than those mentioned above, which are soluble in milk. The proteins with an affinity for calcium ions in milk represent those naturally present therein such as lactalbumin, lactoglobulin and immunoglobulin. These proteins may also represent recombinant proteins presented in the milk of transgenic animals, for example blood coagulation factors, in particular factor VII, factor VIII and factor IX.

Most of the drugs available in

¹ trade is chemical substances obtained by synthesis. Bn • ^• effect, until recently, the

Modern medicine has relied heavily on drugs produced by chemical synthesis for the treatment or diagnosis of diseases.

However, proteins are an essential part of molecules carrying biological information. This is particularly the case of a large number of hormones, growth factors, blood coagulation factors or antibodies.

In general, proteins are amino acid-based polymers most often of high molecular weight can not be obtained at reasonable costs by chemical synthesis. Such therapeutically useful proteins are usually isolated and purified from, for example, living organisms, tissues or human or human blood.

-animal. This is the case of insulin extracted from pig pancreas, the factors ^"of coagulation, such as factor VIII or factor IX, blood plasma extracts, or immunoglobulins.

Although the methods of making the above proteins are widely used today, however, they have disadvantages. The low level of certain proteins, such as erythropoietin, extracted from blood platelets, does not allow them to be isolated in sufficient quantities to meet the ever increasing therapeutic needs. In addition, the presence of viruses, prions or other pathogens in human plasma necessitates the inclusion of additional viral inactivation and / or viral elimination steps in plasma protein production processes in order to obtain such products that can be used for therapeutic purposes. To overcome these drawbacks, it has recourse to genetic engineering, also widely used technique for the synthesis of proteins from a single gene, transferred to ^"a cell, which then supports the secretion of the protein. This protein , obtained out of its original cellular system, is called "recombinant".

According to this technique, different cellular systems can be used.

Bacterial systems, for example E. CoIi, are widely used and effective. They allow the production of recombinant proteins at low cost. However, such systems are limited to preparation of simple, non-glycosylated proteins that do not require an elaborate folding process.

Fungal systems are also used for the production of secreted proteins. The disadvantage of these fungal systems lies in the fact that they are at the source of post-translational modifications, consisting, for example, in a grafting of glycan units and sulphate groups, which strongly affect the pharmacokinetic properties of the proteins produced, in particular by the addition of various groups of mannose derivatives.

Systems using baculoviruses can produce a variety of proteins, such as vaccine proteins or growth hormone, but their application on an industrial scale is not optimized.

Mammalian cell culture is also used for the preparation of complex recombinant proteins, such as monoclonal antibodies. Cell expression systems lead to correctly folded and modified recombinant proteins. The ^weak performance against the production cost is a major drawback.

An alternative to such cell systems is to use transgenic plants to obtain proteins in large amounts. These systems, however, generate post-translational modifications specific to plants, in particular by adding to the proteins produced highly immunogenic xylose residues, thus limiting their use for therapeutic purposes.

An alternative to the cellular systems mentioned above is to use transgenic animals for the production of recombinant vaccines or complex therapeutic proteins. The proteins thus obtained have a glycosylation .. close to that of the human being and are correctly folded. These protein complexes are not constituted as a single polypeptide chain such as the growth hormone, but are modified in various ways after the assembly of amino acids, including specific cleavages, glycosylation and ^'of carboxyméthylations . In the vast majority of cases, such modifications can not be made by bacterial or yeast cells. In contrast, transgenic animals can combine both the levels of expression found in bacterial cell systems and the post-translational modifications achieved through cell cultures, while generating lower production costs than by the implementation of cellular expression systems.

Among ^'biological material from transgenic animals, milk was the subject of work leading to regard as _•. a source of very satisfactory secretion of recombinant proteins.

The recombinant proteins, produced from milk of transgenic animals, can be easily obtained by grafting the gene coding for the protein of interest on the regulatory region of one of the milk protein synthesis genes that will direct it. specifically in the mammary gland, then its secretion into the milk.

By way of example, mention may be made of patent application EP 0 527 063, which describes the production of a protein of interest in the milk of a transgenic mammal, the expression of the gene coding for the protein of interest. being controlled by a promoter of a whey protein. Other patent applications or patents describe the preparation of antibodies (EP 0 741 515), collagen (WO 96/03051), human factor IX (US 6,046,380) and VlII factor / von Willebrand factor complexes (EP 0 807 170) in the milk of transgenic mammals.

Despite the satisfactory results of these methods in terms of protein expression, the use of milk as a source of recombinant proteins has disadvantages. The major disadvantage lies in the difficulties, on the one hand, to extract them from the milk with a satisfactory yield and, on the other hand, to purify them later. Indeed, milk is a mixture of 90% water comprising various constituents that can be grouped into three categories. The first category, called whey (or whey), consists of carbohydrates, soluble proteins, minerals and water-soluble vitamins. The second category, called lipid phase (or cream), contains fat in the form of emulsion. The third category, called the protein phase, consists of approximately 80% of caseins, which form a set of precipitable proteins at a pH of 4.6 or under the action of rennet, enzymatic coagulant, in the presence of calcium. The different caseins form a colloidal micellar complex, which can reach diameters

about 0.5 μm, with phosphocalcic salts, for example in the form of tricalcium phosphate aggregates ("clusters"), or Cag (P04). Such micelles are formed from subunits of caseins consisting of a hydrophilic layer rich in casein-K surrounding a hydrophobic core, the phosphocalcic salts being linked by electrostatic interaction on the hydrophilic layer. These phosphocalcic salts can also be present in the internal volume of the micelle without being bound to the casein. This protein phase also contains soluble proteins, such as lactalbumin and lactoglobulins, as well as albumins and immunoglobulins from the blood. Depending on the nature of the recombinant protein secreted in the milk of transgenic animals, it may be present in the whey or in the protein phase, or both. The richness and complexity of each category of milk constituents make it all the more difficult to carry out an extraction of this protein, in particular that trapped in the casein micelles. Another difficulty lies in the fact that the majority presence of this protein in one of the two phases is not predictable with certainty.

A recombinant protein may also have affinities for milk calcium ions that are present as either salts and / or various soluble complexes or phosphocalcic salts of casein micelles. These affinities translate into electrostatic bonds between the protein and divalent calcium cations. The protein / calcium ion affinities make it possible to define the affinity constants which, depending on their value, determine the binding force. In general, most of the proteins having an affinity for calcium ions are related to phosphocalcic salts of micelles. Its extraction requires the implementation of complex steps, which poses problems of implementation and performance.

The conventional solution used in the dairy industry to isolate PtXMM ^ Φ ^ ¹ "with pasteurization followed by enzymatic coagulation or acid precipitation (pH 4.6) can not be applied in this case because the recombinant proteins are often denatured by the combined effect of temperature and pH.In addition, protein trapping in casein micelles leads to low extraction yields.Other solutions consist of implementing physical methods of fractionation milk by filtration techniques, centrifugation and / or sedimentation or precipitation also lead to unacceptable extraction yields and recombinant proteins extracted of low purity. EP 0 264 166 describes the secretion of a desired protein in milk of genetically transformed animals. This document does not mention steps of purification of this protein from milk.

US Patent 4,519,945 describes a method of extracting a recombinant protein by preparing a precipitate of caseins and whey from milk, implementing acidification and heating steps, as mentioned above. This process generates a significant loss of the activity of the protein in question and a low extraction yield.

US Patent 6,984,772 discloses a method of purifying recombinant fibrinogen from milk of a transgenic mammal. This process comprises a step of separating the whey from the casein pellet and the protein phase by successive centrifugations. Whey is isolated

^• then stored for the rest of the process leading to a purified fibrinogen solution. However, this method can not be applied to the production, at satisfactory yield, of recombinant proteins entrapped in and / or on casein micelles, such as plasma coagulation factors, for example factor VII, factor VIII and factor IX.

Patent application WO 2004/076695 describes a method for the filtration of recombinant proteins from milk of transgenic animals. This method comprises a first step of clarifying the milk, that is to say a step of removing the milk components so as to obtain a solution that can be filtered through a membrane of filter whose pores have a diameter of 0.2 μm. Such a step results in the elimination of casein micelles. Therefore, the implementation of this step can be prohibitive, in terms _. yield, if the casein micelles are likely to contain a protein of interest trapped within their structure.

US Pat. No. 6,183,803 describes a process for isolating proteins naturally present in milk, such as lactalbumin, and recombinant proteins, for example human albumin or α1-antitrypsin, from milk. This method comprises an initial step of contacting the milk comprising a protein of interest with a chelating agent. This results in the destructuring of casein micelles, which leads to a clarified milk serum comprising caseins, whey proteins and the protein of interest. The method then comprises a step of restructuring the casein micelles by adding to the liquid medium (clarified milk serum) insoluble divalent cation salts. These micelles precipitate, which ^'leads to a liquid phase containing the protein of interest that is not trapped by the micelles, since the electrostatic salts saturate the binding sites of the caseins. According to this method, the separation of the protein of interest is therefore ultimately carried out by restructuring the micelles and their precipitation.

This process is complex and can not be applied to proteins with relatively high affinity for calcium ions. The coagulation proteins, and especially those known to be synthesized under the influence of vitamin K, are in this category. Starting from a double observation that the separation and purification processes of certain categories of recombinant proteins secreted in milk of transgenic animals present in whey lead to very low yields, and those of other categories of proteins which are trapped in casein micelles, are complex implementation, the Applicant has set a goal to put a method for extracting, from milk, milk proteins, whether natural or not, such as recombinant factor VII, factor VIII and factor IX, having an affinity for the ionic forms of calcium in milk, simplified implementation, further leading to a satisfactory production yield, while maintaining the biological activity of the protein.

The invention thus relates to a process for extracting at least one protein present in milk, said protein exhibiting an affinity for the complexed or non-complexed calcium ions of said milk, comprising the following steps: a) releasing the protein by the precipitation of calcium compounds obtained by contacting the milk with a soluble salt, whose anion is chosen for its ability to form in such a medium said insoluble calcium compounds, thereby obtaining a liquid phase enriched in the protein, b ) separating the liquid phase enriched in the protein from the precipitate of calcium compounds, said liquid phase being further separated into a lipid phase and a non-lipidic aqueous phase comprising the protein, and c) recovering the non-lipidic aqueous phase comprising the protein .

The Applicant has surprisingly found that adding a soluble salt, whose anion is chosen for its ability to form precipitates of calcium compounds in milk, containing a protein, especially recombinant, having an affinity for complexed or non-complexed calcium ions, that is to say having sites for fixing to calcium ions, allows the precipitation of calcium compounds, whereas the protein of interest is released from these complexed ions or not and is found in solution in the liquid phase.

The complexed or non-complexed calcium ions, as indicated above, represent the different salts and / or organic and / or inorganic complexes of calcium soluble in milk. These salts or complexes may be present in the internal volume of the casein micelle (see further in Figure 1).

These calcium ions also represent the phosphocalcic salts in interaction with the casein micelles, in particular in the form of aggregates ("clusters"). These salts are also present in the milk in the form of monocalcium phosphate and / or dicalcium phosphate, which are in equilibrium with the other ionic forms of calcium as a function of the chemical and biochemical reactions used.

Finally, these calcium ions represent calcium / casein complexes, that is to say representing casein subunits which are associated, by electrostatic interaction, phosphocalcic salts. These calcium / casein complexes also refer to casein micelles associated with phosphocalcic salts and with salts. and / or soluble organic and / or inorganic calcium complexes.

The term "insoluble calcium compounds" means calcium salts or complexes whose solubility in milk is less than 0.5%.

In most cases, the proteins of interest will be mainly associated with phosphocalcic salts of casein micelles. The term "protein having affinity for complexed or non-complexed calcium ions" means any protein having a sufficient number of binding sites. calcium ions to be associated, totally or partially, or to be associated, totally or partially, with the phophocalcic salts of casein micelles. By way of example, in the case of proteins of interest having numerous sites for fixing to calcium ions, for example 8 to 10 GLA domains, which are domains rich in γ-carboxyglutamic acids making it possible to fix the calcium ions, at less than 70% up to 90% of the proteins of interest are trapped in and / or on casein micelles. For other proteins having lower binding sites to calcium ions, for example 2 to 8 GLA domains, at least 30% to 60% of these are trapped in and / or on casein micelles. Finally, even proteins with very few calcium ion binding sites, for example 0 to 2 GLA domains, are susceptible to being trapped in and / or on casein micelles, for example at least 5%. up to 20%. Such quantities of trapped proteins are not negligible for the implementation of a process on an industrial scale, which involves achieving the highest possible yield. The rest of the proteins of interest, not entrapped in and / on the micelles, have an affinity for the other forms of milk calcium ions mentioned above.

Therefore, the process of the invention can be applied to protein extraction of which at least 2% up to 10%, or at least 40% up to. 60% or, in particular, at least 90% are associated with these calcium ions.

Such affinity of the protein for calcium ions may result from interactions of unmodified or modified protein in vivo or in vitro, for example by post-translational modifications.

Thus, proteins having numerous calcium binding sites complexed or not can find themselves associated with different forms of calcium found in milk.

Without being bound by any interpretation of the mechanisms observed, the Applicant assumes that the addition of the soluble salt displaces the equilibrium of the phosphocalcic salts of the micelles, in particular the calcium / phosphate ratio, thus causing their destructuration and the precipitation of sub-aggregates. - casein units. The proteins of interest associated with the phosphocalcium salts trapped in and / or on the micelles are released into the medium during this destructuration. In addition, the proteins of interest are then also released or dissociated from the phosphocalcic salts, because they precipitate in the form of insoluble calcium compounds under the effect of the soluble salt used in the process of the invention. Similarly, the proteins of interest which can also be associated with soluble organic and / or inorganic salts or complexes of calcium would also be dissociated by the same type of reaction.

An example of such a mechanism is shown in Figure 1.

In the context of the invention, the soluble salt represents any salt that makes it possible to obtain the desired effect. The soluble salt used in the process of the invention may be added to the milk at a concentration chosen by those skilled in the art to achieve the release of the protein from these interactions with calcium ions. As such, it is a concentration sufficient to allow the release of at least 20%, or preferably at least 30% up to 50% of the proteins of interest. Particularly advantageously, it is a concentration sufficient to allow the separation of at least 60% to 80%, or at least 90% of the proteins of interest. In addition, the process of the invention can also be applied to proteins only a part of which has calcium ion binding sites. For example, the process of the invention can be applied to the extraction of proteins present in milk of which 1% of the total is associated with calcium ions. The method can also be applied to proteins of which at least 2% up to 10%, or at least 40% up to 60% or, in particular, at least 90% are associated with these calcium ions.

The method of the invention allows the precipitation in particular aggregates of casein subunits. This precipitation is due to the destructuring of the casein micelles, as indicated above. The implementation of the process of the invention destabilizes, by precipitation, the colloidal state in which the milk is.

The method of the invention is therefore a method for the passage of milk from a colloidal state to a liquid state, which corresponds to a direct colloid / liquid extraction. ^'

The process of the invention also makes it possible to obtain the whey and the lipid phase whose coloring is lighter than that of the starting milk. Indeed, it is the caseins related to calcium ions that give their white color to milk. Once precipitated, they can no longer give this color to milk.

The method of the invention thus has several advantages: it is first of a very easy implementation, since it allows the separation of the proteins of interest by simplified implementation steps. In addition, it allows recovery of the proteins of interest in the non-lipidic aqueous phase with a very good yield. Advantageously, the extraction process of the invention has a yield of at least 50%, or at least 60%, or at least 80%. In a particularly advantageous manner, the yield is at least 90%.

This method will also make it possible to obtain the non-lipidic aqueous phase comprising the protein of interest in a form compatible with the implementation of subsequent steps of purification thereof, in particular chromatography steps.

Finally, the proteins of interest are still biologically active, since the steps of the process of the invention are carried out at a pH that does not alter their biological activity. The pH is advantageously basic, for example close to 8.

Soluble salt according to the invention means a salt whose solubility in milk is at least 0.5 part of salt per part of milk (w / w).

Advantageously, the soluble salt used in the process is a phosphate salt. The salt can be in an aqueous solution that is added to the milk, or it can be added directly to the milk as a powder.

Preferably, the phosphate salt is selected from the group consisting of sodium phosphate, lithium phosphate, potassium phosphate, rubidium phosphate and cesium phosphate, and is, in particular, sodium phosphate.

Alternatively, the soluble salt used for carrying out the process of the invention may be an oxalate of an alkali metal, especially 1 sodium or potassium oxalate, or an alkali metal carbonate, particularly the sodium or potassium carbonate, or their mixture.

Advantageously, the concentration of the soluble salt in aqueous solution, which is thus prepared for carrying out the process, is between 100 mM and 3 M, more preferably between 200 mM and 500 mM and, in particular, between 200 mM and 500 mM. mM and 300 mM. Thus, according to a preferred embodiment of the invention, the soluble salt of the invention is sodium phosphate, the concentration of which in aqueous solution is between 100 mM and 3 M, more preferably between 200 mM and 500 mM and in particular between 200 mM and 300 mM.

The milk in which the protein of interest to be extracted may be unsprouted raw milk or skimmed milk. The advantage of applying the method of the invention to skim milk is that it contains a lower amount of lipids. The process can also be applied to fresh or frozen milk.

Step b) enables the separation of the liquid phase in a lipid phase and a non-lipidic ^water phase comprising the protein is preferably carried out by centrifugation. The non-lipidic aqueous phase is assimilated to whey. This separation step also makes it possible to isolate the clusters of micellar subunits of caseins and the precipitate of calcium compounds.

The non-lipidic aqueous phase comprising the protein is separated from the lipid phase.

This step advantageously makes it possible to obtain a clear aqueous nonlipidic phase. .

The method may further comprise, after step c), a filtration step of the non-lipidic aqueous phase carried out successively on decreasing porosity filters, preferably 1 μm and then 0.45 μm. The use of these filters, such as those based on glass fibers, makes it possible to reduce the content of lipids that may still be present, fat globules and phospholipids naturally present in the milk. A porosity lower than 0.5 microns makes it possible to maintain the bacteriological quality of the non-lipidic aqueous phase, as well as purification supports subsequently used. (ultrafilters, chromatography column, etc.) (see below). The lipid phase is preferably filtered through these filters which thus completely retain the lipid globules of the milk, and the filtrate is clear.

This step may be followed by a concentration / dialysis step by ultrafiltration.

The concentration makes it possible to reduce the volume of the non-lipidic aqueous phase with a view to its preservation. The ultrafiltration membrane is chosen by those skilled in the art according to the characteristics of the protein of interest. In general, a cutoff threshold whose pore size is less than or equal to the molecular weight of the protein of interest makes it possible to concentrate the product without noticeable loss. For example, a pore size membrane at 50 kDa makes it possible to concentrate lossless FVII with a molecular weight of 50 kDa.

The dialysis is intended to condition the aqueous protein phase for subsequent purification steps, in particular by chromatography. It also makes it possible to eliminate low molecular size components, such as lactoses, salts, peptides, peptone proteoses and any agent that may be detrimental to the preservation of the product.

Preferably, the dialysis buffer is a solution of 0.025M0, 050M sodium phosphate, pH 7.5-8.5. The non-lipidic aqueous phase obtained after step c), or, where appropriate, obtained after the filtration and / or concentration / dialysis steps, may be frozen and stored at a temperature of -30 ^° C. while waiting the implementation of subsequent steps of their purification.

The method of the invention thus allows the extraction and, where appropriate, the separation of one or of several proteins of interest milk calcium ions to which they are linked by electrostatic interactions.

The protein may be a protein naturally present in milk, and represents, for example, β-lactoglobulin, lactoferrin, α-lactalbumin, immunoglobulins or peptone proteoses, or their mixture.

The protein may also be a protein not naturally present in milk. By way of example, mention may be made of factor VII, factor VIII, factor IX, factor X, anti-trypsin alpha-1, anti-thrombin III, albumin, fibrinogen and insulin. , myelin basic protein, proinsulin, tissue plasminogen activator and antibodies.

Thus, according to a preferred embodiment of the invention, the milk containing the protein of interest is a transgenic milk. In fact, proteins not naturally present in milk can be synthesized by non-human transgenic mammals using recombinant DNA techniques and transgenesis.

These techniques, well known to those skilled in the art, make it possible to synthesize any protein of interest in the milk of a transgenic animal.

Such a protein is then a recombinant or transgenic protein, these two terms being considered as equivalent in the present application, synthesized by recombinant DNA techniques.

The term "transgenic animal" is intended to mean any non-human animal having incorporated in its genome an exogenous DNA fragment, in particular coding for a protein of interest, this animal expressing the protein encoded by the exogenous DNA, and capable of transmitting the DNA exogenous to its descendant. As such, any non-human mammal is suitable for the production of such a milk.

Advantageously, the rabbit, the ewe, the goat, the cow, the sow and the mouse can be used, this list not being limiting.

The secretion by the mammary glands of the protein of interest, allowing its secretion in the milk of the transgenic mammal, involves the control of the expression of the recombinant protein in a tissue-dependent manner.

Such control methods are well known to those skilled in the art. Expression control is performed by means of sequences allowing expression of the protein to a particular tissue of the animal. These sequences are in particular the promoter sequences, as well as the signal peptide sequences.

Examples of promoters well known to those skilled in the art are the WAP (whey acidic protein) promoter, the casein promoter, the β-lactoglobulin promoter, this list not being limiting.

A method for producing a recombinant protein in the milk of a transgenic animal may comprise the following steps: a synthetic DNA molecule comprising a gene coding for a protein of interest, this gene being under the control of a promoter of a protein secreted naturally in milk, is integrated into an embryo of a non-human mammal. The embryo is then placed in a female mammal of the same species which gives birth to a transgenic animal. Once this subject has developed sufficiently, the lactation of the mammal is induced, then the milk collected. The milk then contains the recombinant protein of interest.

An example of a method for preparing a protein in the milk of a mammalian female other than a human is given in document EP 0 527 063, whose teaching can be repeated for the production of the protein of interest of the invention.

A plasmid containing the WAP promoter is manufactured by introducing a sequence comprising the promoter of the WAP gene, this plasmid being made in such a way as to be able to receive a foreign gene placed under the control of the WAP promoter. The gene coding for a protein of interest is integrated and placed under the control of the WAP promoter. The plasmid containing the promoter and the gene coding for the protein of interest are used to obtain transgenic animals, for example rabbits, by microinjection into the male pronucleus of rabbit embryos. The embryos are then transferred into the oviduct of hormonally prepared females. The presence of the transgenes is revealed by the Southern technique from the DNA extracted from the transgenic rabbits obtained. Concentrations in animal milk are evaluated using specific radioimmunoassays. Advantageously, the protein produced in the milk and extracted according to the process of the invention is a coagulation protein, or coagulation factor. Indeed, it is known that such proteins have a high affinity for calcium ions (Hibbard et al (1980), J. Biol Chem 1980, Jan 25; 255 (2): 638-645). According to a particular aspect of the invention, the coagulation factor is activated during the extraction process of the invention. It can be in particular proteins - "vitamin • K-dependent", which are essential factors for the coagulation of blood.

Advantageously, the protein produced in the milk and extracted, according to the process of the invention, is a protein comprising "GLA-domains", which have the capacity to fix calcium ions, or else proteins comprising "domains". EGF "(epidermal growth factor) or other areas identified as. having an ability to fix calcium ions, such as in structures called "EF hand" (helix motif ^• loop-helix for fixing calcium ion).

Moreover, the calcium-dependent proteins are also proteins that can be purified by the process of the invention, in particular the antibodies or the monoclonal antibodies.

Advantageously, the protein of the invention is chosen from the factor II (FII), the factor VII (FVII), the factor IX (FIX) and the factor X (FX), as well as their activated forms, the protein C, the activated protein C, protein S and protein Z, or their mixture.

Particularly advantageously, the protein of the invention is FVII, or activated FVII (FVIIa).

In this regard, the FVII or FVIIa can be produced according to the teaching of EP 0 527 063, the summary of which is given above. A DNA fragment whose sequence is that of human FVII is then placed under the control of the WAP promoter. For example, such a DNA sequence appears under the sequence number Ib described in EP 0 200 421.

Advantageously, the FVII of the invention is activated. FVIIa results, in vivo, from cleavage of the zymogen by different proteases (FIXa, FXa, FVIIa) into two chains joined by a disulfide bridge. FVIIa alone has very little enzymatic activity, but complexed with its cofactor, tissue factor (FT), it triggers the coagulation process by activating FX and FIX.

FVIIa has a coagulant activity 25 to 100 times greater than that of FVII when interacting with tissue factor (FT). In one embodiment of the invention, FVII can be activated in vitro by the factors Xa, VIIa, 11a, IXa and XIIa. The FVII of the invention may also be activated during its purification process.

The Applicant has found, surprisingly, that the protein of interest, even placed under the control of a promoter of a protein naturally produced in whey, such as the WAP promoter for example, is nonetheless likely to be associated with calcium ions. , and therefore to casein micelles.

Thus, the method of the invention can be used for the separation of recombinant proteins produced under the control of a whey protein promoter.

Furthermore, the method of the invention is particularly suitable for the separation of recombinant proteins produced under the control of a casein promoter.

The protein may also be selected from factor VIII, anti-trypsin alpha-1, anti-thrombin III, albumin, fibrinogen, insulin, myelin basic protein, proinsulin, Tissue activator of plasminogen and antibodies, or their mixture.

The method of the invention can also be used for the preparation of a lactic recombinant protein. In this case, it may be a lactic protein synthesized by the mammary gland of an animal of another species (Simons et al., (1987), Aug 6-12;

328 (6130): 530-532). As such, there may be mentioned as examples lactoferrin, lactoglobulin, lysozyme and lactalbumin transgenic.

Another subject of the invention relates to a non-lipidic aqueous phase of milk comprising at least one protein that can be obtained by the process of the invention. Advantageously, the aqueous phase is hypersaline, basic, and contains soluble caseins and at least one other protein of interest. By hypersaline, we preferentially mean a concentration of at least 7 g / l of sodium ions, or at least 18 g / l of sodium chloride, or at least 0.3 molar of sodium chloride. Preferentially, this concentration is about 8 g / l of sodium ions or about 20 g / l of sodium chloride. By basic is meant a pH of between 8 to 9, and preferably greater than 7.8. Soluble caseins represent at least 25% of total caseins, and preferably at least 50% of total caseins.

Such a phase comprises at least 50%, or advantageously at least 60% up to 80% of the total of the proteins of interest to be purified relative to the milk that has not undergone the process steps. Particularly advantageously, the non-lipidic aqueous phase comprises at least 90% of the total of the proteins of interest present in the milk before extraction.

According to a preferred embodiment of the invention, the protein of interest present in the non-lipidic aqueous phase is factor VII (FVII) or activated factor VII (FVIIa) ^' .

^• The non-aqueous lipid phase -l'invention, even if it no longer contains casein micelles and insoluble calcium compounds, however, still comprises mainly impurities. Therefore, it is necessary, depending on the case, to carry out a purification of the protein in the aqueous phase.

The method of the invention may further comprise the subsequent steps of ^purification of the non-lipid aqueous phase comprising the protein ^'interest, obtained after step c) or, optionally,

^After the steps of filtration and concentration / dialysis implemented after step c).

Thus, step c) is followed by a step d) of affinity chromatography, using a device conventional chromatography, advantageously carried out on a chromatographic column whose support is a hydroxyapatite gel (Caχo (PO ₄ ) 6 (OH) ₂ ) or a fluoroapatite gel (Caio (PO4) 6F2). the non-lipidic aqueous phase is retained by the support, the major part of the lactic proteins not retained being eliminated. The detection is ensured by measuring the absorbance at λ = 280 nm.

The chromatographic column is preferably equilibrated in aqueous buffer A based on sodium phosphate 0.025 M-0.035 M, pH 7.5-8.5. The non-lipidic aqueous phase is injected onto the column, which allows the retention of the protein of interest. The unbound fraction is removed by percolation of buffer A until baseline return (RLB), which ensures proper removal of undesirable compounds, such as lactic proteins.

The elution of the protein is carried out by a phosphate salt-based buffer, such as sodium or potassium phosphate or a mixture thereof, at a predetermined concentration, preferably representing a phosphate-based buffer B sodium 0.25M-0.35M, pH 7.5-8.5. The eluted fraction is collected until the return to baseline. Thanks to this step, more than 90% of the total lactic proteins are eliminated and more than 90% of the proteins of interest are recovered. The purity of this eluted fraction is about 5% at this stage.

Purity is defined as the mass ratio between the protein of interest and the total proteins present in the sample, the fraction or the eluate under consideration.

Advantageously, the specific activity of the protein or proteins is increased by a factor of 10 to 25 because of the affinity of the protein of interest to the chromatographic support. The eluate obtained at the end of step d) is then advantageously subjected to a tangential filtration.

The tangential filtration membrane is chosen by those skilled in the art according to the characteristics of the protein of interest. In general, a cutoff threshold whose pore size is twice the molecular weight of the protein of interest allows the product to be advantageously filtered.

For example, a pore size membrane of 100 kDa makes it possible to filter the FVII in good yield.

The purpose of this filtration step is to reduce the charge, in particular to proteins of higher molecular weight than the protein of interest and, in particular, to eliminate the atypical forms of the protein of interest (for example proteins polymerized form), as well as proteases likely to eventually degrade it.

Very preferably, the filtered eluate obtained is then concentrated and dialyzed. A suitable system has already been described for the ultrafiltration concentration / dialysis step.

According to a preferred embodiment of the invention, the method comprises at least one ion exchange chromatography step to thereby purify the protein of interest, and, in particular, two successive chromatographic steps on ion exchangers. . Their implementation notably allows the elimination of residual lactic proteins.

The choice of the ion exchange medium and the equilibration, washing and elution buffers depend on the nature of the protein to be purified.

This or these steps can be carried out directly after step c), or possibly after the affinity chromatography and / or tangential filtration steps.

Preferably, the at least one step and the two chromatography steps are chromatographies anion exchange. Very preferably, these are carried out with low base type chromatographic supports. The detection of the compounds is ensured by measuring the absorbance at K = 280 nm.

The second chrornatographic step is intended to limit a possible proteolytic degradation of the protein.

By way of example, a chromatographic support of Q-Sepharose® FF gel type on which factor VII is retained is used for the first factor VII purification chromatographic step from the non-lipidic aqueous phase. An aqueous elution buffer based on Tris, preferably 0.05M, and calcium chloride, preferably 0.020M-0.05M, pH 7.0-8.0, is used in order to obtain a factor VII eluate of intermediate purity, i.e., of 25% to 75% purity.

The FVII eluate can then be subjected to a dialysis step, as previously described, whose buffer is a 0.15M sodium chloride solution.

For the second chromatographic step, use is made, for example for the purification of the factor VII eluate obtained by the preceding step, optionally diluted to allow its adsorption, a Q-Sepharose® FF type chromatographic support on which factor VII is retained. An aqueous elution buffer based on Tris, preferably 0.05M, and calcium chloride, preferably 0.005M, pH 7.0-8.0, is used for the elution of a factor fraction. VII of high purity, with a purity greater than 90%.

According to a preferred embodiment of the invention, the process comprises, after the two anion exchange chromatographic steps, a third anion exchange chromatographic step. This step allows the formulation of the enriched composition to be protein, so as to make it suitable for medical use. Very preferably, the third chromatographic step is carried out using a weak base type chromatographic support. The detection of the compounds is also ensured by measuring the absorbance at X = 280 nm.

By way of example, the eluate obtained by the second anion exchange chromatographic step is injected, after dilution, onto a column filled with Q-Sepharose® FF gel-type support on which the factor VII is retained. The factor VII retained on the support is eluted with an aqueous buffer consisting of Tris, preferably 0.02 M, and sodium chloride 0.20-0.30 M, pH 6.5-7.5. Therefore, the three anion exchange gel chromatography steps further purify the protein of interest. In addition, they allow concentration and formulation of the composition of the protein of interest. According to a preferred embodiment of the invention, and when the protein of interest to be purified is a coagulation factor, at least one of the three chromatography steps on the anion exchange supports allow the activation of any or part of the coagulation factor. Advantageously, the first chromatography allows activation of the coagulation factor.

After the recovery of the last eluate, it can be subjected to filtration on filters of 0.22 microns, distribution in vials and frozen at -30 ⁰ C and stored at this temperature.

The method of the invention may also comprise at least one of the following steps: formulation, virus inactivation and sterilization. In general, the method may comprise, before the affinity chromatography step, an anti-viral treatment step which is advantageously carried out solvent / detergent, in particular in the presence of a mixture of Tween® 80 (1% w / v) and TnBP (tri-n-butyl phosphate) (0.3% v / v), which makes it possible to inactivate enveloped viruses. In addition, the eluate derived from the second anion exchange chromatographic step is preferably subjected to a nanofiltration step for effective removal of viruses, particularly non-enveloped viruses, such as parvovirus B19. It is possible to use ASAHI PLANOVA ™ 15 filters allowing the retention of viruses having a size greater than 15 nm.

Other aspects and advantages of the invention will be described in the examples which follow, which should be considered as illustrative and do not limit the scope of the invention.

Examples

The examples below illustrate the application of the extraction and purification process of the invention to the preparation of an activated factor VII concentrate.

(FVIIa) from transgenic milk of rabbits

(FVII-tg: transgenic FVII).

These raw milks are from the first lactation of five female Fl ^(2nd generation of founder lines). Females were selected on the basis of lactic secretion rate of FVII antigen (FVII: Ag). The STAGO kit (ASSERACHROM VII) made it possible to monitor the human FVII content from day 4 to day 25 (day of milking) from the first lactation. This secretion was relatively stable for these females (between 188 and 844 IU / ml of FVII), depending on the female and the day of collection). The purification process used made it possible to purify, for example, 12 mg of FVII-tg from a 500 ml pool of raw milk. The overall purification yield is 22%.

This concentrate is pure according to SDS-PAGE electrophoresis analysis under unreduced conditions, that is to say that the disulfide bridges are preserved, and has a complete cleavage of the heavy and light chains in a reduced condition, which translates into total conversion to activated FVII (FVIIa) during the process.

Example 1 Extraction of FVII from Milk

500 ml of raw non skimmed milk are considered which are diluted with 9 volumes of 0.25 M sodium phosphate buffer, pH 8.2. After stirring for 30 minutes at room temperature, the aqueous phase enriched with

FVII is centrifuged at 10,000 g for 1 hour at 15 ^° C.

(Sorvall Evolution RC centrifuge - 6700 rpm - SLC-6000 rotor). 6 pots of about 835 ml are needed.

After centrifugarti _^one> three phases are present: a surface lipid phase (cream), a clear non-lipid aqueous phase enriched in FVII (major phase) and a white phase solid pellet (precipitates of insoluble casein and calcium compounds ).

The non-lipidic aqueous phase comprising FVII is collected at the peristaltic pump until the creamy phase. The creamy phase is collected separately. The solid phase (precipitate) is removed.

The non-lipidic aqueous phase, however, still containing very small amounts of lipids, is filtered through a filter sequence (PAIl SLK7002U010ZP - 1 μm pore size glass fiber pre-filter - then SLK7002NXP - nylon 66 0.45 μm pores). At the end of filtration, the lipid phase is passed on this sequence of filtration that completely retains lipid globules from milk, and the filtrate is clear.

The filtered non-lipidic aqueous phase is then dialyzed on an ultrafiltration membrane (Millipore Biomax 50 kDa - 0.1 m ² ) to make it compatible with the chromatography phase. The molecular weight FVII of about 50 kDa does not filter through the membrane, unlike the milk salts, sugars and peptides. Initially, the solution (about 5,000 ml) is concentrated to 500 ml, and then ultrafiltration dialysis while maintaining constant volume allows the removal of electrolytes and conditioning the biological material for the chromatography step. The dialysis buffer is a 0.025M sodium phosphate buffer, pH 8.2.

This non-lipidic aqueous phase comprising FVII can be assimilated to whey enriched in FVII-tg. This preparation is stored at -30 ^° C. before continuing the process. The overall recovery yield of FVII by this step is very satisfactory: 90% (91% phosphate extraction + 99% Dialysis / concentration).

The non-lipidic aqueous phase comprising FVII at the end of this step is perfectly clear and is compatible with the chromatographic steps that follow.

About 93,000 IU of FVII-tg are extracted at this stage. The purity in FVII of this preparation is of the order of 0.2%. Example 2: purification process of FVIIa

1. Chromatography on hydroxyapatite gel

An Amicon 90 column (9 cm diameter - 64 cm ² section) is filled with BioRad Ceramic Hydroxyapatite Gel Type I (CHT-I). The detection is carried out by measuring the absorbency at λ = 280 nm.

The gel is equilibrated in aqueous buffer A consisting of a mixture of 0.025 M sodium phosphate and 0.04 M sodium chloride, pH 8.0. The entire preparation stored at -30 ^° C. is thawed on a water bath at 37 ^° C. until the ice cube is completely dissolved and is then injected onto the gel (linear flow rate 100 cm / h, ie 105 ml / min). The non-retained fraction is removed by passing ^"of a buffer consisting of sodium phosphate and 0.025 M sodium chloride 0.04 M, pH 8.2, until return to baseline (RLB).

Elution of the fraction containing FVII-tg is via buffer B consisting of 0.25 M sodium phosphate and 0.4 M sodium chloride, pH 8.0. The eluted fraction is collected until the return to baseline.

This chromatography makes it possible to recover more than 90% of the FVII-tg, while eliminating more than 95% of the lactic proteins. The specific activity (A.S.) is multiplied by 25. About 85,000 IU of FVII-tg of 4% purity are available at this stage.

2. Tangential filtration 100 kDa and concentration / dialysis 50 kDa

The whole of the eluate of the previous step is filtered in tangential fashion on a membrane ^'of 100 kDa ultrafiltration (Pall OMEGA SC 100K - 0.1 m ^2). FVII is filtered through the 100 kDa membrane, while proteins with a molecular weight greater than 100 kDa are not filterable.

The filtered fraction is then concentrated to about 500 ml and then dialyzed on the 50 kDa ultrafilter already described in Example 1. The dialysis buffer is 0.15 M sodium chloride.

At this stage of the process, the product is stored at -30 ^° C. before passing through ion exchange chromatography.

This step made it possible to reduce the protein load of molecular weight greater than 100 kDa and in particular proenzymes. The 100 kDa membrane treatment makes it possible to retain about 50% of the proteins including the high molecular weight proteins, while filtering 95% of the FVII-tg, ie 82,000 IU of FVII-tg.

This treatment makes it possible to reduce the risks of proteolytic hydrolysis during the downstream stages.

3. Q-Sepharose® FF Gel Chromatography

These three successive chromatographies on Q-Sepharose® Fast Flow (QSFF) ion exchange gel are carried out to purify the active principle, to allow the activation of FVII in activated FVII (FVIIa) and finally to concentrate and formulate the FVII composition. The detection of the compounds is ensured by measuring the absorbance at λ = 280 nm.

3.1 Step Q-Sepharose® FF 1 - Elution "High Calcium"

A column 2.6 cm in diameter (5.3 cm ² section) is filled with 100 ml of Q-Sepharose® FF gel (GE Healthcare).

The gel is equilibrated in 0.05 M Tris buffer, pH 7.5. The entire fraction stored at -30 ⁰ C is thawed in a water bath at 37 ⁰ C until complete dissolution of the ice cube. The fraction is diluted to ¹ A [v / v] with the equilibration buffer before injection on the gel (flow rate 13 ml / min, ie linear flow of 150 cm / h), then the non-retained fraction is eliminated by passage of the buffer until RLB.

A first low FVII protein fraction is eluted at 9 ml / min (ie 100 cm / h) with a buffer of 0.05 M Tris and 0.15 M sodium chloride, pH 7.5, and is then eliminated.

A second protein fraction rich in FVII is eluted at 9 ml / min (ie 100 cm / h) with a buffer of 0.05 M Tris, 0.05 M sodium chloride and 0.05 M calcium chloride, pH 7.5.

This second fraction is dialysed on the 50 kDa ultrafilter already described in Example 1. The dialysis buffer is 0.15 M sodium chloride. This fraction is stored at + ^{40 °} C. overnight before the 2 ^nd passage. in anion exchange chromatography.

This step makes it possible to recover 73% of the FVII (ie 60000 IU of FVII-tg), while eliminating 80% of the accompanying proteins. It also allows the activation of FVII in FVIIa.

3.2 Step Q-Sepharose® FF 2 - elution "Low Calcium"

A 2.5 cm diameter column (4.9 cm ² section) is filled with 30 ml of Q-Sepharose® FF gel (GE Healthcare).

The gel is equilibrated in 0.05 M Tris buffer, pH 7.5.

The preceding eluted fraction (second fraction), stored at + ^{40 °} C., is diluted before injection on the gel (flow rate 9 ml / min, ie linear flow rate of 100 cm / h). After injection, the gel is washed with the equilibration buffer to remove the non-retained fraction.

A fraction containing very high purity FVII is eluted at 4.5 ml / min (ie 50 cm / h) in buffer of 0.05 M Tris, 0.05 M sodium chloride and 0.005 M calcium chloride, pH 7.5.

About 23,000 IU of FVII-tg were purified, ie 12 mg of FVII-tg. This step eliminates more than 95% of the accompanying proteins (rabbit milk proteins).

This eluate, of greater than 90% purity, has structural and functional characteristics close to the natural molecules of human FVII. It is concentrated and formulated by the third pass in ion exchange chromatography.

3.3 Step Q-Sepharose® FF 3 - elution "Sodium"

A column 2.5 cm in diameter (4.9 cm ² section) is filled with 10 ml of Q-Sepharose® FF gel (GE Healthcare). The gel is equilibrated in 0.05 M Tris buffer, pH 7.5.

The purified eluted fraction of the preceding step is diluted five times with purified water for injection (PPI) before injection on the gel (flow rate 4.5 ml / min, ie linear flow of 50 cm / h).

After injection, the gel is washed with the equilibration buffer to remove the non-retained fraction.

The FVII-tg is then eluted at a flow rate of 3 ml / min (ie 36 cm / h) with the buffer of 0.02 M Tris and 0.28 M sodium chloride, pH 7.0. A concentrate of FVII-tg has been prepared with purity greater than 95%. The product is compatible with intravenous injection. The process has a cumulative yield of 22%, which makes it possible to purify at least 20 mg of FVII per liter of milk used.

Table A summarizes the process steps according to a preferred embodiment of the invention, and provides the different yields, purity and specific activities obtained at each step.

Table A

Yield: Yield

Claims

claims

A method for extracting at least one protein present in milk, said protein exhibiting an affinity for complexed or non-complexed calcium ions of said milk, comprising the following steps: a) releasing the protein by precipitation of compounds of calcium obtained by contacting the milk with a soluble salt, whose anion is chosen for its ability to form in such a medium said insoluble calcium compounds, thereby obtaining a liquid phase enriched in the protein, b) separating the phase a liquid enriched in the protein of the precipitate of calcium compounds, said liquid phase being further separated into a lipid phase and a non-lipidic aqueous phase comprising the protein, and c) recovering the non-lipidic aqueous phase comprising the protein.

The process according to claim 1, wherein the soluble salt is a phosphate salt.

The process according to claim 2, wherein the phosphate salt is selected from the group consisting of sodium phosphate, lithium phosphate, potassium phosphate, rubidium phosphate and cesium phosphate, and is in particular, sodium phosphate.

4. The process according to claim 1, wherein the soluble salt is an oxalate of an alkali metal, in particular sodium or potassium oxalate, or an alkali metal carbonate, in particular sodium carbonate or sodium carbonate. potassium, or their mixture.

5. Method according to one of claims 1 to 4, wherein the concentration of the soluble salt in aqueous solution is between 100 mM and 3 M, more preferably preferred, between 200 mM and 500 inM and, in particular, between 200 mM and 300 mM.

6. ^" Method according to one of claims 1 to 5, wherein step b) is carried out by centrifugation.

7. Method according to one of claims 1 to 6, comprising, after step c), a step of filtering the non-lipid aqueous phase carried out successively on decreasing porosity filters, preferably 1 micron and then 0, 45 μm, followed by a concentration / dialysis step by ultrafiltration.

8. Method according to one of claims 1 to 7, wherein the lipid phase is filtered through decreasing porosity filters, preferably 1 micron and then 0.45 microns.

9. Method according to one of claims 1 to 8, wherein the protein is a protein not naturally present in the milk.

10. Method according to one of claims 1 to 9, wherein the milk is a transgenic non-human mammalian milk.

The method of claim 10, wherein said mammal is selected from rabbit, ewe, goat, cow, sow and mouse.

The method according to one of claims 9 to 11, wherein the protein is a coagulation protein.

The method of claim 12, wherein the protein is selected from factor II, the factor

VII, factor IX and factor X, as well as their activated forms, protein C, activated protein C, protein S and protein Z, or their mixture.

The method according to one of claims 9 to 11, wherein the protein is a protein having

GLA-domains, EGF domains (epidermal growth factor) or other areas identified as having the ability to fix calcium ions.

15. The method according to one of claims 9 to 11, wherein the protein is a vitamin K-dependent protein.

The method according to one of claims 9 to 11, wherein the protein is a calcium dependent protein.

17. The method according to one of claims 9 to 11, wherein the protein is selected from the factor

VIII, anti-trypsin alpha-1, anti-thrombin III, albumin, fibrinogen, insulin, myelin basic protein, proinsulin, tissue plasminogen activator and antibodies, or their mixture.

18. The method according to one of claims 9 to 11, wherein the protein is transgenic lactoferrin, lactoglobulin, lysozyme and lactalbumin.

19. A non-lipidic aqueous phase of milk characterized in that it is hypersaline and basic and contains soluble caseins and at least one other protein, obtainable by the method according to one of claims 1 to 18. .

20. The method according to one of claims 1 to 18, wherein step c) is followed by a step d) of affinity chromatography, the elution of the protein being carried out by a buffer based on a phosphate salt at a predetermined concentration.

21. The method of claim 20, wherein the affinity chromatography is carried out on a chromatographic column whose support is a hydroxyapatite gel (CaI ₀ (PO ₄ ) E (OH) ₂ ) or a gel of

^• fluoroapatite (Ca (PO _{4) 6} F2).

22. The method of claim 20 or 21, wherein the eluate obtained at the end of step d) is then subjected to tangential filtration.

23. Method according to one of claims 1 to 18, comprising at least one ion exchange chromatography step, and in particular two successive chromatographic steps on ion exchangers performed directly after _. step c).

24. The method of claim 23, wherein the at least one step and the two chromatography steps are anion exchange chromatography.

25. The method of claim 24, comprising, after the two anion exchange chromatographic steps, a third anion exchange chromatographic step.

26. Method according to one of claims 20 to 25, comprising, before the affinity chromatography step, an anti-viral treatment step which is carried out by solvent / detergent.

27. Method according to one of claims 23 to 25, wherein the eluate from the second anion exchange chromatographic step is subjected to a nanofiltration step.