2.6.In de authentieke Engelse versie van de beschrijving van EP 455 is voorts - voor zover hier van belang - het volgende opgenomen:
[0001]This invention relates generally to protein purification.
Description of Related Art
[0002]The large-scale, economic purification of proteins is increasingly an important problem for the biotechnology industry. (…)
[0003]Procedures for purification of proteins from cell debris initially depend on the site of expression of the protein. Some proteins can be caused to be secreted directly from the cell into the surrounding growth media: others are made intracellularly. For the latter proteins, the first step of a purification process involves lysis of the cell, which can be done by a variety of methods, including mechanical shear, osmotic shock, or enzymatic treatments. Such disruption releases the entire contents of the cell into the homogenate, and in addition produces subcellular fragments that are difficult to remove due to their small size. These are generally removed by differential centrifugation or by filtration. The same problem arises, although on a smaller scale, with directly secreted proteins due to the natural death of cells and release of intracellular host cell proteins in the course of the protein production run.
[0004]Once a clarified solution containing the protein of interest has been obtained, its separation from the other proteins produced by the cell is usually attempted using a combination of different chromatography techniques.
[0005]Ion exchange chromatography is a chromatographic technique that is commonly used for the purification of proteins. In ion exchange chromatography, charged patches on the surface of the solute are attracted by opposite charges attached to a chromatography matrix, provided the ionic strength of the surrounding buffer is low. Elution is generally achieved by increasing the ionic strength (i.e. conductivity) of the buffer to compete with the solute for the charged sites of the ion exchange matrix. Changing the pH and thereby altering the charge of the solute is another way to achieve elution of the solute. The change in conductivity or pH may be gradual (gradient elution) or stepwise (step elution). In the past, these changes have been progressive: i.e., the pH or conductivity is increased or decreased in a single direction.
[0006]WO 92/22653 (Genentech) discloses methods for making humanised antibodies, including anti-HER2 antibodies.
[0007]WO 96/33208 (Genentech) discloses methods of purifying antibodies (for example from incorrectly disulphide linked contaminents) by low pH hydrophobic interaction chromatography.
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[0011]Disclosed herein is an ion exchange chromatographiemethod wherein a polypeptide of interest is bound to the ion exchange material at an initial conductivity or pH and then the ion exchange material is washed with an intermediate buffer at a different conductivity or pH, or both. At a specific point following this intermediate wash, and contrary to ion exchange chromatography standard practice, the ion exchange material is washed with a wash buffer where the change in conductivity or pH, or both, from the intermediate buffer to the wash buffer is in an opposite direction to the change in conductivity or pH, or both, achieved in the previous steps. Only after washing with the wash buffer, is the ion exchange material prepared for the polypeptide molecule of interest to be eluted by the application of the elution buffer having a conductivity or pH, or both, which differ from the conductivity or pH, or both, of the buffers used in previous steps.
[0012]This novel approach to ion exchange chromatography is particularly useful in situations where a product molecule must be separated from a very closely related contaminant molecule at full manufacturing scale, where both purity and high recovery of polypeptide product are desired.
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[0018]In the compositions of the invention as defined in claim 1 the amount of the acidic variant(s) in the composition is less than about 25% and preferably less than about 20%, e.g. in the range from about 1% to about 18%. Optionally, the composition further comprises a pharmaceutically acceptable carrier.
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Detailed Description Of The Preferred Embodiments
Definitions:
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[0022]A 'contaminant" is a material that is different from the desired polypeptide product. The contaminant may be a variant of the desired polypeptide (e.g. a deamidated variant or an amino-aspartate variant of the desired polypeptide) or another polypeptide, nucleic acid, endotoxin etc.
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[0024]An "acidic variant' is a variant of a polypeptide of interest which is more acidic (e.g. as determined by cation exchange chromatography) than the polypeptide of interest. An example of an acidic variant is a deamidated variant.
[0025]A "deamidated" variant of a polypeptide molecule is a polypeptide wherein one or more asparagine residue(s) of the original polypeptide have been converted to aspartate, i.e. the neutral amide side chain has been converted to a residue with an overall acidic character. Deamidated humMAb4D5 antibody from the Example below has Asn30 in CDRI of either or both of the VL regions thereof converted to aspartate. The term "deamidated human DNase" as used herein means human DNase that is deamidated at the asparagine residue that occurs at position 74 in the amino acid sequence of native mature human DNase (US Patent 5,279,823; expressly incorporated herein by reference).
[0026]The term "mixture" as used herein in reference to a composition comprising an anti-HER2 antibody, means the presence of both the desired anti-H ER2 antibody and one or more acidic variants thereof. The acidic variants may comprise predominantly deamidated anti-HER2 antibody, with minor amounts of other acidic variant(s). It has been found, for example, that in preparations of anti-HER2 antibody obtained from recombinant expression, as much as about 25% of the anti-HER2 antibody is deamidated.
Modes for Carrying Out the invention
[0072]The invention herein provides a composition as defined in claim 1. Also disclosed herein is a method for purifying a polypeptide from a composition (e.g. an aqueous solution) comprising the polypeptide and one or more contaminants. The composition is generally one resulting from the recombinant production of the polypeptide, but may be that resulting from production of the polypeptide by peptide synthesis (or other synthetic means) or the polypeptide may be purified from a native source of the polypeptid. The polypeptide is an antibody which binds the HER2 antigen.
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[0081]The polypeptide is then subjected to one or more purification steps, including the ion exchange chromatography method as disclosed herein. Examples of additional purification procedures which may be performed prior to, during, or following the ion exchange chromatography method include fractionation on a hydrophobic interaction chromatography (e.g. on phenyl sepharose), ethanol precipitation, isoelectric focusing, Reverse Phase HPLC, chromatography on silica, chromatography on HEPARIN SEPHAROSETM, further anion exchange chromatography and/or further cation exchange
chromatography, chromatofocusing, SDS-PAGE, ammonium sulfate precipitation, hydroxylapatite chromatography, gel electrophoresis, dialysis, and affinity chromatography (e.g. using protein A, protein G, an antibody, a specific substrate, ligand or antigen as the capture reagent).
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[0087]Following washing with the intermediate buffer, the cation exchange resin is washed or re-equilibrated with the wash buffer which has a conductivity or pH. or both, which is/are less than that of the intermediate buffer (i.e. the conductivity, or pH, or both, is/are changed in an opposite, i.e. reverse, direction to the preceding step, unlike ion exchange chromatography steps in the literature). In the Example below, the wash buffer had about the same conductivity as the loading buffer (i.e. in the range from about 5.2 to about 6.6 mmhos) and its conductivity was, therefore, less than that of the intermediate buffer. In another embodiment, one may reduce the conductivity of the wash buffer to a conductivity
that is less than, or greater than, that of the loading buffer, provided the conductivity of the wash buffer is less than that of the intermediate buffer. In another embodiment, the pH of the wash buffer may be less than the pH of the intermediate buffer (e.g. the pH of the wash buffer may about 5.0). The change in conductivity and/or pH of the wash buffer compared
to the intermediate buffer may be achieved by step-wise or gradual change of either or both of these parameters.
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[0092]The method herein is particularly useful for resolving a polypeptide molecule of interest from at least one contaminant, where the contaminant and polypeptide molecule of interest differ only slightly in ionic charge. For example, the pI’s of the polypeptide and contaminant may be only “slightly different”, for example they may differ by only about 0.05 to about 0.2 pI units. In the Example below, this method could be used to resolve an anti-HER2 antibody having a pI of 8.97, from a singly-deamidated variant thereof having a pI of 8.79.
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[0101]The following examples are offered by way of illustration and not by way of limitation. The disclosures of all citations in the specification are expressly incorporated herein by reference.
[0102]Full length human IgG rhumAb HER2 (humAb4D5-8 in Carter et al. Proc. Natl. Acad. Sci. 89: 4285.
[0103]4289 (1992) comprising the light chain amino acid sequence of SEQ ID NO: 1 and heavy chain amino acid sequence of SEQ ID NO:2) was produced recombinantly in CHO cells. Following protein production and secretion to the cell culture medium, the CHO cells were separated from the cell culture medium by tangential flow filtration (PROSTACKTM).
Protein A chromatography was then performed by applying the Harvested Cell Culture Fluid (HCCF) from the CHO cells directly to an equilibrated PROSEP ATM column (Bioprocessing. Ltd).
[0104]Following Protein A chromatography, cation exchange chromatography was performed using a sulphopropyl (SP)-SEPHAROSE FAST FLOWTM (SPSFF) column (Pharmacia) to further separate the desired anti-HER2 antibody molecule. The chromatography operation was performed in bind and elute mode.
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[0109]Determination of rhuMAb HER2 Antibody Variants (CSx HPIEX): The rhuMAb HER2 SPSFF chromatography column resolves antibody variants. Fractions from each of the study chromatographies were tested for the relative amount of variant antibody by CSx HPIEX chromatography. A BAKERBOND WIDEPORETM CSx HPIEX column (4.6 x
250mm) was run at 1 mL/min at 55°C. The mobile phase was formed from a tertiary gradient (Table 2).
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[0113]Deamidated and other acidic variants of rhuMAb HER2 were produced when the antibody was made by recombinant DNA technology (see e.g., CSx peaks a, b and 1 in Figure 5). The deamidated and other acidic variants constituted about 25% (calculated as area under the integrated curve or profile obtained by CSx chromatography) of the composition obtained from the initial Protein A chromatography step. It was discovered that the ion exchange method described herein could be used to substantially reduce the amount of deamidated and other acidic variants in the anti-HER2 composition, i.e. to about 13% or less (i.e. the amount of acidic variants in the preparation subjected to cation exchange chromatography as described herein was decreased by about 50% or more).
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