Patent Application
20050224355
The present invention relates to methods for the removal of biological contaminants, particularly removal of biological contaminants from biological preparations.
The modern biotechnology industry is faced with a number of problems especially concerning the processing of complex biological solutions which ordinarily include proteins, nucleic acid molecules and complex sugars and which are contaminated with unwanted biological materials. Contaminants include microorganisms such as bacteria and viruses or biomolecules derived from microorganisms or the processing procedure. The demand is, therefore, for a high purity, scalable separation, which can be confidently used both in product development and production, which in one step will both purify macromolecules and separate these biological contaminants.
Viruses are some of the smallest non-cellular organisms known. These simple parasites are composed of nucleic acid and a protein coat. Viruses are typically very small and range in size from 1.5×10−8 m to 5.0×10−5 m. Viruses depend on the host cells that they infect to reproduce by inserting their genetic material into the host. Often literally taking over the host's function. An infected cell produces more viral protein and genetic material, often instead of its usual products. Some viruses may remain dormant inside host cells. However, when a dormant virus is stimulated, it can enter the lytic phase where new viruses are formed. Self-assemble occurs and burst out of the host cell results in killing the cell and releasing new viruses to infect other cells. Viruses cause a number of diseases in humans including smallpox, the common cold, chicken pox, influenza, shingles, herpes, polio, rabies. Ebola, hanta fever, and AIDS. Some types of cancer have been linked to viruses.
Pyrogens are agents which induce fever. Bacteria are a common source for the production of endotoxins which are pyrogenic agents. Furthermore, another detrimental effect of endotoxins is their known adjuvant effect which could potentially intensify immune responses against therapeutic drugs. The endotoxin limit set by the Food and Drug Administration (FDA) guidelines for most pharmaceutical products is for a single dose 0.5 ng endotoxin per kilogram body weight or 25 ng endotoxin/dose for a 50 kg adult. Due to their size and charge heterogeneity, separation of endotoxins from proteins in solution can often be difficult. Endotoxin inactivation by chemical methods are unsuitable because they are stable under extremes of temperature and pH which would destroy the proteins. Furthermore, due to their amphipathic nature, endotoxins tend to adhere to proteins in a fashion similar to detergents. In such cases, endotoxin activity often clusters with the protein when chromatographic procedures such as ion exchange chromatography or gel filtration are employed.
Presently, the purification of biomolecules is sometimes a long and cumbersome process especially when purifying blood proteins. The process is made all the more complex by the additional step of ensuring the product is “bug” free. The costs associated with this task is large and further escalates the purification costs in total. The Gradiflow technology rapidly purifies target proteins with high yield. For example, a proteins like fibrinogen (a clotting protein) can be # separated in three hours using the Gradiflow while the present industrial separation is 3 days. Certain monoclonal antibodies can be purified in 35 minutes compared to present industrial methods which take 35 hours.
The membrane configuration in the Gradiflow enables the system to be configured so that the purification procedure can also include the separation of bacteria viruses and vectors. It has now been found by the present inventors that appropriate membranes can be used and the cartridge housing the membrane configured to include separate chambers for the isolated bacteria and viruses.
The Gradiflow Technology
Gradiflow is a unique preparative electrophoresis technology for macromolecule separation which utilises tangential flow across a polyacrylamide membrane when a charge is applied across the membrane (AU 601040). The general design of the Gradiflow system facilitates the purification of proteins and other macromolecules under near native conditions. This results in higher yields and excellent recovery.
In essence the Gradiflow technology is bundled into a cartridge comprising of three membranes housed in a system of specially engineered grids and gaskets which allow separation of macromolecules by charge and/or molecular weight. The system can also concentrate and desalt/dialyse at the same time. The multimodal nature of the system allows this technology to be used in a number of other areas especially in the production of biological components for medical use. The structure of the membranes may be configured so that bacteria and viruses can be separated at the point of separation—a task which is not currently available in the biotechnology industry and adds to the cost of production through time delays and also because of the complexity of the task.
In a first aspect, the present invention consists in a method of removing a biological contaminant from a mixture containing a biomolecule and the biological contaminant, the method comprising:
In a second aspect the present invention consists in a method of removing a biological contaminant from a mixture containing a biomolecule and the biological contaminant, the method comprising:
In the first and second aspects of the present invention, preferably the biomolecule is selected from the group consisting of blood protein, immunoglobulin, and recombinant protein.
The biological contaminant can be a virus, bacterium, prion or an unwanted biomolecule such as lipopolysaccharide, toxin or endotoxin.
Preferably, the biological contaminant is collected or removed from the first stream.
Preferably, the buffer for the first solvent stream has a pH lower than the isoelectric point of biomolecule to be separated.
In a further preferred embodiment of the first aspect of the present invention, the electrophoretic membrane has a molecular mass cut-off close to the apparent molecular mass of biomolecule. It will be appreciated however, that the membrane may have any required molecular mass cut-off depending on the application. Usually, the electrophoretic membrane has a molecular mass cut-off of between about 3 and 1000 kDa. A number of different membranes may also be used in a desired or useful configuration.
The electric potential applied during the method is selected to ensure the required movement of the biomolecule, or contaminant if appropriate, through the membrane. An electric potential of up to about 300 volts has been found to be suitable. It will be appreciated, however, that greater or lower voltages may be used.
The benefits of the method according to the first aspect of the present invention are the possibility of scale-up, and the removal of biological contaminants present in the starting material without adversely altering the properties of the purified biomolecule.
In a third aspect, the present invention consists in use of Gradiflow in the purification or separation of biomolecule from a biological contaminant.
In a fourth aspect, the present invention consists in biomolecule substantially free from biological contaminants purified by the method according to the first aspect of the present invention.
In a fifth aspect, the present invention consists in use of biomolecule according to the third aspect of the present invention in medical and veterinary applications.
In a sixth aspect, the present invention consists in a substantially isolated biomolecule substantially free from biological contaminants.
Throughout this specification, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
In order that the present invention may be more clearly understood a preferred forms will be described with reference to the accompanying drawings.
Virus Removal During Plasma Protein Purification
Contamination with virus is a major concern when purifying plasma proteins, such as IgG and human serum albumin (HSA). A contaminant virus can potentially infect a patient receiving the contaminated plasma products. A virus that infects bacteria is known as a phage, and they are readily detected by examining culture plates for cleared zones in a coating or lawn of bacteria.
1. IgG Purification Procedure
IgG is the most abundant of the immunoglobulins, representing almost 7000 of the total immunoglobulins in human serum. This class of immunoglobulins has a molecular mass of approximately 150 kDa and consists of 4 subunits, two of which are light chains and two of which are heavy chains. The concentration of IgG in normal serum is approximately 10 mg/mL.
IgGs are conventionally purified using Protein A affinity columns in combination with DEAB-cellulose or DEAE-Sephadex columns. The main biological contaminants in IgG isolations are β-lipoprotein and transferrin. The product of conventional protein purification protocols is concentrated using ultrafiltration. Immunoaffinity can also be used to isolate specific IgGs.
Platelet free plasma was diluted one part in three with Tris-borate, pH 9.0 running buffer and placed in stream 1 56 of separation apparatus 200 and spiked with either Lambda or T7 phage to a concentration of approximately 108 pfu/mL (plaque forming units/mL). A potential of 250V was placed across a separating membrane 34 with a molecular weight cut off of 200 kDa and with 3 kDa restriction membranes 30 and 32. A membrane 34 of this size restricts IgG migration while allowing smaller molecular weight contaminants to pass through the membrane 34, leaving IgG and other large molecular weight compounds in the stream 1 56. A second purification phase was carried out using a GABA/Acetic acid buffer, pH 4.6 with a 500 kDa cut off separating membrane 34 and with 3 kDa restriction membranes 30 and 32. A potential of 250V reversed polarity was placed across the system resulting in IgG migration through the separation membrane 34 leaving other high molecular weight contaminants stream 1 56.
Examination of samples taken at 30 minutes intervals was made on reduced SDS-PAGE 4-20% gels.
One hundred and fifty microliter samples were taken at each time point sample and mixed with 100 iL of appropriate Escherichia coli culture (Strain HB 101 was used for T7 and strain JM101 for Lambda). The mixtures were incubated for 15 minutes at 37° C. and then added to 2.5 mL of freshly prepared molten soft agar, and vortexed. The mixtures were poured over culture plates of Luria Agar, and incubated at 37° C. overnight. The plates were inspected for the presence of virus colonies (plaques) in the lawn of E. coli and the number of plaques was recorded. If the virus had infected the entire E. coli population, the result was recorded as confluent lysis.
2. HSA Purification Procedure
Albumin is the most abundant protein component (50 mg/mL) in human plasma and functions to maintain blood volume and oncotic pressure. Albumin regulates the transport of protein, fatty acids, hormones and drugs in the body. Clinical uses for HAS purification include blood volume replacement during surgery, shock, serious burns and other medical emergencies. Albumin is 67 kDa and has an isoelectric point of approximately 4.9. The protein consists of a single subunit and is globular in shape. About 440 metric tons of albumin is used annually internationally with worldwide sales of US $1.5 billion.
Albumin is currently purified using Cohn fractionation and commercial product contains many contaminants in addition to multimers of albumin. The high concentration, globular nature and solubility of albumin make it an ideal candidate for purification from plasma using the separation technology of the present invention.
Pooled normal plasma was diluted one in three with Tris-Borate (TB) 10 running buffer, pH 9.0 and spiked with approximately 108 pfu/mL of Lambda or T7 phage. The mixture was placed in stream 1 56 of the separation apparatus 200. Albumin was isolated from platelet free plasma in a one-phase process using the charge of albumin at a pH above its isoelectric point (pI) and its molecular weight. Thus a cartridge 100 having a 75 kDa cutoff separation membrane 34 and two 50 kDa restriction membranes 30 and 32 was used. The albumin was removed from high molecular weight contaminants by its migration through the separation membrane 34 while small molecular weight contaminants dissipated through the 50 kDa restriction membrane 30. Samples were taken at regular intervals throughout a 90 minute run.
The presence of the purified HSA in the stream 2 was demonstrated by examination by SDS-PAGE. Virus was detected as previously described in the IgG purification procedure.
3. Fibrinogen Purification Procedure
Commercially, fibrinogen has a role as fibrin glue, which is used to arrest bleeding and assist in the wound healing process. Fibrinogen is an elongated molecule of 340 kDa that consists of three non-identical subunit pairs that are linked by a disulfide knot in a coiled coil conformation. The isoelectric point of fibrinogen is 5.5 and it is sparingly soluble as compared to other plasma proteins.
Fibrinogen is conventionally purified from plasma by a series of techniques including ethanol precipitation, affinity columns and traditional electrophoresis. This process takes about 48-72 hours and the harsh physical and chemical stresses placed on fibrinogen are believed to denature the molecule. Cryo-precipitation is the first step in the production of Factor VIII and involves the loss of most of the fibrinogen in plasma. Processing of this waste fibrinogen is of considerable interest to major plasma processors and provides an opportunity to demonstrate the rapid purification of fibrinogen from cryo-precipitate using the separation technology of the present invention.
Cryo-precipitate 1, produced by thawing frozen plasma at 4° C. overnight was removed from plasma by centrifugation at 10000 g at 4° C. for 5 minutes. The precipitate was re-dissolved in Tris-Borate buffer (pH 9.0) and placed in stream 1 56 of separation apparatus 200. Stream 1 56 was spiked with either Lambda or T7 phage to a concentration of approximately 108 pfu/mL. A potential of 250V was applied across a cartridge 100 having a 300 kDa separation membrane 34 for a period of 2 hours. Stream 2 66 was replaced with fresh buffer 38 at 30 minute intervals. # A second cartridge 100 was then inserted having a 500 kDa cutoff separation membrane 34. A second phase was used to concentrate the fibrinogen through the second cartridge 100 at pH 9.0. Stream 2 66 was harvested at 60 minutes. The product was dialyzed against PBS pH 7.2 and analyzed for clotting activity by the addition of calcium and thrombin (final concentrations 10 mM and 10NIG unit/mL respectively).
The presence of purified fibrinogen was confirmed by examination on reduced SDS PAGE 4-20% gels. The presence of either T7 or Lambda in the time point samples was tested using the previously described method.
4. Results of IgG, HSA and Fibrinogen Purification
The procedures described successfully purified IgG, albumin and fibrinogen as judged by electrophoresis. Neither T7 nor Lambda phage were detected in the stream 2 products, but were present in the stream 1 samples.
Prion diseases have recently become a focus of intense research, especially in Europe and the US. The unique mechanism of replication and transmission, and the ability of related prion diseases to transmit between species have contributed significantly to this area. While there is no epidemiological evidence yet to support Creutzfeldt-Jakob disease (CJD) transmission by human blood or blood products, a related disease in transmissible spongiform encephalopathy (TSE). Animal studies have highlighted that whole blood and its components such as plasma and buffy boat, are capable of transmitting the disease. The emergence of a new variant CJD has raised increased concerns about the safety of blood components and plasma products derived from vCJD-infected donors. Recent risk-minimization strategies have included a ban on the use of UK-sourced plasma for the preparation of licensed blood products and leukodepletion of blood donations. Although processes such as precipitation, depth filtration and chromatographic procedures during plasma fractionation, have the potential to remove TSE agents to the limit of detection, whether or not these processes would have been capable of completely removing all the spiked TSE infectivity is uncertain. Using normal bovine prion protein as a surrogate for the abnormal form associated with TSE infectivity, complete prion clearance of the input spike was achieved during the purification of human albumin, immunoglobulin and α1-proteinase inhibitor from human plasma by the present invention.
Human plasma (1/3 ratio), were mixed with bovine brain homogenate, containing PrPC and placed in stream 1 of a separation apparatus. Purification of albumin was performed at 250 V using a cartridge with a separation membrane of 150 kDa and two restriction membranes of 5 kDa and 20 mM Tris-Borate (TB) running buffer, pH 9.0. Stream 2 fractions were collected every 60 minutes over a 5-hour run. The running conditions were selected such that the running buffer pH was higher than albumin pI, but lower than pI of PrPC and the separation of albumin and PrPc was achieved based on their charge differences. The presence of purified albumin in stream 2 was examined by SDS-PAGE and the yield was measured using a Bromocresol Green Assay (Trace Scientific). Anti-PrP Western blot, used to detect PrPC, showed that PrPC remained in stream 1 and stream 2 albumin fractions were completely free of PrPC as shown in
Similar partitioning experiments were carried out in the purification of Immunoglobulin from human plasma. Human plasma (1/3 ratio) were mixed with bovine brain homogenate, containing PrPc and placed in stream 1 of a separation apparatus. By using an 800 kDa separation membrane, 5 kDa and 80 kda-restriction membranes cartridge and 30 mM GABA/Acetic Acid (pH 4.6), the spiked bovine PrPc was completely removed from stream 2 fractions which contained the purified human Immunoglobulin as shown in
1. Albumin Quantitation
Fifty microliters of sample from each time point were diluted with 50 uL of PBS buffer 36, 38. A 20 uL aliquot of each diluted sample was placed in a microplate well. A standard curve with a maximum concentration of 40 mg/mL albumin was prepared using PBS as the diluent. The standard curve dilutions were also placed in the microplate (2T1 plasma/well). The bromocresol green reagent was added to all the wells (200 uL/well) and the absorbance at 630 nm was read using a Versamax microplate reader. A standard curve was drawn on a linear scale and the concentration of albumin in stream 1 56 and stream 2 66 samples were read from the curve. The volume in the appropriate stream 1 56 or stream 2 66 at the time of sampling was multiplied by the concentration of each sample, thus providing a value for the total HSA present in each stream.
2. Prion Detection
Anti-PrP Western Blot
After subjecting the samples to SDS-PAGE analysis, a semi-dry transfer of proteins onto the nitrocellulose (NC) was performed for 1 hour at 15V. The NC was then blocked at 37° C. for 30 minutes before being incubated with anti-PrP antibody, R029, (Prionics, Switzerland) and subsequently incubated with HRP-conjugated secondary antibody. Western blot was developed by Enhanced Chemiluminescence ECL™ (Amersham Pharmacia Biotech).
3. Results
Albumin was transferred to the stream 2 66 and was detected in the BCG assay (
Referring to
Endotoxin Removal During Plasma Protein Purification
Contamination with bacterial endotoxin is a major concern when purifying plasma proteins, such as IgG and HSA. Endotoxins are a lipopolysaccharide derived from the lipid membrane of gram negative bacteria. The presence of endotoxin in a human blood fraction therapeutic can lead to death of the receiving patients.
1. IgG Purification Procedure
Platelet free plasma was diluted one part in three with Tris-borate, pH 9.0 running buffer and placed in stream 1 67 of a separation apparatus 200 and spiked with purified E. Coli endotoxin to a concentration of 600 EU/mL (endotoxin units/mL). A potential of 250V was placed across a cartridge 100 having a separating membrane 34 with a molecular weight cut off of 75 kDa restriction membranes 30 and 32 with a molecular weight cut off of 50 kDa. A separation membrane 34 of this size restricts IgG migration whilst allowing smaller molecular weight contaminants to pass through the membrane 34, leaving IgG and other large molecular weight compounds in the stream 1 56. A second purification phase was carried out using a MES/bis-tris buffer, pH 5.4 with a cartridge 100 having a separating membrane 34 with a molecular weight cut off of 500 kDa restriction membranes 30 and 32 with a molecular weight cut off of 80 kDa. A potential of 250V reversed polarity was placed across the system resulting in IgG migration through the separation membrane 34 leaving other high molecular weight contaminants in stream 1 56.
Examination of samples taken at 30 minutes intervals was made on reduced SDS-PAGE 4-20% gels. Endotoxin was tested for using a LAL Pyrochrome Chromogenic assay purchased from Cape Cod Associates. All samples were appropriately diluted and the endotoxin assay was performed according to the manufacturer instructions.
2. HSA Purification Procedure
Pooled normal plasma was diluted one in three with Tris-Borate (TB) running buffer, pH 9.0 and spiked with 600 EU/mL of purified endotoxin. The mixture was placed in stream 1 56 of a separation apparatus 200. Albumin was isolated from platelet free plasma in a one-phase process using the charge of albumin at a pH above its pI and its molecular weight. Thus a cartridge 100 having a separation membrane 34 with 75 kDa cutoff and restriction membranes 30 and 32 with 50 kDa cutoffs. The albumin was removed from high molecular weight contaminants by its migration through the separation membrane 34 while small molecular weight contaminants dissipated through the 50 kDa restriction membrane 30. Samples were taken at regular intervals throughout a 180 minutes run.
The presence of the purified HSA in stream 2 66 was demonstrated by examination by SDS-PAGE. Endotoxin was tested for in both stream 1 56 and stream 2 66 samples using a LAL Chromogenic assay supplied by Cape Cod Associates. All samples were appropriately diluted and the endotoxin assay was performed according to the manufacturer instructions.
3. Results of IgG and HSA Purification
Stream 1 56 and stream 2 66 samples taken at 30 minute intervals during the second phase of an IgG purification from endotoxin spiked plasma were tested for endotoxin using a LAL Chromogenic assay. The results showed that the endotoxin was almost entirely found in the stream 1 at all time points (
Referring to
Analysis of samples taken at 30 minute intervals during the purification of HSA from plasma spiked with endotoxin found the majority of endotoxin remained in stream 1 56. Only 4% of the total endotoxin was found in the stream 2 66 at the end of the run (
Referring to
Referring to
Bacteria Removal During Plasma Protein Purification
Contamination with bacteria is a major concern when purifying plasma proteins, such as IgG and HSA. Contaminant bacteria can potentially infect a patient receiving plasma products, or during pasteurization of plasma products when bacteria dies releasing dangerous endotoxins that are harmful to the patient. Bacteria are easily detected by culturing samples on nutrient agar plates.
1. IgG Purification Procedure
Platelet free plasma was diluted one part in three with Tris-borate, pH 9.0 running buffer and placed in stream 1 56 of the separation apparatus 200 and spiked with E. coli to a concentration of 4×108 cells/mL. A potential of 250V was placed across a cartridge 100 having a separation membrane 34 with 200 kDa cutoff and restriction membranes 30 and 32 with 100 kDa cutoffs. A separation membrane 34 of this size restricts IgG migration while allowing smaller molecular weight contaminants to pass through the separation membrane 34, leaving IgG and other large molecular weight compounds in stream 1 56. A second purification phase was carried out using a GABA/Acetic acid buffer, pH 4.6 with a cartridge 100 having a separation membrane 34 with 500 kDa cutoff and restriction membranes 30 and 32 with 3 kDa cutoffs. A potential of 250V reversed polarity was placed across the system resulting in IgG migration through the separation membrane 34 leaving other high molecular weight contaminants in stream 1 56.
Examination of samples taken at 30 minutes intervals was made on reduced SDS-PAGE 4-20% gels. Twenty microliters of stream 1 56 or 100 uL of stream 2 66 samples were spread plated onto Luria agar culture plates. The plates were incubated for 24 hours at 37° C., and the number of colonies was counted.
2. HSA Purification Procedure
Pooled normal plasma was diluted one in three with Tris-Borate (TB) running buffer, pH 9.0 and spiked with approximately 4×10′ cells/mL of E. coli. The mixture was placed in stream 1 56 of a separation apparatus 200. Albumin was isolated from platelet free plasma in a one-phase process using the charge of albumin at a pH above its pI and its molecular weight. Thus a cartridge 100 with a 75 kDa cutoff separation membrane 34 and 50 kDa cutoff restriction membranes 30 and 32 was used. The albumin was removed from high molecular weight contaminants by its migration through the separation membrane 34 while small molecular weight contaminants dissipated through the 50 kDa restriction membrane 30. Samples were taken at regular intervals throughout a 90 minutes run.
The presence of the purified HSA in stream 2 was demonstrated by examination by SDS-PAGE. Bacteria were detected as previously described above.
4. Results of IgG, and HSA Purification
The procedures described successfully purified IgG, and albumin as judged by electrophoretic examination. The stream 2 samples containing the purified protein products did not contain detectable E. coli colonies, while stream 1 56 samples produced greatly in excess of 500 colonies/plate.
It is possible to purify proteins such as IgG, albumin and fibrinogen from plasma, while simultaneously removing contaminating virus by the methods according to the present invention.
The present invention has shown to be able to separate or retain spiked prior protein from or in plasma, and thus allows simultaneous removal of prion protein during albumin or IgG purification from plasma.
Evidence has been provided by the present inventors that it is possible to purify proteins such as IgG and albumin from plasma, while simultaneously removing endotoxin contamination in the starting plasma using the separation technology of the present invention.
Furthermore, it has been found that it is also possible to purify proteins such as IgG, and albumin from plasma, while simultaneously removing contaminating bacteria.
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Other features and aspects of this invention will be appreciated by those skilled in the art upon reading and comprehending this disclosure. Such features, aspects, and expected variations and modifications of the reported results and examples are clearly within the scope of the invention where the invention is limited solely by the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| PP7906 | Dec 1999 | AU | national |
This application is a continuation-in-part of application Ser. No. 09/931,342, filed Aug. 16, 2001.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09931342 | Aug 2001 | US |
| Child | 10006241 | Dec 2001 | US |
