Virus elimination during the purification of monoclonal antibodies by column chromatography and additional steps

The theoretical potential for virus transmission by monoclonal antibody based therapeutic products has led to the inclusion of appropriate virus reduction steps. In this study, virus elimination by the chromatographic steps used during the purification process for two (IgG‐1 & ?3) monoclonal antibodies (MAbs) have been investigated. Both the Protein G (>7log) and ion‐exchange (5 log) chromatography steps were very effective for eliminating both enveloped and non‐enveloped viruses over the life‐time of the chromatographic gel. However, the contribution made by the final gel filtration step was more limited, i.e., 3 log. Because these chromatographic columns were recycled between uses, the effectiveness of the column sanitization procedures (guanidinium chloride for protein G or NaOH for ion‐exchange) were tested. By evaluating standard column runs immediately after each virus spiked run, it was possible to directly confirm that there was no cross contamination with virus between column runs (guanidinium chloride or NaOH). To further ensure the virus safety of the product, two specific virus elimination steps have also been included in the process. A solvent/detergent step based on 1% triton X‐100 rapidly inactivating a range of enveloped viruses by >6 log inactivation within 1 min of a 60 min treatment time. Virus removal by virus filtration step was also confirmed to be effective for those viruses of about 50 nm or greater. In conclusion, the combination of these multiple steps ensures a high margin of virus safety for this purification process. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1341–1347, 2014     

Production of human immunodeficiency virus by chronically infected cells grown in protein-free medium.

A human T cell line chronically infected with Human Immunodeficiency Virus (HIV) has been adapted to grow in a chemically defined, protein-free medium. Virus particles are produced at rates comparable to those of serum-supplemented cultures; virus preparations free of undesirable proteins can be produced in preparative amounts by simple ultrafiltration procedures and cell culture supernatants can be used as such for the preparation of ELISA solid phases. This material has been used very conveniently for studies concerning characterization of antibodies against HlV-specific proteins, interaction of HIV with complement components and inclusion of human cell-derived proteins into virions; we propose its use as a powerful tool for the structural as well as functional analysis of the virus particle itself.     

A novel purification strategy for retrovirus gene therapy vectors using heparin affinity chromatography

Membrane separation and chromatographic technologies are regarded as an attractive alternative to conventional academic small-scale ultracentrifugation procedures used for retrovirus purification. However, despite the increasing demands for purified retroviral vector preparations, new chromatography adsorbents with high specificity for the virus have not been reported. Heparin affinity chromatography is presented here as a novel convenient tool for retrovirus purification. The ability of bioactive retroviral particles to specifically bind to heparin ligands immobilized on a chromatographic gel is shown. A purification factor of 63 with a recovery of 61% of functional retroparticles was achieved using this single step. Tentacle heparin affinity supports captured retroviral particles more efficiently than conventional heparin affinity chromatography supports with which a lower recovery was obtained (18%). Intact, infective retroviral particles were recovered by elution with low salt concentrations (350 mM NaCl). Mild conditions for retrovirus elution from chromatographic columns are required to preserve virus infectivity. VSV-G pseudotyped retroviruses have shown to be very sensitive to high ionic strength, losing 50% of their activity and showing membrane damage after a short exposure to 1M NaCl. We also report a complete scaleable downstream processing scheme for the purification of MoMLV-derived vectors that involves sequential microfiltration and ultra/diafiltration steps for virus clarification and concentration respectively, followed by fractionation by heparin affinity chromatography and final polishing by size-exclusion chromatography. Overall, by using this strategy, a 38% yield of infective particles can be achieved with a final purification factor of 2,000.     

Concentration and purification of rubella virus using monolithic chromatographic support

The production of economically acceptable viral vaccines of high quality requires simple and efficient methods for purification and concentration of viral particles. Ion-exchange chromatography (IEC) has become one of commonly used methods for large-scale downstream purification of viruses. Viruses possess different biological and/or biochemical properties and therefore IEC conditions must be established specifically for each virus. Live attenuated rubella virus vaccines have been manufactured and successfully used widely to protect people from rubella and congenital rubella syndrome for almost 40 years. The aim of this study was to search for an efficient method for concentration and purification of rubella virus using IEC. The selected operating conditions using quaternary amine monolithic supports enabled highly efficient binding, purification and concentration of rubella virus from complex biological suspension without additional procedures. Eluted viral particles maintained their infectivity and viral recovery was almost 100%. At the same time, viral preparation was successfully depleted from host cell protein and DNA. This work indicates the possibility of using monoliths to improve the rubella virus yields in productions where high virus titers during cultivation can hardly be achieved.     

Lymphocytic Choriomeningitis virus. I. Concentration and purification of the infectious virus.

Two procedures for the purification of infectious lymphocytic choriomeningitis virus from cell culture fluid have been developed. If large quantities of very pure virus are to be prepared, infected L cells are maintained with a medium supplemented with calf serum, the proteins of which have been largely removed by pretreatment with polyethylene glycol. Two days after infection of the cultures, the media are collected and the virus is concentrated by treatment with polyethylene glycol 40,000. Purification with a 10,000-fold increase of specific infectivity is achieved with steric chromatography on controlled-pore glass beads with pore sizes of 42 to 44 nm and centrifugation in density gradients prepared with amido trizoate. An alternative method begins with precipitation of the virus from infected cell cuture medium with zinc acetate, followed by controlled-pore glass chromatography and density centrifugation in a discontinuous sucrose gradient. Purification thus obtained is 200-fold in terms of specific infectivity.     

Studies of the housefly virus structure and disruption during purification procedures

When purifying preparations of the newly discovered virus from the housefly Musca domestica, the virus particles were rendered undetectable by electron microscopic examination, following attempted separation on density gradients of sucrose prepared in distilled water. When this procedure was repeated using gradients consisting of sucrose in phosphate buffer (pH 7.2), virus fragments were found during E.M. examination of the virus fractions. Ficoll 400 density gradients in phosphate buffer were also used in attempts to purify the virus. These resulted in breakdown of the virus and the production of small virus-like particles, which were interpreted as being the virus nucleoprotein cores. The structures revealed in partially degraded virions during the extraction procedures, with special reference to the second treatment with carbon tetrachloride and subsequent purification procedures, have suggested a possible structure for the virion. From these studies it is emphasized that a proteinaceous middle layer exists between the inner shell and the virus nucleoprotein core.     

Production of viral vectors for gene therapy applications

Advances in cell culture engineering, cell metabolism, bioreactor design and operation, and downstream processing will all positively impact the bioprocessing of viral vectors. Design of appropriate vectors and tailoring of packaging cells to support more productive infections will be of paramount importance for production of high-titer and high-quality vectors. Furthermore, quantitative analysis of the infection parameters during virus propagation, such as time of infection, multiplicity of infection, the length of replication cycle, virus half-life, and burst size, will also be important to the process optimization. Finally, procedures for separation, purification and formulation of vector preparations have to be further developed.     

正辛酸沉淀在单克隆抗体纯化中的工艺优化与应用

为应对治疗性抗体快速增长的市场需求,抗体上游细胞培养规模和表达量水平已显著提高,而下游纯化工艺的生产效率则相对落后,下游处理能力已成为限制抗体产能的瓶颈。本研究以单克隆抗体mab-X为实验材料,优化了细胞培养液、低pH病毒灭活收集液2种模式的正辛酸(caprylic acid,CA)沉淀工艺条件,并研究了CA处理去除聚体、CA处理灭活病毒等2种应用,在小试的基础上,采用低pH病毒灭活收集液CA沉淀的模式进行了500 L细胞培养规模生产放大研究,对沉淀前后的产品质量和收率进行了检测和对比。结果显示,两种模式的CA沉淀均可显著降低宿主细胞蛋白(host cell protein,HCP)残留和聚体含量,在聚体去除实验中CA沉淀可去除约15%的聚体,病毒灭活研究显示CA对逆转录模型病毒具有完全的病毒灭活能力。在放大生产规模中,下游依次进行了深层过滤收获、亲和层析、低pH病毒灭活、CA沉淀及深层过滤、阳离子交换层析,CA沉淀过程中混合时间和搅拌速度显著影响CA沉淀效果,CA沉淀处理后低pH病毒灭活液中的HCP残留量降低了895倍,沉淀后产品纯度和HCP残留均已控制在单克隆抗体质量要求范围内,CA沉淀可以减少传统纯化工艺中的一个精纯步骤。总之,下游工艺中采用CA沉淀,能够精简传统纯化工艺,并完全满足mab-X的纯化质量要求,而且能提高生产效率、降低生产成本。本研究结果将推动CA沉淀在单克隆抗体下游纯化生产中的应用,为解决目前传统纯化工艺的问题提供参考。     

Purification of rabies virus glycoprotein produced in Drosophila melanogaster S2 cells: An efficient immunoaffinity method

Most rabies vaccines are based on inactivated virus, which production process demands a high level of biosafety structures. In the past decades, recombinant rabies virus glycoprotein (RVGP) produced in several expression systems has been extensively studied to be used as an alternative vaccine. The immunogenic characteristics of this protein depend on its correct conformation, which is present only after the correct post-translational modifications, typically performed by animal cells. The main challenge of using this protein as a vaccine candidate is to keep its trimeric conformation after the purification process. We describe here a new immunoaffinity chromatography method using a monoclonal antibody for RVGP Site II for purification of recombinant rabies virus glycoprotein expressed on the membrane of Drosophila melanogaster S2 cells. RVGP recovery achieved at least 93%, and characterization analysis showed that the main antigenic proprieties were preserved after purification.     

Suitability of a generic virus safety evaluation for monoclonal antibody investigational new drug applications

Biologics produced from CHO cell lines with endogenous virus DNA can produce retrovirus-like particles in cell culture at high titers, and other adventitious viruses can find their way through raw materials into the process to make a product. Therefore, it is the industry standard to have controls to avoid introduction of viruses into the production process, to test for the presence of viral particles in unclarified cell culture, and to develop purification procedures to ensure that manufacturing processes are robust for viral clearance. Data have been accumulated over the past four decades on unit operations that can inactivate and clear adventitious virus and provide a high degree of assurance for patient safety. During clinical development, biological products are traditionally tested at process set points for viral clearance. However, the widespread implementation of platform production processes to produce highly similar IgG antibodies for many indications makes it possible to leverage historical data and knowledge from representative molecules to allow for better understanding and control of virus safety. More recently, individualized viral clearance studies are becoming the rate-limiting step in getting new antibody molecules to clinic, particularly in Phase 0 and eIND situations. Here, we explore considerations for application of a generic platform virus clearance strategy that can be applied for relevant investigational antibodies within defined operational parameters in order to increase speed to the clinic and reduce validation costs while providing a better understanding and assurance of process virus safety.     

Extra- and Intracellular Laccases of the Chestnut Blight Fungus, Cryphonectria parasitica

A double-stranded RNA virus of the chestnut blight pathogen, Cryphonectria parasitica, has been shown previously to reduce accumulation of mRNAs of extracellular laccase (laccase A) produced by this fungus. Both extra- and intracellular laccases have been detected after growth of the fungus in liquid culture. In addition to cellular localization, the two laccases are distinguishable by time of appearance during growth and electrophoretic mobility. Laccase A was purified from the culture filtrate by standard protein purification procedures. The enzyme was characterized as a glycoprotein with a molecular mass of approximately 77 kDa. Both laccase A and laccase B activities were significantly reduced in the hypovirulent (double-stranded RNA-infected) strain UEP1 compared with the isogenic virulent (double-stranded RNA-free) strain EP155/2.     

Development of a platform process for adenovirus purification that removes human set and nucleolin and provides high purity vector for gene delivery

The manufacturing of virus occurs at a modest scale in comparison to many therapeutic proteins mainly because a gene therapy dose is typically only µg of vector. Although modest in scale the generation of high purity virus is challenging due to low viral expression levels and the difficulties in adequately characterizing such a large and complex molecule. A 100 L bioreactor might produce only 100 mg of virus that must be separated from host and process impurities that are typically greater by several orders of magnitude. Furthermore, in the later purification stages the main milieu component is often virus at low concentration (µg/mL) which may non‐specifically adsorb to purification surfaces resulting in a lowered virus recovery. This study describes our approach to develop a scalable, manufacturable robust process for an Adenovirus (Ad) gene therapy vector. A number of analytical tools were developed to guide the purification design. During process development, two human proteins, SET and nucleolin, were identified in viral preparations. To our knowledge, this is the first time that SET and nucleolin have been described in Ad. In this report we detail a process for their removal and the robust removal of all process, product and host cell impurities. Biotechnol. Bioeng. 2013; 110: 848–856. © 2012 Wiley Periodicals, Inc.     

Purification of murine oncornaviral phosphoproteins using alkyl agarose derivatives..

Methods for the purification of both murine mammary tumor (type B) and murine leukemia (type C) oncornaviral phosphoproteins are described, in which chromatography on alkyl-agarose derivatives is used as the primary fractionation step. Gel filtration or ion exchange chromatography on phosphocellulose was the only subsequent step required for the purification of the type B and type C viral proteins, respectively. The two-step protocols also resulted in the co-purification of a low molecular weight core protein from each virus. Recoveries of the viral proteins purified by this method, based on per cent contribution of individual polypeptides to total virion proteins, were 70% or greater. Radioimmunocompetition analysis of the purified murine mammary tumor virus major core protein as well as analysis of the RNA binding properties of purified low molecular weight type C virus proteins suggests that neither antigenic reactivity nor specific RNA binding characteristics are altered by the purification protocols. The availability of these procedures should aid studies on the possible function and immunochemical properties of the native murine oncornaviral phosphoproteins and may also be extended to the purification of other oncornaviral proteins.     

Virus elimination during the recycling of chromatographic columns used during the manufacture of coagulation factors

Various chromatographic procedures are used during the purification and manufacture of plasma products such as coagulation factors. These steps contribute to the overall safety of such products by removing potential virus contamination. Virus removal by two affinity chromatography procedures, i.e. monoclonal antibody chromatography and metal chelate chromatography (immobilised metal ion affinity chromatography), used during the manufacture of the high purity factor VIII (Replenate^®) and factor IX (Replenine^®-VF), respectively, has been investigated. In addition, as these columns are recycled after use, the effectiveness of the sanitisation procedures for preventing possible cross-contamination, has also been investigated.Both chromatographic steps proved effective for eliminating a range of model enveloped and non-enveloped viruses by 4 to >6 and 5 to >8 log for the monoclonal and metal chelate columns, respectively. The effectiveness of the relatively mild column sanitisation conditions used, i.e. ethanol for factor IX and acetic acid for factor VIII, was confirmed using non-spiked column runs. The chemicals used contributed to virus elimination by inactivation and/or by physical removal of the virus. In summary, these studies demonstrate that potential virus contamination between chromatographic runs can be prevented when an effective column recycling and sanitisation procedure is included.     

The purification of alphavirus virions and subviral particles using ultrafiltration and gel exclusion chromatography

Conventional methods of virus purification using ultracentrifugation frequently result in distorted particles with low levels of biological activity, and are thus unsuitable for preparing samples for high-resolution techniques such as neutron scattering, X-ray scattering in solution, and X-ray crystallography. Moreover, in the event of an instrument failure, ultracentrifugation can also pose a significant hazard when preparing pathogenic viruses or subunits derived from them. By employing exclusively ultrafiltration and gel exclusion chromatography, a method has been developed to prepare highly purified, intact alphavirus particles retaining high levels of biological activity. These procedures have also been adapted to prepare aggregates of viral envelope protein with a defined immunogenic content.     

Purification process monitoring in monoclonal antibody preparation: contamination with viruses, DNA and peptide growth factors.

Administration in vivo of monoclonal antibodies to humans is challenged by considerations regarding their safety. Contamination with viruses, potentially oncogenic nucleic acids and biologically active components like growth factors and hormones forms a serious point of concern in this respect. We have investigated the potential risk of viral contamination by measuring the reduction of 12 different viruses (after spiking) in the standard downstream purification process of ascitic fluid. Depending on the type of virus added and the purification step employed, the reduction of infectious virus particles varies considerably. The overall reduction ranges from about 10(3), observed for a member of the family of Papovaviridae, to more than 10(12) for members of the families of Herpesviridae and Orthomyxoviridae. Using hybridization analysis with a mouse (genomic) DNA probe, we show that the amount of residual DNA in ascitic fluids may also vary considerably, ranging from 75 ng/ml to 1 microgram/ml. In crude preparations produced in cell culture, much lower DNA concentrations are found (0.3 ng/ml). When standard downstream purification procedures are applied to ascitic fluid, a significant reduction of residual DNA levels is observed in the purified monoclonal antibody preparations and in intermediate fractions. The overall reduction factors vary from about 10(3) to 10(4), which is also confirmed by spiking experiments with either purified DNA or crude chromatin-like DNA. Using in-vitro cellular assays, we further show that peptide growth factors like PDGF and TGF beta are present in considerable amounts in ascitic fluids. The observed biological activities, however, are completely eliminated during the purification steps applied.     

Production of high titre disabled infectious single cycle (DISC) HSV from a microcarrier culture

Disabled Infectious Single Cycle (DISC) HSV-2 has been cultured in the complimentary cell line CR2 to provide high titre bulk material suitable for the purification of the virus as a live viral vaccine. CR2 cells are cultured on the microcarrier Cytodex-1 at 5 g l-1 in small scale (1 l) and larger scale (15 l) reactors. The cells are infected at an MOI of 0.01 pfu cell-1 and the culture harvested 60–72 h later. The infected cells are removed from the microcarriers by the addition of a hypotonic saline and the virus released by low-pressure disruption techniques. Virus titres achieved are compared to the standard roller bottle process. The resulting material is the starting point for the purification of the DISC-HSV virus. This revised version was published online in July 2006 with corrections to the Cover Date.     

Purify First: rapid expression and purification of proteins from XMRV

Purifying proteins from recombinant sources is often difficult, time-consuming, and costly. We have recently instituted a series of improvements in our protein purification pipeline that allows much more accurate choice of expression host and conditions and purification protocols. The key elements are parallel cloning, small scale parallel expression and lysate preparation, and small scale parallel protein purification. Compared to analyzing expression data only, results from multiple small scale protein purifications predict success at scale-up with greatly improved reliability. Using these new procedures we purified eight of nine proteins from xenotropic murine leukemia virus-related virus (XMRV) on the first attempt at large scale.