Scale-Up of Protein Purification: Downstream Processing Issues

Continuous background correction of refractive index signal to improve monoclonal antibody concentration monitoring during UF/DF and SPTFF operations

Inline refractive index (RI) has the potential for monitoring protein concentration during final bulk concentration. While useful for monitoring and controlling product concentration, RI is sensitive to the respective background buffer being used for processing. This raises concerns around variations in buffer preparations, and during diafiltration where the buffer background is a mixture of different buffers during exchange. This study evaluated whether the use of a RI probe in the permeate line could facilitate continuous background subtraction (dual RI) and improve concentration monitoring during ultrafiltration/diafiltration and single pass TFF concentration for IgG1 and IgG4 antibodies. The proposed dual RI strategy yielded reductions in % error compared to the use of a single refractive index estimate from the retentate line (6.18% vs 8.63% for IgG4 and 2.65% vs 8.85% for IgG1) during traditional ultrafiltration/diafiltration. The improvement in IgG estimates were best during diafiltration where the continuous background subtraction of the permeate RI-enabled continuous monitoring of antibody material without knowledge of what the background buffer was compared to the use of a single RI estimate (6.47% vs 10.79% for IgG4 and 3.29% vs 19.59% for IgG1). In contrast minimal improvement to accuracy was obtained when using SPTFF as a concentration step. The ability to monitor product concentration changes via the proposed dual RI approach removes the need for complex calibrations, minimal worry about changing buffer backgrounds during diafiltration, and could enable better process control during product concentration in the cGMP manufacture of biologics.

Production and purification of Clostridium perfringens type D epsilon toxin and IgY antitoxin

The aim of this study was to purify Clostridium perfringens type D epsilon toxin and produce and purify anti-epsilon chicken immunoglobulin Y (IgY). A single-step ion exchange chromatography resulted in a high-yield and high-purity toxin, while ion exchange chromatography followed by gel filtration resulted in the highest purity of the toxin, but at a lower yield. Purified and inactivated epsilon toxin were then administered in chickens via four inoculations and IgY was obtained at a high purity and yield, with an antibody titer of 50 IU/mL and high levels of avidity (73.2%). In summary, C. perfringens type D epsilon toxin and chicken anti-epsilon IgY were successfully produced and purified, and may be used for the diagnosis of enterotoxemia caused by the epsilon toxin, as well as in potency tests of existing and future vaccines against enterotoxemia.

A review of solvent freeze-out technology for protein crystallization

In this review, we summarize important advances in solvent freeze-out (SFO) technology for protein crystallization, including the background of SFO, its fundamental principle, and some crucial conditions and factors for optimizing SFO technology.

Opportunities and challenges of the tag-assisted protein purification techniques: Applications in the pharmaceutical industry

Tag-assisted protein purification is a method of choice for both academic researches and large-scale industrial demands. Application of the purification tags in the protein production process can help to save time and cost, but the design and application of tagged fusion proteins are challenging. An appropriate tagging strategy must provide sufficient expression yield and high purity for the final protein products while preserving their native structure and function. Thanks to the recent advances in the bioinformatics and emergence of high-throughput techniques (e.g. SEREX), many new tags are introduced to the market. A variety of interfering and non-interfering tags have currently broadened their application scope beyond the traditional use as a simple purification tool. They can take part in many biochemical and analytical features and act as solubility and protein expression enhancers, probe tracker for online visualization, detectors of post-translational modifications, and carrier-driven tags. Given the variability and growing number of the purification tags, here we reviewed the protein- and peptide-structured purification tags used in the affinity, ion-exchange, reverse phase, and immobilized metal ion affinity chromatographies. We highlighted the demand for purification tags in the pharmaceutical industry and discussed the impact of self-cleavable tags, aggregating tags, and nanotechnology on both the column-based and column-free purification techniques.

Multiplex secretome engineering enhances recombinant protein production and purity

Host cell proteins (HCPs) are process-related impurities generated during biotherapeutic protein production. HCPs can be problematic if they pose a significant metabolic demand, degrade product quality, or contaminate the final product. Here, we present an effort to create a "clean" Chinese hamster ovary (CHO) cell by disrupting multiple genes to eliminate HCPs. Using a model of CHO cell protein secretion, we predict that the elimination of unnecessary HCPs could have a non-negligible impact on protein production. We analyze the HCP content of 6-protein, 11-protein, and 14-protein knockout clones. These cell lines exhibit a substantial reduction in total HCP content (40%-70%). We also observe higher productivity and improved growth characteristics in specific clones. The reduced HCP content facilitates purification of a monoclonal antibody. Thus, substantial improvements can be made in protein titer and purity through large-scale HCP deletion, providing an avenue to increased quality and affordability of high-value biopharmaceuticals.

Attenuated total reflection fourier transform infrared spectroscopy based methods for identification of chromatography media formulations used in downstream processes

Chromatographic media play a crucial role in the downstream processing of biotechnology products. The physical and chemical properties of these processing aids are mostly monitored by expensive and time-consuming preparative tests, but spectroscopic techniques may also be used to measure chromatographic media samples. In this study, chromatographic media formulations used in downstream processes were investigated using attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy. Samples were measured both in original suspension form and after drying to examine the possibilities of a potential spectroscopic method without sample preparation. Principal component analysis (PCA) was employed to identify the spectral differences among the formulations with distinct support matrices and functional groups and soft independent modeling of class analogy (SIMCA) was performed to creating classification models for identification of chromatography media. To increase the number of samples in the SIMCA, simulated spectra were generated based on the experimental spectra. PCA models indicated that spectra of samples in original suspension form and after drying contained similar information about the chemical properties of chromatographic media samples. Moreover, during the classification of spectra based on SIMCA, both measurement techniques gave high sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) results. These results show that ATR FT-IR could be applied as a simple alternative method for monitoring the chromatography media samples. This technique is also feasible without sample preparation. Thereby the multi-hours drying steps may be omitted, the measurements can be performed in a few minutes, and the potential effects of sample preparations can be eliminated.

Proteomics as a tool for live attenuated influenza vaccine characterisation

Many viral vaccines, including the majority of influenza vaccines, are grown in embryonated chicken eggs and purified by sucrose gradient ultracentrifugation. For influenza vaccines this process is well established, but the viral strains recommended for use in vaccines are updated frequently. As viral strains can have different growth properties and responses to purification, these updates risk changes in the composition of the vaccine product. Changes of this sort are hard to assess, as influenza virions are complex structures containing variable ratios of both viral and host proteins. To address this, we used liquid chromatography and tandem mass spectrometry (LC-MS/MS), a flexible and sensitive method ideally suited to identifying and quantifying the proteins present in complex mixtures. By applying LC-MS/MS to the pilot scale manufacturing process of the live attenuated influenza vaccine (LAIV) FluMist® Quadrivalent vaccine (AstraZeneca), we were able to obtain a detailed description of how viral and host proteins are removed or retained at each stage of LAIV purification. LC-MS/MS allowed us to quantify the removal of individual host proteins at each stage of the purification process, confirming that LAIV purification efficiently depletes the majority of host proteins and identifying the small subset of host proteins which are associated with intact virions. LC-MS/MS also identified substantial differences in the retention of the immunosuppressive viral protein NS1 in purified virions. Finally, LC-MS/MS allowed us to detect subtle variations in the LAIV production process, both upstream of purification and during downstream purification stages. This demonstrates the potential utility of LC-MS/MS for optimising the purification of complex biological mixtures and shows that it is a promising approach for process optimisation in a wide variety of vaccine manufacturing platforms.

Purification of common light chain IgG-like bispecific antibodies using highly linear pH gradients

Monovalent bispecific antibodies (BsAbs) are projected to have broad clinical applications due to their ability to bind two different targets simultaneously. Although they can be produced using recombinant technologies, the correct pairing of heavy and light chains is a significant manufacturing problem. Various approaches exploit mutations or linkers to favor the formation of the desired BsAb, but a format using a single common light chain has the advantage that no other modification to the antibody is required. This strategy reduces the number of formed molecules to three (the BsAb and the two parent mAbs), but the separation of the BsAb from the two monovalent parent molecules still poses a potentially difficult purification challenge. Current methods employ ion exchange chromatography and linear salt gradients, but are only successful if the difference in the observed isoelectric points (pIs) of two parent molecules is relatively large. Here, we describe the use of highly linear pH gradients for the facile purification of common light chain BsAbs. The method is effective at separating molecules with differences in pI as little as 0.10, and differing in their sequence by only a single charged amino acid. We also demonstrate that purification resins validated for manufacturing are compatible with this approach.