The agony of choice: Impact of the host animal species on the enzyme-linked immunosorbent assay performance for host cell protein quantification.

Host cell proteins (HCPs) are inevitable process-related impurities in biotherapeutics commonly monitored by enzyme-linked immunosorbent assays (ELISAs). Of particular importance for their reliable detection are the anti-HCP polyclonal antibodies (pAbs), supposed to detect a broad range of HCPs. The present study focuses on the identification of suitable host animal species for the development of high-performance CHO-HCP ELISAs, assuming the generation of pAbs with adequate coverage and specificity. Hence, antibodies derived from immunization of sheep, goats, donkeys, rabbits, and chickens were compared concerning their amount of HCP-specific antibodies, coverage, and performance in a sandwich ELISA. Immunization of sheep, goats, donkeys, and rabbits met all test criteria, whereas the antibodies from chickens cannot be recommended based on the results of this study. Additionally, a mixture of antibodies from the five host species was prepared to assess if coverage and ELISA performance can be improved by a multispecies approach. Comparable results were obtained for the single- and multispecies ELISAs in different in-process samples, indicating no substantial improvement for the latter in ELISA performance while raising ethical and financial concerns.

Best practices on critical reagent characterization, qualification, and life cycle management for HCP immunoassays.

The performance of immunoassays for the detection and quantification of host-cell proteins (HCPs) in biopharmaceuticals depends on the quality of the critical assay reagents. Not only their preparation, but also a stringent life-cycle management, including reagent qualification, requalification, and replacement, plays a crucial role in ensuring consistent and reliable results. To provide a cross-industry perspective on HCP reagent management, we conducted a survey on common practices among several pharmaceutical and biotech companies. Based on its outcome, as well as informed by a corresponding roundtable session ("Managing critical reagents over time") at the BioPharmaceutical Emerging Best Practices Association HCP conference in 2019, this study presents specific recommendations and proven concepts to support immunoassay reagent management for monitoring HCPs.

Questioning coverage values determined by 2D western blots: A critical study on the characterization of anti-HCP ELISA reagents.

Host cell proteins (HCPs) constitute a major class of process-related impurities, whose substantial clearance must be demonstrated by suitable analytical methods to warrant product quality and reduce potential safety risks for patients. In this regard, enzyme linked immunosorbent assays (ELISAs), which primarily rely on the quality of the HCP reference standard (immunogen) and HCP-specific polyclonal antibodies, are considered the gold standard for HCP monitoring. For the qualification of the employed antibodies, two-dimensional (2D) western blots (2D-WBs) are the preferred technique to determine the coverage, though a number of practical constraints are well recognized. By using several orthogonal approaches, such as affinity-based mass spectrometry and indirect ELISA, the present study revealed potential detection gaps (i.e., noncovered HCPs) of conventional 2D-WBs, which can be primarily attributed to two different root causes: (i) low amounts of proteins or antibodies being unable to overcome the detection limit and (ii) western blot artifacts due to the loss of conformational epitopes through protein denaturation hindering HCP-antibody recognition. In contrast, the lack of specific antibodies against certain (particularly, low molecular weight) HCPs, as proposed in previous studies, seems to play only a minor role. Together, these findings imply that CHO-HCP ELISA antibodies are better than qualification studies by 2D-WBs indicate.

A fast and sensitive high-throughput assay to assess polysorbate-degrading hydrolytic activity in biopharmaceuticals.

Hydrolysis of polysorbate in biopharmaceutical products has been ascribed to the enzymatic activity from trace levels of residual host cell proteins. In recent years, significant efforts to identify the causative enzymes typically used elaborate, material-intensive and time-consuming approaches. Therefore, the lack of fast and sensitive assays to monitor their activity remains a major bottleneck for supporting process optimization and troubleshooting activities where time and sample throughput are crucial constraints. To address this bottleneck, we developed a novel Electrochemiluminescence-based Polysorbase Activity (EPA) assay to measure hydrolytic activities in biotherapeutics throughout the drug substance manufacturing process. By combining the favorable features of an in-house designed surrogate substrate with a well-established detection platform, the method yields fast (∼36 h turnaround time) and highly sensitive readouts compatible with high-throughput testing. The assay capability for detecting substrate conversion in a precise and reliable manner was demonstrated by extensive qualification studies and by employing a number of recombinant hydrolases associated with polysorbate hydrolysis. In addition, high assay sensitivity and wide applicability were confirmed for in-process pool samples of three different antibody products by performing a head-to-head comparison between this method and an established liquid chromatography - mass spectrometry based assay for the quantification of free fatty acids. Overall, our results suggest that this new approach is well-suited to resolve differences in hydrolytic activity through all stages of purification.

Toward optimal clearance: A universal affinity-based mass spectrometry approach for comprehensive ELISA reagent coverage evaluation and HCP hitchhiker analysis.

In the control strategy for process related impurities in biopharmaceuticals, the enzyme linked immunosorbent assay (ELISA) is the method of choice for the quantification of host cell proteins (HCPs). Besides two dimensional-western blots (2D-WB), the coverage of ELISA antibodies is increasingly evaluated by affinity purification-based liquid chromatography-tandem mass spectrometry (AP-MS) methods. However, all these methods face the problem of unspecific binding issues between antibodies and the matrix, involving the application of arbitrarily defined thresholds during data evaluation. To solve this, a new approach (optimized AP-MS) was developed in this study, for which a cleavable linker was conjugated to the ELISA antibodies enabling the subsequent isolation of specifically interacting HCPs. By comparing both approaches in terms of method variability and the number of false positive or negative hits, we could demonstrate that the optimized AP-MS method is very reproducible and superior in the identification of antibody detection gaps, while previously described strategies suffered from over- or underestimating the coverage. As only antibody associated HCPs were identified, we demonstrated that the method is beneficial for hitchhiker analysis. Overall, the method described herein has proven as a powerful tool for reliable coverage determination of ELISA antibodies, without the need to arbitrarily exclude HCPs during the coverage evaluation.

HIV-1, HCV and HBV seronegative window reduction by the new Roche cobas TaqScreen MPX test in seroconverting donors.

BACKGROUND: By shortening the pre-seroconversion window in the viral screening of donated blood, nucleic acid amplification testing greatly improves safety and efficiency, particularly when combined with multiple target detection and maximal automation. OBJECTIVES: Evaluation of seronegative window reduction during HIV-1, HCV and HBV infection by the novel cobas TaqScreen MPX test for simultaneous nucleic acid detection of HIV-1 (groups M and O), HIV-2, HCV and HBV using the cobas s 201 system. STUDY DESIGN: Testing of HIV-1, HCV, and HBV seroconversion panels (20 each) using the cobas TaqScreen MPX test versus reference immuno- and nucleic acid technology assays. RESULTS: The cobas TaqScreen MPX test detected HIV-1 and HCV infection earlier than immunoassays in 20/20 and 19/20 panels, and HBV DNA earlier than or on the same day as HBsAg in 19/20 and 18/20 panels, and later in 1 and 2 panels on neat samples and 1:6 dilutions. Pre-seroconversion sensitivity exceeded that of COBAS AmpliScreen testing in pools of 24. CONCLUSION: The cobas TaqScreen MPX test shortens the pre-seroconversion window in minipools of six, evidencing high sensitivity, and significantly enhances blood-screening efficiency by the simultaneous automated detection of multiple viruses in a single test.

Assessment of chemical modifications of sites in the CDRs of recombinant antibodies: Susceptibility vs. functionality of critical quality attributes.

Modifications like asparagine deamidation, aspartate isomerization, methionine oxidation, and lysine glycation are typical degradations for recombinant antibodies. For the identification and functional evaluation of antibody critical quality attributes (CQAs) derived from chemical modifications in the complementary-determining regions (CDRs) and the conserved regions, an approach employing specific stress conditions, elevated temperatures, pH, oxidizing agents, and forced glycation with glucose incubation, was applied. The application of the specific stress conditions combined with ion exchange chromatography, proteolytic peptide mapping, quantitative liquid chromatography mass spectrometry, and functional evaluation by surface plasmon resonance analysis was adequate to identify and functionally assess chemical modification sites in the CDRs of a recombinant IgG1. LC-Met-4, LC-Asn-30/31, LC-Asn-92, HC-Met-100c, and HC Lys-33 were identified as potential CQAs. However, none of the assessed degradation products led to a complete loss of functionality if only one light or heavy chain of the native antibody was affected.

Identification and monitoring of host cell proteins by mass spectrometry combined with high performance immunochemistry testing.

Biotherapeutics are often produced in non-human host cells like Escherichia coli, yeast, and various mammalian cell lines. A major focus of any therapeutic protein purification process is to reduce host cell proteins to an acceptable low level. In this study, various E. coli host cell proteins were identified at different purifications steps by HPLC fractionation, SDS-PAGE analysis, and tryptic peptide mapping combined with online liquid chromatography mass spectrometry (LC-MS). However, no host cell proteins could be verified by direct LC-MS analysis of final drug substance material. In contrast, the application of affinity enrichment chromatography prior to comprehensive LC-MS was adequate to identify several low abundant host cell proteins at the final drug substance level. Bacterial alkaline phosphatase (BAP) was identified as being the most abundant host cell protein at several purification steps. Thus, we firstly established two different assays for enzymatic and immunological BAP monitoring using the cobas® technology. By using this strategy we were able to demonstrate an almost complete removal of BAP enzymatic activity by the established therapeutic protein purification process. In summary, the impact of fermentation, purification, and formulation conditions on host cell protein removal and biological activity can be conducted by monitoring process-specific host cell proteins in a GMP-compatible and high-throughput (> 1000 samples/day) manner.

Simultaneous assessment of Asp isomerization and Asn deamidation in recombinant antibodies by LC-MS following incubation at elevated temperatures.

The degradation of proteins by asparagine deamidation and aspartate isomerization is one of several chemical degradation pathways for recombinant antibodies. In this study, we have identified two solvent accessible degradation sites (light chain aspartate-56 and heavy chain aspartate-99/101) in the complementary-determining regions of a recombinant IgG1 antibody susceptible to isomerization under elevated temperature conditions. For both hot-spots, the degree of isomerization was found to be significantly higher than the deamidation of asparagine-(387, 392, 393) in the conserved CH3 region, which has been identified as being solvent accessible and sensitive to chemical degradation in previous studies. In order to reduce the time for simultaneous identification and functional evaluation of potential asparagine deamidation and aspartate isomerization sites, a test system employing accelerated temperature conditions and proteolytic peptide mapping combined with quantitative UPLC-MS was developed. This method occupies the formulation buffer system histidine/HCl (20 mM; pH 6.0) for denaturation/reduction/digestion and eliminates the alkylation step. The achieved degree of asparagine deamidation and aspartate isomerization was adequate to identify the functional consequence by binding studies. In summary, the here presented approach greatly facilitates the evaluation of fermentation, purification, formulation, and storage conditions on antibody asparagine deamidation and aspartate isomerization by monitoring susceptible marker peptides located in the complementary-determining regions of recombinant antibodies.

Nuclease-resistant single-stranded DNA controls for nucleic acid amplification assays.

Molecular diagnostic tests based on the PCR or alternative nucleic acid amplification technologies are commonly used for pathogen screening at blood drawing centers. Contrived process surveillance using test-specific external and internal controls is critical for the efficient leverage of PCR power. We describe here novel control constructs for use in nucleic acid amplification assays for pathogens with a single-stranded DNA genome, e.g., parvovirus B19. These controls are derived from a deletion mutant of the filamentous phage fd-tet, fKN16, and consist of single-stranded DNA packaged in a protein coat. They are essentially noninfectious to Escherichia coli and highly resistant to nuclease degradation. fKN16 based controls can be readily manufactured and highly purified. Despite their confirmed filamentous morphology, they can be precisely and accurately diluted over a wide range. Stability studies reveal that the novel control constructs are highly resistant to temperature stress, regardless of whether they are tested as concentrated stocks in storage buffer or diluted in buffer or human plasma. Real-time amplification curves derived from recombinant control constructs containing a parvovirus B19 specific sequence fragment match those derived from native virus. In summary, our data demonstrate the feasibility of novel nuclease-resistant single-stranded DNA controls as surrogates for parvovirus B19 and their applicability in routine molecular diagnostics.