A Novel, Q-PCR Based Approach to Measuring Endogenous Retroviral Clearance by Capture Protein A Chromatography

The prevention of an anomalous chromatographic behavior and the resulting successful removal of viruses from monoclonal antibody with an asymmetric charge distribution by using a membrane adsorber in highly efficient, anion-exchange chromatography in flow-through mode

Anion exchange (AEX) chromatography in the flow-through mode is a widely employed purification process for removal of process/product-related impurities and exogenous/endogenous viruses from monoclonal antibodies (mAbs). The pH of the mobile phase for AEX chromatography is typically set at half a unit below the isoelectric point (pI) of each mAb (i.e., pI - 0.5) or lower and, in combination with a low ionic strength, these conditions are usually satisfactory for both the recovery of the mAb and removal of impurities. However, we have recently encountered a tight binding of mAb1 to AEX resins under these standard chromatographic conditions. This anomalous adsorption behavior appears to be an effect of the asymmetric charge distribution on the surface of the mAb1. We found that mAb1 did not bind to the AEX resins if the mobile phase has a much lower pH and higher ionic strength, but those conditions would not allow adequate virus removal. We predicted that the use of membrane adsorbers might provide effective mAb1 purification, since the supporting matrix has a network structure that would be less susceptible to interactions with the asymmetric charge distribution on the protein surface. We tested the Natriflo HD-Q AEX membrane adsorber under standard chromatographic conditions and found that mAb1 flowed through the membrane adsorber, resulting in successful separation from murine leukemia virus. This AEX membrane adsorber is expected to be useful for process development because mAbs can be purified under similar standard chromatographic conditions regardless of their charge distributions.

Cation exchange chromatography performed in overloaded mode is effective in removing viruses during the manufacturing of monoclonal antibodies

Viral safety is a critical concern with regard to monoclonal antibody (mAb) products produced in mammalian cells such as Chinese hamster ovary cells. Manufacturers are required to ensure the safety of such products by validating the clearance of viruses in downstream purification steps. Cation exchange (CEX) chromatography is widely used in bind/elute mode as a polishing step in mAb purification. However, bind/elute modes require a large volume of expensive resin. To reduce the production cost, the use of CEX chromatography in overloaded mode has recently been investigated. The viral clearance ability in overloaded mode was evaluated using murine leukemia virus (MLV). Even under high-load conditions such as 2,000 g mAb/L resin, MLV was removed from mAb solutions. This viral clearance ability was not significantly affected by resin type or mAb type. The overloaded mode can also remove other types of viruses such as pseudorabies virus and reovirus Type 3 from mAb solutions. Based on these results, this cost-effective overloaded mode is comparable to the bind-elute mode in terms of viral removal.

Integrated viral clearance strategies-reflecting on the present, projecting to the future

Viral clearance and inactivation are critical steps in ensuring the safety of biological products derived from mammalian cell culture and are a component of an adventitious agent control strategy which spans both upstream and downstream processes. Although these approaches have been sufficient to support the development of biologics to date, the empirical and semi-quantitative nature of the approach leaves some potential gaps. For example, the concept of performing a quantitative risk assessment for the downstream components of virus safety was introduced in ICH Q5A for XMuLV. An ideal future state would be to perform a similar quantitative risk assessment for a range of viruses based on an assessment of potential virus risk in both upstream and downstream processes. This assessment combined with an integrated control strategy (including monitoring) would be extremely beneficial in minimizing potential adventitious agent risks. Significant progress has been achieved towards this goal in the last several years including recent advances in quantification of virus sequences in cell banks (ADVTIG), development of truly modular or generic viral clearance claims for specific unit operations, enhanced controls of upstream media (HTST/nanofiltration) and the use of RVLP for in-process monitoring. The recent shift towards continuous processing has the potential to enhance the criticality of in-line monitoring and the complexity of viral clearance and inactivation (owing to a wide range of potential 'worst case' viral clearance scenarios). However, gaps exist in, firstly, the ability to quantify potential virus risk levels in process streams in real-time, secondly, mechanistic understanding of virus/chromatography media interactions, and thirdly, mechanistic understanding of virus/filter interactions. Some new technologies may also need to be developed to allow for real-time confirmation of virus inactivation and clearance to support process development (both batch and continuous) and assessment of the impact of process deviations during manufacturing. This review paper provides an overview of the current state of an overall integrated control strategy for upstream and downstream processing and highlights the investments that could be pursued to achieve the future state of a quantitative virus risk assessment for a range of viruses. One potential approach to address these gaps is the use of data mining from large, comprehensive and diverse data sets to establish heuristic rules for virus detection, clearance and inactivation followed by specific hypothesis-driven experiments for cases that fall outside of the normal paradigm. Once this approach reaches a mature state suitable for implementation, there is an opportunity to update regulatory guidance (e.g. ICH Q5A) accordingly.

Mechanistic evaluation of virus clearance by depth filtration

Virus clearance by depth filtration has not been well-understood mechanistically due to lack of quantitative data on filter charge characteristics and absence of systematic studies. It is generally believed that both electrostatic interactions and sized based mechanical entrapment contribute to virus clearance by depth filtration. In order to establish whether the effectiveness of virus clearance correlates with the charge characteristics of a given depth filter, a counter-ion displacement technique was employed to determine the ionic capacity for several depth filters. Two depth filters (Millipore B1HC and X0HC) with significant differences in ionic capacities were selected and evaluated for their ability to eliminate viruses. The high ionic capacity X0HC filter showed complete porcine parvovirus (PPV) clearance (eliminating the spiked viruses to below the limit of detection) under low conductivity conditions (≤2.5 mS/cm), achieving a log10 reduction factor (LRF) of > 4.8. On the other hand, the low ionic capacity B1HC filter achieved only ∼2.1-3.0 LRF of PPV clearance under the same conditions. These results indicate that parvovirus clearance by these two depth filters are mainly achieved via electrostatic interactions between the filters and PPV. When much larger xenotropic murine leukemia virus (XMuLV) was used as the model virus, complete retrovirus clearance was obtained under all conditions evaluated for both depth filters, suggesting the involvement of mechanisms other than just electrostatic interactions in XMuLV clearance.

Quality by design approach for viral clearance by protein a chromatography

Protein A chromatography is widely used as a capture step in monoclonal antibody (mAb) purification processes. Antibodies and Fc fusion proteins can be efficiently purified from the majority of other complex components in harvested cell culture fluid (HCCF). Protein A chromatography is also capable of removing modest levels of viruses and is often validated for viral clearance. Historical data mining of Genentech and FDA/CDER databases systematically evaluated the removal of model viruses by Protein A chromatography. First, we found that for each model virus, removal by Protein A chromatography varies significantly across mAbs, while remains consistent within a specific mAb product, even across the acceptable ranges of the process parameters. In addition, our analysis revealed a correlation between retrovirus and parvovirus removal, with retrovirus data generally possessing a greater clearance factor. Finally, we describe a multivariate approach used to evaluate process parameter impacts on viral clearance, based on the levels of retrovirus-like particles (RVLP) present among process characterization study samples. It was shown that RVLP removal by Protein A is robust, that is, parameter effects were not observed across the ranges tested. Robustness of RVLP removal by Protein A also correlates with that for other model viruses such as X-MuLV, MMV, and SV40. The data supports that evaluating RVLP removal using process characterization study samples can establish multivariate acceptable ranges for virus removal by the protein A step for QbD. By measuring RVLP instead of a model retrovirus, it may alleviate some of the technical and economic challenges associated with performing large, design-of-experiment (DoE)-type virus spiking studies. This approach could also serve to provide useful insight when designing strategies to ensure viral safety in the manufacturing of a biopharmaceutical product.

Phylogeny-directed search for murine leukemia virus-like retroviruses in vertebrate genomes and in patients suffering from myalgic encephalomyelitis/chronic fatigue syndrome and prostate cancer

Gammaretrovirus-like sequences occur in most vertebrate genomes. Murine Leukemia Virus (MLV) like retroviruses (MLLVs) are a subset, which may be pathogenic and spread cross-species. Retroviruses highly similar to MLLVs (xenotropic murine retrovirus related virus (XMRV) and Human Mouse retrovirus-like RetroViruses (HMRVs)) reported from patients suffering from prostate cancer (PC) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) raise the possibility that also humans have been infected. Structurally intact, potentially infectious MLLVs occur in the genomes of some mammals, especially mouse. Mouse MLLVs contain three major groups. One, MERV G3, contained MLVs and XMRV/HMRV. Its presence in mouse DNA, and the abundance of xenotropic MLVs in biologicals, is a source of false positivity. Theoretically, XMRV/HMRV could be one of several MLLV transspecies infections. MLLV pathobiology and diversity indicate optimal strategies for investigating XMRV/HMRV in humans and raise ethical concerns. The alternatives that XMRV/HMRV may give a hard-to-detect “stealth” infection, or that XMRV/HMRV never reached humans, have to be considered.