The beneficial impact of kosmotropic salts on the resolution and selectivity of Protein A chromatography

During the manufacturing of therapeutic antibodies, effective Protein A chromatography as initial column step is crucial to simplify the remaining purification effort for subsequent polishing steps. This is particularly relevant for molecules with high impurity content so that desired product purity can be attained. The present study demonstrates beneficial effects on impurity removal when applying kosmotropic salts, e.g., sodium sulfate or sodium chloride, in the elution phase. Initially, a screen using negative linear pH gradient elution evaluated the impact of the kosmotropic salts in comparison to no additive and chaotropic urea using three mAbs and three common resins. Retaining acceptable yield, the kosmotropic salts improved resolution of monomer and impurities and reduced the contents of process-related host cell proteins and DNA as well as of product-related low and high molecular weight forms, despite some resin- and mAb-dependent variations. Moreover, a decrease in hydrolytic activity measured by a new assay for polysorbase activity was observed. In contrast, urea was hardly effective. The findings served to establish optimized step elution conditions with 0.25 M of sodium sulfate for a challenging mAb with complex format (bispecific 2 + 1 CrossMab) displaying high relative hydrophobicity and impurity levels. With yield and purity both in the range of 90 %, the contents of all impurity components were reduced, e.g., low molecular weight forms by two-fold and polysorbase activity by four-fold. The study indicates the potential of kosmotropic salts to establish efficient and comprehensive impurity separation by Protein A for facilitated downstream processing and economic manufacturing of complex antibodies.

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.

Implementation of in vitro glycoengineering of monoclonal antibodies into downstream processing of industrial production

In vitro glycoengineering using exoenzymes for specific modification is recognized as appropriate method to tailor sugar moieties of glycan structures during the recombinant production of monoclonal antibodies (mAbs). This report describes enhanced in vitro glycoengineering approaches using β1,4-galactosyltransferase and α2,6-sialyltransferase to improve the efficiency of galactosylation and sialylation with the aim to implement in vitro glycoengineering into common mAb purification processes. Feasibility studies tested the potential of different in vitro glycoengineering protocols (2-step vs. 1-step) to facilitate the overall procedure. Scalability of the reactions was demonstrated for mAb amounts ranging from 1 mg to 1 g. Additionally, the reactions of β1,4-galactosyltransferase and α2,6-sialyltransferase were shown to work on column during affinity chromatography using Protein A or KappaSelect, the latter providing more efficient galactosylation and sialylation of IgG1 and IgG4 mAbs. Performing in vitro glycoengineering on column enabled the use of cell culture harvest which yielded results comparable to that of purified bulk. Based thereon, an optimized 2-step mixed mode approach was found most appropriate to integrate in vitro glycoengineering of the IgG1 mAb into the overall manufacturing process. Using harvest for on-column reaction of β1,4-galactosyltransferase combined with in-solution reaction of α2,6-sialyltransferase, this approach yielded 100 percent biantennary galactosylation and 61 percent biantennary sialylation. Moreover, the enzymes applied in in vitro glycoengineering could be separated, recycled, and reused in further reactions to improve economic efficiency. Overall, the study provides a toolbox for in vitro glycoengineering and presents an optimized easy-to-handle workflow to implement this method into the downstream processing of industrial mAb production.

Identification and Characterization of Polysorbate-Degrading Enzymes in a Monoclonal Antibody Formulation

Degradation of polysorbate (PS) by hydrolytically active host cell proteins (HCPs) in drug products may impair the protein-stabilizing properties of PS and lead to the formation of particles due to the accumulation of poorly soluble free fatty acids upon long-term storage. The identification of the causative enzymes is challenging due to their low-abundance even when using state-of-the-art instrumentation and workflows. To overcome these challenges, we developed a rigorous enrichment strategy for HCPs, utilizing both Protein A and anti-HCP affinity chromatography, which facilitated the in-depth characterization of the HCP population in a monoclonal antibody formulation prone to PS hydrolysis. Based on the HCPs identified by liquid chromatography coupled to tandem mass spectrometry, a number of enzymes annotated as hydrolases were recombinantly expressed and characterized in terms of polysorbate degradation. Among the selected candidates, Lipoprotein Lipase, Lysosomal Acid Lipase (LIPA) and Palmitoyl-Protein Thioesterase 1 (PPT1) exhibited notable activity towards PS. To our knowledge, this is the first report to identify LIPA and PPT1 as residual HCPs that can contribute to PS degradation in a biological product.

Characterization of 30 76 Ge enriched Broad Energy Ge detectors for GERDA Phase II

The GERmanium Detector Array (Gerda) is a low background experiment located at the Laboratori Nazionali del Gran Sasso in Italy, which searches for neutrinoless double-beta decay of 76 Ge into 76 Se+2e - . Gerda has been conceived in two phases. Phase II, which started in December 2015, features several novelties including 30 new ⁷⁶Ge enriched detectors. These were manufactured according to the Broad Energy Germanium (BEGe) detector design that has a better background discrimination capability and energy resolution compared to formerly widely-used types. Prior to their installation, the new BEGe detectors were mounted in vacuum cryostats and characterized in detail in the Hades underground laboratory in Belgium. This paper describes the properties and the overall performance of these detectors during operation in vacuum. The characterization campaign provided not only direct input for Gerda Phase II data collection and analyses, but also allowed to study detector phenomena, detector correlations as well as to test the accuracy of pulse shape simulation codes.

Probing Majorana neutrinos with double-β decay

A discovery that neutrinos are Majorana fermions would have profound implications for particle physics and cosmology. The Majorana character of neutrinos would make possible the neutrinoless double-β (0νββ) decay, a matter-creating process without the balancing emission of antimatter. The GERDA Collaboration searches for the 0νββ decay of ⁷⁶Ge by operating bare germanium detectors in an active liquid argon shield. With a total exposure of 82.4 kg⋅year, we observe no signal and derive a lower half-life limit of T _1/2 > 0.9 × 10²⁶ years (90% C.L.). Our T _1/2 sensitivity, assuming no signal, is 1.1 × 10²⁶ years. Combining the latter with those from other 0νββ decay searches yields a sensitivity to the effective Majorana neutrino mass of 0.07 to 0.16 electron volts.

Improved Limit on Neutrinoless Double-β Decay of ^{76}Ge from GERDA Phase II

The GERDA experiment searches for the lepton-number-violating neutrinoless double-β decay of ^{76}Ge (^{76}Ge→^{76}Se+2e^{-}) operating bare Ge diodes with an enriched ^{76}Ge fraction in liquid argon. The exposure for broad-energy germanium type (BEGe) detectors is increased threefold with respect to our previous data release. The BEGe detectors feature an excellent background suppression from the analysis of the time profile of the detector signals. In the analysis window a background level of 1.0_{-0.4}^{+0.6}×10^{-3}  counts/(keV kg yr) has been achieved; if normalized to the energy resolution this is the lowest ever achieved in any 0νββ experiment. No signal is observed and a new 90% C.L. lower limit for the half-life of 8.0×10^{25}  yr is placed when combining with our previous data. The expected median sensitivity assuming no signal is 5.8×10^{25}  yr.

Results on neutrinoless double-β decay of 76Ge from phase I of the GERDA experiment

Neutrinoless double beta decay is a process that violates lepton number conservation. It is predicted to occur in extensions of the standard model of particle physics. This Letter reports the results from phase I of the Germanium Detector Array (GERDA) experiment at the Gran Sasso Laboratory (Italy) searching for neutrinoless double beta decay of the isotope (76)Ge. Data considered in the present analysis have been collected between November 2011 and May 2013 with a total exposure of 21.6 kg yr. A blind analysis is performed. The background index is about 1 × 10(-2) counts/(keV kg yr) after pulse shape discrimination. No signal is observed and a lower limit is derived for the half-life of neutrinoless double beta decay of (76)Ge, T(1/2)(0ν) >2.1 × 10(25) yr (90% C.L.). The combination with the results from the previous experiments with (76)Ge yields T(1/2)(0ν)>3.0 × 10(25) yr (90% C.L.).