Quantitative Laser Diffraction for Quantification of Protein Aggregates: Comparison With Resonant Mass Measurement, Nanoparticle Tracking Analysis, Flow Imaging, and Light Obscuration

Impact of stirring material on formation of submicron and subvisible aggregates in mAbs by quantitative laser diffraction, dynamic light scattering and background membrane imaging

Aggregation of monoclonal antibodies (mAbs) is the driving force for their undesirable immunogenic effects. There are multiple factors responsible for aggregation in therapeutic proteins. One significant cause is the process-related shear and interfacial stress generated due to impellers and stirrers. This investigation focuses on understanding the possible aggregation arising upon stirring mAb formulations using stirrers made of different materials. We used quantitative laser diffraction (qLD) to monitor and quantify the stirring induced formation of submicron and subvisible aggregates in the size range from 100 nm to 10 µm. We analysed various aspects of aggregate generation, such as onset of aggregation, particle size distribution, and concentration of aggregates generated using stirrers of different materials. We observed that mixing with stainless steel stirrers resulted in a quicker onset of aggregation and led to significantly higher concentrations of aggregates. Analysis of the stirred samples using dynamic light scattering (DLS) and background imaging technique (BMI) were conducted to complement the qLD analysis. All the three techniques resulted in a similar trend, showing presence of larger and higher quantities of aggregates in steel stirred samples, as compared to those stirred using PEEK and glass. Additionally, we performed SEC-HPLC to quantify the soluble fraction of monomer and recorded that the least amount was present in the steel stirred samples. This work highlights the need for optimizing the materials used for fabricating the stirrers/impellers.

Stability of Protein Pharmaceuticals: Recent Advances

There have been significant advances in the formulation and stabilization of proteins in the liquid state over the past years since our previous review. Our mechanistic understanding of protein-excipient interactions has increased, allowing one to develop formulations in a more rational fashion. The field has moved towards more complex and challenging formulations, such as high concentration formulations to allow for subcutaneous administration and co-formulation. While much of the published work has focused on mAbs, the principles appear to apply to any therapeutic protein, although mAbs clearly have some distinctive features. In this review, we first discuss chemical degradation reactions. This is followed by a section on physical instability issues. Then, more specific topics are addressed: instability induced by interactions with interfaces, predictive methods for physical stability and interplay between chemical and physical instability. The final parts are devoted to discussions how all the above impacts (co-)formulation strategies, in particular for high protein concentration solutions.'

Prediction models for the flux decay profile and initial flux of microfiltration for therapeutic proteins

Microfiltration (MF) is an essential step during biopharmaceutical manufacturing. However, unexpected flux decay can occur. Although the flux decay profile and initial flux are important factors determining MF filterability, predicting them accurately is challenging, as the root cause of unexpected flux decay remains elusive. In this study, the methodology for developing a prediction model of flux decay profiles was established. First, the filtration profiles of different monodisperse polystyrene latex and silica beads of various sizes were evaluated. These results revealed that the size and surface electrostatic properties of the beads affect the flux decay profile. Taking the size and surface electrostatic properties of protein aggregates into account, we constructed a predictive model using model bead filtration profiles. We showed that this methodology was applicable to two different MF filters to predict the flux decay profile of therapeutic proteins. Because our proposed prediction model is based on normalized flux, the initial flux is required to predict the overall filtration profile. Then, we applied the Hagen-Poiseuille equation using sample viscosity values to estimate the initial flux. The developed prediction models can be used for effective MF scale-up assessment during the early stages of process development.

Optimization of Flow Imaging Microscopy Setting Using Spherical Beads with Optical Properties Similar to Those of Biopharmaceuticals

Flow imaging microscopy (FIM) is widely used to characterize biopharmaceutical subvisible particles (SVPs). The segmentation threshold, which defines the boundary between the particle and the background based on pixel intensity, should be properly set for accurate SVP quantification. However, segmentation thresholds are often subjectively and empirically set, potentially leading to variations in measurements across instruments and operators. In the present study, we developed an objective method to optimize the FIM segmentation threshold using poly(methyl methacrylate) (PMMA) beads with a refractive index similar to that of biomolecules. Among several candidate particles that were evaluated, 2.5-µm PMMA beads were the most reliable in size and number, suggesting that the PMMA bead size analyzed by FIM could objectively be used to determine the segmentation threshold for SVP measurements. The PMMA bead concentrations measured by FIM were highly consistent with the indicative concentrations, whereas the PMMA bead size analyzed by FIM decreased with increasing segmentation threshold. The optimal segmentation threshold where the analyzed size was closest to the indicative size differed between an instrument with a black-and-white camera and that with a color camera. Inter-instrument differences in SVP concentrations in acid-stressed recombinant adeno-associated virus (AAV) and protein aggregates were successfully minimized by setting an optimized segmentation threshold specific to the instrument. These results reveal that PMMA beads can aid in determining a more appropriate segmentation threshold to evaluate biopharmaceutical SVPs using FIM.

Quantitative analysis of antibody aggregates by combination of pinched-flow fractionation and coulter method

For the pharmaceutical development of proteins, multiple methods of analysis are recommended for evaluating aggregation, and the development of more quantitative and simpler analytical techniques for subvisible particles is expected. This study introduces the Pinched-Flow Fractionation (PFF)-Coulter method, which combines the Pinched-flow fractionation (PFF) and Coulter methods to analyze the concentration of submicron-sized particles. The PFF method separates the particles by size. Separated particles were individually detected using the Coulter method. We have utilized the PFF-Coulter method to quantitatively analyze particle concentrations using standard particles, evaluate detection limits, variability, and correlation between theoretical and measured values, and analyze mixtures of different particle sizes. The PFF-Coulter method allows for quantitatively analyzing of particle sizes from 0.2 to 2.0 μm. The quantifiable weight concentration range was 2.5 × 10-2 - 50 μg/mL, and the number concentration range was 104-1010 particles/mL. The sample volume was small (<10 μL). The PFF-Coulter method is capable of quantitative analysis that complements data from conventional measurement techniques, and when used in conjunction with existing submicron-size particle analysis techniques, will enable more accurate particle analysis.

Comparative study between a gravity-based and peristaltic pump for intravenous infusion with respect to generation of proteinaceous microparticles

Subvisible particles generated during the preparation or administration of biopharmaceuticals might increase the risk of immunogenicity, inflammation, or organ dysfunction. To investigate the impact of an infusion system on the level of subvisible particles, we compared two types of infusion set based on peristaltic movement (Medifusion DI-2000 pump) and a gravity-based infusion system (Accu-Drip) using intravenous immunoglobulin (IVIG) as a model drug. The peristaltic pump was found to be more susceptible to particle generation compared to the gravity infusion set owing to the stress generated due to constant peristaltic motion. Moreover, the 5-µm in-line filter integrated into the tubing of the gravity-based infusion set further contributed to the reduction of particles mostly in the range ≥ 10 µm. Furthermore, the filter was also able to maintain the particle level even after the pre-exposure of samples to silicone oil lubricated syringes, drop shock, or agitation. Overall, this study suggests the need for the selection of an appropriate infusion set equipped with an in-line filter based on the sensitivity of the product.

Evaluation of subvisible particles in human immunoglobulin and lipid nanoparticles repackaged from a multi-dose vial using plastic syringes

The multi-dose vial (MDV) is widely used for most biopharmaceuticals that are repackaged in plastic syringes before use. However, subvisible particle formation with the use of plastic syringes containing silicone oil (SO syringes) for handling therapeutic proteins can be problematic. This study aimed to evaluate the extent of and trends in microparticle (>1 μm) formation and accumulation in repackaged syringes from MDVs containing human immunoglobulin (IgG) and lipid nanoparticles (LNPs). Light obscuration (LO) and flow imaging (FI) were used to analyze the microparticles. The number of microparticles observed with the use SO syringes was greater than that with SO-free syringes, and the number of microparticles continuously increased as did the number of times of repackaging in syringes for both drugs. However, a large variation was observed across different brands of SO syringes. In contrast, using a different technique of drug withdrawal from the vial significantly reduced the number of microparticles. Furthermore, the use of filter-integrated needles or the inclusion of stabilizers such as acetyl-arginine and Tween 20 into the formulation also helped reduce particle formation.

Sensitivity and Uncertainty Analysis of Micro-Flow Imaging for Sub-Visible Particle Measurements Using Artificial Neural Network

PURPOSE

During biopharmaceutical drug manufacturing, storage, and distribution, proteins in both liquid and solid dosage forms go through various processes that could lead to protein aggregation. The extent of aggregation in the sub-micron range can be measured by analyzing a liquid or post-reconstituted powder sample using Micro-Flow Imaging (MFI) technique. MFI is widely used in biopharmaceutical industries due to its high sensitivity in detecting and analyzing particle size distribution. However, the MFI's sensitivity to various factors makes accurate measurement challenging. Therefore, in light of the inherent variability of the method, this work aims to explore the capabilities of an adopted coupled sensitivity analysis and machine learning algorithm to quantify the influencing factors on the formed sub-visible particles and method variability.

METHODS

The proposed algorithm consists of two interconnected components, namely a surrogate model with a neural network and a sensitivity analyzer. A machine learning tool based on artificial neural networks (ANN) is constructed with MFI data. The best fit with an optimized configuration is found. Sensitivity and uncertainty analysis is performed using this network as the surrogate model to understand the impacts of input parameters on MFI data.

RESULTS

Results reveal the most impactful reconstitution preparation factors and others that are masked by the instrument variabilities. It is shown that instrument inaccuracy is a function of size category, with higher variabilities associated with larger size ranges.

CONCLUSION

Utilizing this tool while assessing the sensitivity of outputs to various parameters, measurement variabilities for analytical characterization tests can be quantified.

Relationship between aggregation of therapeutic proteins and agitation parameters: Acceleration and frequency

An increase in protein aggregates during transportation should be suppressed in therapeutic protein products because the aggregates have a potential risk of immunogenicity. In this study, three protein solutions in vials were exposed to tri-axial vibration with various combinations of frequency and acceleration using a transportation test system to investigate the relationship between low g-force stresses and protein aggregate generation. The number concentration of micron aggregates detected by flow imaging analysis increased markedly when the acceleration and frequency of agitation were within a specific range, in other words, above a threshold. This threshold was common among the three protein solutions. The suppression of micron aggregate formation by adding a surfactant suggested that agitation above the threshold increased micron aggregates mainly via interface-mediated routes. Notably, agitation, including agitation below the threshold, accelerated spontaneous oligomerization (nanometer aggregate generation) of proteins in bulk solution even in the presence of the surfactant. Studies of stability against mechanical stresses (e.g., a random vibration test to simulate actual shipment, with a time-compressed setting by increasing acceleration) need to be performed and discussed with careful consideration of the threshold for generating micron aggregates.

Utility of Three Flow Imaging Microscopy Instruments for Image Analysis in Evaluating four Types of Subvisible Particle in Biopharmaceuticals

Subvisible particles (SVPs) are a critical quality attribute of parenteral and ophthalmic products. United States Pharmacopeia recommends the characterizations of SVPs which are classified into intrinsic, extrinsic, and inherent particles. Flow imaging microscopy (FIM) is useful as an orthogonal method in both the quantification and classification of SVPs because FIM instruments provide particle images. In addition to the conventionally used FlowCam (Yokogawa Fluid Imaging Technologies) and Micro-Flow Imaging (Bio-Techne) instruments, the iSpect DIA-10 (Shimadzu) instrument has recently been released. The three instruments have similar detection principles but different optical settings and image processing, which may lead to different results of the quantification and classification of SVPs based on the information from particle images. The present study compares four types of SVP (protein aggregates, silicone oil droplets, and surrogates for solid free-fatty-acid particles, milled-lipid particles, and sprayed-lipid particles) to compare the results of size distributions and classification abilities obtained using morphological features and a deep-learning approach. Although the three FIM instruments were effective in classifying the four types of SVP through convolutional neural network analysis, there was no agreement on the size distribution for the same protein aggregate solution, suggesting that using the classifiers of the FIM instruments could result in different evaluations of SVPs in the field of biopharmaceuticals.

Current Status and Challenges of Analytical Methods for Evaluation of Size and Surface Modification of Nanoparticle-Based Drug Formulations

The present review discusses the current status and difficulties of the analytical methods used to evaluate size and surface modifications of nanoparticle-based pharmaceutical products (NPs) such as liposomal drugs and new SARS-CoV-2 vaccines. We identified the challenges in the development of methods for (1) measurement of a wide range of solid-state NPs, (2) evaluation of the sizes of polydisperse NPs, and (3) measurement of non-spherical NPs. Although a few methods have been established to analyze surface modifications of NPs, the feasibility of their application to NPs is unknown. The present review also examined the trends in standardization required to validate the size and surface measurements of NPs. It was determined that there is a lack of available reference materials and it is difficult to select appropriate ones for modified NP surface characterization. Research and development are in progress on innovative surface-modified NP-based cancer and gene therapies targeting cells, tissues, and organs. Next-generation nanomedicine should compile studies on the practice and standardization of the measurement methods for NPs to design surface modifications and ensure the quality of NPs.

An Interlaboratory Comparison on the Characterization of a Sub-micrometer Polydisperse Particle Dispersion

The measurement of polydisperse protein aggregates and particles in biotherapeutics remains a challenge, especially for particles with diameters of ≈ 1 µm and below (sub-micrometer). This paper describes an interlaboratory comparison with the goal of assessing the measurement variability for the characterization of a sub-micrometer polydisperse particle dispersion composed of five sub-populations of poly(methyl methacrylate) (PMMA) and silica beads. The study included 20 participating laboratories from industry, academia, and government, and a variety of state-of-the-art particle-counting instruments. The received datasets were organized by instrument class to enable comparison of intralaboratory and interlaboratory performance. The main findings included high variability between datasets from different laboratories, with coefficients of variation from 13 % to 189 %. Intralaboratory variability was, on average, 37 % of the interlaboratory variability for an instrument class and particle sub-population. Drop-offs at either end of the size range and poor agreement on maximum counts of particle sub-populations were noted. The mean distributions from an instrument class, however, showed the size-coverage range for that class. The study shows that a polydisperse sample can be used to assess performance capabilities of an instrument set-up (including hardware, software, and user settings) and provides guidance for the development of polydisperse reference materials.

Characterization of Grinding-Induced Subvisible Particles and Free Radicals in a Freeze-Dried Monoclonal Antibody Formulation

PURPOSES

The primary objectives of this study were to investigate the degradation mechanisms of freeze-dried monoclonal antibody (mAb) formulations under mechanical grinding, assess the sensitivity and suitability of various particle analysis techniques, analyze the structure of the collected subvisible particles (SbVPs), and analyze the antioxidant mechanism of methionine (Met) under degradation process to gain a thorough understanding of the phenomenon.

METHODS

The freeze-dried mAb-X formulations underwent grinding, and the resultant SbVPs were characterized through visual inspection, flow imaging microscopy, dynamic light scattering, ultraviolet-visible spectroscopy, and size-exclusion high-performance liquid chromatography. We further evaluated the effect of different temperatures and the free radical scavenger Met on SbVP formation. The produced free radicals were detected using electron paramagnetic resonance, and Met S-oxide formation was detected using liquid chromatography-mass spectrometry. In addition, we analyzed the obtained SbVPs using capillary electrophoresis sodium dodecyl sulfate and Fourier transform infrared spectroscopy.

RESULTS

Grinding leads to SbVP formation under high temperature and free radical formation. Free radicals produced during grinding require the participation of a macromolecule. Met could then bind to the produced free radicals, thus partially protecting mAb-X from degradation while itself undergoing oxidation to form Met(O). Sensitivity differences between different particle analysis techniques were evaluated, and the obtained SbVPs showed significant changes in secondary structure and the formation of covalent aggregates and fragments.

CONCLUSIONS

Met plays the role of an antioxidant in protecting macromolecules by quenching the free radicals produced during grinding. To thoroughly characterize SbVPs, multiple and orthogonal particle analysis techniques should be used, and if necessary, SbVPs should be processed by enrichment to accurately analyze primary and high order structures.

Plate Reader-Based Analytical Method for the Size Distribution of Submicron-Sized Protein Aggregates Using Three-Dimensional Homodyne Light Detection

The assessment of aggregates is essential in biopharmaceutical development. Although submicron-sized aggregates are considered to have a potential immunogenicity risk, analytical techniques are limited. In this study, we present a new analytical technique using three-dimensional homodyne light detection (3D-HLD). In this system, submicron-sized particles are quantified by combining the reflected light detection of each particle by high-speed 3D scan and then enhancing the amplitude of the reflected light using HLD. The particle concentrations and size distributions of human tetanus immune globulin (TIG) aggregates generated by stirring were measured using 3D-HLD. Both concentrations and distributions were comparable to those obtained via resonant mass measurement (RMM), a technique commonly used for submicron-sized particle measurement. Aiming at feasibility assessment of 3D-HLD for the high-through-put formulation development, 30 formulations of TIG and rituximab under agitation stress were analyzed by 3D-HLD. The results showed that 3D-HLD can automatically and simultaneously assess the aggregate concentrations and size distributions of at least 90 samples. This study demonstrates that 3D-HLD can be used for submicron-sized aggregate analysis as an orthogonal method to RMM and also as a screening tool during formulation development.

Application of Tunable Resistive Pulse Sensing for the Quantification of Submicron Particles in Pharmaceutical Monoclonal Antibody Preparations

Tunable resistive pulse sensing (TRPS, qNano Gold, IZON Ltd.) was investigated as a method to quantify submicron particles (SMPs) between 0.1 and 1 µm in solutions of biopharmaceuticals. To reduce sample dilution, a spiking-in approach was used to add the appropriate amount of electrolytes required for the measurement. For correct particle quantification, an electrolyte concentration of at least 50 mM sodium chloride was needed. Intra- and inter-nanopore variability were below 5% for size and below 10% for concentration measurements when analyzing polystyrene standard beads. Submicron particle counts in a stir stressed IgG1 monoclonal antibody formulation resulted in a non-symmetrical, almost bell-shaped size distribution with a maximum at 250 nm when using a NP300 nanopore (IZON Ltd.). It was shown that particle counts are heavily underestimated below 250 nm, and therefore it is recommended to quantify particle counts by TRPS in samples with heterogeneous particle size distributions (e.g., biopharmaceuticals) only starting from the maximum of the histogram towards the upper limit of detection.

Protein microbeadification to achieve highly concentrated protein formulation with reversible properties and in vivo pharmacokinetics after reconstitution

A protein precipitation technique was optimized to produce biophysically stable 'protein microbeads', applicable to highly concentrated protein formulation. Initially, production of BSA microbeads was performed using rapid dehydration by vortexing in organic solvents followed by cold ethanol treatment and a vacuum drying. Out of four solvents, n-octanol produced the most reversible microbeads upon reconstitution. A Shirasu porous glass (SPG) membrane emulsification technique was utilized to enhance the size distribution and manufacturing process of the protein microbeads with a marketized human IgG solution. Process variants such as dehydration time, temperature, excipients, drying conditions, and initial protein concentration were evaluated in terms of the quality of IgG microbeads and their reversibility. The hydrophobized SPG membrane produced a narrow size distribution of the microbeads, which were further enhanced by shorter dehydration time, low temperature, minimized the residual solvents, lower initial protein concentration, and addition of trehalose to the IgG solution. Final reversibility of the IgG microbeads with trehalose was over 99% at both low and high protein concentrations. Moreover, the formulation was highly stable under repeated mechanical shocks and at an elevated temperature compared to its liquid state. Its in vivo pharmacokinetic profiles in rats were consistent before and after the 'microbeadification'.

Measurement of the Size Distribution of Multimodal Colloidal Systems by Laser Diffraction

Laser diffraction (LD) is a well-established tool for the measurement of particle size distribution. Recently, its demand and use for the measurement of complex biological systems have increased. Among the challenges that these types of samples present, there is the presence of multiple particle populations whose modal size may span across several orders of magnitude. In this study, we assessed the accuracy of LD for the measurement of the modal diameter of both single and mixed populations of polystyrene particles with diameters ranging from 60 nm to 40 μm. We discuss the application of different available algorithms to the analysis of the data and their impact on the measurement results. Independent methods were applied to guide the selection of the algorithms and validate the measured size distributions. We found that the modal diameters of the particle size distribution measured by LD for the mixed suspension was accurate within 2 % for particles larger than 1 μm and generally within 25 % for the particles tested. Method repeatability was found to be robust, with deviations below 1%. The method was also found to be useful for estimating the relative concentration of the particle populations in the mixed samples. This study provides confidence in the use of LD for the measurement of complex multimodal colloidal samples.

Particle density determination using resonant mass measurement method combined with asymmetrical flow field-flow fractionation method

A novel characterization system using a combinational analysis of the resonant mass measurement (RMM) and asymmetrical flow field-flow fractionation (AF4) methods is developed as a hybrid analytical tool for the particle density of mixtures of different-sized materials. The function of the RMM method is to determine the particle mass by observing the shift in frequency proportional to the particle mass. However, to determine the density of particles using the RMM method, information on the size or size distribution is necessary. Because the size distribution of the particles could influence the accuracy of the determination of the density of the particles, this study addresses the weak point of the RMM method using the AF4 method. First, AF4 is used to fractionate the narrow-sized distributed particles as an effective sample preparation method before the RMM assessment. Moreover, the accurate size distribution determined by the AF4 method with multi-angle light scattering analysis supports the reliable density determination by the RMM method on the transformation from the mass distribution of the particles to the density distribution. Using our developed combinational analytical method of RMM and AF4 methods for mixed particle samples (different sizes and different materials), the densities of the respective particles are evaluated. This approach clearly resolved the problems of the RMM method using a combination analysis with the AF4 method for RMM assessment on the density of particles. The investigated analysis method can have an important role in developing new applications of colloidal nano- and micro-materials in industrial and biological research.

Stirring rate affects thermodynamics and unfolding kinetics in isothermal titration calorimetry

Isothermal titration calorimetry (ITC) directly provides thermodynamic parameters depicting the energetics of intermolecular interactions in solution. During ITC experiments, a titration syringe with a paddle is continuously rotating to promote a homogeneous mixing. Here, we clarified that the shape of the paddles (flat, corkscrew and small-pitched corkscrew) and the stirring rates influence on the thermodynamic parameters of protein-ligand interaction. Stirring with the flat paddle at lower and higher rate both yielded a lower exothermic heat due to different reasons. The complete reaction with no incompetent fractions was achieved only when the stirring was performed at 500 or 750 rpm using the small-pitched corkscrew paddle. The evaluation of the protein solution after 1,500 rpm stirring indicated that proteins in the soluble fraction decreased to 94% of the initial amount, among which 6% was at an unfolded state. In addition, a significant increase of micron aggregates was confirmed. Furthermore, a new approach for the determination of the unfolding kinetics based on the time dependence of the total reaction heat was developed. This study demonstrates that a proper stirring rate and paddle shape are essential for the reliable estimation of thermodynamic parameters in ITC experiments.

Recent Achievements and Current Interests in Research on the Characterization and Quality Control of Biopharmaceuticals in Japan

As reported in the previous commentary (Ishii-Watabe et al., J Pharm Sci 2017), the Japanese biopharmaceutical research group is promoting collaborative multilaboratory studies to evaluate and standardize new methodologies for biopharmaceutical characterization and quality control. We have conducted the studies and held 2 annual meetings in 2018 and 2019. At the 2018 meeting, Dr. Rukman DeSilva of the U.S. Food and Drug Administration and Dr. Srivalli Telikepalli of the National Institute of Standards and Technology participated as guest speakers. At the 2019 meeting, we invited Prof. John Carpenter of the University of Colorado, Prof. Gerhard Winter and Prof. Wolfgang Friess of Ludwig Maximilian University of Munich, and Dr. Tim Menzen of Coriolis Pharma Research, as guest commentators. In both meetings, the main research topic was strategies for the characterization and control of protein aggregates/subvisible particles in drug products. Specifically, the use of the light obscuration method for insoluble particulate matter testing with reduced injection volumes, and a comparison of analytical performance between flow imaging and light obscuration were discussed. Other topics addressed included host cell protein analysis, bioassay, and quality control strategies. In this commentary, the recent achievements of the research group, meeting discussions, and future perspectives are summarized.

Fcγ Receptor Activation by Human Monoclonal Antibody Aggregates

Protein aggregates are a potential risk factor for immunogenicity. The measurement, characterization, and control of protein aggregates in drug products are indispensable for the development of biopharmaceuticals, including therapeutic mAbs. In this study, Fcγ receptor (FcγR)-expressing reporter cell lines were used to analyze the FcγR-activation properties of mAb aggregates. Comparison of aggregates of mAbs harboring different IgG subclasses revealed that the FcγR-activation profiles of the mAb aggregates were dependent on IgG subclass. In addition, aggregates of Fc-engineered mAb with enhanced FcγR-activation properties exhibited stronger activation of FcγRs than was observed in the wild-type aggregates, whereas aggregates of Fc-engineered mAb with decreased FcγR-activation properties showed reduced activation. These results suggest that FcγR activation by mAb aggregates depends greatly on the Fc functions of the native (nonaggregated) mAbs. We also showed that aggregates of mAbs smaller than 1 μm in size have the potential to directly activate FcγRs. Unintended immune cell activation can be induced on account of FcγR activation by mAb aggregates and such FcγR activation may contribute to immunogenicity, and therefore, analysis of the FcγR-activation properties of mAb aggregates using FcγR-expressing reporter cell lines is a promising approach for the characterization of mAb aggregates.

Detection and Sizing of Submicron Particles in Biologics With Interferometric Scattering Microscopy

We demonstrate the application of interferometric scattering microscopy (IFS) for characterizing submicron particles in stir-stressed monoclonal antibody. IFS uses a layered silicon sensor and modified optical microscope to rapidly visualize and determine the particle size distribution (PSD) of submicron particles based on their scattering intensity, which is directly proportional to particle mass. Limits for particle size and optimal solution concentration were established for IFS characterization of submicron particles. We critically compare IFS data with dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) and find IFS is superior to NTA and DLS for determining the realistic shape of the number-based PSD, whereas NTA and DLS provide superior information about absolute particle size. Together, IFS, NTA, and DLS provide complementary information on submicron particles and enable quantitative characterization of the PSD of submicron aggregates. Finally, we explore quantifying particle size with IFS by developing a calibration curve for particle scattering intensity based on correlative scanning electron microscopy imaging. We found that only a subset of isotropic-shaped particles followed the expected proportionality between IFS intensity and particle mass. Overall, this study demonstrates IFS is a simple approach for detecting and quantifying submicron aggregate PSD in protein-based therapeutics.