Rapid whole monoclonal antibody analysis by mass spectrometry: An ultra scale-down study of the effect of harvesting by centrifugation on the post-translational modification profile

Mobile Affinity Selection Chromatography Analysis of Therapeutic Monoclonal Antibodies

Federal regulatory agencies require continuous verification of recombinant therapeutic monoclonal antibody (mAb) quality that is commonly achieved in a two-step process. First, the host-cell proteome and metabolome are removed from the production medium by protein A affinity chromatography. Second, following recovery from the affinity column with an acidic wash, mAb quality is assessed in multiple ways by liquid chromatography-mass spectrometry (LC-MS). However, lengthy sample preparation and the lack of higher-order structure analyses are limitations of this approach. To address these issues, this report presents an integrated approach for the analysis of two critical quality attributes of mAbs, namely titer and relative aggregate content. Integration of sample preparation and molecular-recognition-based analyses were achieved in a single step utilizing an isocratically eluted mobile affinity selection chromatography (MASC) column. MASC circumvents the protein A step, simplifying sample preparation. Within 10 min, (i) mAbs are fluorescently coded for specific detection, (ii) monomers and aggregates are resolved, (iii) the mAb titer is quantified, (iv) relative aggregate content is determined, (v) analytes are detected, and (vi) the column is ready for the next sample. It is suggested herein that this mode of rapid quality assessment will be of value at all stages of discovery (screening, clone selection, characterization), process R&D, and manufacturing. Rapid monitoring of variant formation is a critical element of quality evaluation.

Transient pentameric IgM fulfill biological function-Effect of expression host and transfection on IgM properties

Recombinant production of IgM antibodies poses a special challenge due to the complex structure of the proteins and their not yet fully elucidated interactions with the immune effector proteins, especially the complement system. In this study, we present transient expression of IgM antibodies (IgM617, IgM012 and IgM012_GL) in HEK cells and compared it to the well-established stable expression system in CHO cells. The presented workflow investigates quality attributes including productivity, polymer distribution, glycosylation, antibody structure and activation of the classical complement pathway. The HEK293E transient expression system is able to generate comparable amounts and polymer distribution as IgM stably produced in CHO. Although the glycan profile generated by HEK293E cells contained a lower degree of sialylation and a higher portion of oligomannose structures, the potency to activate the complement cascade was maintained. Electron microscopy also confirmed the structural integrity of IgM pentamers produced in HEK293E cells, since the conventional star-shaped structure is observed. From our studies, we conclude that the transient expression system provides an attractive alternative for rapid, efficient and high-throughput production of complex IgM antibodies with slightly altered post-translational modifications, but comparable structure and function.

High throughput screening of ultrafiltration and diafiltration processing of monoclonal antibodies via the ambr® crossflow system

As the biopharmaceutical industry moves toward high concentration of monoclonal antibody drug substance, additional development is required early on when material is still limited. A key constraint is the availability of predictive high-throughput low-volume filtration screening systems for bioprocess development. This particularly impacts final stages such as ultrafiltration/diafiltration steps where traditional scale-down systems need hundreds of milliliters of material per run. Recently, the ambr® crossflow system has been commercialized by Sartorius Stedim Biotech (SSB) to meet this need. It enables parallel high throughput experimentation by only using a fraction of typical material requirements. Critical parameters for predictive filtration systems include loading, mean transmembrane pressure (Δ P ¯ _TMP ), and crossflow rate (Q_F ). While axial pressure drop (ΔP_axial ) across the cartridge is a function of these parameters, it plays a key role and similar values should result across scales. The ambr® crossflow system is first presented describing typical screening experiments. Its performance is then compared to a traditional pilot-scale tangential flow filtration (TFF) at defined conditions. The original ambr® crossflow (CF) cartridge underperformed resulting in ~20x lower ΔP_axial than the pilot-scale TFF flat-sheet cassette. With an objective to improve the scalability of the system, efforts were made to understand this scale difference. The ambr® CF cartridge was successfully modified by restricting the flow of the feed channel, and thus increasing its ΔP_axial . Additional studies across a range of loading (100-823 gm^-2 ); Δ P ¯ _TMP (12-18 psi); and Q_F (4-8 L/min/m² ) were conducted in both scales. Comparable flux and aggregate levels were achieved.

Exploring the analytical power of the QTOF MS platform to assess monoclonal antibodies quality attributes

The biopharmaceutical industry is growing at a fast pace, making nowadays 20% of the pharma market. Within this market, therapeutic monoclonal antibodies (mAbs) are the dominant product class. With the patent expirations, biosimilars and, perhaps more relevant, biobetters, are in fast development. Thus, a comprehensive characterization at the molecular level of antibodies heterogeneity such as glycoforms, post-translational modifications (PTMs) and sequence variations is of utmost importance. Mass spectrometry (MS)-based approaches are undoubtedly the most powerful analytical strategies to monitor and define an array of critical quality attributes on mAbs. In this work, we demonstrate the analytical power of the Q-TOF MS platform for comprehensive and detailed analysis at molecular levels of an in-house produced mAb. This methodology involves minimal sample preparation procedures and provides an extensive collection of valuable data in a short period of time.

An ultra scale-down method to investigate monoclonal antibody processing during tangential flow filtration using ultrafiltration membranes

The availability of material for experimental studies is a key constraint in the development of full‐scale bioprocesses. This is especially true for the later stages in a bioprocess sequence such as purification and formulation, where the product is at a relatively high concentration and traditional scale‐down models can require significant volumes. Using a combination of critical flow regime analysis, bioprocess modelling, and experimentation, ultra scale‐down (USD) methods can yield bioprocess information using only millilitre quantities before embarking on highly demanding full‐scale studies. In this study the performance of a pilot‐scale tangential flow filtration (TFF) system based on a membrane flat‐sheet cassette using pumped flow was predicted by devising an USD device comprising a stirred cell using a rotating disc. The USD device operates with just 2.1 cm² of membrane area and, for example, just 1.7 mL of feed for diafiltration studies. The novel features of the design involve optimisation of the disc location and the membrane configuration to yield an approximately uniform shear rate. This is characterised using computational fluid dynamics for a defined layer above the membrane surface. A pilot‐scale TFF device operating at ~500‐fold larger feed volume and membrane area was characterised in terms of the shear rate derived from flow rate‐pressure drop relationships for the cassette. Good agreement was achieved between the USD and TFF devices for the flux and resistance values at equivalent average shear rates for a monoclonal antibody diafiltration stage.

LC/MS-based Intact IgG and Released Glycan Analysis for Bioprocessing Applications

Robust plate based antibody glycan analysis platforms are urgently needed for biopharmaceutical development and manufacturing as well as for clinical biomarker research. A 96-well plate based workflow has been developed to analyze both intact IgG antibodies and released N-glycans using an Orbitrap Fusion Mass Spectrometer and an LC/MS method on the Waters UNIFI platform. Here, such a workflow including protein A purification, PNGaseF digestion, 2-AB labeling, and SPE clean-up is described. The measured IgG glycan profile is consistent with that obtained from non-plate based method and commercial kit and has the advantage of less hands-on time. Also the application of the workflow in cell culture monitoring and clonal selection work is demonstrated. Apart from checking the major glycan structure changes among clones, post translational modifications (PTMs) such as C-terminal lysine residue clipping and N-terminal pyroglutamic acid formation can also be deduced from the workflow.

A novel rapid analysis using mass spectrometry to evaluate downstream refolding of recombinant human insulin-like growth factor-1 (mecasermin)

RATIONALE

Mecasermin is used to treat elevated blood sugar as well as growth-hormone-resistant Laron-type dwarfism. Mecasermin isolated from inclusion bodies in extracts of E. coli must be refolded to acquire sufficient activity. However, there is no rapid analytical method for monitoring refolding during the purification process.

METHODS

We prepared mecasermin drug product, in-process samples during the oxidation of mecasermin, forced-reduced mecasermin, and aerially oxidized mecasermin after forced reduction. Desalted mecasermin samples were analyzed using MALDI-ISD. The peak intensity ratio of product to precursor ion was determined. The charge-state distribution (CSD) of mecasermin ions was evaluated using ESI-MS coupled with SEC-mode HPLC. The drift time and collision cross-sectional area (CCS) of mecasermin ions were evaluated using ESI-IMS-MS coupled with SEC-mode HPLC.

RESULTS

MALDI-ISD data, CSD values determined using ESI-MS, and the CCS acquired using ESI-IMS-MS revealed the relationship between the folded and unfolded proteoforms of forced-reduced mecasermin and aerially oxidized mecasermin with the free-SH:protein ratio of mecasermin drug product. The CCS area, which is determined using ESI-IMS-MS, provided proteoform information through rapid monitoring (<2 min) of in-process samples during the manufacture of mecasermin.

CONCLUSIONS

ESI-IMS-MS coupled with SEC-mode HPLC is a rapid and robust method for analyzing the free-SH:protein ratio of mecasermin that allows proteoform changes to be evaluated and monitored during the oxidation of mecasermin. ESI-IMS-MS is applicable as a process analytical technology tool for identifying the "critical quality attributes" and implementing "quality by design" for manufacturing mecasermin.

Characterization of intact protein conjugates and biopharmaceuticals using ion-exchange chromatography with online detection by native electrospray ionization mass spectrometry and top-down tandem mass spectrometry

Characterization of biopharmaceutical products is a challenging task, which needs to be carried out at several different levels (including both primary structure and conformation). An additional difficulty frequently arises due to the structural heterogeneity inherent to many protein-based therapeutics (e.g., extensive glycosylation or "designer" modifications such as chemical conjugation) or introduced postproduction as a result of stress (e.g., oxidation and deamidation). A combination of ion-exchange chromatography (IXC) with online detection by native electrospray ionization mass spectrometry (ESI MS) allows characterization of complex and heterogeneous therapeutic proteins and protein conjugates to be accomplished at a variety of levels without compromising their conformational integrity. The IXC/ESI MS measurements allow protein conjugates to be profiled by analyzing conjugation stoichiometry and the presence of multiple positional isomers, as well as to establish the effect of chemical modifications on the conformational integrity of each species. While mass profiling alone is not sufficient for identification of nonenzymatic post-translational modifications (PTMs) that result in a very small mass change of the eluting species (e.g., deamidation), this task can be completed using online top-down structural analysis, as demonstrated using stressed interferon-β as an example. The wealth of information that can be provided by IXC/native ESI MS and tandem mass spectrometry (MS/MS) on protein-based therapeutics will undoubtedly make it a very valuable addition to the experimental toolbox of biopharmaceutical analysis.

Continuous bioprocessing: the real thing this time? 10(th) Annual bioProcessUK Conference, December 3-4, 2013, London, UK

The Annual bioProcessUK Conference has acted as the key networking event for bioprocess scientists and engineers in the UK for the past 10 years. The following article is a report from the sessions that focused on continuous bioprocessing during the 10^th Annual bioProcessUK Conference (London, December 2013). These sessions were organized by the ‘EPSRC Centre for Innovative Manufacturing in Emergent Macromolecular Therapies’ hosted at University College London. A plenary lecture and workshop provided a forum for participants to debate topical issues in roundtable discussions with industry and academic experts from institutions such as Genzyme, Janssen, Novo Nordisk, Pfizer, Merck, GE Healthcare and University College London. The aim of these particular sessions was to understand better the challenges and opportunities for continuous bioprocessing in the bioprocessing sector.

Comparative analysis of monoclonal antibody N-glycosylation using stable isotope labelling and UPLC-fluorescence-MS

A twoplex method using ¹²C₆ and ¹³C₆ stable isotope analogies of 2-aminobenzoic acid (2-AA) is described for LC-fluorescence-MS based quantitative and comparative analysis of N-glycans present on monoclonal antibodies.

Approaches to Interchain Cysteine-Linked ADC Characterization by Mass Spectrometry

Therapeutic antibody-drug conjugates (ADCs) harness the cell-killing potential of cytotoxic agents and the tumor targeting specificity of monoclonal antibodies to selectively kill tumor cells. Recent years have witnessed the development of several promising modalities that follow the same basic principles of ADC based therapies but which employ unique cytotoxic agents and conjugation strategies in order to realize therapeutic benefit. The complexity and heterogeneity of ADCs present a challenge to some of the conventional analytical methods that industry has relied upon for biologics characterization. This current review will highlight some of the more recent methodological approaches in mass spectrometry that have bridged the gap that is created when conventional analytical techniques provide an incomplete picture of ADC product quality. Specifically, we will discuss mass spectrometric approaches that preserve and/or capture information about the native structure of ADCs and provide unique insights into the higher order structure (HOS) of these therapeutic molecules.

White paper on continuous bioprocessing. May 20-21, 2014 Continuous Manufacturing Symposium

There is a growing interest in realizing the benefits of continuous processing in biologics manufacturing, which is reflected by the significant number of industrial and academic researchers who are actively involved in the development of continuous bioprocessing systems. These efforts are further encouraged by guidance expressed in recent US FDA conference presentations. The advantages of continuous manufacturing include sustained operation with consistent product quality, reduced equipment size, high-volumetric productivity, streamlined process flow, low-process cycle times, and reduced capital and operating cost. This technology, however, poses challenges, which need to be addressed before routine implementation is considered. This paper, which is based on the available literature and input from a large number of reviewers, is intended to provide a consensus of the opportunities, technical needs, and strategic directions for continuous bioprocessing. The discussion is supported by several examples illustrating various architectures of continuous bioprocessing systems.

A pilot study showing differences in glycosylation patterns of IgG subclasses induced by pneumococcal, meningococcal, and two types of influenza vaccines

The presence of a carbohydrate moiety on asparagine 297 in the Fc part of an IgG molecule is essential for its effector functions and thus influences its vaccine protective effect. Detailed structural carbohydrate analysis of vaccine induced IgGs is therefore of interest as this knowledge can prove valuable in vaccine research and design and when optimizing vaccine schedules. In order to better understand and exploit the protective potential of IgG antibodies, we carried out a pilot study; collecting serum or plasma from volunteers receiving different vaccines and determining the IgG subclass glycosylation patterns against specific vaccine antigens at different time points using LC-ESI-MS analysis. The four vaccines included a pneumococcal capsule polysaccharide vaccine, a meningococcal outer membrane vesicle vaccine, a seasonal influenza vaccine, and a pandemic influenza vaccine. The number of volunteers was limited, but the results following immunization indicated that the IgG subclass which dominated the response showed increased galactose and the level of sialic acid increased with time for most vaccinees. Fucose levels increased for some vaccinees but in general stayed relatively unaltered. The total background IgG glycosylation analyzed in parallel varied little with time and hence the changes seen were likely to be caused by vaccination. The presence of an adjuvant in the pandemic influenza vaccine seemed to produce simpler and less varied glycoforms compared to the adjuvant-free seasonal influenza vaccine. This pilot study demonstrates that detailed IgG glycosylation pattern analysis might be a necessary step in addition to biological testing for optimizing vaccine development and strategies.

Characterization of immunoglobulin by mass spectrometry with applications for the clinical laboratory

Studies monitoring immunoglobulin (Ig) antigen specificity have brought to light key Ig biomarkers for immunity, autoimmunity, cancer detection, and immune system function evaluation. A fundamentally new approach to the detection of Igs based on the primary structure of the Ig is beginning to emerge in the literature. This approach has only become feasible in light of advances in proteomics and rapid improvements in mass spectrometry (MS). Driven primarily by the development of Ig pharmaceuticals, Ig MS-based proteomic methods are revealing structural features which were previously unavailable with other characterization techniques. The task of adapting these techniques to clinical chemistry is in its infancy, but these methods have the potential to dramatically alter testing for Ig biomarkers. The purpose of this article is to review the advances that have been made in proteomic characterization of Igs by MS and the early attempts to apply these methods to clinical samples.

Ultra scale-down characterization of the impact of conditioning methods for harvested cell broths on clarification by continuous centrifugation-Recovery of domain antibodies from rec E. coli

The processing of harvested E. coli cell broths is examined where the expressed protein product has been released into the extracellular space. Pre-treatment methods such as freeze–thaw, flocculation, and homogenization are studied. The resultant suspensions are characterized in terms of the particle size distribution, sensitivity to shear stress, rheology and solids volume fraction, and, using ultra scale-down methods, the predicted ability to clarify the material using industrial scale continuous flow centrifugation. A key finding was the potential of flocculation methods both to aid the recovery of the particles and to cause the selective precipitation of soluble contaminants. While the flocculated material is severely affected by process shear stress, the impact on the very fine end of the size distribution is relatively minor and hence the predicted performance was only diminished to a small extent, for example, from 99.9% to 99.7% clarification compared with 95% for autolysate and 65% for homogenate at equivalent centrifugation conditions. The lumped properties as represented by ultra scale-down centrifugation results were correlated with the basic properties affecting sedimentation including particle size distribution, suspension viscosity, and solids volume fraction. Grade efficiency relationships were used to allow for the particle and flow dynamics affecting capture in the centrifuge. The size distribution below a critical diameter dependant on the broth pre-treatment type was shown to be the main determining factor affecting the clarification achieved. Biotechnol. Bioeng. 2014;111: 913–924. © 2013 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

Different glycosylation pattern of human IgG1 and IgG3 antibodies isolated from transiently as well as permanently transfected cell lines

The effector functions of IgG depend on the presence of carbohydrates attached to asparagine 297 in the Fc-portion. In this report, glycosylation profiles of recombinant wild-type and mutant IgG1 and IgG3 antibodies produced from three cell lines were analysed using LC-ESI-Orbitrap. Clear differences were detected between IgG1 and IgG3 glycoforms, where IgG1 generally contained fucosylated glycoforms, whilst IgG3 mainly were non-fucosylated. When using NS-0 and J558L cells for permanent transfection, IgG1 wt glycoforms differed between the two cell lines, whilst IgG3 wt glycoforms did not. Transiently transfected HEK 293E cells were used to produce IgG1 and IgG3 wt and mutants, affecting complement activation. Cell supernatants were harvested at early and late time points and analysed separately. IgGs harvested late showed simpler and less developed glycosylation structure compared to those harvested early. The IgG harvested early was slightly more effective in complement activation than those harvested late, whilst the antibody-dependent cell-mediated cytotoxicity was unaltered. Generally, the glycosylation pattern of the mutants tested, including a hinge truncate mutant of IgG3, did not differ significantly from the wild-type IgGs. The striking difference in glycosylation pattern of IgG1 compared to IgG3 therefore appears not to be due to the long hinge region of IgG3 (62 amino acids) relative to the IgG1 hinge region (15 amino acids). Furthermore, mutation variants at or near the C1q binding site showed similar glycosylation structure and difference in their complement activation activity observed earlier is thus most likely due to differences in protein structure only.

Differential response in downstream processing of CHO cells grown under mild hypothermic conditions

The manufacture of complex therapeutic proteins using mammalian cells is well established, with several strategies developed to improve productivity. The application of sustained mild hypothermic conditions during culture has been associated with increases in product titer and improved product quality. However, despite associated cell physiological effects, very few studies have investigated the impact on downstream processing (DSP). Characterization of cells grown under mild hypothermic conditions demonstrated that the stationary phase was prolonged by delaying the onset of apoptosis. This enabled cells to maintain viability for extended periods and increase volumetric productivity from 0.74 to 1.02 g L⁻¹. However, host cell proteins, measured by ELISA, increased by ∼50%, attributed to the extended time course and higher peak and harvest cell densities. The individual components making up this impurity, as determined by SELDI-TOF MS and 2D-PAGE, were shown to be largely comparable. Under mild hypothermic conditions, cells were less shear sensitive than those maintained at 37°C, enhancing the preliminary primary recovery step. Adaptive changes in membrane fluidity were further investigated by adopting a pronounced temperature shift immediately prior to primary recovery and the improvement observed suggests that such a strategy may be implementable when shear sensitivity is of concern. Early and late apoptotic cells were particularly susceptible to shear, at either temperature, even under the lowest shear rate investigated. These findings demonstrate the importance of considering the impact of cell culture strategies and cell physiology on DSP, by implementing a range of experimental methods for process characterization. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:688–696, 2013

Glycomics using mass spectrometry

Mass spectrometry plays an increasingly important role in structural glycomics. This review provides an overview on currently used mass spectrometric approaches such as the characterization of glycans, the analysis of glycopeptides obtained by proteolytic cleavage of proteins and the analysis of glycosphingolipids. The given examples are demonstrating the application of mass spectrometry to study glycosylation changes associated with congenital disorders of glycosylation, lysosomal storage diseases, autoimmune diseases and cancer.

Impact of aeration strategy on CHO cell performance during antibody production

Stirred tank bioreactors using suspension adapted mammalian cells are typically used for the production of complex therapeutic proteins. The hydrodynamic conditions experienced by cells within this environment have been shown to directly impact growth, productivity, and product quality and therefore an improved understanding of the cellular response is critical. Here we investigate the sub-lethal effects of different aeration strategies on Chinese hamster ovary cells during monoclonal antibody production. Two gas delivery systems were employed to study the presence and absence of the air-liquid interface: bubbled direct gas sparging and a non-bubbled diffusive silicone membrane system. Additionally, the effect of higher gas flow rate in the sparged bioreactor was examined. Both aeration systems were run using chemically defined media with and without the shear protectant Pluronic F-68 (PF-68). Cells were unable to grow with direct gas sparging without PF-68; however, when a silicone membrane aeration system was implemented growth was comparable to the sparged bioreactor with PF-68, indicating the necessity of shear protectants in the presence of bubbles. The cultures exposed to increased hydrodynamic stress were shown by flow cytometry to have decreased F-actin intensity within the cytoskeleton and enter apoptosis earlier. This indicates that these conditions elicit a sub-lethal physiological change in cells that would not be detected by the at-line assays which are normally implemented during cell culture. These physiological changes only result in a difference in continuous centrifugation performance under high flow rate conditions. Product quality was more strongly affected by culture age than the hydrodynamic conditions tested.

C-terminal modification of monoclonal antibody drugs: amidated species as a general product-related substance

Twelve therapeutic mAbs, comprising 10 IgG1s and 2 IgG4s, were analyzed by a peptide mapping technique to detect and quantify C-terminal modifications. C-terminal amidated structures were found in 8 out of the 12 mAbs. An in vitro study using a commercially available peptidylglycine alpha-amidating monooxygenase (PAM) revealed that both IgG1 and IgG4 can be substrates for PAM. This study showed that C-terminal amidation is a general C-terminal modification on the heavy chains of therapeutic mAbs and that C-terminal amidation of mAbs can be catalyzed by a certain PAM(s) in the Chinese hamster ovary (CHO) cells that are widely used for manufacturing therapeutic mAbs.

Overexpression of CHOP alone and in combination with chaperones is effective in improving antibody production in mammalian cells

Secretory capacities including folding and assembly are believed to be limiting factors in the establishment of mammalian cell lines producing high levels of recombinant therapeutic proteins. To achieve industrial success, it is also important to improve protein folding, assembly, and secretory processes in combination with increasing transcription and translation. Here, we identified the expression of CHOP/Gadd153 and GRP78, which are unfolded protein response (UPR)-related genes, correlated with recombinant antibody production in stable CHO cells. Subsequently, CHOP overexpression resulted in increasing recombinant antibody production in some mammalian cell lines, and in addition a threefold further enhancement was obtained by combining expression with UPR-related genes or ER chaperones in transient assays. Overexpression of CHOP had no effect on the biochemical characteristics of the product. These results suggest overexpression of CHOP and its combinations may be an effective method to efficiently select a single cell line with a high level of antibody production in the development of cell lines for manufacturing.

Advances and challenges in analytical characterization of biotechnology products: mass spectrometry-based approaches to study properties and behavior of protein therapeutics

Biopharmaceuticals are a unique class of medicines due to their extreme structural complexity. The structure of these therapeutic proteins is critically important for their efficacy and safety, and the ability to characterize it at various levels (from sequence to conformation) is critical not only at the quality control stage, but also throughout the discovery and design stages. Biological mass spectrometry (MS) offers a variety of approaches to study structure and behavior of complex protein drugs and has already become a default tool for characterizing the covalent structure of protein therapeutics, including sequence and post-translational modifications. Recently, MS-based methods have also begun enjoying a dramatic growth in popularity as a means to provide information on higher order structure and dynamics of biotechnology products. In particular, hydrogen/deuterium exchange MS and charge state distribution analysis of protein ions in electrospray ionization (ESI) MS offer a convenient way to assess the integrity of protein conformation. Native ESI MS also allows the interactions of protein drugs with their therapeutic targets and other physiological partners to be monitored using simple model systems. MS-based methods are also applied to study pharmacokinetics of biopharmaceutical products, where they begin to rival traditional immunoassays. MS already provides valuable support to all stages of development of biopharmaceuticals, from discovery to post-approval monitoring, and its impact on the field of biopharmaceutical analysis will undoubtedly continue to grow.