[Recent progress of chromatographic techniques for antibody purification].

Antibody drugs are becoming increasingly popular in disease diagnosis, targeted therapy, and immunoprevention owing to their characteristics of high targeting ability, strong specificity, low toxicity, and mild side effects. The demand for antibody drugs is steadily increasing, and their production scale is expanding. Upstream cell culture technology has been greatly improved by the high-capacity production of monoclonal antibodies. However, the downstream purification of antibodies presents a bottleneck in the production process. Moreover, the purification cost of antibodies is extremely high, accounting for approximately 50%-80% of the total cost of antibody production. Chromatographic technology, given its selectivity and high separation efficiency, is the main method for antibody purification. This process usually involves three stages: antibody capture, intermediate purification, and polishing. Different chromatographic techniques, such as affinity chromatography, ion-exchange chromatography, hydrophobic interaction chromatography, mixed-mode chromatography, and temperature-responsive chromatography, are used in each stage. Affinity chromatography, mainly protein A affinity chromatography, is applied for the selective capture and purification of antibodies from raw biofluids or harvested cell culture supernatants. Other chromatographic techniques, such as ion-exchange chromatography, hydrophobic interaction chromatography, and mixed-mode chromatography, are used for intermediate purification and antibody polishing. Affinity biomimetic chromatography and hydrophobic charge-induction chromatography can produce antibodies with purities comparable with those obtained through protein A chromatography, by employing artificial chemical/short peptide ligands with good selectivity, high stability, and low cost. Temperature-responsive chromatography is a promising technique for the separation and purification of antibodies. In this technique, antibody capture and elution is controlled by simply adjusting the column temperature, which greatly eliminates the risk of antibody aggregation and inactivation under acidic elution conditions. The combination of different chromatographic methods to improve separation selectivity and achieve effective elution under mild conditions is another useful strategy to enhance the yield and quality of antibodies. This review provides an overview of recent advances in the field of antibody purification using chromatography and discusses future developments in this technology.

Native ion mobility-mass spectrometry reveals the binding mechanisms of anti-amyloid therapeutic antibodies.

One of the most important attributes of anti-amyloid antibodies is their selective binding to oligomeric and amyloid aggregates. However, current methods of examining the binding specificities of anti-amyloid ß (Aß) antibodies have limited ability to differentiate between complexes that form between antibodies and monomeric or oligomeric Aß species during the dynamic Aß aggregation process. Here, we present a high-resolution native ion-mobility mass spectrometry (nIM-MS) method to investigate complexes formed between a variety of Aß oligomers and three Aß-specific IgGs, namely two antibodies with relatively high conformational specificity (aducanumab and A34) and one antibody with low conformational specificity (crenezumab). We found that crenezumab primarily binds Aß monomers, while aducanumab preferentially binds Aß monomers and dimers and A34 preferentially binds Aß dimers, trimers, and tetrameters. Through collision induced unfolding (CIU) analysis, our data indicate that antibody stability is increased upon Aß binding and, surprisingly, this stabilization involves the Fc region. Together, we conclude that nIM-MS and CIU enable the identification of Aß antibody binding stoichiometries and provide important details regarding antibody binding mechanisms.

Identification of sorbitol esterification of glutamic acid by LC-MS/MS in a monoclonal antibody stability assessment.

The stability of monoclonal antibodies (mAbs) is vital for their therapeutic success. Sorbitol, a common mAb stabilizer used to prevent aggregation, was evaluated for any potential adverse effects on the chemical stability of mAb X. An LC-MS/MS based analysis focusing on the post-translational modifications (PTMs) of mAb X was conducted on samples that had undergone accelerated aging at 40°C. Along with PTMs that are known to affect mAbs' structure function and stability (such as deamidation and oxidation), a novel mAb PTM was discovered, the esterification of glutamic acid by sorbitol. Incubation of mAb X with a 1:1 ratio of unlabeled sorbitol and isotopically labeled sorbitol (13C6) further corroborated that the modification was the consequence of the esterification of glutamic acid by sorbitol. Levels of esterification varied across glutamic acid residues and correlated with incubation time and sorbitol concentration. After 4 weeks of accelerated stability with isotopically labeled sorbitol, it was found that 16% of the total mAb possesses an esterified glutamic acid. No esterification was observed at aspartic acid sites despite the free carboxylic acid side chain. This study unveils a unique modification of mAbs, emphasizing its potential significance for formulation and drug development.

The role of the size of affinity ligands in the detection and characterization of extracellular vesicles.

Surface proteins on the membrane of nano-sized extracellular vesicles (EVs) not only play crucial roles in cell-to-cell communication, but also are specific binding targets for EV detection, isolation and tracking. The low abundance of protein biomarkers on EV surface, the formation of clusters and the complex EV surface network impose significant challenges to the study of EVs. Employing bulky sized affinity ligands, such as antibodies, in the detection and characterization of these vesicles often result in reduced sensitivity of detection or poor quantification of proteins on the EV surface. By virtue of their small size and high specificity, Affibody molecules emerge as a potential alternative to their monoclonal antibody counterparts as robust affinity ligands in EV research. In this study, we present a theoretical framework on the superiority of anti-HER2 Affibodies over anti-HER2 antibodies in labeling and detecting HER2-positive EVs, followed by the demonstration of the advantages of HER2 Affibodies in accessing EV surface and the detection of EVs through multiple types of approaches including fluorescence intensity, colorimetry, and fluorescence polarization. HER2 Affibodies outperformed by 10-fold over three HER2 antibody clones in accessing HER2-positive EVs derived from different human cancer cell lines. Furthermore, HRP-Affibody molecules could detect EVs from cancer cells spiked into human serum with at least a 2-fold higher sensitivity compared with that of their antibody counterparts. In addition, in fluorescence polarization assays in which no separation of free from bound ligand is required, FITC-labeled HER2 Affibodies could sensitively detect HER2-positive EVs with a clinically relevant limit of detection, whilst HER2 antibodies failed to detect EVs in the same conditions. With the demonstrated superiority in accessing and detecting surface targets over bulky-sized antibodies in EVs, Affibodies may become the next-generation of affinity ligands in the precise characterization and quantification of molecular architecture on the surface of EVs.

Structural Characterization of Monoclonal Antibodies and Epitope Mapping by FFAP Footprinting.

Covalent labeling in combination with mass spectrometry is a powerful approach used in structural biology to study protein structures, interactions, and dynamics. Recently, the toolbox of covalent labeling techniques has been expanded with fast fluoroalkylation of proteins (FFAP). FFAP is a novel radical labeling method that utilizes fluoroalkyl radicals generated from hypervalent Togni reagents for targeting aromatic residues. This report further demonstrates the benefits of FFAP as a new method for structural characterization of therapeutic antibodies and interaction interfaces of antigen-antibody complexes. The results obtained from human trastuzumab and its complex with human epidermal growth factor receptor 2 (HER2) correlate well with previously published structural data and demonstrate the potential of FFAP in structural biology.

A Förster Resonance Energy Transfer (FRET)-Based Immune Assay for the Detection of Microcystin-LR in Drinking Water.

Cyanobacteria bloom is the term used to describe an abnormal and rapid growth of cyanobacteria in aquatic ecosystems such as lakes, rivers, and oceans as a consequence of anthropic factors, ecosystem degradation, or climate change. Cyanobacteria belonging to the genera Microcystis, Anabaena, Planktothrix, and Nostoc produce and release toxins called microcystins (MCs) into the water. MCs can have severe effects on human and animal health following their ingestion and inhalation. The MC structure is composed of a constant region (composed of five amino acid residues) and a variable region (composed of two amino acid residues). When the MC variable region is composed of arginine and leucine, it is named MC-LR. The most-common methods used to detect the presence of MC-LR in water are chromatographic-based methods (HPLC, LC/MS, GC/MS) and immunological-based methods (ELISA). In this work, we developed a new competitive Förster resonance energy transfer (FRET) assay to detect the presence of traces of MC-LR in water. Monoclonal antibody anti-MC-LR and MC-LR conjugated with bovine serum albumin (BSA) were labeled with the near-infrared fluorophores CF568 and CF647, respectively. Steady-state fluorescence measurements were performed to investigate the energy transfer process between anti-MC-LR 568 and MC-LR BSA 647 upon their interaction. Since the presence of unlabeled MC-LR competes with the labeled one, a lower efficiency of FRET process can be observed in the presence of an increasing amount of unlabeled MC-LR. The limit of detection (LoD) of the FRET assay is found to be 0.245 nM (0.245 µg/L). This value is lower than the provisional limit established by the World Health Organization (WHO) for quantifying the presence of MC-LR in drinking water.

Identity verification of monoclonal antibodies by triple injection capillary zone electrophoresis.

This paper presents an approach based on triple injection capillary zone electrophoresis for identification of monoclonal antibodies. The analyte to be identified is injected between two zones of a known reference. The distances between the reference zones (plug I and III) and the target zone (plug II) are adjusted by partial electrophoresis of the first and second injection plugs. The full migration time of the target analyte is calculated from the observed migration time by considering the migration times of the reference in the first and third injection plugs. The relative migration time, that is, the ratio between the full migration time of the analyte and the migration time of the reference in the third injection plug provides the basis for identification. Here, eight monoclonal antibodies, including a pair of biosimilars, were used interchangeably as both analyte and reference to investigate potential of the method. The relative migration time for a preliminary positive identification were found to vary between 0.994 and 1.006 (1.000 ± 0.006, p = 95%). Beside the relative migration time, isoform distribution, peak profiles, and early migrating peaks, originating from components in the pharmaceutical formulations, were successfully used to verify the identity of all tested monoclonal antibodies.

Deep learning framework for peak detection at the intact level of therapeutic proteins.

While automated peak detection functionalities are available in commercially accessible software, achieving optimal true positive rates frequently necessitates visual inspection and manual adjustments. In the initial phase of this study, hetero-variants (glycoforms) of a monoclonal antibody were distinguished using liquid chromatography-mass spectrometry, revealing discernible peaks at the intact level. To comprehensively identify each peak (hetero-variant) in the intact-level analysis, a deep learning approach utilizing convolutional neural networks (CNNs) was employed in the subsequent phase of the study. In the current case study, utilizing conventional software for peak identification, five peaks were detected using a 0.5 threshold, whereas seven peaks were identified using the CNN model. The model exhibited strong performance with a probability area under the curve (AUC) of 0.9949, surpassing that of partial least squares discriminant analysis (PLS-DA) (probability AUC of 0.8041), and locally weighted regression (LWR) (probability AUC of 0.6885) on the data acquired during experimentation in real-time. The AUC of the receiver operating characteristic curve also illustrated the superior performance of the CNN over PLS-DA and LWR.

Re-assessment of monoclonal antibodies against diclofenac for their application in the analysis of environmental waters.

The non-steroidal anti-inflammatory drug (NSAID) diclofenac (DCF) is an important environmental contaminant occurring in surface waters all over the world, because, after excretion, it is not adequately removed from wastewater in sewage treatment plants. To be able to monitor this pollutant, highly efficient analytical methods are needed, including immunoassays. In a medical research project, monoclonal antibodies against diclofenac and its metabolites had been produced. Based on this monoclonal anti-DCF antibody, a new indirect competitive enzyme-linked immunosorbent assay (ELISA) was developed and applied for environmental samples. The introduction of a spacer between diclofenac and the carrier protein in the coating conjugate led to higher sensitivity. With a test midpoint of 3 µg L-1 and a measurement range of 1-30 µg L-1, the system is not sensitive enough for direct analysis of surface water. However, this assay is quite robust against matrix influences and can be used for wastewater. Without adjustment of the calibration, organic solvents up to 5%, natural organic matter (NOM) up to 10 mg L-1, humic acids up to 2.5 mg L-1, and salt concentrations up to 6 g L-1 NaCl and 75 mg L-1 CaCl2 are tolerated. The antibody is also stable in a pH range from 3 to 12. Cross-reactivity (CR) of 1% or less was determined for the metabolites 4'-hydroxydiclofenac (4'-OH-DCF), 5-hydroxydiclofenac (5-OH-DCF), DCF lactam, and other NSAIDs. Relevant cross-reactivity occurred only with an amide derivative of DCF, 6-aminohexanoic acid (DCF-Ahx), aceclofenac (ACF) and DCF methyl ester (DCF-Me) with 150%, 61% and 44%, respectively. These substances, however, have not been found in samples. Only DCF-acyl glucuronide with a cross-reactivity of 57% is of some relevance. For the first time, photodegradation products were tested for cross-reactivity. With the ELISA based on this antibody, water samples were analysed. In sewage treatment plant effluents, concentrations in the range of 1.9-5.2 µg L-1 were determined directly, with recoveries compared to HPLC-MS/MS averaging 136%. Concentrations in lakes ranged from 3 to 4.4 ng L-1 and were, after pre-concentration, determined with an average recovery of 100%.

Evaluation of the Inhibitory Potential of Synthetic Peptides Homologous to CDR3 Regions of a Monoclonal Antibody against Bothropic Venom Serine Proteases.

Snakebite accidents, neglected tropical diseases per the WHO, pose a significant public health threat due to their severity and frequency. Envenomation by Bothrops genus snakes leads to severe manifestations due to proteolytic enzymes. While the antibothropic serum produced by the Butantan Institute saves lives, its efficacy is limited as it fails to neutralize certain serine proteases. Hence, developing new-generation antivenoms, like monoclonal antibodies, is crucial. This study aimed to explore the inhibitory potential of synthetic peptides homologous to the CDR3 regions of a monoclonal antibody targeting a snake venom thrombin-like enzyme (SVTLE) from B. atrox venom. Five synthetic peptides were studied, all stable against hydrolysis by venoms and serine proteases. Impressively, four peptides demonstrated uncompetitive SVTLE inhibition, with Ki values ranging from 10-6 to 10-7 M. These findings underscore the potential of short peptides homologous to CDR3 regions in blocking snake venom toxins, suggesting their promise as the basis for new-generation antivenoms. Thus, this study offers potential advancements in combatting snakebites, addressing a critical public health challenge in tropical and subtropical regions.

A High-Homology Region Provides the Possibility of Detecting ß-Barrel Pore-Forming Toxins from Various Bacterial Species.

The pathogenicity of many bacteria, including Bacillus cereus and Staphylococcus aureus, depends on pore-forming toxins (PFTs), which cause the lysis of host cells by forming pores in the membranes of eukaryotic cells. Bioinformatic analysis revealed a region homologous to the Lys171-Gly250 sequence in hemolysin II (HlyII) from B. cereus in over 600 PFTs, which we designated as a "homologous peptide". Three ß-barrel PFTs were used for a detailed comparative analysis. Two of them-HlyII and cytotoxin K2 (CytK2)-are synthesized in Bacillus cereus sensu lato; the third, S. aureus α-toxin (Hla), is the most investigated representative of the family. Protein modeling showed certain amino acids of the homologous peptide to be located on the surface of the monomeric forms of these ß-barrel PFTs. We obtained monoclonal antibodies against both a cloned homologous peptide and a 14-membered synthetic peptide, DSFNTFYGNQLFMK, as part of the homologous peptide. The HlyII, CytK2, and Hla regions recognized by the obtained antibodies, as well as an antibody capable of suppressing the hemolytic activity of CytK2, were identified in the course of this work. Antibodies capable of recognizing PFTs of various origins can be useful tools for both identification and suppression of the cytolytic activity of PFTs.

De novo synthesis of a novel hapten and development of a monoclonal antibody-based immunoassay for the detection of dichlorvos and trichlorfon.

The absence of high-affinity antibodies has hindered the development of satisfactory immunoassays for dichlorvos (DDVP) and trichlorfon (TCP), two highly toxic organophosphorus pesticides. Herein, the de novo synthesis of a novel anti-DDVP hapten was introduced. Subsequently, a specific anti-DDVP monoclonal antibody (Mab) was produced with satisfying affinity to DDVP (IC50: 12.4 ng mL-1). This Mab was highly specific to DDVP, and TCP could readily convert into DDVP under mild alkaline conditions. Leveraging this insight, an indirect competitive ELISA was successfully developed for simultaneous detection of DDVP and TCP. The limit of detection in rice, cabbage and apple for DDVP /TCP was found to be 12.1/14.6 µg kg-1, 7.3/8.8 µg kg-1 and 6.9/8.3 µg kg-1, respectively. This study not only provides an effective strategy for producing a high-quality anti-DDVP Mab but also affords a reliable and cost-effective tool suitable for high-throughput detection of DDVP and TCP in food samples.

Fluorescent and Colorimetric Dual-Readout Immunochromatographic Assay for the Detection of Phenamacril Residues in Agricultural Products.

The fungicide phenamacril has been employed to manage Fusarium and mycotoxins in crops, leading to persistent residues in the environment and plants. Detecting phenamacril is pivotal for ensuring environmental and food safety. In this study, haptens and artificial antigens were synthesized to produce antiphenamacril monoclonal antibodies (mAbs). Additionally, gold nanoparticles coated with a polydopamine shell were synthesized and conjugated with mAbs, inducing fluorescence quenching in quantum dots. Moreover, a dual-readout immunochromatographic assay that combines the positive signal from fluorescence with the negative signal from colorimetry was developed to enable sensitive and precise detection of phenamacril within 10 min, achieving detection limits of 5 ng/mL. The method's reliability was affirmed by using spiked wheat flour samples, achieving a limit of quantitation of 0.05 mg/kg. This analytical platform demonstrates high sensitivity, outstanding accuracy, and robust tolerance to matrix effects, making it suitable for the rapid, onsite, quantitative screening of phenamacril residues.

Multidimensional LC-MS with 1D multi-method option and parallel middle-up and bottom-up MS acquisition for in-depth characterization of antibodies.

Monoclonal antibodies (mAbs) are large and highly heterogeneous species typically characterized using a plethora of analytical methodologies. There is a trend within the biopharmaceutical industry to combine several of these methods in one analytical platform to simultaneously assess multiple structural attributes. Here, a protein analyzer for the fully automated middle-up and bottom-up liquid chromatography-mass spectrometry (LC-MS) analysis of charge, size and hydrophobic variants is described. The multidimensional set-up combines a multi-method option in the first dimension (1D) (choice between size exclusion - SEC, cation exchange - CEX or hydrophobic interaction chromatography - HIC) with second dimension (2D) on-column reversed-phase (RPLC) based desalting, denaturation and reduction prior to middle-up LC-MS analysis of collected 1D peaks and parallel on-column trypsin digestion of denatured and reduced peaks in the third dimension (3D) followed by bottom-up LC-MS analysis in the fourth dimension (4D). The versatile and comprehensive workflow is applied to the characterization of charge, hydrophobic and size heterogeneities associated with an engineered Fc fragment and is complemented with hydrogen-deuterium exchange (HDX) MS and FcRn affinity chromatography - native MS to explain observations in a structural/functional context.

The Evaluation of a Lateral Flow Strip Based on the Covalently Fixed "End-On" Orientation of an Antibody for Listeria monocytogenes Detection.

In this study, the covalently fixed "end-on" orientation of a monoclonal Listeria monocytogenes antibody (mAb-Lis) to amino terminated oligo (ethylene glycol)-capped gold nanoparticles (NH2-TEG-AuNPs) was used to fabricate an in-house lateral flow strip (LFS), namely, the fixed "end-on" Lis-mAb-NH-TEG-AuNPs LFS. The aim was to evaluate the performance of the fixed "end-on" Lis-mAb-NH-TEG-AuNPs LFS in detecting L. monocytogenes. The proposed LFS enabled the sensitive detection of L. monocytogenes in 15 min with a visual limit of detection of 102 CFU/mL. Quantitative analysis indicated an LOD at 10 CFU/mL. The fixed "end-on" Lis-mAb-NH-TEG-AuNPs LFS showed no cross-reactivity with other pathogenic bacteria and practical performance across different food matrices, including human blood, milk, and mushroom samples. Furthermore, the clinical performance of the fixed "end-on" Lis-mAb-NH-TEG-AuNPs LFS for detecting L. monocytogenes was evaluated by using 12 clinical samples validated by the hemoculture method. It demonstrated excellent concordance with the reference methods, with no false-positive or false-negative results observed. Therefore, the fixed "end-on" Lis-mAb-NH-TEG-AuNPs LFS serves as a promising candidate for a point-of-care test (POCT), enabling the rapid, precise, and highly sensitive detection of L. monocytogenes in clinical samples and contaminated food.

Hapten synthesis, monoclonal antibody production and immunoassay development for analyzing spiropidion residues.

Spiropidion developed by Syngenta shows high insecticidal and acaricidal activity against a wide range of sucking pests. In this study, according to the structure of spiropidion, two haptens were synthesized by introducing carboxyl groups from the ester group. After cell fusion, a monoclonal antibody (mAb 8B5) of spiropidion was obtained. The IC50 of the established heterologous indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was 7.36 ng/mL, and its working range was 1.75-34.92 ng/mL. The average recoveries were 76.05-124.78% in the Yangtze River and citrus samples. Moreover, the ic-ELISA results of 15 citrus samples agreed well with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Overall, the established ic-ELISA could be applied for the spiropidion residue monitor in food and agricultural samples.

An important consideration when expressing mAbs in Escherichiacoli.

Monoclonal antibodies (mAbs) are a driving force in the biopharmaceutical industry. Therapeutic mAbs are usually produced in mammalian cells, but there has been a push towards the use of alternative production hosts, such as Escherichia coli. When the genes encoding for a mAb heavy and light chains are codon-optimized for E. coli expression, a truncated form of the heavy chain can form along with the full-length product. In this work, the role of codon optimization in the formation of a truncated product was investigated. This study used the amino acid sequences of several therapeutic mAbs and multiple optimization algorithms. It was found that several algorithms incorporate sequences that lead to a truncated product. Approaches to avoid this truncated form are discussed.

Hepatitis B Virus Neutralization with DNA Origami Nanoshells.

We demonstrate the use of DNA origami to create virus-trapping nanoshells that efficiently neutralize hepatitis B virus (HBV) in cell culture. By modification of the shells with a synthetic monoclonal antibody that binds to the HBV envelope, the effective neutralization potency per antibody is increased by approximately 100 times compared to using free antibodies. The improvements in neutralizing the virus are attributed to two factors: first, the shells act as a physical barrier that blocks the virus from interacting with host cells; second, the multivalent binding of the antibodies inside the shells lead to stronger attachment to the trapped virus, a phenomenon known as avidity. Pre-incubation of shells with HBV and simultaneous addition of both components separately to cells lead to comparable levels of neutralization, indicating rapid trapping of the virions by the shells. Our study highlights the potential of the DNA shell system to rationally create antivirals using components that, when used individually, show little to no antiviral effectiveness.

A Highly Sensitive and Group-Specific Enzyme-Linked Immunosorbent Assay (ELISA) for the Detection of AFB1 in Agriculture and Aquiculture Products.

Aflatoxins (AFs) including AFB1, AFB2, AFG1 and AFG2 are widely found in agriculture products, and AFB1 is considered one of the most toxic and harmful mycotoxins. Herein, a highly sensitive (at the pg mL-1 level) and group-specific enzyme-linked immunosorbent assay (ELISA) for the detection of AFB1 in agricultural and aquiculture products was developed. The AFB1 derivative containing a carboxylic group was synthesized and covalently linked to bovine serum albumin (BSA). The AFB1-BSA conjugate was used as an immunogen to immunize mice. A high-quality monoclonal antibody (mAb) against AFB1 was produced by hybridoma technology, and the mAb-based ELISA for AFB1 was established. IC50 and limit of detection (LOD) of the ELISA for AFB1 were 90 pg mL-1 and 18 pg mL-1, respectively. The cross-reactivities (CRs) of the assay with AFB2, AFG1, and AFG2 were 23.6%, 42.5%, and 1.9%, respectively, revealing some degree of group specificity. Corn flour, wheat flour, and crab roe samples spiked with different contents of AFB1 were subjected to ELISA procedures. The recoveries and relative standard deviation (RSD) of the ELISA for AFB1 in spiked samples were 78.3-116.6% and 1.49-13.21% (n = 3), respectively. Wheat flour samples spiked with the mixed AF (AFB1, AFB2, AFG1, AFG2) standard solution were measured by ELISA and LC-MS/MS simultaneously. It was demonstrated that the proposed ELISA can be used as a screening method for evaluation of AFs (AFB1, AFB2, AFG1, AFG2) in wheat flour samples.

Characterization of Complex Proteoform Mixtures by Online Nanoflow Ion-Exchange Chromatography-Native Mass Spectrometry.

The characterization of proteins and complexes in biological systems is essential to establish their critical properties and to understand their unique functions in a plethora of bioprocesses. However, it is highly difficult to analyze low levels of intact proteins in their native states (especially those exceeding 30 kDa) with liquid chromatography (LC)-mass spectrometry (MS). Herein, we describe for the first time the use of nanoflow ion-exchange chromatography directly coupled with native MS to resolve mixtures of intact proteins. Reference proteins and protein complexes with molecular weights between 10 and 150 kDa and a model cell lysate were separated using a salt-mediated pH gradient method with volatile additives. The method allowed for low detection limits (0.22 pmol of monoclonal antibodies), while proteins presented nondenatured MS (low number of charges and limited charge state distributions), and the oligomeric state of the complexes analyzed was mostly kept. Excellent chromatographic separations including the resolution of different proteoforms of large proteins (>140 kDa) and a peak capacity of 82 in a 30 min gradient were obtained. The proposed setup and workflows show great potential for analyzing diverse proteoforms in native top-down proteomics, opening unprecedented opportunities for clinical studies and other sample-limited applications.