Sexually transmitted infections (STI) and antenatal care (ANC) clinics in Malawi: effective platforms for improving engagement of men at high HIV risk with voluntary medical male circumcision services.

INTRODUCTION: Voluntary medical male circumcision (VMMC), an effective HIV prevention programme for men, is implemented in East and Southern Africa. Approximately 50% of VMMC clients are aged below 15 years. More targeted interventions to reach older men and others at higher short-term HIV risk are needed. METHODS: We implemented a quality improvement project testing the effectiveness of an active referral-based VMMC recruitment approach, targeting men attending STI clinics and those escorting partners to antenatal care (ANC) clinics, at Bwaila Hospital in Lilongwe, Malawi. We compared the proportions aged older than 15 years among men who received VMMC following referral from STI and ANC clinics with those among men referred from standard community mobilisation. We also analysed referral cascades to VMMC. RESULTS: In total, 330 clients were circumcised after referral from STI (242) and ANC (88) clinics, as compared with 3839 other clients attributed to standard community mobilisation. All clients from ANC and STI clinics were aged over 15 years, as compared with 69% from standard community mobilisation. STI clinics had a higher conversion rate from counselling to VMMC than ANC (12% vs 9%) and a higher contribution to total circumcisions performed at the VMMC clinic (6% vs 2%). CONCLUSIONS: Integrating VMMC recruitment and follow-up in STI and ANC clinics co-located with VMMC services can augment demand creation and targeting of men at risk of HIV, based on age and STI history. This approach can be replicated at least in similar health facilities with ANC and STI services in close proximity to VMMC service delivery.

Integrated Family Planning and Immunization Service Delivery at Health Facility and Community Sites in Dowa and Ntchisi Districts of Malawi: A Mixed Methods Process Evaluation.

The Government of Malawi's Health Sector Strategic Plan II highlights the importance of service integration; however, in practice, this has not been fully realized. We conducted a mixed methods evaluation of efforts to systematically implement integrated family planning and immunization services in all health facilities and associated community sites in Ntchisi and Dowa districts during June 2016-September 2017. Methods included secondary analysis of service statistics (pre- and postintervention), focus group discussions with mothers and fathers of children under age one, and in-depth interviews with service providers, supervisors, and managers. Results indicate statistically significant increases in family planning users and shifts in use of family planning services from health facilities to community sites. The intervention had no effect on immunization doses administered or dropout rates. According to mothers and fathers, benefits of service integration included time savings, convenience, and improved understanding of services. Provision and use of integrated services were affected by availability of human resources and commodities, community linkages, data collection procedures and availability, sociocultural barriers, organization of services, and supervision and commitment of health surveillance assistants. The integration approach was perceived to be feasible and beneficial by clients and providers.

The Molecular Interaction Process.

Noncovalent molecular interactions, which are central to life, are thermodynamic processes that follow common interaction pathways. This commentary provides a foundation for both considering noncovalent interactions and the interplay between the protein properties and the solvent properties in determining the energetics. In biopharmaceutics, noncovalent interactions are a 2-edged sword. Foremost, they provide a core function for biopharmaceutical agents, binding to targets, substrates, or receptors. At the same time, they are at the root of the solubility and viscosity difficulties encountered in the manufacture, formulation, and delivery of protein-based pharmaceuticals. This commentary describes the interaction process and summarizes the energetics of the interaction pathway. The focus will be on protein-protein interactions, while recognizing that the processes and energetics are entirely general and applicable to all solution interactions. The contributions of protein molecular properties and protein colloidal properties to the pathway are described, and the relationship between the two is developed. The processes leading to protein-protein binding are described with respect to the attractive interactions that lead to aggregation and high viscosity. The concept of emergent heterogeneity is introduced, and a model presented for how noncontacting interactions may lead to high viscosities without simultaneously causing low solubility.

The Effect of Low Ionic Strength on Diffusion and Viscosity of Monoclonal Antibodies.

PURPOSE: To determine the effect of solution conditions, especially low ionic strength, on the dynamics of molecular diffusion and protein-protein interactions in monoclonal antibody solutions. METHODS: The interaction parameter, kD, was calculated from diffusion data obtained from dynamic light scattering (DLS) measurements performed using a Zetasizer. Theoretical considerations were utilized to evaluate the hard sphere and electrostatic contribution to molecular interactions. RESULTS: At low ionic strengths, repulsions were the dominant forces governing the behavior of both mAbs. As ionic strength increased, attractions contributed to the behavior of mAb1, while repulsions remained the dominant factor affecting mAb3 behavior. Repulsions alone were not sufficient to affect mAb3 viscosity in water, while the presence of repulsions as well as specific attractions was suggested to cause an increase in the viscosity of mAb1 in water compared to 15 mM ionic strength. CONCLUSIONS: Solution physical properties varied for the mAbs investigated. Our findings highlighted the importance of developing a fundamental understanding of interplay of forces governing solution properties of each individual mAb under low ionic strength conditions. Such understanding is critical in enabling successful development of self-buffered formulations.

Effect of Aggregation on the Hydrodynamic Properties of Bovine Serum Albumin.

PURPOSE: To systematically analyze shape and size of soluble irreversible aggregates and the effect of aggregate formation on viscosity. METHODS: Online light scattering, refractive index and viscosity detectors attached to HPLC (Viscotek®) were used to study aggregation, molecular weight and intrinsic viscosity of bovine serum albumin (BSA). Irreversible aggregates were generated by heat stress. Bulk viscosity was measured by an oscillating piston viscometer. RESULTS: As BSA was heated at a higher concentration or for a longer time, the relative contribution, molecular weight and intrinsic viscosity of aggregate species increased. Molecular shape was evaluated from intrinsic viscosity values, and aggregates were estimated to be more asymmetric than monomer species. The presence of aggregates resulted in an increase in bulk viscosity when relative contribution of very high molecular weight species exceeded 10%. CONCLUSIONS: For model system and conditions studied, generation of higher order aggregate species was concluded to be associated with an increase in molecular asymmetry. Elevated viscosity in the presence of aggregated species points to molecular asymmetry being a critical parameter affecting solution viscosity of BSA.

Challenges in Determining Intrinsic Viscosity Under Low Ionic Strength Solution Conditions.

PURPOSE: To determine the intrinsic viscosity of several monoclonal antibodies (mAbs) under varying pH and ionic strength solution conditions. METHODS: An online viscosity detector attached to HPLC (Viscotek®) was used to determine the intrinsic viscosity of mAbs. The Ross and Minton equation was used for viscosity prediction at high protein concentrations. Bulk viscosity was determined by a Cambridge viscometer. RESULTS: At 15 mM ionic strength, intrinsic viscosity of the mAbs determined by the single-point approach varied from 5.6 to 6.4 mL/g with changes in pH. High ionic strength did not significantly alter intrinsic viscosity, while a significant increase (up to 24.0 mL/g) was observed near zero mM. No difference in bulk viscosity of mAb3 was observed around pH 6 as a function of ionic strength. Data analysis revealed that near zero mM ionic strength limitations of the single-point technique result in erroneously high intrinsic viscosity. CONCLUSIONS: Intrinsic viscosity is a valuable tool that can be used to model baseline viscosity at higher protein concentrations. However, it is not predictive of solution non-ideality at higher protein concentrations. Furthermore, breakdown of numerous assumptions limits the applicability of experimental techniques near zero mM ionic strength conditions. For molecules and conditions studied, the single-point approach produced reliable intrinsic viscosity results at 15 mM. However, this approach must be used with caution near zero mM ionic strength. Data analysis can be used to reveal whether determined intrinsic viscosity is reliable or erroneously high.

Solubility Challenges in High Concentration Monoclonal Antibody Formulations: Relationship with Amino Acid Sequence and Intermolecular Interactions.

The purpose of this work was to elucidate the molecular interactions leading to monoclonal antibody self-association and precipitation and utilize biophysical measurements to predict solubility behavior at high protein concentration. Two monoclonal antibodies (mAb-G and mAb-R) binding to overlapping epitopes were investigated. Precipitation of mAb-G solutions was most prominent at high ionic strength conditions and demonstrated strong dependence on ionic strength, as well as slight dependence on solution pH. At similar conditions no precipitation was observed for mAb-R solutions. Intermolecular interactions (interaction parameter, kD) related well with high concentration solubility behavior of both antibodies. Upon increasing buffer ionic strength, interactions of mAb-R tended to weaken, while those of mAb-G became more attractive. To investigate the role of amino acid sequence on precipitation behavior, mutants were designed by substituting the CDR of mAb-R into the mAb-G framework (GM-1) or deleting two hydrophobic residues in the CDR of mAb-G (GM-2). No precipitation was observed at high ionic strength for either mutant. The molecular interactions of mutants were similar in magnitude to those of mAb-R. The results suggest that presence of hydrophobic groups in the CDR of mAb-G may be responsible for compromising its solubility at high ionic strength conditions since deleting these residues mitigated the solubility issue.

Analytical Ultracentrifugation and Its Role in Development and Research of Therapeutical Proteins.

The historical contributions of analytical ultracentrifugation (AUC) to modern biology and biotechnology drug development and research are discussed. AUC developed by Svedberg was used to show that proteins are actually large defined molecular entities and also provided the first experimental verification for the semiconservative replication model for DNA initially proposed by Watson and Crick. This chapter reviews the use of AUC to investigate molecular weight of recombinant-DNA-produced proteins, complex formation of antibodies, intermolecular interactions in dilute and high concentration protein solution, and their impact on physical properties such as solution viscosity. Recent studies using a "competitive binding" analysis by AUC have been useful in critically evaluating the design and interpretation of surface plasmon resonance measurements and are discussed. The future of this technology is also discussed including prospects for a new higher precision analytical ultracentrifuge.

Comparative study of analytical techniques for determining protein charge.

As interest in high-concentration protein formulations has increased, it has become apparent that routine, accurate protein charge measurements are necessary. There are several techniques for charge measurement, and a comparison of the methods is needed. The electrophoretic mobility, effective charge, and Debye-Hückel-Henry charge have been determined for bovine serum albumin, and human serum albumin. Three different electrophoretic methods were used to measure the electrophoretic mobility: capillary electrophoresis, electrophoretic light scattering, and membrane confined electrophoresis. In addition, the effective charge was measured directly using steady-state electrophoresis. Measurements made at different NaCl concentrations, pH, and temperatures allow comparison with previous charge estimates based on electrophoresis, Donnan equilibrium, and pH titration. Similar charge estimates are obtained by all of the methods. The strengths and limitations of each technique are discussed, as are some general considerations about protein charge and charge determination.

Comparison of binding characteristics and in vitro activities of three inhibitors of vascular endothelial growth factor A.

The objectives of this study were to evaluate the relative binding and potencies of three inhibitors of vascular endothelial growth factor A (VEGF), used to treat neovascular age-related macular degeneration, and assess their relevance in the context of clinical outcome. Ranibizumab is a 48 kDa antigen binding fragment, which lacks a fragment crystallizable (Fc) region and is rapidly cleared from systemic circulation. Aflibercept, a 110 kDa fusion protein, and bevacizumab, a 150 kDa monoclonal antibody, each contain an Fc region. Binding affinities were determined using Biacore analysis. Competitive binding by sedimentation velocity analytical ultracentrifugation (SV-AUC) was used to support the binding affinities determined by Biacore of ranibizumab and aflibercept to VEGF. A bovine retinal microvascular endothelial cell (BREC) proliferation assay was used to measure potency. Biacore measurements were format dependent, especially for aflibercept, suggesting that biologically relevant, true affinities of recombinant VEGF (rhVEGF) and its inhibitors are yet to be determined. Despite this assay format dependency, ranibizumab appeared to be a very tight VEGF binder in all three formats. The results are also very comparable to those reported previously.1-3 At equivalent molar ratios, ranibizumab was able to displace aflibercept from preformed aflibercept/VEGF complexes in solution as assessed by SV-AUC, whereas aflibercept was not able to significantly displace ranibizumab from preformed ranibizumab/VEGF complexes. Ranibizumab, aflibercept, and bevacizumab showed dose-dependent inhibition of BREC proliferation induced by 6 ng/mL VEGF, with average IC50 values of 0.088 ± 0.032, 0.090 ± 0.009, and 0.500 ± 0.091 nM, respectively. Similar results were obtained with 3 ng/mL VEGF. In summary Biacore studies and SV-AUC solution studies show that aflibercept does not bind with higher affinity than ranibizumab to VEGF as recently reported,4 and both inhibitors appeared to be equipotent with respect to their ability to inhibit VEGF function.

Dipole-dipole interaction in antibody solutions: correlation with viscosity behavior at high concentration.

PURPOSE: The purpose of this study was to investigate the contribution of the dipole moment to overall protein-protein interactions and viscosity of a monoclonal antibody MAb1. METHODS: The dipole moment of MAb1 was measured at various solution pH conditions using dielectric relaxation spectroscopy. RESULTS: The dipole moment for MAb1 was highest at pH 6.5, and the pH dependent change in molecular dipole correlated fairly well with previously observed trends of viscosity and storage modulus versus pH. Moreover, the magnitude of the dielectric increment at pH 6.5 and 7.0 showed strong concentration dependence, indicating the presence of relatively strong dipole-dipole interactions at these pHs. To test if the cluster of charged residues present in the Fab contributes to the mean dipole moment observed for MAb1, additional mutants involving charge mutations in the CDR were investigated. In contrast to MAb1, all of the other MAbs showed significantly reduced pH and concentration dependence of the measured dipole moments and dielectric increments, respectively. CONCLUSIONS: The solution pH dependent measured dipole moments of MAb1 appears to be in line with the observed intermolecular interactions and viscosity behavior suggesting that dipole-dipole interaction plays an important role in governing the high concentration solution behavior of this MAb.

Small-angle neutron scattering characterization of monoclonal antibody conformations and interactions at high concentrations.

Small-angle neutron scattering (SANS) is used to probe the solution structure of two protein therapeutics (monoclonal antibodies 1 and 2 (MAb1 and MAb2)) and their protein-protein interaction (PPI) at high concentrations. These MAbs differ by small sequence alterations in the complementarity-determining region but show very large differences in solution viscosity. The analyses of SANS patterns as a function of different solution conditions suggest that the average intramolecular structure of both MAbs in solution is not significantly altered over the studied protein concentrations and experimental conditions. Even though a strong repulsive interaction is expected for both MAbs due to their net charges and low solvent ionic strength, analysis of the SANS data shows that the effective PPI for MAb1 is dominated by a very strong attraction at small volume fraction that becomes negligible at large concentrations. The MAb1 PPI cannot be modeled simply by a spherically symmetric central forces model. It is proposed that an anisotropic attraction strongly affects the local interprotein structure and leads to an anomalously large viscosity of concentrated MAb1 solutions. Conversely, MAb2 displays a repulsive interaction potential throughout the concentration series probed and a comparatively small solution viscosity.

Monoclonal antibody self-association, cluster formation, and rheology at high concentrations.

The rheological properties of macromolecular and colloidal suspensions are dependent on the thermodynamic and kinetic parameters that define viscous flow, and remain an active field of study with broad implications in cellular biophysics, soft-matter theory, and biopharmaceutical technology. Here we use static light scattering, small-angle X-ray scattering, and viscosity measurements as a function of protein concentration to semiquantitatively correlate the oligomeric state of an IgG1 antibody (mAb1) with its rheological behavior at solution pH 6.0 and varying ionic strength (modified by 0.01-0.1 M Na2SO4). Solution SAXS characterization of 100 mM Na2SO4 solutions confirmed that mAb1 forms reversible dimers with extended structures in dilute solutions. Light-scattering measurements over a wide range of concentrations (1-175 mg/mL) provide detailed information on the equilibrium thermodynamic mAb1 interactions and their modulation by modest increases of Na2SO4. Through the use of interacting hard sphere models to fit light-scattering data, we establish that protein cluster formations consisting of 2-9 mAb1 molecules also increase the viscosity of 175 mg/mL IgG solutions from 52 up to 450 cP. The analysis of dilute and semidilute mAb1 solution rheology correlates linearly with the thermodynamic equilibrium cluster size, consistent with the viscosity behavior of elongated oligomeric structures that are not significantly dendrimeric or in a state of globular collapse. Furthermore, SAXS- and rheology-based structural modeling illustrate that only a small set of anisotropic interactions between complementary surfaces are required to nucleate and propagate protein clusters.

The role of amino acid sequence in the self-association of therapeutic monoclonal antibodies: insights from coarse-grained modeling.

Coarse-grained computational models of therapeutic monoclonal antibodies and their mutants can be used to understand the effect of domain-level charge-charge electrostatics on the self-association phenomena at high protein concentrations. The coarse-grained models are constructed for two antibodies at different coarse-grained resolutions by using six different concentrations. It is observed that a particular monoclonal antibody (hereafter referred to as MAb1) forms three-dimensional heterogeneous structures with dense regions or clusters compared to a different monoclonal antibody (hereafter referred to as MAb2) that forms homogeneous structures without clusters. The potential of mean force (PMF) and radial distribution functions (RDF) plots for the mutants (hereafter referred to as M1, M5, M7, and M10) show trends consistent with previously reported experimental observation of viscosities. The mutant referred to as M6 shows strongly attractive interactions that are consistent with previously reported negative second virial coefficients (B(22)) obtained from light-scattering experiments (Yadav et al. Pharm. Res. 2011, 28, 1750-1764; Yadav et al. Mol. Pharmaceutics. 2012, 9, 791-802). Clustering data on MAb1 reveal a small number of large clusters that are hypothesized to be the reason for the high experimental viscosity. This is in contrast with M6 (that differs from MAb1 in only a few amino acids), where cluster analysis reveals the formation of a large number of smaller clusters that is hypothesized to be the reason for the observed lower viscosity. The coarse-grained representations are effective in picking up differences based on local charge distributions of domains to make predictions on the self-association characteristics of these protein solutions.

Assessment and significance of protein-protein interactions during development of protein biopharmaceuticals.

Early development of protein biotherapeutics using recombinant DNA technology involved progress in the areas of cloning, screening, expression and recovery/purification. As the biotechnology industry matured, resulting in marketed products, a greater emphasis was placed on development of formulations and delivery systems requiring a better understanding of the chemical and physical properties of newly developed protein drugs. Biophysical techniques such as analytical ultracentrifugation, dynamic and static light scattering, and circular dichroism were used to study protein-protein interactions during various stages of development of protein therapeutics. These studies included investigation of protein self-association in many of the early development projects including analysis of highly glycosylated proteins expressed in mammalian CHO cell cultures. Assessment of protein-protein interactions during development of an IgG1 monoclonal antibody that binds to IgE were important in understanding the pharmacokinetics and dosing for this important biotherapeutic used to treat severe allergic IgE-mediated asthma. These studies were extended to the investigation of monoclonal antibody-antigen interactions in human serum using the fluorescent detection system of the analytical ultracentrifuge. Analysis by sedimentation velocity analytical ultracentrifugation was also used to investigate competitive binding to monoclonal antibody targets. Recent development of high concentration protein formulations for subcutaneous administration of therapeutics posed challenges, which resulted in the use of dynamic and static light scattering, and preparative analytical ultracentrifugation to understand the self-association and rheological properties of concentrated monoclonal antibody solutions.

Weak interactions govern the viscosity of concentrated antibody solutions: high-throughput analysis using the diffusion interaction parameter.

Weak protein-protein interactions are thought to modulate the viscoelastic properties of concentrated antibody solutions. Predicting the viscoelastic behavior of concentrated antibodies from their dilute solution behavior is of significant interest and remains a challenge. Here, we show that the diffusion interaction parameter (k(D)), a component of the osmotic second virial coefficient (B(2)) that is amenable to high-throughput measurement in dilute solutions, correlates well with the viscosity of concentrated monoclonal antibody (mAb) solutions. We measured the k(D) of 29 different mAbs (IgG(1) and IgG(4)) in four different solvent conditions (low and high ion normality) and found a linear dependence between k(D) and the exponential coefficient that describes the viscosity concentration profiles (|R| ≥ 0.9). Through experimentally measured effective charge measurements, under low ion normality where the electroviscous effect can dominate, we show that the mAb solution viscosity is poorly correlated with the mAb net charge (|R| ≤ 0.6). With this large data set, our results provide compelling evidence in support of weak intermolecular interactions, in contrast to the notion that the electroviscous effect is important in governing the viscoelastic behavior of concentrated mAb solutions. Our approach is particularly applicable as a screening tool for selecting mAbs with desirable viscosity properties early during lead candidate selection.

Influence of the cosolute environment on IgG solution structure analyzed by small-angle X-ray scattering.

Small-angle X-ray scattering experiments of two monoclonal antibodies (mAbs) were performed as a function of Hofmeister salt type and concentration including 100 mM Na(2)SO(4), 100-600 mM of NaSCN, or 100-600 mM arginine chloride at pH 6.0 to yield information on the effects of cosolutes on mAb solution conformation and flexibility. Minimal selected ensemble (MSE) procedures used to reconstruct the SAXS form factors revealed that both IgG1 mAbs exist in a conformational equilibrium with two subpopulations that vary in overall shape and size. The "closed" mAb conformation is characterized by a maximum dimension of ∼155 Šand shorter distances between Fab-Fab and Fab-FC domains. The "open" mAb conformation has a maximum dimension of ∼175 Šand an increase in the interdomain distances with concomitant increases in overall mAb flexibility. Analysis of the distribution of shapes and sizes of mAb structures within the conformational equilibrium indicates that they remain essentially unchanged under conditions with a broad range of chaotropic and kosmotropic salts including 100-600 mM NaSCN and 100 mM Na(2)SO(4). Analysis of the conformations within each MSE population under various conditions reveals a striking similarity between many of the MSE structures, IgG crystal structures, and single-molecule imaging studies; MSE analysis of mAb form factors also identified an overall relaxation of the mAb structure unique to solution conditions containing arginine chloride, characterized by an increased maximum dimension and a shift toward the population of the "open" mAb conformation. Our results provide the first comprehensive characterization of mAb conformational diversity in solution and are of direct relevance to understanding the effects of solution conditions on protein structural dynamics and stability.

Coarse-grained modeling of the self-association of therapeutic monoclonal antibodies.

Coarse-grained computational models of two therapeutic monoclonal antibodies are constructed to understand the effect of domain-level charge-charge electrostatics on the self-association phenomena at high protein concentrations. The coarse-grained representations of the individual antibodies are constructed using an elastic network normal-mode analysis. Two different models are constructed for each antibody for a compact Y-shaped and an extended Y-shaped configuration. The resulting simulations of these coarse-grained antibodies that interact through screened electrostatics are done at six different concentrations. It is observed that a particular monoclonal antibody (hereafter referred to as MAb1) forms three-dimensional heterogeneous structures with dense regions or clusters compared to a different monoclonal antibody (hereafter referred to as MAb2) that forms more homogeneous structures (no clusters). These structures, together with the potential mean force (PMF) and radial distribution functions (RDF) between pairs of coarse-grained regions on the MAbs, are qualitatively consistent with the experimental observation that MAb1 has a significantly higher viscosity compared to MAb2, especially at concentrations >50 mg/mL, even though the only difference between the MAbs lies with a few amino acids at the antigen-binding loops (CDRs). It is also observed that the structures in MAb1 are formed due to stronger Fab-Fab interactions in corroboration with experimental observations. Evidence is also shown that Fab-Fc interactions can be equally important in addition to Fab-Fab interactions. The coarse-grained representations are effective in picking up differences based on local charge distributions of domains and make predictions on the self-association characteristics of these protein solutions. This is the first computational study of its kind to show that there are differences in structures formed by two different monoclonal antibodies at high concentrations.

Issues and challenges of subvisible and submicron particulate analysis in protein solutions.

The analysis of particulates has been a longstanding challenge in biopharmaceutical drug product development and quality control because the active constituents themselves may form particulate matter as a degradation product that may be difficult to quantify. These analytical challenges were met with success as long as the definition of particulate matter remained well within the capabilities of the instruments and methods used to measure it. The current testing as per USP <788> for parenterals at ≤100 mL stipulates that the sample "passes" the test if the average number of particles present does not exceed 6,000 per container at ≥10 µm and does not exceed 600 per container at ≥25 µm. The new challenge, posed by regulatory direction and academic research, is to count and to characterize subvisible particulates that are ≤10 µm with the goal of providing higher resolution information about the particulate levels and potential consequences of this product quality attribute in vivo. The present discussion focuses on two parallel efforts: (a) to develop a model system for protein subvisible particulates in samples with high protein concentrations and (b) to evaluate the capabilities and limitations of different technologies available (at the time these studies were conducted) for subvisible and submicron particle (<1 µm in diameter) sizing and counting. Our findings illustrate the importance of using appropriate instrumentation that is adapted to the characteristics of the samples to be analyzed. Any sample manipulation to meet the capabilities and to accommodate the limitations of the analytical technique should be carefully evaluated.

The influence of charge distribution on self-association and viscosity behavior of monoclonal antibody solutions.

The present work investigates the influence of electrostatic surface potential distribution of monoclonal antibodies (MAbs) on intermolecular interactions and viscosity. Electrostatic models suggest MAb-1 has a less uniform surface charge distribution than MAb-2. The patches of positive and negative potential on MAb-1 are predicted to favor intermolecular attraction, even in the presence of a small net positive charge. Consistent with this expectation, MAb-1 exhibits a negative second virial coefficient (B22), an increase in static structure factor, S((q→0)), and a decrease in hydrodynamic interaction parameter, H((q→0)), with increase in MAb-1 concentration. Conversely, MAb-2 did not show such heterogeneous charge distribution as MAb-1 and hence favors intermolecular repulsion (positive B22), lower static structure factor, S((q→0)), and repulsion induced increase in momentum transfer, H((q→0)), to result in lower viscosity of MAb-2. Charge swap mutants of MAb-1, M-5 and M-7, showed a decrease in charge asymmetry and concomitantly a loss in self-associating behavior and lower viscosity than MAb-1. However, replacement of charge residues in the sequence of MAb-2, M-10, did not invoke charge distribution to the same extent as MAb-1 and hence exhibited a similar viscosity and self-association profile as MAb-2.