Structural and Functional Analysis of the D614G SARS-CoV-2 Spike Protein Variant.

The SARS-CoV-2 spike (S) protein variant D614G supplanted the ancestral virus worldwide, reaching near fixation in a matter of months. Here we show that D614G was more infectious than the ancestral form on human lung cells, colon cells, and on cells rendered permissive by ectopic expression of human ACE2 or of ACE2 orthologs from various mammals, including Chinese rufous horseshoe bat and Malayan pangolin. D614G did not alter S protein synthesis, processing, or incorporation into SARS-CoV-2 particles, but D614G affinity for ACE2 was reduced due to a faster dissociation rate. Assessment of the S protein trimer by cryo-electron microscopy showed that D614G disrupts an interprotomer contact and that the conformation is shifted toward an ACE2 binding-competent state, which is modeled to be on pathway for virion membrane fusion with target cells. Consistent with this more open conformation, neutralization potency of antibodies targeting the S protein receptor-binding domain was not attenuated.

VSIG4 interaction with heparan sulfates inhibits VSIG4-complement binding.

V-set and immunoglobulin domain-containing 4 (VSIG4) is a complement receptor of the immunoglobulin superfamily that is specifically expressed on tissue resident macrophages, and its many reported functions and binding partners suggest a complex role in immune function. VSIG4 is reported to have a role in immune surveillance as well as in modulating diverse disease phenotypes such as infections, autoimmune conditions, and cancer. However, the mechanism(s) governing VSIG4's complex, context-dependent role in immune regulation remains elusive. Here, we identify cell surface and soluble glycosaminoglycans, specifically heparan sulfates, as novel binding partners of VSIG4. We demonstrate that genetic deletion of heparan sulfate synthesis enzymes or cleavage of cell-surface heparan sulfates reduced VSIG4 binding to the cell surface. Furthermore, binding studies demonstrate that VSIG4 interacts directly with heparan sulfates, with a preference for highly sulfated moieties and longer glycosaminoglycan chains. To assess the impact on VSIG4 biology, we show that heparan sulfates compete with known VSIG4 binding partners C3b and iC3b. Furthermore, mutagenesis studies indicate that this competition occurs through overlapping binding epitopes for heparan sulfates and complement on VSIG4. Together these data suggest a novel role for heparan sulfates in VSIG4-dependent immune modulation.

Kappa-on-Heavy (KoH) bodies are a distinct class of fully-human antibody-like therapeutic agents with antigen-binding properties.

We describe a Kappa-on-Heavy (KoH) mouse that produces a class of highly diverse, fully human, antibody-like agents. This mouse was made by replacing the germline variable sequences of both the Ig heavy-chain (IgH) and Ig kappa (IgK) loci with the human IgK germline variable sequences, producing antibody-like molecules with an antigen binding site made up of 2 kappa variable domains. These molecules, named KoH bodies, structurally mimic naturally existing Bence-Jones light-chain dimers in their variable domains and remain wild-type in their antibody constant domains. Unlike artificially diversified, nonimmunoglobulin alternative scaffolds (e.g., DARPins), KoH bodies consist of a configuration of normal Ig scaffolds that undergo natural diversification in B cells. Monoclonal KoH bodies have properties similar to those of conventional antibodies but exhibit an enhanced ability to bind small molecules such as the endogenous cardiotonic steroid marinobufagenin (MBG) and nicotine. A comparison of crystal structures of MBG bound to a KoH Fab versus a conventional Fab showed that the KoH body has a much deeper binding pocket, allowing MBG to be held 4 Å further down into the combining site between the 2 variable domains.

High affinity human Fc specific monoclonal antibodies for capture kinetic analyses of antibody-antigen interactions.

We recently demonstrated that capturing human monoclonal antibodies (hmAbs) using high affinity anti-human Fc (AHC) antibodies allows reliable characterization of antibody-antigen interactions. Here, we characterized six human Fc specific mouse monoclonal antibodies (mAbs) and compared their binding profiles with three previously characterized goat AHC polyclonal antibodies (pAbs), exhibiting properties of a good capture reagent. All six mouse AHC mAbs specifically bound with high affinity to the Fc region of hIgG1, hIgG2, hIgG4 and to 43 different hIgG variants, containing substitutions and/or mutations in the hinge and/or Fc region, that have been reported to exhibit modified antibody effector function and/or pharmacokinetics. Biacore sensor surfaces individually derivatized with mouse AHC mAbs exhibited >2.5-fold higher hIgG binding capacity compared to the three goat AHC pAb surfaces and reproducibly captured hIgG over 300 capture-regeneration cycles. The results of the capture kinetic analyses performed on 31 antibody-antigen interactions using surfaces derivatized with either of the two highest affinity AHC mAbs (REGN7942 or REGN7943) were in concordance with those performed using goat AHC pAb surfaces. Our data demonstrate that AHC mAbs such as REGN7942 and REGN7943 that have properties superior than the three goat AHC pAbs are highly valuable research reagents, especially to perform capture kinetic analyses of antibody-antigen interactions on optical biosensors.

Dual blockade of IL-4 and IL-13 with dupilumab, an IL-4Rα antibody, is required to broadly inhibit type 2 inflammation.

BACKGROUND: Dupilumab, a fully human monoclonal antibody that binds IL-4Rα and inhibits signaling of both IL-4 and IL-13, has shown efficacy across multiple diseases with underlying type 2 signatures and is approved for treatment of asthma, atopic dermatitis, and chronic sinusitis with nasal polyposis. We sought to provide a comprehensive analysis of the redundant and distinct roles of IL-4 and IL-13 in type 2 inflammation and report dupilumab mechanisms of action. METHODS: Using primary cell assays and a mouse model of house dust mite-induced asthma, we compared IL-4 vs IL-13 vs IL-4Rα blockers. RESULTS: Intranasal administration of either IL-4 or IL-13 confers an asthma-like phenotype in mice by inducing immune cell lung infiltration, including eosinophils, increasing cytokine/chemokine expression and mucus production, thus demonstrating redundant functions of these cytokines. We further teased out their respective contributions using human in vitro culture systems. Then, in a mouse asthma model by comparing in head-to-head studies, either IL-4 or IL-13 inhibition to dual IL-4/IL-13 inhibition, we demonstrate that blockade of both IL-4 and IL-13 is required to broadly block type 2 inflammation, which translates to protection from allergen-induced lung function impairment. Notably, only dual IL-4/IL-13 blockade prevented eosinophil infiltration into lung tissue without affecting circulating eosinophils, demonstrating that tissue, but not circulating eosinophils, contributes to disease pathology. CONCLUSIONS: Overall, these data support IL-4 and IL-13 as key drivers of type 2 inflammation and help provide insight into the therapeutic mechanism of dupilumab, a dual IL-4/IL-13 blocker, in multiple type 2 diseases.

The impact of different human IgG capture molecules on the kinetics analysis of antibody-antigen interaction.

Surface plasmon resonance (SPR) is a well-established method to characterize biomolecular interactions and is widely used in drug discovery and development. Here, we demonstrate that capture surfaces profoundly impact the binding kinetics parameters that are measured for antibody-antigen interactions. Six unique antibody-antigen interactions were characterized using eight different anti-human IgG capture surfaces. The antigen binding affinities for six different human monoclonal antibodies (hmAbs) captured using three different goat anti-human Fc (AHC) polyclonal antibody (pAb) surfaces were in reasonable agreement (3-7-fold weaker) with those measured by kinetic exclusion assay (KinExA). In contrast, up to 81, 32, 489, 2826, and 219-fold weaker antigen binding affinities were measured using mouse AHC mAb, Protein G, Protein A, Protein A/G, and Protein L surfaces, respectively. Protein A, Protein A/G and Protein G interacted with the Fab of hmAbs, possibly affecting antigen binding to hmAbs captured over these surfaces. Additional studies revealed that mouse AHC mAb binds hmAbs with a weak affinity (5.5-36.3 nM) and t½ values of 1.4-3.3min, compared to the sub-nanomolar affinities of the goat AHC pAbs. These results emphasize the value of measuring binding kinetics of the capture molecule before immobilizing them onto the sensor surface to perform capture kinetics assays on label-free biosensors.

Development of Clinical-Stage Human Monoclonal Antibodies That Treat Advanced Ebola Virus Disease in Nonhuman Primates.

Background: For most classes of drugs, rapid development of therapeutics to treat emerging infections is challenged by the timelines needed to identify compounds with the desired efficacy, safety, and pharmacokinetic profiles. Fully human monoclonal antibodies (mAbs) provide an attractive method to overcome many of these hurdles to rapidly produce therapeutics for emerging diseases. Methods: In this study, we deployed a platform to generate, test, and develop fully human antibodies to Zaire ebolavirus. We obtained specific anti-Ebola virus (EBOV) antibodies by immunizing VelocImmune mice that use human immunoglobulin variable regions in their humoral responses. Results: Of the antibody clones isolated, 3 were selected as best at neutralizing EBOV and triggering FcγRIIIa. Binding studies and negative-stain electron microscopy revealed that the 3 selected antibodies bind to non-overlapping epitopes, including a potentially new protective epitope not targeted by other antibody-based treatments. When combined, a single dose of a cocktail of the 3 antibodies protected nonhuman primates (NHPs) from EBOV disease even after disease symptoms were apparent. Conclusions: This antibody cocktail provides complementary mechanisms of actions, incorporates novel specificities, and demonstrates high-level postexposure protection from lethal EBOV disease in NHPs. It is now undergoing testing in normal healthy volunteers in preparation for potential use in future Ebola epidemics.

Designing binding kinetic assay on the bio-layer interferometry (BLI) biosensor to characterize antibody-antigen interactions.

The Octet biosensors provide a high-throughput alternative to the well-established surface plasmon resonance (SPR) and SPR imaging (SPRi) biosensors to characterize antibody-antigen interactions. However, the utility of the Octet biosensors for accurate and reproducible measurement of binding rate constants of monoclonal antibodies (mAbs) is limited due to challenges such as analyte rebinding, and mass transport limitation (MTL). This study focuses on addressing these challenges and provides experimental conditions to reliably measure kinetics of mAb-antigen interactions. The mAb capture density of less than 0.6 nm was found to be optimal to measure a wide range of binding affinities on Octet HTX biosensor. The titration kinetic and single cycle kinetic assays performed on Octet HTX generated reproducible binding kinetic parameters and correlated with the values measured on Biacore 4000 and MASS-1. Kinetic assays performed on 0.1 nm density mAb surfaces significantly reduced MTL and enabled characterization of picomolar affinity mAbs. Finally, kinetic analysis performed on 150 antibodies to 10 antigens with molecular weights ranging from 21kD to 105kD showed concordance between Octet HTX, Biacore 4000 and MASS-1 (R2 > 0.90). The data presented in this study suggest that under optimal experimental conditions, Octet biosensor is capable of generating kinetic values comparable to SPR/SPRi biosensors.

Exploring sensitivity & throughput of a parallel flow SPRi biosensor for characterization of antibody-antigen interaction.

Rapid growth in the field of biotherapeutics has led to an increased demand for high-throughput, label-free biosensors exhibiting high sensitivity. To support the current needs, Sierra Sensors introduced a surface plasmon resonance imaging (SPRi) based biosensor, Molecular Affinity Screening System (MASS-1). We assessed the potential utility of MASS-1 to support Regeneron's therapeutic antibody discovery. A large panel of antibody-antigen interactions was characterized using MASS-1 and the kinetic data were compared with the Biacore 4000 biosensor. Less than 10% deviation in the binding rate constants measured across eight flow channels of MASS-1 was observed. The single injection cycle kinetic assay allowed rapid measurement of binding rate constants for antibody-antigen interactions. MASS-1 sensitivity was independent of protein immobilization level and kinetic analysis performed using ultra-low density mAb surfaces allowed characterization of picomolar affinity interactions without mass transport limitation. High-throughput characterization of a panel of 189 monoclonal antibodies to 13 different antigens with molecular weights ranging from 14kD to 105kD revealed that binding kinetic parameters measured on MASS-1 were comparable to those measured on Biacore 4000. Our data demonstrate that MASS-1 measures reliable binding kinetic parameters and has an appropriate combination of throughput and sensitivity to support discovery and development of therapeutic antibodies.

Extending the throughput of Biacore 4000 biosensor to accelerate kinetic analysis of antibody-antigen interaction.

The surface plasmon resonance (SPR) biosensors are being routinely used in different stages of drug discovery and development. However, the lack of high throughput SPR biosensors continues to be a primary bottleneck for the rapid kinetic screening of large panels of monoclonal antibodies (mAbs). To further increase the throughput of the Biacore 4000 biosensor, we have developed three kinetic screening assays to characterize mAb-antigen interactions - (i) 16-mAb capture kinetic, (ii) single cycle kinetic (SCK), and (iii) parallel kinetic (PK). The performance of all three kinetic assays was evaluated by characterizing the binding of kinetically diverse human mAbs to four antigens with molecular weights of 14kD, 29kD, 38kD, and 48kD and binding affinities ranging from 130pM to 200 nM. The binding rate constants measured using all three kinetic assays were reproducible across multiple experiments and correlated with the values generated using the conventional 8-mAb capture kinetic assay on the Biacore 4000 (R2 > 0.94). Moreover, the 16-mAb capture assay decreased experiment time and analyte consumption by 35% and 50%, respectively. This work illustrates the significance of the 16-mAb capture kinetic, SCK, and PK assays to increase the throughput of Biacore 4000 and to support rapid kinetic screening of mAbs.

Aflibercept exhibits VEGF binding stoichiometry distinct from bevacizumab and does not support formation of immune-like complexes.

Anti-vascular endothelial growth factor (VEGF) therapies have improved clinical outcomes for patients with cancers and retinal vascular diseases. Three anti-VEGF agents, pegaptanib, ranibizumab, and aflibercept, are approved for ophthalmic indications, while bevacizumab is approved to treat colorectal, lung, and renal cancers, but is also used off-label to treat ocular vascular diseases. The efficacy of bevacizumab relative to ranibizumab in treating neovascular age-related macular degeneration has been assessed in several trials. However, questions persist regarding its safety, as bevacizumab can form large complexes with dimeric VEGF165, resulting in multimerization of the Fc domain and platelet activation. Here, we compare binding stoichiometry, Fcγ receptor affinity, platelet activation, and binding to epithelial and endothelial cells in vitro for bevacizumab and aflibercept, in the absence or presence of VEGF. In contrast to bevacizumab, aflibercept forms a homogenous 1:1 complex with each VEGF dimer. Unlike multimeric bevacizumab:VEGF complexes, the monomeric aflibercept:VEGF complex does not exhibit increased affinity for low-affinity Fcγ receptors, does not activate platelets, nor does it bind to the surface of epithelial or endothelial cells to a greater degree than unbound aflibercept or control Fc. The latter finding reflects the fact that aflibercept binds VEGF in a unique manner, distinct from antibodies not only blocking the amino acids necessary for VEGFR1/R2 binding but also occluding the heparin-binding site on VEGF165.

ANGPTL3 blockade with a human monoclonal antibody reduces plasma lipids in dyslipidemic mice and monkeys.

Angiopoietin-like protein 3 (ANGPTL3) is a circulating protein synthesized exclusively in the liver that inhibits LPL and endothelial lipase (EL), enzymes that hydrolyze TGs and phospholipids in plasma lipoproteins. Here we describe the development and testing of a fully human monoclonal antibody (REGN1500) that binds ANGPTL3 with high affinity. REGN1500 reversed ANGPTL3-induced inhibition of LPL activity in vitro. Intravenous administration of REGN1500 to normolipidemic C57Bl/6 mice increased LPL activity and decreased plasma TG levels by ≥50%. Chronic administration of REGN1500 to dyslipidemic C57Bl/6 mice for 8 weeks reduced circulating plasma levels of TG, LDL-cholesterol (LDL-C), and HDL-cholesterol (HDL-C) without any changes in liver, adipose, or heart TG contents. Studies in EL knockout mice revealed that REGN1500 reduced serum HDL-C through an EL-dependent mechanism. Finally, administration of a single dose of REGN1500 to dyslipidemic cynomolgus monkeys caused a rapid and pronounced decrease in plasma TG, nonHDL-C, and HDL-C. REGN1500 normalized plasma TG levels even in monkeys with a baseline plasma TG greater than 400 mg/dl. Collectively, these data demonstrate that neutralization of ANGPTL3 using REGN1500 reduces plasma lipids in dyslipidemic mice and monkeys, and thus provides a potential therapeutic agent for treatment of patients with hyperlipidemia.

TRAPnSeq allows high-throughput profiling of antigen-specific antibody-secreting cells.

Following activation by cognate antigen, B cells undergo fine-tuning of their antigen receptors and may ultimately differentiate into antibody-secreting cells (ASCs). While antigen-specific B cells that express surface receptors (B cell receptors [BCRs]) can be readily cloned and sequenced following flow sorting, antigen-specific ASCs that lack surface BCRs cannot be easily profiled. Here, we report an approach, TRAPnSeq (antigen specificity mapping through immunoglobulin [Ig] secretion TRAP and Sequencing), that allows capture of secreted antibodies on the surface of ASCs, which in turn enables high-throughput screening of single ASCs against large antigen panels. This approach incorporates flow cytometry, standard microfluidic platforms, and DNA-barcoding technologies to characterize antigen-specific ASCs through single-cell V(D)J, RNA, and antigen barcode sequencing. We show the utility of TRAPnSeq by profiling antigen-specific IgG and IgE ASCs from both mice and humans and highlight its capacity to accelerate therapeutic antibody discovery from ASCs.

Structural analysis of cancer-relevant TCR-CD3 and peptide-MHC complexes by cryoEM.

The recognition of antigenic peptide-MHC (pMHC) molecules by T-cell receptors (TCR) initiates the T-cell mediated immune response. Structural characterization is key for understanding the specificity of TCR-pMHC interactions and informing the development of therapeutics. Despite the rapid rise of single particle cryoelectron microscopy (cryoEM), x-ray crystallography has remained the preferred method for structure determination of TCR-pMHC complexes. Here, we report cryoEM structures of two distinct full-length α/ß TCR-CD3 complexes bound to their pMHC ligand, the cancer-testis antigen HLA-A2/MAGEA4 (230-239). We also determined cryoEM structures of pMHCs containing MAGEA4 (230-239) peptide and the closely related MAGEA8 (232-241) peptide in the absence of TCR, which provided a structural explanation for the MAGEA4 preference displayed by the TCRs. These findings provide insights into the TCR recognition of a clinically relevant cancer antigen and demonstrate the utility of cryoEM for high-resolution structural analysis of TCR-pMHC interactions.

Structure of the Inmazeb cocktail and resistance to Ebola virus escape.

Monoclonal antibodies can provide important pre- or post-exposure protection against infectious disease for those not yet vaccinated or in individuals that fail to mount a protective immune response after vaccination. Inmazeb (REGN-EB3), a three-antibody cocktail against Ebola virus, lessened disease and improved survival in a controlled trial. Here, we present the cryo-EM structure at 3.1 Å of the Ebola virus glycoprotein, determined without symmetry averaging, in a simultaneous complex with the antibodies in the Inmazeb cocktail. This structure allows the modeling of previously disordered portions of the glycoprotein glycan cap, maps the non-overlapping epitopes of Inmazeb, and illuminates the basis for complementary activities and residues critical for resistance to escape by these and other clinically relevant antibodies. We further provide direct evidence that Inmazeb protects against the rapid emergence of escape mutants, whereas monotherapies even against conserved epitopes do not, supporting the benefit of a cocktail versus a monotherapy approach.

Monoclonal antibodies against GFRα3 are efficacious against evoked hyperalgesic and allodynic responses in mouse join pain models but, one of these, REGN5069, was not effective against pain in a randomized, placebo-controlled clinical trial in patients with osteoarthritis pain.

The artemin-GFRα3 signaling pathway has been implicated in various painful conditions including migraine, cold allodynia, hyperalgesia, inflammatory bone pain, and mouse knees contain GFRα3-immunoreactive nerve endings. We developed high affinity mouse (REGN1967) and human (REGN5069) GFRα3-blocking monoclonal antibodies and, following in vivo evaluations in mouse models of chronic joint pain (osteoarthritic-like and inflammatory), conducted a first-in-human phase 1 pharmacokinetics (PK) and safety trial of REGN5069 (NCT03645746) in healthy volunteers, and a phase 2 randomized placebo-controlled efficacy and safety trial of REGN5069 (NCT03956550) in patients with knee osteoarthritis (OA) pain. In three commonly used mouse models of chronic joint pain (destabilization of the medial meniscus, intra-articular monoiodoacetate, or Complete Freund's Adjuvant), REGN1967 and REGN5069 attenuated evoked behaviors including tactile allodynia and thermal hyperalgesia without discernably impacting joint pathology or inflammation, prompting us to further evaluate REGN5069 in humans. In the phase 1 study in healthy subjects, the safety profiles of single doses of REGN5069 up to 3000 mg (intravenous) or 600 mg (subcutaneous) were comparable to placebo; PK were consistent with a monoclonal antibody exhibiting target-mediated disposition. In the phase 2 study in patients with OA knee pain, two doses of REGN5069 (100 mg or 1000 mg intravenous every 4 weeks) for 8 weeks failed to achieve the 12-week primary and secondary efficacy endpoints relative to placebo. In addition to possible differences in GFRα3 biology between mice and humans, we highlight here differences in experimental parameters that could have contributed to a different profile of efficacy in mouse models versus human OA pain. Additional research is required to more fully evaluate any potential role of GFRα3 in human pain.

Evaluation of Molecular Properties versus In Vivo Performance of Aflibercept, Brolucizumab, and Ranibizumab in a Retinal Vascular Hyperpermeability Model.

Purpose: To evaluate the molecular, pharmacokinetic, and pharmacological properties of three anti-vascular endothelial growth factor (VEGF) agents-aflibercept, brolucizumab, and ranibizumab-and to provide a prediction of the optimal design of an intravitreal VEGF challenge in rabbits to assess the preclinical in vivo activity of the different anti-VEGF agents. Methods: Biochemical analyses and cellular and animal models of retinopathy were used to characterize anti-VEGF efficacy. Anti-VEGF biochemical binding affinity was determined through a kinetic exclusion assay. The in vitro potency was investigated by a calcium mobilization assay. Pharmacokinetic parameters were estimated for each drug to predict intraocular exposure relationships among the agents. The in silico modeling efforts informed the design of an in vivo rabbit model of VEGF-induced retinal hyperpermeability to determine the extent of VEGF neutralization in vivo. Consequently, data generated from the in vivo study enabled pharmacokinetic analysis and the generation of a logistical model describing the impact of the anti-VEGF agents on the VEGF-induced vascular leakage in rabbits. Results: The three anti-VEGF agents ranked from most efficacious to least efficacious as aflibercept, brolucizumab, and ranibizumab, with results consistent and significant within each individual characterization experiment. Conclusions: This composite study demonstrated how the molecular properties of aflibercept, brolucizumab, and ranibizumab translate into differences of in vivo efficacy, with results in line with the reported literature. Translational Relevance: In silico, in vitro, and in vivo integrated studies provide information that enables the enhanced characterization of translational properties of anti-VEGF agents currently used for the treatment of retinal diseases.

Combinatorial Inhibition of Myostatin and Activin A Improves Femoral Bone Properties in the G610C Mouse Model of Osteogenesis Imperfecta.

Osteogenesis imperfecta (OI) is a collagen-related bone disorder characterized by fragile osteopenic bone and muscle weakness. We have previously shown that the soluble activin receptor type IIB decoy (sActRIIB) molecule increases muscle mass and improves bone strength in the mild to moderate G610C mouse model of OI. The sActRIIB molecule binds multiple transforming growth factor-ß (TGF-ß) ligands, including myostatin and activin A. Here, we investigate the musculoskeletal effects of inhibiting activin A alone, myostatin alone, or both myostatin and activin A in wild-type (Wt) and heterozygous G610C (+/G610C) mice using specific monoclonal antibodies. Male and female Wt and +/G610C mice were treated twice weekly with intraperitoneal injections of monoclonal control antibody (Ctrl-Ab, Regn1945), anti-activin A antibody (ActA-Ab, Regn2476), anti-myostatin antibody (Mstn-Ab, Regn647), or both ActA-Ab and Mstn-Ab (Combo, Regn2476, and Regn647) from 5 to 16 weeks of age. Prior to euthanasia, whole body composition, metabolism and muscle force generation assessments were performed. Post euthanasia, hindlimb muscles were evaluated for mass, and femurs were evaluated for changes in microarchitecture and biomechanical strength using micro-computed tomography (µCT) and three-point bend analyses. ActA-Ab treatment minimally impacted the +/G610C musculoskeleton, and was detrimental to bone strength in male +/G610C mice. Mstn-Ab treatment, as previously reported, resulted in substantial increases in hindlimb muscle weights and overall body weights in Wt and male +/G610C mice, but had minimal skeletal impact in +/G610C mice. Conversely, the Combo treatment outperformed ActA-Ab alone or Mstn-Ab alone, consistently increasing hindlimb muscle and body weights regardless of sex or genotype and improving bone microarchitecture and strength in both male and female +/G610C and Wt mice. Combinatorial inhibition of activin A and myostatin more potently increased muscle mass and bone microarchitecture and strength than either antibody alone, recapturing most of the observed benefits of sActRIIB treatment in +/G610C mice. © 2022 American Society for Bone and Mineral Research (ASBMR).

Assay pH and critical reagent optimization in measuring concentrations of a monoclonal antibody and its target.

Aim: To mitigate assay interference in the drug and target assays to support the development of monoclonal antibody REGN-Z. Results: Mild acidic assay conditions and capture and detection antibodies with different affinities and t1/2 under different assay pHs were used to mitigate interference in the total drug and total target assays. A free target assay was also developed using a lower-affinity capture antibody with a much slower association and dissociation rate. The impact of sample incubation, dilution and storage on the accurate detection of the free target was also evaluated. Conclusion: The total drug, total and free target assays can accurately quantitate drug and target concentrations when tested with a subset of clinical study samples.