Btk-specific inhibition blocks pathogenic plasma cell signatures and myeloid cell-associated damage in IFNα-driven lupus nephritis.

Systemic lupus erythematosus (SLE) is often associated with exaggerated B cell activation promoting plasma cell generation, immune-complex deposition in the kidney, renal infiltration of myeloid cells, and glomerular nephritis. Type-I IFNs amplify these autoimmune processes and promote severe disease. Bruton's tyrosine kinase (Btk) inhibitors are considered novel therapies for SLE. We describe the characterization of a highly selective reversible Btk inhibitor, G-744. G-744 is efficacious, and superior to blocking BAFF and Syk, in ameliorating severe lupus nephritis in both spontaneous and IFNα-accelerated lupus in NZB/W_F1 mice in therapeutic regimens. Selective Btk inhibition ablated plasmablast generation, reduced autoantibodies, and - similar to cyclophosphamide - improved renal pathology in IFNα-accelerated lupus. Employing global transcriptional profiling of spleen and kidney coupled with cross-species human modular repertoire analyses, we identify similarities in the inflammatory process between mice and humans, and we demonstrate that G-744 reduced gene expression signatures essential for splenic B cell terminal differentiation, particularly the secretory pathway, as well as renal transcriptional profiles coupled with myeloid cell-mediated pathology and glomerular plus tubulointerstitial disease in human glomerulonephritis patients. These findings reveal the mechanism through which a selective Btk inhibitor blocks murine autoimmune kidney disease, highlighting pathway activity that may translate to human SLE.

Characterization of a sensitive mouse Aß40 PD biomarker assay for Alzheimer's disease drug development in wild-type mice.

AIM: Transgenic mice that overexpress human amyloid precursor protein with Swedish or London (APPswe or APPlon) mutations have been widely used for preclinical Alzheimer's disease (AD) drug development. AD patients, however, rarely possess these mutations or overexpress APP. RESULTS: We developed a sensitive ELISA that specifically and accurately measures low levels of endogenous Aß40 in mouse plasma, brain and CSF. In wild-type mice treated with a bispecific anti-TfR/BACE1 antibody, significant Aß reductions were observed in the periphery and the brain. APPlon transgenic mice showed a slightly less reduction, whereas APPswe mice did not have any decrease. CONCLUSION: This sensitive and well-characterized mouse Aß40 assay enables the use of wild-type mice for preclinical PK/PD and efficacy studies of potential AD therapeutics.

A novel immunoassay to measure total serum lymphotoxin-α levels in the presence of an anti-LTα therapeutic antibody.

During drug development, measurement of suitable pharmacodynamic biomarkers is key to establishing in vivo drug activity. Binding of monoclonal antibody (mAb) therapeutics to soluble target proteins often results in elevated serum levels of their target antigen, and measuring total (free and bound) concentration of the target antigen can be an important means of demonstrating that the mAb has reached its specific target. However, accurately measuring soluble circulating antigen in preclinical or clinical samples in the presence of a therapeutic mAb presents a bioanalytical challenge. Particularly in the case of low molecular weight and/or multimeric targets, epitopes for capture and detection of the target by reagent antibodies can be obscured by bound therapeutic mAb. Lymphotoxin-alpha (LTα) is a cytokine in the TNF superfamily that has been implicated in the pathophysiology of autoimmune disease, and is a therapeutic target for neutralizing mAb. During preclinical safety studies in cynomolgus macaques, we encountered difficulties in measuring total LTα in serum of dosed animals. When serum LTα trimer was saturated with the anti-LTα mAb, binding of two reagent antibodies, as required for a classic sandwich ELISA, was not feasible, and dissociation methods were also found to be unsuitable. We therefore developed an approach in which excess anti-LTα mAb was added to the in vitro assay system to fully saturate all binding sites, and an anti-idiotypic antibody was used to detect bound therapeutic antibody. Using this method, total LTα could be accurately measured in cynomolgus macaque serum, and was observed to increase with increasing anti-LTα therapeutic mAb dose. Additional in vitro studies demonstrated that the method worked equally well in human serum. This assay strategy will be useful for quantifying total concentrations of other small and/or multimeric target proteins in the presence of a therapeutic antibody.

Dual B cell immunotherapy is superior to individual anti-CD20 depletion or BAFF blockade in murine models of spontaneous or accelerated lupus.

OBJECTIVE: To determine whether a combination of B cell depletion and BAFF blockade is more effective than monotherapy in treating models of spontaneous or accelerated systemic lupus erythematosus (SLE) in (NZB × NZW)F1 mice. METHODS: Clinical parameters such as disease progression-free survival, proteinuria, and renal injury were assessed in models of spontaneous, interferon-α (IFNα)-accelerated, or pristane-accelerated lupus in (NZB × NZW)F1 mice. Treatment arms included anti-CD20 (B cell depletion), B lymphocyte stimulator receptor 3 fusion protein (BR-3-Fc) (BAFF blockade), the combination of anti-CD20 and BR-3-Fc, isotype control, or cyclophosphamide. In models of spontaneous, IFNα-accelerated, or pristane-accelerated lupus, mice were treated for 24 weeks, 8 weeks, or 12 weeks, respectively. Peripheral and resident B cell subsets and various autoantibodies were examined. RESULTS: Compared to B cell depletion or BAFF blockade alone, combined therapy significantly improved disease manifestations in all 3 lupus models. In addition, marginal zone B cells, plasmablasts, and circulating and tissue plasma cells were decreased more effectively. Dual B cell immunotherapy also reduced multiple classes of pathogenic autoantibodies, consistent with its observed effectiveness in reducing immune complex-mediated renal injury. CONCLUSION: Dual immunotherapy via B cell depletion and BAFF blockade is more efficacious than single agent immunotherapy in murine SLE models, and this combination treatment is predicted to be an effective strategy for immunotherapy in human SLE.

Complement inhibition in cynomolgus monkeys by anti-factor d antigen-binding fragment for the treatment of an advanced form of dry age-related macular degeneration.

Anti-factor D (AFD; FCFD4514S, lampalizumab) is a humanized IgG Fab fragment directed against factor D (fD), a rate-limiting serine protease in the alternative complement pathway (AP). Evaluation of AFD as a potential intravitreal (IVT) therapeutic for dry age-related macular degeneration patients with geographic atrophy (GA) is ongoing. However, it is unclear whether IVT administration of AFD can affect systemic AP activation and potentially compromise host-immune responses. We characterized the pharmacologic properties of AFD and assessed the effects of AFD administered IVT (2 or 20 mg) or intravenous (0.2, 2, or 20 mg) on systemic complement activity in cynomolgus monkeys. For the IVT groups, serum AP activity was reduced for the 20 mg dose group between 2 and 6 hours postinjection. For the intravenous groups, AFD inhibited systemic AP activity for periods of time ranging from 5 minutes (0.2 mg group) to 3 hours (20 mg group). Interestingly, the concentrations of total serum fD increased up to 10-fold relative to predose levels following administration of AFD. Furthermore, AFD was found to inhibit systemic AP activity only when the molar concentration of AFD exceeded that of fD. This occurred in cynomolgus monkeys at serum AFD levels ≥2 µg/ml, a concentration 8-fold greater than the maximum serum concentration observed following a single 10 mg IVT dose in a clinical investigation in patients with GA. Based on these findings, the low levels of serum AFD resulting from IVT administration of a clinically relevant dose are not expected to appreciably affect systemic AP activity.

Polyclonal hyper-IgE mouse model reveals mechanistic insights into antibody class switch recombination.

Preceding antibody constant regions are switch (S) regions varying in length and repeat density that are targets of activation-induced cytidine deaminase. We asked how participating S regions influence each other to orchestrate rearrangements at the IgH locus by engineering mice in which the weakest S region, Sε, is replaced with prominent recombination hotspot Sµ. These mice produce copious polyclonal IgE upon challenge, providing a platform to study IgE biology and therapeutic interventions. The insertion enhances ε germ-line transcript levels, shows a preference for direct vs. sequential switching, and reduces intraswitch recombination events at native Sµ. These results suggest that the sufficiency of Sµ to mediate IgH rearrangements may be influenced by context-dependent cues.

Micro-volume wall-less immunoassays using patterned planar plates.

Miniaturization of immunoassays has numerous potential advantages over traditional ELISAs. Here we present a novel approach using patterned planar plates (PPPs). These 'wall-less' plates consist of a 16 × 24 array of 2 mm diameter hydrophilic regions surrounded by a hydrophobic polytetrafluoroethylene (PTFE) coating. Assays are performed by adding 2 µL droplets to the hydrophilic areas. These droplets are overlaid with an immiscible mixture of perfluorocarbon liquid (PFCL) that essentially eliminates evaporation. During wash steps, a thin film of PFCL covers the hydrophobic coating and prevents its wetting by wash buffer; as a result, the hydrophilic wells remain intact and inter-well cross-contamination is prevented. We compared the performance of three immunoassays using PPPs versus traditional 384-well ELISA plates. These included assays for soluble FcRH5 in human serum, SDF-1 in mouse serum, and human IgG in mouse plasma. The results show that the PPP assays were closely comparable to the ELISAs in terms of sensitivity, linearity of dilution, and sample quantitation. Moreover, the PPP assays were rapid to perform, easily adapted from ELISA protocols, and used 10- to 50-fold less sample and reagent volume as compared to 384- or 96-well plate ELISAs. As an additional advantage, PPPs conform to established microplate dimensional standards making them compatible with pre-existing equipment and workflows. PPPs therefore represent an attractive and broadly applicable approach to flexible miniaturization of plate-based immunochemical assays.

Effects of altered FcγR binding on antibody pharmacokinetics in cynomolgus monkeys.

Antibody interactions with Fcγ receptors (FcγRs), like FcγRIIIA, play a critical role in mediating antibody effector functions and thereby contribute significantly to the biologic and therapeutic activity of antibodies. Over the past decade, considerable work has been directed towards production of antibodies with altered binding affinity to FcγRs and evaluation of how the alterations modulate their therapeutic activity. This has been achieved by altering glycosylation status at N297 or by engineering modifications in the crystallizable fragment (Fc) region. While the effects of these modifications on biologic activity and efficacy have been examined, few studies have been conducted to understand their effect on antibody pharmacokinetics (PK). We present here a retrospective analysis in which we characterize the PK of three antibody variants with decreased FcγR binding affinity caused by amino acid substitutions in the Fc region (N297A, N297G, and L234A/L235A) and three antibody variants with increased FcγRIIIA binding affinity caused by afucosylation at N297, and compare their PK to corresponding wild type antibody PK in cynomolgus monkeys. For all antibodies, PK was examined at a dose that was known to be in the linear range. Since production of the N297A and N297G variants in Chinese hamster ovary cells results in aglycosylated antibodies that do not bind to FcγRs, we also examined the effect of expression of an aglycosylated antibody, without sequence change(s), in E. coli. All the variants demonstrated similar PK compared with that of the wild type antibodies, suggesting that, for the six antibodies presented here, altered FcγR binding affinity does not affect PK.

Activation of the alternative complement pathway in vitreous is controlled by genetics in age-related macular degeneration.

PURPOSE: To determine if the progression of age-related macular degeneration (AMD) is associated with complement activation in the eye. METHODS: Immunohistochemistry and ELISAs were used to determine the distribution, concentration, and activation of the alternative pathway complement proteases factor B (FB) and factor D (FD) and the central complement protein C3 in genotyped human postmortem donor eyes graded as having no or minimal drusen (category 1; controls), large drusen (category 3), and large drusen with advanced AMD (category 4). RESULTS: C3, FB, and FD were present in vitreous and Bruch's membrane choroid (BM/C) interface of the macula of eyes in all tested AMD severity categories (n = 100). C3, FB, and FD were predominantly located to the choroidal vasculature and Bruch's membrane and, together with the serum proteins transferrin and albumin, elevated in BM/C extracts of category 4 eyes (n = 23) compared with category 1 eyes (n = 24). A significant increase in FB activation was found only in vitreous of category 4 eyes (n = 23) compared with category 1 eyes (n = 25). Genetic variants of complement factor H (CFH), C3, C2, and FB associated with increased risk of AMD were correlated with alternative pathway complement activation in vitreous, but not with complement proteins in BM/C protein extracts. CONCLUSIONS: Increased activation of the alternative complement pathway in vitreous was controlled by disease stage and genetic variation in the complement pathway, supporting a role for complement activation in AMD disease pathogenesis.

A case study on Sema3E-Fc aggregation and assay-dependent differences in quantitation.

BACKGROUND: In evaluating the serum concentrations in mice of a Sema3E IgG1 Fc fusion protein, a possible antitumor agent, two ELISAs were developed: a generic assay detecting only the Fc portion of the therapeutic and a specific receptor-binding assay detecting intact protein. RESULTS: An unexpected discrepancy was observed in the measured in vivo serum concentrations, with the generic ELISA yielding higher concentrations than the specific ELISA. Size-exclusion HPLC and SDS-PAGE analysis of in vitro serum stability samples revealed extensive aggregation of Sema3E-Fc. The generic assay recovered more Sema3E-Fc in the presence of aggregates than the specific assay. CONCLUSION: Biophysical characterization combined with immunochemical analysis was key to elucidating not only the nature of the protein instability, but also the cause for the assay discrepancy.

Subcutaneous bioavailability of therapeutic antibodies as a function of FcRn binding affinity in mice.

The neonatal Fc receptor (FcRn) plays an important and well-known role in immunoglobulin G (IgG) catabolism; however, its role in the disposition of IgG after subcutaneous (SC) administration, including bioavailability, is relatively unknown. To examine the potential effect of FcRn on IgG SC bioavailability, we engineered three anti-amyloid ß monoclonal antibody (mAb) reverse chimeric mouse IgG2a (mIgG2a) Fc variants (I253A.H435A, N434H and N434Y) with different binding affinities to mouse FcRn (mFcRn) and compared their SC bioavailability to that of the wild-type (WT) mAb in mice. Our results indicated that the SC bioavailability of mIgG2a was affected by mFcRn-binding affinity. Variant I253A.H435A, which did not bind to mFcRn at either pH 6.0 or pH 7.4, had the lowest bioavailability (41.8%). Variant N434Y, which had the greatest increase in binding affinity at both pH 6.0 and pH 7.4, had comparable bioavailability to the WT antibody (86.1% vs. 76.3%), whereas Variant N434H, which had modestly increased binding affinity at pH 6.0 to mFcRn and affinity comparable to the WT antibody at pH 7.4, had the highest bioavailability (94.7%). A semi-mechanism-based pharmacokinetic model, which described well the observed data with the WT antibody and variant I253A.H435A, is consistent with the hypothesis that the decreased bioavailability of variant I253A.H435A was due to loss of the FcRn-mediated protection from catabolism at the absorption site. Together, these data demonstrate that FcRn plays an important role in SC bioavailability of therapeutic IgG antibodies.

Specific Btk inhibition suppresses B cell- and myeloid cell-mediated arthritis.

Bruton's tyrosine kinase (Btk) is a therapeutic target for rheumatoid arthritis, but the cellular and molecular mechanisms by which Btk mediates inflammation are poorly understood. Here we describe the discovery of CGI1746, a small-molecule Btk inhibitor chemotype with a new binding mode that stabilizes an inactive nonphosphorylated enzyme conformation. CGI1746 has exquisite selectivity for Btk and inhibits both auto- and transphosphorylation steps necessary for enzyme activation. Using CGI1746, we demonstrate that Btk regulates inflammatory arthritis by two distinct mechanisms. CGI1746 blocks B cell receptor-dependent B cell proliferation and in prophylactic regimens reduces autoantibody levels in collagen-induced arthritis. In macrophages, Btk inhibition abolishes FcγRIII-induced TNFα, IL-1ß and IL-6 production. Accordingly, in myeloid- and FcγR-dependent autoantibody-induced arthritis, CGI1746 decreases cytokine levels within joints and ameliorates disease. These results provide new understanding of the function of Btk in both B cell- or myeloid cell-driven disease processes and provide a compelling rationale for targeting Btk in rheumatoid arthritis.

Evaluation of heterophilic antibody blocking agents in reducing false positive interference in immunoassays for IL-17AA, IL-17FF, and IL-17AF.

IL-17AA, IL-17FF, and IL-17AF are proinflammatory cytokines that have been implicated in the pathogenesis of autoimmune diseases such as rheumatoid arthritis (RA). In order to measure the levels of these cytokines in synovial fluid and serum samples from RA patients, immunoassays specific for IL-17AA, FF, and AF were developed. Although these assays could tolerate up to 50% pooled normal human serum, false positive reactivity was problematic in patient samples suggesting interference from heterophilic antibodies. We therefore evaluated the ability of several commercially available heterophilic antibody blocking agents to reduce false positive reactivity by testing them against samples that were confirmed as false positives in the IL-17AA, FF, and AF assays. Several of the blockers performed well, including HBR-1, HBR-9, HBR-11, HBR-Plus, Serum Cytokine Assay Diluent, and IIR. We chose to move forward using IIR blocker for sample analysis and verified that IIR had no effect on the assay standard curves and did not affect IL-17 quantitation in plasma from ex vivo stimulated human whole blood. IL-17FF and IL-17AF were below the limits of quantitation of the assays (12.3 and 10.5pg/ml, respectively) in synovial fluid and serum samples from patients with RA and osteoarthritis (OA). For the more sensitive IL-17AA assay (1.6pg/ml limit of quantitation), low levels of IL-17AA were measurable in 48% of RA synovial fluid samples (mean, 7.9pg/ml; median, <1.6pg/ml; range, <1.6-29.7pg/ml; n=23) but not in synovial fluid from patients with OA (n=33). For serum samples, however, IL-17AA was below the limit of detection for both RA and OA patients. When these same serum samples were analyzed in the absence of a heterophilic antibody blocker, false positive reactivity yielded apparent mean IL-17AA levels of 43.3pg/ml (28% positive; n=50) and 14.8pg/ml (12% positive; n=50) for RA and OA patients, respectively, results that could potentially be interpreted as consistent with disease biology. These studies demonstrate the importance of ensuring that HAb interference is well controlled, particularly when measuring low concentrations of cytokines in samples from patients with autoimmune disease.

Increased targeting of donor switch region and IgE in Sgamma1-deficient B cells.

Ab class switch recombination involves a recombination between two repetitive DNA sequences known as switch (S) regions that vary in length, content, and density of the repeats. Abs expressed by B cells are diversified by somatic hypermutation and class switch recombination. Both class switch recombination and somatic hypermutation are initiated by activation-induced cytidine deaminase (AID), which preferentially recognizes certain hot spots that are far more enriched in the S regions. We found that removal of the largest S region, Sgamma1 (10 kb), in mice can result in the accumulation of mutations and short-range intra-S recombination in the donor Smu region. Furthermore, elevated levels of IgE were detected in trinitrophenol-OVA-immunized mice and in anti-CD40 plus IL-4-stimulated B cells in vitro. We propose that AID availability and targeting in part might be regulated by its DNA substrate. Thus, prominently transcribed S regions, such as Sgamma1, might provide a sufficient sink for AID protein to titrate away AID from other accessible sites within or outside the Ig locus.

Antibodies specific for a segment of human membrane IgE deplete IgE-producing B cells in humanized mice.

IgE-mediated hypersensitivity is central to the pathogenesis of asthma and other allergic diseases. Although neutralization of serum IgE with IgE-specific antibodies is in general an efficacious treatment for allergic asthma, one limitation of this approach is its lack of effect on IgE production. Here, we have developed a strategy to disrupt IgE production by generating monoclonal antibodies that target a segment of membrane IgE on human IgE-switched B cells that is not present in serum IgE. This segment is known as the M1' domain, and using genetically modified mice that contain the human M1' domain inserted into the mouse IgE locus, we demonstrated that M1'-specific antibodies reduced serum IgE and IgE-producing plasma cells in vivo, without affecting other immunoglobulin isotypes. M1'-specific antibodies were effective when delivered prophylactically and therapeutically in mouse models of immunization, allergic asthma, and Nippostrongylus brasiliensis infection, likely by inducing apoptosis of IgE-producing B cells. In addition, we generated a humanized M1'-specific antibody that was active on primary human cells in vivo, as determined by its reduction of serum IgE levels and IgE plasma cell numbers in a human PBMC-SCID mouse model. Thus, targeting of human IgE-producing B cells with apoptosis-inducing M1'-specific antibodies may be a novel treatment for asthma and allergy.

Lymphotoxin-alphabeta heterotrimers are cleaved by metalloproteinases and contribute to synovitis in rheumatoid arthritis.

Tumor necrosis factor-superfamily (TNF-SF) members, lymphotoxin (LT)-alpha and LTbeta, are proinflammatory cytokines associated with pathology in rheumatoid arthritis. LTalpha3 homotrimers are secreted, whereas LTalpha(1)beta(2) heterotrimers are expressed on the surface of activated lymphocytes. As many TNF-SF members are actively cleaved from cell membranes, we determined whether LTalphabeta heterotrimers are also cleaved, and are biologically active in rheumatoid arthritis (RA) patients. LTalphabeta heterotrimers were detected in culture supernatants from activated human T-helper (Th) 0, Th1, and Th17 cells, together with LTalpha3 and TNFalpha. The heterotimers were actively cleaved from the cell surface by ADAM17 metalloproteinase (MMP) and MMP-8, and cleavage was inhibited by TAPI-1, a TNF-alpha converting enzyme (TACE) inhibitor. Soluble LTalphabeta was detected in serum from both normal donors and RA patients, and was elevated in synovial fluid from RA patients compared to osteoarthritis (OA) patients. Levels of LTalphabeta in RA patient synovial fluid correlated with increased TNFalpha, IL-8, IL-12, IL-1beta, IFN-gamma, and IL-6 cytokines. Moreover, recombinant LTalpha1beta2-induced CXCL1, CXCL2, IL-6, IL-8, VCAM-1, and ICAM-1 from primary synovial fibroblasts isolated from RA patients. Therefore, soluble LTalphabeta in synovial fluid is associated with a proinflammatory cytokine milieu that contributes to synovitis in RA.

Pharmacokinetics of humanized monoclonal anti-tumor necrosis factor-{alpha} antibody and its neonatal Fc receptor variants in mice and cynomolgus monkeys.

The neonatal Fc receptor (FcRn) plays a critical role in maintaining homeostasis of IgG antibodies. Recent studies have shown that the FcRn-IgG interaction can be modulated to alter the pharmacokinetics of the antibody. This has been achieved by altering amino acid residues in the FcRn-binding domain of the antibody, resulting in a change in the pH-dependent binding affinity of the antibody to FcRn. The purpose of this study was to examine the impact of the pH-dependent FcRn binding affinity on the pharmacokinetics of the antibody with changes in the Asn434 residue. Two anti-tumor necrosis factor-alpha monoclonal antibody (mAb) FcRn variants (N434A and N434H) were engineered, and pharmacokinetic studies of the two FcRn variants together with the wild type (WT) were conducted in mice and cynomolgus monkeys. N434A, which had binding properties to murine FcRn similar to those of the WT, had the same pharmacokinetic profile as the WT in mice. N434H, with the highest binding affinity to murine FcRn at pH 7.4, had a faster clearance (16.1 ml/day/kg) and a lower bioavailability (61.3%) compared with the WT (5.07 ml/day/kg, 73.2%) and N434A (5.90 ml/day/kg, 72.4%) in mice. N434A and N434H, which had higher binding affinity at pH 6.0 to monkey FcRn with comparable affinity at pH 7.4, had significantly higher areas under the serum concentration-time curve from time 0 to day 7 than the WT (749 +/- 71.9 and 819 +/- 81.5 versus 592 +/- 56.8 microg/ml . day) in monkeys. Thus, increasing the binding affinity of mAbs to FcRn at pH 6.0 while keeping a low binding affinity at pH 7.4 improves the pharmacokinetics of these molecules.

Improving therapeutic efficacy of a complement receptor by structure-based affinity maturation.

CRIg is a recently discovered complement C3 receptor expressed on a subpopulation of tissue-resident macrophages. The extracellular IgV domain of CRIg (CRIg-ECD) holds considerable promise as a potential therapeutic because it selectively inhibits the alternative pathway of complement by binding to C3b and inhibiting proteolytic activation of C3 and C5. However, CRIg binds weakly to the convertase subunit C3b (K(D) = 1.1 microm), and thus a relatively high concentration of protein is required to reach nearly complete complement inhibition. To improve therapeutic efficacy while minimizing risk of immunogenicity, we devised a phage display strategy to evolve a high affinity CRIg-ECD variant with a minimal number of mutations. Using the crystal structure of CRIg in complex with C3b as a guide for library design, we isolated a CRIg-ECD double mutant (Q64R/M86Y, CRIg-v27) that showed increased binding affinity and improved complement inhibitory activity relative to CRIg-ECD. In a mouse model of arthritis, treatment with a Fc fusion of CRIg-v27 resulted in a significant reduction in clinical scores compared with treatment with an Fc fusion of CRIg-ECD. This study clearly illustrates how phage display technology and structural information can be combined to generate proteins with nearly natural sequences that act as potent complement inhibitors with greatly improved therapeutic efficacy.

Technology comparisons for anti-therapeutic antibody and neutralizing antibody assays in the context of an anti-TNF pharmacokinetic study.

A single-dose cynomolgus monkey pharmacokinetic study was performed comparing two monoclonal anti-TNF antibodies (mAbs), GNExTNFvF and Humira. Normal pharmacokinetic profiles were observed over the first week of the study, followed by a rapid drop in serum mAb levels after day 8. In order to determine whether an anti-therapeutic antibody (ATA) response led to the abnormal clearance of antibody in this study, ATA assays were developed using two electrochemiluminescent technologies, BioVeris and Meso Scale Discovery (MSD). Characterization of the assays demonstrated that the two platforms gave similar sensitivities and tolerance to the presence of therapeutic antibody. Analysis of the cynomolgus monkey serum samples revealed that all animals developed significant ATA titers with log titer values of 2-4, with the BioVeris and MSD technologies giving very similar results. Immunodepletion studies confirmed the CDR-specificity of the ATA response for the GNExTNFvF-dosed cynos, although the Humira-dosed cynos showed both CDR-specific and human IgG1 framework-specific ATAs. To further characterize the ATA response, neutralizing antibody (NAb) assays were developed using two different approaches, flow cytometry and MSD. Flow cytometry and MSD cell-binding assays used Jurkat cells transfected with noncleavable TNF (huTNF(NC)). Neutralizing activity was assessed by the ability of ATA-positive serum samples to block the binding of biotinylated anti-TNF to huTNF(NC) Jurkat cells, showing that all but one animal developed neutralizing antibodies. Although both technologies displayed similar trends, the MSD approach showed greater differentiation between samples and could detect a broader range of neutralizing activities.

Structural and functional analysis of a C3b-specific antibody that selectively inhibits the alternative pathway of complement.

Amplification of the complement cascade through the alternative pathway can lead to excessive inflammation. Targeting C3b, a component central to the alternative pathway of complement, provides a powerful approach to inhibit complement-mediated immune responses and tissue injury. In the present study, phage display technology was employed to generate an antibody that selectively recognizes C3b but not the non-activated molecule C3. The crystal structure of C3b in complex with a Fab fragment of this antibody (S77) illustrates the structural basis for this selectivity. Cleavage of C3 to C3b results in a plethora of structural changes within C3, including the rearrangement of macroglobulin domain 6 enabling binding of S77 to the adjacent macroglobulin domain 7 domain. S77 blocks binding of factor B to C3b inhibiting the first step in the formation of the alternative pathway C3 convertase. In addition, S77 inhibits C5 binding to C3b. This results in significantly reduced formations of anaphylatoxins and membrane-attack complexes. This study for the first time demonstrates the structural basis for complement inhibition by a C3b-selective antibody and provides insights into the molecular mechanisms of alternative pathway complement activation.