Affinity For FcγRIIIa Research Articles

Cleavage of the interchain disulfide bonds in rituximab increases its affinity for FcγRIIIA

The Fc region of human IgG1 mediates effector function via binding to Fcγ receptors and complement activation. The H and L chains of IgG1 antibodies are joined by four interchain disulfide bonds. In this study, these bonds within the therapeutic IgG1 rituximab (RTX) were cleaved either by mild reduction followed by alkylation or by mild S-sulfonation; consequently, two modified RTXs – A-RTX (alkylated) and S-RTX (S-sulfonated) – were formed, and both were almost as potent as unmodified RTX when binding CD20 antigen. Unexpectedly, each modified RTX had a higher binding affinity for FcγRIIIA (CD16A) than did unmodified RTX. However, S-RTX and A-RTX were each less potent than RTX in an assay of antibody-dependent cellular cytotoxicity (ADCC). In this ADCC assay, each modified RTX showed decreased secretion of granzyme B, but no change in perforin secretion, from effector cells. These results provide significant information on the structures within IgG1 that are involved in binding FcγRIIIA, and they may be useful in the development of therapeutic antagonists for FcγRIIIA.

Preclinical Study of Ublituximab, a Glycoengineered Anti-Human CD20 Antibody, in Murine Models of Primary Cerebral and Intraocular B-Cell Lymphomas

Primary cerebral lymphoma (PCL) and primary intraocular lymphoma (PIOL) belong to the systemic diffuse large B-cell lymphoma family and are characterized by the presence of CD20(+) lymphoma B cells in the brain or the eye. These highly aggressive malignancies have a poor prognosis and no specific therapy. The presence of effector immune cells in the damaged brain and vitreous suggests that treatment with anti-human CD20 (hCD20) monoclonal antibodies might be effective. We developed murine models of PCL and PIOL to assess the intracerebral and intraocular antitumor effect of ublituximab, a promising glycoengineered anti-hCD20 mAb with a high affinity for FcγRIIIa (CD16) receptors. The murine lymphoma B-cell line A20.IIA-GFP-hCD20 (H-2(d)) was injected into the right cerebral striatum or the vitreous of immunocompetent adult BALB/c mice (H-2(d)). Four to 7 days later, ublituximab was injected intracerebrally or intravitreously into the tumor site. Rituximab was the reference compound. Survival was monitored for injected mice; histopathological and flow cytometric analyses were performed to study tumor growth and T-cell infiltration. Single doses of ublituximab, injected intracerebrally or intravitreously, had a marked antitumor effect, more pronounced than that obtained with the same dose of rituximab in these conditions. The reduction in tumor cells was correlated with an increased proportion of CD8(+) T cells. This efficacy was observed only against lymphoma B cells expressing hCD20. These in vivo results confirm the potential of the glycoengineered anti-hCD20 mAb ublituximab as an innovative therapeutic approach to treat primary central nervous system lymphoma and other B-cell lymphomas.

Ublituximab, an Optimized Anti-CD20 Monoclonal Antibody, Demonstrates Greater NK-Mediated ADCC Than Rituximab in Waldenstrom's Macroglobulinemia Patients Supporting a Therapeutic Strategy with Ublituximab

AbstractAbstract 1654 Background:Anti-CD20 monoclonal antibody (mAb) therapy is an important therapeutic option in the treatment of Waldenström’s Macroglobulinemia (WM), exhibiting an ORR up to 55% when used as monotherapy. NK cells are involved in mAb therapy by an antibody-dependent cellular cytotoxicity (ADCC) mechanism through their FcγRIIIa (CD16) receptor. Ublituximab (TGTX-1101 or LFB-R603) is a novel, glycoengineered chimeric anti-CD20 mAb that has a high affinity for FcγRIIIa (CD16) receptors. In this study, we evaluate the ADCC functional capacities of NK cells in the presence of ublituximab compared to rituximab. Patients and Methods:Blood samples from 37 un-treated, or without ongoing treatment WM patients and from 30 age-matched healthy donors (Ctl) were collected to quantify CD16 expression (clone 3G8, Quantibrite) on NK cells and/or to measure their functional capacities. Patients were divided in two groups relative to the presence (WM clone+) or absence (WM clone-) of blood clonal B cells. NK cell degranulation was assessed by the surface expression of CD107a on NK cells after incubation of PBMC with or without Raji CD20+ target cells in the presence of anti-CD20 mAbs at 10 and 1,000 ng/ml. ADCC experiments were performed using a chromium assay with purified NK cells and autologous B cells or Raji target cells, in the presence of anti-CD20 mAbs at 1 and 100 ng/ml. Statistical analyses were performed with Prism 5 software. Intergroup comparisons were assessed with the nonparametric Krustal–Walis test, with the Dunns postanalysis test. Results:In the presence of Raji cells, at low concentration, a significantly greater amount of CD107a expression was observed with ublituximab compared to rituximab (P<0.01), regardless of patient’s groups. In contrast, at the highest concentration, similar effects were obtained with both anti-CD20 mAbs. These results were confirmed by ADCC. In the presence of Raji cells, a high level of ADCC (>40%) was detected at low concentration of ublituximab and remained stable at 100 ng/ml. In contrast, with rituximab the highest concentration was necessary to reach similar efficacy. In the presence of autologous B cells, degranulation assays revealed that none of the NK cells from WM clone- patients exhibited degranulation, irrespectively of the anti-CD20 mAb or its concentration. More importantly, NK cells of 3/8 WM clone+ patients exhibited CD107a+ NK cells in the presence of both concentrations of ublituximab. In contrast, with rituximab only 1/8 patients expressed CD107a+ NK cells, and only at the highest concentration. Of note, similar frequency and cell-surface expression level of CD16 on NK cells were detected in both patient groups. Importantly, these data were confirmed by ADCC. In the presence of autologous purified B cells from WM clone- patients, absence or low levels of ADCC were detected, irrespective of the concentration and the anti-CD20 mAb used. Interestingly, in WM clone+ patients, ADCC was detected in all of the 5 tested patients with ublituximab, but only in 2/5 patients with rituximab, and at the highest concentration. These results are confirmed by polyfunctionality assays of NK cells against Raji cells (assessment of CD107a degranulation and intracellular production of IFN-γ and TNF-α). Conclusion:These results show that ublituximab is more efficient than rituximab in inducing ADCC at low doses, in the presence of Raji cells. More importantly, our results suggest that ublituximab could be more efficient than rituximab both to induce NK cell degranulation and ADCC in the presence of autologous peripheral tumor cells. These findings highlight a new putative role of this optimized anti-CD20 mAb in the control of WM, and prompt further investigations in a large cohort of WM patients. A Phase I/II trial with single agent ublituximab in patients with rituximab relapsed/refractory NHL, including WM patients is currently ongoing. Disclosures:Le Garff-Tavernier:LFB: 2012 filed patent application Other, Research Funding. Herbi:LFB: Employment, Research Funding. de Romeuf:LFB: 2012 filed patent application Other, Employment. Prost:LFB: Employment. Urbain:LFB: Employment. Leblond:LFB: 2012 filed patent application Other. Vieillard:LFB: 2012 filed patent application Other. Merle-Béral:LFB: 2012 filed patent application Other, Research Funding.

Ublituximab (TGTX-1101), a Novel, Third-Generation Anti-CD20 Antibody Demonstrates Enhanced Antitumor Activity Compared to Rituximab in Primary CNS and Intraocular Lymphoma Murine Models.

AbstractAbstract 2755 Background:Primary Central Nervous lymphomas (PCNSL), that comprise primary cerebral lymphoma (PCL) and primary intraocular lymphoma (PIOL), are typically CD20+ diffuse large B-cell lymphomas that have no detectable disease outside the brain or eye. Rituximab (RTX), an anti-CD20 antibody, has demonstrated encouraging clinical benefit in systemic B-cell lymphomas as well as PCL and PIOL, however, the role of RTX in treatment of PCNSL/PIOL remains controversial, and these highly aggressive malignancies are often incurable with available therapies. Therefore, additional treatment options are needed. Ublituximab (UTX) is a novel, glycoengineered chimeric anti-CD20 monoclonal antibody (mAb) that has a high affinity for FcγRIIIa (CD16) receptors, and therefore greater ADCC activity than RTX (Le Garff-Tavernier et al., 2011). Herein, we assess the antitumor effects of UTX compared to RTX in murine models of PCL and PIOL. Methods:The murine lymphoma B-cell line A20.IIA-GFP-hCD20 (H-2d) was injected into the right cerebral striatum (PCL model) or the vitreous (PIOL model) of adult BALB/c mice (H-2d); 7 days later, single doses of UTX were injected either into the tumor site intracerebrally (PCL) or intravitreously (PIOL), or at distance of the tumor site (intrathecally, PCL). RTX was used as a reference compound. Survival was monitored for injected mice for up to 100 days, and flow cytometric analyses were performed to assess tumor growth and T-cell infiltration. Results:In PCL and PIOL models, single doses of UTX had a marked antitumor effect more pronounced than that obtained with an equivalent dose of RTX. In the PCL model, there was an overall survival (OS) advantage with intracerebral injections of UTX compared to RTX (50% vs. 10%, n=10 in each group, p=0.0028). The reduction in tumor cells was correlated with an increased proportion of CD8+ T cells. Moreover, intrathecal injections of UTX increased OS compared to buffer solution. In the PIOL model, the absolute number of tumor cells analyzed 8 days after treatment had decreased more significantly (p=0.027) with UTX compared to the RTX group. This finding again confirmed the superiority of UTX in this setting. Conclusions:These results confirm that the novel, third-generation mAb, UTX has a sustained and greater antitumor effect than RTX on primary cerebral and intraocular lymphomas when assessed in vivo. Additional experiments evaluating the combination of UTX + methotrexate are ongoing. Clinical trials to evaluate UTX as an innovative therapeutic approach to treat primary cerebral and intraocular B-cell lymphomas are currently being evaluated. Disclosures:Jacquet:LFB Biotechnologies: Employment. Fridman:LFB Biotechnologies: Membership on an entity's Board of Directors or advisory committees. Sportelli:TG Therapeutics, Inc.: Employment, Equity Ownership. Urbain:LFB Biotechnologies: Employment.

Unique carbohydrate–carbohydrate interactions are required for high affinity binding between FcγRIII and antibodies lacking core fucose

Antibody-mediated cellular cytotoxicity (ADCC), a key immune effector mechanism, relies on the binding of antigen-antibody complexes to Fcγ receptors expressed on immune cells. Antibodies lacking core fucosylation show a large increase in affinity for FcγRIIIa leading to an improved receptor-mediated effector function. Although afucosylated IgGs exist naturally, a next generation of recombinant therapeutic, glycoenginereed antibodies is currently being developed to exploit this finding. In this study, the crystal structures of a glycosylated Fcγ receptor complexed with either afucosylated or fucosylated Fc were determined allowing a detailed, molecular understanding of the regulatory role of Fc-oligosaccharide core fucosylation in improving ADCC. The structures reveal a unique type of interface consisting of carbohydrate-carbohydrate interactions between glycans of the receptor and the afucosylated Fc. In contrast, in the complex structure with fucosylated Fc, these contacts are weakened or nonexistent, explaining the decreased affinity for the receptor. These findings allow us to understand the higher efficacy of therapeutic antibodies lacking the core fucose and also suggest a unique mechanism by which the immune system can regulate antibody-mediated effector functions.

Abstract LB-212: XGFR, an Fc-engineered dual signaling inhibitor targeting IGF-1R and EGFR

Abstract Background: Elevated signaling via the receptor tyrosine kinases IGF-1R and EGFR has been identified as common characteristic of multiple cancer type. IGF-1R and EGFR signal predominantly through the PI3K and MAPK signaling pathways and thereby mediate growth and survival signals crucial for the development and progression of cancer. There is strong cross talk on multiple levels between IGF-1R and EGFR dependent signaling pathways. Therefore, targeting IGF-1R and EGFR simultaneously is an attractive way to achieve maximal inhibition of signal transduction and to avoid resistance formation. Methods: Bispecific IGF1R-EGFR antibodies were engineered by linking scFv domains of an EGFR Mab (GA201) via Serine-Glycine linkers to an IgG1 IGF-1R Mab (RG1507). The functional properties of the bispecific antibodies were evaluated in cellular in vitro assays (IGF-1R/EGFR phosphorylation, downregulation, 3D proliferation and ADCC assays) and in in vivo xenograft models for tumor growth inhibition and survival. Results: Bispecific IGF-1R-EGFR antibodies (XGFR2, XGFR3, XGFR4) were successfully generated with yields and stability comparable to conventional IgG1 antibodies. XGFR antibodies effectively inhibited IGF-1R and EGFR phosphorylation and 3D proliferation in H322M tumor cells and induced strong downmodulation of IGF-1R and enhanced EGFR downmodulation compared to the parental EGFR antibody GA201. XGFR antibodies showed strong anti-tumor efficacy comparable to the combination of monospecific IGF-1R and EGFR Mabs in the BxPC3 and H322M xenograft models. To enhance the ADCC properties of XGFR, afucosylated, glycoengineered bispecific antibodies with enhanced affinity for FcγRIIIA were generated using the GlycoMab technology. Glycoengineered bispecific antibodies were shown to have superior ADCC properties in in vitro ADCC assays and XGFR4 significantly prolonged median and overall survival of mice in an ADCC competent in vivo model (A549 i.v.). Conclusions: Bispecific IGF-1R-EGFR antibodies represent an attractive therapeutic strategy to simultaneously target two key components of multiple cancer types (IGF-1R and EGFR), resulting in effective inhibition of the PI3K and MAPK signaling pathway and to avoid the formation of resistance to therapy. Having overcome issues of stability and productivity, bispecific antibodies may become an advantageous way to reduce costs and infusion times in cancer therapy, while at the same time, achieving maximal anti-tumor effects through inhibition of multiple targets. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-212. doi:10.1158/1538-7445.AM2011-LB-212

Identification of IgG1 variants with increased affinity to FcγRIIIa and unaltered affinity to FcγRI and FcRn: Comparison of soluble receptor-based and cell-based binding assays

Clinical response to the anti-CD20 antibody rituximab has been demonstrated to correlate with the polymorphism in the FcγRIIIa receptor where patients homozygous for the higher affinity V158 allotype showed a better response rate. This finding suggests that engineering of anti-CD20 for increased FcγRIIIa affinity could result in improved clinical outcome. To identify variants with increased affinity to FcγRIIIa, we developed quantitative assays using soluble receptors as well as engineered cell lines expressing FcγRI or FcγRIIIa on the cell surface. We assayed a set of anti-CD20 IgG1 variants that had identical Fab regions, but alterations in the Fc regions, in both the soluble receptor-based and cell-based FcγRIIIa binding assays. We obtained similar relative binding affinity increases and assay precisions. The increase in affinity for FcγRIIIa correlated with the increase in activity in the antibody-dependent cellular cytotoxicity assay. These variants had unaltered FcγRI binding. In addition to Fcγ receptors, IgG also binds to FcRn, the receptor responsible for the long circulating half-life of IgG. The mutations in the anti-CD20 variants were previously found not to affect FcRn binding in the soluble receptor-based assays; consequently, we used anti-Her2 variants with different binding affinities to FcRn to study FcRn binding assays. We generated a cell line expressing FcRn on the cell surface to measure IgG binding and obtained similar ranking of these anti-Her2 variants in the cell-based and the soluble receptor-based FcRn binding assays. In conclusion, both the soluble receptor-based and cell-based binding assays can be used to identify IgG1 variants with increased affinity to FcγRIIIa and unaltered affinity to FcγRI and FcRn.

Enhanced binding affinity for FcγRIIIa of fucose-negative antibody is sufficient to induce maximal antibody-dependent cellular cytotoxicity

Antibody-dependent cellular cytotoxicity (ADCC) is considered to be an important therapeutic function for clinical efficacy of monoclonal antibodies. Recent studies have revealed two methods to increase binding affinity for FcγRIIIa and enhance ADCC more efficiently for antibodies: (i) fucose removal from antibody N-linked complex oligosaccharides and (ii) amino acid mutations in the antibody Fc region. In this study, we compare the biological activities of the methods of generating high ADCC antibodies. We used a fucose-negative antibody and two antibodies with sets of mutations, demonstrated previously to optimally enhance ADCC using the chimeric anti-CD20 antibody, rituximab, as the model. Both amino acid mutant antibodies showed a significantly higher affinity for recombinant FcγRIIIa than fucose-negative antibody when compared using biosensor analysis. The removal of fucose from the antibodies bearing amino acid mutations exhibited a further enhancement of binding to recombinant FcγRIIIa and significantly increased binding to natural killer (NK) cells. Despite the differences manifested in binding for the FcγR, ADCCs were indistinguishable between methods and even when the methods were combined. These results indicate that the affinity of binding to FcγRIIIa does not predict ADCC beyond a certain threshold and that each method alone is sufficient to induce maximal ADCC of the antibody.

Fucose Depletion from Human IgG1 Oligosaccharide Enhances Binding Enthalpy and Association Rate Between IgG1 and FcγRIIIa

Depletion of fucose from human IgG1 oligosaccharide improves its affinity for Fcγ receptor IIIa (FcγRIIIa). This is the first case where a glycoform modification is shown to improve glycoprotein affinity for the receptors without carbohydrate-binding capacity, suggesting a novel glyco-engineering strategy to improve ligand–receptor binding. To address the mechanisms of affinity improvement by the fucose depletion, we used isothermal titration calorimetry (ITC) and biosensor analysis with surface plasmon resonance. ITC demonstrated that IgG1–FcγRIIIa binding was driven by favorable binding enthalpy (Δ H) but opposed by unfavorable binding entropy change (Δ S). Fucose depletion from IgG1 enhanced the favorable Δ H, leading to the increase in the binding constant of IgG1 for the receptor by a factor of 20–30. The increase in the affinity was mainly attributed to an enhanced association rate. A triple amino acid substitution in IgG1, S298A/E333A/K334A, is also known to improve IgG1 affinity for FcγRIIIa. ITC demonstrated that the amino acid substitution attenuated the unfavorable Δ S, resulting in a three- to fourfold increase in the binding constant. The affinity enhancement by the amino acid substitution was due to a reduced dissociation rate. These results indicate that the mechanism of affinity improvement by the fucose depletion is quite distinct from that by the amino acid substitution. Defucosylated IgG1 exhibited higher antibody-dependent cellular cytotoxicity (ADCC) than S298A/E333A/K334A-IgG1, showing a correlation between IgG1 affinity for FcγRIIIa and ADCC. We also examined the effect of FcγRIIIa polymorphism (Val158/Phe158) on IgG1–FcγRIIIa binding. The Phe to Val substitution increased FcγRIIIa affinity for IgG1 in an enthalpy-driven manner with the reduced dissociation rate. These results together highlight the distinctive functional improvement of affinity by IgG1 defucosylation and suggest that engineering of non-interfacial monosaccharides can improve glycoprotein affinity for receptors via an enthalpy-driven and association rate-assisted mechanism.