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T-cell bispecific antibodies (TCBs) are a novel class of engineered immunoglobulins that unite monovalent binding to the T-cell receptor (TCR) CD3e chain and bivalent binding to tumor-associated antigens in order to recruit and activate T-cells for tumor cell killing. In vivo, T-cell activation is usually initiated via the interaction of the TCR with the peptide-HLA complex formed by the human leukocyte antigen (HLA) and peptides derived from intracellular proteins. TCR-like antibodies (TCRLs) that recognize pHLA-epitopes extend the target space of TCBs to peptides derived from intracellular proteins, such as those overexpressed during oncogenesis or created via mutations found in cancer. One challenge during lead identification of TCRL-TCBs is to identify TCRLs that specifically, and ideally exclusively, recognize the desired pHLA, but not unrelated pHLAs. In order to identify TCRLs suitable for TCRL-TCBs, large numbers of TCRLs have to be tested in the TCB format. Here, we propose a novel approach using chimeric antigen receptors (CARs) to facilitate the identification of highly selective TCRLs. In this new so-called TCRL-CAR-J approach, TCRL-candidates are transduced as CARs into Jurkat reporter-cells, and subsequently assessed for their specificity profile. This work demonstrates that the CAR-J reporter-cell assay can be applied to predict the profile of TCRL-TCBs without the need to produce each candidate in the final TCB format. It is therefore useful in streamlining the identification of TCRL-TCBs.

Monoclonal antibody-based therapeutics are an integral part of treatment of different human diseases, and the selection of suitable antibody candidates during the discovery phase is essential. Here, we describe a novel, cellular screening approach for the identification and characterization of therapeutic antibodies suitable for conversion into T cell bispecific antibodies using chimeric antigen receptor (CAR) transduced Jurkat-NFAT-luciferase reporter cells (CAR-J). For that purpose, we equipped a Jurkat-NFAT reporter cell line with a universal CAR, based on a monoclonal antibody recognizing the P329G mutation in the Fc-part of effector-silenced human IgG1-antibodies. In addition to scFv-based second generation CARs, Fab-based CARs employing the P329G-binder were generated. Using these anti-P329G-CAR-J cells together with the respective P329G-mutated IgG1-antibodies, we established a system, which facilitates the rapid testing of therapeutic antibody candidates in a flexible, high throughput setting during early stage discovery. We show that both, scFv- and Fab-based anti-P329G-CAR-J cells elicit a robust and dose-dependent luciferase signal if the respective antibody acts as an adaptor between tumor target and P329G-CAR-J cells. Importantly, we could demonstrate that functional characteristics of the antibody candidates, derived from the anti-P329G-CAR-J screening assay, are predictive for the functionality of these antibodies in the T cell bispecific antibody format.

Introduction: In the rapidly growing field of chimeric antigen receptor (CAR) engineered T cells new approaches aim to make CAR-T cell therapy safer and more effective. Recent, designs aim towards universal or modular CARs that do not directly recognize the target antigen itself, but instead facilitate contact to CAR-adaptor molecules, which in turn bind to the target antigen. Current CAR-adaptor molecules include human antibodies of the IgG1 isotype binding to CD16 or antibodies modified by peptide or hapten tags. We developed a modular CAR-T approach that recognizes the P329G mutation clinically used to silence the Fc effector function of therapeutic antibodies. These modular anti-P329G-CAR-T cells are only functional in the presence of antibodies that possess the P329G mutation. Methods: The anti-P329G interaction with P329G-containing Fc fragment was analyzed using surface plasmon resonance and co-crystallography. Lentivirus transfected anti-P329G CAR-T cells were characterized in vitro for their selectivity and potential to mediate antigen specific tumor cell lysis, cytokine secretion and proliferation. Immunological synapse formation was investigated using confocal microscopy. Results: Anti-P329G-CAR-T cells allow the precise recognition of the P329G mutation present in therapeutic IgG1 based adaptor-molecules. Crystal structure- and SPR-analysis revealed a 1:1 binding stoichiometry with low nanomolar affinity of the P329G-Fab fragment applied in the CAR for P329G-containing IgG1 antibodies. Potent tumor cell lysis was demonstrated for multiple tumor antigens e.g. CD20, HER2, FOLR1, EpCAM, FAP and others. For all tested antigens, a huIgG1 dose-dependent activation of anti-P329G-CAR-T cells as well as dose-dependent tumor cell lysis was observed. For selected antigens P329G-CAR-T activity was found comparable to the activity mediated by T cell bispecific antibodies recognizing the respective tumor antigen. Finally, the immunological synapse formed by P329-CAR-T cells was compared to the one formed by T cell bispecific antibodies in a 2+1 format. Conclusions: P329G-CAR-T cells mediate potent and specific tumor cell killing using various tumor targeted antibodies as adaptor molecules. Based on these data in vivo studies to investigate efficacy and safety of the approach are foreseen. Notably, this approach allows control of CAR-T activity and potential side effects by titrating the adaptor molecule, as well as the simultaneous targeting of more than one antigen at the same time with the goal to prevent tumor escape mechanisms. Combining the P329G-CAR with allogenic T-cells may provide a truly off-the-shelf P329G-CAR-T cell therapy approach. Citation Format: Diana Darowski, Christian Jost, Zeno Riester, Mohamed Benmebarek, Kay Stubenrauch, Anne Freimoser-Grundschober, Uwe Wessels, Jörg Benz, Ekkehard Mössner, Renier Myburgh, Floriana Cremasco, Mario Perro, Pablo Umana, Sebastian Kobold, Christian Klein. Anti-P329G-CAR-T cells as a novel universal CAR-T cell platform [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4229.

CD20 is a B-lymphocyte specific integral membrane protein, an activated-glycosylated phosphoprotein expressed on the surface of B-cells and a clinically validated target of monoclonal antibodies such as rituximab, ocrelizumab, ofatumumab and obinutuzumab in the treatment of all B cell lymphomas and leukemias as well as autoimmune diseases. Here, we report the extraction and purification of native CD20 from SUDHL4 and RAMOS cell lines. To improve the protein yield, we applied a calixarene-based detergent approach to solubilize, stabilize and purify native CD20 from HEK293 cells. Size Exclusion Chromatography (SEC) and Analytical Ultracentrifugation show that purified CD20 was non-aggregated and that CD20 oligomerization is concentration dependent. Negative stain electron microscopy and atomic force microscopy revealed homogenous populations of CD20. However, no defined structure could be observed. Interestingly, micellar solubilized and purified CD20 particles adopt uniformly confined nanodroplets which do not fuse and aggregate. Finally, purified CD20 could bind to rituximab and obinutuzumab as demonstrated by SEC, and Surface Plasmon Resonance (SPR). Specificity of binding was confirmed using CD20 antibody mutants to human B-cell lymphoma cells. The strategy described in this work will help investigate CD20 binding with newly developed antibodies and eventually help to optimize them. This approach may also be applicable to other challenging membrane proteins.

Recombinant human IgG antibodies (hIgGs) completely devoid of binding to Fcγ receptors (FcγRs) and complement protein C1q, and thus with abolished immune effector functions, are of use for various therapeutic applications in order to reduce FcγR activation and Fc-mediated toxicity. Fc engineering approaches described to date only partially achieve this goal or employ a large number of mutations, which may increase the risk of anti-drug antibody generation. We describe here two new, engineered hIgG Fc domains, hIgG1-P329G LALA and hIgG4-P329G SPLE, with completely abolished FcγR and C1q interactions, containing a limited number of mutations and with unaffected FcRn interactions and Fc stability. Both 'effector-silent' Fc variants are based on a novel Fc mutation, P329G that disrupts the formation of a proline sandwich motif with the FcγRs. As this motif is present in the interface of all IgG Fc/FcγR complexes, its disruption can be applied to all human and most of the other mammalian IgG subclasses in order to create effector silent IgG molecules.

Dysregulated cellular apoptosis and resistance to cell death are hallmarks of neoplastic initiation and disease progression. Therefore, the development of agents that overcome apoptosis dysregulation in tumor cells is an attractive therapeutic approach. Activation of the extrinsic apoptotic pathway is strongly dependent on death receptor (DR) hyperclustering on the cell surface. However, strategies to activate DR5 or DR4 through agonistic antibodies have had only limited clinical success. To pursue an alternative approach for tumor-targeted induction of apoptosis, we engineered a bispecific antibody (BsAb), which simultaneously targets fibroblast-activation protein (FAP) on cancer-associated fibroblasts in tumor stroma and DR5 on tumor cells. We hypothesized that bivalent binding to both FAP and DR5 leads to avidity-driven hyperclustering of DR5 and subsequently strong induction of apoptosis in tumor cells but not in normal cells. Here, we show that RG7386, an optimized FAP-DR5 BsAb, triggers potent tumor cell apoptosis in vitro and in vivo in preclinical tumor models with FAP-positive stroma. RG7386 antitumor efficacy was strictly FAP dependent, was independent of FcR cross-linking, and was superior to conventional DR5 antibodies. In combination with irinotecan or doxorubicin, FAP-DR5 treatment resulted in substantial tumor regression in patient-derived xenograft models. FAP-DR5 also demonstrated single-agent activity against FAP-expressing malignant cells, due to cross-binding of FAP and DR5 across tumor cells. Taken together, these data demonstrate that RG7386, a novel and potent antitumor agent in both mono- and combination therapies, overcomes limitations of previous DR5 antibodies and represents a promising approach to conquer tumor-associated resistance to apoptosis. Mol Cancer Ther; 15(5); 946–57. ©2016 AACR.

T cell bispecific antibodies that recruit and engage T cells for tumor cell killing through binding to the T cell receptor (TCR) upon binding to a tumor antigen (TA) and subsequent crosslinking have attracted broad interest. Here, we describe a novel asymmetric head-to-tail 2+1 T cell bispecific antibody (2+1 TCB) platform characterized by the fusion of a flexible Fab fragment to the N-terminus of the CD3e Fab of a heterodimeric asymmetric bispecific TA-CD3e IgG1 antibody in head-to-tail geometry via a flexible linker. The resulting TCB is monovalent for CD3e (KD 70-100 nM) and binds bivalently with avidity to the TA on the target cell. Correct heavy chain pairing is enabled by knob-into-holes technology, correct light chain pairing by CrossMAb technology or using a common light chain. This enables production with standard processes in CHO cells. To exclude FcgR-mediated unspecific TCR and FcgR co-activation resulting in unspecific cytokine release, Fc- effector functions (ADCC, ADCP, CDC) are abolished by introduction of P329G LALA mutations while FcRn binding and IgG-like pharmacokinetic properties are retained as shown in mouse and Cynomolgus. For comparative profiling, the following TCBs were generated with specificity for the tumor antigens MCSP/CSPG4, FOLR1/FRalpha, CD19 and CD20: 2+1 TCBCD3-inside, 2+1 TCBCD3-outside, one-armed 1+1 TCBCD3-inside and a classical asymmetric 1+1 IgG TCB. In vitro Jurkat-NFAT, T cell killing, activation and proliferation assays show that both 2+1 TCB formats mediate superior potency of killing (for CSPG4, FOLR1, CD19, CD20) and superior absolute killing (for CSPG4, CD19) compared to the respective classical asymmetric 1+1 IgG TCB. Surprisingly, the 2+1 TCBCD3-inside format was found to be superior in potency compared to the 2+1 TCBCD3-outside format, although its binding affinity for CD3e is reduced. These data confirm that TCBs mediate extremely potent T cell killing with fM-pM EC50 values based on CD3e antibodies with affinities of only 70-100 nM. Notably, for CD19 both, 2+1 TCBCD3-inside and one-armed 1+1 TCBCD3-inside, mediate comparable potency and overall killing, and both were superior compared to the asymmetric 1+1 IgG TCB. These data underline the importance of the head-to-tail geometry with two Fabs on one arm attached to each other via a flexible G4S-linker. Finally, using 2+1 and 1+1 FOLR1 TCBs we demonstrate that bivalent binding allows better differentiation in killing of cells with high vs. low FOLR1 expression as compared to monovalent binding. Taken together, we demonstrate that the 2+1 TCBCD3-inside is the most potent, efficacious and versatile TCB design. Due to its orientation with the CD3e Fab inside, it allows the conversion of existing antibodies into potent TCBs without format restriction. Based on this platform, CEA CD3 TCB (RG7802, Phase I/Ib) and CD20 CD3 TCB (RG6026, Phase I) have entered clinical trials. Citation Format: Christian Klein, Christiane Neumann, Tanja Fauti, Tina Weinzierl, Anne Freimoser-Grundschober, Inja Waldhauer, Linda Fahrni, Sylvia Herter, Erwin van Puijenbroek, Sara Colombetti, Johannes Sam, Sabine Lang, Sherri Dudal, Wolfgang Schäfer, Jörg T. Regula, Samuel Moser, Oliver Ast, Ralf Hosse, Ekkehard Mössner, Peter Brünker, Marina Bacac, Pablo Umana. Engineering a novel asymmetric head-to-tail 2+1 T-cell bispecific (2+1 TCB) IgG antibody platform with superior T-cell killing compared to 1+1 asymmetric TCBs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3629. doi:10.1158/1538-7445.AM2017-3629

Several novel anti-CD20 monoclonal antibodies are currently in development with the aim of improving the treatment of B cell malignancies. Mutagenesis and epitope mapping studies have revealed differences between the CD20 epitopes recognized by these antibodies. Recently, X-ray crystallography studies confirmed that the Type I CD20 antibody rituximab and the Type II CD20 antibody obinutuzumab (GA101) differ fundamentally in their interaction with CD20 despite recognizing a partially overlapping epitope on CD20. The Type I CD20 antibodies rituximab and ofatumumab are known to bind to different epitopes. The differences suggest that the biological properties of these antibodies are not solely determined by their core epitope sequences, but also depend on other factors, such as the elbow hinge angle, the orientation of the bound antibody and differential effects mediated by the Fc region of the antibody. Taken together, these factors may explain differences in the preclinical properties and clinical efficacy of anti-CD20 antibodies.

CD20 is a cell-surface marker of normal and malignant B cells. Rituximab, a monoclonal antibody targeting CD20, has improved the treatment of malignant lymphomas. Therapeutic CD20 antibodies are classified as either type I or II based on different mechanisms of killing malignant B cells. To reveal the molecular basis of this distinction, we fine-mapped the epitopes recognized by both types. We also determined the first X-ray structure of a type II antibody by crystallizing the obinutuzumab (GA101) Fab fragment alone and in complex with a CD20 cyclopeptide. Despite recognizing an overlapping epitope, GA101 binds CD20 in a completely different orientation than type I antibodies. Moreover, the elbow angle of GA101 is almost 30° wider than in type I antibodies, potentially resulting in different spatial arrangements of 2 CD20 molecules bound to a single GA101 or rituximab molecule. Using protein tomography, different CD20 complexes were found to be associated with the 2 antibodies, and confocal microscopy showed different membrane compartmentalization of these subpopulations of the cellular CD20 pool. Our findings offer a possible molecular explanation for the different cellular responses elicited by type I and II antibodies.

CD20 is an important target for the treatment of B-cell malignancies, including non-Hodgkin lymphoma as well as autoimmune disorders. B-cell depletion therapy using monoclonal antibodies against CD20, such as rituximab, has revolutionized the treatment of these disorders, greatly improving overall survival in patients. Here, we report the development of GA101 as the first Fc-engineered, type II humanized IgG1 antibody against CD20. Relative to rituximab, GA101 has increased direct and immune effector cell-mediated cytotoxicity and exhibits superior activity in cellular assays and whole blood B-cell depletion assays. In human lymphoma xenograft models, GA101 exhibits superior antitumor activity, resulting in the induction of complete tumor remission and increased overall survival. In nonhuman primates, GA101 demonstrates superior B cell–depleting activity in lymphoid tissue, including in lymph nodes and spleen. Taken together, these results provide compelling evidence for the development of GA101 as a promising new therapy for the treatment of B-cell disorders.

Background & Aim: T-cell bispecific antibodies (TCBs) binding to a target on tumor cells and CD3 on T cells induce potent T-cell mediated killing of cells carrying the target. In contrast to targets like e.g. CD38 or CD138, B-cell maturation antigen (BCMA) is suggested to be only expressed on plasma cells (PCs) and multiple myeloma (MM) PCs. Therefore, a BCMA-TCB should specifically act on these cell types. We report on a new class of BCMA-TCBs designed for effective and convenient therapy of MM. Molecular structure & its rationale (fig. 1A): The new class of BCMA-TCBs are asymmetric two-arm IgG-based human antibodies, bivalent to BCMA, monovalent to CD3 and comprising an engineered Fc. To achieve tumor specificity of the BCMA-TCBs and avoid unspecific T-cell activation, monovalent binding to CD3 was fixed at an affinity of KD= 70 nM, whereas various BCMA-TCBs with binding affinities to BCMA ranging from KD= 50 pM to 10 nM have been investigated (measurement of binding affinities by surface plasmon resonance and flow cytometry (FC)). For long elimination half-life, an Fc was introduced to enable once a week intravenous or subcutaneous administration. Fc is engineered to abolish binding to FcgR and C1q to minimize risk of infusion reactions without interfering with FcRn binding. The BCMA-TCBs can be well-manufactured and have no tendency to aggregation. In vitro profile: Potency of BCMA-TCBs to activate T cells and to induce killing of human MM cell lines was measured in a 24h co-culture assay with human PBMCs and MM cells in a ratio of 10:1. Results: (i) NCI-H929 cells expressing on cell surface up to 100 times more BCMA than primary patient MM cells were killed in presence of BCMA-TCBs with EC50 ranging from 5 to 50 pM, but not in presence of a control-TCB binding to CD3 only. (ii) As next, RPMI-8226 cells were used as target cells because surface BCMA expression was found to be only slightly higher than on primary patient MM cells (specific antigen binding capacity SABC as measured by FC between 1165 and 5461 per RPMI-8226 cell compared to 116 to 4479 per primary patient MM cell). Effective killing of RPMI-8226 MM cells was observed; the killing potency was higher respectively EC50 lower with the BCMA-TCBs having binding affinities below 1 nM (fig. 1B; EC50 from 50 pM to 1000 pM). (iii) Killing of U266 and L363 human MM cell lines was also observed with BCMA-TCBs. (iv) T-cell activation and increased T-cell function go in parallel with lysis of MM target cells as observed by an upregulation of CD69 and CD25 expression, release of granzyme B (>20 ng/mL at 3 nM vs. 20 pg/mL for control) and proinflammatory cytokines e.g. IFN-g, TNF-a, IL-2, IL-6, and IL-10. (v) At 120h incubation, BCMA-TCBs induced concentration dependant CD4 and CD8 T-cell proliferation as observed by CFSE dilution. A small exploratory study in whole bone marrow (BM) aspirates from MM patients (n=3) suggested a concentration dependent killing of MM PCs induced by BCMA-TCBs in presence of autologous T cells, thus justifying for a much larger trial to investigate one of the BCMA-TCB of this new class to induce killing and T-cell activation/function in MM patient BM aspirates performed by two clinical groups (Abstract also submitted to ASH). In vivo profile: New BCMA-TCBs bind to BCMA as well as CD3 of cynomolgus monkeys (cyno). Single dose pharmacokinetics (PK) and pharmacodynamics of a BCMA-TCB was studied in cyno at 0.003, 0.03, 0.3 mg/kg intravenously. Dose linear PK was observed. Mean serum concentrations in the first 7 days after 0.03 mg/kg were ≈1 to 2 nM, BM aspirates collected at 96h showed also concentrations of ≈1 to 2 nM. Elimination between 24 h and 504 h was found to be first order with a half-life of approximately 6 to 8 days. These data suggest a convenient clinical dosing schedule, e.g. once a week. Peripheral blood T-cell redistribution was observed 24h after dosing. Reduction of PCs could be observed by FC while total B cells and other cell types were unaffected. Summary: Effective and specific killing of MM cells was demonstrated with the BCMA-TCBs. Killing goes in parallel with T-cell activation and increased function. TCB with binding affinity to BCMA below 1 nM have higher potency/lower EC50 than those with affinity above 1 nM. TCBs could be produced with high purity and were stable with no tendency to aggregation. In cynomolgus monkeys, a PK profile has been found, suitable for once a week administration. This new class of BCMA-TCB has promises for clinical development. Disclosures Vu: EngMab AG: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Moser:Roche: Employment. Delon:Roche: Employment. Latzko:Roche: Employment. Gianotti:Roche: Employment. Lüoend:Roche: Employment. Friang:Roche: Employment. Murr:Roche: Employment. Duerner:Roche: Employment. Weinzierl:Roche: Employment. Fauti:Roche: Employment. Bacac:Roche: Employment. Ast:Roche: Employment. Freimoser-Grundschober:Roche: Employment. Rodriguez Diaz:Roche: Employment. Zielonka:Roche: Employment. van Puijenbroek:Roche: Employment. Hosse:Roche: Employment. Bruenker:Roche: Employment. Mössner:Roche: Employment. Klein:Roche: Employment. Umaña:Roche: Employment. Strein:EngMab AG: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; BB Biotech AG: Membership on an entity's Board of Directors or advisory committees; Novimmune SA: Membership on an entity's Board of Directors or advisory committees.

Dear Editor, Please allow us to briefly reply to the comments by Dr. Goldenberg and colleagues. As stated in the disclosures, some authors are employees of Roche Glycart AG or Roche Diagnostics GmbH and have contributed to the (non-) clinical development of the glycoengineered Type II CD20 antibody GA101 (obinutuzumab). In writing this review, we aimed to give a general overview of the epitopes, structural and mechanistic features of CD20 antibodies in development. Due to length restrictions, this work could not necessarily be comprehensive and did not cover, for example, bispecific antibodies. Furthermore, the discussion of clinical data was intentionally not within the scope of this review because it is covered in other expert reviews.1-3 Overall, we do not agree with the conclusions drawn by Dr. Goldenberg and colleagues. In their publication, Goldenberg et al. show indeed that veltuzumab has a slower off-rate than rituximab on B cells, however, scatchard analysis showed that the KD values were comparable, with 8.6 nM for rituximab and 10.8 nM for veltuzumab.4 More importantly, this finding did not appear to translate into major functional differentiation. Veltuzumab showed in vitro anti-proliferative activity, antibody-dependent cell-mediated cytotoxicity and B cell depletion in human peripheral blood lymphocytes of healthy volunteers comparable to rituximab.4 There was only a significant difference in complement-dependent cytotoxicity (CDC) induction reported where veltuzumab was less than 2-fold more potent than rituximab.4 While statistically significant, we think that this small difference in EC50 values is not biologically relevant, in particular, as the authors demonstrate themselves by depletion of natural killer cells and neutrophils that the in vivo efficacy of veltuzumab in xenograft models relies on antibody-dependent effector cell function, but not on CDC. In light of these in vitro data the reported superiority of veltuzumab over rituximab in nonclinical xenograft models as well as a potential for clinical superiority is difficult to rationalize. We believe that it is not justified to claim clinical superiority of the 80 mg (for the subcutaneous formulation) or 80 mg/m2 (for intravenous infusions) weekly x 4 doses of veltuzumab over the standard rituximab regimen of 375 mg/mm2 based solely on a historical comparison of complete response (CR)/unconfirmed CR rates from non-randomized Phase 1/2 clinical trials in (relapsed/refractory) follicular non-Hodgkin lymphoma (NHL) patients as it is stated in the letter of Goldenberg and colleagues. In line with this, the cited publications by Morschhauser et al.5 and Negrea et al.6 do not claim superiority over rituximab. To claim superiority, the authors would have to provide clinical data where veltuzumab and rituximab are compared head-to-head at the respective (standard) doses. The dose and schedule of obinutuzumab (GA101) cannot be extrapolated from the rituximab dose and schedule due to the differences in the antibodies and their mechanisms of action. In the case of obinutuzumab, we have shown that by increasing the dose from 10 to 30 mg/kg in the SU-DHL4 diffuse large B cell lymphoma (DLBCL) nonclinical xenograft model we could induce complete tumor remissions, whereas increasing the dose of rituximab from 10 to 30 mg/kg did not result in enhanced efficacy and only slowed down tumor progression.7 These nonclinical data and data from Phase 2 clinical trials comparing doses of 400/400 mg vs 1600/ 800 mg obinutuzumab in relapsed/refractory iNHL and DLBCL patients8,9 support the rationale that in the case of obinutuzumab a flat dose of 1000 mg is studied in clinical trials. This may be particularly true for patients with higher tumor loads. We also want to point out that there is no clinical evidence available supporting the statement that higher doses of CD20 antibodies result in more pronounced side effects. In the best interest of patients, we believe that novel CD20 antibodies such as obinutuzumab, ofatumumab or veltuzumab have to be studied in clinical trials first, at the optimal dose for that antibody as determined in clinical Phase 1/2 studies, and second, in randomized clinical trials in direct comparison to the approved/standard of care rituximab based regimen. This belief is the basis of the development paradigm for obinutuzumab, which is currently being studied in combination with chemotherapy head-to-head to rituximab in three first line Phase 3 clinical trials in CLL, indolent NHL and DLBCL. Ultimately, only these clinical data can tell whether nonclinical findings translate into superior clinical benefit in patients with B cell malignancies.

The thioredoxin superfamily consists of enzymes that catalyze the reduction, formation, and isomerization of disulfide bonds and exert their activity through a redox active disulfide in a Cys-Xaa(1)-Xaa(2)-Cys motif. The individual members of the family differ strongly in their intrinsic redox potentials. However, the role of the different redox potentials for the in vivo function of these enzymes is essentially unknown. To address the question of in vivo importance of redox potential for the most reducing member of the enzyme family, thioredoxin, we have employed a set of active site variants of thioredoxin with increased redox potentials (-270 to -195 mV) for functional studies in the cytoplasm of Escherichia coli. The variants proved to be efficient substrates of thioredoxin reductase, providing a basis for an in vivo characterization of NADPH-dependent reductive processes catalyzed by the thioredoxin variants. The reduction of sulfate and methionine sulfoxide, as well as the isomerization of periplasmic disulfide bonds by DsbC, which all depend on thioredoxin as catalyst in the E. coli cytoplasm, proved to correlate well with the intrinsic redox potentials of the variants in complementation assays. The same correlation could be established in vitro by using the thioredoxin-catalyzed reduction of lipoic acid by NADPH as a model reaction. We propose that the rate of direct reduction of substrates by thioredoxin, which largely depends on the redox potential of thioredoxin, is the most important parameter for the in vivo function of thioredoxin, as recycling of reduced thioredoxin through NADPH and thioredoxin reductase is not rate-limiting for its catalytic cycle.

The thiol/disulfide oxidoreductase DsbA is the strongest oxidant of the thioredoxin superfamily and is required for efficient disulfide bond formation in the periplasm of Escherichia coli. To determine the importance of the redox potential of the final oxidant in periplasmic protein folding, we have investigated the ability of the most reducing thiol/disulfide oxidoreductase, E.coli thioredoxin, of complementing DsbA deficiency when secreted to the periplasm. In addition, we secreted thioredoxin variants with increased redox potentials as well as the catalytic a-domain of human protein disulfide isomerase (PDI) to the periplasm. While secreted wild-type thioredoxin and the most reducing thioredoxin variant could not replace DsbA, all more oxidizing thioredoxin variants as well as the PDI a-domain could complement DsbA deficiency in a DsbB-dependent manner. There is an excellent agreement between the activity of the secreted thioredoxin variants in vivo and their ability to oxidize polypeptides fast and quantitatively in vitro. We conclude that the redox potential of the direct oxidant of folding proteins and in particular its reactivity towards reduced polypeptides are crucial for efficient oxidative protein folding in the bacterial periplasm.

Thiol/disulfide oxidoreductases like thioredoxin, glutaredoxin, DsbA, or protein disulfide isomerase (PDI) share the thioredoxin fold and a catalytic disulfide bond with the sequence Cys-Xaa-Xaa-Cys (Xaa corresponds to any amino acid). Despite their structural similarities, the enzymes have very different redox properties, which is reflected by a 100,000-fold difference in the equilibrium constant (K(eq)) with glutathione between the most oxidizing member, DsbA, and the most reducing member, thioredoxin. Here we present a systematic study on a series of variants of thioredoxin from Escherichia coli, in which the Xaa-Xaa dipeptide was exchanged by that of glutaredoxin, PDI, and DsbA. Like the corresponding natural enzymes, all thioredoxin variants proved to be stronger oxidants than the wild-type, with the order wild-type < PDI-type < DsbA-type < glutaredoxin-type. The most oxidizing, glutaredoxin-like variant has a 420-fold decreased value of K(eq), corresponding to an increase in redox potential by 75 mV. While oxidized wild-type thioredoxin is more stable than the reduced form (delta deltaG(ox/red) = 16.9 kJ/mol), both redox forms have almost the same stability in the variants. The pH-dependence of the reactivity with the alkylating agent iodoacetamide proved to be the best method to determine the pKa value of thioredoxin's nucleophilic active-site thiol (Cys32). A pKa of 7.1 was measured for Cys32 in the reduced wild-type. All variants showed a lowered pKa of Cys32, with the lowest value of 5.9 for the glutaredoxin-like variant. A correlation of redox potential and the Cys32 pKa value could be established on a quantitative level. However, the predicted correlation between the measured delta deltaG(ox/red) values and Cys32 pKa values was only qualitative.

MCSP/CSPG4 is a large transmembrane proteoglycan identified in melanomas as HMW-MAA. In the mouse it is known as neurite growth factor 2 (NG2), a marker of pericyte recruitment. MCSP has been used as a target for clinical imaging of (uveal) melanomas by immunoscintigraphy. MCSP shows uniform and abundant expression in ca. 60-80% of melanoma, and was described in lobular breast carcinoma, glioblastoma, osteo- & chondrosarcoma, and basal cell carcinoma. It is present at high levels on pericytes of tumor neovasculature, but down-regulated as vessels mature. Normal tissue expression is low and it is not detected on PBMCs. We have generated human/Cynomolgus cross-reactive antibodies against a membrane-proximal MCSP epitope by mouse immunization with a linear peptide derived from the membrane proximal D3 domain followed by boosting with melanoma cells. The mouse antibody LC007 was selected for humanization due to its potent induction of ADCC as a chimeric antibody, compared to antibodies to membrane distal epitopes of MCSP. LC007 as chimeric IgG1 and its humanized IgG1 derivative M4-3-ML2 are characterized by the following properties: i) Specific binding to the native epitope on MCSP+ melanoma cells, but no induction of internalization; ii) Specific IHC staining of MCSP+ cells in FFPET samples; iii) ca 10 nM monovalent affinity for hMCSP D3 domain. Moreover, glycoengineering of LC007 and M4-3-ML2 antibodies using GlycoMab technology resulted in increased binding affinity for hFcgRIIIa and enhanced ADCC potency and absolute killing of melanoma cell lines. As expected, neither up to 10 ug/mL wildtype, nor glycoengineered M4-3-ML2 induced relevant cytokine (IL-6, TNF-α, IFN-γ) release in human whole blood supporting that MCSP is not expressed there. Subsequently, we studied anti-tumoral efficacy of the chimeric antibody LC007 and the humanized antibody M4-3-ML2 in disseminated models of MV3 and MDA-MB435 melanoma after i.v. injection of tumor cells in hCD16 transgenic Scid mice, which express the functional human high affinity FcgRIIIa receptor on NK cells. Both, glycoengineered LC007 and M4-3-ML2 mediated efficacy in terms of enhanced median and overall survival in both disseminated xenograft models, and were superior to the respective non-glycoengineered antibodies. Taken together, our studies support MCSP/CSPG4 as an attractive target for antibody-based cancer immunotherapy. Further studies investigating the anti-angiogenic effect of MCSP antibodies via their action on pericytes/vascular smooth muscle cells are ongoing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-236. doi:1538-7445.AM2012-LB-236