Two humanized IgG4 antibodies, natalizumab and gemtuzumab, are approved for human use, and several others, like TGN1412, are or have been in clinical development. Although IgG4 antibodies can dynamically exchange half-molecules, Fab-arm exchange with therapeutic antibodies has not been demonstrated in humans. Here, we show that natalizumab exchanges Fab arms with endogenous human IgG4 in natalizumab-treated individuals. Gemtuzumab, in contrast, contains an IgG4 core-hinge mutation that blocks Fab-arm exchange to undetectable levels both in vitro and in a mouse model. The ability of IgG4 therapeutics to recombine with endogenous IgG4 may affect their pharmacokinetics and pharmacodynamics. Although pharmacokinetic modeling lessens concerns about undesired cross-linking under normal conditions, unpredictability remains and mutations that completely prevent Fab-arm exchange in vivo should be considered when designing therapeutic IgG4 antibodies.

Development of human therapeutic Abs has led to reduced immunogenicity and optimal interactions with the human immune system in patients. Humanization had as a consequence that efficacy studies performed in mouse models, which represent a crucial step in preclinical development, are more difficult to interpret because of gaps in our knowledge of the activation of murine effector cells by human IgG (hIgG) remain. We therefore developed full sets of human and mouse isotype variants of human Abs targeting epidermal growth factor receptor and CD20 to explore the crosstalk with mouse FcγRs (mFcγRs) and murine effector cells. Analysis of mFcγR binding demonstrated that hIgG1 and hIgG3 bound to all four mFcγRs, with hIgG3 having the highest affinity. hIgG1 nevertheless was more potent than hIgG3 in inducing Ab-dependent cellular cytotoxicity (ADCC) and Ab-dependent cellular phagocytosis with mouse NK cells, mouse polymorphonuclear leukocytes, and mouse macrophages. hIgG4 bound to all mFcγRs except mFcγRIV and showed comparable interactions with murine effector cells to hIgG3. hIgG4 is thus active in the murine immune system, in contrast with its inert phenotype in the human system. hIgG2 bound to mFcγRIIb and mFcγRIII, and induced potent ADCC with mouse NK cells and mouse polymorphonuclear leukocytes. hIgG2 induced weak ADCC and, remarkably, was unable to induce Ab-dependent cellular phagocytosis with mouse macrophages. Finally, the isotypes were studied in s.c. and i.v. tumor xenograft models, which confirmed hIgG1 to be the most potent human isotype in mouse models. These data enhance our understanding of the crosstalk between hIgGs and murine effector cells, permitting a better interpretation of human Ab efficacy studies in mouse models.

The CD38 molecule, with its high expression on Multiple Myeloma (MM), is considered a suitable target for antibody therapy of MM. We developed daratumumab (DARA), a human CD38 monoclonal antibody (mAb) with direct and Fc-mediated cell killing activity. DARA induces killing of tumor cells, mainly via complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC) (de Weers M. J Immunol 2011), and antibody-dependent cellular phagocytosis (ADCP) by macrophages (both murine and human). In addition, DARA induces apoptosis upon secondary cross-linking and modulates CD38 enzymatic function. DARA is currently in phase I, II and III clinical evaluation in patients with MM. Besides DARA, several other anti-CD38 mAb are in development; SAR650894 (SAR; clone 38SB19; Sanofi-Aventis) for MM and other CD38+ hematological malignancies, MOR03087 (MOR; Morphosys) for relapsed/refractory MM and Ab79 (Millenium/Takeda) which is in preclinical development. Similar mechanisms of action (MoA) are described for these mAb; nevertheless direct comparison studies would be critical for differentiation among these antibodies. . In this study, the efficacy of these anti-CD38 mAb was directly compared to DARA with respect to binding, apoptosis, CD38 ectoenzyme activity, and the induction of ADCC, ADCP and CDC. Surrogate antibodies of MOR, SAR and Ab79 were generated on the basis of protein sequences, as published in their corresponding patents families, and were attached to the backbone of DARA. Binding to CD38 expressing Daudi tumor cells was assessed by flow cytomery. All CD38 antibodies showed similar EC50 (~0.1 µg/mL) and maximal binding, except MOR which showed a lower apparent affinity (~0.3 µg/mL). Previously, CD38 amino acid residues Q272 and S274 were reported as critical for DARA binding. ELISA analyses using CD38 point mutants revealed MOR, SAR and Ab79 not to be affected by mutation of these residues. All CD38 mAb were equally potent in inducing ADCC of Daudi cells (40-60% lysis, 0.02 µg/mL), in classic Cr51-release ADCC assay using human PBMC effector cells (E:T ratio 100:1). Important differences were observed with respect to induction of CDC. SAR was unable to induce CDC in Daudi cells at concentrations up to 30 µg/mL, while DARA induced more than 80% lysis at concentrations above 1 µg/mL. Ab79 and MOR induced CDC, yet maximum lysis was 50% and 20%, respectively. Evaluation of Annexin V/propidium iodide (AnnV/PI) staining and activation of caspase-3 showed that only SAR induced AnnV/PI+ in Ramos cells (~40%) after 48 h exposure without Fc crosslinking, but did not activate caspase-3. In the presence of Fc crosslinking antibodies, all anti-CD38 mAb induced AnnV/PI+, caspase-3 mediated apoptosis. In enzyme activity assays using purified CD38 protein, SAR inhibited generation of cGDPR (indicative of the combined CD38 cyclase activity generating fluorescent cGDPR and hydrolase activity converting cGDPR into GDPR)more effectively than DARA (~70% vs. ~20% inhibition at 30 µg/mL). Ab79 had a modest effect on CD38 enzyme activity (~10% inhibition). MOR did not affect CD38 enzyme activity at all. The capacity to induce ADCP was only tested for DARA, MOR and Ab79 using mouse macrophages (mφ) as effector cells and Daudi target cells. mφ, isolated and matured from bone marrow cells, and calcein-AM labelled target cells (E:T ratio 1:1) were cultured in the presence of 0.0006-5 µg/mL antibody for 4 h. Non-phagocytosed target cells and mφ were collected and ADCP was evaluated by flow cytometry. All CD38 mAb induced mφ-mediated phagocytosis, as observed by a concentration dependent increase in the number of double positive mφ and killing of target cells. Ab79 was as effective as DARA (EC50 ~0.01 µg/mL) in ADCP induction, whereas MOR was less effective (EC50 0.04 µg/mL). In summary, DARA and surrogate mAb of MOR, SAR and Ab79 showed similar binding to cells and induced similar amounts of ADCC. Differences between these mAb involved the ability to directly induce apoptosis, to inhibit the enzymatic activity of CD38 and to induce ADCP. The most striking difference was observed for the ability to induce CDC, the MoA which is currently believed the most important mechanism of MM cell killing in the clinic. DARA efficiently induced high levels of CDC at low concentrations, whereas the other CD38 mAb were unable or less capable to induce CDC. Disclosures Lammerts van Bueren: Genmab: Employment, warrents Other. Jakobs:Genmab: Employment, warrents Other. Kaldenhoven:Genmab: Employment, warrents Other. Roza:Genmab: Employment, warrents Other. Hiddingh:Genmab: Employment. Meesters:Genmab: Employment, warrents Other. Voorhorst:Genmab: Employment, warrents Other. Gresnigt:Genmab: Employment, warrents Other. Wiegman:Genmab: Employment, warrents Other. Ortiz Buijsse:Genmab: Employment, warrents Other. Andringa:Genmab: Employment, warrents Other. Overdijk:Genmab: Employment, warrents Other. Doshi:Janssen R&D: Employment. Sasser:Janssen R&D: Employment. de Weers:Genmab: Employment, warrents Other. Parren:Genmab: Employment, inventor on patents regarding daratumumab Patents & Royalties, stock and warrents Other.

Higher order DR5 clustering can induce tumor cell death, however therapeutic compounds targeting DR5 have achieved limited clinical efficacy. We describe HexaBody-DR5/DR5, an equimolar mixture of two DR5-specific IgG1 antibodies with an Fc-domain mutation that augments antibody hexamerization after cell surface target binding. The two antibodies do not compete for binding to DR5 as demonstrated using binding competition studies, and binding to distinct epitopes in the DR5 extracellular domain was confirmed by crystallography. The unique combination of dual epitope targeting and increased IgG hexamerization resulted in potent DR5 agonist activity by inducing efficient DR5 outside-in signaling and caspase-mediated cell death. Preclinical studies in vitro and in vivo demonstrated that maximal DR5 agonist activity could be achieved independent of Fcγ receptor-mediated antibody crosslinking. Most optimal agonism was observed in the presence of complement complex C1, although without inducing complement-dependent cytotoxicity. It is hypothesized that C1 may stabilize IgG hexamers that are formed after binding of HexaBody-DR5/DR5 to DR5 on the plasma membrane, thereby strengthening DR5 clustering and subsequent outside-in signaling. We observed potent antitumor activity in vitro and in vivo in large panels of patient-derived xenograft models representing various solid cancers. The results of our preclinical studies provided the basis for an ongoing clinical trial exploring the activity of HexaBody-DR5/DR5 (GEN1029) in patients with malignant solid tumors.

Hyperclustering of Death Receptor 5 (DR5) after binding of its ligand TRAIL induces apoptosis. Targeting DR5 with agonistic antibodies has been evaluated for the treatment of cancer, however clinical efficacy of conventional DR5-targeting monoclonal antibodies (mAbs) has been disappointing. We applied the HexaBody® technology to improve antibody-mediated DR5 clustering on cancer cells. This technology is based on the natural concept that, upon binding to antigens on a cell surface, immunoglobulin G (IgG) molecules can organize into ordered hexamers through intermolecular Fc-Fc interactions. HexaBody molecules are IgG1 molecules with a single point mutation in the Fc domain that enhances these Fc-Fc interactions upon binding to membrane-bound targets, while retaining solution-monomericity. HexaBody-DR5/DR5 (Hx-DR5-01/05) is a 1:1 mixture of two humanized non-competing DR5-specific mAbs, each carrying an E430G hexamerization-enhancing mutation. We previously demonstrated that both dual epitope targeting and enhanced hexamerization through Fc-Fc interactions are required for DR5 agonist activity of Hx-DR5-01/05 in vitro. Here, we confirmed that Hx-DR5-01/05 showed superior anti-tumor activity compared to the single HexaBody molecules or a 1:1 mixture of their wild type counterparts in vivo, using a mouse xenograft model. Furthermore, we screened the potency of Hx-DR5-01/05 in vitro in a broad panel of human tumor cells lines using a cell viability assay, and in vivo in xenograft models. As IgG hexamers are known to provide an optimal docking site for complement component C1q, we studied if there was a role for C1q in Hx-DR5-01/05-dependent DR5 agonist activity. Hx-DR5-01/05 induced potent cytotoxicity in 104 tumor cell lines and in more than ten xenograft models representing many solid cancer lineages. For optimal cytotoxicity in vitro, Hx-DR5-01/05 required the presence of serum or purified C1q. In contrast, polyclonal IgG crosslinking, a mimic for FcγR-mediated antibody crosslinking, did not enhance potency. These data were confirmed in vivo. A Hx-DR5-01/05 variant deficient for both C1q and FcγR binding, showed significantly reduced anti-tumor activity in a colon cancer xenograft model, while a Hx-DR5-01/05 variant deficient in FcγR but not C1q binding showed anti-tumor activity comparable to Hx-DR5-01/05. In summary, Hx-DR5-01/05 is a mixture of two DR5-specific HexaBody molecules that shows potent DR5 agonist activity in a multitude of preclinical models through enhanced IgG hexamerization upon binding to two different DR5 epitopes on the cell surface. Cytotoxicity of Hx-DR5-01/05 was most optimal in the presence of C1q and completely independent of FcγR-mediated antibody crosslinking or effector functions in vitro and in vivo. A clinical trial to assess clinical safety of Hx-DR5-01/05 in patients is currently ongoing. Citation Format: Marije B. Overdijk, Kristin Strumane, Antonio Ortiz Buijsse, Claudine Vermot-Desroches, Thessa Kroes, Bart de Jong, Naomi Hoevenaars, Frank J. Beurskens, Rob N. de Jong, Andreas Lingnau, Paul W. Parren, Ulf Forssmann, A Kate Sasser, Janine Schuurman, Esther C. Breij. DR5 agonist activity of HexaBody®-DR5/DR5 (GEN1029) is potentiated by C1q and independent of Fc-gamma receptor binding in preclinical tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2391.

Death receptor 5 (DR5) is a highly interesting tumor target based on the enhanced sensitivity of cancer cells for DR5-dependent apoptosis. In recent years, multiple therapeutic DR5 antibodies have been evaluated in the clinic for which results however have been disappointing. IgG molecules against membrane-bound targets have shown an ability to form ordered hexameric structures upon antigen binding, a process that is dependent on Fc-Fc interactions between IgG molecules. We identified specific mutations in the human IgG1 Fc domain that enhance such antigen-dependent hexamerization while retaining solution-monomericity and developability characteristics of regular IgG1 molecules (HexaBody technology). We hypothesized that antibody-mediated hexamerization, when applied to DR5-specific antibodies, would enhance DR5 signaling and apoptosis, resulting in strongly improved therapeutic potential. The technology was applied to two non-crossblocking DR5-specific IgG1 antibodies, IgG1-DR5-01 and IgG1-DR5-05, by mutating a glutamic acid residue at position 430 in the Fc domain to glycine (the HexaBody mutants were designated Hx-DR5-01 and Hx-DR5-05). Cytotoxicity of the DR5 antibodies was explored in vitro using the CellTiter-Glo luminescent cell viability assay and the Caspase-Glo 3/7 assay in a broad panel of cancer cell lines, and in vivo in xenograft models. Both Hx-DR5-01 and Hx-DR5-05 induced increased cytotoxicity compared to their wild type (WT) IgG1 counterparts. Moreover, the combination of Hx-DR5-01 and Hx-DR5-05 (referred to as Hx-DR5-01/05) was found to be more potent than either Hx-DR5-01 or Hx-DR5-05 alone, or than the combination of the WT antibodies (IC50 in BxPC3 cells 0.5 and 1.5 μg/ml; maximal cytotoxicity 91% and 25% for Hx-DR5-01/05 and WT IgG1-DR5-01/05 respectively). In contrast to wild type agonistic DR5 antibodies, tumor cell killing by Hx-DR5-01/05 was independent of secondary crosslinking. Potent anti-tumor activity was observed in seven xenograft models for multiple indications, with Hx-DR5-01/05 consistently showing significantly better efficacy than the WT DR5 comparator antibody conatumumab. The cytotoxic activity of DR5 antibodies was significantly enhanced by the introduction of a hexamer-enhancing mutation in the IgG1 Fc domain. Maximal killing activity was obtained by combining two non-crossblocking DR5 antibodies carrying this mutation (Hx-DR5-01 and Hx-DR5-05). The strong cytotoxicity of Hx-DR5-01/05 was completely dependent on target binding but, in contrast to WT antibodies, did not require secondary crosslinking. These promising pre-clinical results support the selection of Hx-DR5-01/05 for clinical development for the treatment of cancer. Citation Format: Marije B. Overdijk, Kristin Strumane, Antonio Ortiz Buijsse, Claudine Vermot-Desroches, Andreas Lingnau, Esther C.W. Breij, Janine Schuurman, Paul W.H.I. Parren. Improving therapeutic activity of agonistic DR5 antibodies by inducing target binding-dependent hexamer formation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 592.

No abstract

<p>Supplemental Tables Supplemental Figures Supplemental Methods</p>