HERA-GITRL activates T cells and promotes anti-tumor efficacy independent of FcγR-binding functionality

Background

Glucocorticoid-induced TNFR-related protein (TNFRSF18, GITR, CD357), expressed by T cells, and its ligand (TNFSF18, GITRL), expressed by myeloid populations, provide co-stimulatory signals that boost T cell activity. Due to the important role that GITR plays in regulating immune functions, agonistic stimulation of GITR is a promising therapeutic concept. Multiple strategies to induce GITR signaling have been investigated. The limited clinical efficacy of antibody-based GITR agonists results from structural and functional characteristics of antibodies that are unsuitable for stimulating the well-defined trimeric members of the TNFRSF.

Methods

To overcome limitations of antibody-based TNFRSF agonists, we have developed HERA-GITRL, a fully human hexavalent TNF receptor agonist (HERA) targeting GITR and mimicking the natural signaling concept. HERA-GITRL is composed of a trivalent but single-chain GITRL-receptor-binding-domain (scGITRL-RBD) unit fused to an IgG1 derived silenced Fc-domain serving as dimerization scaffold. A specific mouse surrogate, mmHERA-GITRL, was also generated to examine in vivo activity in respective mouse tumor models.

Results

For functional characterization of HERA-GITRL in vitro, human immune cells were isolated from healthy-donor blood and stimulated with anti-CD3 antibody in the presence of HERA-GITRL. Consistently, HERA-GITRL increased the activity of T cells, including proliferation and differentiation, even in the presence of regulatory T cells.

In line with these findings, mmHERA-GITRL enhanced antigen-specific clonal expansion of both CD4+ (OT-II) and CD8+ (OT-I) T cells in vivo while having no effect on non-specific T cells. In addition, mmHERA-GITRL showed single-agent anti-tumor activity in two subcutaneous syngeneic colon cancer models (CT26wt and MC38-CEA). Importantly, this activity is independent of its FcγR-binding functionality, as both mmHERA-GITRL with a functional Fc- and a silenced Fc-domain showed similar tumor growth inhibition.

Finally, in a direct in vitro comparison to a bivalent clinical benchmark anti-GITR antibody and a trivalent GITRL, only the hexavalent HERA-GITRL showed full biological activity independent of additional crosslinking.

Conclusion

In this manuscript, we describe the development of HERA-GITRL, a true GITR agonist with a clearly defined mechanism of action. By clustering six receptor chains in a spatially well-defined manner, HERA-GITRL induces potent agonistic activity without being dependent on additional FcγR-mediated crosslinking.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0671-4) contains supplementary material, which is available to authorized users.

Abstract 5015: HERA-CD40L a hexavalent CD40 agonist induces T cell mediated anti-tumor immune response and shows superior activity in direct comparison to benchmark agonistic antibodies

CD40 ligand is a member of the TNF superfamily (TNF-SF) and a key regulator of the immune system. Its cognate receptor CD40 is expressed on antigen-presenting cells and on many tumor types, and has emerged as an attractive target for immunological cancer treatment.

Effective signaling for CD40/CD40L depends on the formation of a defined ligand/receptor complex triggered by interaction of a trimeric CD40L with three CD40 receptor chains allowing correct assembly of intracellular signaling complexes and respective signal transduction. Trimerization is a hallmark of the TNF-SF and has pivotal implications for the generation of respective TNFR-SF agonists in particular. However, ignoring the underlying trimeric structural concept bivalent antibodies are still the main agonistic biotherapeutic development candidates to address TNFR-SF members including CD40. Such bivalent antibodies are inherently associated with limited agonistic activity that requires Fc/FcγR interactions or potentially show increased toxicity caused by super-clustering of endogenous ligand receptor pairs.

To overcome the inadequacies of antibodies, we have developed HERA-CD40L composed of three receptor binding domains in a single chain arrangement, linked to an Fc-silenced human IgG1 thereby generating a hexavalent molecule. HERA-CD40L mimics the natural ligand, induces potent agonistic activity and, importantly, does not require FcγR mediated crosslinking. Comparison of HERA-CD40L to anti-CD40 benchmark antibodies (including CP-870,893) revealed superiority for HERA-CD40L in all assays tested. (i) In contrast to antibodies, HERA-CD40L showed strong activation of NFkB signaling upon treatment of B cells. (ii) HERA-CD40L treatment, but not clinical benchmark antibodies, converts immature phagocytic macrophages into mature/professional APCs and promoted differentiation towards the M1 spectrum macrophages. (iii) Furthermore, HERA-CD40L treated PBMCs stimulate potent allogeneic anti-tumor T cell response that was not detectable for CD40-antibodies.

In vivo, a murine surrogate of HERA-CD40L stimulated clonal expansion of OT-I specific murine CD8+ T cells without affecting non-specific immune cells. In the syngeneic CT26wt mouse model mHERA-CD40L treatment converts cold into hot tumors by increasing infiltration of CD8+ and CD4+ T cells. In addition mHERA-CD40L showed single agent anti-tumor activity in the CD40-negative syngeneic MC38-CEA mouse model, suggesting an involvement of the immune system in controlling tumor growth.

In summary HERA-CD40L is a potent agonist able to establish single agent anti-tumor immune responses. Comparison to bivalent benchmark antibodies showed superior biological activity of HERA-CD40L and qualifies this molecule as an ideal candidate for combinatorial cancer treatments.

Citation Format: Christian Gieffers, Jaromir Sykora, Christian Merz, Mauricio Redondo Müller, David M. Richards, Julian Sefrin, Katharina Billian-Frey, Karl Heinonen, Viola Marschall, Matthias Schröder, Harald Fricke, Meinolf Thiemann, Hill Oliver. HERA-CD40L a hexavalent CD40 agonist induces T cell mediated anti-tumor immune response and shows superior activity in direct comparison to benchmark agonistic antibodies [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 5015.

Abstract 4845: HERA-CD27L, a true CD27 agonist, is a hexavalent CD27 ligand that enhances T cell activation and induces potent anti-tumor immunity

Agonistic stimulation of TNFRSF members like CD27 is a promising strategy to boost anti-tumor responses. Although antibodies are effective inhibitors of signaling, they have shown minimal agonistic activity due to their limited binding domains, flexibility and the toxicity mediated by Fc/FcγR interactions. TNFRSF signaling is a structurally well-defined event that takes place during cell contact. The trimeric-trivalent TNFSF-receptor binding domain (TNFSF-RBD) on the conducting cell and the resulting multi-trimer-based receptor clustering on the receiving cell are essential for signaling. In contrast to antibodies, HERA-CD27L mimics the natural ligand and induces potent activity. In order to understand the activity of HERA-CD27L, human T cells were stimulated in the presence of HERA-CD27L, the trimeric CD27L or a clinical benchmark anti-CD27 antibody. In all assays, treatment with the hexavalent HERA-CD27L significantly boosted T cell activation, proliferation and differentiation. Furthermore, the hexavalent molecule was always superior to the trimeric CD27L and bivalent antibody. In fact, treatment with the anti-CD27 antibody resulted in significantly weaker proliferation compared to anti-CD3 antibody alone. To understand early events, we tested CD27 signaling using a reporter cell assay. Treatment with HERA-CD27L and CD27L resulted in high and intermediate, respectively, reporter activity. In contrast, the anti-CD27 antibody failed to show any signaling activity across a wide range of concentrations. Since most T cells express CD27, there is potential for non-specific T cell activation. This was examined by comparing OVA-specific and non-specific T cells in the same environment using the CD8+ “OT-I” T cell adoptive transfer mouse model. Following a single dose of HERA-CD27L, serial blood samples showed a significant and HERA-CD27L dose-dependent clonal expansion of OT-I T cells. OT-I T cells expressed high levels of activation markers, while the endogenous T cells failed to show any response. The potent single-agent anti-tumor efficacy of the hexavalent HERA-CD27L was demonstrated in two different mouse models. With CT26wt, HERA-CD27L also showed superior activity compared to anti-PD-1 antibody. Furthermore, combination of HERA-CD27L and anti-PD-1 antibody showed additive effects. Finally, early treatment with HERA-CD27L significantly increased overall survival, from 19 to 41 days, and tumor-free animals still alive at the end of the study were protected from tumor re-challenge. Various strategies have been proposed for targeting CD27 for cancer therapy. As we have shown here, the hexavalent HERA-CD27L has superior activity compared to bivalent antibodies. Altogether, HERA-CD27L shows single-agent anti-tumor efficacy, is well tolerated by multiple relevant species and the lead candidate is currently ready for GMP cell line development.

Citation Format: Julian P. Sefrin, David M. Richards, Katharina Billian-Frey, Karl Heinonen, Viola Marschall, Christian Merz, Mauricio Redondo Müller, Matthias Schröder, Jaromir Sykora, Meinolf Thiemann, Harald Fricke, Christian Gieffers, Oliver Hill. HERA-CD27L, a true CD27 agonist, is a hexavalent CD27 ligand that enhances T cell activation and induces potent anti-tumor immunity [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 4845.

A Single-Chain-Based Hexavalent CD27 Agonist Enhances T Cell Activation and Induces Anti-Tumor Immunity

Tumor necrosis factor receptor superfamily member 7 (TNFRSF7, CD27), expressed primarily by T cells, and its ligand CD27L (TNFSF7, CD70) provide co-stimulatory signals that boost T cell activation, differentiation, and survival. Agonistic stimulation of CD27 is therefore a promising therapeutic concept in immuno-oncology intended to boost and sustain T cell driven anti-tumor responses. Endogenous TNFSF/TNFRSF-based signal transmission is a structurally well-defined event that takes place during cell-to-cell-based contacts. It is well-established that the trimeric-trivalent TNFSF-receptor binding domain (TNFSF-RBD) exposed by the conducting cell and the resulting multi-trimer-based receptor clustering on the receiving cell are essential for agonistic signaling. Therefore, we have developed HERA-CD27L, a novel hexavalent TNF receptor agonist (HERA) targeting CD27 and mimicking the natural signaling concept. HERA-CD27L is composed of a trivalent but single-chain CD27L-receptor-binding-domain (scCD27L-RBD) fused to an IgG1 derived silenced Fc-domain serving as dimerization scaffold. The hexavalent agonist significantly boosted antigen-specific T cell responses while having no effect on non-specific T cells and was superior over stabilized recombinant trivalent CD27L. In addition, HERA-CD27L demonstrated potent single-agent anti-tumor efficacy in two different syngeneic tumor models, MC38-CEA and CT26wt. Furthermore, the combination of HERA-CD27L and an anti-PD-1 antibody showed additive anti-tumor effects highlighting the importance of both T cell activation and checkpoint inhibition in anti-tumor immunity. In this manuscript, we describe the development of HERA-CD27L, a true CD27 agonist with a clearly defined forward-signaling mechanism of action.

Abstract 1760: The hexavalent CD40 agonist HERA-CD40L augments multi-level crosstalk between T cells and antigen-presenting cells

Introduction: HERA-CD40L is a novel hexavalent CD40 agonist engineered with the HERA-Technology developed by Apogenix. We have previously shown that the natural binding mode via the receptor/ligand binding domains and the high clustering capacity for the cognate receptor clearly distinguish HERA-CD40L from other, e.g. antibody-based, CD40-targeting compounds. Here, we report on the effects of HERA-CD40L on crosstalk between T cells and antigen presenting cells (APC) and the functional consequences in vitro. Materials & Methods: Biological activity of CD40 agonists was analyzed using co-cultures of primary T cells with B cells or monocytes/macrophages. All primary cells were isolated by negative selection using magnetic sorting from healthy donor buffy coats. Expression of CD markers upon CD40 ligation on B cells and monocytes was analyzed by flow cytometry (FC). Monitoring of T cell-induced killing of tumor cells primed in direct co-cultures with APC was done on a real-time cell analysis system (xCELLigence). For analysis of phagocytosis, we developed an FC-based assay employing primary monocytes/macrophages and Jurkat A3 cells. Results: Treatment of primary B cells and monocytes with HERA-CD40L induced expression of co-stimulatory molecules, like CD86, and promotes M1 maturation of naïve (M0) monocytes. In vitro, treatment of alternatively activated M2 macrophages with HERA-CD40L induced an M2 to M1 phenotype switch (re-programming) which concurs with CD16 downregulation and a dose-dependent decrease of phagocytic activity of re-programmed macrophages compared to M0 or M2 macrophages. Primary B cells and M1 macrophages enhanced the proliferation and cytotoxic activity of naïve T cells in direct co-cultures in the presence of HERA-CD40L. The activating effect on T cells required direct cell-cell contact with APC and was not observed in indirect co-cultures. Functionally, neutralization of either MHC-I or CD80/CD86 in direct co-cultures inhibited full activation of the T cells in vitro as shown by kill assays with various tumor cell lines. Conclusion: The hexavalent CD40 agonist HERA-CD40L produced by the Apogenix HERA-Technology is a potent immune-regulator acting on B cells and myeloid cells. HERA-CD40L promotes activation of B cells, maturation of APC and induces an M2 to M1 phenotype switch which inhibits tolerance-inducing phagocytic activity of the repolarized macrophages in vitro. In response to CD40 ligation on APC, an efficient anti-tumor response is conferred to primary T cells through cell-cell interactions via MHC-I and CD80/CD86.

Citation Format: Christian Merz, Jaromir Sykora, Viola Marschall, David M. Richards, Meinolf Thiemann, Harald Fricke, Oliver Hill, Christian Gieffers. The hexavalent CD40 agonist HERA-CD40L augments multi-level crosstalk between T cells and antigen-presenting cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1760.

Abstract 3754: The novel hexavalent human CD137/4-1BB agonist HERA-CD137L promotes anti-cancer immunity by activating CD8 T cells while regulatory T cells are not affected

CD137/4-1BB is an inducible costimulatory receptor mainly expressed on immune cells following activation. Binding of the cognate ligand CD137L/4-1BBL leads to receptor trimerization and activation of signaling cascades involved in expansion and survival of T cells and myeloid cells as well as memory formation and protection against autoimmunity. Apogenix´ HERA technology is based on trivalent single-chain molecular mimics of the TNF-SF receptor binding domains fused to a silenced human IgG1-Fc-domain which serves exclusively as a dimerization scaffold. This results in hexavalent agonists replicating the natural receptor binding mode. Due to their inherent high receptor clustering capacity, HERA compounds are true agonists and their biological activity is, in contrast to bivalent anti-TNFR-SF antibodies, independent of FcR-mediated crosslinking events. HERA-CD137L was produced in CHO-S cells and purified resulting in highly pure non-aggregating protein lots. PK studies in mice demonstrated a terminal half-life of 75 hours indicating excellent in vivo stability. To study the effects on immune cells in vitro, T cells were isolated from healthy-donor buffy coats and stimulated with anti-CD3 antibody alone or in combination with HERA-CD137L. Using multicolor flow cytometry, we confirmed that expression of CD137 increased on CD8+ T cells following stimulation with anti-CD3 antibody. In accord with upregulation of the activation markers CD25 and CD69 and the memory marker CD45RO, treatment with HERA-CD137L enhanced proliferation of both CD4+ and CD8+ T cells, as determined by CFSE analysis. Intracellular accumulation of IFN-γ, TNF-α, Granzyme B and Perforin upon CD137 ligation was observed in CD8+ but not CD4+ T cells. HERA-CD137L treatment of THP-1 monocytes co-cultured with primary T cells also increased their cytotoxic activity against multiple tumor cell lines, including colorectal and mammary, as shown in a real-time live cell analysis (RTCA) assay. Primary human monocytes express low levels of CD137 and differentiation to macrophages in vitro did not increase expression. However, pro-inflammatory cytokines such as TNF-α and the chemokine CCL4 were secreted after stimulation with HERA-CD137L. RTCA assays further demonstrated enhanced antigen-specific killing of MDA-MB231 tumor cells by HERA-CD137L treated T cells. HERA-CD137L conveys its activity through effector T cell proliferation while regulatory T (Treg) cell proliferation or production of anti-inflammatory cytokines are not altered in Treg cell cultures. In contrast, HERA-CD137L prevented Treg-mediated suppression of effector T cells. Based on the in vitro data presented, HERA-CD137L is a promising candidate to promote anti-tumor immune responses either as single agent or in combination with other IO-compounds.

Citation Format: Meinolf Thiemann, Jaromir Sykora, David M. Richards, Christian Merz, Viola Marschall, Mauricio Redondo Mueller, Julian P. Sefrin, Karl Heinonen, Harald Fricke, Christian Gieffers, Oliver Hill. The novel hexavalent human CD137/4-1BB agonist HERA-CD137L promotes anti-cancer immunity by activating CD8 T cells while regulatory T cells are not affected [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3754.

Abstract 630: Novel hexavalent HVEM agonist HERA-LIGHT promotes T cell activation and expansion

The tumor necrosis factor superfamily (TNFSF) member LIGHT (TNFSF14) plays an important role in regulating the activity of immune cells, especially T cells. Several studies have shown that engagement of HVEM (herpesvirus entry mediator), one of the known receptors of LIGHT, can deliver a co-stimulatory signal to support T cell activation and expansion and promote tumor clearance. The HERA technology platform developed by Apogenix generates fully human hexavalent TNFSF fusion proteins that mimic the natural receptor binding mode in order to co-stimulate T cells. HERA ligands are pure agonists whose signaling capacity does not rely on secondary Fcγ-receptor crosslinking. Here we report the in vitro and in vivo properties of a novel HERA-LIGHT construct. Similar to all HERA fusion proteins, HERA-LIGHT has been engineered as a perfect molecular mimic of the natural ligand with high clustering capacity for the cognate receptor. The core unit consists of a single chain polypeptide comprising the three minimal LIGHT-subsequences necessary for folding into a functional trivalent receptor binding domain (RBD). By fusing a silenced IgG1 Fc-domain as a dimerization scaffold to the C-terminus of the RBD we generated HERA-LIGHT, a hexavalent fusion protein. HERA-LIGHT was expressed in CHO suspension cells followed by a lab-scale purification process including AFC- and SEC-based polishing, resulting in homogenous, aggregate-free protein lots. HERA-LIGHT was proven to bind both the human and murine HVEM receptor, as determined by ELISA. Qualitative analytics revealed excellent stability following heat- and pH-stress as well as freeze-thaw cycles. Analyzing serum samples from a PK study in CD1-mice, the terminal half-life of the compound was 36.5 hours. This short half-life, relative to antibodies, allows for fast-in/fast-out dynamics essential for improving combination therapy and reducing serious side effects associated with immune system overstimulation. In order to test biological activity, T cells were isolated by magnetic sorting from human PBMCs and treated with HERA-LIGHT in vitro. Flow cytometric analysis revealed that HERA-LIGHT enhanced activation and proliferation of naïve effector T cells (Teff) following stimulation with anti-CD3 antibody, as determined by CFSE dilution. Importantly, co-stimulation with HERA-LIGHT prevented regulatory T cell (Treg)-mediated suppression of Teff proliferation. In vivo, treatment with a murine surrogate of HERA-LIGHT resulted in significant tumor growth inhibition in a pilot study using the syngeneic CT-26 colorectal cancer model.In summary, the unique hexavalent design of HERA-LIGHT mediates efficient co-stimulation of Teff even in the presence of Treg cells and independent of secondary crosslinking events. Being true agonists, all HERA molecules are unique from current antibody-based concepts rendering them attractive candidates for cancer immunotherapy.

Citation Format: Julian P. Sefrin, David M. Richards, Jaromir Sykora, Meinolf Thiemann, Christian Merz, Viola Marschall, Mauricio Redondo Müller, Karl Heinonen, Harald Fricke, Christian Gieffers, Oliver Hill. Novel hexavalent HVEM agonist HERA-LIGHT promotes T cell activation and expansion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 630.

Abstract 4963: Novel hexavalent GITR agonists stimulate T cells and enhance memory formation

Introduction: The co-stimulatory receptor GITR plays an important role in initiating the immune response in the lymph nodes and in maintaining the immune response in the tumor tissue. Binding of GITR to its natural ligand directly leads to increased anti-tumor T cell activation and their survival. It also reduces the suppressive abilities of Treg cells, further increasing the anti-tumor immune response. The HERA-technology developed by Apogenix targets the TNF-receptor superfamily and generates fully human hexavalent fusion proteins with high clustering capacity for the cognate receptor. Hexavalent HERA-ligands are pure agonists whose signaling capacity is independent of secondary Fcγ-receptor crosslinking. Here we report in vitro and in vivo properties of novel hexavalent HERA-GITRL constructs.

Experimental procedures: For the assessment of in vivo stability, serum samples from a PK study with three HERA-GITRL constructs in CD1-mice were analyzed with respect to their drug levels employing a specific ELISA assay. For functional characterization of HERA-GITRL in vitro, immune cells were isolated from healthy-donor blood samples and profiled by multicolor flow cytometry (MC-FC). Subsequently, immune cells were cultured in growth media containing different HERA-GITRL constructs and anti-CD3. Changes in activation and memory markers on T cells (e.g. CD25, CD69, CD45RA, CD45RO), their proliferation rate (CFSE assay) and the intracellular staining of cytokines (e.g. TNF-α and IFN-γ) was assessed by MC-FC.

Results: Minor modifications led to three HERA-GITRL drug candidates with unique pharmacokinetic properties / in vivo stability as explored in mice. Terminal half-life was between 61.7 and 200.6 hours. Stimulation of pan T cells as well as naïve CD4+ T-lymphocytes by anti-CD3 was further augmented by HERA-GITRL as demonstrated by CD69 and CD25 expression. This effect was accompanied by an increased proliferation and an increased memory formation. Furthermore, we observed an increased level of intracellular TNF-α and IFN-γ in naïve CD4+ T-lymphocytes incubated with anti-CD3 that could be further raised by the addition of HERA-GITRL.

Conclusion: HERA-GITRL demonstrate excellent in vivo stability. Their ability to enhance proliferation and activation of naïve CD4+ T cells and to induce memory formation render them as attractive candidates for immunotherapeutic treatments of cancer.

Citation Format: Meinolf Thiemann, Christian Gieffers, David M. Richards, Christian Merz, Karl Heinonen, Mauricio Redondo Mueller, Viola Marschall, Jaromir Sykora, Harald Fricke, Oliver Hill. Novel hexavalent GITR agonists stimulate T cells and enhance memory formation [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 4963. doi:10.1158/1538-7445.AM2017-4963

Abstract 1688: HERA-CD40L: A novel hexavalent CD40 agonist with superior biological activity

Introduction: Targeted therapeutics for cancer treatment are mostly developed as antibodies, however, the natural signaling complexes of the members of the TNF superfamily and their receptors consist of clusters of trimers. Consequently, most of these bivalent agonistic antibodies depend on Fc receptor mediated crosslinking for biological activity. The HERA-Technology developed by Apogenix generates hexavalent fusion proteins targeting the TNF-receptor superfamily with high clustering capacity for the cognate receptor, which overcomes this disadvantage of antibody-based drugs. Here we compared the efficacy of different CD40 agonist formats, including the novel HERA-CD40L and the functional consequences of differential receptor clustering.

Materials & Methods: Biological activity of CD40 agonists was compared using an engineered reporter cell line and by flow cytometric analysis of CD40-induced IκBα degradation in Ramos B cells. T lymphocytes and monocytes were isolated from buffy coats and expression of CD markers upon CD40 ligation was analysed by multicolor flow cytometry (MC-FC). Secretion of cytokines in response to CD40 ligation was determined by ELISA. Monitoring of T cell-induced killing of tumor cells in direct co-cultures employed a real-time cell analysis system (xCELLigence).

Results: Direct comparison of bivalent CD40 antibodies with trivalent CD40L and the hexavalent HERA-CD40L in two independent bioactivity assay formats demonstrated that only the hexavalent agonist was fully active without additional crosslinking. In contrast to HERA-CD40L, neither the bivalent agonistic CD40 antibody nor the trivalent CD40L were able to upregulate expression of activation markers on B cells or to induce secretion of proinflammatory cytokines such as IL-12 and TNFα by PBMCs. In vitro generated M2-macrophages acquired an M1 phenotype and enhanced proliferation of naïve CD4+ T cells in direct co-culture. Similarly, direct co-culture of CD4+ T cells with Ramos B cells in the presence of HERA-CD40L induced cytotoxic activity of CD4+ cells against tumor cells. The activating effect was dependent on cell-cell contacts and was not observed in indirect co-cultures. Importantly, only the hexavalent HERA-CD40L showed full biological activity without additional crosslinking.

Conclusion: The hexavalent CD40 agonist HERA-CD40L produced by Apogenix HERA-Technology platform triggers CD40 signaling on B cells and cells of the monocytic lineage, leads to direct cytolytic activation and proliferation of CD4+ T cells and shifts the M1/M2 balance towards proinflammatory conditions. Unlike bivalent CD40 antibodies or trivalent CD40L_ based agonists, the hexavalent HERA-CD40L forms highly clustered signaling complexes and thus exhibits superior biological activity over other agonistic formats without the need for Fc receptor mediated crosslinking.

Citation Format: Christian Merz, Jaromir Sykora, Meinolf Thiemann, Viola Marschall, Karl H. Heinonen, Harald Fricke, Christian Gieffers, Oliver Hill. HERA-CD40L: A novel hexavalent CD40 agonist with superior biological activity [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 1688. doi:10.1158/1538-7445.AM2017-1688

Abstract 4690: Hexavalent CD27 agonists show single agent anti-tumor activity and enhanced memory formation in mouse syngeneic tumor models

Tumor necrosis factor receptor superfamily (TNFRSF) proteins are widely expressed by immune and tumor cells highlighting their importance in multiple locations and phases of the anti-tumor immune response. Apogenix has developed a proprietary technology platform for the construction of novel hexavalent TNFRSF agonists (HERA) for the treatment of cancer. HERA fusion proteins comprise a perfect molecular mimic of the TNFSF cytokine structure and are based on dimerization of trivalent single-chain TNFSF receptor-binding domains (scTNFSF-RBD) via a Fc-γ receptor (FcγR) binding deficient immunoglobulin Fc domain. As a result of this molecular design, HERA proteins are capable of clustering six receptors in a spatially well-defined manner. Signaling following treatment with the Apogenix HERA “scTNFSF-RBD-Fc fusion proteins” is entirely independent of secondary crosslinking through FcγRs that is required for many agonistic anti-TNFRSF antibodies. The HERA engineering concept has been successfully translated to TRAIL, GITRL, CD40L, LIGHT and CD27L resulting in agonists that are currently in development. CD27L is a potent co-stimulatory molecule that drives T cell activation and survival through interaction with its receptor (CD27). HERA-CD27L is expressed in CHO suspension cells followed by a lab-scale purification process that results in homogenous aggregate-free protein lots. The purified protein binds its respective target-receptor with high affinity. In vitro, HERA-CD27L was able to bind CD27 expressed on primary human CD4+ and CD8+ T cells. Binding significantly increased T cell expansion following αCD3/αCD28 stimulation and leads to increased expression of OX40 on CD4+ T cells and 4-1BB on CD8+ T cells, respectively. In vivo, a single dose of 10mg/kg HERA-CD27L increases clonal expansion of antigen-specific CD8+ T cells upon immunization with Ovalbumin (Ova) in the mouse OT-1 model with a kinetics leading to peak levels of >25% Ova-specific CD8+ T cells at day 6 after treatment. Anti-tumor efficacy of HERA-CD27 was evaluated in MC38-CEA and CT26 colorectal syngeneic murine tumor models. In both models treatment with HERA-CD27L resulted in a dose dependent inhibition of tumor growth. CT26 tumor bearing mice treated with 1mg/kg HERA-CD27L, twice weekly showed an 85% tumor-growth inhibition (TGI) compared to the control group. A significant TGI of 48% could be observed in the MC38-CEA model upon treatment with 10mg/kg, twice weekly. Analysis of peripheral lymphoid tissues in the MC38-CEA bearing mice could furthermore show that HERA-CD27L treatment is accompanied with enhanced memory formation in both CD4+ & CD8+ T cells. In summary, the data on the hexavalent HERA-CD27L indicate a potent immune cell driven anti tumor efficacy. Therefore, HERA-CD27 agonists could be applied for the treatment of cancer as a single agent or in combination with check-point Inhibitors.

Citation Format: Christian Gieffers, David Richards, Jaromir Sykora, Mauricio Redondo-Müller, Meinolf Thiemann, Christian Merz, Karl Heinonen Heinonen, Viola Marschall, Harald Fricke, Oliver Hill. Hexavalent CD27 agonists show single agent anti-tumor activity and enhanced memory formation in mouse syngeneic tumor models [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 4690. doi:10.1158/1538-7445.AM2017-4690

Abstract A83: Hexavalent agonists targeting co-stimulatory receptors of the tumor necrosis factor superfamily

Tumor necrosis factor receptor superfamily (TNFRSF) proteins are widely expressed by immune and tumor cells highlighting their importance in multiple locations and phases of the anti-tumor immune response. Whereas agonistic stimulation of TRAIL-Receptor-1 or -2 can directly induce apoptosis in tumor cells, signaling through many TNFRSF members, such as CD40, CD27, OX40, HVEM, GITR and 4-1BB, results in co-stimulation of immune cells. Therefore, agonistic stimulation of certain members of the TNFRSF is considered to have a positive impact on immune-based therapeutic concepts in clinical oncology. Apogenix has developed a proprietary technology platform for the construction of novel hexavalent TNFRSF agonists (HERA) for the treatment of cancer. HERA fusion proteins are based on a perfect molecular mimic of the TNFSF cytokine structure. The HERA core unit consists of one single polypeptide chain comprising the three receptor-binding domain-forming subsequences (TNFSF-protomers). These single-chain TNFSF receptor-binding domains (scTNFSF-RBD) preserve the structural organization of the trimeric natural TNFSF cytokine and can be utilized to engineer fully human fusion-proteins in a modular manner. Fusing an IgG1 Fc-domain as a dimerization scaffold to the C-terminus of a scTNFSF-RBD creates a hexavalent agonist from two trivalent scTNFSF-RBDs. As a result of this molecular design, each molecule is capable of clustering six receptors in a spatially well-defined manner in close proximity to each other. Therefore, signaling following treatment with the Apogenix HERA scTNFSF-RBD-Fc fusion proteins in vivo is independent of secondary clustering through Fc-γ receptors that is required for many agonistic anti-TNFRSF antibodies (e.g., anti-TRAIL-R2 or anti-CD40). The described HERA engineering concept has been successfully translated to TRAIL, CD40L, LIGHT and CD27L resulting in hexavalent agonists suitable for further development. CD27-Ligand is a potent co-stimulatory molecule that drives T-cell activation and survival through interaction with its receptor (CD27). Here we show in vitro and in vivo data for APG1293 (scCD27L-RBD-Fc), a hexavalent CD27 agonist. APG1293 was expressed in CHO suspension cells followed by a lab-scale purification process including affinity chromatography and SEC-based polishing, resulting in homogenous aggregate-free protein lots. The purified protein binds its respective target-receptor with high affinity. In vivo stability/PK studies have been performed in addition to in vitro experiments with primary human and mouse lymphoid and myeloid cell populations. Specifically, APG1293 was able to bind CD27 expressed on primary human CD4+ and CD8+ T cells and importantly, binding significantly increased T-cell expansion following activation. In vivo the efficacy of APG1293 was evaluated in the colorectal syngeneic murine tumor models MC38-CEA and CT26. In both models APG1293 treatment resulted in a dose dependent tumor growth inhibition. In summary, the data on the hexavalent APG1293 indicate a potent immune cell driven anti tumor efficacy. Therefore, APG1293 could be applied as a single agent or in combination with check-point inhibitors.

Citation Format: Christian Gieffers, Christian Merz, David Richards, Mauricio Redondo, Viola Marschall, Jaromir Sykora, Meinolf Thiemann, Harald Fricke, Oliver Hill. Hexavalent agonists targeting co-stimulatory receptors of the tumor necrosis factor superfamily. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr A83.

Smac Mimetic-Induced Upregulation of CCL2/MCP-1 Triggers Migration and Invasion of Glioblastoma Cells and Influences the Tumor Microenvironment in a Paracrine Manner

Second mitochondria-derived activator of caspase (Smac) mimetics are considered as promising anticancer therapeutics that are currently under investigation in early clinical trials. They induce apoptosis by antagonizing inhibitor of apoptosis proteins, which are frequently overexpressed in cancer. We previously reported that Smac mimetics, such as BV6, additionally exert non-apoptotic functions in glioblastoma (GBM) cells by stimulating migration and invasion in a nuclear factor kappa B (NF-κB)-dependent manner. Because NF-κB target genes mediating these effects are largely unknown, we performed whole-genome expression analyses. Here, we identify chemokine (C-C motif) ligand 2 (CCL2) as the top-listed NF-κB-regulated gene being upregulated upon BV6 treatment in GBM cells. BV6-induced upregulation and secretion of CCL2 are required for migration and invasion of GBM cells because knockdown of CCL2 in GBM cells abolishes these effects. Co-culture experiments of GBM cells with non-malignant astroglial cells reveal that BV6-stimulated secretion of CCL2 by GBM cells into the supernatant triggers migration of astroglial cells toward GBM cells because CCL2 knockdown in BV6-treated GBM cells impedes BV6-stimulated migration of astroglial cells. In conclusion, we identify CCL2 as a BV6-induced NF-κB target gene that triggers migration and invasion of GBM cells and exerts paracrine effects on the GBM's microenvironment by stimulating migration of astroglial cells. These findings provide novel insights into the biological functions of Smac mimetics with important implications for the development of Smac mimetics as cancer therapeutics.

Expression, assembly and function of novel C-terminal truncated variants of the mouse P2X7 receptor: re-evaluation of P2X7 knockouts

BACKGROUND AND PURPOSE

Splice variants of P2X7 receptor transcripts contribute to the diversity of receptor-mediated responses. Here, we investigated expression and function of C-terminal truncated (ΔC) variants of the mP2X7 receptor, which are predicted to escape inactivation in one strain of P2X7(-/-) mice (Pfizer KO).

EXPERIMENTAL APPROACH

Expression in wild-type (WT) and Pfizer KO tissue was investigated by reverse transcription (RT)-PCR and Western blot analysis. ΔC variants were also cloned and expressed in HEK293 cells to investigate their assembly, trafficking and function.

KEY RESULTS

RT-PCR indicates expression of a ΔC splice variant in brain, salivary gland (SG) and spleen from WT and Pfizer KO mice. An additional ΔC hybrid transcript, containing sequences of P2X7 upstream of exon 12, part of exon 13 followed in-frame by the sequence of the vector used to disrupt the P2X7 gene, was also identified in the KO mice. By blue native (BN) PAGE analysis and the use of cross linking reagents followed by SDS-PAGE, P2X7 trimers, dimers and monomers were detected in the spleen and SG of Pfizer KO mice. The molecular mass was reduced compared with P2X7 in WT mice tissue, consistent with a ΔC variant. When expressed in HEK293 cells the ΔC variants were inefficiently trafficked to the cell surface and agonist-evoked whole cell currents were small. Co-expressed with P2X7A, the ΔC splice variant acted in a dominant negative fashion to inhibit function.

CONCLUSIONS AND IMPLICATIONS

Pfizer KO mice are not null for P2X7 receptor expression but express ΔC variants with reduced function.

Splice variants of the P2X7 receptor reveal differential agonist dependence and functional coupling with pannexin-1

P2X7 receptors function as ATP-gated cation channels but also interact with other proteins as part of a larger signalling complex to mediate a variety of downstream responses that are dependent upon the cell type in which they are expressed. Receptor-mediated membrane permeabilization to large molecules precedes the induction of cell death, but remains poorly understood. The mechanisms that underlie differential sensitivity to NAD are also unknown. By studying alternative variants of the mouse P2X7 receptor we show that sensitivity to NAD is mediated through the P2X7k variant, which has a much more restricted distribution than the P2X7a receptor, but is expressed in T lymphocytes. The altered N-terminus and TM1 of the P2X7k receptor enhances the stability of the active state of this variant compared with P2X7a, thereby increasing the efficacy of NAD-dependent ADP ribosylation as measured by ethidium uptake, a rise in intracellular Ca(2+) and the activation of inward currents. Co-expression of P2X7k and P2X7a receptors reduced NAD sensitivity. P2X7k-receptor-mediated ethidium uptake was also triggered by much lower BzATP concentrations and was insensitive to the P451L single nucleotide polymorphism. P2X7k-receptor-mediated ethidium uptake occurred independently of pannexin-1 suggesting a pathway intrinsic to the receptor. Only for the P2X7aL451 receptor could we resolve a component of dye uptake dependent upon pannexin-1. Signalling occurred downstream of the activation of caspases rather than involving direct cross talk between the channels. However, an in situ proximity assay showed close association between P2X7 receptors and pannexin-1, which would facilitate ATP efflux through pannexin-1 acting in an autocrine manner.

NF-κB is required for Smac mimetic-mediated sensitization of glioblastoma cells for γ-irradiation-induced apoptosis

Evasion of apoptosis contributes to radioresistance of glioblastoma, calling for novel strategies to overcome apoptosis resistance. In this study, we investigated the potential of the small molecule Smac mimetic BV6 to modulate radiosensitivity of glioblastoma cells. Here, we identify a novel proapoptotic function of NF-κB in γ-irradiation-induced apoptosis of glioblastoma cells by showing, for the first time, that NF-κB is critically required for Smac mimetic-mediated radiosensitization. BV6 significantly increases γ-irradiation-triggered apoptosis in several glioblastoma cell lines in a dose- and time-dependent manner. Calculation of combination index (CI) reveals that the interaction of BV6 and γ-irradiation is highly synergistic (CI < 0.3). Molecular studies show that BV6 stimulates NF-κB activation, which is critical for radiosensitization, because genetic inhibition of NF-κB by overexpression of the dominant-negative superrepressor IκBα-SR significantly decreases BV6- and γ-irradiation-induced apoptosis. Also, the BV6-mediated enhancement of γ-irradiation-triggered caspase activation, drop of mitochondrial membrane potential, and cytochrome c release is abolished in cells overexpressing IκBα-SR. Similarly, NF-κB inhibition by ectopic expression of a kinase dead mutant of IKKβ prevents the BV6-mediated sensitization for γ-irradiation. The clinical relevance is underscored by experiments with primary tumor samples showing that BV6 sensitizes primary cultured glioma cells as well as glioblastoma-initiating cancer stem cells derived from surgical specimens for γ-irradiation. In conclusion, we identify NF-κB as a critical mediator of Smac mimetic-conferred radiosensitization of glioblastoma cells. These results have important implications for the development of Smac mimetic-based combination protocols for radiosensitization of glioblastoma.