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Supplementary Figure from A Novel EGFRvIII T-Cell Bispecific Antibody for the Treatment of Glioblastoma

Supplementary Figure 1 shows more details on the mode of action and design of the used antibodies. Supplementary Figure 2 displays additional APC activation data of the human and murine FAP-CD40 molecules. Supplementary Figure 3 shows additional data for FRC in vitro assays and the OVA vaccination study. Supplementary Figure 4 shows additional data on the in vivo study comparing FAP-huCD40 and SGN40 moIgG1. Supplementary Figure 5 displays additional data on the in vivo comparison of selicrelumab and FAP-huCD40. Supplementary Figure 6 shows the data of a FAP-huCD40 dose escalation study in cynomolgus monkeys.

Supplemental data details

Supplemental Video 3. In vitro visualization of the dynamics of CD20-TCB (white) during interaction between CD8+ T-cells (green) and tumor cells (blue). The video focuses on an example of CD20-TCB-mediated CD8+ T-cell cytotoxicity of tumor cells. T-cells surround the tumor cells and create stable synapses where CD20-TCB is localized (white). Tumor cells are killed upon certain time of T-cell/tumor cell interaction as evidenced by the formation of tumor blebs.

Supplementary Methods and Figure Legends.

Purpose: CEA TCB (RG7802, RO6958688) is a novel T-cell bispecific antibody, engaging CD3ϵ upon binding to carcinoembryonic antigen (CEA) on tumor cells. Containing an engineered Fc region, conferring an extended blood half-life while preventing side effects due to activation of innate effector cells, CEA TCB potently induces tumor lysis in mouse tumors. Here we aimed to characterize the pharmacokinetic profile, the biodistribution, and the mode of action of CEA TCB by combining in vitro and in vivo fluorescence imaging readouts.Experimental Design: CEA-expressing tumor cells (LS174T) and human peripheral blood mononuclear cells (PBMC) were cocultured in vitro or cografted into immunocompromised mice. Fluorescence reflectance imaging and intravital 2-photon (2P) microscopy were employed to analyze in vivo tumor targeting while in vitro confocal and intravital time-lapse imaging were used to assess the mode of action of CEA TCB.Results: Fluorescence reflectance imaging revealed increased ratios of extravascular to vascular fluorescence signals in tumors after treatment with CEA TCB compared with control antibody, suggesting specific targeting, which was confirmed by intravital microscopy. Confocal and intravital 2P microscopy showed CEA TCB to accelerate T-cell–dependent tumor cell lysis by inducing a local increase of effector to tumor cell ratios and stable crosslinking of multiple T cells to individual tumor cells.Conclusions: Using optical imaging, we demonstrate specific tumor targeting and characterize the mode of CEA TCB–mediated target cell lysis in a mouse tumor model, which supports further clinical evaluation of CEA TCB. Clin Cancer Res; 22(17); 4417–27. ©2016 AACR.See related commentary by Teijeira et al., p. 4277

Purpose:CD40 agonists hold great promise for cancer immunotherapy (CIT) as they enhance dendritic cell (DC) activation and concomitant tumor-specific T-cell priming. However, the broad expression of CD40 accounts for sink and side effects, hampering the efficacy of anti-CD40 antibodies. We hypothesized that these limitations can be overcome by selectively targeting CD40 agonism to the tumor. Therefore, we developed a bispecific FAP-CD40 antibody, which induces CD40 stimulation solely in presence of fibroblast activation protein α (FAP), a protease specifically expressed in the tumor stroma.Experimental Design:FAP-CD40's in vitro activity and FAP specificity were validated by antigen-presenting cell (APC) activation and T-cell priming assays. In addition, FAP-CD40 was tested in subcutaneous MC38-FAP and KPC-4662-huCEA murine tumor models.Results:FAP-CD40 triggered a potent, strictly FAP-dependent CD40 stimulation in vitro. In vivo, FAP-CD40 strongly enhanced T-cell inflammation and growth inhibition of KPC-4662-huCEA tumors. Unlike nontargeted CD40 agonists, FAP-CD40 mediated complete regression of MC38-FAP tumors, entailing long-term protection. A high dose of FAP-CD40 was indispensable for these effects. While nontargeted CD40 agonists induced substantial side effects, highly dosed FAP-CD40 was well tolerated. FAP-CD40 preferentially accumulated in the tumor, inducing predominantly intratumoral immune activation, whereas nontargeted CD40 agonists displayed strong systemic but limited intratumoral effects.Conclusions:FAP-CD40 abrogates the systemic toxicity associated with nontargeted CD40 agonists. This enables administration of high doses, essential for overcoming CD40 sink effects and inducing antitumor immunity. Consequently, FAP-targeted CD40 agonism represents a promising strategy to exploit the full potential of CD40 signaling for CIT.

Supplemental Figure 1. Assessment of the binding characteristics and cynomolgus monkey cross-reactivity of CD20-TCB. Supplemental Figure 2. Tumor cell lysis mediated by different CD20-targeting TCB antibodies. Supplemental Figure 3. T-cell and B-cell counts along with E:T ratio upon CD20-TCB treatment of primary bone marrow aspirates from patients with lymphoma and leukemia. Supplemental Figure 4. Quantification of interactions between T-cells and tumor cells from live imaging experiments and kinetic analysis of T-cell activation and exhaustion marker expression. Supplemental Figure 5. Secretion of cytokines, cytotoxic granules and T-cell proliferation upon tumor lysis. Supplemental Figure 6. Assessment of the cytokine-mediated endothelial cell activation. Supplemental Figure 7. Characterization of stem cell humanized mice (HSC-NSG) generated in house.

In vitro live cell confocal imaging of LS174T RFP cells co-cultured with CFSE-labeled T-cells (E:T = 3:1) in the presence of CEA or a control TCB, respectively.

List of antibodies used for flow cytometry

Supplemental Video 1. In vitro visualization of the dynamics of untargeted TCB (white) during the interaction between CD8+ T-cells (green) and tumor cells (blue).

Supplementary Figure S1. CEA TCB leads stimulates the expression of CD25, a T-cell activation marker, on both T-helper (CD4+) and cytotoxic T-cells (CD8+) after incubation with LS174T tumor cells. Supplementary Figure S2. CEA TCB induces efficient MKN45 tumor cell lysis and T-cell activation in the presence of these tumor cells. Supplementary Figure S3. Both CD4+ and CD8+ T-cells contribute to CEA-TCB mediated killing. Supplementary Figure S4. Ex vivo analysis of in vivo tumor targeting. Supplementary Figure S5. Analysis of T-cell migratory persistence index.

Additional details on methods used for SPR assays, NanoString RNAseq and cynomolgus monkey studies

Purpose: Despite promising clinical activity, T-cell–engaging therapies including T-cell bispecific antibodies (TCB) are associated with severe side effects requiring the use of step-up-dosing (SUD) regimens to mitigate safety. Here, we present a next-generation CD20-targeting TCB (CD20-TCB) with significantly higher potency and a novel approach enabling safer administration of such potent drug.Experimental Design: We developed CD20-TCB based on the 2:1 TCB molecular format and characterized its activity preclinically. We also applied a single administration of obinutuzumab (Gazyva pretreatment, Gpt; Genentech/Roche) prior to the first infusion of CD20-TCB as a way to safely administer such a potent drug.Results: CD20-TCB is associated with a long half-life and high potency enabled by high-avidity bivalent binding to CD20 and head-to-tail orientation of B- and T-cell–binding domains in a 2:1 molecular format. CD20-TCB displays considerably higher potency than other CD20-TCB antibodies in clinical development and is efficacious on tumor cells expressing low levels of CD20. CD20-TCB also displays potent activity in primary tumor samples with low effector:target ratios. In vivo, CD20-TCB regresses established tumors of aggressive lymphoma models. Gpt enables profound B-cell depletion in peripheral blood and secondary lymphoid organs and reduces T-cell activation and cytokine release in the peripheral blood, thus increasing the safety of CD20-TCB administration. Gpt is more efficacious and safer than SUD.Conclusions: CD20-TCB and Gpt represent a potent and safer approach for treatment of lymphoma patients and are currently being evaluated in phase I, multicenter study in patients with relapsed/refractory non-Hodgkin lymphoma (NCT03075696). Clin Cancer Res; 24(19); 4785–97. ©2018 AACR.See related commentary by Prakash and Diefenbach, p. 4631

List of all genes analyzed in NanoString gene expression analysis comparing gene expression in tumors of selicrelumab and FAP-huCD40-treated mice

2P time-lapse acquisition of LS174T / human PBMC cografts on day 4 after implantation (baseline), 24 h after control and 24 h after CEA TCB treatment. LS174T RFP tumor cells (red), CFSE labeled T-cells (green). Scale bar indicates 50 μm.

Additional data of cynomolgus monkey study showing body weight and plasma cytokine levels over the course of the study

Ex vivo analysis of the CEA TCB (magenta) mediated cross-linking of CFSE labeled T-cells (green) to tumor cells. 3D reconstructions of confocal z-stacks acquired on tumor sections obtained from huPBMC (CFSE labeled T-cells)/LS174T RFP co-grafts, 24 h after intravenous A647 labeled CEA TCB injections are shown. Bar, 10 μm. Cell nuclei (DAPI) are shown in blue.

Supplemental Video 2. In vitro visualization of the dynamics of CD20-TCB (white) during the interaction between CD8+ T-cells (green) and tumor cells (blue).

Supplemental materials and methods

Supplemental Table 1. Overview of CD20-targeting T-cell bispecific molecules evaluated in the current study. Supplemental Table 2. Tumor cell lines and EC50 values of tumor cell lysis. Supplemental Table 3. Assessment of the activity in ex vivo primary tumor samples derived from aggressive lymphoma and leukemia patients. Supplemental Table 4. Absolute values of cytokines measured by multiplex analysis of blood samples reported as heatmap in Figure 3e, 4b, 5d, and 6b. Supplemental Table 5. Average score of perivascular CD3 positive T-cells in the lung (assessed by blinded pathologist analysis) referring to T-cell staining of lungs from tumor-bearing, HSC NSG mice 7 days after the first treatment and 24 h after the second treatment (treatment groups are indicated on Figure 6D panels).

T-cell bispecific antibodies (TCB) are engineered molecules that bind both the T-cell receptor and tumor-specific antigens. Epidermal growth factor receptor variant III (EGFRvIII) mutation is a common event in glioblastoma (GBM) and is characterized by the deletion of exons 2–7, resulting in a constitutively active receptor that promotes cell proliferation, angiogenesis, and invasion. EGFRvIII is expressed on the surface of tumor cells and is not expressed in normal tissues, making EGFRvIII an ideal neoantigen target for TCBs. We designed and developed a novel 2+1 EGFRvIII-TCB with optimal pharmacologic characteristics and potent antitumor activity. EGFRvIII-TCB showed specificity for EGFRvIII and promoted tumor cell killing as well as T-cell activation and cytokine secretion only in patient-derived models expressing EGFRvIII. Moreover, EGFRvIII-TCB promoted T-cell recruitment into intracranial tumors. EGFRvIII-TCB induced tumor regression in GBM animal models, including humanized orthotopic GBM patient-derived xenograft models. Our results warrant the clinical testing of EGFRvIII-TCB for the treatment of EGFRvIII-expressing GBMs.

BackgroundChimeric antigen receptor (CAR) T cell therapy has proven its clinical utility in hematological malignancies. Optimization is still required for its application in solid tumors. Here, the lack of cancer-specific structures along with tumor heterogeneity represent a critical barrier to safety and efficacy. Modular CAR T cells indirectly binding the tumor antigen through CAR-adaptor molecules have the potential to reduce adverse events and to overcome antigen heterogeneity. We hypothesized that a platform utilizing unique traits of clinical grade antibodies for selective CAR targeting would come with significant advantages. Thus, we developed a P329G-directed CAR targeting the P329G mutation in the Fc part of tumor-targeting human antibodies containing P329G L234A/L235A (LALA) mutations for Fc silencing.MethodsA single chain variable fragment-based second generation P329G-targeting CAR was retrovirally transduced into primary human T cells. These CAR T cells were combined with IgG1 antibodies carrying P329G LALA mutations in their Fc part targeting epidermal growth factor receptor (EGFR), mesothelin (MSLN) or HER2/neu. Mesothelioma, pancreatic and breast cancer cell lines expressing the respective antigens were used as target cell lines. Efficacy was evaluated in vitro and in vivo in xenograft mouse models.ResultsUnlike CD16-CAR T cells, which bind human IgG in a non-selective manner, P329G-targeting CAR T cells revealed specific effector functions only when combined with antibodies carrying P329G LALA mutations in their Fc part. P329G-targeting CAR T cells cannot be activated by an excess of human IgG. P329G-directed CAR T cells combined with a MSLN-targeting P329G-mutated antibody mediated pronounced in vitro and in vivo antitumor efficacy in mesothelioma and pancreatic cancer models. Combined with a HER2-targeting antibody, P329G-targeting CAR T cells showed substantial in vitro activation, proliferation, cytokine production and cytotoxicity against HER2-expressing breast cancer cell lines and induced complete tumor eradication in a breast cancer xenograft mouse model. The ability of the platform to target multiple antigens sequentially was shown in vitro and in vivo.ConclusionsP329G-targeting CAR T cells combined with antigen-binding human IgG1 antibodies containing the P329G Fc mutation mediate pronounced in vitro and in vivo effector functions in different solid tumor models, warranting further clinical translation of this concept.

BackgroundT cell engaging therapies, like chimeric antigen receptor T cells and T cell bispecific antibodies (TCBs), efficiently redirect T cells towards tumor cells, facilitating the formation of a cytotoxic synapse and resulting in subsequent tumor cell killing, a process that is accompanied by the release of cytokines. Despite their promising efficacy in the clinic, treatment with TCBs is associated with a risk of cytokine release syndrome (CRS). The aim of this study was to identify small molecules able to mitigate cytokine release while retaining T cell-mediated tumor killing.MethodsBy screening a library of 52 Food and Drug Administration approved kinase inhibitors for their impact on T cell proliferation and cytokine release after CD3 stimulation, we identified mTOR, JAK and Src kinases inhibitors as potential candidates to modulate TCB-mediated cytokine release at pharmacologically active doses. Using an in vitro model of target cell killing by human peripheral blood mononuclear cells, we assessed the effects of mTOR, JAK and Src kinase inhibitors combined with 2+1 T cell bispecific antibodies (TCBs) including CEA-TCB and CD19-TCB on T cell activation, proliferation and target cell killing measured by flow cytometry and cytokine release measured by Luminex. The combination of mTOR, JAK and Src kinase inhibitors together with CD19-TCB was evaluated in vivo in non-tumor bearing stem cell humanized NSG mice in terms of B cell depletion and in a lymphoma patient-derived xenograft (PDX) model in humanized NSG mice in terms of antitumor efficacy.ResultsThe effect of Src inhibitors differed from those of mTOR and JAK inhibitors with the suppression of CD19-TCB-induced tumor cell lysis in vitro, whereas mTOR and JAK inhibitors primarily affected TCB-mediated cytokine release. Importantly, we confirmed in vivo that Src, JAK and mTOR inhibitors strongly reduced CD19-TCB-induced cytokine release. In humanized NSG mice, continuous treatment with a Src inhibitor prevented CD19-TCB-mediated B cell depletion in contrast to mTOR and JAK inhibitors, which retained CD19-TCB efficacy. Ultimately, transient treatment with Src, mTOR and JAK inhibitors minimally interfered with antitumor efficacy in a lymphoma PDX model.ConclusionsTaken together, these data support further evaluation of the use of Src, JAK and mTOR inhibitors as prophylactic treatment to prevent occurrence of CRS.

Simlukafusp alfa (FAP-IL2v, RO6874281/RG7461) is an immunocytokine comprising an antibody against fibroblast activation protein α (FAP) and an IL-2 variant with a retained affinity for IL-2Rβγ > IL-2 Rβγ and abolished binding to IL-2 Rα. Here, we investigated the immunostimulatory properties of FAP-IL2v and its combination with programmed cell death protein 1 (PD-1) checkpoint inhibition, CD40 agonism, T cell bispecific and antibody-dependent cellular cytotoxicity (ADCC)-mediating antibodies. The binding and immunostimulatory properties of FAP-IL2v were investigated in vitro and compared with FAP-IL2wt. Tumor targeting was investigated in tumor-bearing mice and in a rhesus monkey. The ability of FAP-IL2v to potentiate the efficacy of different immunotherapies was investigated in different xenograft and syngeneic murine tumor models. FAP-IL2v bound IL-2 Rβγ and FAP with high affinity in vitro, inducing dose-dependent proliferation of natural killer (NK) cells and CD4+/CD8+ T cells while being significantly less potent than FAP-IL2wt in activating immunosuppressive regulatory T cells (Tregs). T cells activated by FAP-IL2v were less sensitive to Fas-mediated apoptosis than those activated by FAP-IL2wt. Imaging studies demonstrated improved tumor targeting of FAP-IL2v compared to FAP-IL2wt. Furthermore, FAP-IL2v significantly enhanced the in vitro and in vivo activity of therapeutic antibodies that mediate antibody-dependent or T cell-dependent cellular cytotoxicity (TDCC) and of programmed death-ligand 1 (PD-L1) checkpoint inhibition. The triple combination of FAP-IL2v with an anti-PD-L1 antibody and an agonistic CD40 antibody was most efficacious. These data indicate that FAP-IL2v is a potent immunocytokine that potentiates the efficacy of different T- and NK-cell-based cancer immunotherapies.

Expansion of antigen-specific effector CD8 T cells is central to the control of chronic viral infections and cancer. In particular, differentiation of antigen-experienced, PD-1+TCF-1+ stem -like CD8 T cells, termed here “resource T cells”, into effector cells is critical for the success of immunotherapies based on immune checkpoint PD-1 signaling blockade1-4. In the accompanying article, Hashimoto et al. show that in chronic infections, administration of the cytokine interleukin- 2 (IL-2) triggers an alternative differentiation path from resource T cells leading to the expansion of a distinct population of effector CD8 T cells, termed “better effectors”, which are similar to effector cells generated in an acute infection. IL-2 binding to the non-signaling component of its receptor, IL-2Rα-chain, also known as CD25, was essential to trigger this alternative differentiation path and to expand better effectors with distinct transcriptional and epigenetic profiles. However, as IL-2 binding to CD25 constitutively expressed on immunosuppressive regulatory T cells and on some endothelial cells contributes to unwanted systemic effects of IL-2 therapy that have hampered its broad clinical application, a new generation of engineered IL-2Rβγ-biased agonists with reduced/abolished CD25 binding is currently being developed5-9. Here we show that IL-2Rβγ-biased agonists devoid of CD25 binding are unable to preferentially expand better effectors in cancer models, and describe a novel antibody-cytokine fusion protein, PD1-IL2v, that overcomes the need for CD25 binding by using PD-1 binding in cis in order to generate this distinct effector cell population. PD1-IL2v comprises an engineered IL-2 variant devoid of CD25 binding, fused to a high affinity PD-1 blocking antibody. In cis binding of PD1-IL2v to PD-1 and IL-2Rβγ on the same cell surface recovers the ability to differentiate resource CD8 T cells into better effectors in the absence of CD25 binding in both chronic infection and cancer models, while providing superior treatment efficacy. In contrast, PD-1/-L1 blocking antibodies alone, or their combination with clinically relevant doses of IL-2-based molecules with abolished CD25 binding and not targeted to PD-1, could not expand this unique subset of better effector T cells, and rather led to the accumulation of terminally-differentiated, exhausted T cells. These findings provide the basis for the development of a new generation of IL-2R agonists with enhanced therapeutic potential for the treatment of cancer and chronic infections.

Expansion and differentiation of antigen-experienced PD-1

Chimeric antigen receptor (CAR) T cells have shown promising results for the treatment of blood cancers and various CAR-T cell approaches are in development for use in different tumor indications. Universal or modular CARs do not directly recognize the tumor target antigen, but bind via an adaptor molecule to their respective tumor target. We describe the P329G-CAR-T platform as a novel modular CAR-T cell platform that recognizes the P329G mutation in the Fc portion of IgG1 antibodies, a mutation frequently applied to abolish the Fc immune effector function of therapeutic antibodies. In contrast to other adaptor CAR-T cell platforms this approach does not rely on haptens or artificial tags fused to the targeting antibody.The crystal structure analysis of the anti-P329G Fab fragment in complex with a P329G-Fc portion showed that the Fab fragment recognizes the Fc mutation with 1:1 binding stoichiometry. Surface plasmon resonance analysis determined the equilibrium binding affinity of the P329G antibody to the P329G Fc-portion to be 15 nM. Cell assays using Jurkat-NFAT reporter cell lines and primary T cells transduced with the P329G-CAR showed specific recruitment of P329G CAR-T cells by P329G-containing antibodies, and potent and dose dependent tumor cell killing accompanied by IFNg release and subsequent T cell activation for several unrelated tumor antigens including CD20, CD33, HER2, FOLR1 and mesothelin. Notably, P329G-CAR-T cell killing activity was comparable to the activity of the respective direct scFv-based CAR-T cells, both in terms of kinetics and absolute killing potency. Finally, comparable activity was determined in comparison to CD16 extracellular domain (ECD)-based CAR-T cells engaging the CAR-T cells via the Fc-CD16-ECD interaction. In summary, P329G-CAR-T cells mediate potent tumor cell killing in combination with various tumor targeting antibodies as adaptor molecules. The combination with tumor targeting antibodies enables control of CAR-T activity by adjusting the dose and schedule of the respective antibody adaptor molecule. Importantly, different from CD16-ECD-based CAR-T cells, P329G-CAR-T cells cannot be engaged by endogenous immunoglobulins. In vivo studies to investigate efficacy and safety of P329G CAR-T cells are currently being completed and will be reported. Citation Format: Diana Darowski, Mohamed-Reda Benmebarek, Christian Jost, Kay Stubenrauch, Uwe Wessels, Joerg Benz, Anne Freimoser-Grundschober, Ekkehard Moessner, Pablo Umana, Sebastian Kobold, Christian Klein. Developing a novel adaptor CAR-T cell platform based on the recognition of the P329G Fc mutation in therapeutic IgG1 antibodies for adoptive T cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 570.

Traditional drug safety assessment often fails to predict complications in humans, especially when the drug targets the immune system. Here, we show the unprecedented capability of two Organs-on-Chips to evaluate the safety profile of T-cell bispecific antibodies (TCBs) targeting tumor antigens. Although promising for cancer immunotherapy, TCBs are associated with an on-target, off-tumor risk due to low levels of expression of tumor antigens in healthy tissues. We leveraged in vivo target expression and toxicity data of TCBs targeting folate receptor 1 (FOLR1) or carcinoembryonic antigen (CEA) to design and validate human immunocompetent Organs-on-Chips safety platforms. We discovered that the Lung-Chip and Intestine-Chip could reproduce and predict target-dependent TCB safety liabilities, based on sensitivity to key determinants thereof, such as target expression and antibody affinity. These novel tools broaden the research options available for mechanistic understandings of engineered therapeutic antibodies and assessing safety in tissues susceptible to adverse events.

Purpose: CD40 agonists hold great promise for cancer immunotherapy (CIT) as they enhance dendritic cell (DC) activation and concomitant tumor-specific T-cell priming. However, the broad expression of CD40 accounts for sink and side effects, hampering the efficacy of anti-CD40 antibodies. We hypothesized that these limitations can be overcome by selectively targeting CD40 agonism to the tumor. Therefore, we developed a bispecific FAP-CD40 antibody, which induces CD40 stimulation solely in presence of fibroblast activation protein α (FAP), a protease specifically expressed in the tumor stroma. Experimental Design: FAP-CD40's in vitro activity and FAP specificity were validated by antigen-presenting cell (APC) activation and T-cell priming assays. In addition, FAP-CD40 was tested in subcutaneous MC38-FAP and KPC-4662-huCEA murine tumor models. Results: FAP-CD40 triggered a potent, strictly FAP-dependent CD40 stimulation in vitro. In vivo, FAP-CD40 strongly enhanced T-cell inflammation and growth inhibition of KPC-4662-huCEA tumors. Unlike nontargeted CD40 agonists, FAP-CD40 mediated complete regression of MC38-FAP tumors, entailing long-term protection. A high dose of FAP-CD40 was indispensable for these effects. While nontargeted CD40 agonists induced substantial side effects, highly dosed FAP-CD40 was well tolerated. FAP-CD40 preferentially accumulated in the tumor, inducing predominantly intratumoral immune activation, whereas nontargeted CD40 agonists displayed strong systemic but limited intratumoral effects. Conclusions: FAP-CD40 abrogates the systemic toxicity associated with nontargeted CD40 agonists. This enables administration of high doses, essential for overcoming CD40 sink effects and inducing antitumor immunity. Consequently, FAP-targeted CD40 agonism represents a promising strategy to exploit the full potential of CD40 signaling for CIT.

Interleukin-2 (IL2) is a cytokine that can stimulate cytotoxic immune cells to attack infected and malignant cells. Unfortunately, IL2 can also cause serious immune-related toxicity. Recently, a mutant of IL2 (IL2v) with abolished CD25 binding, increased plasma half-life and less toxicity was engineered. Unlike wild-type IL2 (wt-IL2), mutant IL2v does not bind to the α-subunit (CD25) of the high affinity IL2αβγ receptor, but only to its β and γ subunit. Here, we investigated the biological properties of IL2v and compared with the wt-IL2 using fluorine-18 and PET. [18F]FB-IL2v binds specifically to IL2 receptors (IL2R) on activated human peripheral blood monocytes (hPBMCs) and is cleared mainly by the kidneys (Balb/c mice). [18F]FB-IL2v PET studies in SCID mice injected with hPBMCs revealed high uptake in the implant (0.85 ± 0.15 SUV), which was significantly reduced after pretreatment with wt-IL2 or mutant IL2v (SUV 0.26 ± 0.1 and 0.46 ± 0.1,p< 0.01). Compartment modeling and Logan graphical analysis in wistar rats inoculated with hPBMCs indicated that the binding of [18F]FB-IL2v to IL2R was reversible. The volume of distribution (VT) and the non-displaceable binding potential (BPnd) of mutant [18F]FB-IL2v in the implant were approximately 3 times lower than those of wild-type [18F]FB-IL2 (p< 0.01). Pretreatment with wt-IL2 significantly reduced the VTand BPnd of mutant [18F]FB-IL2v in the implant (p< 0.001). This demonstrates that wild-type [18F]FB-IL2 binds stronger to IL2R and has faster kinetics than [18F]FB-IL2v, which makes it less suitable as a therapeutic drug. [18F]FB-IL2v, on the other hand, seems to have better properties for use as a therapeutic drug.

T-cell bispecific antibodies (TCBs) crosslink tumor and T-cells to induce tumor cell killing. While TCBs are very potent, on-target off-tumor toxicity remains a challenge when selecting targets. Here, we describe a protease-activated anti-folate receptor 1 TCB (Prot-FOLR1-TCB) equipped with an anti-idiotypic anti-CD3 mask connected to the anti-CD3 Fab through a tumor protease-cleavable linker. The potency of this Prot- FOLR1-TCB is recovered following protease-cleavage of the linker releasing the anti-idiotypic anti-CD3 scFv. In vivo, the Prot-FOLR1-TCB mediates antitumor efficacy comparable to the parental FOLR1-TCB whereas a noncleavable control Prot-FOLR1-TCB is inactive. In contrast, killing of bronchial epithelial and renal cortical cells with low FOLR1 expression is prevented compared to the parental FOLR1-TCB. The findings are confirmed for mesothelin as alternative tumor antigen. Thus, masking the anti-CD3 Fab fragment with an anti-idiotypic mask and cleavage of the mask by tumor-specific proteases can be applied to enhance specificity and safety of TCBs., The clinical application of T cell bispecific antibodies (TCBs) is often limited by the lack of tumour-specific antigens. In this study, the authors present a strategy to increase TCB tumour-selectivity by adding an anti-CD3 moiety that can be specifically activated by tumor specific proteases in the tumor microenvironment.

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.

Therapeutic antibodies can elicit an immune response through different mechanisms, either cell independent via complement activation (CDC) or through activation of immune-effector cells (such as macrophages and NK cells). After target binding, the Fc part of the antibody will interact with Fc receptors on the surface of effector cells, leading to activation and lysis of the target cells by a mechanism called antibody-dependent cell-mediated cytotoxicity (ADCC). The ADCC of an antibody can be increased by modifying the carbohydrates on the Fc part. If the fucose on the first N-acetylglucosamine is absent, the affinity for the FcγRIIIa is increased and the ADCC enhanced. We describe the development of a chromatography method that is based on the differential affinity of the Fc receptor FcγRIIIa (high affinity V158 variant) for fucosylated and a-fucosylated antibodies. Immobilized FcγRIIIa can be used for the separation of immunoglobulins carrying these glycosylation variants for both, analytical and preparative purposes. The biological activity and fucose content of three pools enriched for fully fucosylated, mono-fucosylated or a-fucosylated carbohydrates could be characterized. Mono-fucosylated and a-fucosylated immunoglobulins have the same enhanced biological activity compared to fully fucosylated IgGs. A direct, label- and modification-free analytical method for screening of IgGs from culture supernatant was developed and was amenable to high-throughput screening. Clones producing antibodies with a high content of a-fucosylated oligosaccharides could be successfully selected.

Endogenous costimulatory molecules on T cells such as 4-1BB (CD137) can be leveraged for cancer immunotherapy. Systemic administration of agonistic anti–4-1BB antibodies, although effective preclinically, has not advanced to phase 3 trials because they have been hampered by both dependency on Fcγ receptor–mediated hyperclustering and hepatotoxicity. To overcome these issues, we engineered proteins simultaneously targeting 4-1BB and a tumor stroma or tumor antigen: FAP–4-1BBL (RG7826) and CD19–4-1BBL. In the presence of a T cell receptor signal, they provide potent T cell costimulation strictly dependent on tumor antigen–mediated hyperclustering without systemic activation by FcγR binding. We could show targeting of FAP–4-1BBL to FAP-expressing tumor stroma and lymph nodes in a colorectal cancer–bearing rhesus monkey. Combination of FAP–4-1BBL with tumor antigen–targeted T cell bispecific (TCB) molecules in human tumor samples led to increased IFN-γ and granzyme B secretion. Further, combination of FAP– or CD19–4-1BBL with CEA-TCB (RG7802) or CD20-TCB (RG6026), respectively, resulted in tumor remission in mouse models, accompanied by intratumoral accumulation of activated effector CD8(+) T cells. FAP– and CD19–4-1BBL thus represent an off-the-shelf combination immunotherapy without requiring genetic modification of effector cells for the treatment of solid and hematological malignancies.

Background: Activated synovial fibroblasts (SF) contribute to rheumatoid arthritis (RA) by producing a multitude of cytokines, chemokines and proteases thus aggravating disease. Activated SF can be distinguished from quiescent fibroblasts by their expression of fibroblast activation protein (FAP). Selective depletion of FAP+ SF in inflamed joints could decrease their contribution to the arthritis process and thus constitute a viable treatment option. Further focussing of the treatment to only those areas affected by the disease can be accomplished by applying targeted photodynamic therapy (tPDT). In tPDT a light sensitive molecule, a photosensitizer (PS), is conjugated to a targeting moiety. Upon activation by light this construct produces reactive oxygen species, killing the targeted cells. Objectives: To this end we developed and tested a therapy that selectively depletes activated SF by targeting FAP on these cells with an antibody, 28H1, to which the PS, IRDye700DX, for tPDT is attached. Here we investigated the feasibility of using FAP-tPDT to induce cell death in murine arthritic synovium ex vivo. Methods: After conjugation of the IDRye700DX to 28H1 (28H1-700DX), binding and specificity of the conjugate was determined. Subsequently, tPDT efficiency in vitro was established using a 3T3 fibroblast cell line stably transfected with FAP. Biodistribution using an [111In] In-DTPA-28H1 conjugate with and without IRDye700DX was performed in healthy C57BL/6N mice as well as in C57BL/6N mice with antigen induced arthritis (AIA). Finally, the potential of FAP-tPDT to induce targeted cell death in the synovial lining was determined by treating knee joints from mice with AIA ex vivo. Results: Conjugation of IRDye700DX to the antibody did not negatively influence the immunoreactive fraction or binding capacity of the conjugate (94.7% for 28H1-700DX). 28H1-700DX was able to efficiently induce FAP-specific cell death in vitro. At 17.6 J/cm2 radiant exposure, 89.24% ± 3.67% of fibroblasts died in the group incubated with antibody compared to control incubated with buffer only (p Conclusion: Here we demonstrated the feasibility of conjugating a PS to an antibody targeting FAP on activated SF without negatively impacting the binding capacity thereof. Furthermore we showed that this construct can then be used to deliver cell specific cytotoxicity through tPDT both in vitro and ex vivo in a mouse model of arthritis. This approach may have therapeutic potential in the treatment of RA. Disclosure of Interests: Daphne Dorst: None declared, Mark Rijpkema: None declared, Mijke Buitinga: None declared, Peter Laverman: None declared, Marti Boss: None declared, Christian Klein Employee of: Roche pharmaceutics, Anne Freimoser-Grundschober Employee of: Roche pharmaceutics, Birgitte Walgreen: None declared, Peter van der Kraan: None declared, Martin Gotthardt: None declared, Marije Koenders: None declared

Career situation of first and presenting author Student for a master or a PhD. Introduction Activated synovial fibroblasts (ASF) play an important role in the pathogenesis of rheumatoid arthritis (RA). They contribute to the pro-inflammatory environment in the joint and degradation of cartilage and bone. Depleting ASF could ameliorate both these hallmarks of RA. ASF are characterized by the expression of fibroblast activation protein (FAP). Objectives Here, we investigated the potential of FAP-targeted photodynamic therapy (tPDT) using the photosensitizer IRDye700DX conjugated to the anti-FAP antibody 28 H1 (28H1–700DX) to selectively kill these cells. Methods To demonstrate the proof-of-concept of FAP-based tPDT in ex vivo human tissue, RA synovial tissue obtained during joint replacement surgery was trypsin digested and fibroblasts were cultured for at least 5 passages. Cells were incubated with or without 1 ug/well 28H1–700DX for 4 hour, washed with PBS and either exposed to 690 nm light or not exposed. A luminescent cell viability assay (CellTiter-Glo) was used to measure cell viability. In parallel, 6 mm biopsies of synovial tissue were taken and used for FAP-based tPDT (n=8 patients). They were subjected to tPDT as described above and formalin fixed after 1 hour. To measure cell death, 5 µm paraffin slices were stained for FAP, gamma-H2AX and caspase-3 expression for activated fibroblasts, DNA double-strand breaks and early apoptosis, respectively. Results FAP-tPDT performed on the cultured fibroblasts showed a light dose dependent increase in cell death when incubated with 28H1–700DX for 4 hour. Cell viability was not affected when cells were incubated with 28H1-700DX without illumination (101.37%±3.9% remaining compared to 100%±5.07% in the normalized control). Radiant exposure of 17.6 J/cm2 did not significantly decrease cell viability (6.4%±9.8% decrease, ns). Radiant exposures of 52.8, 105.6 and 158.4 J/cm2 significantly decreased cell viability (38.6%±6.9%, 67.5%±10.9% and 80.6%±5.8% respectively, p Conclusions FAP-tPDT induces cell death of FAP-positive activated fibroblasts in synovial tissue from RA patients. This is a first indication that FAP-targeted PDT can be a feasible new treatment strategy in RA. Disclosure of Interest D. Dorst: None declared, M. Rijpkema: None declared, M. Buitinga: None declared, P. Laverman: None declared, M. Brom: None declared, D. Bos: None declared, A. Freimoser-Grundschober Grant/research support from: support in kind, C. Klein Grant/research support from: support in kind, B. Walgreen: None declared, P. Van der Kraan: None declared, M. Gotthardt: None declared, M. Koenders: None declared.

Purpose: CEA TCB (RG7802, RO6958688) is a novel T-cell bispecific antibody, engaging CD3ϵ upon binding to carcinoembryonic antigen (CEA) on tumor cells. Containing an engineered Fc region, conferring an extended blood half-life while preventing side effects due to activation of innate effector cells, CEA TCB potently induces tumor lysis in mouse tumors. Here we aimed to characterize the pharmacokinetic profile, the biodistribution, and the mode of action of CEA TCB by combining in vitro and in vivo fluorescence imaging readouts. Experimental Design: CEA-expressing tumor cells (LS174T) and human peripheral blood mononuclear cells (PBMC) were cocultured in vitro or cografted into immunocompromised mice. Fluorescence reflectance imaging and intravital 2-photon (2P) microscopy were employed to analyze in vivo tumor targeting while in vitro confocal and intravital time-lapse imaging were used to assess the mode of action of CEA TCB. Results: Fluorescence reflectance imaging revealed increased ratios of extravascular to vascular fluorescence signals in tumors after treatment with CEA TCB compared with control antibody, suggesting specific targeting, which was confirmed by intravital microscopy. Confocal and intravital 2P microscopy showed CEA TCB to accelerate T-cell–dependent tumor cell lysis by inducing a local increase of effector to tumor cell ratios and stable crosslinking of multiple T cells to individual tumor cells. Conclusions: Using optical imaging, we demonstrate specific tumor targeting and characterize the mode of CEA TCB–mediated target cell lysis in a mouse tumor model, which supports further clinical evaluation of CEA TCB. Clin Cancer Res; 22(17); 4417–27. ©2016 AACR. See related commentary by Teijeira et al., p. 4277

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.

In the past decade, many checkpoint inhibitors (CPI) have been approved for melanoma, demonstrating the increasing potential of immunotherapy as a lifesaving treatment for this devastating disease. However, many patients relapse or need to discontinue treatment due to adverse effects. Patients failing CPI have very limited treatment options and very poor outcomes. This supports the need for novel and more effective immunotherapies, including combination approaches. Bispecific antibodies like blinatumomab have been approved for hematologic malignancies but positive benefit in solid tumors has been more challenging to demonstrate. Given the relative high T cell content in melanoma, we considered this indication highly promising to investigate whether synthetic immunity also works in solid tumors. Here we present a novel potent treatment approach based on an off the shelf T cell engaging bispecific antibody directed against a melanoma associated target. The tyrosinase-related protein 1 antigen (TYRP1), an enzyme expressed in normal melanosomes and involved in melanin synthesis, is overexpressed in more than 50% of metastatic melanoma patients. TYRP1-TCB is a new 2+1 format T cell bispecific antibody targeting TYRP1 on tumor cells and CD3 on T cells. CD3 bispecific molecules do not depend on HLA expression or antigen presentation and could therefore overcome immune evasion mechanisms in patients failing CPI; as such, T cell redirection via TYRP1-TCB has the potential to be the foundation for new and improved CIT combinations. In vitro TYRP1-TCB mediated strong killing of patient derived melanoma cells from a dermatology cell bank as observed by LDH release, T cell activation and cytokine secretion with EC50 ranging from 30-1500 pM. Pre-clinical investigation in vivo with a murine surrogate molecule showed potent efficacy in subcutaneous as well as aggressive lung metastatic B16 melanoma mouse models that do not respond to anti-PD1 or anti-PD-L1 therapy. Furthermore, the combination with immunomodulatory agents like FAP-IL2v and FAP-4-1BBL molecules demonstrated enhanced efficacy as compared to the respective single agents. These preclinical data support the clinical evaluation of TYRP1 targeted CD3 bispecific antibody as a single agent and in combination in metastatic relapsed/refractory melanoma patients. Citation Format: Valeria G. Nicolini, Inja Waldhauer, Anne Freimoser-Grundschober, Marine Richard, Linda Fahrni, Esther Bommer, Christina Claus, Johannes Sam, Sara Colombetti, Roger Sutmuller, Mitchell P. Levesque, Anja Irmisch, Conrad Bleul, Neil Campbell, Marina Bacac, Ekkehard Moessner, Christian Klein, Pablo Umana. Combination of TYRP1-TCB, a novel T cell bispecific antibody for the treatment of melanoma, with immunomodulatory agents [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 LB-389.

T cell bispecific antibodies (TCBs) are engineered molecules that include, within a single entity, binding sites to the T cell receptor and to tumor-associated or tumor-specific antigens. The receptor tyrosine kinase HER2 is a tumor-associated antigen in ~25% of breast cancers. TCBs targeting HER2 may result in severe toxicities, likely due to the expression of HER2 in normal epithelia. About 40% of HER2-positive tumors express p95HER2, a carboxyl-terminal fragment of HER2. Using specific antibodies, here, we show that p95HER2 is not expressed in normal tissues. We describe the development of p95HER2-TCB and show that it has a potent antitumor effect on p95HER2-expressing breast primary cancers and brain lesions. In contrast with a TCB targeting HER2, p95HER2-TCB has no effect on nontransformed cells that do not overexpress HER2. These data pave the way for the safe treatment of a subgroup of HER2-positive tumors by targeting a tumor-specific antigen.