CD19-CD28: an affinity-optimized CD28 agonist for combination with glofitamab (CD20-TCB) as off-the-shelf immunotherapy

ABSTRACT

Effective T-cell responses not only require the engagement of T-cell receptors (TCRs; "signal 1"), but also the availability of costimulatory signals ("signal 2"). T-cell bispecific antibodies (TCBs) deliver a robust signal 1 by engaging the TCR signaling component CD3ε, while simultaneously binding to tumor antigens. The CD20-TCB glofitamab redirects T cells to CD20-expressing malignant B cells. Although glofitamab exhibits strong single-agent efficacy, adding costimulatory signaling may enhance the depth and durability of T-cell-mediated tumor cell killing. We developed a bispecific CD19-targeted CD28 agonist (CD19-CD28), RG6333, to enhance the efficacy of glofitamab and similar TCBs by delivering signal 2 to tumor-infiltrating T cells. CD19-CD28 distinguishes itself from the superagonistic antibody TGN1412, because its activity requires the simultaneous presence of a TCR signal and CD19 target binding. This is achieved through its engineered format incorporating a mutated Fc region with abolished FcγR and C1q binding, CD28 monovalency, and a moderate CD28 binding affinity. In combination with glofitamab, CD19-CD28 strongly increased T-cell effector functions in ex vivo assays using peripheral blood mononuclear cells and spleen samples derived from patients with lymphoma and enhanced glofitamab-mediated regression of aggressive lymphomas in humanized mice. Notably, the triple combination of glofitamab with CD19-CD28 with the costimulatory 4-1BB agonist, CD19-4-1BBL, offered substantially improved long-term tumor control over glofitamab monotherapy and respective duplet combinations. Our findings highlight CD19-CD28 as a safe and highly efficacious off-the-shelf combination partner for glofitamab, similar TCBs, and other costimulatory agonists. CD19-CD28 is currently in a phase 1 clinical trial in combination with glofitamab. This trial was registered at www.clinicaltrials.gov as #NCT05219513.

Dissecting the Mechanisms Underlying the Cytokine Release Syndrome (CRS) Mediated by T-Cell Bispecific Antibodies

PURPOSE

Target-dependent TCB activity can result in the strong and systemic release of cytokines that may develop into cytokine release syndrome (CRS), highlighting the need to understand and prevent this complex clinical syndrome.

EXPERIMENTAL DESIGN

We explored the cellular and molecular players involved in TCB-mediated cytokine release by single-cell RNA-sequencing of whole blood treated with CD20-TCB together with bulk RNA-sequencing of endothelial cells exposed to TCB-induced cytokine release. We used the in vitro whole blood assay and an in vivo DLBCL model in immunocompetent humanized mice to assess the effects of dexamethasone, anti-TNFα, anti-IL6R, anti-IL1R, and inflammasome inhibition, on TCB-mediated cytokine release and antitumor activity.

RESULTS

Activated T cells release TNFα, IFNγ, IL2, IL8, and MIP-1β, which rapidly activate monocytes, neutrophils, DCs, and NKs along with surrounding T cells to amplify the cascade further, leading to TNFα, IL8, IL6, IL1β, MCP-1, MIP-1α, MIP-1β, and IP-10 release. Endothelial cells contribute to IL6 and IL1β release and at the same time release several chemokines (MCP-1, IP-10, MIP-1α, and MIP-1β). Dexamethasone and TNFα blockade efficiently reduced CD20-TCB-mediated cytokine release whereas IL6R blockade, inflammasome inhibition, and IL1R blockade induced a less pronounced effect. Dexamethasone, IL6R blockade, IL1R blockade, and the inflammasome inhibitor did not interfere with CD20-TCB activity, in contrast to TNFα blockade, which partially inhibited antitumor activity.

CONCLUSIONS

Our work sheds new light on the cellular and molecular players involved in cytokine release driven by TCBs and provides a rationale for the prevention of CRS in patients treated with TCBs. See related commentary by Luri-Rey et al., p. 4320.

A novel EGFRvIII-T cell bispecific antibody for the treatment of glioblastoma

T cell bispecific antibodies (TCBs) 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 pharmacological characteristics and potent anti-tumor 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 (PDX) models. Our results warrant the clinical testing of EGFRvIII-TCB for the treatment of EGFRvIII-expressing GBMs.

JAK and mTOR inhibitors prevent cytokine release while retaining T cell bispecific antibody in vivo efficacy

Background

T 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.

Methods

By 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.

Results

The 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.

Conclusions

Taken together, these data support further evaluation of the use of Src, JAK and mTOR inhibitors as prophylactic treatment to prevent occurrence of CRS.

Human immunocompetent Organ-on-Chip platforms allow safety profiling of tumor-targeted T-cell bispecific antibodies

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 human 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.

Src/lck inhibitor dasatinib reversibly switches off cytokine release and T cell cytotoxicity following stimulation with T cell bispecific antibodies

Background

T cell engagers are bispecific antibodies recognizing, with one moiety, the CD3ε chain of the T cell receptor and, with the other moiety, specific tumor surface antigens. Crosslinking of CD3 upon simultaneous binding to tumor antigens triggers T cell activation, proliferation and cytokine release, leading to tumor cell killing. Treatment with T cell engagers can be associated with safety liabilities due to on-target on-tumor, on-target off-tumor cytotoxic activity and cytokine release syndrome (CRS). Tyrosine kinases such as SRC, LCK or ZAP70 are involved in downstream signaling pathways after engagement of the T cell receptor and blocking these kinases might serve to abrogate T cell activation when required (online supplemental material 1). Dasatinib was previously identified as a potent kinase inhibitor that switches off CAR T cell functionality.

Methods

Using an in vitro model of target cell killing by human peripheral blood mononuclear cells, we assessed the effects of dasatinib combined with 2+1 T cell bispecific antibodies (TCBs) including CEA-TCB, CD19-TCB or HLA-A2 WT1-TCB on T cell activation, proliferation and target cell killing measured by flow cytometry and cytokine release measured by Luminex. To determine the effective dose of dasatinib, the Incucyte system was used to monitor the kinetics of TCB-mediated target cell killing in the presence of escalating concentrations of dasatinib. Last, the effects of dasatinib were evaluated in vivo in humanized NSG mice co-treated with CD19-TCB. The count of CD20⁺ blood B cells was used as a readout of efficacy of TCB-mediated killing and cytokine levels were measured in the serum.

Results

Dasatinib concentrations above 50 nM prevented cytokine release and switched off-target cell killing, which were subsequently restored on removal of dasatinib. In addition, dasatinib prevented CD19-TCB-mediated B cell depletion in humanized NSG mice. These data confirm that dasatinib can act as a rapid and reversible on/off switch for activated T cells at pharmacologically relevant doses as they are applied in patients according to the label.

Conclusion

Taken together, we provide evidence for the use of dasatinib as a pharmacological on/off switch to mitigate off-tumor toxicities or CRS by T cell bispecific antibodies.

Cross-linking of T cell to B cell lymphoma by the T cell bispecific antibody CD20-TCB induces IFNγ/CXCL10-dependent peripheral T cell recruitment in humanized murine model

Diffuse large B cell lymphomas (DLBCL) are a highly heterogeneous subtype of Non Hodgkin Lymphoma (NHL), accounting for about 25% of NHL. Despite an increased progression-free survival upon therapy, 40-50% of patients develop relapse/refractory disease, therefore there remains an important medical need. T cell recruiting therapies, such as the CD20xCD3 T cell bi-specific antibody CD20-TCB (RG6026 or glofitamab), represent a novel approach to target all stages of DLBCL, especially those that fail to respond to multiple lines of treatment. We aimed for a better understanding of the molecular features related to the mode of action (MoA) of CD20-TCB in inducing Target/T cell synapse formation and human T cell recruitment to the tumor. To directly evaluate the correlation between synapse, cytokine production and anti-tumor efficacy using CD20-TCB, we developed an innovative preclinical human DLBCL in vivo model that allowed tracking in vivo human T cell dynamics by multiphoton intravital microscopy (MP-IVM). By ex vivo and in vivo approaches, we revealed that CD20-TCB is inducing strong and stable synapses between human T cell and tumor cells, which are dependent on the dose of CD20-TCB and on LFA-1 activity but not on FAS-L. Moreover, despite CD20-TCB being a large molecule (194.342 kDa), we observed that intra-tumor CD20-TCB-mediated human T cell-tumor cell synapses occur within 1 hour upon CD20-TCB administration. These tight interactions, observed for at least 72 hours post TCB administration, result in tumor cell cytotoxicity, resident T cell proliferation and peripheral blood T cell recruitment into tumor. By blocking the IFNγ-CXCL10 axis, the recruitment of peripheral T cells was abrogated, partially affecting the efficacy of CD20-TCB treatment which rely only on resident T cell proliferation. Altogether these data reveal that CD20-TCB's anti-tumor activity relies on a triple effect: i) fast formation of stable T cell-tumor cell synapses which induce tumor cytotoxicity and cytokine production, ii) resident T cell proliferation and iii) recruitment of fresh peripheral T cells to the tumor core to allow a positive enhancement of the anti-tumor effect.

CD25-Treg-depleting antibodies preserving IL-2 signaling on effector T cells enhance effector activation and antitumor immunity

Intratumoral regulatory T cell (Treg) abundance associates with diminished anti-tumor immunity and poor prognosis in human cancers. Recent work demonstrates that CD25, the high affinity receptor subunit for IL-2, is a selective target for Treg depletion in mouse and human malignancies; however, anti-human CD25 antibodies have failed to deliver clinical responses against solid tumors due to bystander IL-2 receptor signaling blockade on effector T cells, which limits their anti-tumor activity. Here we demonstrate potent single-agent activity of anti-CD25 antibodies optimized to deplete Tregs whilst preserving IL-2-STAT5 signaling on effector T cells, and demonstrate synergy with immune checkpoint blockade in vivo. Pre-clinical evaluation of an anti-human CD25 (RG6292) antibody with equivalent features demonstrates, in both non-human primates and humanized mouse models, efficient Treg depletion with no overt immune-related toxicities. Our data supports the clinical development of RG6292 and evaluation of novel combination therapies incorporating non-IL-2 blocking anti-CD25 antibodies in clinical studies.

Combination of T-Cell Bispecific Antibodies With PD-L1 Checkpoint Inhibition Elicits Superior Anti-Tumor Activity

T-cell Bispecific Antibodies (TCBs) elicit anti-tumor responses by cross-linking T-cells to tumor cells and mediate polyclonal T-cell expansion that is independent of T-cell receptor specificity. TCBs thus offer great promise for patients who lack antigen-specific T-cells or have non-inflamed tumors, which are parameters known to limit the response of checkpoint inhibitors. The current study deepens the understanding of TCB mode of action and elaborates on one of the adaptive resistance mechanisms following its treatment in vivo in humanized mice and syngeneic pre-clinical tumor models. Single-agent TCB treatment reduced tumor growth compared with controls and led to a 2-10-fold increase in tumor-infiltrating T-cells, regardless of the baseline tumor immune cell infiltration. TCB treatment strongly induced the secretion of CXCL10 and increased the frequency of intra-tumor CXCR3+ T-cells pointing to the potential role of the CXCL10-CXCR3 pathway as one of the mechanisms for T-cell recruitment to tumors upon TCB treatment. Tumor-infiltrating T-cells displayed a highly activated and proliferating phenotype, resulting in the generation of a highly inflamed tumor microenvironment. A molecular signature of TCB treatment was determined (CD8, PD-1, MIP-a, CXCL10, CXCL13) to identify parameters that most robustly characterize TCB activity. Parallel to T-cell activation, TCB treatment also led to a clear upregulation of PD-1 on T-cells and PD-L1 on tumor cells and T-cells. Combining TCB treatment with anti-PD-L1 blocking antibody improved anti-tumor efficacy compared to either agent given as monotherapy, increasing the frequency of intra-tumoral T-cells. Together, the data of the current study expand our knowledge of the molecular and cellular features associated with TCB activity and provide evidence that the PD-1/PD-L1 axis is one of the adaptive resistance mechanisms associated with TCB activity. This mechanism can be managed by the combination of TCB with anti-PD-L1 blocking antibody translating into more efficacious anti-tumor activity and prolonged control of the tumor outgrowth. The elucidation of additional resistance mechanisms beyond the PD-1/PD-L1 axis will constitute an important milestone for our understanding of factors determining tumor escape and deepening of TCB anti-tumor responses in both solid tumors and hematological disorders.

Abstract 4553: The CD25 antibody RG6292 selectively depletes Tregs while preserving IL-2 signaling and CTL activity for tumor control

Despite the advances in cancer immunotherapy, in particular in the field of checkpoint inhibitors (CPI), many patients fail to respond (primary resistance) or initially benefit but then progress upon treatment (secondary resistance). High regulatory T-cell (Treg) counts correlate with poor prognosis and reduced responsiveness to CPI therapy in humans, underscoring their potential as an immunotherapy target. Clinical attempts aiming to lower Treg counts, however, either failed to deliver convincing Treg reduction or lacked specificity for Treg over tumor antigen specific cytotoxic T cells (CTL). CD25 (the interleukin-2 receptor alpha (IL-2Ra) chain) is a recently revisited target for Treg depletion. For privileged access to IL-2, activated CTL up-regulate CD25 expression only transiently during clonal expansion. Further confirmation of an > 20 fold higher cell surface expression of CD25 on Tregs versus CTLs in human malignancies is provided. The novel compound RG6292 was developed as an ADCC and ADCP competent monoclonal antibody of human IgG1 isotype with afucosylated glycans in the Fc region. RG6292 binds with low monovalent affinity (KD 250 nM) to the extracellular domain of CD25 antigen. A high density of CD25 receptors promotes bivalent avidity of RG6292 increasing its binding strength to CD25 by at least 100 fold (KD 2-3 nM). RG6292 selectively favors the depletion of CD25 high Tregs over CD25 low activated CTLs, here shown in comparison to ipilimumab and mogamulizumab in human αCD3 activated PBMC, human tumor explants and immunopharmacodynamic studies in tumor bearing (BxPC-3), stem cell humanized mice and cynomolgus monkeys. IL-2 is an essential prerequisite for clonal expansion of CTLs, which is necessary to generate effective anti-tumor responses. Earlier immunosuppressant anti-CD25 antibodies (e.g. daclizumab and basiliximab) interfered with the formation of the high affinity IL-2R complex. Their evidenced lack of therapeutic activity in immunoncology tempered enthusiasm and highlights the pivotal role of IL-2. RG6292 is the first anti-human CD25 antibody developed to deplete Tregs selectively while fully preserving IL-2 signaling and CTL activity. Pre-clinically, a single administration of the RG6292 surrogate effectively promoted eradication of established tumors in several tumor mouse models and synergized with CPI in models of CPI resistance. RG6292 is expected to unleash the potential of selective Treg depletion while allowing for unrestricted access of IL 2 to CTLs and could therefore result in clinically superiority compared to other Treg depleting antibodies. RG6292 provides a novel therapeutic approach to alleviate a major mechanism of immune suppression in the tumor microenvironment. Clinical testing is currently ongoing to evaluate the safety and tolerability of RG6292 in patients with advanced solid tumors (NCT04158583).

Citation Format: Maria Amann, Gabriel Schnetzler, Kolben Theresa, Isabelle Solomon, Christophe Boetsch, Estelle Marrer-Berger, Reto Flury, Claudio Murgia, Vaios Karanikas, Johannes Sam, Roger Sutmuller, Jan Eckmann, Hans Koll, Sara Belli, Frederic Arce Vargas, Dimitrios Zervas, Chen Qing, Mark A. Brown, Josephine Salimu, Anne Goubier, Sebastian Neumann, Karl S. Peggs, Sergio A. Quezada. The CD25 antibody RG6292 selectively depletes Tregs while preserving IL-2 signaling and CTL activity for tumor control [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 4553.

Innovations, challenges, and minimal information for standardization of humanized mice

Mice xenotransplanted with human cells and/or expressing human gene products (also known as "humanized mice") recapitulate the human evolutionary specialization and diversity of genotypic and phenotypic traits. These models can provide a relevant in vivo context for understanding of human-specific physiology and pathologies. Humanized mice have advanced toward mainstream preclinical models and are now at the forefront of biomedical research. Here, we considered innovations and challenges regarding the reconstitution of human immunity and human tissues, modeling of human infections and cancer, and the use of humanized mice for testing drugs or regenerative therapy products. As the number of publications exploring different facets of humanized mouse models has steadily increased in past years, it is becoming evident that standardized reporting is needed in the field. Therefore, an international community-driven resource called "Minimal Information for Standardization of Humanized Mice" (MISHUM) has been created for the purpose of enhancing rigor and reproducibility of studies in the field. Within MISHUM, we propose comprehensive guidelines for reporting critical information generated using humanized mice.

Tumor-targeted 4-1BB agonists for combination with T cell bispecific antibodies as off-the-shelf therapy

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.

Protease-activation using anti-idiotypic masks enables tumor specificity of a folate receptor 1-T cell bispecific antibody

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 PET-Tracer 89Zr-Df-IAB22M2C Enables Monitoring of Intratumoral CD8 T-cell Infiltrates in Tumor-Bearing Humanized Mice after T-cell Bispecific Antibody Treatment

CD8-expressing T cells are the main effector cells in cancer immunotherapy. Treatment-induced changes in intratumoral CD8⁺ T cells may represent a biomarker to identify patients responding to cancer immunotherapy. Here, we have used a ⁸⁹Zr-radiolabeled human CD8-specific minibody (⁸⁹Zr-Df-IAB22M2C) to monitor CD8⁺ T-cell tumor infiltrates by PET. The ability of this tracer to quantify CD8⁺ T-cell tumor infiltrates was evaluated in preclinical studies following single-agent treatment with FOLR1-T-cell bispecific (TCB) antibody and combination therapy of CEA-TCB (RG7802) and CEA-targeted 4-1BB agonist CEA-4-1BBL. In vitro cytotoxicity assays with peripheral blood mononuclear cells and CEA-expressing MKN-45 gastric or FOLR1-expressing HeLa cervical cancer cells confirmed noninterference of the anti-CD8-PET-tracer with the mode of action of CEA-TCB/CEA-4-1BBL and FOLR1-TCB at relevant doses. In vivo, the extent of tumor regression induced by combination treatment with CEA-TCB/CEA-4-1BBL in MKN-45 tumor-bearing humanized mice correlated with intratumoral CD8⁺ T-cell infiltration. This was detectable by ⁸⁹Zr-IAB22M2C-PET and γ-counting. Similarly, single-agent treatment with FOLR1-TCB induced strong CD8⁺ T-cell infiltration in HeLa tumors, where ⁸⁹Zr-Df-IAB22M2C again was able to detect CD8 tumor infiltrates. CD8-IHC confirmed the PET imaging results. Taken together, the anti-CD8-minibody ⁸⁹Zr-Df-IAB22M2C revealed a high sensitivity for the detection of intratumoral CD8⁺ T-cell infiltrates upon either single or combination treatment with TCB antibody-based fusion proteins. These results provide further evidence that the anti-CD8 tracer, which is currently in clinical phase II, is a promising monitoring tool for intratumoral CD8⁺ T cells in patients treated with cancer immunotherapy. SIGNIFICANCE: Monitoring the pharmacodynamic activity of cancer immunotherapy with novel molecular imaging tools such as ⁸⁹Zr-Df-IAB22M2C for PET imaging is of prime importance to identify patients responding early to cancer immunotherapy.

Abstract 1552: A novel PD1-IL2v immunocytokine for preferential cis-activation of IL-2R signaling on PD-1 expressing T cell subsets strongly potentiates anti-tumor T cell activity of PD-1 checkpoint inhibition and IL-2R-beta-gamma agonism

High-dose IL-2 is approved for patients with metastatic melanoma and renal cell cancer, but is associated with significant toxicity. We have described tumor-targeted CEA-IL2v and FAP-IL2v immunocytokines that are based on an engineered IL2v moiety with abolished binding to IL-2Ra (CD25) to avoid undesired CD25-mediated toxicities and Treg expansion. Their antibodies bind with high affinity to either CEA or FAP, which are broadly expressed in various tumors, and mediate retention/accumulation in malignant lesions. In an effort to further maximize the potency of IL-2R activation of T cells (aka signal 3) without the side effects of wildtype IL-2, we have generated PD1-IL2v that binds to the checkpoint inhibitor PD-1 and delivers IL2v preferentially in cis to PD-1+ T cells substituting binding to CD25. This enables high affinity IL2R signaling selectively in recently primed antigen specific TILs and stem-cell like subsets. Binding/competition experiments demonstrated that PD1-IL2v is 50-fold more potent than FAP-IL2v in inducing p-STAT5 in PD-1 positive T cells, whereas it has equivalent potency on PD-1 negative T cells. Notably, although Tregs can express low constitutive levels of PD-1, PD1-IL2v shows preferential binding to Teff vs. Tregs. Furthermore, PD1-IL2v can overcome Treg suppression of Tconv effector cells to a greater extent than PD-1, FAP-IL2v or their combination. For use in syngeneic mouse models muPD1-IL2v was generated. In an orthotopic pancreatic Panc02-Luciferase model administration of muPD1-IL2v (1 mg/kg IV, qw) resulted in rapid and complete elimination of tumor cells (loss of luciferase signal) and in long term survival (> 140 days) in 7/7 treated animals with protection from tumor cell re-challenge, whereas only 1/7 animals in the muPD-1 + muFAP-IL2v combination group (10 mg/kg + 2.5 mg/kg IV, qw) and none of the animals treated with the respective monotherapies showed long term survival. IHC showed that the improved outcome with muPD1-IL2v was related to a strong intra-tumoral increase of CD3+ CD8+ T cells expressing PD-1 and GrzB. In an immuno-PD study with s.c. Panc02 tumors muPD1-IL2v strongly increased the number of IFNg+ TNFa+ multifunctional and cytotoxic GrzB+ PD-1+ T cells in the tumor accompanied with a 20-fold increase in CD8/CD4 ratio and a strong increase in the CD8+ TEM population resulting in subsequent tumor control or remission in 50% of the animals, respectively. In summary, our data demonstrate that preferential cis-targeting of IL2v to PD-1+ antigen specific T cells with PD1-IL2v results in a strong potentiation of T cell response and anti-tumor efficacy as compared to the combination of PD-1 checkpoint inhibition with FAP-IL2v. These preclinical data establish PD1-IL2v as a promising next generation IL-2 for cancer immunotherapy.

Citation Format: Christian Klein, Laura Codarri-Deak, Valeria Nicolini, Stefan Seeber, Laura Lauener, Marine Richard, Esther Bommer, Maria Karagianni, Johannes Sam, Ramona Schlenker, Marisa Mariani, Petra Petra Schwalie, Sylvia Herter, Marina Bacac, Inja Waldhauer, Anne Freimoser-Grundschober, Volker Teichgraeber, Pablo Umana. A novel PD1-IL2v immunocytokine for preferential cis-activation of IL-2R signaling on PD-1 expressing T cell subsets strongly potentiates anti-tumor T cell activity of PD-1 checkpoint inhibition and IL-2R-beta-gamma agonism [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 1552.

Abstract 1129: Monitoring intratumoral CD8 T cell infiltrates in human stem cell engrafted mice during single agent and combination immunotherapy with T cell bispecific antibodies using the human PET-tracer 89Zr-Df-IAB22M2C

A persisting challenge in cancer immunotherapies (CIT) is the determination of patients responding early during therapy. As major effector cells, CD8 cytotoxic T cells are a primary target of many CIT approaches. ImaginAb is developing a human CD8 specific minibody 89Zr-Df-IAB22M2C to monitor CD8 tumor infiltrates non-invasively, longitudinally and throughout the whole body using positron emission tomography (PET). We evaluated pre-clinically the capability of this tracer to quantify CD8 tumor infiltrates upon treatment with T cell activating molecules using both, single agent FOLR1-T cell bispecific (TCB) antibody and the combination of CEA-TCB with a CEA-targeted 4-1BBL (CEA-4-1BBL).

In the first study, HeLa-cervical cancer xenograft bearing CD34+ human stem cell engrafted NSG mice (HSC-NSG) were treated for 2 weeks with FOLR1-TCB (2 mg/kg, once weekly), an untargeted control DP47-TCB and vehicle followed by PET imaging with the CD8 specific 89Zr-Df-IAB22M2C tracer (90-95 µCi/10 µg). In the second study, MKN-45 gastric cancer bearing HSC-NSG mice were treated with CEA-TCB (2.5 mg/kg, 2x/week), CEA 4-1BBL (3.0 mg/kg, 1x/week) or the combination of both compounds for two weeks followed by PET imaging with the CD8 tracer (50-60 µCi/10 µg). Ex vivo γ-counting of tumors and organs of interest as well as CD8 IHC was performed for both studies.

Treatment with FOLR1-TCB induced the highest tumor regression and strongest CD8+ T cell infiltrates. 89Zr-Df-IAB22M2C was able to detect tumor infiltrates by PET and γ-counting (13.6±2.7 %ID/g), whereas treatment with untargeted DP47-TCB induced a low T cell infiltrate (8.7±3.2 %ID/g) as compared to the vehicle group (5.6±1.2 %ID/g). In the second study, combined treatment with CEA-TCB and CEA-4-1BBL induced the highest tumor regression accompanied by the highest intratumoral CD8 T cell infiltrates, which were detectable by PET and γ-counting

(8.95±2.47 %ID/g). Single agent CEA-TCB (6.91±1.61 %ID/g) and CEA-4-1BBL (6.24±1.11 %ID/g) showed higher signals compared to vehicle (4.87±1.18 %ID/g). The differences in CD8 infiltrate upon single and combination treatment was confirmed by IHC.

The 89Zr-Df-IAB22M2 PET-tracer proved to be highly sensitive for the detection of intratumoral CD8 T cell infiltrates upon single and combination treatment with T cell activating compounds. These data correlated with CD8 IHC. These results provide further evidence that the CD8 imaging probe, which is currently in Phase II clinical testing (NCT03107663), may be a promising tool for the monitoring of CD8 T cells in patients treated with immunotherapies.

Citation Format: Christoph M. Griessinger, Alessandro Mascioni, Fang Jia, Michael Torgov, Tapan Nayak, Preethi Latha Bhavani Mohan, Valeria G. Nicolini, Johannes Sam, Christina Claus, Claudia Ferrara-Koller, Marina Bacac, Pablo Umana, Ian Wilson, Christian Klein, Jean J. Tessier. Monitoring intratumoral CD8 T cell infiltrates in human stem cell engrafted mice during single agent and combination immunotherapy with T cell bispecific antibodies using the human PET-tracer 89Zr-Df-IAB22M2C [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 1129.

p95HER2-T cell bispecific antibody for breast cancer treatment

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.

Abstract LB-292: p95HER2-T cell bispecific antibody for breast cancer treatment

T cell bispecific antibodies (TCBs) are engineered molecules that include, within a single entity, binding sites to the T cell receptor and to a tumor-specific or a tumor-associated antigen. The receptor tyrosine kinase HER2 is a tumor-associated antigen in ~25% of breast cancers. Clinical evidence shows that TCBs targeting HER2 may result in severe toxicities, likely due to the physiologic levels of HER2 in normal epithelia. Approximately 40% of HER2-positive tumors express detectable levels of p95HER2, a carboxy-terminal fragment of HER2. We previously developed different antibodies that specifically recognize p95HER2 but not full-length HER2 and hypothesized that a TCB antibody recognizing p95HER2 would be exquisitely specific for tumor cells. Here, we describe the development of such p95HER2-TCB and show that it has a potent anti-tumor effect on p95HER2-expressing breast cancers. Since p95HER2 is not expressed in normal tissues, in contrast with HER2-TCB, it has no effect on non-transformed cells expressing physiological levels of HER2. These data paves the way for the safe targeting of a subtype of HER2-positive tumors with a novel tumor-specific TCB.

Citation Format: Rocío Vicario, Irene Rius Ruiz, Beatriz Morancho, Cristina Bernadó Morales, Sylvia Herter, Anne Freimoser-Grundscholber, Jitka Somandin, Johannes Sam, Oliver Ast, Águeda Martinez Barriocanal, Antonio Luque, Marta Escorihuela, Ismael Varela, Paolo Nuciforo, Roberta Fasani, Vicente Peg, Isabel Rubio, Javier Cortés, Violeta Serra, Santiago Escrivá, Jeff Sperinde, Ahmed Chenna, Weidong Huang, John Winslow, Maurizio Scaltriti, Josep Baselga, Josep Tabernero, Pablo Umaña, Marina Bacac, Cristina Saura, Christian Klein, Joaquín Arribas. p95HER2-T cell bispecific antibody for breast cancer treatment [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 LB-292.

Abstract 957: Design of CD19-4-1BBL, a novel CD19-targeted 4-1BB ligand for combination therapy with CD20 T-cell bispecific antibodies and CD20 antibodies

Co-stimulation through 4-1BB has shown promising anti-tumor activity in preclinical models, but the development of 4-1BB agonistic antibodies in the clinic has been hampered by Fc-mediated liver toxicity. Here, we describe a novel CD19-targeted 4-1BB ligand designed to deliver a safe but potent 4-1BB agonist to effector T and NK cells with the goal to improve treatment of B cell malignancies. The antibody fusion protein is composed of split trimeric 4-1BB ligands and a tumor antigen targeting moiety recognizing CD19 fused to a silent Fc part (CD19-4-1BBL). The construct is devoid of FcgR-mediated crosslinking responsible for Fc-mediated toxicity and reintroduces 4-1BB hyperclustering upon binding to CD19 on B cells exclusively. In mice and cynomolgus monkeys, CD19-4-1BBL shows IgG-like pharmacokinetic properties. When cross-linked via CD19 on Non-Hodgkin Lymphoma cell lines or normal B cells, CD19-4-1BBL is biologically active in co-stimulating T cells. As 4-1BB is an inducible protein on activated T cells and NK cells, we combined CD19-4-1BBL with a T cell bispecific Ab targeting CD20 (CD20-TCB) to provide initial T cell activation while engaging with CD19+CD20+ tumor cells. In vitro, pre-treatment with CD20-TCB mediates the clustering of CD19-4-1BBL molecules to the interaction synapse of T cells and tumor cells. Live imaging revealed that the addition of CD19-4-1BBL induces significantly prolonged T cell-tumor contact (>30 min), leading to fast and efficient killing of tumor cells. In vivo in WSU-DLCL2-bearing human stem cell engrafted NSG mice (HSC-NSG) mice, CD20-TCB treatment quickly up-regulates 4-1BB on activated T cells, resulting in tumor growth inhibition. The combination of CD19-4-1BBL and CD20-TCB (used at a suboptimal dose) synergizes to eradicate the tumor completely. The combination induces strong T cell infiltration into the tumor, accompanied by an elevated CD8/Treg ratio, as compared to the monotherapies. Similarly, the combination also induces complete remission in a “difficult-to-treat” Nalm6 tumor model associated with low and patchy CD20 expression, mimicking patterns seen in the ABC subtype of DLBCL. Finally, the combination of CD19-4-1BBL and the ADCC-enhanced Type II CD20 antibody obinutuzumab induces complete tumor remissions in WSU-DLCL2 tumor-bearing HSC-NSG mice, confirming effective 4-1BB co-stimulation on NK cells. Taken together, tumor-targeted cross-linking of 4-1BB mediated by CD19-4-1BBL provides safe and efficient co-stimulation of T cells that are pre-activated by a TCB, or of NK cells pre-activated by an ADCC mediating antibody. This novel and effective combination immunotherapy warrants clinical investigation and offers possible “chemo-free” treatment of B cell malignancies.

Citation Format: Wei Xu, Johannes Sam, Mario Perro, John Challier, Christina Claus, Stanford Chen, Claudia Ferrara Koller, Michael Mølhøj, Stella Tournaviti, Marina Bacac, Tom Moore, Christian Klein, Pablo Umana. Design of CD19-4-1BBL, a novel CD19-targeted 4-1BB ligand for combination therapy with CD20 T-cell bispecific antibodies and CD20 antibodies [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 957.

Abstract 5621: FAP-4-1BBL: A novel versatile tumor-stroma targeted 4-1BB agonist for combination immunotherapy with checkpoint inhibitors, T-cell bispecific antibodies, and ADCC-mediating antibodies

For tumor specific co-stimulation via 4-1BB (CD137) a novel tumor-stroma targeted FAP-4-1BB ligand (FAP-4-1BBL) was designed composed of a trimeric split 4-1BBL, a tumor-stroma targeted 4B9 Fab moiety recognizing fibroblast activation protein (FAP) and a heterodimeric Fc-region devoid of FcgR binding but maintained FcRn binding. In presence of a TCR signal 1 either from a T cell receptor MHCI/peptide interaction or through TCR engagement by a T-cell bispecific antibody, FAP-4-1BBL provides co-stimulation to T cells strictly dependent on cross-linking by FAP-expressing fibroblasts. Similarly, FAP-4-1BBL can provide co-stimulation to NK cells with activated FcgRIIIa signaling. FAP-4-1BBL was tested as monotherapy and combined with CEA-TCB, an anti-CEA T-cell bispecific antibody, in the s.c. gastric MKN45 xenograft model co-grafted with NIH-3T3 fibroblasts in human stem cell engrafted (HSC) NSG mice in comparison to DP47-4-1BBL, an analogous untargeted 4-1BBL fusion protein. For use in syngeneic mouse models in immunocompetent mice muFAP-4-1BB, a murine surrogate made of a mu4-1BB agonistic surrogate antibody fused to the variable region of the FAP antibody 4B9, was used. muFAP-4-1BB was tested as monotherapy and combined with a murine specific CEA-TCB surrogate (muCEA-TCB) and the muPD-L1 specific surrogate antibody 6E11 in the s.c. colorectal MC38-CEA model in CEA transgenic (Tg) C57BL/6 mice. For combination with ADCC-mediating antibodies FAP-mu4-1BBL, a hybrid FAP-mu4-1BBL fusion protein, was generated. FAP-mu4-1BBL was tested as monotherapy and combined with the ADCC-mediating anti-HER2 antibody trastuzumab in the s.c. gastric N87 xenograft model in human CD16 Tg Scid mice. In the s.c. gastric MKN45 xenograft model co-grafted with NIH-3T3 fibroblasts in HSC-NSG mice FAP-4-1BBL resulted in combined anti-tumoral efficacy in combination with CEA-TCB, whereas the respective monotherapies as well as the combination with the untargeted DP47-4-1BBL did not improve anti-tumor efficacy. In the syngeneic s.c. MC38-CEA model in CEA Tg C56BL/6 mice, a model with natural FAP expression due to fibroblast infiltration, the muFAP-4-1BB surrogate antibody resulted in combined anti-tumor efficacy, both combined with muCEA-TCB and muPD-L1 antibodies including the induction of tumor remission. Finally, the hybrid FAP-mu4-1BBL surrogate resulted in improved anti-tumor efficacy combined with the ADCC-mediating antibody trastuzumab in the s.c. gastric N87 xenograft model in human CD16 Tg Scid mice. These data show that FAP-4-1BBL is a versatile combination partner for cancer immunotherapy mediating FAP-dependent co-stimulation to T and NK cells in combination with PD-L1 checkpoint inhibition, TCBs and ADCC-mediating antibodies. Clinical evaluation of this novel therapeutic approach is planned early 2018.

Citation Format: Johannes Sam, Christina Claus, Claudia Ferrara, Sabine Lang, Valeria Nicolini, Sara Colombetti, Volker Teichgräber, Stefan Evers, Marina Bacac, Pablo Umana, Christian Klein. FAP-4-1BBL: A novel versatile tumor-stroma targeted 4-1BB agonist for combination immunotherapy with checkpoint inhibitors, T-cell bispecific antibodies, and ADCC-mediating antibodies [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 5621.

CD20-TCB with Obinutuzumab Pretreatment as Next-Generation Treatment of Hematologic Malignancies

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.

Abstract PD2-16: Risk of breast cancer after a false-positive screening mammogram in relation to mammographic abnormality: A population-based study in British Columbia

Background

Breast cancer screening by mammography has been shown to reduce breast cancer mortality, however false positive recall rates have consistently been identified as a harm of organized screening. The extent to which these recalled women are at increased risk of future breast cancer remains unclear.

Methods

The British Columbia Cancer Agency Screening Mammography Program (SMP), the first organized breast screening program in Canada offers screening mammography for women aged 40-74 since 1988. All women who had two or more screening mammograms between1988-2013 within the SMP were included in the study. They were followed until a breast cancer diagnosis, last screen date +5 years, or end of follow-up on Dec 31, 2013, whichever came first. The relative risk (RR) of breast cancer for women with a false-positive test compared with women with negative tests was estimated with Poisson regression, adjusted for age, and five calendar periods.

Results

A total of 772,289 women with 4.82 million screening mammograms and a median follow up of 11.8 years were included. There were 238,860 women with false positive findings and 26,950 cancers of which 16,084 screen detected and 10,866 non screen detected. Women without any false positive mammogram had a cancer incidence rate of 245/100 000 person-years at risk, whereas women with a false-positive test had an absolute rate of 447/100 000 person-years at risk. The adjusted RR [Value (95% CI)] of breast cancer after the first false-positive test was 1.73(1.68-1.77) for all, 1.65(1.61-1.70) for invasive, and 2.13(2.01-2.27) for in situ cancers respectively. The RR remained increased beyond 8 years after the false-positive test. Of the 5157 screen detected cancers after the first false positive test, 3358 (65%) were on the ipsilateral breast while 1799 (35%) were on the contralateral breast. Women with only one, two, three or four+ false positive test(s) had RR of 1.88(1.83-1.93), 1.42(1.35-1.49), 1.17(1.05-1.30), and 1.08(0.87-1.34) respectively for all cancers. Women with breast density >50% at the time of false positive test had a twofold risk of breast cancer with a RR of 2.07(1.99-2.14), while those with breast density <50% had a RR of 1.58(1.54-1.63). When stratified for mammographic features found on the first false positive mammogram, architectural distortion plus mass had the highest RR 4.68(3.16-6.93) for invasive cancers while calcifications alone and calcifications plus asymmetry had highest RR 5.57(4.88-6.36) and 4.07(2.49-6.66) for in situ cancers.

Conclusion

False positive mammogram correlates with an increased risk of developing breast cancer. 65% of the screen detected breast cancers post false positive mammogram occur in the ipsilateral breast. Mammographic abnormality features of the false positive mammogram are found to be predictors for the type of future breast cancer. Mammographic features at the time of recall predicts risk of subsequent cancer and may warrant increased surveillance.

Citation Format: Rajapakshe R, Miao H, Sam J, Farnquist B, Hartman M. Risk of breast cancer after a false-positive screening mammogram in relation to mammographic abnormality: A population-based study in British Columbia [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD2-16.

Abstract 3634: A novel tumor-targeted 4-1BB agonist and its combination with T-cell bispecific antibodies: an off-the-shelf cancer immunotherapy alternative to CAR T-cells

Immune cell costimulation via 4-1BB agonism has shown anti-tumor activity in the clinic and is an important element of next-generation chimeric-antigen-receptor (CAR) adoptive T-cell therapy approaches. However, the clinical development of first-generation, 4-1BB agonistic antibodies has been hampered by significant hepatic toxicity. Activity of such first-generation, 4-1BB agonistic antibodies typically depends on their hyperclustering via Fc-gamma-receptor (FcgR)-binding. Here we describe a next generation, tumor-targeted 4-1BB agonist whose activity is independent of FcgR-binding. The molecule consists of an IgG fusion protein composed of a trimeric, human 4-1BB ligand (4-1BBL), a targeting Fab moiety recognizing fibroblast activation protein (FAP), and a heterodimeric Fc region engineered to be devoid of interactions with FcgRs and C1q. The molecule mediates potent costimulation of CD8 T-, CD4 T- and NK-cells, but only in the presence of FAP-expressing cells, such as cancer associated fibroblasts, which are highly prevalent in many solid tumors. This FAP-targeted 4-1BB agonist is significantly more potent and efficacious than first generation, standard 4-1BB agonistic antibodies when compared side-by-side in preclinical models. We show its activity in a variety of preclinical models including reporter cell assays, assays with primary T- and NK-cells, ex-vivo assays with patient tumor-derived material including cancer cells, stroma cells and tumor-infiltrating lymphocytes, fully immunocompetent murine tumor models (employing a surrogate, murinized molecule targeting murine FAP and carrying murine 4-1BBL), and in human hematopoietic stem cell-humanized mice with human tumor xenografts. We also demonstrate its activity in combination with checkpoint inhibitors and with T-cell redirecting approaches, such as a CEA-CD3 T-cell bispecific antibody. We show that hepatic toxicity of first generation, standard 4-1BB antibodies is dependent on FgR interactions and the next generation, FcgR-independent and FAP-targeted molecule described here is safe and does not induce any hepatotoxicity in preclinical models including non-human primates where it was tested at doses of up to 50 mg/kg and where it showed a long circulatory half-life. Its combination with T-cell bispecific antibodies induces a massive T cell accumulation in the tumor, accompanied with an elevated CD8/Treg ratio, as compared to the respective monotherapies. Therefore, we conclude that the tumor-targeted cross-linking of 4-1BB provides a safe and effective way for the co-stimulation of T cells for cancer immunotherapy and its combination with T-cell bispecific antibodies may provide an alternative, but more convenient, off-the-shelf approach to CAR T-cell therapies. The molecule is scheduled to enter clinical trials soon.

Citation Format: Christina Claus, Claudia Ferrara, Sabine Lang, Rosmarie Albrecht, Sylvia Herter, Maria Amann, Sandra Richards-Grau, Johannes Sam, Sara Colombetti, Marina Bacac, Christian Klein, Pablo Umana. A novel tumor-targeted 4-1BB agonist and its combination with T-cell bispecific antibodies: an off-the-shelf cancer immunotherapy alternative to CAR T-cells [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 3634. doi:10.1158/1538-7445.AM2017-3634

Abstract 1594: Enhancement of the anti-tumor activity of CEA TCB via combination with checkpoint blockade by PD-L1 and interleukin-2 variant immunocytokine

Cancer immunotherapy represents a promising therapeutic approach to extend the overall survival of cancer patients. However, several mechanisms within the tumor microenvironment orchestrate the suppression of host immune response requiring combination strategies to prolong the durability of effect. Among suppressive pathways, up-regulation of PD-1 ligand (PD-L1) and its interaction with PD-1 receptor plays a key role in suppression of T-cell activity, a mechanism also called adaptive immune resistance. Therefore, approaches able to inhibit the tumor immune suppressive mechanisms along with those expanding the frequency of intra-tumor T-cells and enhancing/prolonging their functionality are required.

CEA TCB (RG7802, RO6958688) is a novel T cell bispecific antibody targeting carcinoembryonic antigen (CEA) on tumor cells and CD3 on T cells, currently being investigated as single agent and in combination with atezolizumab in Phase 1/1b studies in patients with advanced and/or metastatic CEA-expressing tumors (NCT02324257; NCT02650713). CEA TCB treatment leads to increased intra-tumoral T cell infiltration and T-cell activation along with up-regulation of PD-1/PD-L1 suppressive pathway. Here we show that combination of CEA TCB with PD-L1 blocking antibody in vitro enhances T cell activation as detected by increased CD3 signaling and secretion of pro-inflammatory cytokines. Combination in vivo performed in both stem cell humanized NOG mice (HSC mice engrafted with MKN45) and fully immunocompetent human CEA transgenic C56BL/6 mice (hCEA Tg mice engrafted with MC38-hCEA) demonstrated significantly improved anti-tumor activity of combination as compared to activity of single agents, yielding to increased number of tumor-free animals. Randomization of animals that progressed to CEA TCB monotherapy revealed that combination of CEA TCB with PD-L1 blocking antibody is required to control tumor outgrowth, as tumors treated with corresponding monotherapy arms progressed to treatment. Efficacy of CEA TCB was also potentiated when administered in combination with a half-life-extended IL-2 variant (untargeted (IgG-IL2v) or fibroblast-activating protein-targeted IL-2 variant (FAP-IL2v)), resulting in stronger tumor growth inhibition in MKN45-bearing HSC mice or prolonged survival in PanCO2-hCEA-bearing hCEA Tg C56BL/6 mice. Synergy likely reflects ability of IL2v to enhance anti-tumor efficacy by increasing number of effector T cells in tumors.

In conclusion, CEA TCB treatment leads to intra-tumoral T cell infiltration and T-cell activation. This is accompanied by up-regulation of PD-1/PD-L1 suppressive pathway, which can be overcome by combination therapy with a PD-L1 inhibitor. In vivo efficacy of CEA TCB is further potentiated when administered in combination with immunotherapies that increase the pool of available tumor-infiltrating effector cells.

Citation Format: Marina Bacac, Sara Colombetti, Linda Fahrni, Tanja Fauti, Valeria Nicolini, Johannes Sam, Petros Papastogiannidis, Marine Le Clech, Xavier Miot, Inja Waldhauer, Karolin Rommel, Christian Gerdes, Christian Klein, Pablo Umaña. Enhancement of the anti-tumor activity of CEA TCB via combination with checkpoint blockade by PD-L1 and interleukin-2 variant immunocytokine [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 1594. doi:10.1158/1538-7445.AM2017-1594

Abstract 3629: Engineering a novel asymmetric head-to-tail 2+1 T-cell bispecific (2+1 TCB) IgG antibody platform with superior T-cell killing compared to 1+1 asymmetric TCBs

T cell bispecific antibodies that recruit and engage T cells for tumor cell killing through binding to the T cell receptor (TCR) upon binding to a tumor antigen (TA) and subsequent crosslinking have attracted broad interest. Here, we describe a novel asymmetric head-to-tail 2+1 T cell bispecific antibody (2+1 TCB) platform characterized by the fusion of a flexible Fab fragment to the N-terminus of the CD3e Fab of a heterodimeric asymmetric bispecific TA-CD3e IgG1 antibody in head-to-tail geometry via a flexible linker. The resulting TCB is monovalent for CD3e (KD 70-100 nM) and binds bivalently with avidity to the TA on the target cell. Correct heavy chain pairing is enabled by knob-into-holes technology, correct light chain pairing by CrossMAb technology or using a common light chain. This enables production with standard processes in CHO cells. To exclude FcgR-mediated unspecific TCR and FcgR co-activation resulting in unspecific cytokine release, Fc- effector functions (ADCC, ADCP, CDC) are abolished by introduction of P329G LALA mutations while FcRn binding and IgG-like pharmacokinetic properties are retained as shown in mouse and Cynomolgus. For comparative profiling, the following TCBs were generated with specificity for the tumor antigens MCSP/CSPG4, FOLR1/FRalpha, CD19 and CD20: 2+1 TCBCD3-inside, 2+1 TCBCD3-outside, one-armed 1+1 TCBCD3-inside and a classical asymmetric 1+1 IgG TCB. In vitro Jurkat-NFAT, T cell killing, activation and proliferation assays show that both 2+1 TCB formats mediate superior potency of killing (for CSPG4, FOLR1, CD19, CD20) and superior absolute killing (for CSPG4, CD19) compared to the respective classical asymmetric 1+1 IgG TCB. Surprisingly, the 2+1 TCBCD3-inside format was found to be superior in potency compared to the 2+1 TCBCD3-outside format, although its binding affinity for CD3e is reduced. These data confirm that TCBs mediate extremely potent T cell killing with fM-pM EC50 values based on CD3e antibodies with affinities of only 70-100 nM. Notably, for CD19 both, 2+1 TCBCD3-inside and one-armed 1+1 TCBCD3-inside, mediate comparable potency and overall killing, and both were superior compared to the asymmetric 1+1 IgG TCB. These data underline the importance of the head-to-tail geometry with two Fabs on one arm attached to each other via a flexible G4S-linker. Finally, using 2+1 and 1+1 FOLR1 TCBs we demonstrate that bivalent binding allows better differentiation in killing of cells with high vs. low FOLR1 expression as compared to monovalent binding. Taken together, we demonstrate that the 2+1 TCBCD3-inside is the most potent, efficacious and versatile TCB design. Due to its orientation with the CD3e Fab inside, it allows the conversion of existing antibodies into potent TCBs without format restriction. Based on this platform, CEA CD3 TCB (RG7802, Phase I/Ib) and CD20 CD3 TCB (RG6026, Phase I) have entered clinical trials.

Citation Format: Christian Klein, Christiane Neumann, Tanja Fauti, Tina Weinzierl, Anne Freimoser-Grundschober, Inja Waldhauer, Linda Fahrni, Sylvia Herter, Erwin van Puijenbroek, Sara Colombetti, Johannes Sam, Sabine Lang, Sherri Dudal, Wolfgang Schäfer, Jörg T. Regula, Samuel Moser, Oliver Ast, Ralf Hosse, Ekkehard Mössner, Peter Brünker, Marina Bacac, Pablo Umana. Engineering a novel asymmetric head-to-tail 2+1 T-cell bispecific (2+1 TCB) IgG antibody platform with superior T-cell killing compared to 1+1 asymmetric TCBs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3629. doi:10.1158/1538-7445.AM2017-3629

Anti-tumoral, anti-angiogenic and anti-metastatic efficacy of a tetravalent bispecific antibody (TAvi6) targeting VEGF-A and angiopoietin-2

Vascular endothelial growth factor (VEGF)-A blockade has been validated clinically as a treatment for human cancers. Angiopoietin-2 (Ang-2) is a key regulator of blood vessel remodeling and maturation. In tumors, Ang-2 is up-regulated and an unfavorable prognostic factor. Recent data demonstrated that Ang-2 inhibition mediates anti-tumoral effects. We generated a tetravalent bispecific antibody (Ang-2-VEGF-TAvi6) targeting VEGF-A with 2 arms based on bevacizumab (Avastin®), and targeting Ang-2 with 2 arms based on a novel anti-Ang-2 antibody (LC06). The two Ang-2-targeting single-chain variable fragments are disulfide-stabilized and fused to the C-terminus of the heavy chain of bevacizumab. Treatment with Ang-2-VEGF-A-TAvi6 led to a complete abrogation of angiogenesis in the cornea micropocket assay. Metastatic spread and tumor growth of subcutaneous, orthotopic and anti-VEGF-A resistant tumors were also efficiently inhibited. These data further establish Ang-2-VEGF bispecific antibodies as a promising anti-angiogenic, anti-metastatic and anti-tumor agent for the treatment of cancer.

In Vivo Fluorescence Imaging of the Activity of CEA TCB, a Novel T-Cell Bispecific Antibody, Reveals Highly Specific Tumor Targeting and Fast Induction of T-Cell-Mediated Tumor Killing

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 AACRSee related commentary by Teijeira et al., p. 4277.

Abstract 2481: CEA TCB, a novel T-cell bispecific antibody with potent in vitro and in vivo antitumor activity against solid tumors

T cell bispecific antibodies (TCBs) are potent molecules that upon simultaneous binding to tumor cells and T cells trigger strong T cell activation resulting in the killing of tumor cells. CEA TCB (RG7813) is a novel bispecific antibody targeting carcinoembryonic antigen (CEA), often overexpressed on solid tumors (e.g. colorectal, gastric, pancreatic, lung carcinoma etc.), and the CD3 epsilon chain present on T cells.

CEA TCB bears several innovative technological features that distinguish it from other bispecific antibodies currently in (pre-)clinical development: (a) bivalency for tumor antigen translating into higher avidity, superior potency and better differentiation between high and low antigen-expressing cells; (b) head-to-tail fusion geometry for anti-tumor and CD3-binding domains, resulting in higher potency compared to conventional IgG-based TCBs; (c) extended half-life compared to non-Fc-based TCBs; (d) fully silent Fc ensuring lower risk of FcgR-mediated infusion reactions; and (e) robust production using standard manufacturing processes (enabled by “CrossMAb” and knob-into-hole bispecific antibody technologies).

In vitro, CEA TCB mediates potent target-dependent T cell cytotoxicity, T cell activation, proliferation, and cytokine release in killing assays, exclusively in the presence of CEA-expressing target-cells. CEA TCB activity correlates with CEA expression level, showing higher potency against tumor cells with high expression of CEA. In vivo, CEA TCB induces dose- and time-dependent regression of CEA-expressing tumors with variable amounts of immune cell infiltrate. In fully humanized NOG mice, CEA TCB is efficacious in poorly-infiltrated tumors and converts non-inflamed into highly-inflamed tumors. Histological and FACS analyses revealed that CEA TCB recruits new T cells into tumors and/or expands pre-existing ones and is able to induce T cell re-localization from the tumor periphery into the tumor bed. Surprisingly, CEA TCB treatment also qualitatively alters the composition of intratumoral T cells resulting in an increased frequency of activated (CD69, CD25), proliferating (Ki67) and differentiated T cells (having effector memory phenotype) that are ready to kill (express high levels of Granzyme B).

Taken together, these preclinical data show that CEA TCB is a novel tumor-targeted T cell bispecific antibody with promising anti-tumor activity and the novel ability to modify the tumor microenvironment. Phase 1 clinical trials with CEA TCB are currently ongoing. Future studies will focus on identification of combination partners that inhibit T cell suppression and unleash the full potential of T cell activity.

Citation Format: Marina Bacac, Tanja Fauti, Sara Colombetti, Johannes Sam, Valeria Nicolini, Nathalie Steinhoff, Oliver Ast, Peter Bruenker, Ralf Hosse, Thomas Hofer, Ekkehard Moessner, Christiane Jaeger, Jose Saro, Vaios Karanikas, Christian Klein, Pablo Umana. CEA TCB, a novel T-cell bispecific antibody with potent in vitro and in vivo antitumor activity against solid tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2481. doi:10.1158/1538-7445.AM2015-2481

Nanoscale oxidative patterning of metallic surfaces to modulate cell activity and fate

In the field of regenerative medicine, nanoscale physical cuing is clearly becoming a compelling determinant of cell behavior. Developing effective methods for making nanostructured surfaces with well-defined physicochemical properties is thus mandatory for the rational design of functional biomaterials. Here, we demonstrate the versatility of simple chemical oxidative patterning to create unique nanotopographical surfaces that influence the behavior of various cell types, modulate the expression of key determinants of cell activity, and offer the potential of harnessing the power of stem cells. These findings promise to lead to a new generation of improved metal implants with intelligent surfaces that can control biological response at the site of healing.

Simultaneous antegrade and retrograde reperfusion after cardioplegic arrest for coronary artery bypass

Retrograde coronary sinus reperfusion with warm blood during proximal anastomoses permits completion of myocardial revascularization under a single cross-clamp application. Reperfusion with both antegrade (via arterial and vein grafts) and retrograde (via coronary sinus catheter) warm blood has raised concerns about maldistribution of perfusate or overpressurization of capillary beds. This prospective, randomized design compares postcardioplegic myocardial recovery among patients receiving retrograde reperfusion only and patients receiving simultaneous antegrade/retrograde reperfusion. Twenty-four patients were selected among all presenting as outpatients for elective coronary artery bypass (CAB). Each patient underwent CAB with cardioplegic arrest and single cross-clamp technique. During proximal anastomoses the heart was reperfused with warm blood from the cardiopulmonary bypass (CPB) circuit. Twelve received retrograde reperfusion only, and 12 received simultaneous antegrade/retrograde reperfusion via an internal mammary artery (IMA) graft, all vein grafts, and the coronary sinus catheter. Vein graft perfusion was interrupted in each vein as the proximal anastomosis was performed. Myocardial recovery time (interval from initiating reperfusion until electrical and mechanical activity), cardioversion incidence, requirement for inotropic support, and Swan-Ganz hemodynamic parameters measured immediately 6 and 24 hours postoperatively were compared between groups. There were no differences between groups in age, ventricular function, number of grafts, or CPB time. Also, there were no differences in cardioversion, inotropic need, or postoperative hemodynamic performance. Myocardial recovery time was reduced in patients receiving simultaneous antegrade/retrograde reperfusion (13.9+/-7.0 vs 2.6+/-2.1 minutes). Simultaneous reperfusion of warm blood antegrade and retrograde is not deleterious to the myocardium. More rapid recovery of myocardial function may represent a shorter period of warm ischemia but does not appear to translate to improved postoperative myocardial performance.

Use of a heat exchanger to prevent hypothermia during thoracic and thoracoabdominal aneurysm repairs

Hypothermia is a common unplanned occurrence in many patients undergoing repair of thoracic and thoracoabdominal aneurysms. Many undesirable side effects of hypothermia have been documented, including decreased cardiac output, conduction abnormalities, and blood coagulopathies. We have developed a simple system that incorporates a Sci-Med Biotherm heat exchanger into our left heart bypass circuit. This provides us with the ability to actively rewarm the patient safely and efficiently. This study looks at 16 consecutive patients undergoing repair of thoracic or thoracoabdominal aneurysms. In the 9 patients in whom the heat exchanger was used, there were no adverse effects related to the heat exchanger. All patients had significantly higher temperatures at the conclusion of the procedure than the 7 patients in whom the heat exchanger was not used.

Phase I and pharmacokinetic evaluation of thiotepa in the cerebrospinal fluid and plasma of pediatric patients: evidence for dose-dependent plasma clearance of thiotepa

A Phase I trial of thiotepa (TT) administered as an i.v. bolus was performed in 19 children with refractory malignancies. The starting dose was 25 mg/m2 with escalations to 50, 65, and 75 mg/m2. Seven additional patients were treated with 8-h infusions at 50 or 65 mg/m2. The maximum tolerated bolus dose was 65 mg/m2. Reversible myelosuppression was the dose-limiting toxicity. The plasma and cerebrospinal fluid (CSF) pharmacokinetic parameters of TT and its major active metabolite tepa (TP) were also evaluated. When the bolus or infusion methods of TT administration were compared, there was little difference observed in any pharmacokinetic parameter for either TT or TP. The plasma disappearance of TT was rapid and biphasic with half-lives of 0.14 to 0.32 and 1.34 to 2.0 h. Dose-dependent pharmacokinetics was demonstrated by steadily declining plasma clearance with increasing TT dose. Clearance values declined from 28.6 liters/m2/h at the 25-mg/m2 dose to 11.9 liters/m2/h at the 75-mg/m2 dose. The half-life of TP was longer than that of TT and ranged between 4.3 and 5.6 h. There was evidence of the saturation of TP production. TT and TP both exhibited excellent penetration into the CSF, producing lumbar and ventricular concentrations which were nearly identical to simultaneous plasma concentrations. In one patient with a Rickham reservoir, the CSF:plasma area under the (concentration x time) curve ratios for TT and TP were 1.01 and 0.95, respectively. The above data indicate that TT can be safely administered to pediatric patients at doses higher than conventionally used. The favorable CSF penetration of TT and TP suggests that Phase II studies of TT be considered in patients with central nervous system tumors.

Epimeric 5-hydroxy-5-phenyl-1-azabicyclo [5.4.0] undecanes

The development of order during the aging of aluminum hydroxide gel prepared by the reaction of aluminum chloride and ammonium hydroxide to a final pH of 7.0 can be monitored by differential thermal analysis. The loss fo acid reactivity upon aging is accompanied by an increase in the temperature and intensity of the dehydroxylation endotherm and an accompanying decrease in the intensity of the water of hydration endotherm. With continued aging, the thermogram develops the characteristics of a crystalline aluminum hydroxide.

3-Arylquinolizidines, potential antidepressant agents

The synthesis, structure elucidation, and pharmacological evaluation of some 3-arylquinolizidines as semirigid phenethylamines are described. Many of the derivatives posses antidepressant activity. Some anticonvulsant effects are noted.