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NHS-muIL12 and avelumab combination treatment enhanced the necrotic fraction in EMT-6 tumors.

Purpose: To determine whether combination therapy with NHS-muIL12 and the anti-programmed death ligand 1 (PD-L1) antibody avelumab can enhance antitumor efficacy in preclinical models relative to monotherapies.Experimental Design: BALB/c mice bearing orthotopic EMT-6 mammary tumors and μMt− mice bearing subcutaneous MC38 tumors were treated with NHS-muIL12, avelumab, or combination therapy; tumor growth and survival were assessed. Tumor recurrence following remission and rechallenge was evaluated in EMT-6 tumor-bearing mice. Immune cell populations within spleen and tumors were evaluated by FACS and IHC. Immune gene expression in tumor tissue was profiled by NanoString® assay and plasma cytokine levels were determined by multiplex cytokine assay. The frequency of tumor antigen–reactive IFNγ-producing CD8+ T cells was evaluated by ELISpot assay.Results: NHS-muIL12 and avelumab combination therapy enhanced antitumor efficacy relative to either monotherapy in both tumor models. Most EMT-6 tumor–bearing mice treated with combination therapy had complete tumor regression. Combination therapy also induced the generation of tumor-specific immune memory, as demonstrated by protection against tumor rechallenge and induction of effector and memory T cells. Combination therapy enhanced cytotoxic NK and CD8+ T-cell proliferation and T-bet expression, whereas NHS-muIL12 monotherapy induced CD8+ T-cell infiltration into the tumor. Combination therapy also enhanced plasma cytokine levels and stimulated expression of a greater number of innate and adaptive immune genes compared with either monotherapy.Conclusions: These data indicate that combination therapy with NHS-muIL12 and avelumab increased antitumor efficacy in preclinical models, and suggest that combining NHS-IL12 and avelumab may be a promising approach to treating patients with solid tumors. Clin Cancer Res; 23(19); 5869–80. ©2017 AACR.

Supplementary Materials and Methods

Although PD-1/PD-L1 therapies have shown significant activity across a range of tumor types, only a subset of patients (10-30%) achieve durable responses. With the goal of improving response and application to PD-1/PD-L1 therapies, we have leveraged our proprietary Xilio Advanced Cytokine Therapies (X-ACT) platform to develop PD1/IL2-ACT, a PD-1 blocker enhanced with a tumor-activated, engineered IL-2 agonist. The activity of IL-2 is blocked by a protein domain that prevents IL-2Rβγ binding until activated in the tumor microenvironment by matrix metalloproteinases . Tumor selective activation of IL-2 enables dosing of PD1/IL2-ACT at sufficient exposure levels to block immunosuppressive PD1/PD-L1 signaling as well as mitigating systemic IL-2 driven toxicity. PD1/IL2-ACT is designed to enable in cis engagement of IL-2 receptors on antigen experienced PD-1+ CD8+ T cells in the tumor microenvironment (TME), inducing effector T cell functions while preventing regulatory T cell (Treg) mediated immune suppression. In a preclinical model, PD1/IL2-ACT, compared to anti-PD1 alone, induced significant tumor growth inhibition. Further, PD1/IL2-ACT was better tolerated than a PD-1 directed unmasked IL-2Rβγ biased agonist in the same preclinical model. Pharmacodynamic studies showed that PD1/IL2-ACT did not significantly change immune cell profiles in the periphery but increased antigen specific CD8+ T cells in the TME, consistent with preferential engagement of PD1+ effector T cells at the tumor site. Ex vivo protease cleavage assays performed in human tumors demonstrated significant activation of PD1/IL2-ACT by tumors of multiple indications but minimal activation in human plasma. A pharmacokinetic study in nonhuman primates revealed PD1/IL2-ACT can achieve comparable exposure levels to existing PD-1 blocking immunotherapies. Taken together, these data illustrate that PD1/IL2-ACT has the potential to broaden the activity of existing immunotherapies by inhibiting the PD1/PDL1 axis as well as directing an immunostimulatory cytokine to antigen specific T cells in the TME. Citation Format: Ertan Eryilmaz, Wilson Guzman, Dheeraj S. Tomar, Parker Johnson, Stephanie Hsiao, Lisa Quinn, Nancy Chan, Jimit Lakhani, Brendan Whalen, Rosa Quiroz, Kurt Jenkins, Oleg Yerov, Will Scott, Justin Greene, Zhen Liu, Megan McLaughlin, Sallyann Vu, Chelsea Turcotte, Hanumantha R. Madala, Jacob Taylor, Caitlin O'Toole, Magali Pederzoli-Ribeil, Haley Duprey, Natalia Malkova, Damiano Fantini, David Crowe, Sean Yang, Kyle Smith, Joseph Card, Janice Lee, Kerri Smith, Benjamin Nicholson, Jijun Dong, Jennifer O'Neil, Carl U. Bialucha. Tumor-activated PD1-directed IL-2 increased antigen specific T cells in tumors and demonstrated anti-tumor activity in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 572.

Interleukin-12 (IL-12) is a proinflammatory cytokine, which bridges innate and adaptive immunity via induction of T helper 1 differentiation and promotes cytolytic activity of natural killer and T cells. IL-12 has demonstrated potent antitumor activity in syngeneic mouse models and promising anti-tumor efficacy in humans. However, development of IL-12-based treatments has been limited by severe systemic toxicities in the clinical setting. To overcome toxicity and potentially improve the therapeutic index of IL-12 in a clinical setting, XTX301 was engineered as a half-life extended and masked IL-12. The masking domain of XTX301 is designed to pharmacologically inactivate IL-12 in circulation and non-tumor tissue, while enabling generation of an active IL-12 moiety upon cleavage of a linker sequence by matrix metalloproteinases that are enriched in the tumor microenvironment. To confirm the ability of human tumor associated proteases to activate XTX301, cleavage was assessed in primary human tumor samples and in plasma from cancer patients. We observed cleavage of XTX301 in the majority of human tumors samples tested, but no activation was observed in plasma from cancer patients. Human IL-12 does not bind and signal through the mouse IL-12 receptors, hence three murine surrogates were created for in vivo studies: mXTX301, a non-cleavable control, and an unmasked control molecule. Tumor growth inhibition was observed after a single dose of mXTX301 as low as 0.039 mg/kg. The non-cleavable form of mXTX301 was less potent than mXTX301, demonstrating that the anti-tumor activity of mXTX301 is dependent on protease activation. The unmasked control was not well tolerated, with a > 20% body weight loss observed by Day 6, resulting in 75% of animals being euthanized by Day 11. Unlike the unmasked control, mXTX301 was well-tolerated at all tested doses, as evidenced by no loss in animals’ body weights, and demonstrated minimal pharmacodynamic activity in non-tumor tissues. In tumors, mXTX301 stimulated the infiltration of cytotoxic CD8+ T cells and induced the expression of several immune-related genes including those associated with IFN-γ cell signaling, antigen processing and presentation, and defense response as well as enrichment of gene signatures for T cells, natural killer (NK) cells, macrophages and dendritic cells as determined by RNA sequencing. In non-human primates, the highest non-severely toxic dose of XTX301 was 2mg/kg dosed weekly for a total of 4 doses. In summary, a half-life extended tumor-activated IL-12 molecule, mXTX301, demonstrated anti-tumor activity in preclinical mouse models with improved tolerability compared to a systemically active IL-12 molecule suggesting that XTX301 has potential for exerting potent anti-tumor activity while widening the therapeutic index of IL-12 treatment. Citation Format: Natalia Malkova, Ekta Patel, Sallyann Vu, Damiano Fantini, Rebekah O'Donnell, Manoussa Fanny, Justin Greene, Wilson Guzman, David Crowe, Stephanie Hsiao, Parker Johnson, Megan McLaughlin, Oleg Yerov, Kurt Jenkins, Katarina Halpin-Veszeleiova, Hanumantha Rao Madala, Caitlin O'Toole, Jake Taylor, Magali Pederzoli-Ribeil, Benjamin Nicholson, Carl Uli Bialucha, Jennifer E. O'Neil. A half-life extended, tumor-activated IL-12 increased the infiltration of effector immune cells into the tumor microenvironment and demonstrated anti-tumor activity in syngeneic mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 587.

BackgroundInterleukin-12 (IL-12) is a proinflammatory cytokine which bridges innate and adaptive immunity via induction of T helper 1 differentiation and promoting cytolytic activity of natural killer and T cells. IL-12 has demonstrated potent antitumor activity in syngeneic mouse models and promising anti-tumor efficacy in humans. However, development of IL-12 has been limited by severe systemic toxicities. To overcome toxicity and improve the therapeutic index of IL-12, we employed protein engineering to generate XTX301, a highly potent, half-life extended and masked IL-12. The masking domain of XTX301 is designed to pharmacologically inactivate IL-12 systemically and render an active IL-12 moiety upon cleavage by proteases that are enriched in the tumor microenvironment.MethodsWe conducted experiments to assess the binding, bioactivity, safety, and anti-tumor efficacy of XTX301. Binding interactions were measured via SPR, bioactivity was measured using STAT-4 phosphorylation in a reporter cell line, and IFN-g production was assessed in human PBMCs via ELISA. Anti-tumor efficacy and pharmacodynamics were assessed in MC38 and B16F10 syngeneic tumor mouse models using a XTX301 murine surrogate, mXTX301. Safety and pharmacokinetics of XTX301 were evaluated in non-human primates (NHP).ResultsXTX301 showed no detectable binding to the high affinity IL12RB2 demonstrating that the masking domain indeed prevents interaction with the receptor. Upon cleavage of the masking domain by relevant proteases, binding was observed and was comparable to XTX300 unmasked control. Likewise, restoration of activity upon proteolytic cleavage was observed in an IL-12-dependent reporter gene assay and in primary human PBMCs. Human IL-12 does not cross react with mouse IL-12 receptors; hence a murine surrogate (mXTX301) was created for in vivo anti-tumor efficacy evaluation. A single dose of mXTX301 demonstrated up to 90% tumor growth inhibition in an inflamed MC38 and non-inflamed B16F10 syngeneic mouse models. mXTX301 induced a ~3 fold increase in IFN-g in tumors compared to vehicle control and ~150 fold less peripheral IFN-g compared to mXTX300. XTX301 exhibits minimal elevation in liver enzymes and a 50-fold improvement in tolerability compared to XTX300, in a repeat dose NHP safety study.ConclusionsOur data demonstrates that both XTX301 and mXTX301 are inactive when in masked form and become activated upon proteolytic cleavage to exert bioactivity comparable to recombinant IL-12. For efficacy, mXTX301 demonstrated tumor selective activity in syngeneic mouse models. XTX301 was well tolerated in repeat dose NHP safety study. In conclusion, XTX301 has potential for exerting potent anti-tumor activity with a favorable tolerability profile.

Background High-dose recombinant human interleukin-2 (aldesleukin) elicits durable anti-tumor immunity and gained FDA approval two decades prior to checkpoint blockers. However, use of aldesleukin is limited due to treatment-related life-threatening toxicities. Second generation efforts to alleviate toxicities have largely focused on eliminating binding to IL-2Rα, often with half-life extension. We have determined that mice and non-human primates (NHPs) treated with a 2nd generation IL-2 surrogate that does not bind IL-2Rα still experience characteristic dose-limiting toxicities, including vascular leak syndrome (VLS), and exhibit dysregulated peripheral immune function due to reduced Treg activation. To overcome these toxicities and improve the therapeutic index of IL-2 as an anti-tumor immunotherapy, we employed protein engineering to generate XTX201, a highly potent 3rd generation IL-2 that is designed to be selectively active in tumors, stimulating cytolytic responses against tumor cells while sparing systemic immune activation. Methods XTX201 binding interactions were measured with SPR, and bioactivity was measured using STAT-5 phosphorylation in human PBMCs and reporter cell lines. Anti-tumor efficacy and immune activation was evaluated in tumors compared to peripheral organs in syngeneic tumor mouse models. Safety and pharmacokinetics were evaluated in rodents and NHPs. Results Non-activated XTX201 showed no detectable binding to IL-2Rα or IL-2Rβ, and limited IL-2R-dependent STAT-5 signaling in vitro. Activation of XTX201 resulted in high-affinity binding to IL-2Rβ and no binding to IL-2Rα, leading to a ~1000-fold reduction in Treg activation as compared to WT IL-2, while retaining CD8+ T and NK cell activation. Mice and NHPs treated with a 2nd generation IL-2 surrogate experienced toxicities that are commonly observed in patients treated with aldesleukin, including pulmonary edema, VLS, fever and lethality. However, XTX201 did not induce toxicities at exposures 100-fold higher than the MTD of the activated version, and achieved similar anti-tumor efficacy in mice. Experiments in primary human solid tumors and human plasma indicated that XTX201 is preferentially activated in the tumor microenvironment. Conclusions Our data demonstrate that 2nd generation IL-2s that are systemically active and lack binding to IL-2Rα exhibit dose-limiting toxicities unless further engineered for selective activity in tumors. XTX201, a 3rd generation, tumor-selective IL-2, exhibits a long half-life and is innocuous outside of tumors. XTX201 is activated within tumors to release an IL-2Rβ/γ biased cytokine that inhibits tumor growth in syngeneic models, and exhibits tumor-specific pharmacodynamic effects without peripheral toxicities. XTX201 has the potential to be a best-in-class IL-2 immunotherapy by expanding the curative anti-tumor activity of aldesleukin while minimizing dose-limiting toxicities.

Background The clinical benefit of CTLA-4 blockade to cancer patients has been well established. However, the promising antitumor activity shown by anti-CTLA-4 monoclonal antibodies (mAb) has been limited by the occurrence of immune-mediated adverse reactions, especially when CTLA-4 inhibition is used in combination with anti-PD-1 therapy. These dose-limiting toxicities restrict the therapeutic use of CTLA-4 blockade. To overcome these limitations, we have developed a potent anti-CTLA-4 antibody that is selectively active in the tumor microenvironment (TME). This antibody is engineered with an Fc region for enhanced FcγR binding and peptides that mask antigen-binding regions. The masking peptides are designed to be selectively cleaved and released by proteases that are more active in the TME, resulting in restoration of full activity of the antibody in the TME. Methods A novel, fully-humanized anti-huCTLA-4 mAb was shown to bind human CTLA-4 with improved affinity compared to ipilimumab, as measured by SPR. Engineering of the Fc region enhanced FcγR binding and ADCC function. In addition, CDR-binding peptides identified by phage display were covalently linked to the antibody using a protease-sensitive polypeptide linker. This engineered anti-CTLA-4 antibody (XTX101) showed protease-dependent binding to CTLA-4 both with recombinant and tumor tissue derived proteases. Results XTX101 demonstrated a 100-fold reduction in binding to human CTLA-4 by ELISA, compared to the non-masked antibody. Incubation with recombinant protease led to cleavage and release of the masking peptides and restored full binding to CTLA-4. Similarly, in vitro ADCC activity was impaired by masking and restored in a protease-dependent manner. SEB-stimulated human PMBCs were minimally responsive in vitro to XTX101, whereas PBMCs treated with proteolytically-activated XTX101 exhibited robust activation of T cell function. In human CTLA-4 knock-in mice with syngeneic MB49 tumors, XTX101 treatment led to complete tumor regression, enhanced CD8+ T cell proliferation, and depletion of tumor Tregs in the TME. By contrast, XTX101 had minimal pharmacodynamic effects in the periphery. In addition, XTX101 is effectively activated in culture supernatants from human solid tumor explants obtained from a broad range of tumor types. Conclusions XTX101 is a tumor-selective anti-CTLA-4 mAb capable of: 1) effective CTLA-4 blockade, 2) depletion of intratumoral Tregs through enhanced antibody-dependent cellular cytotoxicity (ADCC) function, 3) minimization of systemic immune cell activation, and 4) potent anti-tumor activity. These pre-clinical data support the further evaluation of XTX101 in clinical studies.

CD137 (4-1BB) is a member of the TNFR superfamily that represents a promising target for cancer immunotherapy. Recent insights into the function of TNFR agonist antibodies implicate epitope, affinity, and IgG subclass as critical features, and these observations help explain the limited activity and toxicity seen with clinically tested CD137 agonists. Here, we describe the preclinical characterization of CTX-471, a fully human IgG4 agonist of CD137 that engages a unique epitope that is shared by human, cynomolgus monkey, and mouse and is associated with a differentiated pharmacology and toxicology profile. In vitro, CTX-471 increased IFN-γ production by human T cells in an Fcγ receptor–dependent (FcγR-dependent) manner, displaying an intermediate level of activity between 2 clinical-stage anti-CD137 antibodies. In mice, CTX-471 exhibited curative monotherapy activity in various syngeneic tumor models and showed a unique ability to cure mice of very large (~500 mm(3)) tumors compared with validated antibodies against checkpoints and TNFR superfamily members. Extremely high doses of CTX-471 were well tolerated, with no signs of hepatic toxicity. Collectively, these data demonstrate that CTX-471 is a unique CD137 agonist that displays an excellent safety profile and an unprecedented level of monotherapy efficacy against very large tumors.

2563 Background: High-dose recombinant human interleukin-2 (aldesleukin) elicits anti-tumor immunity and is approved for the treatment of renal cell carcinoma and melanoma based on durable complete remissions. However, use of aldesleukin is limited due to treatment-related life-threatening toxicities. Recent second-generation efforts to alleviate toxicities have largely focused on eliminating binding to IL-2Rα, often with half-life extension. We have determined that mice and non-human primates (NHPs) treated with a second generation IL-2 surrogate still experience characteristic dose-limiting toxicities, including vascular leak syndrome. To overcome these toxicities and improve the therapeutic index (TI) of IL-2 as an anti-tumor immunotherapy, we employed protein engineering to generate XTX202, a highly potent third generation masked IL-2. XTX202 is unmasked in the tumor microenvironment by proteolytic activation resulting in full restoration of binding to IL-2Rβ without binding to IL-2Rα. The current study characterizes the therapeutic index of XTX202 versus aldesleukin and a second generation IL-2 surrogate. Methods: XTX202 bioactivity was measured using STAT-5 phosphorylation in human PBMCs and reporter cell lines. Anti-tumor efficacy and peripheral immune activation were evaluated in mice bearing syngeneic tumor models. Safety was evaluated in rodents and Cynomolgus monkeys. XTX200, an unmasked half-life extended IL-2 that does not bind to IL-2Rα, was used as a surrogate second generation IL-2. Results: Masked XTX202 showed limited IL-2R-dependent STAT-5 signaling in vitro. Proteolytic activation of XTX202 resulted in CD8+ T and NK cell activation and over 1000-fold reduction in Treg activation as compared to WT IL-2. XTX202 achieved potent tumor growth inhibition in syngeneic mouse models as a single agent with no evidence of toxicity or peripheral immune activation, thus demonstrating tumor selective activity. XTX202 efficacy in mice at 2 mg/kg dose was equivalent to that achieved with the MTD dose of 0.5 mg/kg of a second generation IL-2 surrogate. XTX202 was well tolerated in NHPs in a 4-week repeat dose study at doses up to 30 mg/kg QW whereas a second generation IL-2 surrogate was not tolerated beyond 0.7 mg/kg QW. Based on these data, XTX202 has a 10 fold improvement in TI vs second generation IL-2. Based on comparative efficacy studies with aldesleukin and literature NHP tolerability data, XTX202 is projected to have a ≥150 fold greater TI than aldesleukin. Conclusions: XTX202, a third generation, tumor-selective IL-2, inhibits tumor growth and is well tolerated in repeat dose studies in NHPs at high doses. GLP toxicity studies with XTX202 are underway and first-in-human studies are expected to initiate this year. XTX202 has the potential to be a best-in-class IL-2 immunotherapy by expanding the curative anti-tumor activity of IL-2 while minimizing dose-limiting toxicities.

Purpose: To determine whether combination therapy with NHS-muIL12 and the anti-programmed death ligand 1 (PD-L1) antibody avelumab can enhance antitumor efficacy in preclinical models relative to monotherapies. Experimental Design: BALB/c mice bearing orthotopic EMT-6 mammary tumors and μMt− mice bearing subcutaneous MC38 tumors were treated with NHS-muIL12, avelumab, or combination therapy; tumor growth and survival were assessed. Tumor recurrence following remission and rechallenge was evaluated in EMT-6 tumor-bearing mice. Immune cell populations within spleen and tumors were evaluated by FACS and IHC. Immune gene expression in tumor tissue was profiled by NanoString® assay and plasma cytokine levels were determined by multiplex cytokine assay. The frequency of tumor antigen–reactive IFNγ-producing CD8+ T cells was evaluated by ELISpot assay. Results: NHS-muIL12 and avelumab combination therapy enhanced antitumor efficacy relative to either monotherapy in both tumor models. Most EMT-6 tumor–bearing mice treated with combination therapy had complete tumor regression. Combination therapy also induced the generation of tumor-specific immune memory, as demonstrated by protection against tumor rechallenge and induction of effector and memory T cells. Combination therapy enhanced cytotoxic NK and CD8+ T-cell proliferation and T-bet expression, whereas NHS-muIL12 monotherapy induced CD8+ T-cell infiltration into the tumor. Combination therapy also enhanced plasma cytokine levels and stimulated expression of a greater number of innate and adaptive immune genes compared with either monotherapy. Conclusions: These data indicate that combination therapy with NHS-muIL12 and avelumab increased antitumor efficacy in preclinical models, and suggest that combining NHS-IL12 and avelumab may be a promising approach to treating patients with solid tumors. Clin Cancer Res; 23(19); 5869–80. ©2017 AACR.

// Jonathan Fallon 1,* , Robert Tighe 2,* , Giorgio Kradjian 2 , Wilson Guzman 2 , Anna Bernhardt 2 , Berend Neuteboom 2 , Yan Lan 2 , Helen Sabzevari 2 , Jeffrey Schlom 1 , John W. Greiner 1 1 Laboratory of Tumor Immunology and Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland USA; 2 EMD Serono Research and Development Institute, Billerica, Massachusetts USA * These authors contributed equally to this work. Correspondence: Jeffrey Schlom, email: // Keywords : immunocytokine, interleukin-12, tumor necrosis therapy, T cells, immunotherapy Received : February 19, 2014 Accepted : March 23, 2014 Published : March 24, 2014 Abstract Targeted delivery of IL-12 might turn this cytokine into a safer, more effective cancer therapeutic. Here we describe a novel immunocytokine, NHS-IL12, consisting of two molecules of IL-12 fused to a tumor necrosis-targeting human IgG1 (NHS76). The addition of the human IgG1 moiety resulted in a longer plasma half-life of NHS-IL12 than recombinant IL-12, and a selective targeting to murine tumors in vivo . Data from both in vitro assays using human PBMCs and in vivo primate studies showed that IFN-gamma production by immune cells is attenuated following treatment with the immunocytokine, suggesting an improved toxicity profile than seen with recombinant IL-12 alone. NHS-IL12 was superior to recombinant IL-12 when evaluated as an anti-tumor agent in three murine tumor models. Mechanistic studies utilizing immune cell subset-depleting antibodies, flow cytometric methods, and in vitro cytotoxicity and ELISA assays all indicated that the anti-tumor effects of NHS-IL12 were primarily CD8+ T cell-dependent and likely IL-12-mediated. Combining NHS-IL12 treatment with a cancer vaccine, radiation, or chemotherapy resulted in greater anti-tumor effects than each individual therapy alone. These preclinical findings provide a rationale for the clinical testing of this immunocytokine, both as a single agent and in combination with vaccines, radiation and chemotherapy.

O1 IL-15 primes an mTOR-regulated gene-expression program to prolong anti-tumor capacity of human natural killer cells #### Andreas Lundqvist1, Vincent van Hoef1, Xiaonan Zhang1, Erik Wennerberg2, Julie Lorent1, Kristina Witt1, Laia Masvidal Sanz1, Shuo Liang1, Shannon Murray3, Ola Larsson1

Blockade of inhibitory checkpoint pathways, such as PD-1/PD-L1 and CTLA-4, has provided significant benefit to subsets of patients and changed the cancer therapy landscape. These checkpoint inhibitors promote adaptive T cell-mediated anti-tumor immunity while signaling regulatory protein alpha (SIRPα)/CD47 axis represents an innate specific checkpoint that has become an attractive target for immunotherapy. CD47 is expressed by virtually all cells, providing an anti-phagocytic “don’t eat me” signal through its interaction with the inhibitory immune receptor SIRPα which is expressed on myeloid cells. Blockade of the CD47-SIRPα interaction has been shown to promote phagocytosis and antigen presentation. Bispecific antibodies are emerging as an attractive therapeutic modality capable of simultaneously engaging two targets with a single drug to improve efficacy. Here we describe the discovery and characterization of a series of fully human, tetravalent common light chain SIRPαxPD-L1 bispecific antibodies. CTX-5861 was identified based on epitope binning and functional studies. The CD47 binding domain of SIRPα is known to be highly polymorphic, with allelic variants differing by as many as 13 amino acids. CTX-5861 bound to all tested polymorphic variants with higher specificity towards SIRPα expressed on myeloid cells as opposed SIRPγ expressed on T cells. In vitro studies showed that, CTX-5861 enhanced antibody-dependent cell mediated phagocytosis by macrophages and increased antigen presentation by dendritic cells. In vivo, CTX-5861 combination with tumor targeting antibodies significantly reduced tumor burden in the B16F10 lung metastasis and subcutaneous MC38 models without inducing hematological toxicities commonly associated with anti-CD47 antibodies. In the MC38 model, the addition of either PD-L1 blockade or CD137 agonism to the combination regimen led to curative anti-tumor activity in 40-60% of the mice. Quadruple combination of tumor targeting antibody, CTX-5861, PD-L1 blockade, and CD137 agonism achieved a 100% cure rate. These results suggest that SIRPα blockade, as mediated by CTX-5861, could be of central importance in rationally-designed, multi-agent immunotherapy combinations. Through its ability to enhance tumor antigen processing and presentation without incurring hematological toxicity, CTX-5861 represents a highly promising novel agent for cancer immunotherapy. Note: This abstract was not presented at the meeting. Citation Format: Ugur Eskiocak, Wilson Guzman, Thomas Daly, Allison Nelson, Pearl Bakhru, Jason Lajoie, Sara Haserlat, Samantha Ottinger, Lucy Liu, Amanda Oliphant, Alan Leung, Girish Hemashettar, Rachel Rennard, Benjamin Wolf, Monia Draghi, Michael Schmidt, Robert Tighe. CTX-5861 mediated SIRPα blockade combines with tumor targeting antibodies, checkpoint blockade and/or CD137 agonism to elicit curative anti-tumor activity in syngeneic mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3239.

Background Tecemotide is a MUC1 antigen-specific therapeutic cancer vaccine. In phase III clinical studies, delivery of tecemotide is preceded by a single low dose of cyclophosphamide (CPA) to inhibit regulatory T cells (Tregs) and enhance the response to the tumor-associated antigen. Here, we investigated effects of CPA on the immune environment and tumor growth in preclinical murine models. Methods The effect of CPA was investigated in tumor-free human MUC1 transgenic mice and anti-tumor responses were evaluated in the mice engrafted with syngeneic colorectal and ovarian cancer cells expressing human MUC1. The mice received either vehicle control, CPA (100 mg/ kg), tecemotide (100 μg) or CPA + tecemotide. The immune cell phenotype and function in the spleen were assessed on Days 1, 3 and 7 post-administration.