Low-dose ionizing γ-radiation elicits the extrusion of neutrophil extracellular traps

PURPOSE

Cancer patients frequently undergo radiotherapy in their clinical management with unintended irradiation of blood vessels and copiously irrigated organs in which polymorphonuclear leukocytes circulate. Following the observation that such low doses of ionizing radiation are able to induce neutrophils to extrude neutrophil extracellular traps (NETs), we have investigated the mechanisms, consequences and the occurrence of such phenomena in patients undergoing radiotherapy.

EXPERIMENTAL DESIGN

NETosis was analyzed in cultures of neutrophils isolated from healthy donors, cancer patients and cancer-bearing mice under confocal microscopy. Cocultures of radiation-induced NETs, immune effector lymphocytes and tumor cells were used to study the effects of irradiation-induced NETs on immune cytotoxicity. Radiation-induced NETs were intravenously injected to mice assessing their effects on metastasis. Circulating NETs in irradiated cancer patients were measured by ELISA methods detecting MPO-DNA complexes and citrullinated H3.

RESULTS

Very low γ-radiation doses (0.5-1 Gy) given to neutrophils elicit NET formation in a manner dependent on oxidative stress, NADPH oxidase activity and autocrine interleukin-8. Radiation-induced NETs interfere with NK- and T-cell cytotoxicity. As a consequence, pre-injection of irradiation-induced NETs increases the number of successful metastases in mouse tumor models. Increases in circulating NETs were readily detected in two prospective series of patients following the first fraction of their radiotherapy courses.

CONCLUSIONS

NETosis is induced by low-dose ionizing irradiation in a neutrophil-intrinsic fashion and radiation-induced NETs are able to interfere with immune-mediated cytotoxicity. Radiation-induced NETs foster metastasis in mouse models and can be detected in the circulation of patients undergoing conventional radiotherapy treatments.

Intratumoral immunotherapy with mRNAs encoding chimeric protein constructs encompassing IL-12, CD137 agonists, and TGF-β antagonists

Intratumoral immunotherapy strategies for cancer based on interleukin-12 (IL-12)-encoding cDNA and mRNA are under clinical development in combination with anti-PD-(L)1 monoclonal antibodies. To make the most of these approaches, we have constructed chimeric mRNAs encoding single-chain IL-12 fused to single-chain fragment variable (scFv) antibodies that bind to transforming growth factor β (TGF-β) and CD137 (4-1BB). Several neutralizing TGF-β agents and CD137 agonists are also undergoing early-phase clinical trials. To attain TGF-β and CD137 binding by the constructions, we used bispecific tandem scFv antibodies (taFvs) derived from the specific 1D11 and 1D8 monoclonal antibodies (mAbs), respectively. Transfection of mRNAs encoding the chimeric constructs achieved functional expression of the proteins able to act on their targets. Upon mRNA intratumoral injections in the transplantable mouse cancer models CT26, MC38, and B16OVA, potent therapeutic effects were observed following repeated injections into the tumors. Efficacy was dependent on the number of CD8+ T cells able to recognize tumor antigens that infiltrated the malignant tissue. Although the abscopal effects on concomitant uninjected lesions were modest, such distant effects on untreated lesions were markedly increased when combined with systemic PD-1 blockade.

CD137 (4-1BB) requires physically associated cIAPs for signal transduction and antitumor effects

CD137 (4-1BB) is a member of the TNFR family that mediates potent T cell costimulatory signals upon ligation by CD137L or agonist monoclonal antibodies (mAbs). CD137 agonists attain immunotherapeutic antitumor effects in cancer mouse models, and multiple agents of this kind are undergoing clinical trials. We show that cIAP1 and cIAP2 are physically associated with the CD137 signaling complex. Moreover, cIAPs are required for CD137 signaling toward the NF-κB and MAPK pathways and for costimulation of human and mouse T lymphocytes. Functional evidence was substantiated with SMAC mimetics that trigger cIAP degradation and by transfecting cIAP dominant-negative variants. Antitumor effects of agonist anti-CD137 mAbs are critically dependent on the integrity of cIAPs in cancer mouse models, and cIAPs are also required for signaling from CARs encompassing CD137's cytoplasmic tail.

Synergistic effects of combined immunotherapy strategies in a model of multifocal hepatocellular carcinoma

Immune checkpoint-inhibitor combinations are the best therapeutic option for advanced hepatocellular carcinoma (HCC) patients, but improvements in efficacy are needed to improve response rates. We develop a multifocal HCC model to test immunotherapies by introducing c-myc using hydrodynamic gene transfer along with CRISPR-Cas9-mediated disruption of p53 in mouse hepatocytes. Additionally, induced co-expression of luciferase, EGFP, and the melanosomal antigen gp100 facilitates studies on the underlying immunological mechanisms. We show that treatment of the mice with a combination of anti-CTLA-4 + anti-PD1 mAbs results in partial clearance of the tumor with an improvement in survival. However, the addition of either recombinant IL-2 or an anti-CD137 mAb markedly improves both outcomes in these mice. Combining tumor-specific adoptive T cell therapy to the aCTLA-4/aPD1/rIL2 or aCTLA-4/aPD1/aCD137 regimens enhances efficacy in a synergistic manner. As shown by multiplex tissue immunofluorescence and intravital microscopy, combined immunotherapy treatments enhance T cell infiltration and the intratumoral performance of T lymphocytes.

Intratumoral Gene Transfer of mRNAs Encoding IL12 in Combination with Decoy-Resistant IL18 Improves Local and Systemic Antitumor Immunity

IL12-based local gene therapy of cancer constitutes an active area of clinical research using plasmids, mRNAs, and viral vectors. To improve antitumor effects, we have experimentally tested the combination of mRNA constructs encoding IL12 and IL18. Moreover, we have used a form of IL18 [decoy-resistant IL18 (DR-18)] which has preserved bioactivity but does not bind to the IL18 binding protein decoy receptor. Both cytokines dramatically synergize to induce IFNγ release from mouse splenocytes, and, if systemically cotransferred to the liver, they mediate lethal toxicity. However, if given intratumorally to B16OVA tumor-bearing mice, the combination attains efficacy against the directly treated tumor and moderate tumor-delaying activity on distant noninjected lesions. Cotreatment was conducive to the presence of more activated CD8+ T cells in the treated and noninjected tumors. In keeping with these findings, the efficacy of treatment was contingent on the integrity of CD8+ T cells and cDC1 dendritic cells in the treated mice. Furthermore, efficacy of IL12 plus DR-18 local mRNA coinjection against distant concomitant tumors could be enhanced upon combination with anti-PD-1 mAb systemic treatment, thus defining a feasible synergistic immunotherapy strategy.

Depletion of Conventional Type-1 Dendritic Cells in Established Tumors Suppresses Immunotherapy Efficacy

The ability of conventional type-1 dendritic cells (cDC1) to cross-present tumor antigens to CD8+ T cells is critical for the induction of antitumor CTLs. Mice that are constitutively deficient in cDC1 cells have been reported to fail to respond to immunotherapy strategies based on checkpoint inhibitors. However, further work is needed to clarify the precise time during immunotherapy treatment that cDC1 cells are required for the beneficial effect of treatment. Here, we used a refined XCR1-DTR-Venus transgenic mouse model to acutely deplete cDC1 cells and trace their behavior using intravital microscopy. Diphtheria toxin-mediated cDC1 depletion prior to immunotherapy treatment with anti-PD-1 and/or anti-CD137 immunostimulatory mAbs completely ablated antitumor efficacy. The efficacy of adoptive T-cell therapy was also hampered by prior cDC1 depletion. After the onset of immunotherapy treatment, depletion of cDC1s only moderately reduced the therapeutic efficacy of anti-PD-1 and anti-CD137 mAbs. Intravital microscopy of liver-engrafted tumors revealed changes in the intratumoral behavior of cDC1 cells in mice receiving immunotherapy, and treatment with diphtheria toxin to deplete cDC1s impaired tumor T-cell infiltration and function. These results reveal that the functional integrity of the cDC1 compartment is required at the onset of various immunotherapies to successfully treat established tumors.

SIGNIFICANCE

These findings reveal the intratumoral behavior of cDC1 dendritic cells in transgenic mouse models and demonstrate that the efficacy of immunotherapy regimens is precluded by elimination of these cells.

A Therapeutically Actionable Protumoral Axis of Cytokines Involving IL-8, TNFα, and IL-1β

Interleukin-8 (CXCL8) produced in the tumor microenvironment correlates with poor response to checkpoint inhibitors and is known to chemoattract and activate immunosuppressive myeloid leukocytes. In human cancer, IL8 mRNA levels correlate with IL1B and TNF transcripts. Both cytokines induced IL-8 functional expression from a broad variety of human cancer cell lines, primary colon carcinoma organoids, and fresh human tumor explants. Although IL8 is absent from the mouse genome, a similar murine axis in which TNFα and IL-1β upregulate CXCL1 and CXCL2 in tumor cells was revealed. Furthermore, intratumoral injection of TNFα and IL-1β induced IL-8 release from human malignant cells xenografted in immunodeficient mice. In all these cases, the clinically used TNFα blockers infliximab and etanercept or the IL-1β inhibitor anakinra was able to interfere with this pathogenic cytokine loop. Finally, in paired plasma samples of patients with cancer undergoing TNFα blockade with infliximab in a clinical trial, reductions of circulating IL-8 were substantiated.

SIGNIFICANCE

IL-8 attracts immunosuppressive protumor myeloid cells to the tumor microenvironment, and IL-8 levels correlate with poor response to checkpoint inhibitors. TNFα and IL-1β are identified as major inducers of IL-8 expression on malignant cells across cancer types and models in a manner that is druggable with clinically available neutralizing agents. This article is highlighted in the In This Issue feature, p. 2007.

Abstract 3826: A therapeutically actionable pro-tumoral axis of cytokines involving interleukin-8, TNFα and IL-1β

Background: Interleukin-8 produced in the tumor microenvironment correlates with poor response to checkpoint inhibitors and is known to chemoattract and activate immunosuppressive myeloid leukocytes. An important question is what are the mechanisms that control IL-8 transcription in tumors. Various factors have been described but the main common denominator is NF-кB activation. In this regard, considering inflammatory mediators present in the tumor and whose receptors act as NF-кB inducers, TNFα and IL-1β became obvious candidates. In this study, we provide multiple lines of evidence that TNFα and IL-1β are able to elicit functional IL-8 from malignant cells in a manner that can be inhibited by clinically grade blockade agents.

Methods: Short-term cultured human tumor cell lines, fresh human tumor explants and primary organoids were stimulated with TNFα or IL-1β to test for IL-8 induction. Moreover, syngeneic and xenografted tumors were also used to study IL-8 induction in response to TNFα or to IL-1β. Correlation between these cytokines and IL-8 transcripts were studied in TCGA and other databases to search.

Results: We have been able to correlate IL-8 mRNA levels with IL-1β and TNFα transcripts in human cancers. Both cytokines induced IL-8 functional expression from a broad variety of human cancer cell lines, primary colon carcinoma organoids and fresh human tumor explants. Although IL-8 is absent from the mouse genome, a similar murine axis in which TNFα and IL-1β upregulate CXCL1 and CXCL2 in several mouse tumor cells was revealed. Furthermore, intratumoral injection of TNFα and IL-1β induced IL-8 release from human malignant cells xenografted in immunodeficient mice. In all these cases, the clinically used TNFα-blockers infliximab and etanercept, or the IL-1β inhibitor anakinra were able to interfere with this pathogenic cytokine loop. Moreover, treatment with checkpoint inhibitors augments TNFα in syngeneic and xenografted tumors thereby turning on this immunosuppressive chemokine-driven axis. However, we have demonstrated that co-blockade of TNFα and IL-1β could equally enhance anti-tumor efficacy of αPD1+αCTLA-4 regimens as CXCR1/CXCR2 inhibitors, reparixin and AZD5069, did.

Conclusions: In this study, we have identified TNFα and IL-1β as major inducers of IL-8 transcription on human cancers. In keeping with these findings, both TNFα and IL-1β induce functional IL-8 release from all tested human tumor cell lines representing a variety of tissue origins, as well as from primary organoids and fresh human cancer explants. In all these cases, including xenografted human tumors, IL-8 induction could be blunted by the pharmacological blockade of TNFα or IL-1β. Finally, inhibition of this pathogenic cytokine loop could increase the anti-tumoral effect of checkpoint inhibitors.

Citation Format: Irene Olivera, Rebeca Sanz-Pamplona, Elixabet Bolaños, Inmaculada Rodriguez, Iñaki Etxeberria, Assunta Cirella, Saray Garasa, Itziar Migueliz, Iñaki Eguren, Miguel F. Sanmamed, Javier Glez-Vaz, Arantza Azpilikueta, Maite Alvarez, Maria C. Ochoa, Carlos E. De Andrea, Pedro Berraondo, Álvaro Teijeira, Ignacio Melero. A therapeutically actionable pro-tumoral axis of cytokines involving interleukin-8, TNFα and IL-1β [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3826.

Abstract 628: Soluble CD137 as a dynamic biomarker to monitor agonist CD137 immunotherapies

Background: On the basis of efficacy in mouse tumor models, multiple CD137 (4-1BB) agonist agents are being preclinically and clinically developed. The costimulatory molecule CD137 is inducibly expressed as a transmembrane or as a soluble protein (sCD137). Moreover, the CD137 cytoplasmic signaling domain is a key part in approved Chimeric Antigen Receptors (CARs). Reliable pharmacodynamic biomarkers for CD137 ligation and co-stimulation of T cells will facilitate clinical development of CD137 agonists in the clinic.

Methods: We used human and mouse CD8 T cells undergoing activation to measure CD137 transcription and protein expression levels determining both of the membrane-bound and soluble forms. In tumor-bearing mice plasma sCD137 concentrations were monitored upon treatment with agonist anti-CD137 mAbs. Human CD137 knock-in mice were treated with clinical-grade agonist anti-human CD137 (Urelumab). Sequential plasma samples were collected from the first patients intratumorally treated with Urelumab in the INTRUST clinical trial. Anti-Mesothelin CD137-encompassing CAR-transduced T cells were stimulated with mesothelin coated microbeads. sCD137 was measured by sandwich ELISAs and Luminex and flow cytometry was used to monitor CD137 surface expression.

Results: CD137 co-stimulation upregulates transcription and protein expression of CD137 itself including sCD137 in human and mouse CD8 T cells. Immunotherapy with anti-CD137 agonist mAb resulted in increased plasma sCD137 in mice bearing syngeneic tumors. sCD137 induction is also observed in human CD137 knock-in mice treated with Urelumab and in mice transiently humanized with T cells undergoing CD137 co-stimulation inside subcutaneous implanted Matrigel® plugs. CD137 signaling domain-containing CAR T cells readily released sCD137 upon antigen recognition in a manner favored by the CD137 signaling domain. Patients treated intratumorally with low dose Urelumab showed increased plasma concentrations of sCD137.

Conclusion: sCD137 in plasma and CD137 surface expression can be used as quantitative parameters dynamically reflecting therapeutic co-stimulatory activity elicited by agonist CD137-targeted agents.

Citation Format: Javier Glez-Vaz, Arantza Azpilikueta, Irene Olivera, Assunta Cirella, Álvaro Teijeira, Carmen Ochoa, Maite Álvarez, Iñaki Eguren, Carlos Luri-Rey, Miguel F. Sanmamed, Ignacio Melero. Soluble CD137 as a dynamic biomarker to monitor agonist CD137 immunotherapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 628.

Soluble CD137 as a dynamic biomarker to monitor agonist CD137 immunotherapies

Background

On the basis of efficacy in mouse tumor models, multiple CD137 (4-1BB) agonist agents are being preclinically and clinically developed. The costimulatory molecule CD137 is inducibly expressed as a transmembrane or as a soluble protein (sCD137). Moreover, the CD137 cytoplasmic signaling domain is a key part in approved chimeric antigen receptors (CARs). Reliable pharmacodynamic biomarkers for CD137 ligation and costimulation of T cells will facilitate clinical development of CD137 agonists in the clinic.

Methods

We used human and mouse CD8 T cells undergoing activation to measure CD137 transcription and protein expression levels determining both the membrane-bound and soluble forms. In tumor-bearing mice plasma sCD137 concentrations were monitored on treatment with agonist anti-CD137 monoclonal antibodies (mAbs). Human CD137 knock-in mice were treated with clinical-grade agonist anti-human CD137 mAb (Urelumab). Sequential plasma samples were collected from the first patients intratumorally treated with Urelumab in the INTRUST clinical trial. Anti-mesothelin CD137-encompassing CAR-transduced T cells were stimulated with mesothelin coated microbeads. sCD137 was measured by sandwich ELISA and Luminex. Flow cytometry was used to monitor CD137 surface expression.

Results

CD137 costimulation upregulates transcription and protein expression of CD137 itself including sCD137 in human and mouse CD8 T cells. Immunotherapy with anti-CD137 agonist mAb resulted in increased plasma sCD137 in mice bearing syngeneic tumors. sCD137 induction is also observed in human CD137 knock-in mice treated with Urelumab and in mice transiently humanized with T cells undergoing CD137 costimulation inside subcutaneously implanted Matrigel plugs. The CD137 signaling domain-containing CAR T cells readily released sCD137 and acquired CD137 surface expression on antigen recognition. Patients treated intratumorally with low dose Urelumab showed increased plasma concentrations of sCD137.

Conclusion

sCD137 in plasma and CD137 surface expression can be used as quantitative parameters dynamically reflecting therapeutic costimulatory activity elicited by agonist CD137-targeted agents.

CD137 (4-1BB) costimulation of CD8+ T cells is more potent when provided in cis than in trans with respect to CD3-TCR stimulation

CD137 (4-1BB; TNFSR9) is an activation-induced surface receptor that through costimulation effects provide antigen-primed T cells with augmented survival, proliferation and effector functions as well as metabolic advantages. These immunobiological mechanisms are being utilised for cancer immunotherapy with agonist CD137-binding and crosslinking-inducing agents that elicit CD137 intracellular signaling. In this study, side-by-side comparisons show that provision of CD137 costimulation in-cis with regard to the TCR-CD3-ligating cell is superior to that provided in-trans in terms of T cell activation, proliferation, survival, cytokine secretion and mitochondrial fitness in mouse and human. Cis ligation of CD137 relative to the TCR-CD3 complex results in more intense canonical and non-canonical NF-κB signaling and provides a more robust induction of cell cycle and DNA damage repair gene expression programs. Here we report that the superiority of cis versus trans CD137-costimulation is readily observed in vivo and is relevant for understanding the immunotherapeutic effects of CAR T cells and CD137 agonistic therapies currently undergoing clinical trials, which may provide costimulation either in cis or in trans.

Two alternative cell line models for the study of multiorganic metastasis and immunotherapy in Lung Squamous Cell Carcinoma

There is a paucity of adequate mouse models and cell lines available to study lung squamous cell carcinoma (LUSC). We have generated and characterized two models of phenotypically different transplantable LUSC cell lines (UN-SCC679 and UN-SCC680) derived from an N-nitroso-tris-chloroethylurea (NTCU) chemically-induced mouse model in A/J mice. Furthermore, we genetically characterized and compared both LUSC cell lines by performing whole exome and RNA sequencing. These experiments revealed similar genetic and transcriptomic patterns that may correspond to the classical LUSC human subtype. In addition, we compared the immune landscape generated by both tumor cells lines in vivo and assessed their response to immune checkpoint inhibition. The differences between the two cell lines are a good model for the remarkable heterogeneity of human squamous cell carcinoma. Study of the metastatic potential of these models revealed that both cell lines represent the human LUSC organotropism to the brain, bones, liver and adrenal glands. In summary, we have generated a very valuable cell line tools for LUSC research that recapitulates the complexity of the human disease.

Abstract 1691: CD137 (4-1BB) costimulation of CD8 T cells is more potent when provided in cis than in trans with respect to CD3-TCR stimulation

CD137 (4-1BB, TNFSFR9) costimulation provides antigen-primed T cells with increased survival, proliferation and effector functions as well as metabolic advantages. These immunobiological mechanisms are being harnessed for cancer immunotherapy with agonist CD137-binding and crosslinking-inducing agents that elicit CD137 intracellular signaling. In this study, side-by-side comparisons show that provision of CD137 costimulation in-cis with regard to the TCR-CD3-ligating cells is far superior to that provided in-trans in terms of T-cell activation, proliferation, survival, cytokine secretion and mitochondrial fitness in mice and humans. Cis ligation of CD137 relative to the TCR-CD3 complex results in more intense canonical and non-canonical NF-κB signaling and provides a more robust induction of cell-cycle and DNA damage repair gene expression programs. Superiority of cis versus trans CD137-costimulation is readily observed in vivo and is relevant for understanding the immunotherapeutic effects of CAR T cells and CD137 agonistic therapies currently undergoing clinical trials, which provide costimulation either in cis or in trans.

Citation Format: Itziar Otano, Arantza Azpilikueta, Javier Glez-Vaz, Peter Ellmark, Sara Fritzell, Gabriela Fernandez-Hoyos, Michelle Hase Nelson, Maite Alvarez, María del Carmen Ochoa, Elixabet Bolaños, Doina Cuculescu, Patricia Jauregui, Sandra Sanchez, Iñaki Etxeberría, María E. Rodriguez-Ruiz, Miguel F. Sanmamed, Alvaro Teijeira, Pedro Berraondo, Igancio Melero. CD137 (4-1BB) costimulation of CD8 T cells is more potent when provided in cis than in trans with respect to CD3-TCR stimulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1691.

Cellular cytotoxicity is a form of immunogenic cell death

Background

The immune response to cancer is often conceptualized with the cancer immunity cycle. An essential step in this interpretation is that antigens released by dying tumors are presented by dendritic cells to naive or memory T cells in the tumor-draining lymph nodes. Whether tumor cell death resulting from cytotoxicity, as mediated by T cells or natural killer (NK) lymphocytes, is actually immunogenic currently remains unknown.

Methods

In this study, tumor cells were killed by antigen-specific T-cell receptor (TCR) transgenic CD8 T cells or activated NK cells. Immunogenic cell death was studied analyzing the membrane exposure of calreticulin and the release of high mobility group box 1 (HMGB1) by the dying tumor cells. Furthermore, the potential immunogenicity of the tumor cell debris was evaluated in immunocompetent mice challenged with an unrelated tumor sharing only one tumor-associated antigen and by class I major histocompatibility complex (MHC)-multimer stainings. Mice deficient in Batf3, Ifnar1 and Sting1 were used to study mechanistic requirements.

Results

We observe in cocultures of tumor cells and effector cytotoxic cells, the presence of markers of immunogenic cell death such as calreticulin exposure and soluble HMGB1 protein. Ovalbumin (OVA)-transfected MC38 colon cancer cells, exogenously pulsed to present the gp100 epitope are killed in culture by mouse gp100-specific TCR transgenic CD8 T cells. Immunization of mice with the resulting destroyed cells induces epitope spreading as observed by detection of OVA-specific T cells by MHC multimer staining and rejection of OVA⁺ EG7 lymphoma cells. Similar results were observed in mice immunized with cell debris generated by NK-cell mediated cytotoxicity. Mice deficient in Batf3-dependent dendritic cells (conventional dendritic cells type 1, cDC1) fail to develop an anti-OVA response when immunized with tumor cells killed by cytotoxic lymphocytes. In line with this, cultured cDC1 dendritic cells uptake and can readily cross-present antigen from cytotoxicity-killed tumor cells to cognate CD8⁺ T lymphocytes.

Conclusion

These results support that an ongoing cytotoxic antitumor immune response can lead to immunogenic tumor cell death.

Abstract 1698: Cellular cytotoxicity is a form of immunogenic cell death

Background: The immune response to cancer is often conceptualized with the Cancer Immunity Cycle. An essential step in this interpretation is that antigens released by dying tumors are presented by dendritic cells to naive or memory T cells in the tumor-draining lymph nodes. Whether tumor cell death resulting from cytotoxicity, as mediated by T cells or NK lymphocytes, is actually immunogenic currently remains unknown.

Methods: In this study, tumor cells were killed by antigen-specific T-cell receptor (TCR) transgenic CD8 T cells or activated natural killer cells. Immunogenic cell death was studied analyzing the membrane exposure of calreticulin and the release of high mobility group box 1 (HMGB1) by the dying tumor cells. Furthermore, the potential immunogenicity of the tumor cell debris was evaluated in immunocompetent mice challenged with an unrelated tumor sharing only one tumor-associated antigen and by class I MHC-multimer stainings. Mice deficient in BATF-3, IFNAR and STING were used to study mechanistic requirements.

Results: We observe in co-cultures of tumor cells and effector cytotoxic cells, the presence of markers of immunogenic cell death such as calreticulin exposure and soluble HMGB1 protein. OVA-transfected MC38 colon cancer cells, exogenously pulsed to present the gp100 epitope are killed in culture by mouse gp100 specific TCR transgenic CD8 T cells. Immunization of mice with the resulting destroyed cells induces epitope spreading as observed by detection of OVA-specific T cells by MHC multimer staining and rejection of OVA+ EG7 lymphoma cells. Similar results were observed in mice immunized with cell debris generated by NK-cell mediated cytotoxicity. Mice deficient in BATF3-dependent dendritic cells (cDC1) fail to develop an anti-OVA response when immunized with tumor cells killed by cytotoxic lymphocytes. In line with this, cultured cDC1 dendritic cells uptake and can readily cross-present antigen from cytotoxicity-killed tumor cells to cognate CD8+ T lymphocytes.

Conclusion: These results support that an ongoing cytotoxic antitumor immune response can lead to immunogenic tumor cell death.

Citation Format: Luna Minute, Alvaro Teijeira, Alfonso Rodriguez Sánchez-Paulete, Maria del Carmen Ochoa, Maite Alvarez, Itziar Otano, Iñaki Etxeberria, Elixabet Bolaños, Arantza Azpilikueta, Saray Garasa, Noelia Casares, José Luiz Pérez-Gracia, Maria Esperanza Rodríguez-Ruiz, Pedro Berraondo, Ignacio Melero. Cellular cytotoxicity is a form of immunogenic cell death [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 1698.

CXCR1 and CXCR2 Chemokine Receptor Agonists Produced by Tumors Induce Neutrophil Extracellular Traps that Interfere with Immune Cytotoxicity

Neutrophils are expanded and abundant in cancer-bearing hosts. Under the influence of CXCR1 and CXCR2 chemokine receptor agonists and other chemotactic factors produced by tumors, neutrophils, and granulocytic myeloid-derived suppressor cells (MDSCs) from cancer patients extrude their neutrophil extracellular traps (NETs). In our hands, CXCR1 and CXCR2 agonists proved to be the major mediators of cancer-promoted NETosis. NETs wrap and coat tumor cells and shield them from cytotoxicity, as mediated by CD8⁺ T cells and natural killer (NK) cells, by obstructing contact between immune cells and the surrounding target cells. Tumor cells protected from cytotoxicity by NETs underlie successful cancer metastases in mice and the immunotherapeutic synergy of protein arginine deiminase 4 (PAD4) inhibitors, which curtail NETosis with immune checkpoint inhibitors. Intravital microscopy provides evidence of neutrophil NETs interfering cytolytic cytotoxic T lymphocytes (CTLs) and NK cell contacts with tumor cells.

Human CD8 T cells are susceptible to TNF-mediated activation-induced cell death

Activation-induced cell death (AICD) is a complex immunoregulatory mechanism that causes the demise of a fraction of T-lymphocytes upon antigen-driven activation. In the present study we investigated the direct role of TNF in AICD of CD8 T lymphocytes.

Methods: Human peripheral mononuclear cells were isolated from healthy donors and fresh tumor-infiltrating lymphocytes were obtained from cancer patients undergoing surgery. T cells were activated with anti-CD3/CD28 mAbs or with a pool of virus peptides, in combination with clinical-grade TNF blocking agents.

Results: A portion of CD8 T cells undergoes apoptosis upon CD3/CD28 activation in a manner that is partially prevented by the clinically used anti-TNF agents infliximab and etanercept. TNF-mediated AICD was also observed upon activation of virus-specific CD8 T cells and tumor-infiltrating CD8 T lymphocytes. The mechanism of TNF-driven T cell death involves TNFR2 and production of mitochondrial oxygen free radicals which damage DNA.

Conclusion: The use of TNF blocking agents reduces oxidative stress, hyperpolarization of mitochondria, and the generation of DNA damage in CD8 T celss undergoing activation. The fact that TNF mediates AICD in human tumor-reactive CD8 T cells suggests that the use of TNF-blocking agents can be exploited in immunotherapy strategies.

Repurposing the yellow fever vaccine for intratumoral immunotherapy

Live 17D is widely used as a prophylactic vaccine strain for yellow fever virus that induces potent neutralizing humoral and cellular immunity against the wild-type pathogen. 17D replicates and kills mouse and human tumor cell lines but not non-transformed human cells. Intratumoral injections with viable 17D markedly delay transplanted tumor progression in a CD8 T-cell-dependent manner. In mice bearing bilateral tumors in which only one is intratumorally injected, contralateral therapeutic effects are observed consistent with more prominent CD8 T-cell infiltrates and a treatment-related reduction of Tregs. Additive efficacy effects were observed upon co-treatment with intratumoral 17D and systemic anti-CD137 and anti-PD-1 immunostimulatory monoclonal antibodies. Importantly, when mice were preimmunized with 17D, intratumoral 17D treatment achieved better local and distant antitumor immunity. Such beneficial effects of prevaccination are in part explained by the potentiation of CD4 and CD8 T-cell infiltration in the treated tumor. The repurposed use of a GMP-grade vaccine to be given via the intratumoral route in prevaccinated patients constitutes a clinically feasible and safe immunotherapy approach.

Intratumor Adoptive Transfer of IL-12 mRNA Transiently Engineered Antitumor CD8+ T Cells

Retroviral gene transfer of interleukin-12 (IL-12) into T cells markedly enhances antitumor efficacy upon adoptive transfer but has clinically shown unacceptable severe side effects. To overcome the toxicity, we engineered tumor-specific CD8⁺ T cells to transiently express IL-12. Engineered T cells injected intratumorally, but not intravenously, led to complete rejections not only of the injected lesion but also of distant concomitant tumors. Efficacy was further enhanced by co-injection with agonist anti-CD137 mAb or by transient co-expression of CD137 ligand. This treatment induced epitope spreading of the endogenous CD8⁺ T cell immune response in a manner dependent on cDC1 dendritic cells. Mouse and human tumor-infiltrating T lymphocyte cultures can be transiently IL-12 engineered to attain marked immunotherapeutic effects.

Abstract 1474: Repurposing the yellow fever vaccine for intratumoral immunotherapy

Introduction: Yellow Fever attenuated virus vaccine (17D) induces very potent cellular and humoral immunity. Its delivery in situ in the tumor bed may induce an immune response leading to the killing of infected cells.

Experimental procedures: 17D virus was propagated in Vero cells and infectious supernatants were harvested. To evaluate in vitro sensitivity of tumors to 17D infection, a panel of human and mouse tumor cell lines were infected with increasing MOIs and viability was quantified.

To evaluate the antitumor efficacy of intratumor (i.t.) injection of 17D, 4x106pfu/50μl were injected (4 doses) in MC38- and in B16-OVA-tumor bearing C57BL/6 mice. Systemic antitumor effects of i.t 17D were examined in bilateral MC38 models in which one of the tumors was left uninjected. Depletion experiments were performed to assess the contribution of CD4, CD8, Gr1 and NK cells. To determine the role of conventional type-I dendritic cells (cDC1), identical experiments were performed in BATF3-/- mice. Tumor and lymph node immune infiltrates were examined by multiparametric flow cytometry. Combination with intraperitoneal anti-PD1 or anti-CD137 was performed to improve antitumor efficacy.

To evaluate the effects of 17D-preexisting immunity, mice were preimmunized with 17D prior to MC38 bilateral inoculation and were subsequently treated. To assess the individual cell type contribution to the antitumor effects induced upon 17D pre-immunization, CD8, CD4, CD8+CD4 or sera from preimmunized mice were passively transferred 24h prior to first 17D i.t injection to MC38-tumor bearing mice.

Results: 17D live attenuated strain is able to induce cell death of mouse and human tumor cell lines. In MC38 or B16-OVA mice models, repeated i.t. injections of 17D clearly delayed tumor progression. Regarding the systemic effect of i.t. 17D, certain contralateral therapeutic efficacy was induced upon i.t injection in bilateral MC38 models. These local and distant effects were dependent on CD8+ and cDC1 cells. 17D i.t injection increased in CD8+ T cell infiltrates and decreased in Tregs in injected tumors, while in contralateral tumors induced an increase of CD8+ and NK cells expressing key immunomodulatory receptors. I.t. 17D with anti-CD137 monoclonal antibody (mAb) induced a strong synergistic effect, while combination with anti-PD-1 mAb showed mild local additive efficacy compared to 17D monotherapy. Both combinatorial treatments delayed contralateral tumor growth. Notably, 17D preimmunization induced an important improvement of local and distant antitumor immunity. Such beneficial effects of preimmunization were transferred along with CD8+ T cells.

Conclusions: 17D can be safely injected i.t. in preclinical models, giving rise to immune-mediate antitumor effects that can be combined with other immunotherapy agents. The repurposed use of this GMP-grade vaccine in preimmunized patients represents a promising and feasible immunotherapy approach.

Citation Format: M. Angela Aznar, Carmen Molina, Alvaro Teijeira, Arantza Azpilikueta, Saray Garasa, Alfonso R. Sanchez-Paulete, Iñaki Etxeberria, Maite Alvarez, Pedro Berraondo, Ignacio Melero. Repurposing the yellow fever vaccine for intratumoral immunotherapy [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 1474.

TGFβ Blockade Enhances Radiotherapy Abscopal Efficacy Effects in Combination with Anti-PD1 and Anti-CD137 Immunostimulatory Monoclonal Antibodies

Radiotherapy can be synergistically combined with immunotherapy in mouse models, extending its efficacious effects outside of the irradiated field (abscopal effects). We previously reported that a regimen encompassing local radiotherapy in combination with anti-CD137 plus anti-PD-1 mAbs achieves potent abscopal effects against syngeneic transplanted murine tumors up to a certain tumor size. Knowing that TGFβ expression or activation increases in irradiated tissues, we tested whether TGFβ blockade may further enhance abscopal effects in conjunction with the anti-PD-1 plus anti-CD137 mAb combination. Indeed, TGFβ blockade with 1D11, a TGFβ-neutralizing mAb, markedly enhanced abscopal effects and overall treatment efficacy against subcutaneous tumors of either 4T1 breast cancer cells or large MC38 colorectal tumors. Increases in CD8 T cells infiltrating the nonirradiated lesion were documented upon combined treatment, which intensely expressed Granzyme-B as an indicator of cytotoxic effector capability. Interestingly, tumor tissue but not healthy tissue irradiation results in the presence of higher concentrations of TGFβ in the nonirradiated contralateral tumor that showed smad2/3 phosphorylation increases in infiltrating CD8 T cells. In conclusion, radiotherapy-induced TGFβ hampers abscopal efficacy even upon combination with a potent immunotherapy regimen. Therefore, TGFβ blockade in combination with radioimmunotherapy results in greater efficacy.

Intratumoral Immunotherapy with XCL1 and sFlt3L Encoded in Recombinant Semliki Forest Virus-Derived Vectors Fosters Dendritic Cell-Mediated T-cell Cross-Priming

: Multiple lines of evidence indicate a critical role of antigen cross-presentation by conventional BATF3-dependent type 1 classical dendritic cells (cDC1) in CD8-mediated antitumor immunity. Flt3L and XCL1, respectively, constitute a key growth/differentiation factor and a potent and specific chemoattractant for cDC1. To exploit their antitumor functions in local immunotherapy, we prepared Semliki Forest Virus (SFV)-based vectors encoding XCL1 and soluble Flt3L (sFlt3L). These vectors readily conferred transgene expression to the tumor cells in culture and when engrafted as subcutaneous mouse tumor models. In syngeneic mice, intratumoral injection of SFV-XCL1-sFlt3L (SFV-XF) delayed progression of MC38- and B16-derived tumors. Therapeutic activity was observed and exerted additive effects in combination with anti-PD-1, anti-CD137, or CTLA-4 immunostimulatory mAbs. Therapeutic effects were abolished by CD8β T-cell depletion and were enhanced by CD4 T-cell depletion, but not by T regulatory cell predepletion with anti-CD25 mAb. Antitumor effects were also abolished in BATF3- and IFNAR-deficient mice. In B16-OVA tumors, SFV-XF increased the number of infiltrating CD8 T cells, including those recognizing OVA. Consistently, following the intratumoral SFV-XF treatment courses, we observed increased BATF3-dependent cDC1 among B16-OVA tumor-infiltrating leukocytes. Such an intratumoral increase was not seen in MC38-derived tumors, but both resident and migratory cDC1 were boosted in SFV-XF-treated MC38 tumor-draining lymph nodes. In conclusion, viral gene transfer of sFlt3L and XCL1 is feasible, safe, and biologically active in mice, exerting antitumor effects that can be potentiated by CD4 T-cell depletion. SIGNIFICANCE: These findings demonstrate that transgenic expression of sFLT3L and XCL1 in tumor cells mediates cross-priming of, and elicits potent antitumor activity from, CD8 T lymphocytes, particularly in combination with CD4 T-cell depletion.

CD137 (4-1BB) Signalosome: Complexity Is a Matter of TRAFs

CD137 (4-1BB, Tnsfr9) is a member of the TNF-receptor (TNFR) superfamily without known intrinsic enzymatic activity in its cytoplasmic domain. Hence, akin to other members of the TNFR family, it relies on the TNFR-Associated-Factor (TRAF) family of adaptor proteins to build the CD137 signalosome for transducing signals into the cell. Thus, upon CD137 activation by binding of CD137L trimers or by crosslinking with agonist monoclonal antibodies, TRAF1, TRAF2, and TRAF3 are readily recruited to the cytoplasmic domain of CD137, likely as homo- and/or heterotrimers with different configurations, initiating the construction of the CD137 signalosome. The formation of TRAF2-RING dimers between TRAF2 molecules from contiguous trimers would help to establish a multimeric structure of TRAF-trimers that is probably essential for CD137 signaling. In addition, available studies have identified a large number of proteins that are recruited to CD137:TRAF complexes including ubiquitin ligases and proteases, kinases, and modulatory proteins. Working in a coordinated fashion, these CD137-signalosomes will ultimately promote CD137-mediated T cell proliferation and survival and will endow T cells with stronger effector functions. Current evidence allows to envision the molecular events that might take place in the early stages of CD137-signalosome formation, underscoring the key roles of TRAFs and of K63 and K48-ubiquitination of target proteins in the signaling process. Understanding the composition and fine regulation of CD137-signalosomes assembly and disassembly will be key to improve the therapeutic activities of chimeric antigen receptors (CARs) encompassing the CD137 cytoplasmic domain and a new generation of CD137 agonists for the treatment of cancer.

Mitochondrial Morphological and Functional Reprogramming Following CD137 (4-1BB) Costimulation

T and NK lymphocytes express CD137 (4-1BB), a costimulatory receptor of the TNFR family whose function is exploitable for cancer immunotherapy. Mitochondria regulate the function and survival of T lymphocytes. Herein, we show that CD137 costimulation provided by agonist mAb and CD137L (4-1BBL) induced mitochondria enlargement that resulted in enhanced mitochondrial mass and transmembrane potential in human and mouse CD8⁺ T cells. Such mitochondrial changes increased T-cell respiratory capacities and were critically dependent on mitochondrial fusion protein OPA-1 expression. Mass and function of mitochondria in tumor-reactive CD8⁺ T cells from cancer-bearing mice were invigorated by agonist mAb to CD137, whereas mitochondrial baseline mass and function were depressed in CD137-deficient tumor reactive T cells. Tumor rejection induced by the synergistic combination of adoptive T-cell therapy and agonistic anti-CD137 was critically dependent on OPA-1 expression in transferred CD8⁺ T cells. Moreover, stimulation of CD137 with CD137 mAb in short-term cultures of human tumor-infiltrating lymphocytes led to mitochondria enlargement and increased transmembrane potential. Collectively, these data point to a critical link between mitochondrial morphology and function and enhanced antitumor effector activity upon CD137 costimulation of T cells. Cancer Immunol Res; 6(7); 798-811. ©2018 AACR.

Deubiquitinases A20 and CYLD modulate costimulatory signaling via CD137 (4-1BB)

TRAF2 dependent K63-polyubiquitinations have been recently shown to connect CD137 (4-1BB) stimulation to NF-κB activation. In a search of deubiquitinase enzymes (DUBs) that could regulate such a signaling route, A20 and CYLD were found to coimmunoprecipitate with CD137 and TRAF2 complexes. Indeed, overexpression of A20 or CYLD downregulated CD137-elicited ubiquitination of TRAF2 and TAK1 upon stimulation with agonist monoclonal antibodies. Moreover, overexpression of A20 or CYLD downregulated CD137-induced NF-κB activation in cultured cells and in gene-transferred hepatocytes in vivo, while silencing these deubiquitinases enhanced CD137 costimulation of primary human CD8 T cells. Therefore A20 and CYLD directly downregulate the signaling from a T and NK-cell costimulatory receptor under exploitation for cancer immunotherapy in clinical trials.

Abstract 639: Morphological changes in mitochondria induced by CD137 (4-1BB) co-stimulation on CD8 T cells

Metabolism has emerged as a fundamental biological process in the control of immunological functions of T cells, playing essential roles in survival and differentiation of these immune cells. Mitochondria are key organelles in controlling these processes by performing fundamental steps in aerobic respiration, fatty acid metabolism and in the control of apoptosis. Recently, Carl June and colleagues showed that CARs engineered with the cytoplasmic tail of 4-1BB were able to promote oxidative phosphorylation in T cells as a result of enhanced mitochondrial biogenesis. CD137 (4-1BB) is an immunostimulatory receptor of the TNFR family expressed on the surface of antigen-activated T cells. Treatment with agonist monoclonal antibodies targeting 4-1BB is showing promising results for immunotherapy of cancer.

In this work, we observed that stimulation of 4-1BB with agonistic mAbs was able to raise the mitochondrial membrane potential on human CD8 T cells. 4-1BB co-stimulated CD8 T cells showed enlarged mitochondria (up to 3μm diameter) with a round shape when observed by confocal or transmission electron microscopy. We observed that CD8 T cells from DLNs (drainig lymph nodes) of tumors in mice treated with agonistic anti-4-1BB antibodies also contained enlarged mitochondria.

By double fluorescence labeling of mitochondria prior and after activation, we could ascertain that enlarged mitochondria were a product of preexisting mitochondria rather than de novo generated organelles. This observation prompted us to study the regulation of mitochondrial dynamics by 4-1BB receptor. 4-1BB stimulation induced an increase in expression of the mitochondrial fusion protein OPA-1. By Super-resolution microscopy with AiryScan detectors we observed more pronounced co-localization of OPA-1 with mitochondrial membrane in 4-1BB co-stimulated T cells than in T cells activated only by CD3 crosslinking.

Our results indicate an important role of 4-1BB in the regulation of mitochondrial morphology and performance in such a way that can be relevant for various T cell functions.

Citation Format: Sara Labiano, Álvaro Teijeira, Arantza Azpilikueta, Ángela Aznar, Elixabet Bolaños, Ignacio Melero. Morphological changes in mitochondria induced by CD137 (4-1BB) co-stimulation on CD8 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 639. doi:10.1158/1538-7445.AM2017-639

CD69 is a direct HIF-1α target gene in hypoxia as a mechanism enhancing expression on tumor-infiltrating T lymphocytes

CD69 is an early activation marker on the surface of T lymphocytes undergoing activation by cognate antigen. We observed intense expression of CD69 on tumor-infiltrating T-lymphocytes that reside in the hypoxic tumor microenvironment and hypothesized that CD69 could be, at least partially, under the control of the transcriptional hypoxia response. In line with this, human and mouse CD3-stimulated lymphocytes cultured under hypoxia (1% O₂) showed increased expression of CD69 at the protein and mRNA level. Consistent with these findings, mouse T lymphocytes that had recently undergone hypoxia in vivo, as denoted by pimonidazole staining, were more frequently CD69⁺ in the tumor and bone marrow hypoxic tissue compartments. We found evidence for HIF-1α involvement both when using T-lymphocytes from inducible HIF-1α^-/- mice and when observing tumor-infiltrating T-lymphocytes in mice whose T cells are HIF-1α^-/-. Direct pro-transcriptional activity of HIF-1α on a newly identified hypoxia response element (HRE) found in the human CD69 locus was demonstrated by ChIP experiments. These results uncover a connection between the HIF-1α oxygen-sensing pathway and CD69 immunobiology.

Abscopal Effects of Radiotherapy Are Enhanced by Combined Immunostimulatory mAbs and Are Dependent on CD8 T Cells and Crosspriming

Preclinical and clinical evidence indicate that the proimmune effects of radiotherapy can be synergistically augmented with immunostimulatory mAbs to act both on irradiated tumor lesions and on distant, nonirradiated tumor sites. The combination of radiotherapy with immunostimulatory anti-PD1 and anti-CD137 mAbs was conducive to favorable effects on distant nonirradiated tumor lesions as observed in transplanted MC38 (colorectal cancer), B16OVA (melanoma), and 4T1 (breast cancer) models. The therapeutic activity was crucially performed by CD8 T cells, as found in selective depletion experiments. Moreover, the integrities of BATF-3-dependent dendritic cells specialized in crosspresentation/crosspriming of antigens to CD8⁺ T cells and of the type I IFN system were absolute requirements for the antitumor effects to occur. The irradiation regimen induced immune infiltrate changes in the irradiated and nonirradiated lesions featured by reductions in the total content of effector T cells, Tregs, and myeloid-derived suppressor cells, while effector T cells expressed more intracellular IFNγ in both the irradiated and contralateral tumors. Importantly, 48 hours after irradiation, CD8⁺ TILs showed brighter expression of CD137 and PD1, thereby displaying more target molecules for the corresponding mAbs. Likewise, PD1 and CD137 were induced on tumor-infiltrating lymphocytes from surgically excised human carcinomas that were irradiated ex vivo These mechanisms involving crosspriming and CD8 T cells advocate clinical development of immunotherapy combinations with anti-PD1 plus anti-CD137 mAbs that can be synergistically accompanied by radiotherapy strategies, even if the disease is left outside the field of irradiation. Cancer Res; 76(20); 5994-6005. ©2016 AACR.

Abstract 4012: Improving radiotherapy abscopal effects with anti-PD1 and anti-CD137-based immunotherapy

Radiotherapy is considered an efficacious local tool to erradicate or at least control cancer progression. However, recent lines of preclinical and clinical evidence indicate that proimmune effects of radiotherapy can be synergistically augmented with immunostimulatory monoclonal antibodies (mAb) to act both on irradiated tumor lessions and on distant, non-irradiated tumor sites. The combination of radiotherapy with immunostimulatory anti-PD1 and anti-CD137 mAbs was conducive to favourable effects on distant non-irradiated tumor lesions as observed on transplanted MC38 (colorectal cancer), B16OVA (melanoma) and 4T1 (breast cancer) models. Immunotherapy and radiotherapy synergized both when irradiation was given using external beams or provided with brachytherapy. The therapeutic activity was crucially performed by CD8 T cells, as found in selective depletion experiments. The irradiation regimen induced immune infiltrate changes in the irradiated and non-irradiated lesions featured by reductions in the content of effector T cells, Tregs, and myeloid-derived supresor cells (MDSC), while effector T cells were expressing more intracellular IFN gamma in both the irradiated and contralateral tumors. Importantly, 48h following irradiation CD8+ TILs showed brighter expression of CD137 and PD-1 thereby displaying more target molecules for the activity of the corresponding monoclonal antibodies. Likewise, PD-1 and CD137 were induced on tumor infiltrating lymphocytes from surgically excised of human carcinoma lessions that were irradiated ex-vivo. These findings advocate for clinical development of immunotherapy combinations with anti-PD1 plus anti-CD137 mAbs that can be synergistically accompained by radiotherapy strategies on treatable lesions, even if leaving disease outside the irradiation field.

Citation Format: MariaE. Rodríguez-Ruiz, Inmaculada Rodriguez, Saray Garasa, Benigno Barbes, Jose Luis Solorzano, Jose Luis Perez Gracia, Sara Labiano, Arantza Azpilikueta, Elixabet Bolanos, Alfonso R. Sanchez-Paulete, M. Angela Aznar, Ana Rouzaut, Maria Jure-Kunkel, Iñaki Etxeberria, Carlos Alfaro, Carmen Oñate, Mariano Ponz, Ignacio Melero. Improving radiotherapy abscopal effects with anti-PD1 and anti-CD137-based immunotherapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4012.

Tumor-Produced Interleukin-8 Attracts Human Myeloid-Derived Suppressor Cells and Elicits Extrusion of Neutrophil Extracellular Traps (NETs)

PURPOSE

Myeloid-derived suppressor cells (MDSC) are considered an important T-cell immunosuppressive component in cancer-bearing hosts. The factors that attract these cells to the tumor microenvironment are poorly understood. IL8 (CXCL8) is a potent chemotactic factor for neutrophils and monocytes.

EXPERIMENTAL DESIGN

MDSC were characterized and sorted by multicolor flow cytometry on ficoll-gradient isolated blood leucokytes from healthy volunteers (n = 10) and advanced cancer patients (n = 28). In chemotaxis assays, sorted granulocytic and monocytic MDSC were tested in response to recombinant IL8, IL8 derived from cancer cell lines, and patient sera. Neutrophil extracellular traps (NETs) formation was assessed by confocal microscopy, fluorimetry, and time-lapse fluorescence confocal microscopy on short-term MDSC cultures.

RESULTS

IL8 chemoattracts both granulocytic (GrMDSC) and monocytic (MoMDSC) human MDSC. Monocytic but not granulocytic MDSC exerted a suppressor activity on the proliferation of autologous T cells isolated from the circulation of cancer patients. IL8 did not modify the T-cell suppressor activity of human MDSC. However, IL8 induced the formation of NETs in the GrMDSC subset.

CONCLUSIONS

IL8 derived from tumors contributes to the chemotactic recruitment of MDSC and to their functional control. Clin Cancer Res; 22(15); 3924-36. ©2016 AACR.

Deciphering CD137 (4-1BB) signaling in T-cell costimulation for translation into successful cancer immunotherapy

CD137 (4-1BB, TNF-receptor superfamily 9) is a surface glycoprotein of the TNFR family which can be induced on a variety of leukocyte subsets. On T and NK cells, CD137 is expressed following activation and, if ligated by its natural ligand (CD137L), conveys polyubiquitination-mediated signals via TNF receptor associated factor 2 that inhibit apoptosis, while enhancing proliferation and effector functions. CD137 thus behaves as a bona fide inducible costimulatory molecule. These functional properties of CD137 can be exploited in cancer immunotherapy by systemic administration of agonist monoclonal antibodies, which increase anticancer CTLs and enhance NK-cell-mediated antibody-dependent cell-mediated cytotoxicity. Reportedly, anti-CD137 mAb and adoptive T-cell therapy strongly synergize, since (i) CD137 expression can be used to select the T cells endowed with the best activities against the tumor, (ii) costimulation of the lymphocyte cultures to be used in adoptive T-cell therapy can be done with CD137 agonist antibodies or CD137L, and (iii) synergistic effects upon coadministration of T cells and antibodies are readily observed in mouse models. Furthermore, the signaling cytoplasmic tail of CD137 is a key component of anti-CD19 chimeric antigen receptors that are used to redirect T cells against leukemia and lymphoma in the clinic. Ongoing phase II clinical trials with agonist antibodies and the presence of CD137 sequence in these successful chimeric antigen receptors highlight the importance of CD137 in oncoimmunology.

Cancer Immunotherapy with Immunomodulatory Anti-CD137 and Anti-PD-1 Monoclonal Antibodies Requires BATF3-Dependent Dendritic Cells

Weak and ineffective antitumor cytotoxic T lymphocyte (CTL) responses can be rescued by immunomodulatory mAbs targeting PD-1 or CD137. Using Batf3(-/-) mice, which are defective for cross-presentation of cell-associated antigens, we show that BATF3-dependent dendritic cells (DC) are essential for the response to therapy with anti-CD137 or anti-PD-1 mAbs. Batf3(-/-) mice failed to prime an endogenous CTL-mediated immune response toward tumor-associated antigens, including neoantigens. As a result, the immunomodulatory mAbs could not amplify any therapeutically functional immune response in these mice. Moreover, administration of systemic sFLT3L and local poly-ICLC enhanced DC-mediated cross-priming and synergized with anti-CD137- and anti-PD-1-mediated immunostimulation in tumor therapy against B16-ovalbumin-derived melanomas, whereas this function was lost in Batf3(-/-) mice. These experiments show that cross-priming of tumor antigens by FLT3L- and BATF3-dependent DCs is crucial to the efficacy of immunostimulatory mAbs and represents a very attractive point of intervention to enhance their clinical antitumor effects.

SIGNIFICANCE

Immunotherapy with immunostimulatory mAbs is currently achieving durable clinical responses in different types of cancer. We show that cross-priming of tumor antigens by BATF3-dependent DCs is a key limiting factor that can be exploited to enhance the antitumor efficacy of anti-PD-1 and anti-CD137 immunostimulatory mAbs.

Abstract 261: Nivolumab and urelumab enhance antitumor activity of human T lymphocytes engrafted in Rag2-/-IL2Rγnull immunodeficient mice

To evaluate the pharmacodynamics effects and antitumor activities of immunostimulatory mAb, we have developed a “humanized” murine model in which the receptors targeted by such mAbs become expressed. Human lymphocytes transferred into immunodeficient mice undergo activation and redistribute to organs with surface expression of hCD137 and hPD-1. Systemic lymphocyte infiltrations result in lethal xenograft-versus-host disease, which is aggravated when mice are given clinical-grade anti-hCD137 (urelumab) and anti-hPD-1 (nivolumab) mAbs. In mice engrafted with either a human colorectal carcinoma cell line (HT-29) and allogeneic human PBMCs or a primary gastric carcinoma and PBMCs from the patient, urelumab and nivolumab significantly slowed tumor growth (p<0.01). Increased activated human T lymphocytes producing IFN-ϒ and decreased human regulatory T lymphocytes in the xenografted tumors may explain such therapeutic activities. These mouse models permit surrogate analyses to test and make predictions on immunotherapy strategies encompassing immunostimulatory mAbs and their combinations.

Citation Format: Miguel F. Sanmamed, Inmaculada Rodriguez, Carmen Oñate, Arantza Azpilikueta, Maria E. Rodriguez-Ruiz, Aizea Morales-Kastresana, Sara Labiano, Jose L. Perez-Gracia, Salvador Martín-Algarra, Carlos Alfaro, Kurt A. Schalper, Guillermo Mazzolini, Francesca Sarno, Manuel Hidalgo, Alan J. Korman, Maria Jure-Kunkel, Ignacio Melero. Nivolumab and urelumab enhance antitumor activity of human T lymphocytes engrafted in Rag2-/-IL2Rγnull immunodeficient mice. [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 261. doi:10.1158/1538-7445.AM2015-261

Nivolumab and Urelumab Enhance Antitumor Activity of Human T Lymphocytes Engrafted in Rag2-/-IL2Rγnull Immunodeficient Mice

A current pressing need in cancer immunology is the development of preclinical model systems that are immunocompetent for the study of human tumors. Here, we report the development of a humanized murine model that can be used to analyze the pharmacodynamics and antitumor properties of immunostimulatory monoclonal antibodies (mAb) in settings where the receptors targeted by the mAbs are expressed. Human lymphocytes transferred into immunodeficient mice underwent activation and redistribution to murine organs, where they exhibited cell-surface expression of hCD137 and hPD-1. Systemic lymphocyte infiltrations resulted in a lethal CD4(+) T cell-mediated disease (xenograft-versus-host disease), which was aggravated when murine subjects were administered clinical-grade anti-hCD137 (urelumab) and anti-hPD-1 (nivolumab). In mice engrafted with human colorectal HT-29 carcinoma cells and allogeneic human peripheral blood mononuclear cells (PBMC), or with a patient-derived gastric carcinoma and PBMCs from the same patient, we found that coadministration of urelumab and nivolumab was sufficient to significantly slow tumor growth. Correlated with this result were increased numbers of activated human T lymphocytes producing IFNγ and decreased numbers of human regulatory T lymphocytes in the tumor xenografts, possibly explaining the efficacy of the therapeutic regimen. Our results offer a proof of concept for the use of humanized mouse models for surrogate efficacy and histology investigations of immune checkpoint drugs and their combinations.

Hypoxia-induced soluble CD137 in malignant cells blocks CD137L-costimulation as an immune escape mechanism

Hypoxia is a common feature in solid tumors that has been implicated in immune evasion. Previous studies from our group have shown that hypoxia upregulates the co-stimulatory receptor CD137 on activated T lymphocytes and on vascular endothelial cells. In this study, we show that exposure of mouse and human tumor cell lines to hypoxic conditions (1% O₂) promotes CD137 transcription. However, the resulting mRNA is predominantly an alternatively spliced form that encodes for a soluble variant, lacking the transmembrane domain. Accordingly, soluble CD137 (sCD137) is detectable by ELISA in the supernatant of hypoxia-exposed cell lines and in the serum of tumor-bearing mice. sCD137, as secreted by tumor cells, is able to bind to CD137-Ligand (CD137L). Our studies on primed T lymphocytes in co-culture with stable transfectants for CD137L demonstrate that tumor-secreted sCD137 prevents co-stimulation of T lymphocytes. Such an effect results from preventing the interaction of CD137L with the transmembrane forms of CD137 expressed on T lymphocytes undergoing activation. Indeed, silencing CD137 with shRNA renders more immunogenic tumor-cell variants upon inoculation to immunocompetent mice but which readily grafted on immunodeficient or CD8⁺ T-cell-depleted mice. These mechanisms are interpreted as a molecular strategy deployed by tumors to repress lymphocyte co-stimulation via CD137/CD137L.

Virotherapy with a Semliki Forest Virus-Based Vector Encoding IL12 Synergizes with PD-1/PD-L1 Blockade

Virotherapy and checkpoint inhibitors can be combined for the treatment of cancer with complementarity and potential for synergistic effects. We have developed a cytolytic but nonreplicative viral vector system based on Semliki Forest virus that encodes IL12 (SFV-IL12). Following direct intratumoral injection, infected cells release transgenic IL12, die, and elicit an inflammatory response triggered by both abundantly copied viral RNA and IL12. In difficult-to-treat mouse cancer models, such as those derived from MC38 and bilateral B16-OVA, SFV-IL12 synergized with an anti-PD-1 monoclonal antibody (mAb) to induce tumor regression and prolong survival. Similar synergistic effects were attained upon PD-L1 blockade. Combined SFV-IL12 + anti-PD-1 mAb treatment only marginally increased the elicited cytotoxic T-lymphocyte response over SFV-IL12 as a single agent, at least when measured by in vivo killing assays. In contrast, we observed that SFV-IL12 treatment induced expression of PD-L1 on tumor cells in an IFNγ-dependent fashion. PD-L1-mediated adaptive resistance thereby provides a mechanistic explanation of the observed synergistic effects achieved by the SFV-IL12 + anti-PD-1 mAb combination.

Combined immunostimulatory monoclonal antibodies extend survival in an aggressive transgenic hepatocellular carcinoma mouse model

PURPOSE

Immunostimulatory monoclonal antibodies (ISmAb) that unleash antitumor immune responses are showing efficacy in cancer clinical trials. Anti-B7-H1 (PD-L1) monoclonal antibodies (mAb) block a critical inhibitory pathway in T cells, whereas anti-CD137 and OX40 mAbs provide T-cell costimulation. A combination of these ISmAbs (anti-CD137 + anti-OX40 + anti-B7-H1) was tested using a transgenic mouse model of multifocal and rapidly progressing hepatocellular carcinoma, in which c-myc drives transformation and cytosolic ovalbumin (OVA) is expressed in tumor cells as a model antigen.

EXPERIMENTAL DESIGN

Flow-cytometry and immunohistochemistry were used to quantify tumor-infiltrating lymphocytes (TIL) elicited by treatment and assess their activation status and cytolytic potential. Tolerance induction and its prevention/reversal by treatment with the combination of ISmAbs were revealed by in vivo killing assays.

RESULTS

The triple combination of ISmAbs extended survival of mice bearing hepatocellular carcinomas in a CD8-dependent fashion and synergized with adoptive T-cell therapy using activated OVA-specific TCR-transgenic OT-1 and OT-2 lymphocytes. Mice undergoing therapy showed clear increases in tumor infiltration by activated and blastic CD8(+) and CD4(+) T lymphocytes containing perforin/granzyme B and expressing the ISmAb-targeted receptors on their surface. The triple combination of ISmAbs did not result in enhanced OVA-specific cytotoxic T lymphocyte (CTL) activity but other antigens expressed by cell lines derived from such hepatocellular carcinomas were recognized by endogenous TILs. Adoptively transferred OVA-specific OT-1 lymphocytes into tumor-bearing mice were rendered tolerant, unless given the triple mAb therapy.

CONCLUSION

Extension of survival and dense T-cell infiltrates emphasize the translational potential of combinational immunotherapy strategies for hepatocellular carcinoma. Clin Cancer Res; 19(22); 6151-62. ©2013 AACR.

Essential complicity of perforin-granzyme and FAS-L mechanisms to achieve tumor rejection following treatment with anti-CD137 mAb

BACKGROUND

Treatment with agonist anti-CD137 (4-1BB) immunostimulatory monoclonal antibodies elicits complete tumor regressions in a number of transplanted hematological and solid malignancies in mice. Rejection is mainly dependent on cytotoxic T lymphocytes (CTL) and IFNγ, although a role for NK cells and dendritic cells has been observed in some tumor models. Rejection of EG7-derived thymomas has been shown to be CTL-dependent but not NK-dependent.

FINDINGS

In this therapeutic setting, we show that both the perforin-granzyme and FasL effector systems are readily expressed by CD8(+) T lymphocytes infiltrating the EG7 lymphomas which are undergoing rejection. Using knock-out mice, we demonstrate that both effector cytolytic systems are involved in the execution of complete immune rejections against EG7 established tumors. In accordance, EG7 tumor cells were susceptible in vitro to both killing mechanisms acting in a synergistic fashion.

CONCLUSIONS

CD137-elicited rejection of EG7-derived tumors involves the interplay of at least two final effector cytolytic mechanisms that act in cooperation.

T cell costimulation with anti-CD137 monoclonal antibodies is mediated by K63-polyubiquitin-dependent signals from endosomes

Agonist anti-CD137 (4-1BB) mAbs enhance CD8-mediated antitumor immunity. Agonist anti-human CD137 mAbs binding to four distinct epitopes on the CD137 glycoprotein costimulated T cell activation irrespective of the engaged epitope or its interference with CD137L binding. CD137 perturbation with all these agonist mAbs resulted in Ag and Ab internalization toward an endosomal vesicular compartment. Internalization was observed in activated T lymphocytes from humans and mice, not only in culture but also in Ab-injected living animals. These in vivo experiments were carried out upon systemic i.v. injections with anti-CD137 mAbs and showed CD137 internalization in tumor-infiltrating lymphocytes and in activated human T cells transferred to immunodeficient mice. Efficient CD137 internalization required K63 polyubiquitination and endocytosed CD137-containing vesicles recruited TNFR-associated factor (TRAF) 2 and were decorated with K63 polyubiquitins. CD137 stimulation activates NF-κB through a K63-linked polyubiquitination-dependent route, and CD137-associated TRAF2 becomes K63 polyubiquitinated. Consistent with a role for TRAF2 in CD137 signaling, transgenic mice functionally deficient in TRAF2 showed delayed immunotherapeutic activity of anti-CD137 mAbs. As a whole, these findings advance our knowledge of the mechanisms of action of anti-CD137 immunostimulatory mAbs such as those currently undergoing clinical trials in cancer patients.

Abstract LB-330: Therapeutic activity of a combination of immunostimulatory monoclonal antibodies (anti-B7-H1, CD137 and OX40) on a c-myc-driven spontaneous transgenic model of hepatocellular carcinoma

Several immunostimulatory monoclonal antibodies (ISmAbs) that derepress and unleash antitumor immune responses are showing efficacy in cancer clinical trials. MAbs anti-B7-H1 (PD-L1) block a critical inhibitory pathway for T cells, while antibodies anti-CD137 and OX40 provide intense T cell costimulation. Documenting efficacy of immunotherapies on spontaneous tumors arising in oncogene transgenic mice is considered more predictive than experiments on transplanted tumors. A combination of these ISmAbs has been tested on a transgenic mouse model of spontaneous primary liver cancer in which c-myc drives transformation and the tumor cells express ovalbumin as a surrogate transgenic antigen. The induced tumor lymphocyte infiltrates and immune mechanisms of action were studied. The triple combination of mAbs clearly extended survival of mice bearing hepatocellular carcinomas (HCC) and synergized with adoptive T cell therapy with activated TCR-transgenic T cells that recognize OVA. Mice undergoing therapy showed a clear increase in the tumor tissue infiltration by activated and blastic CD8 T lymphocytes expressing the ISmAb-targeted receptors. The triple combination of ISmAbs did not result in enhanced OVA-specific CTL activity but other antigens in cell lines derived from such HCC were recognized by the elicited tumor infiltrating T lymphocytes. Indeed adoptive transfer of OT-1 cells to tumor bearing mice resulted in their tolerization, unless the triple mAb therapy was instigated. Our results emphasize the role of combinational immunotherapy approaches including ISmAbs to impact on agressive and highly T cell-tolerizing hepatocellular carcinomas.

Citation Format: Aizea Morales-Kastresana, Miguel F. Sanmamed, Inmaculada Rodriguez, Asis Palazon, Ivan Martinez-Forero, Sara Labiano, Sandra Hervas-Stubbs, Bruno Sangro, Carmen Ochoa, Arantza Azpilikueta, Elixabet Bolaños, Ines Gütgemann, Ignacio Melero. Therapeutic activity of a combination of immunostimulatory monoclonal antibodies (anti-B7-H1, CD137 and OX40) on a c-myc-driven spontaneous transgenic model of hepatocellular carcinoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-330. doi:10.1158/1538-7445.AM2013-LB-330

Lymphatic endothelium forms integrin-engaging 3D structures during DC transit across inflamed lymphatic vessels

Dendritic cell (DC) transmigration across the lymphatic endothelium is critical for the initiation and sustenance of immune responses. Under noninflammatory conditions, DC transit across the lymphatic endothelial cell (LEC) has been shown to be integrin independent. In contrast, there is increasing evidence for the participation of integrins and their ligands in DC transit across lymphatic endothelium under inflammation. In this sense, we describe the formation of ICAM-1 (CD54)-enriched three-dimensional structures on LEC/DC contacts, as these DCs adhere to inflamed skin lymphatic vessels and transmigrate into them. In vitro imaging revealed that under inflammation ICAM-1 accumulated on microvilli projections surrounding 60% of adhered DCs. In contrast, these structures were scarcely formed in noninflammatory conditions. Furthermore, ICAM-1-enriched microvilli were important in promoting DC transendothelial migration and DC crawling over the LEC surface. Microvilli formation was dependent on the presence of β-integrins on the DC side and on integrin conformational affinity to ligand. Finally, we observed that LEC microvilli structures appeared in close vicinity of CCL21 depots and that their assembly was partially inhibited by CCL21-neutralizing antibodies. Therefore, under inflammatory conditions, integrin ligands form three-dimensional membrane projections around DCs. These structures offer docking sites for DC transit from the tissue toward the lymphatic vessel lumen.

Intratumoral injection of interferon-α and systemic delivery of agonist anti-CD137 monoclonal antibodies synergize for immunotherapy

CD137 artificial costimulation results in complete tumor rejection in several mouse models. Type I interferons (IFN) exert antitumor effects through an array of molecular functions on malignant cells, tumor stroma and immune system cells. The fact that agonist anti-CD137 mAb induce tumor regressions in mice deficient in the unique receptor for Type I IFNs (IFNAR(-/-) ) indicated potential for treatment combinations. Indeed, combination of intratumor injections of mouse IFN-α and intraperitoneal injections of anti-CD137 mAb synergized as seen on subcutaneous lesions derived from the MC38 colon carcinoma, which is resistant to each treatment if given separately. Therapeutic activity was achieved both against lesions directly injected with IFN-α and against distant concomitant tumors. Experiments in bone marrow chimeras prepared with IFNAR(-/-) and WT mice concluded that expression of the receptor for Type I interferons is mainly required on cells of the hematopoietic compartment. Synergistic effects correlated with a remarkable cellular hyperplasia of the tumor draining lymph nodes (TDLNs). Enlarged TDLNs contained more plasmacytoid and conventional dendritic cells (DC) that more readily cross-presented. Importantly, numbers of both DC subtypes inversely correlated with the tumor size. Numbers of CD8 T cells specific for a dominant tumor antigen were increased at TDLNs by each separate treatment but only with slight augments due to the combination. Combined antitumor effects of the therapeutic strategy were also seen on subcutaneous TC-1 tumors established for 24 days before treatment onset. The described strategy is realistic because (i) agents of each kind are clinically available and (ii) equivalent procedures in humans are feasible.

In vivo depletion of DC impairs the anti-tumor effect of agonistic anti-CD137 mAb

Anti-CD137 mAb are capable of inducing tumor rejection in several syngeneic murine tumor models and are undergoing clinical trials for cancer. The anti-tumor effect involves co-stimulation of tumor-specific CD8(+) T cells. Whether antigen cross-presenting DC are required for the efficacy of anti-CD137 mAb treatment has never been examined. Here we show that the administration of anti-CD137 mAb eradicates EG7-OVA tumors by a strictly CD8beta(+) T-cell-dependent mechanism that correlates with increased CTL activity. Ex vivo analyses to determine the identity of the draining lymph node cell type responsible for tumor antigen cross-presentation revealed that CD11c(+) cells, most likely DC, are the main players in this tumor model. A minute number of tumor cells, revealed by the presence of OVA cDNA, reach tumor-draining lymph nodes. Direct antigen presentation by tumor cells themselves also participates in anti-OVA CTL induction. Using CD11c diphtheria toxin receptor-green fluorescent protein-->C57BL/6 BM chimeric mice, which allow for sustained ablation of DC with diphtheria toxin, we confirmed the involvement of DC in tumor antigen cross-presentation in CTL induction against OVA(257-264) epitope and in the antitumor efficacy induced by anti-CD137 mAb.

Therapeutic antitumor efficacy of anti-CD137 agonistic monoclonal antibody in mouse models of myeloma

PURPOSE

Eradication of post-treatment residual myeloma cells is needed to prevent relapses, and immunostimulatory monoclonal antibodies (mAb) such as anti-CD137, CTLA-4, CD40, etc., which enhance the immune response against malignancies, represent a means of achieving this purpose. This study explores anti-CD137 mAbs for multiple myeloma treatment in preclinical models of the disease because they safely augment tumor immunity and are in clinical trials for other cancers.

EXPERIMENTAL DESIGN

The antitumor effect of anti-CD137 mAb on mouse plasmacytomas derived from HOPC and NS0 cell lines was studied and compared with that of anti-CTLA-4, anti-CD40, and anti-ICAM-2 mAbs. The antitumor effect of anti-CD137 mAb was also examined in a mouse syngeneic disseminated myeloma (5TGM1) model, which more closely resembles human multiple myeloma. Depletions of specific cell populations and gene-targeted mice were used to unravel the requirements for tumor rejection.

RESULTS

Agonistic mAb against CD137 and blocking anti-CTLA-4 mAb showed activity against i.p. HOPC tumors, resulting in extended survival of mice that also became immune to rechallenge. Anti-CD137 mAbs induced complete eradications of established s.c. NS0-derived tumors that were dependent on IFN-gamma, natural killer cells, and CD8(+) T lymphocytes. Natural killer cells accumulated in tumor draining lymph nodes and showed increased IFN-gamma production. Antitumor efficacy of anti-CD137 mAb was preserved in CD28-deficient mice despite the fact that CD28 signaling increases the expression of CD137 on CD8(+) T cells. Importantly, anti-CD137 mAb treatment significantly decreased systemic tumor burden in the disseminated 5TGM1 model.

CONCLUSIONS

The immune-mediated antitumor activity of anti-CD137 mAb in mouse models holds promise for myeloma treatment in humans.

Interleukin-15 liver gene transfer increases the number and function of IKDCs and NK cells

The surface phenotype CD3-NK1.1+DX5+CD11c(int)B220+GR1- has been recently ascribed to a novel subset of mouse leukocytes termed interferon (IFN)-producing killer dendritic cells (IKDCs) that shares functions with natural killer (NK) cells and DCs. Interleukin-15 (IL-15) is critical for NK cells but its relationship with IKDC remained unexplored. An expression cassette encoding human IL-15 (hIL-15) has been transferred by hydrodynamic injection into the liver of mice, resulting in transient expression of the cytokine that is detectable during the first 48 h. hIL-15 hydrodynamic gene transfer resulted in an expansion of NK cells and IKDCs. Relative expansions of IKDCs were more dramatic in the IL-15 gene-transferred hepatic tissue than in the spleen. Adoptively transferred DX5+ cells comprising both NK cells and IKDCs proliferated in response to hydrodynamic injection of hIL-15, indicating that quantitative increases are at least in part the result of proliferation from already differentiated cells. Expansion is accompanied by enhanced cytolytic activity and increased expression of TRAIL and CD137 (4-1BB), without augmenting interferon-gamma production. The effects of a single hydrodynamic injection surpassed those of two intraperitoneal doses of the recombinant protein. The novel functional link between circulating IL-15 and IKDCs opens new possibilities to study the biology and applications of this minority cell subset.

The combined actions of NK and T lymphocytes are necessary to reject an EGFP+ mesenchymal tumor through mechanisms dependent on NKG2D and IFN gamma

Better understanding of the mechanisms that mediate spontaneous immune rejections ought to be important in the quest for improvements in immunotherapy of cancer. A set of intraperitoneal tumors of mesenchymal origin that had been chemically induced in ubiquitously expressing EGFP transgenic mice provided a model in which both T and NK cells were absolutely required for tumor rejection. Tumor cells were traceable because of being fluorescent and readily grafted in RAG1(-/-) immunodeficient mice, whereas they were rejected in a majority of syngeneic C57BL/6 and EGFP-transgenic mice. Tumor-cell clones with the highest EGFP expression tended to be rejected, but a direct involvement of EGFP as the antigen recognized for the immune rejections was ruled out. Rejections were absolutely dependent on NK cells as well as on CD4(+) and CD8(+) T lymphocytes according to selective depletion studies. Furthermore, CD8(+) and CD4(+) T lymphocytes as well as NK cells were detected in the inflammatory infiltrate that mediates tumor rejection along with some DC. The effects of IFN gamma, produced at the tumor site by T and NK lymphocytes, were only required at the malignant cell level and were necessary for tumor eradication. NK recognition of tumor cells was mediated by the NKG2D-activating receptor and blocking its function in vivo partially interfered with rejection. Therefore, complete rejection of these mesenchymal tumors requires a concerted set of activities including direct tumor-cell destruction and IFN gamma production that are mediated by both NK and T cells.