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Tumor-associated macrophages (TAM) are one of the most abundant cell types in many solid tumors and typically exert protumor effects. This has led to an interest in macrophage-depleting agents for cancer therapy, but approaches developed to date have had limited success in clinical trials. Here, we report the development of a strategy for TAM depletion in mouse solid tumor models using chimeric antigen receptor (CAR) T cells targeting the macrophage marker F4/80 (F4.CAR-T). F4.CAR-T cells effectively killed macrophages in vitro and in vivo without toxicity. When injected into mice bearing orthotopic lung tumors, F4.CAR-T cells infiltrated tumor lesions and delayed tumor growth comparably with PD-1 blockade, and significantly extended mouse survival. Antitumor effects were mediated by F4.CAR-T–produced IFNγ, which promoted upregulation of MHC molecules on cancer cells and tumor-infiltrating myeloid cells. Notably, F4.CAR-T promoted expansion of endogenous CD8 T cells specific for tumor-associated antigen and led to immune editing of highly antigenic tumor cell clones. Antitumor impact was also observed in mouse models of ovarian and pancreatic cancer. These studies provide proof of principle to support CAR T-cell targeting of TAMs as a means to enhance antitumor immunity.

Conventional type 1 dendritic cells (cDC1s) are central to antitumor immunity and their presence in the tumor microenvironment associates with improved outcomes in patients with cancer. DNGR-1 (CLEC9A) is a dead cell-sensing receptor highly restricted to cDC1s. DNGR-1 has been involved in both cross-presentation of dead cell-associated antigens and processes of disease tolerance, but its role in antitumor immunity has not been clarified yet.

BackgroundThe 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.MethodsIn 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 inBatf3,Ifnar1andSting1were used to study mechanistic requirements.ResultsWe 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 inBatf3-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.ConclusionThese results support that an ongoing cytotoxic antitumor immune response can lead to immunogenic tumor cell death.

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., The attenuated vaccine for yellow fever virus exerts antitumor effects when intratumorally injected which are mediated by immune responses and enhanced in pre‐vaccinated mice.

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.

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.

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. This project was supported by imCORE Network (Roche Genentech), MINECO (SAF2014-52361-R, 2017-83267-C2-1-R; I. Melero), European Commission VII Framework and Horizon 2020 programs (IACT and PROCROP), Fundacion de la Asociaci on Espa nola Contra el C ~ ancer (AECC), and Fundacion BBVA. A. Teijeira receives support from a Juan de la Cierva contract, MINECO. Electron and light microscopy CIMA services as well as Flow Cytometry CIMA facilities (Diego Alignani) and personnel at blood bank of Navarra are acknowledged for their technical support. We are also grateful to Drs. Lasarte and HervasStubbs for scientific discussion and to Dr. Paul Miller for editing the manuscript. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Sí

T-cell- and NK-cell-mediated immunity are under tight control since their functions involve the elimination of cells showing signs of infection, genetic stress, and/or the promotion of tissue inflammation. Thymic selection processes ensure that the repertoire of antigen T-cell receptors (TCRs) is purged of self-reactivity and is biased to recognize foreign peptides bound to self MHC molecules.

Purpose/Objectives Preclinical and clinical evidence indicate that the proimmune effects of radiotherapy can be synergistically augmented with immunostimulatory monoclonal antibodies (mAb) to act both on irradiated tumor lesions and on tumors at distant, nonirradiated sites. We have recently reported that external beam radiotherapy achieves abscopal effects when combined with antagonist anti-PD1 mAbs and agonist anti-CD137 (4-1BB) mAbs. The goal of this work is to study the abscopal effects of radiotherapy instigated by brachytherapy techniques. Methods and Materials Mice bearing a subcutaneous colorectal carcinoma, MC38 (colorectal cancer), in both flanks were randomly assigned to receive brachytherapy or not (8 Gy × three fractions) to only one of the two grafted tumors, in combination with intraperitoneal immunostimulatory monoclonal antibodies (anti-PD1, anti-CD137, and/or their respective isotype controls). To study the abscopal effects of brachytherapy, we established an experimental set up that permits irradiation of mouse tumors sparing a distant site resembling metastasis. Such second nonirradiated tumor was used as indicator of abscopal effect. Tumor size was monitored every 2 days. Results Abscopal effects on distant nonirradiated subcutaneous tumor lesions of transplanted MC38-derived tumors only took place when brachytherapy was combined with immunostimulatory anti-PD1 and/or anti-CD137 mAbs. Conclusions Our results demonstrate that immunotherapy-potentiated abscopal effects can be attained by brachytherapy. Accordingly, immunotherapy plus brachytherapy combinations are suitable for clinical translation.

Immune mechanisms have evolved to cope with local entry of microbes acting in a confined fashion but eventually inducing systemic immune memory. Indeed, in situ delivery of a number of agents into tumors can mimic in the malignant tissue the phenomena that control intracellular infection leading to the killing of infected cells. Vascular endothelium activation and lymphocyte attraction, together with dendritic cell–mediated cross-priming, are the key elements. Intratumoral therapy with pathogen-associated molecular patterns or recombinant viruses is being tested in the clinic. Cell therapies can be also delivered intratumorally, including infusion of autologous dendritic cells and even tumor-reactive T lymphocytes. Intralesional virotherapy with an HSV vector expressing GM-CSF has been recently approved by the Food and Drug Administration for the treatment of unresectable melanoma. Immunomodulatory monoclonal Abs have also been successfully applied intratumorally in animal models. Local delivery means less systemic toxicity while focusing the immune response on the malignancy and the affected draining lymph nodes.

UNLABELLED: 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. Work at the I. Melero lab is funded by MICINN (SAF200803294 and SAF2011-22831), Departamento de salud del Gobierno de Navarra, Redes temáticas de investigación cooperativa RETIC (RD06/0020/0065), and the European commission 7th framework program (ENCITE and IACT). Work in the D. Sancho laboratory is funded by the CNIC and grants from the Spanish Ministry of Economy and Competitiveness (SAF-2013-42920R) and the European Research Council (ERC Starting Independent Researcher Grant 2010, ERC-2010-StG 260414). The CNIC is supported by the Spanish Ministry of Economy and Competitiveness and the Pro-CNIC Foundation. I. Melero and D. Sancho are funded by the European Commission (635122-PROCROP H2020). Sí

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.

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. Cancer Immunol Res; 3(5); 449–54. ©2015 AACR.

Weak and ineffective antitumor cytotoxic T lymphocyte (CTL) responses can be rescued by immunomodulatory monoclonal antibodies (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 (DCs) 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-OVA-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. Citation Format: Alfonso R. Sánchez-Paulete, Francisco J. Cueto, María Martínez-López, Sara Labiano, Aizea Morales-Kastresana, Maria E. Rodríguez-Ruiz, Maria Jure-Kunkel, Arantza Azpilikueta, José I. Quetglas, David Sancho, Ignacio Melero. Cancer immunotherapy with immunomodulatory anti-CD137 and anti-PD-1 monoclonal antibodies requires Batf3-dependent dendritic cells. [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 4908.

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.

CD137 (4-1BB) is a surface protein initially discovered to mark activated T lymphocytes. However, its broader expression pattern also encompasses activated NK cells, B cells and myeloid cells, including mature dendritic cells. In this study, we have immunostained for CD137 on paraffin-embedded lymphoid tissues including tonsils, lymph nodes, ectopic tertiary lymphoid tissue in Hashimoto thyroiditis and cancer. Surprisingly, immunostaining mainly decorated intrafollicular lymphocytes in the tissues analyzed, with only scattered staining in interfollicular areas. Moreover, pathologic lymphoid follicles in follicular lymphoma and tertiary lymphoid tissue associated with non-small cell lung cancer showed a similar pattern of immunostaining. Multispectral fluorescence cytometry demonstrated that CD137 expression was restricted to CD4+ CXCR5+ follicular T helper lymphocytes (TFH cells) in tonsils and lymph nodes. Short-term culture of lymph node cell suspensions in the presence of either an agonistic anti-CD137 monoclonal antibody (mAb) or CD137-ligand stimulated the functional upregulation of TFH cells in 3 out of 6 cases, as indicated by CD40L surface expression and cytokine production. As a consequence, immunostimulatory monoclonal antibodies targeting CD137 (such as urelumab and PF-05082566) should be expected to primarily act on this lymphocyte subset, thus modifying ongoing humoral immune responses in patients with autoimmune disease and cancer.