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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 cytotoxic T lymphocytes. 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 monoclonal antibodies (mAbs) completely ablated anti-tumor 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. This work was supported by Spanish Ministry of Economy and Competitiveness and Spanish Ministry of Research (MINECO SAF2014-52361-R and SAF 2017-83267-C2-1R and PID2020-112892RB-100, PID2020-113174-RA-100 [AEI/FEDER,UE], financed by MCIN/AEI/10.13039/501100011033), Cancer Research Institute under the CRI-CLIP, Asociación Española Contra el Cancer (AECC) Foundation under Grant GCB15152947MELE, Joint Translational Call for Proposals 2015 (JTC 2015) TRANSCAN-2 (code: TRS-2016-00000371), projects PI14/01686, PI13/00207, PI16/00668, PI19/01128, funded by Instituto de Salud Carlos III and co-funded by European Union (ERDF, “A way to make Europe”), European Commission within the Horizon 2020 Programme (PROCROP - 635122), Gobierno de Navarra Proyecto LINTERNA Ref: 0011–1411, Mark Foundation, Fundación BBVA and Fundación Olga Torres. AT is supported by the Ramon y Cajal program from the Spanish Ministry of Science (RYC2019-026406-I financiada por MCIN/AEI /10.13039/501100011033 y por El FSE invierte en tu futuro). Sí

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

Supplementary Figure from 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

CD137 (4-1BB) costimulation imprints long-term changes that instruct the ultimate behavior of T cells that have previously experienced CD137 ligation. Epigenetic changes could provide a suitable mechanism for these long-term consequences. Genome-wide DNA methylation arrays were carried out on human peripheral blood CD8+ T lymphocytes stimulated with agonist monoclonal antibody to CD137, including urelumab, which is in phase I/II clinical trials for cancer immunotherapy. Several genes showed consistent methylation patterns in response to CD137 costimulation, which were confirmed by pyrosequencing in a series of healthy donors. CD96, HHLA2, CCR5, CXCR5, and CCL5 were among the immune-related genes regulated by differential DNA methylation, leading to changes in mRNA and protein expression. These genes are also differentially methylated in naïve versus antigen-experienced CD8+ T cells. The transcription factor TCF1 and the microRNA miR-21 were regulated by DNA methylation upon CD137 costimulation. Such gene-expression regulatory factors can, in turn, broaden the effects of DNA methylation by controlling expression of their target genes. Overall, chromatin remodeling is postulated to leave CD137-costimulated T lymphocytes poised to differentially respond upon subsequent antigen recognition. Accordingly, CD137 connects costimulation during priming to genome-wide DNA methylation and chromatin reprogramming. Cancer Immunol Res; 6(1); 69–78. ©2017 AACR.

DNA methylation array results with urelumab

Primer sequences

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.

DNA methylation array results with 6B4 antiCD137 mAb

Figure S1 shows that CD8 T cells with high mitochondrial transmembrane potential after CD137 stimulation have enlarged mitochondria. Fig S2 shows that CD137 induced mitochondrial changes are not due to enrichment of specific CD8 T cells subsets. Figure S3 shows that mitochondrial enhanced functions induced by CD137 activation are not a consequence of autocrine secretion of cytokines. Fig S4 shows that spare respiratory capacity induced by CD137 activation is dependent on fatty acid oxidation. Figure S5 explores regulation of mitochondrial biogenesis and fusion related genes upon CD137 activation. Fig S6 shows functional effects of OPA knockdown in CD8 T cells. Figure S7 shows the implication of Akt pathway on enhanced mitochondrial function by CD137 activation. Figure S8 shows that CD137KO CD8 T cells have intrinsic mitochondrial defects upon CD28 activation. Figure S9 shows that CD137 activation enhances mitochondrial parameters in tumor infiltrating lymphocytes. Fig S10 shows engrafment abilities and memory markers of OTI cells in B16OVA tumor bearing mice upon OPA silencing and CD137 mAb treatment.

No change in memory naive proportions and their DNA methylation in relevant genes

single dose radiotherapy and hypofractionated doses increase the level of CD137 and PD-1 expression on the surface of tumor-infiltrating T cells.

Supplementary figures 1-5 Supplementary methods

Radiotherapy reduced the density and absolute numbers of CD4+, CD8+ and CD25+FOXP3+ T cells and Myeloid-derived suppressor cells both in the irradiated and non-irradiated lesions.

Supplementary figure 3. Number of MDSC in peripheral blood of patients using osmotic lysis of erythrocytes instead of samples from ficoll-gradient centrifugation. Experiments as those shown in figure 3B representing the percentage of positively stained cells analyzed by FACS merely following osmotic lysis of erythrocytes instead of Ficoll gradient enrichment.

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.

Supplementary video 2. IL-8 induces NET extrusion of GrMDSCs to entrap or adhere HT29 tumor cells. GrMDSCs nuclei were pre-stained with DRAQ5, (cyan), HT29 cells with PKH26 cell membrane dye (Red seen intracellular vesicles) and treated or not with IL-8. The non-cell permeant DNA probe (SYTOXgreen/green) is present in the culture media and only stains DNA when it is extruded extracelullarly. Image on the left shows the complete field of view with several GrMDSCs and an inset of an individual GrMDSC interacting with tumor cells but not extruding NETs since no IL-8 was added to the medium. Image on the left shows the complete microscopy field with several GrMDSCs and an inset with three GrMDSC contacting with HT29 cells and entrapping or adhering to them by formation of the NETs induced upon addition of IL-8. Video is a maximum intensity projection of a Z stack, (DiC is shown for contrast). Video is 300x accelerated.

Video S3

Statistical comparisons for figures 1, 2, 4 and supplementary figure 1.

Supplementary video 1. IL-8 induces NET extrusion of GrMDSCs using time-lapse in vivo confocal fluorescence microsocopy. GrMDSCs nuclei were pre-stained with DRAQ5 (Red) and treated with IL-8. The non-cell permeant green DNA probe (SYTOXgreen) is present in the culture media and only stains DNA when is extruded extracelullarly. Video represent over five hours a maximum intensity projection of a Zstack. Video is 600x accelerated

4T1-derived spontaneous lung metastases

Supplementary figure 6. IL-8 induction of NETs on GrMDSC is dose dependent, similar in intensity to that induced by LPS and can be blocked by IL-8 neutralizing antibodies. (A and B) Experiments as those in figure 6 showing the indicated conditions NET formation induction by LPS and IL-8. (C) GrMDSC induce to extrude NETs by IL-8 or LPS but cocultured with PKH26-labelled (red) HT 29 tumor cells.

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.

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.

supplementary figure legends and supplementary material and methods section.

Mouse external beam irradiation setting and combinations of radiotherapy and anti-CD137 and/or anti-PD1 immunostimulatory monoclonal antibodies are safe and effective to treat MC38-derived bilateral tumors of which only one of the tumor sites is irradiated.

Ex-vivo irradiation of human carcinoma surgical expecimens gives rise to more intense expression of CD137 and PD-1 on infiltrating lymphocytes.

Supplementary figure 1. Comparative spleen size in tumor-free mice and mice engrafted with CT26-GMCSF tumors for 21 days. Photographs taken in parallel upon necropsy of the indicated group of mice.

Supplementary figure 2. IL-8 hydrodynamic gene transfer effects on tumor free mice. Hydrodynamic gene transfer experiments as in figure 2 but performed in tumor-free mice. Results show the content of the indicated cell subsets in the liver and spleen of euthanized mice.

A course of radiotherapy plus immunostimulatory monoclonal antibodies anti-CD137 and anti-PD-1 mAb increases CD4 and CD8 T cells in the tumor infiltrate as well as the number of tumor antigen-specific CD8 T cells.

Supplementary figure 5. Suppressive activity of MoMDSC on autologous purified CD4 and CD8 T cells. Experiments as in figure 5 but in this case immunomagnetically purified T cells by negative selection were CFSE-labeled co-cultured as indicated. T lymphocytes were differentially analyzed for proliferation in FACS-gated CD4 or CD8 T cell subsets. Representative histograms of one experiment out of two performed are represented.

video S1

Video S2

Supplementary figure 4. MDSC Chemotaxis induction by autologous patient serum. chemotactic migration of the indicated MDSC subsets or dextran-purified PMN from cancer patients in response to autologous serum or serum from healthy volunteers. Statistical comparisons were made by U-Mann-Whitney tests.

Neutrophil extracellular traps (NETs) are webs of extracellular nuclear DNA extruded by dying neutrophils infiltrating tissue. NETs constitute a defence mechanism to entrap and kill fungi and bacteria. Tumours induce the formation of NETs to the advantage of the malignancy via a variety of mechanisms shown in mouse models. Here, we investigated the presence of NETs in a variety of human solid tumours and their association with IL-8 (CXCL8) protein expression and CD8+ T-cell density in the tumour microenvironment. Multiplex immunofluorescence panels were developed to identify NETs in human cancer tissues by co-staining with the granulocyte marker CD15, the neutrophil marker myeloperoxidase and citrullinated histone H3 (H3Cit), as well as IL-8 protein and CD8+ T cells. Three ELISA methods to detect and quantify circulating NETs in serum were optimised and utilised. Whole tumour sections and tissue microarrays from patients with non-small cell lung cancer (NSCLC; n = 14), bladder cancer (n = 14), melanoma (n = 11), breast cancer (n = 31), colorectal cancer (n = 20) and mesothelioma (n = 61) were studied. Also, serum samples collected retrospectively from patients with metastatic melanoma (n = 12) and NSCLC (n = 34) were ELISA assayed to quantify circulating NETs and IL-8. NETs were detected in six different human cancer types with wide individual variation in terms of tissue density and distribution. At least in NSCLC, bladder cancer and metastatic melanoma, NET density positively correlated with IL-8 protein expression and inversely correlated with CD8+ T-cell densities. In a series of serum samples from melanoma and NSCLC patients, a positive correlation between circulating NETs and IL-8 was found. In conclusion, NETs are detectable in formalin-fixed human biopsy samples from solid tumours and in the circulation of cancer patients with a considerable degree of individual variation. NETs show a positive association with IL-8 and a trend towards a negative association with CD8+ tumour-infiltrating lymphocytes. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.