T-cell Cross-priming Research Articles

CD91 and its ligand gp96 confer cross-priming capabilities to multiple APCs during immune responses to nascent, emerging tumors.

During cancer immunosurveillance, dendritic cells (DCs) play a central role in orchestrating T-cell responses against emerging tumors. Capture of miniscule amounts of antigen along with tumor-initiated costimulatory signals can drive maturation of DCs. Expression of CD91 on DCs is essential in cross-priming of T-cell responses in the context of nascent tumors. Multiple DC and macrophage subsets express CD91 and engage tumor-derived gp96 to initiate antitumor immune responses, yet the specific CD91+ antigen-presenting cells (APCs) that are required for T-cell cross-priming during cancer immunosurveillance are unknown. In this study, we determined that CD91 expression on type 1 conventional DCs (cDC1) is necessary for cancer immunosurveillance. Specifically, CD91-expressing cDC1 were found to capture the CD91 ligand gp96 from tumors and, upon migration to the lymph nodes, distribute gp96 among lymph-node resident APCs. However, cDC1 that captured tumor-derived gp96 only provided early tumor control, while sustained and long-term tumor rejection was bestowed to the host by other gp96+ cross-priming DCs. We further found that the CD91-induced transcriptome in APCs promoted cross-priming of T-cell responses while downregulating immune regulatory pathways. Our results show an elaborate and synchronized division of labor of APCs in the successful elimination of cancer cells via CD91. We predict that the specialized functions of APC subsets can be harnessed for immunotherapy of disease.

Pattern recognition receptor agonists in pathogen vaccines mediate antitumor T-cell cross-priming

BackgroundCancer immunotherapies are generally effective in patients whose tumors contain a priori primed T-cells reactive to tumor antigens (TA). One approach to prime TA-reactive T-cells is to administer immunostimulatory molecules,...

Necroptosis-dependent Immunogenicity of Cisplatin: Implications for Enhancing the Radiation-induced Abscopal Effect.

Cisplatin is increasingly used in chemoimmunotherapy and may enhance the T cell-dependent radiation-induced abscopal effect, but how it promotes antitumor immunity is poorly understood. We investigated whether and why cisplatin is immunogenic, and the implications for the cisplatin-enhanced abscopal effect. Cisplatin, carboplatin, and the well-known immunogenic cell death (ICD) inducer oxaliplatin were compared for their potency to enhance the abscopal effect and induce type I IFN (IFN-I) and extracellular ATP, danger signals of ICD. The hypothetical role of necroptosis and associated damage-associated molecular patterns for cisplatin-induced ICD was investigated by inhibitors and knockout cells in vitro and in two tumor models in mice. A novel necroptosis signature for tumor immune cell infiltration and therapy response was developed. Cisplatin enhanced the abscopal effect more strongly than oxaliplatin or carboplatin. This correlated with higher induction of IFN-I and extracellular ATP by cisplatin, in a necroptosis-dependent manner. Cisplatin triggered receptor-interacting protein kinase 3 (RIPK3)-dependent tumor cell necroptosis causing cytosolic mitochondrial DNA (mtDNA) release, initiating the cyclic GMP-AMP synthase-stimulator of interferon genes pathway and IFN-I secretion promoting T-cell cross-priming by dendritic cells (DC). Accordingly, tumor cell RIPK3 or mtDNA deficiency and loss of IFN-I or ATP signaling diminished the cisplatin-enhanced abscopal effect. Cisplatin-treated tumor cells were immunogenic in vaccination experiments, depending on RIPK3 and mtDNA. In human tumor transcriptome analysis, necroptotic features correlated with abundant CD8+ T cells/DCs, sparse immunosuppressive cells, and immunotherapy response. Cisplatin induces antitumor immunity through necroptosis-mediated ICD. Our findings may help explain the benefits of cisplatin in chemo(radio)immunotherapies and develop clinical trials to investigate whether cisplatin enhances the abscopal effect in patients.

Clinical grade adjuvants to mature CD141+ DCs for immunotherapy.

Stimulation of dendritic cells (DC) is considered critical in cancer immunotherapy. BATF-3-dependent subsets, that express in humans CD141 (BDCA-3), promote CD8 T-cell cross-priming against tumor antigens. Here, we evaluate two clinical-grade stimuli for peripheral blood CD141+ myeloid dendritic cells (mDCs), a rare DC subset that is currently being explored for use in immunotherapy. In contrast to routine evaluation methods, which focus on predefined maturation markers on the surface or factors released from the activated cells, we applied an unbiased transcriptome-based method using both RNA-sequencing (RNA-seq) and microarrays. Specifically, we analyzed the mRNA of CD141+ mDCs from five human donors upon activation with two clinical-grade adjuvants, Hiltonol (poly-ICLC, a TLR3 ligand) and protamine RNA (pRNA, a TLR7/8 ligand), and compared these samples to unstimulated counterparts. Both methods, RNA-seq, and microarray showed that Hiltonol and pRNA lead to almost identical changes in the transcriptome of CD141+ mDCs. A gene ontology (GO) term analysis suggested that these changes were mainly related to activation and maturation pathways, including induction of type I IFN and IL-12 transcription, while pathways related to adverse effects or cell damage were not strongly affected. The combination of both reagents in the DC cultures gave a very similar result as compared to either stimulus alone, suggesting no synergistic effect. Furthermore, our analysis demonstrates that microarray and RNA-seq analysis gave similar conclusions about the activation status of these cells. Importantly, microarray analyses instead of the advantages of RNA sequencing may still be suitable for studying the activation of rare cell types that are minimally represented or in very low frequency in the organism. Together, our results indicate that both stimuli are potent clinical grade adjuvants with comparable effects to mature CD141+ mDCs in short-term cultures to be used in immunotherapy.

Allogeneic CAR Invariant Natural Killer T Cells Exert Potent Antitumor Effects through Host CD8 T-Cell Cross-Priming.

The development of allogeneic chimeric antigen receptor (CAR) T-cell therapies for off-the-shelf use is a major goal that faces two main immunologic challenges, namely the risk of graft-versus-host disease (GvHD) induction by the transferred cells and the rejection by the host immune system limiting their persistence. In this work we assessed the direct and indirect antitumor effect of allogeneic CAR-engineered invariant natural killer T (iNKT) cells, a cell population without GvHD-induction potential that displays immunomodulatory properties. After assessing murine CAR iNKT cells direct antitumor effects in vitro and in vivo, we employed an immunocompetent mouse model of B-cell lymphoma to assess the interaction between allogeneic CAR iNKT cells and endogenous immune cells. We demonstrate that allogeneic CAR iNKT cells exerted potent direct and indirect antitumor activity when administered across major MHC barriers by inducing tumor-specific antitumor immunity through host CD8 T-cell cross-priming. In addition to their known direct cytotoxic effect, allogeneic CAR iNKT cells induce host CD8 T-cell antitumor responses, resulting in a potent antitumor effect lasting longer than the physical persistence of the allogeneic cells. The utilization of off-the-shelf allogeneic CAR iNKT cells could meet significant unmet needs in the clinic.

The Innate Immune Signalling Pathways: Turning RIG-I Sensor Activation Against Cancer.

Simple SummaryThe clinical success in immunotherapy has been remarkable, and, at the same time, disappointing. The immune context of the tumour microenvironment has an influence on tumour initiation, response, and therapy. It is an urgent matter to explore mechanisms shaping the tumour microenvironment for further progression of immunotherapy. The immunoreceptor retinoic acid-induced gene-I (RIG-I) has emerged as a promising target molecule to activate adoptive immunity via activation of innate immunity. In this paper, we highlight basic mechanisms of RIG-I signalling in the tumour microenvironment, broadening to the most recent preclinical studies that employ RIG-I agonists. We also present an up-to-date selection of clinical trials designed to prove the antitumour role of RIG I, and that may result in improved therapeutic outcomes for cancer patients.Over the last 15 years, the ability to harness a patient’s own immune system has led to significant progress in cancer therapy. For instance, immunotherapeutic strategies, including checkpoint inhibitors or adoptive cell therapy using chimeric antigen receptor T-cell (CAR-T), are specifically aimed at enhancing adaptive anti-tumour immunity. Several research groups demonstrated that adaptive anti-tumour immunity is highly sustained by innate immune responses. Host innate immunity provides the first line of defence and mediates recognition of danger signals through pattern recognition receptors (PRRs), such as cytosolic sensors of pathogen-associated molecular patterns (PAMPs) and damage-associated molecular pattern (DAMP) signals. The retinoic acid-inducible gene I (RIG-I) is a cytosolic RNA helicase, which detects viral double-strand RNA and, once activated, triggers signalling pathways, converging on the production of type I interferons, proinflammatory cytokines, and programmed cell death. Approaches aimed at activating RIG-I within cancers are being explored as novel therapeutic treatments to generate an inflammatory tumour microenvironment and to facilitate cytotoxic T-cell cross-priming and infiltration. Here, we provide an overview of studies regarding the role of RIG-I signalling in the tumour microenvironment, and the most recent preclinical studies that employ RIG-I agonists. Lastly, we present a selection of clinical trials designed to prove the antitumour role of RIG I and that may result in improved therapeutic outcomes for cancer patients.

Dual functions of angiopoietin-like protein 2 signaling in tumor progression and anti-tumor immunity.

Angiopoietin-like protein 2 (ANGPTL2) is a secreted glycoprotein homologous to angiopoietins. Previous studies suggest that tumor cell-derived ANGPTL2 has tumor-promoting function. Here, we conducted mechanistic analysis comparing ANGPTL2 function in cancer progression in a murine syngeneic model of melanoma and a mouse model of translocation renal cell carcinoma (tRCC). ANGPTL2 deficiency in tumor cells slowed tRCC progression, supporting a tumor-promoting role. However, systemic ablation of ANGPTL2 accelerated tRCC progression, supporting a tumor-suppressing role. The syngeneic model also demonstrated a tumor-suppressing role of ANGPTL2 in host tumor microenvironmental cells. Furthermore, the syngeneic model showed that PDGFRα+ fibroblasts in the tumor microenvironment express abundant ANGPTL2 and contribute to tumor suppression. Moreover, host ANGPTL2 facilitates CD8+ T-cell cross-priming and enhances anti-tumor immune responses. Importantly, ANGPTL2 activates dendritic cells through PIR-B-NOTCH signaling and enhances tumor vaccine efficacy. Our study provides strong evidence that ANGPTL2 can function in either tumor promotion or suppression, depending on what cell type it is expressed in.

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.

A TLR3-Specific Adjuvant Relieves Innate Resistance to PD-L1 Blockade without Cytokine Toxicity in Tumor Vaccine Immunotherapy

Cancer patients having anti-programmed cell death-1 (PD-1)/PD ligand 1 (L1)-unresponsive tumors may benefit from advanced immunotherapy. Double-stranded RNA triggers dendritic cell (DC) maturation to cross-prime antigen-specific cytotoxic T lymphocytes (CTLs) via Toll-like receptor 3 (TLR3). The TLR3-specific RNA agonist, ARNAX, can induce anti-tumor CTLs without systemic cytokine/interferon (IFN) production. Here, we have developed a safe vaccine adjuvant for cancer that effectively implements anti-PD-L1 therapy. Co-administration of ARNAX with a tumor-associated antigen facilitated tumor regression in mouse models, and in combination with anti-PD-L1 antibody, activated tumor-specific CTLs in lymphoid tissues, enhanced CTL infiltration, and overcame anti-PD-1 resistance without cytokinemia. The TLR3-TICAM-1-interferon regulatory factor (IRF)3-IFN-β axis in DCs exclusively participated in CD8+ Tcell cross-priming. ARNAX therapy established Th1 immunity in the tumor microenvironment, upregulating genes involved in DC/T cell/natural killer (NK) cell recruitment and functionality. Human exvivo studies disclosed that ARNAX+antigen induced antigen-specific CTL priming and proliferation in peripheral blood mononuclear cells (PBMCs), supporting the feasibility of ARNAX for potentiating anti-PD-1/PD-L1 therapy in human vaccine immunotherapy.

Indispensable role of IL-10 in the development of antigen cross-presentation capacity of the cDC1 subset

Abstract The conventional type 1 dendritic cell (cDC1) is a distinct DC subset with specialized functions including cross-presentation of antigens to CD8 T cells and CD103 expression. cDC1s require GM-CSF signal for gaining their signature functions; however, the involvement of other cytokines remains unknown. Here we found that cDC1s were normal in number but lacked CD103 expression in IL-10-deficient (Il10−/−) mice, suggesting that IL-10 has some effects on cDC1 function in vivo. Thus, next we assessed the CD8 T-cell priming capacity of cDC1s from Il10+/+ and Il10−/− mice by coculture with OT-I CD8+ T cells in the presence of ovalbumin in vitro. In contrast to Il10+/+ cDC1s, Il10−/− cDC1s failed to induce the expansion and IFN-γ production of OT-I cells. In addition, Il10−/− mice had a significantly lower number of memory CD8 T cells in the lymph nodes in the steady state. These results indicate that cDC1s in Il10−/− mice were defective in antigen cross-presentation. We also found that, whereas Flt3-ligand-induced DCs derived from Il10+/+ bone marrow cells upregulated CD103 expression by and CD8 T-cell cross-priming capacity of the cDC1-equivalent population in response to GM-CSF stimulation, Il10−/− bone marrow-derived DCs did not, suggesting that dysfunction of cDC1s in Il10−/− mice is likely due to unresponsiveness to GM-CSF. Finally, we found that mRNA expression of Csf2ra, which encodes GM-CSF receptor α-chain, was completely deficient in both cDC1s in Il10−/− mice and Il10−/− cDC1-equivalent bone marrow-derived DCs. Collectively, our data suggest that IL-10 critically controls the development of antigen cross-presentation capacity of cDC1s under homeostatic conditions, likely through regulating GM-CSF receptor expression.

Effects of gold nanoparticle-based vaccine size on lymph node delivery and cytotoxic T-lymphocyte responses

Although it has been shown that the size of nanoparticle-based vaccines is a key determining factor for the induction of immune responses, few studies have provided detailed analyses of thresholds or critical sizes of nanoparticle vaccines. Here we report effects of the size of gold nanoparticle (GNP)-based vaccines on their efficiency of delivery to lymph nodes (LNs) and induction of CD8+ T-cell responses. We further propose a threshold size of GNPs for use as an effective vaccine. To examine the effects of GNP size, we synthesized GNPs with diameters of 7, 14 and 28nm, and then conjugated them with recombinant ovalbumin (OVA) as a model antigen. The resulting OVA-GNPs had hydrodynamic diameter (HD) of ~10, 22, and 33nm for 7, 14 and 28nm GNPs, respectively and exhibited a size-dependent increase in cellular uptake by dendritic cells (DCs) and subsequent T-cell cross-priming and activation. Upon injection into a mouse footpad, both 22- and 33-nm OVA-GNPs showed much higher delivery efficiency to draining LNs than did 10-nm OVA-GNPs. An ex vivo restimulation assay using OVA as an antigen revealed that frequencies of OVA-specific CD8+ T cells were higher in mice immunized with 22- and 33-nm OVA-GNPs than in those immunized with 10-nm OVA-GNPs; moreover, these cells were shown to be poly-functional. In a tumor-prevention study, 22-nm OVA-GNPs showed greater antitumor efficacy, and higher infiltration of CD8+ T-cells and greater tumor cell apoptosis and cell death than 10-nm OVA-GNPs. Taken together, our results suggest that the size threshold for induction of potent cellular responses and T-cell poly-functionality by GNPs lies between 10nm and 22nm, and highlight the importance of nanoparticle size as a critical parameter in designing and developing nanoparticle-based vaccines.

Enhanced cross‐priming of naive CD8+T cells by dendritic cells treated by the IMiDs® immunomodulatory compounds lenalidomide and pomalidomide

The IMiDs(®) immunomodulatory compounds lenalidomide and pomalidomide are agents with anti-inflammatory, immunomodulatory and anti-cancer activity. An excellent success rate has been shown for multiple myeloma in phase I/II clinical trials leading to Food and Drug Administration approval of lenalidomide. One mechanism by which these drugs could enhance anti-tumour immunity may be through enhanced dendritic cell (DC) function. Thalidomide, a compound structurally related to lenalidomide and pomalidomide, is known to enhance DC function, and we have investigated whether its analogues, pomalidomide and lenalidomide, also have functional effects on DCs. We used mouse bone marrow-derived DCs treated with 5 or 10 μm pomalidomide, or lenalidomide from day 1 of culture. Treatment with IMiD(®) immunomodulatory compounds increased expression of Class I (H2-Kb), CD86, and pomalidomide also increased Class II (I-Ab) expression in bone marrow-derived DCs, as measured by flow cytometry. Fluorescent bead uptake was increased by up to 45% when DCs were treated with 5 or 10 μm pomalidomide or lenalidomide compared with non-treated DCs. Antigen presentation assays using DCs primed with ovalbumin, and syngeneic T cells from transgenic OTI and OTII mice (containing MHC restricted, ovalbumin-specific, T cells) showed that both pomalidomide and lenalidomide effectively increased CD8(+) T-cell cross-priming (by up to 47%) and that pomalidomide alone was effective in increasing CD4(+) T-cell priming (by 30%). Our observations suggest that pomalidomide and lenalidomide enhance tumour antigen uptake by DCs with an increased efficacy of antigen presentation, indicating a possible use of these drugs in DC vaccine therapies.

A Multifunctional Chimeric Chaperone Serves as a Novel Immune Modulator Inducing Therapeutic Antitumor Immunity

Converting the immunosuppressive tumor environment into one that is favorable to the induction of antitumor immunity is indispensable for effective cancer immunotherapy. Here, we strategically incorporate a pathogen (i.e., flagellin)-derived, NF-κB-stimulating "danger" signal into the large stress protein or chaperone Grp170 (HYOU1/ORP150) that was previously shown to facilitate antigen crosspresentation. This engineered chimeric molecule (i.e., Flagrp170) is capable of transporting tumor antigens and concurrently inducing functional activation of dendritic cells (DC). Intratumoral administration of adenoviruses expressing Flagrp170 induces a superior antitumor response against B16 melanoma and its distant lung metastasis compared with unmodified Grp170 and flagellin. The enhanced tumor destruction is accompanied with significantly increased tumor infiltration by CD8(+) cells as well as elevation of IFN-γ and interleukin (IL)-12 levels in the tumor sites. In situ Ad.Flagrp170 therapy provokes systemic activation of CTLs that recognize several antigens naturally expressing in melanoma (e.g., gp100/PMEL and TRP2/DCT). The mechanistic studies using CD11c-DTR transgenic mice and Batf3-deficient mice reveal that CD8α(+) DCs are required for the improved T-cell crosspriming. Antibody neutralization assays show that IL-12 and IFN-γ are essential for the Flagrp170-elicited antitumor response, which also involves CD8(+) T cells and natural killer cells. The therapeutic efficacy of Flagrp170 and its immunostimulating activity are also confirmed in mouse prostate cancer and colon carcinoma. Together, targeting the tumor microenvironment with this chimeric chaperone is highly effective in mobilizing or restoring antitumor immunity, supporting the potential therapeutic use of this novel immunomodulator in the treatment of metastatic diseases.

Sargramostim (GM-CSF) and lenalidomide in castration-resistant prostate cancer (CRPC): Results from a phase I-II clinical trial

BackgroundGranulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic cytokine that stimulates dendritic cells (DCs) and promotes uptake of tumor antigens by DCs leading to T-cell cross-priming. Lenalidomide (Revlimid) is an immunomodulatory analog of thalidomide with significant T-cell stimulatory and antiangiogenic properties. GM-CSF in combination with thalidomide induces prostate-specific antigen (PSA) responses in 20% to 25% of patients with castration-resistant prostate cancer (CRPC). In an effort to further evaluate the clinical and immune activity of GM-CSF and lenalidomide, we conducted a phase I-II trial in patients with CRPC. MethodsAsymptomatic patients with CRPC were enrolled. Prior immunotherapy or chemotherapy was not allowed. All the patients received 250μg of GM-CSF administered subcutaneously 3 times weekly along with 25mg/d of lenalidomide administered orally on days 1 to 21 of a 28-day cycle. The primary end points were objective, PSA response, and safety. Exploratory end points included activation of circulating DCs, regulatory T cells, and Th1 cytokine production. ResultsThirty-two patients were enrolled in the study. No dose-limiting toxicities occurred in the phase I portion of the study. Although 81% of the patients achieved a decline in the levels of PSA while on therapy, only 4 achieved a PSA level decline of≥50%. The overall response rate among 11 patients with response evaluation criteria in solid tumors-defined measurable disease was 18%. Overall toxicity was G1 and G2 in nature and included fatigue observed in 69% of the patients, nausea/vomiting in 34%, and diarrhea in 28% of the patients. Grade 3 or 4 toxicities occurred in 22% of the patients and were primarily thrombocytopenia (9%) or neutropenia (19%) or both. ConclusionsAdministration of GM-CSF and lenalidomide in patients with CRPC is safe with modest evidence of antitumor activity and no immune changes observed.

ISCOMATRIX vaccines mediate CD8+ T‐cell cross‐priming by a MyD88‐dependent signaling pathway

Generating a cytotoxic CD8+ T-cell response that can eradicate malignant cells is the primary objective of cancer vaccine strategies. In this study we have characterized the innate and adaptive immune response to the ISCOMATRIX adjuvant, and the ability of vaccine antigens formulated with this adjuvant to promote antitumor immunity. ISCOMATRIX adjuvant led to a rapid innate immune cell response at the injection site, followed by the activation of natural killer and dendritic cells (DC) in regional draining lymph nodes. Strikingly, major histocompatibility complex (MHC) class I cross-presentation by CD8α+ and CD8α− DCs was enhanced by up to 100-fold when antigen was formulated with ISCOMATRIX adjuvant. These coordinated features enabled efficient CD8+ T-cell cross-priming, which exhibited prophylactic and therapeutic tumoricidal activity. The therapeutic efficacy of an ISCOMATRIX vaccine was further improved when co-administered with an anti-CD40 agonist antibody, suggesting that ISCOMATRIX-based vaccines may combine favorably with other immune modifiers in clinical development to treat cancer. Finally, we identified a requirement for the myeloid differentiation primary response gene 88 (MyD88) adapter protein for both innate and adaptive immune responses to ISCOMATRIX vaccines in vivo. Taken together, our findings support the utility of the ISCOMATRIX adjuvant for use in the development of novel vaccines, particularly those requiring strong CD8+ T-cell immune responses, such as therapeutic cancer vaccines.

Maximal T Cell–Mediated Antitumor Responses Rely upon CCR5 Expression in Both CD4+ and CD8+ T Cells

Immune responses against cancer rely upon leukocyte trafficking patterns that are coordinated by chemokines. CCR5, the receptor for chemotactic chemokines MIP1alpha, MIP1beta, and RANTES (CCL3, CCL4, CCL5), exerts major regulatory effects on CD4(+)- and CD8(+) T cell-mediated immunity. Although CCR5 and its ligands participate in the response to various pathogens, its relevance to tumoral immune control has been debated. Here, we report that CCR5 has a specific, ligand-dependent role in optimizing antitumor responses. In adoptive transfer studies, efficient tumor rejection required CCR5 expression by both CD4(+) and CD8(+) T cells. CCR5 activation in CD4(+) cells resulted in CD40L upregulation, leading to full maturation of antigen-presenting cells and enhanced CD8(+) T-cell crosspriming and tumor infiltration. CCR5 reduced chemical-induced fibrosarcoma incidence and growth, but did not affect the onset or progression of spontaneous breast cancers in tolerogenic Tg(MMTV-neu) mice. However, CCR5 was required for TLR9-mediated reactivation of antineu responses in these mice. Our results indicate that CCR5 boosts T-cell responses to tumors by modulating helper-dependent CD8(+) T-cell activation.

Thymic but not splenic CD8+ DCs can efficiently cross‐prime T cells in the absence of licensing factors

Cross-presentation is an important mechanism to elicit both immune defenses and tolerance. Although only a few DC subsets possess the machinery required for cross-presentation, little is known about differences in cross-presenting capabilities of DCs belonging to the same subpopulation but localized in different lymphoid organs. In this study, we demonstrate that steady-state thymic CD8(+) DCs can efficiently cross-prime naïve CD8(+) T cells in the absence of costimulation. Surprisingly, cross-priming by splenic CD8(+) DCs was dependent on licensing factors such as GM-CSF. In the absence of GM-CSF, antigen-MHC-class-I complexes were detected on thymic but not on splenic CD8(+) DCs, indicating that the cross-presentation capacity of the thymic subpopulation was higher. The observed cross-priming differences between thymic and splenic CD8(+) DCs did not correlate with differential antigen capture or costimulatory molecules found on the surface of DCs. Moreover, we did not detect overall impairment of antigen presentation, as peptide-loaded splenic CD8(+) DCs were able to induce CD8(+) T-cell proliferation. The observation that thymic CD8(+) DCs are more efficient than splenic CD8(+) DCs in T-cell cross-priming in the absence of licensing factors indicates that the requirements for efficient antigen presentation differ between these cells.

Cyclophosphamide Synergizes with Type I Interferons through Systemic Dendritic Cell Reactivation and Induction of Immunogenic Tumor Apoptosis

Successful chemotherapy accounts for both tumor-related factors and host immune response. Compelling evidence suggests that some chemotherapeutic agents can induce an immunogenic type of cell death stimulating tumor-specific immunity. Here, we show that cyclophosphamide (CTX) exerts two types of actions relevant for the induction of antitumor immunity in vivo: (i) effect on dendritic cell (DC) homeostasis, mediated by endogenous type I interferons (IFN-I), leading to the preferential expansion of CD8α(+) DC, the main subset involved in the cross-presentation of cell-derived antigens; and (ii) induction of tumor cell death with clear-cut immunogenic features capable of stimulating tumor infiltration, engulfment of tumor apoptotic material, and CD8 T-cell cross-priming by CD8α(+) DC. Notably, the antitumor effects of CTX were efficiently amplified by IFN-I, the former providing a source of antigen and a "resetting" of the DC compartment and the latter supplying optimal costimulation for T-cell cross-priming, resulting in the induction of a strong antitumor response and tumor rejection. These results disclose new perspectives for the development of targeted and more effective chemoimmunotherapy treatments of cancer patients.

Efficient and versatile manipulation of the peripheral CD4+ T‐cell compartment by antigen targeting to DNGR‐1/CLEC9A

DC NK lectin group receptor-1 (DNGR-1, also known as CLEC9A) is a C-type lectin receptor expressed by mouse CD8α+ DC and by their putative equivalents in human. DNGR-1 senses necrosis and regulates CD8+ T-cell cross-priming to dead-cell-associated antigens. In addition, DNGR-1 is a target for selective in vivo delivery of antigens to DC and the induction of CD8+ T-cell and Ab responses. In this study, we evaluated whether DNGR-1 targeting can be additionally used to manipulate antigen-specific CD4+ T lymphocytes. Injection of small amounts of antigen-coupled anti-DNGR-1 mAb into mice promoted MHC class II antigen presentation selectively by CD8α+ DC. In the steady state, this was sufficient to induce proliferation of antigen-specific naïve CD4+ T cells and to drive their differentiation into Foxp3+ regulatory lymphocytes. Co-administration of adjuvants prevented this induction of tolerance and promoted immunity. Notably, distinct adjuvants allowed qualitative modulation of CD4+ T-cell behavior: poly I:C induced a strong IL-12-independent Th1 response, whereas curdlan led to the priming of Th17 cells. Thus, antigen targeting to DNGR-1 is a versatile approach for inducing functionally distinct CD4+ T-cell responses. Given the restricted pattern of expression of DNGR-1 across species, this strategy could prove useful for developing immunotherapy protocols in humans.

LOX-1 as a natural IFN-α–mediated signal for apoptotic cell uptake and antigen presentation in dendritic cells

AbstractThe identification of molecules responsible for apoptotic cell (AC) uptake by dendritic cells (DCs) and induction of T-cell immunity against AC-associated antigens is a challenge in immunology. DCs differentiated in the presence of interferon-α (IFN-α–conditioned DCs) exhibit a marked phagocytic activity and a special attitude in inducing CD8+ T-cell response. In this study, we found marked overexpression of the scavenger receptor oxidized low-density lipoprotein receptor 1 (LOX-1) in IFN-α–conditioned DCs, which was associated with increased levels of genes belonging to immune response families and high competence in inducing T-cell immunity against antigens derived from allogeneic apoptotic lymphocytes. In particular, the capture of ACs by IFN-α DCs led to a substantial subcellular rearrangement of major histocompatibility complex class I and class II molecules, along with enhanced cross-priming of autologous CD8+ T cells and CD4+ T-cell activation. Remarkably, AC uptake, CD8+ T-cell cross-priming, and, to a lesser extent, priming of CD4+ T lymphocytes were inhibited by a neutralizing antibody to the scavenger receptor LOX-1 protein. These results unravel a novel LOX-1–dependent pathway by which IFN-α can, under both physiologic and pathologic conditions, render DCs fully competent for presenting AC-associated antigens for cross-priming CD8+ effector T cells, concomitantly with CD4+ T helper cell activation.