Immunostimulatory RNA blocks suppression by regulatory T cells

Activated B-Cells enhance epitope spreading to support successful cancer immunotherapy

Immune checkpoint therapies (ICT) have transformed the treatment of cancer over the past decade. However, many patients do not respond or suffer relapses. Successful immunotherapy requires epitope spreading, but the slow or inefficient induction of functional antitumoral immunity delays the benefit to patients or causes resistances. Therefore, understanding the key mechanisms that support epitope spreading is essential to improve immunotherapy. In this review, we highlight the major role played by B-cells in breaking immune tolerance by epitope spreading. Activated B-cells are key Antigen-Presenting Cells (APC) that diversify the T-cell response against self-antigens, such as ribonucleoproteins, in autoimmunity but also during successful cancer immunotherapy. This has important implications for the design of future cancer vaccines.

The role of toll-like receptors in immune tolerance induced by Helicobacter pylori infection

Helicobacter pylori (H. pylori) is a gram-negative, microaerobic bacterium that colonizes the gastric mucosa in about half of the world's population. H. pylori infection can lead to various diseases. Chronic infection by H. pylori exposes the gastric mucosa to bacterial components such as lipopolysaccharide (LPS), outer membrane vesicles (OMVs), and several toxic proteins. Infected with H. pylori activates the release of pro-inflammatory factors and triggers inflammatory responses that damage the gastric mucosa. As the only microorganism that permanently colonizes the human stomach, H. pylori can suppress host immunity to achieve long-term colonization. Toll-like receptors (TLRs) play a crucial role in T-cell activation, promoting innate immune responses and immune tolerance during H. pylori infection. Among the 10 TLRs found in humans, TLR2, TLR4, TLR5, and TLR9 have been thoroughly investigated in relation to H. pylori-linked immune regulation. In the present review, we provide a comprehensive analysis of the various mechanisms employed by different TLRs in the induction of immune tolerance upon H. pylori infection, which will contribute to the research of pathogenic mechanism of H. pylori.

Systemic Administration of the TLR7/8 Agonist Resiquimod (R848) to Mice Is Associated with Transient, In Vivo-Detectable Brain Swelling

Peripheral administration of the E. coli endotoxin lipopolysaccharide (LPS) to rats promotes secretion of pro-inflammatory cytokines and in previous studies was associated with transient enlargement of cortical volumes. Here, resiquimod (R848) was administered to mice to stimulate peripheral immune activation, and the effects on brain volumes and neurometabolites determined. After baseline scans, 24 male, wild-type C57BL mice were triaged into three groups including R848 at low (50 μg) and high (100 μg) doses and saline controls. Animals were scanned again at 3 h and 24 h following treatment. Sickness indices of elevated temperature and body weight loss were observed in all R848 animals. Animals that received 50 μg R848 exhibited decreases in hippocampal N-acetylaspartate and phosphocreatine at the 3 h time point that returned to baseline levels at 24 h. Animals that received the 100 μg R848 dose demonstrated transient, localized, volume expansion (~5%) detectable at 3 h in motor, somatosensory, and olfactory cortices; and pons. A metabolic response evident at the lower dose and a volumetric change at the higher dose suggests a temporal evolution of the effect wherein the neurochemical change is demonstrable earlier than neurostructural change. Transient volume expansion in response to peripheral immune stimulation corresponds with previous results and is consistent with brain swelling that may reflect CNS edema.

Activation of Innate Immunity by Therapeutic Nucleic Acids

Nucleic acid-based therapeutics have gained increased attention during recent decades because of their wide range of application prospects. Immunostimulatory nucleic acids represent a promising class of potential drugs for the treatment of tumoral and viral diseases due to their low toxicity and stimulation of the body’s own innate immunity by acting on the natural mechanisms of its activation. The repertoire of nucleic acids that directly interact with the components of the immune system is expanding with the improvement of both analytical methods and methods for the synthesis of nucleic acids and their derivatives. Despite the obvious progress in this area, the problem of delivering therapeutic acids to target cells as well as the unresolved issue of achieving a specific therapeutic effect based on activating the mechanism of interferon and anti-inflammatory cytokine synthesis. Minimizing the undesirable effects of excessive secretion of inflammatory cytokines remains an unsolved task. This review examines recent data on the types of immunostimulatory nucleic acids, the receptors interacting with them, and the mechanisms of immunity activation under the action of these molecules. Finally, data on immunostimulatory nucleic acids in ongoing and completed clinical trials will be summarized.

The role of innate immune signals in antitumor immunity

Innate immunity serves as a first line of defense against infectious agents, and germ-line-encoded pattern recognition receptors detect stressed and infected cells and elicit potent effector activities that accomplish efficient microbe containment. Recent evidence demonstrates that these pattern-sensing systems are also applicable to the recognition of tumor-derived stress-related factors. In particular, toll-like receptors and cytosolic sensors for DNA and RNA recognition utilize endogenous host elements containing microbial components, danger-associated molecules, and/or nucleic acids to stimulate innate signaling pathways and generate protective immune responses against nascent tumors in animal models and humans. In this review, we describe recent advances and perspectives about antitumor mechanisms and clinical application of innate immune signals and pathways.

Systemic cancer immunotherapy with Toll-like receptor 7 agonists: Timing is everything

Toll-like receptor (TLR) 7 agonists represent a promising strategy for the immunotherapy of cancer. We have recently investigated the influence of TLR tolerance on the efficacy of systemic tumor treatment with TLR7 ligands. We propose that considering the kinetics of receptor sensitivity highly improves the outcome of cancer immunotherapy.

Supramolecular assembly of Toll-like receptor 7/8 agonist into multimeric water-soluble constructs enables superior immune stimulation in vitro and in vivo

Resiquimod or R848 (RSQD) is a Toll-like receptor (TLR) 7/8 agonist which shows promise as vaccine adjuvant due to its potential to promote highly desirable cellular immunity. The development of this small molecule in the field to date has been largely impeded by its rapid in vivo clearance and lack of association with vaccine antigens. Here, we report a multimeric TLR 7/8 construct of nano-scale size, which results from a spontaneous self-assembly of RSQD with a water-soluble clinical-stage polymer - poly[di(carboxylatophenoxy)phosphazene] (PCPP). The formation of ionically paired construct (PCPP-R) and a ternary complex, which also includes Hepatitis C virus (HCV) antigen, has been demonstrated by dynamic lights scattering (DLS), turbidimetry, fluorescence spectroscopy, asymmetric flow field flow fractionation (AF4), and ¹H NMR spectroscopy methods. The resulting supramolecular assembly PCPP-R enabled superior immunostimulation in cellular assays (mouse macrophage reporter cell line) and displayed improved in vitro hemocompatibility (human erythrocytes). In vivo studies demonstrated that PCPP-R adjuvanted HCV formulation induced higher serum neutralization titers in BALB/c mice and shifted the response towards desirable cellular immunity, as evaluated by antibody isotype ratio (IgG2a/IgG1) and ex vivo analysis of cytokine secreting splenocytes (higher levels of interferon gamma (IFN-γ) single and tumor necrosis factor alpha (TNF-α)/IFN-γ double producing cells). The non-covalent multimerization approach stands in contrast to previously suggested RSQD delivery methods, which involve covalent conjugation or encapsulation, and offers a flexible methodology that can be potentially integrated with other parenterally administered drugs.

Harnessing the immune system to fight cancer with Toll-like receptor and RIG-I-like receptor agonists

Cancer immunotherapy has come of age with the advent of immune checkpoint inhibitors. In this article we review how agonists for receptors of the innate immune system, the Toll-like receptors and the RIG-I-like receptors, impact anticancer immune responses. Treatment with these agonists enhances the activity of anticancer effector cells, such as cytotoxic T cells and NK cells, and at the same time blocks the activity of immunosuppressive cell types such as regulatory T cells and myeloid-derived suppressor cells. These compounds also impact the recruitment of immune cells to the tumor. The phenomena of pattern-recognition receptor tolerance and reprogramming and their implications for immunotherapy are discussed. Finally, novel delivery systems that target the immune-stimulating drugs to the tumor or the tumor-draining lymph nodes to enhance their efficacy and safety are presented.

Extracellular Vesicles Derived Human-miRNAs Modulate the Immune System in Type 1 Diabetes

Extracellular vesicles with their molecular cargo can modulate target cell response and may affect the pathogenesis of diseases. The extracellular vesicles containing micro-RNAs (miRNAs), which are often studied as disease biomarkers, but rarely as mediators of the disease development. The role of extracellular vesicles derived miRNAs in type 1 diabetes is currently not well established. We observed a fraction of blood plasma extracellular vesicles positive for membrane proteins potentially associated with insulin-producing beta-cells and identified differentially expressed extracellular vesicles derived miRNAs in individuals with type 1 diabetes. These differentially expressed extracellular vesicles derived human miRNAs in participants with type 1 diabetes and participants with Langerhans islets beta-cells destruction showed the ability to activate TLR7/8 signaling cascade and increase activation as well as cytotoxicity of the effector blood immune cells with cytokine and chemokine release. Our results illustrate extracellular vesicles derived human miRNAs as modulators of the immune system in type 1 diabetes autoimmunity, providing potentially new insight into the pathogenesis of the disease, and novel molecular targets for intervention and type 1 diabetes prevention.

Molecular Mechanism of the Antiproliferative Activity of Short Immunostimulating dsRNA

Small double-stranded RNAs with certain sequence motifs are able to interact with pattern-recognition receptors and activate the innate immune system. Recently, we identified a set of short double-stranded 19-bp RNA molecules with 3-nucleotide 3′-overhangs that exhibited pronounced antiproliferative activity against cancer cells in vitro, and antitumor and antimetastatic activities in mouse models in vivo. The main objectives of this study were to identify the pattern recognition receptors that mediate the antiproliferative action of immunostimulating RNA (isRNA). Two cell lines, epidermoid carcinoma KB-3-1 cells and lung cancer A549 cells, were used in the study. These lines respond to the action of isRNA by a decrease in the growth rate, and in the case of A549 cells, also by a secretion of IL-6. Two sets of cell lines with selectively silenced genes encoding potential sensors and signal transducers of isRNA action were obtained on the basis of KB-3-1 and A549 cells. It was found that the selective silencing of PKR and RIG-I genes blocked the antiproliferative effect of isRNA, both in KB-3-1 and A549 cells, whereas the expression of MDA5 and IRF3 was not required for the antiproliferative action of isRNA. It was shown that, along with PKR and RIG-I genes, the expression of IRF3 also plays a role in isRNA mediated IL-6 synthesis in A549 cells. Thus, PKR and RIG-I sensors play a major role in the anti-proliferative signaling triggered by isRNA.

CCL22 Signaling in the Tumor Environment

T cell-mediated elimination of malignant cells is one cornerstone of endogenous and therapeutically induced antitumor immunity. Tumors exploit numerous regulatory mechanisms to suppress T cell immunity. Regulatory T cells (T regs) play a crucial role in this process due to their ability to inhibit antitumoral immune responses and they are known to accumulate in various cancer entities. The chemokine CCL22, predominately produced by dendritic cells (DCs), regulates T reg migration via binding to its receptor CCR4. CCL22 controls T cell immunity, both by recruiting T regs to the tumor tissue and by promoting the formation of DC-T reg contacts in the lymph node. Here, we review the current knowledge on the role of CCL22 in cancer immunity. After revising the principal mechanisms of CCL22-induced immune suppression, we address the factors leading to CCL22 expression and ways of targeting this chemokine therapeutically. Therapeutic interventions to the CCL22-CCR4 axis may represent a promising strategy in cancer immunotherapy.

Tumour infiltrating lymphocytes and immune-related genes as predictors of outcome in pancreatic adenocarcinoma

BACKGROUND

We investigated the correlation between pancreatic ductal adenocarcinoma patient prognosis and the presence of tumour infiltrating lymphocytes and expression of 521 immune system genes.

METHODS

Intratumoural CD3+, CD8+, and CD20+ lymphocytes were examined by immunohistochemistry in 12 PDAC patients with different outcomes who underwent pancreaticoduodenectomy. The results were correlated with gene expression profile using the digital multiplexed NanoString nCounter analysis system (NanoString Technologies, Seattle, WA, USA).

RESULTS

Twenty immune system genes were significantly differentially expressed in patients with a good prognosis relative to patients with a worse prognosis: TLR2 and TLR7 (Toll-like receptor superfamily); CD4, CD37, FOXP3, PTPRC (B cell and T cell signalling); IRF5, IRF8, STAT1, TFE3 (transcription factors); ANP32B, CCND3 (cell cycle); BTK (B cell development); TNF, TNFRF1A (TNF superfamily); HCK (leukocyte function); C1QA (complement system); BAX, PNMA1 (apoptosis); IKBKE (NFκB pathway). Differential expression was more than twice log 2 for TLR7, TNF, C1QA, FOXP3, and CD37.

DISCUSSION

Tumour infiltrating lymphocytes were present at higher levels in samples from patients with better prognosis. Our findings indicate that tumour infiltrating lymphocyte levels and expression level of the immune system genes listed above influence pancreatic ductal adenocarcinoma prognosis. This information could be used to improve selection of best responders to immune inhibitors.

5'-triphosphate siRNA targeting HBx elicits a potent anti-HBV immune response in pAAV-HBV transfected mice

RNA with 5'-triphosphate (3p-RNA) is recognized by RNA sensor RIG-I (retinoic acid-inducible gene I protein). Previously, we reported that small interfering RNA targeting HBx (3p-siHBx) could confer potent anti-hepatitis B virus (HBV) efficacy via HBx silencing and RIG-I activation. However, the characteristics of innate and adaptive immunity especially exhaustion profiles in the liver microenvironment in response to 3p-siHBx therapy have not been fully elucidated. Here, we observed that 3p-siHBx more significantly inhibited HBV replication in vivo. 3p-siHBx enhanced natural killer (NK) cell activation with KLRG1 and CD69 upregulation and interferon (IFN)-γ secretion. 3p-siHBx significantly reversed the exhaustion phenotype of CD8⁺ T cells, and augmented CD8⁺ T cell activation and function. Importantly, 3p-siHBx disrupted the differentiation of myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg), accompanied by the reduction of the immunosuppressive cytokines interleukin (IL)-10 and transforming growth factor (TGF)-β. 3p-siHBx also enhanced dendritic cell maturation. Further investigation showed that RIG-I was involved in 3p-siHBx-induced IFN-α, IFN-β, and IFN-λ production. Moreover, RIG-I activation in HBV⁺ hepatocytes would improve the recruitment of CD8⁺ T cells and NK cells. These results reveal that 3p-siHBx therapy can improve the immune microenvironment in HBV-carrier liver and inhibit HBV replication, indicating the potential utility of RIG-I ligands as molecular adjuvants for viral vaccines or candidate drugs.

Polymer-based nanoparticles loaded with a TLR7 ligand to target the lymph node for immunostimulation

Small-molecule agonists for the Toll-like receptors (TLR) 7 and 8 are effective for the immunotherapy of skin cancer when used as topical agents. Their systemic use has however been largely unsuccessful due to dose-limiting toxicity. We propose a polymer-based nanodelivery system to target resiquimod, a TLR7 ligand, to the lymph node in order to focus the immunostimulatory activity and to prevent a generalized inflammatory response. We demonstrate successful encapsulation of resiquimod in methoxypoly(ethylene glycol)-b-poly(DL-lactic acid) (mPEG-PLA) and mixed poly(DL-lactic-co-glycolic acid) (PLGA)/mPEG-PLA nanoparticles. We show that these particles are taken up mainly by dendritic cells and macrophages, which are the prime initiators of anticancer immune responses. Nanoparticles loaded with resiquimod activate these cells, demonstrating the availability of the immune-stimulating cargo. The unloaded particles are non-inflammatory and do not have cytotoxic activity on immune cells. Following subcutaneous injection in mice, mPEG-PLA and PLGA/mPEG-PLA nanoparticles are detected in dendritic cells and macrophages in the draining lymph nodes, demonstrating the targeting potential of these particles. Thus, polymer-based nanoparticles represent a promising delivery system that allows lymph node targeting for small-molecule TLR7 agonists in the context of systemic cancer immunotherapy.

Viral RNA-Unprimed Rig-I Restrains Stat3 Activation in the Modulation of Regulatory T Cell/Th17 Cell Balance

Innate immunity activation by viral RNA-primed retinoid acid inducible gene-I (Rig-I) in CD4⁺ T cells antagonizes TGFβ signaling to suppress the differentiation of regulatory T cells (Tregs). However, how viral RNA-unliganded Rig-I (apo-Rig-I) modulates Treg generation remains unclear. In this article, we show that, in the absence of viral infection, Treg differentiation of Rig-I^-/- CD4⁺ T cells was compromised, in the presence of increased generation of Th17 cells and overactivation of Stat3, a critical regulator tilting the Treg/Th17 cell balance. Mechanistically, apo-Rig-I physically associates with Stat3, thereby inhibiting Jak1's association with Stat3 while facilitating Shp2's association to inhibit p-Stat3 levels. Interestingly, inhibition of Stat3 ameliorates the Treg/Th17 imbalance and the colitis observed in Rig-I^-/- mice. Collectively, these results uncover an independent functional contribution of the apo-Rig-I/Stat3 interaction in the maintenance of Treg/Th17 cell balance.

Immunotherapy of Dual-Function Vector with Both Immunostimulatory and B-Cell Lymphoma 2 (Bcl-2)-Silencing Effects on Gastric Carcinoma

BACKGROUND Tumorigenesis is a kind of pathology marked by infinite proliferation and restrained apoptosis compared with normal cells. The abnormal expression of some proto-oncogenes and apoptosis inhibition are essential for tumor growth, which has been confirmed by molecular biologic and immunologic studies. The hypofunction of the host immune system also drives the development and metastasis of malignant tumors. Bcl-2, which has a critical role in regulating apoptosis, is overexpressed in several cancers. MATERIAL AND METHODS In this study, we constructed a dual-function small hairpin RNA (shRNA) vector containing an Bcl-2-silencing shRNA and a TLR7-stimulating ssRNA and examined it effect on tumor cell growth and proliferation. RESULTS Stimulation with this bi-functional vector in vitro promoted significant apoptosis of MFC cells by regulating the expression of apoptosis-related proteins and induced secretion of type I IFNs. Most importantly, this bi-functional vector more effectively inhibited subcutaneous MFC cell growth than did single shRNA and ssRNA treatment in vivo. Natural killer (NK) and CD4+ T cells were required for effective tumor suppression, and TLR7 was shown to play a helper role in the activation of NK cells and CD4+ T cells, possibly by regulating the expression of receptors or secretion of cytokines. CONCLUSIONS This bi-functional vector that contained ssRNA and shRNA may represent a promising approach for tumor therapy.

Extrinsic MAVS signaling is critical for Treg maintenance of Foxp3 expression following acute flavivirus infection

Given the rapid spread of flaviviruses such as West Nile virus (WNV) and Zika virus, it is critical that we develop a complete understanding of the key mediators of an effective anti-viral response. We previously demonstrated that WNV infection of mice deficient in mitochondrial antiviral-signaling protein (MAVS), the signaling adaptor for RNA helicases such as RIG-I, resulted in increased death and dysregulated immunity, which correlated with a failure of Treg expansion following infection. Thus, we sought to determine if intrinsic MAVS signaling is required for participation of Tregs in anti-WNV immunity. Despite evidence of increased Treg cell division, Foxp3 expression was not stably maintained after WNV infection in MAVS-deficient mice. However, intrinsic MAVS signaling was dispensable for Treg proliferation and suppressive capacity. Further, we observed generation of an effective anti-WNV immune response when Tregs lacked MAVS, thereby demonstrating that Treg detection of the presence of WNV through the MAVS signaling pathway is not required for generation of effective immunity. Together, these data suggest that while MAVS signaling has a considerable impact on Treg identity, this effect is not mediated by intrinsic MAVS signaling but rather is likely an effect of the overproduction of pro-inflammatory cytokines generated in MAVS-deficient mice after WNV infection.

Reprogramming of TLR7 signaling enhances antitumor NK and cytotoxic T cell responses

Toll-like receptor (TLR) 7 agonists are effective in topical application for the immunotherapy of skin cancers, but their performance for the systemic treatment of solid tumors is limited by the development of TLR tolerance. In this study, we describe a novel strategy to overcome TLR tolerance and enhance TLR7-dependent antitumor immune responses through reprogramming of TLR signaling pathways. The sensitivity of TLR7 signaling in dendritic cells (DC) was increased by prior stimulation with the dsRNA poly(I:C) that mimics virally induced immune activation. Timing of the stimulations was important, as sequential stimulation with poly(I:C) and the TLR7 agonist R848 interspaced by 24 h induced higher MAPK and NFkB signaling in DC than the simultaneous application of the same ligands. DC activated by sequential poly(I:C)/R848 stimulation efficiently induced Th1 differentiation and primed NK-cell and cytotoxic T-cell responses. We have developed a treatment regimen taking advantage of TLR7 reprogram-ming that cured over 80% of large immunogenic tumors in mice by the action of NK cells and cytotoxic T cells. These results have direct implications for the use of these clinically established ligands in the immunotherapy of cancer.

TLR7-based cancer immunotherapy decreases intratumoral myeloid-derived suppressor cells and blocks their immunosuppressive function

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells with the capacity to inhibit immunological responses. During cancer progression, MDSC are recruited to the tumor sites and secondary lymphoid organs, leading to the suppression of the antitumor function of NK and T cells. Here, we show that the TLR7/8 agonist resiquimod (R848) has a direct effect on MDSC populations in tumor-bearing mice. Systemic application of R848 led to a rapid reduction in both intratumoral and circulating MDSC. The subpopulation of monocytic MDSC (m-MDSC) was the most affected by R848 treatment with an up to 5-fold decrease in the tumor. We found that TLR7 stimulation in tumor-bearing mice led to a maturation and differentiation of MDSC with upregulation of the surface molecules CD11c, F4/80, MHC-I, and MHC-II. MDSC treated with R848 lost their immunosuppressive function and acquired instead an antigen-presenting phenotype with the capability to induce specific T-cell proliferation. Importantly, we found that MDSC co-injected s.c. with CT26 tumor cells lost their ability to support tumor growth after pretreatment with R848. Our results demonstrate that treatment of tumor-bearing mice with a TLR7/8 agonist acts directly on MDSC to induce their maturation and leads them to acquire a non-suppressive status. Considering the obstacles posed by MDSC for cancer immunotherapy, targeting these cells by a TLR7/8 agonist may improve immune responses against cancer.

Lung Injury Combined with Loss of Regulatory T Cells Leads to De Novo Lung-Restricted Autoimmunity

More than one third of patients with chronic lung disease undergoing lung transplantation have pre-existing Abs against lung-restricted self-Ags, collagen type V (ColV), and k-α1 tubulin (KAT). These Abs can also develop de novo after lung transplantation and mediate allograft rejection. However, the mechanisms leading to lung-restricted autoimmunity remain unknown. Because these self-Ags are normally sequestered, tissue injury is required to expose them to the immune system. We previously showed that respiratory viruses can induce apoptosis in CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs), the key mediators of self-tolerance. Therefore, we hypothesized that lung-tissue injury can lead to lung-restricted immunity if it occurs in a setting when Tregs are impaired. We found that human lung recipients who suffer respiratory viral infections experienced a decrease in peripheral Tregs. Pre-existing lung allograft injury from donor-directed Abs or gastroesophageal reflux led to new ColV and KAT Abs post respiratory viral infection. Similarly, murine parainfluenza (Sendai) respiratory viral infection caused a decrease in Tregs. Intratracheal instillation of anti-MHC class I Abs, but not isotype control, followed by murine Sendai virus infection led to development of Abs against ColV and KAT, but not collagen type II (ColII), a cartilaginous protein. This was associated with expansion of IFN-γ-producing CD4(+) T cells specific to ColV and KAT, but not ColII. Intratracheal anti-MHC class I Abs or hydrochloric acid in Foxp3-DTR mice induced ColV and KAT, but not ColII, immunity, only if Tregs were depleted using diphtheria toxin. We conclude that tissue injury combined with loss of Tregs can lead to lung-tissue-restricted immunity.

Suppression of intratumoral CCL22 by type i interferon inhibits migration of regulatory T cells and blocks cancer progression

The chemokine CCL22 is abundantly expressed in many types of cancer and is instrumental for intratumoral recruitment of regulatory T cells (Treg), an important subset of immunosuppressive and tumor-promoting lymphocytes. In this study, we offer evidence for a generalized strategy to blunt Treg activity that can limit immune escape and promote tumor rejection. Activation of innate immunity with Toll-like receptor (TLR) or RIG-I-like receptor (RLR) ligands prevented accumulation of Treg in tumors by blocking their immigration. Mechanistic investigations indicated that Treg blockade was a consequence of reduced intratumoral CCL22 levels caused by type I IFN. Notably, stable expression of CCL22 abrogated the antitumor effects of treatment with RLR or TLR ligands. Taken together, our findings argue that type I IFN blocks the Treg-attracting chemokine CCL22 and thus helps limit the recruitment of Treg to tumors, a finding with implications for cancer immunotherapy.

Regulatory T-cell homeostasis: steady-state maintenance and modulation during inflammation

Regulatory T (Treg) cells play a vital role in the prevention of autoimmunity and the maintenance of self-tolerance, but these cells also have an active role in inhibiting immune responses during viral, bacterial, and parasitic infections. Although excessive Treg activity can lead to immunodeficiency, chronic infection, and cancer, too little Treg activity results in autoimmunity and immunopathology and impairs the quality of pathogen-specific responses. Recent studies have helped define the homeostatic mechanisms that support the diverse pool of peripheral Treg cells under steady-state conditions and delineate how the abundance and function of Treg cells changes during inflammation. These findings are highly relevant for developing effective strategies to manipulate Treg cell activity to promote allograft tolerance and treat autoimmunity, chronic infection, and cancer.

Analysis of FoxP3+ T-regulatory cells and CD8+ T-cells in ovarian carcinoma: location and tumor infiltration patterns are key prognostic markers

Purpose

Tumor infiltrating CD4+CD25+FoxP3+ regulatory immune cells (Treg) have been associated with impaired anti- tumor immune response and unfavorable prognosis for patients affected by ovarian carcinoma, whereas CD8+ T-cells have been found to positively influence survival rates in a large panel of solid tumors. Recently, density, location and tumor infiltration patterns of the respective immune cell subtypes have been identified as key prognostic factors for different types of tumors.

Patients and Methods

We stained 210 human ovarian carcinoma samples immunhistochemically for FoxP3 and CD8 to identify the impact different immune cell patterns have on generally accepted prognostic variables as well as on overall survival.

Results

We found that FoxP3+ cells located within lymphoid aggregates surrounding the tumor were strongly associated with reduced survival time (P = 0.007). Central accumulation of CD8+ effector cells within the tumor bed shows a positive effect on survival (P = 0,001).

Conclusion

The distribution pattern of immune cells within the tumor environment strongly influences prognosis and overall survival time of patients with ovarian carcinoma.

MicroRNA-29b modulates innate and antigen-specific immune responses in mouse models of autoimmunity

In addition to important regulatory roles in gene expression through RNA interference, it has recently been shown that microRNAs display immune stimulatory effects through direct interaction with receptors of innate immunity of the Toll-like receptor family, aggravating neuronal damage and tumour growth. Yet no evidence exists on consequences of microRNA immune stimulatory actions in the context of an autoimmune disease. Using microRNA analogues, we here show that pancreatic beta cell-derived microRNA sequences induce pro-inflammatory (TNFa, IFNa, IL-12, IL-6) or suppressive (IL-10) cytokine secretion by primary mouse dendritic cells in a sequence-dependent manner. For miR-29b, immune stimulation in RAW264.7 macrophages involved the endosomal Toll-like receptor-7, independently of the canonical RNA interference pathway. In vivo, the systemic delivery of miR-29b activates CD11b+B220- myeloid and CD11b-B220+ plasmacytoid dendritic cells and induces IFNa, TNFa and IL-6 production in the serum of recipient mice. Strikingly, in a murine model of adoptive transfer of autoimmune diabetes, miR-29b reduces the cytolytic activity of transferred effector CD8+ T-cells, insulitis and disease incidence in a single standalone intervention. Endogenous miR-29b, spontaneously released from beta-cells within exosomes, stimulates TNFa secretion from spleen cells isolated from diabetes-prone NOD mice in vitro. Hence, microRNA sequences modulate innate and ongoing adaptive immune responses raising the question of their potential role in the breakdown of tolerance and opening up new applications for microRNA-based immune therapy.

Immunotherapy for hepatoma using a dual-function vector with both immunostimulatory and pim-3-silencing effects

Tumorigenesis is an immortalization process in which the growth of normal cells is uncontrolled and programmed cell death is suppressed. Molecular biologic and immunologic studies have revealed that the aberrant expression of some proto-oncogenes boosts proliferation and inhibits apoptosis, which is vital for tumor development. The hypofunction of the host immune system also drives the development and metastasis of malignant tumors. Pim-3, a member of the Pim family, is aberrantly expressed in several cancers. Data suggest that Pim-3 inhibits apoptosis by phosphorylating the proapoptotic BH3-only protein Bad. Here, we constructed a dual-function small hairpin RNA (shRNA) vector containing an shRNA targeting Pim-3 and a TLR7-stimulating ssRNA. Stimulation with this bi-functional vector in vitro promoted significant apoptosis of Hepa1-6 cells by regulating the expression of apoptosis-related proteins and induced secretion of type I IFNs. Most importantly, this bi-functional vector more effectively inhibited subcutaneous Hepa1-6 cell growth than did single shRNA and ssRNA treatment in vivo. Natural killer (NK), CD4(+) T, and CD8(+) T cells and macrophages were required for effective tumor suppression, and CD4(+) T cells were shown to play a helper role in the activation of NK cells, possibly by regulating the secretion of Th1 or Th2 cytokines. This ssRNA-shRNA bi-functional vector may represent a promising approach for tumor therapy.

A modular approach to suppression assays: TLR ligands, conditioned medium, and viral infection

The suppressive function of regulatory T-cells (Treg) requires precise control to allow an efficient adaption of the T-cell response to the requirements of the immune defense. In the setting of infection, an abrogation of the suppressive effect of Treg on the activation and proliferation of T-effector (Teff) cells is a central precondition to allow fast and efficient clearance of the infectious agent. Experimentally, the suppressive function of Treg on Teff can be indirectly measured in coculture proliferation assays. This versatile tool provides a readout of T cell proliferation in the presence of Treg through the measurement of a proliferation marker such as the incorporation of radioactively labeled thymidine ((3)H Thymidine), carboxyfluorescein succinimidyl ester (CFSE) or 5-Bromo-2'-deoxyuridine (BrdU). In a modular approach, the culture conditions can thereby be adapted to evaluate the effect of any cell type, live and inactivated microorganisms, molecularly defined immunostimulatory ligands, and cytokines on the interplay of Teff and Treg function. Here, we demonstrate how the suppression assay can be used as a multifunctional tool to provide insights into the interaction of Treg with Teff under a variety of conditions in vitro.

Rhinovirus has the unique ability to directly activate human T cells in vitro

BACKGROUND

Rhinovirus infection is a leading cause of exacerbation of airway diseases. We hypothesize that airway viruses activate inflammatory cells, inducing airway dysfunction. We have previously shown that airway viruses can induce eosinophil degranulation when cocultured with T cells and monocyte-derived dendritic cells (moDCs). These findings suggested that antigen presentation was important for T-cell activation.

OBJECTIVE

Given the clinical importance of rhinovirus, we sought to determine whether it had any unique abilities to activate inflammatory cells compared with another common virus, such as respiratory syncytial virus (RSV).

METHODS

We cocultured combinations of human leukocytes (T cells, moDCs, and eosinophils) with each virus. Using assays of BrdU incorporation, flow cytometry, and ELISA, we measured T-cell activation, rhinovirus expression, T-cell death, and eosinophil cysteinyl leukotriene release.

RESULTS

In contrast to RSV, rhinovirus induced T-cell activation without the involvement of moDCs. Without moDCs, rhinovirus induced T-cell proliferation of both CD4 and CD8(+) cells, cytokine production, and ultimately, eosinophil stimulation. Although chloroquine inhibited RSV-induced activation of T cells through moDCs, rhinovirus was not inhibited; UV inactivation did block the rhinovirus effect. We also found that T cells could be infected by rhinovirus in vitro and within human nasal explant tissue. Although Toll-like receptors did not appear to be involved in T-cell activation, antagonists of Jun N-terminal kinase and nuclear factor κB did inhibit T-cell responses to rhinovirus.

CONCLUSION

Rhinovirus has the unique ability to bypass antigen presentation and directly infect and activate human T cells. This could explain the strong association of rhinovirus with exacerbation of airway diseases.

Innate receptors for adaptive immunity

Pattern recognition receptors (PRRs) are commonly known as sensor proteins crucial for the early detection of microbial or host-derived stress signals by innate immune cells. Interestingly, some PRRs are also expressed and functional in cells of the adaptive immune system. These receptors provide lymphocytes with innate sensing abilities; for example, B cells express Toll-like receptors, which are important for the humoral response. Strikingly, certain other NOD-like receptors are not only highly expressed in adaptive immune cells, but also exert functions related specifically to adaptive immune system pathways, such as regulating antigen presentation. In this review, we will focus particularly on the current understanding of PRR functions intrinsic to B and T lymphocytes; a developing aspect of PRR biology.

TLR7 and TLR9 in SLE: when sensing self goes wrong

Autoreactive B and T cells are present in healthy, autoimmunity-free individuals, but they are kept in check by various regulatory mechanisms. In systemic lupus erythematosus (SLE) patients, however, autoreactive cells are expanded, activated, and produce large quantities of autoantibodies, directed especially against nuclear antigens. These antibodies form immune complexes with self-nucleic acids present in SLE serum. Since self-DNA and self-RNA in the form of protein complexes can act as TLR9 and TLR7 ligands, respectively, TLR stimulation is suggested as an additional signal contributing to activation and/or modulation of the aberrant adaptive immune response. Data from mouse models suggest a pathogenic role for TLR7 and a protective role for TLR9 in the pathogenesis of SLE. Future investigations are needed to elucidate the underlying modulatory mechanisms and the role of TLR7 and TLR9 in the complex pathogenesis of human SLE.

Layers of dendritic cell-mediated T cell tolerance, their regulation and the prevention of autoimmunity

The last decades of Nobel prize-honored research have unequivocally proven a key role of dendritic cells (DCs) at controlling both T cell immunity and tolerance. A tight balance between these opposing DC functions ensures immune homeostasis and host integrity. Its perturbation could explain pathological conditions such as the attack of self tissues, chronic infections, and tumor immune evasion. While recent insights into the complex DC network help to understand the contribution of individual DC subsets to immunity, the tolerogenic functions of DCs only begin to emerge. As these consist of many different layers, the definition of a “tolerogenic DC” is subjected to variation. Moreover, the implication of DCs and DC subsets in the suppression of autoimmunity are incompletely resolved. In this review, we point out conceptual controversies and dissect the various layers of DC-mediated T cell tolerance. These layers include central tolerance, Foxp3⁺ regulatory T cells (Tregs), anergy/deletion and negative feedback regulation. The mode and kinetics of antigen presentation is highlighted as an additional factor shaping tolerance. Special emphasis is given to the interaction between layers of tolerance as well as their differential regulation during inflammation. Furthermore, potential technical caveats of DC depletion models are considered. Finally, we summarize our current understanding of DC-mediated tolerance and its role for the suppression of autoimmunity. Understanding the mechanisms of DC-mediated tolerance and their complex interplay is fundamental for the development of selective therapeutic strategies, e.g., for the modulation of autoimmune responses or for the immunotherapy of cancer.

The encephalomyocarditis virus

The encephalomyocarditis virus (EMCV) is a small non-enveloped single-strand RNA virus, the causative agent of not only myocarditis and encephalitis, but also neurological diseases, reproductive disorders and diabetes in many mammalian species. EMCV pathogenesis appears to be viral strain- and host-specific, and a better understanding of EMCV virulence factors is increasingly required. Indeed, EMCV is often used as a model for diabetes and viral myocarditis, and is also widely used in immunology as a double-stranded RNA stimulus in the study of Toll-like as well as cytosolic receptors. However, EMCV virulence and properties have often been neglected. Moreover, EMCV is able to infect humans albeit with a low morbidity. Progress on xenografts, such as pig heart transplantation in humans, has raised safety concerns that need to be explored. In this review we will highlight the biology of EMCV and all known and potential virulence factors.

Regulation of Toll-like receptor 5 gene expression and function on mucosal dendritic cells

Toll-like receptor (TLR) 5 has been shown to maintain intestinal homeostasis and regulate host defense against enterobacterial infection. However, how TLR5 expression is regulated and its function in the intestine have not been fully elucidated. Here we demonstrate that mucosal dendritic cells (DCs), but not splenic DCs, express high levels of TLR5 protein. Alternatively spliced Tlr5 transcripts were identified but it did not explain the selective expression of TLR5 on mucosal DCs. Treatment with various bacterial ligands downregulated BMDC TLR5 expression, while retinoic acid and host stromal cell-derived signals promoted TLR5 expression in a TGF-β-independent mechanism. Signaling through TLR5 restrained regulatory T (Treg) cell generation, and accordingly, TLR5^−/− mice displayed increased frequencies of Foxp3⁺ Treg cells in the intestinal lamina propria. Our data indicate that bacterial and host factors differentially regulate DC TLR5 expression. TLR5 signaling regulates immune responses towards the microbiota via modulation of the Treg/effector T cell balance.

Reversal of hepatitis B virus-induced immune tolerance by an immunostimulatory 3p-HBx-siRNAs in a retinoic acid inducible gene I-dependent manner

It is extensively accepted that hepatitis B virus (HBV) escapes from innate immunity by inhibiting type I interferon (IFN) production, but efficient intervention to reverse the immune tolerance is still not achieved. Here, we report that 5'-end triphosphate hepatitis B virus X gene (HBx)-RNAs (3p-HBx-short interfering [si]RNAs) exerted significantly stronger inhibitory effects on HBV replication than regular HBx-siRNAs in stably HBV-expressing hepatoplastoma HepG2.2.15 cells through extremely higher expression of type I IFNs, IFN-induced genes and proinflammatory cytokines, and retinoic acid inducible gene I (RIG-I) activation. Also, 3p-HBx-siRNA were more efficient to stimulate type I IFN response than HBx sequence-unrelated 3p-scramble-siRNA in HepG2.2.15 cells, indicating that a stronger immune-stimulating effect may partly result from the reversal of immune tolerance through decreasing HBV load. In RIG-I-overexpressed HepG2.2.15 cells, 3p-HBx-siRNAs exerted stronger inhibitory effects on HBV replication with greater production of type I IFNs; on the contrary, in RIG-I-silenced HepG2.2.15 cells or after blockade of IFN receptor by monoclonal antibody, inhibitory effect of 3p-HBx-siRNAs on HBV replication was largely attenuated, indicating that immunostimulatory function of 3p-HBx-siRNAs was RIG-I and type I IFN dependent. Moreover, in HBV-carrier mice, 3p-HBx-siRNA more strongly inhibited HBV replication and promoted IFN production than HBx-siRNA in primary HBV(+) hepatocytes and, therefore, significantly decreased serum hepatitis B surface antigen and increased serum IFN-β.

CONCLUSION

3p-HBx-siRNAs may not only directly inhibit HBV replication, but also stimulate innate immunity against HBV, which are both beneficial for the inversion of HBV-induced immune tolerance.

Repression of the genome organizer SATB1 in regulatory T cells is required for suppressive function and inhibition of effector differentiation

Regulatory T cells (T(reg) cells) are essential for self-tolerance and immune homeostasis. Lack of effector T cell (T(eff) cell) function and gain of suppressive activity by T(reg) cells are dependent on the transcriptional program induced by Foxp3. Here we report that repression of SATB1, a genome organizer that regulates chromatin structure and gene expression, was crucial for the phenotype and function of T(reg) cells. Foxp3, acting as a transcriptional repressor, directly suppressed the SATB1 locus and indirectly suppressed it through the induction of microRNAs that bound the SATB1 3' untranslated region. Release of SATB1 from the control of Foxp3 in T(reg) cells caused loss of suppressive function, establishment of transcriptional T(eff) cell programs and induction of T(eff) cell cytokines. Our data support the proposal that inhibition of SATB1-mediated modulation of global chromatin remodeling is pivotal for maintaining T(reg) cell functionality.

Immune signaling by RIG-I-like receptors

The RIG-I-like receptors (RLRs) RIG-I, MDA5, and LGP2 play a major role in pathogen sensing of RNA virus infection to initiate and modulate antiviral immunity. The RLRs detect viral RNA ligands or processed self RNA in the cytoplasm to trigger innate immunity and inflammation and to impart gene expression that serves to control infection. Importantly, RLRs cooperate in signaling crosstalk networks with Toll-like receptors and other factors to impart innate immunity and to modulate the adaptive immune response. RLR regulation occurs at a variety of levels ranging from autoregulation to ligand and cofactor interactions and posttranslational modifications. Abberant RLR signaling or dysregulation of RLR expression is now implicated in the development of autoimmune diseases. Understanding the processes of RLR signaling and response will provide insights to guide RLR-targeted therapeutics for antiviral and immune-modifying applications.

Systemic cancer therapy with a small molecule agonist of toll-like receptor 7 can be improved by circumventing TLR tolerance

Topical application of small molecule Toll-like receptor 7 (TLR7) agonists is highly effective for the treatment of skin tumors, whereas their systemic application has been largely unsuccessful for cancer therapy. One reason may be that repeated systemic application of TLR ligands can induce a state of immune unresponsiveness, termed TLR tolerance. We show here that a single injection of the TLR7 agonist R848 in mice induces a short period of increased response to TLR stimulation followed by a state of hyporesponsiveness lasting several days. This state is characterized by inhibited secretion of the key cytokines interleukin (IL)-12p70 and IL-6 as well as by a block in IFN-α production. We show for the first time that at the cellular level, TLR7 tolerance occurs in both plasmacytoid and myeloid dendritic cells, two cell populations that play a critical role in the initiation and amplification of antitumor immune responses. We further show that TLR7 tolerance in plasmacytoid dendritic cells is accompanied by downregulation of the adaptor protein IL-1 receptor-associated kinase 1. On the basis of these findings, we have designed a novel strategy for the treatment of tumors by using cycles of repeated R848 injections separated by treatment-free intervals. We show in CT26 tumor-bearing mice that this protocol circumvents TLR7 tolerance and improves the efficacy of cancer immunotherapy.

siRNA-induced immunostimulation through TLR7 promotes antitumoral activity against HPV-driven tumors in vivo

Oncogene-specific downregulation mediated by RNA interference (RNAi) is a promising avenue for cancer therapy. In addition to specific gene silencing, in vivo RNAi treatment with short interfering RNAs (siRNAs) can initiate immune activation through innate immune receptors including Toll-like receptors, (TLRs) 7 and 8. Two recent studies have shown that activation of innate immunity by addition of tri-phosphate motifs to oncogene-specific siRNAs, or by co-treatment with CpG oligos, can potentiate siRNA antitumor effects. To date, there are no reports on applying such approach against human papillomavirus (HPV)-driven cancers. Here, we characterized the antitumor effects of non-modified siRNAs that can target a specific oncogene and/or recruit the innate immune system against HPV-driven tumors. Following the characterization of silencing efficacy and TLR7 immunostimulatory potential of 15 siRNAs targeting the HPV type 16 E6/E7 oncogenes, we identified a bifunctional siRNA sequence that displayed both potent gene silencing and active immunostimulation effect. In vivo systemic administration of this siRNA resulted in reduced growth of established TC-1 tumors in C57BL/6 mice. Ablation of TLR7 recruitment via 2'O-methyl modification of the oligo backbone reduced these antitumor effects. Further, a highly immunostimulatory, but non-HPV targeting siRNA was also able to exert antitumoral effects although for less prolonged time compared with the bifunctional siRNA. Collectively, our work demonstrates for the first time that siRNA-induced immunostimulation can have antitumoral effects against HPV-driven tumors in vivo, even independent of gene silencing efficacy.

Respiratory virus-induced dysregulation of T-regulatory cells leads to chronic rejection

BACKGROUND

Lower respiratory viral infections predispose to bronchiolitis obliterans syndrome (BOS). In addition, there is emerging evidence to support the role of autoimmunity in the pathogenesis of BOS. Because CD4(+)CD25(+)Foxp3(+) regulatory T-cells (Treg) control autoimmunity, we tested the hypothesis that respiratory virus-induced Treg dysfunction leads to BOS.

METHODS

Treg frequency was monitored using flow cytometry. Apoptosis, cytokines, and antibodies were analyzed using annexin V assay, LUMINEX, and enzyme-linked immunosorbent assay, respectively. Murine studies were performed using the orthotopic tracheal transplant model.

RESULTS

(A) Human studies: Treg troughs (decrease >50% of baseline) were found in 13 (43.3%) of 30 lung transplant recipients. Treg isolated during troughs revealed increased apoptosis (37.8%). Patients with Treg troughs had increased prevalence of antibodies to self-antigens collagen type I (23.1% vs 5.8% pretrough), collagen V (7.7% vs 0%), and k-alpha tubulin (30.7% vs 11.7%, p < 0.01) at 6 months post-trough. Increased number of Treg troughs correlated with more rapid onset of BOS. (B) Murine studies: Infection of tracheal transplant recipients with murine parainfleunza sendai virus led to increased Treg apoptosis (50.5%) in the draining lymph nodes. Vaccination against sendai virus prior to transplant abrogated apoptosis of Treg. In vitro, sendai virus-infected, but not naive, tracheal epithelial cells demonstrated upregulation of FasL (>3.5-fold) and induction of co-cultured Treg apoptosis (5.6-fold increase).

CONCLUSIONS

Respiratory viral infections cause Treg apoptosis which leads to the development of de novo autoimmunity that may play a role in the pathogenesis of BOS.

Epitope-specific regulatory CD4 T cells reduce virus-induced illness while preserving CD8 T-cell effector function at the site of infection

The role of epitope-specific regulatory CD4 T cells in modulating CD8 T-cell-mediated immunopathology during acute viral infection has not been well defined. In the murine model of respiratory syncytial virus (RSV) infection, CD8 T cells play an important role in both viral clearance and immunopathology. We have previously characterized two RSV epitope-specific CD4 T-cell responses with distinct phenotypic properties. One of them, the IA(b)M(209)-specific subset, constitutively expresses FoxP3 and modulates CD8 T-cell function in vitro. We show here that the IA(b)M(209)-specific CD4 T-cell response regulates CD8 T-cell function in vivo and is associated with diminished RSV-induced illness without affecting viral clearance at the site of infection. Achieving the optimal balance of regulatory and effector T-cell function is an important consideration for designing future vaccines.

Insights into the role of Toll-like receptors in modulation of T cell responses

The innate immune receptors, such as Toll-like receptors (TLRs), are intimately involved in the early sensing of invading microorganisms or their structural components. Engagement of TLRs with their ligands results in activation of several downstream intracellular pathways leading to activation of innate and adaptive immune system cells. It was initially thought that TLRs are primarily expressed by antigen-presenting cells (APCs), such as macrophages and dendritic cells, and that interactions between microbial ligands and TLRs in these cells will indirectly result in activation of cells of the adaptive immune system, especially T cells. However, it has now become evident that TLRs are also expressed by various T cell subsets, such as conventional αβT cells, regulatory T cells, and γδT cells as well as natural killer T cells. Importantly, it appears that at least in some of these T cell subsets, TLRs are functionally active, because stimulation of these cells with TLR agonists in the absence of APCs results in exertion of effector or regulatory functions of T cells. The present review attempts to summarize the recent findings related to TLR expression in different T cell subsets and the direct role of TLRs in the induction and regulation of T cell responses, including those responses that occur at mucosal surfaces. In addition, the potential use of TLR agonists for steering T cell responses as a prophylactic or therapeutic strategy in the context of infectious, allergic or autoimmune diseases is explored.

Efficient eradication of subcutaneous but not of autochthonous gastric tumors by adoptive T cell transfer in an SV40 T antigen mouse model

In stomach cancer, there is a need for new therapeutic strategies, in particular for the treatment of unresectable tumors and micrometastases. We investigated the efficacy of immunotherapy in an autochthonous model of gastric cancer, the CEA424-SV40 T Ag (TAg) transgenic mice. Treatment efficacy against both the autochthonous tumors and s.c. tumors induced by the derived cell line mGC3 were assessed. In wild-type mice, a dendritic cell vaccine loaded with irradiated tumor cells combined with CpG oligonucleotides induced efficient cytotoxic T cell and memory responses against mGC3 s.c. tumors. In contrast, neither s.c. nor autochthonous tumors responded to vaccination in CEA424-SV40 TAg mice, indicating tolerance to the SV40 TAg. To examine whether tumors in these mice were principally accessible to immunotherapy, splenocytes from immune wild-type mice were adoptively transferred into CEA424-SV40 TAg transgenic mice. Treated mice showed complete regression of the s.c. tumors associated with intratumoral infiltrates of CD8 and CD4 T cells. In contrast, the autochthonous gastric tumors in the same mice were poorly infiltrated and did not regress. Thus, even in the presence of an active anti-tumoral T cell response, autochthonous gastric tumors do not respond to immunotherapy. This is the first comparison of the efficacy of adoptive T cell transfer between transplanted s.c. tumors and autochthonous tumors in the same animals. Our results suggest that in gastric cancer patients, even a strong anti-tumor T cell response will not efficiently penetrate the tumor in the absence of additional therapeutic strategies targeting the tumor microenvironment.