DNA hypomethylating agents increase activation and cytolytic activity of CD8+ T cells.

We demonstrate that DNA hypomethylating agent (HMA) treatment can directly modulate the anti-tumor response and effector function of CD8+ T cells. In vivo HMA treatment promotes CD8+ T cell tumor infiltration and suppresses tumor growth via CD8+ T cell-dependent activity. Ex vivo, HMAs enhance primary human CD8+ T cell activation markers, effector cytokine production, and anti-tumor cytolytic activity. Epigenomic and transcriptomic profiling shows that HMAs vastly regulate T cell activation-related transcriptional networks, culminating with over-activation of NFATc1 short isoforms. Mechanistically, demethylation of an intragenic CpG island immediately downstream to the 3' UTR of the short isoform was associated with antisense transcription and alternative polyadenylation of NFATc1 short isoforms. High-dimensional single-cell mass cytometry analyses reveal a selective effect of HMAs on a subset of human CD8+ T cell subpopulations, increasing both the number and abundance of a granzyme Bhigh, perforinhigh effector subpopulation. Overall, our findings support the use of HMAs as a therapeutic strategy to boost anti-tumor immune response.

Radiomics using computed tomography to predict CD73 expression and prognosis of colorectal cancer liver metastases.

BACKGROUND: Finding a noninvasive radiomic surrogate of tumor immune features could help identify patients more likely to respond to novel immune checkpoint inhibitors. Particularly, CD73 is an ectonucleotidase that catalyzes the breakdown of extracellular AMP into immunosuppressive adenosine, which can be blocked by therapeutic antibodies. High CD73 expression in colorectal cancer liver metastasis (CRLM) resected with curative intent is associated with early recurrence and shorter patient survival. The aim of this study was hence to evaluate whether machine learning analysis of preoperative liver CT-scan could estimate high vs low CD73 expression in CRLM and whether such radiomic score would have a prognostic significance. METHODS: We trained an Attentive Interpretable Tabular Learning (TabNet) model to predict, from preoperative CT images, stratified expression levels of CD73 (CD73High vs. CD73Low) assessed by immunofluorescence (IF) on tissue microarrays. Radiomic features were extracted from 160 segmented CRLM of 122 patients with matched IF data, preprocessed and used to train the predictive model. We applied a five-fold cross-validation and validated the performance on a hold-out test set. RESULTS: TabNet provided areas under the receiver operating characteristic curve of 0.95 (95% CI 0.87 to 1.0) and 0.79 (0.65 to 0.92) on the training and hold-out test sets respectively, and outperformed other machine learning models. The TabNet-derived score, termed rad-CD73, was positively correlated with CD73 histological expression in matched CRLM (Spearman's ρ = 0.6004; P < 0.0001). The median time to recurrence (TTR) and disease-specific survival (DSS) after CRLM resection in rad-CD73High vs rad-CD73Low patients was 13.0 vs 23.6 months (P = 0.0098) and 53.4 vs 126.0 months (P = 0.0222), respectively. The prognostic value of rad-CD73 was independent of the standard clinical risk score, for both TTR (HR = 2.11, 95% CI 1.30 to 3.45, P < 0.005) and DSS (HR = 1.88, 95% CI 1.11 to 3.18, P = 0.020). CONCLUSIONS: Our findings reveal promising results for non-invasive CT-scan-based prediction of CD73 expression in CRLM and warrant further validation as to whether rad-CD73 could assist oncologists as a biomarker of prognosis and response to immunotherapies targeting the adenosine pathway.

Targeting the adenosine pathway for cancer immunotherapy.

Suppression of anti-tumor immunity is recognized as a critical step in the development of many types of cancers. Over the past decade, a multitude of immunosuppressive pathways occurring in the tumor microenvironment (TME) have been identified. Amongst them, the hydrolysis of extracellular ATP into adenosine by ecto-nucleotidases has been increasingly documented as new immune checkpoint pathway that can significantly impair anti-tumor immunity of multiple types of cancer. In this review, we summarize past and recent research on the ecto-nucleotidases CD39 and CD73, conducted by our group and others, that recently lead to the development and clinical testing of adenosine targeting agents for cancer immunotherapy.

Prognostic implications of adaptive immune features in MMR-proficient colorectal liver metastases classified by histopathological growth patterns.

BACKGROUND: After resection, colorectal cancer liver metastases (CRLM) surrounded by a desmoplastic rim carry a better prognosis than the metastases replacing the adjacent liver. However, these histopathological growth patterns (HGPs) are insufficient to guide clinical decision-making. We explored whether the adaptive immune features of HGPs could refine prognostication. METHODS: From 276 metastases resected in 176 patients classified by HGPs, tissue microarrays were used to assess intratumoral T cells (CD3), antigen presentation capacity (MHC class I) and CD73 expression producing immunosuppressive adenosine. We tested correlations between these variables and patient outcomes. RESULTS: The 101 (57.4%) patients with dominant desmoplastic HGP had a median recurrence-free survival (RFS) of 17.1 months compared to 13.3 months in the 75 patients (42.6%) with dominant replacement HGP (p = 0.037). In desmoplastic CRLM, high vs. low CD73 was the only prognostically informative immune parameter and was associated with a median RFS of 12.3 months compared to 26.3, respectively (p = 0.010). Only in dominant replacement CRLM, we found a subgroup (n = 23) with high intratumoral MHC-I expression but poor CD3+ T cell infiltration, a phenotype associated with a short median RFS of 7.9 months. CONCLUSIONS: Combining the assessments of HGP and adaptive immune features in resected CRLM could help identify patients at risk of early recurrence.

Ablation of cells in mice using antibody-functionalized multiwalled carbon nanotubes (Ab-MWCNTs) in combination with microwaves.

This is a proof-of-principle study on the combination of microwaves and multiwalled carbon nanotubes to induce in vivo, localized hyperthermic ablation of cells as a potential methodology for the treatment of localized tumors. Compared to conventional methods, the proposed approach can create higher temperatures in a rapid and localized fashion, under low radiation levels, eliminating some of the unwanted side effects. Following successful ablation of cancer cells in cell culture and zebrafish tumor-xenograft models, it is hypothesized that a cancer treatment can be developed using safe microwave irradiation for selective ablation of tumor cells in vivo using carbon nanotube-Antibody (CNT-Ab) conjugates as a targeting agent. In this study, mice were used as an animal model for the optimization of the proposed microwave treatment strategy. The safe dose of CNT-Ab and microwave radiation levels for mice were determined. Further, CNT-Ab distribution and toxicology in mice were qualitatively determined for a time span of two weeks following microwave hyperthermia. The results indicate no toxicity associated with the CNT-Ab in the absence of microwaves. CNTs are only found in the proximity of the site of injection and have been shown to effectively cause hyperthermia induced necrosis upon exposure to microwaves with no noticeable damage to other tissues that are not in direct contact with the CNT-Ab. To understand the cellular immune response towards CNT-Abs, transgenic zebrafish with fluorescently labeled macrophages and neutrophils were used to assay for their ability to phagocytize CNT-Ab. Our results indicate that macrophages and neutrophils were able to actively phagocytose CNT-Abs shortly after injection. Taken together, this is the first study to show that CNTs can be used in combination with microwaves to cause targeted ablation of cells in mice without any side effects, which would be ideal for cancer therapies.

The ectonucleotidases CD39 and CD73: Novel checkpoint inhibitor targets.

Cancers are able to grow by subverting immune suppressive pathways, to prevent the malignant cells as being recognized as dangerous or foreign. This mechanism prevents the cancer from being eliminated by the immune system and allows disease to progress from a very early stage to a lethal state. Immunotherapies are newly developing interventions that modify the patient's immune system to fight cancer, by either directly stimulating rejection-type processes or blocking suppressive pathways. Extracellular adenosine generated by the ectonucleotidases CD39 and CD73 is a newly recognized "immune checkpoint mediator" that interferes with anti-tumor immune responses. In this review, we focus on CD39 and CD73 ectoenzymes and encompass aspects of the biochemistry of these molecules as well as detailing the distribution and function on immune cells. Effects of CD39 and CD73 inhibition in preclinical and clinical studies are discussed. Finally, we provide insights into potential clinical application of adenosinergic and other purinergic-targeting therapies and forecast how these might develop in combination with other anti-cancer modalities.

Phase I/II trial of Durvalumab plus Tremelimumab and stereotactic body radiotherapy for metastatic head and neck carcinoma.

BACKGROUND: The efficacy of immunotherapy targeting the PD-1/PD-L1 pathway has previously been demonstrated in metastatic head and neck squamous cell carcinoma (HNSCC). Stereotactic Body Radiotherapy (SBRT) aims at ablating metastatic lesions and may play a synergistic role with immunotherapy. The purpose of this study is to assess the safety and efficacy of triple treatment combination (TTC) consisting of the administration of durvalumab and tremelimumab in combination with SBRT in metastatic HNSCC. METHOD: This is a phase I/II single arm study that will include 35 patients with 2-10 extracranial metastatic lesions. Patients will receive durvalumab (1500 mg IV every 4 weeks (Q4W)) and tremelimumab (75 mg IV Q4W for a total of 4 doses) until progression, unacceptable toxicity or patient withdrawal. SBRT to 2-5 metastases will be administered between cycles 2 and 3 of immunotherapy. The safety of the treatment combination will be evaluated through assessment of TTC-related toxicities, defined as grade 3-5 toxicities based on Common Terminology Criteria for Adverse Events (v 4.03), occurring within 6 weeks from SBRT start, and that are definitely, probably or possibly related to the combination of all treatments. We hypothesize that dual targeting of PD-L1 and CTLA-4 pathways combined with SBRT will lead to < 35% grade 3-5 acute toxicities related to TTC. Progression free survival (PFS) will be the primary endpoint of the phase II portion of this study and will be assessed with radiological exams every 8 weeks using the RECIST version 1.1 criteria. DISCUSSION: The combination of synergistic dual checkpoints inhibition along with ablative radiation may significantly potentiate the local and systemic disease control. This study constitutes the first clinical trial combining effects of SBRT with dual checkpoint blockade with durvalumab and tremelimumab in the treatment of metastatic HNSCC. If positive, this study would lead to a phase III trial testing this treatment combination against standard of care in metastatic HNSCC. TRIAL REGISTRATION: NCT03283605 . Registration date: September 14, 2017; version 1.

The hepatic effects in dams that ingested 2-aminoanthracene during gestation and lactation.

Diabetes mellitus has been on a continual rise as one of the top chronic diseases to affect individuals worldwide. The goal of this study was to determine how exposure from a well-known toxicant, a polycyclic aromatic hydrocarbon called 2-aminoanthracene (2AA), could potentially lead to diabetes, damage the liver, and have negative effects to the offspring. Humans are exposed to 2AA from foods cooked in high heat and tobacco smoke, among others. To analyze the effects of 2AA, three groups of Sprague Dawley dams consumed an adulterated 2AA diet from gestation to their postnatal period. Timed-pregnant dams ingested 0 mg/kg (control group (C)), 50 mg/kg (low dose group (LD)), and 100 mg/kg (high dose group (HD)) 2AA. Hepatic gene expressions of Adam8, Bax, Ccng1, CD68, CD93, Cdkn1c, and Ddit4 indicated a significant overexpression of Bax, Ccng1, CD68, CD93, and Cdkn1c in treated groups. Although there was no significant difference in the damage to the liver architecture by 2AA, the positively stained CD68+ cells were slightly increased in treated rats. Significant decreases in the albumin and aspartate aminotransferase levels might indicate an inflammatory response from 2AA exposure in dams. Immunoglobulin A (IgA) concentration was also decreased, in contrast to studies of liver cirrhosis that reported increased serum IgA concentration. Overexpression of genes Ddit4, Cdkn1c, Ccng1, Bax, CD93, and CD68 point to hepatic inflammation and apoptosis. Overall results suggest a link between environmental 2AA exposure and adverse liver effects, which has potential to increase susceptibility to type 2 diabetes and other diseases.

Synergistic effects of host B7-H4 deficiency and gemcitabine treatment on tumor regression and anti-tumor T cell immunity in a mouse model.

B7-H4 (B7x/B7S1), a B7 family inhibitor of T cell activity, is expressed in multiple human cancers and correlates with decreased infiltrating lymphocytes and poor prognosis. In murine models, tumor-expressed B7-H4 enhances tumor growth and reduces T cell immunity, and blockade of tumor-B7-H4 rescues T cell activity and lowers tumor burden. This implicates B7-H4 as a target for cancer immunotherapy, yet limits the efficacy of B7-H4 blockade exclusively to patients with B7-H4+ tumors. Given the expression of B7-H4 on host immune cells, we have previously shown that BALB/c mice lacking host B7-H4 have enhanced anti-tumor profiles, yet similar 4T1 tumor growth relative to control. Given that T cell-mediated immunotherapies work best for tumors presenting tumor-associated neoantigens, we further investigated the function of host B7-H4 in the growth of a more immunogenic derivative, 4T1-12B, which is known to elicit strong anti-tumor CD8 T cell responses due to expression of a surrogate tumor-specific antigen, firefly luciferase. Notably, B7-H4 knockout hosts not only mounted greater tumor-associated anti-tumor T cell responses, but also displayed reduced tumors. Additionally, B7-H4-deficiency synergized with gemcitabine to further inhibit tumor growth, often leading to tumor eradication and the generation of protective T cell immunity. These findings imply that inhibition of host B7-H4 can enhance anti-tumor T cell immunity in immunogenic cancers, and can be combined with other anti-cancer therapies to further reduce tumor burden regardless of tumor-B7-H4 positivity.

Targeting A2 adenosine receptors in cancer.

Tumor cells use various ways to evade anti-tumor immune responses. Adenosine, a potent immunosuppressive metabolite, is often found elevated in the extracellular tumor microenvironment. Therefore, targeting adenosine-generating enzymes (CD39 and CD73) or adenosine receptors has emerged as a novel means to stimulate anti-tumor immunity. In particular, the A2 (A2a and A2b) adenosine receptors exhibit similar immunosuppressive and pro-angiogenic functions, yet have distinct biological roles in cancer. In this review, we describe the common and distinct biological consequences of A2a and A2b adenosine receptor signaling in cancer. We discuss recent pre-clinical studies and summarize the different mechanisms-of-action of adenosine-targeting drugs. We also review the rationale for combining inhibitors of the adenosine pathway with other anticancer therapies such immune checkpoint inhibitors, tumor vaccines, chemotherapy and adoptive T cell therapy.

CD73 plays a protective role in collagen-induced arthritis.

Rheumatoid arthritis (RA) is a chronic autoimmune disease with significant morbidity and mortality. Recent studies suggest that modulation of adenosine signaling, a potent immunosuppressive pathway, is a promising approach for treatment of RA. Extracellular adenosine can come from two sources: transport of intracellular adenosine and hydrolysis of extracellular adenine nucleotides by CD73. In this study, we investigated the susceptibility of CD73-deficient C57BL/6 mice to collagen-induced arthritis (CIA), a well-established mouse model of RA. Our data demonstrated that CD73-deficient mice are significantly more susceptible to CIA than wild-type mice. CD73 deficiency resulted in an increased production of proinflammatory cytokines in the joints, increased Th1 T cell responses, and increased joint destruction. Surprisingly, this was accompanied by delayed anticollagen IgG responses, suggesting defective isotype class switching in CD73-deficient mice. Using bone marrow chimera mice, we demonstrated that CD73 expression on nonhematopoietic cells, but not on hematopoietic cells, was important for protection from CIA. We further demonstrated that administration of a selective A2A adenosine receptor agonist to CD73-deficient mice resulted in arthritis incidence similar to wild-type mice in support of a protective role for A2A signaling. Taken together, our study identifies CD73 as an important regulator of CIA in mice. It also strengthens the notion that CD73-generated adenosine by nonhematopoietic cells plays a protective role in RA and suggests that strategies able to enhance CD73 activity or expression levels may be a valid therapeutic option.

Immune evasion in cancer: Mechanistic basis and therapeutic strategies.

Cancer immune evasion is a major stumbling block in designing effective anticancer therapeutic strategies. Although considerable progress has been made in understanding how cancers evade destructive immunity, measures to counteract tumor escape have not kept pace. There are a number of factors that contribute to tumor persistence despite having a normal host immune system. Immune editing is one of the key aspects why tumors evade surveillance causing the tumors to lie dormant in patients for years through "equilibrium" and "senescence" before re-emerging. In addition, tumors exploit several immunological processes such as targeting the regulatory T cell function or their secretions, antigen presentation, modifying the production of immune suppressive mediators, tolerance and immune deviation. Besides these, tumor heterogeneity and metastasis also play a critical role in tumor growth. A number of potential targets like promoting Th1, NK cell, γδ T cell responses, inhibiting Treg functionality, induction of IL-12, use of drugs including phytochemicals have been designed to counter tumor progression with much success. Some natural agents and phytochemicals merit further study. For example, use of certain key polysaccharide components from mushrooms and plants have shown to possess therapeutic impact on tumor-imposed genetic instability, anti-growth signaling, replicative immortality, dysregulated metabolism etc. In this review, we will discuss the advances made toward understanding the basis of cancer immune evasion and summarize the efficacy of various therapeutic measures and targets that have been developed or are being investigated to enhance tumor rejection.

CD73 promotes anthracycline resistance and poor prognosis in triple negative breast cancer.

Using gene-expression data from over 6,000 breast cancer patients, we report herein that high CD73 expression is associated with a poor prognosis in triple-negative breast cancers (TNBC). Because anthracycline-based chemotherapy regimens are standard treatment for TNBC, we investigated the relationship between CD73 and anthracycline efficacy. In TNBC patients treated with anthracycline-only preoperative chemotherapy, high CD73 gene expression was significantly associated with a lower rate of pathological complete response or the disappearance of invasive tumor at surgery. Using mouse models of breast cancer, we demonstrated that CD73 overexpression in tumor cells conferred chemoresistance to doxorubicin, a commonly used anthracycline, by suppressing adaptive antitumor immune responses via activation of A2A adenosine receptors. Targeted blockade of CD73 enhanced doxorubicin-mediated antitumor immune responses and significantly prolonged the survival of mice with established metastatic breast cancer. Taken together, our data suggest that CD73 constitutes a therapeutic target in TNBC.

Blockade of A2A receptors potently suppresses the metastasis of CD73+ tumors.

CD73 inhibits antitumor immunity through the activation of adenosine receptors expressed on multiple immune subsets. CD73 also enhances tumor metastasis, although the nature of the immune subsets and adenosine receptor subtypes involved in this process are largely unknown. In this study, we revealed that A2A/A2B receptor antagonists were effective in reducing the metastasis of tumors expressing CD73 endogenously (4T1.2 breast tumors) and when CD73 was ectopically expressed (B16F10 melanoma). A2A(-/-) mice were strongly protected against tumor metastasis, indicating that host A2A receptors enhanced tumor metastasis. A2A blockade enhanced natural killer (NK) cell maturation and cytotoxic function in vitro, reduced metastasis in a perforin-dependent manner, and enhanced NK cell expression of granzyme B in vivo, strongly suggesting that the antimetastatic effect of A2A blockade was due to enhanced NK cell function. Interestingly, A2B blockade had no effect on NK cell cytotoxicity, indicating that an NK cell-independent mechanism also contributed to the increased metastasis of CD73(+) tumors. Our results thus revealed that CD73 promotes tumor metastasis through multiple mechanisms, including suppression of NK cell function. Furthermore, our data strongly suggest that A2A or A2B antagonists may be useful for the treatment of metastatic disease. Overall, our study has potential therapeutic implications given that A2A/A2B receptor antagonists have already entered clinical trials in other therapeutic settings.

CD73: a potent suppressor of antitumor immune responses.

Tumors use several strategies to evade immunosurveillance. One such mechanism is the generation of adenosine within the tumor microenvironment, which potently suppresses antitumor T cell responses. Adenosine within the tumor is generated by CD73, a membrane-bound nucleotidase that is expressed by tumor cells, suppressive immune subsets such as T regulatory cells (Tregs) and myeloid-derived suppressor cells and endothelial cells. Recent evidence suggests that targeted inhibition of CD73 has the potential to reduce tumorigenesis and metastasis, as well as enhancing the potency of T-cell-directed therapies. This review outlines the impact of adenosine on suppressing the antitumor response and the evidence supporting the rationale for CD73 targeting in the treatment of cancer.

Anti-CD73 therapy impairs tumor angiogenesis.

CD73 is an ecto-nucleotidase overexpressed in various types of tumors that catabolizes the generation of extracellular adenosine, a potent immunosuppressor. We and others have shown that targeted blockade of CD73 can rescue anti-tumor T cells from the immunosuppressive effects of extracellular adenosine. Another important function of extracellular adenosine is to regulate adaptive responses to hypoxia. However, the importance of CD73 for tumor angiogenesis and the effect of anti-CD73 therapy on tumor angiogenesis remain unknown. In this study, we demonstrated that CD73 expression on tumor cells and host cells contribute to tumor angiogenesis. Our data revealed that tumor-derived CD73 enhances the production of vascular endothelial growth factor (VEGF) by tumor cells that host-derived CD73 is required for in vivo angiogenic responses and that endothelial cells require CD73 expression for tube formation and migration. Notably, the pro-angiogeneic effects of CD73 relied on both enzymatic and non-enzymatic functions. Using a mouse model of breast cancer, we demonstrated that targeted blockade of CD73 with a monoclonal antibody significantly decreased tumor VEGF levels and suppressed tumor angiogenesis in vivo. Taken together, our study strongly suggests that targeted blockade of CD73 can significantly block tumor angiogenesis, and further supports its clinical development for cancer treatment.

Liver grafts from CD39-overexpressing rodents are protected from ischemia reperfusion injury due to reduced numbers of resident CD4+ T cells.

UNLABELLED: Ischemia-reperfusion injury (IRI) is a major limiting event for successful liver transplantation, and CD4+ T cells and invariant natural killer T (iNKT) cells have been implicated in promoting IRI. We hypothesized that hepatic overexpression of CD39, an ectonucleotidase with antiinflammatory functions, will protect liver grafts after prolonged cold ischemia. CD39-transgenic (CD39tg) and wildtype (WT) mouse livers were transplanted into WT recipients after 18 hours cold storage and pathological analysis was performed 6 hours after transplantation. Serum levels of alanine aminotransferase and interleukin (IL)-6 were significantly reduced in recipients of CD39tg livers compared to recipients of WT livers. Furthermore, less severe histopathological injury was demonstrated in the CD39tg grafts. Immune analysis revealed that CD4+ T cells and iNKT cells were significantly decreased in number in the livers of untreated CD39tg mice. This was associated with a peripheral CD4+ T cell lymphopenia due to defective thymocyte maturation. To assess the relative importance of liver-resident CD4+ T cells and iNKT cells in mediating liver injury following extended cold preservation and transplantation, WT mice depleted of CD4+ T cells or mice genetically deficient in iNKT cells were used as donors. The absence of CD4+ T cells, but not iNKT cells, protected liver grafts from early IRI. CONCLUSION: Hepatic CD4+ T cells, but not iNKT cells, play a critical role in early IRI following extended cold preservation in a liver transplant model.

Anti-ErbB-2 mAb therapy requires type I and II interferons and synergizes with anti-PD-1 or anti-CD137 mAb therapy.

Trastuzumab, a monoclonal antibody targeting human epidermal growth factor receptor-2 (HER2/ErbB-2), has become the mainstay of treatment for HER2-positive breast cancer. Nevertheless, its exact mechanism of action has not been fully elucidated. Although several studies suggest that Fc receptor-expressing immune cells are involved in trastuzumab therapy, the relative contribution of lymphocyte-mediated cellular cytotoxicity and antitumor cytokines remains unknown. We report here that anti-ErbB-2 mAb therapy is dependent on the release of type I and type II IFNs but is independent of perforin or FasL. Our study thus challenges the notion that classical antibody-dependent, lymphocyte-mediated cellular cytotoxicity is important for trastuzumab. We demonstrate that anti-ErbB-2 mAb therapy of experimental tumors derived from MMTV-ErbB-2 transgenic mice triggers MyD88-dependent signaling and primes IFN-γ-producing CD8+ T cells. Adoptive cell transfer of purified T cell subsets confirmed the essential role of IFN-γ-producing CD8+ T cells. Notably, anti-ErbB-2 mAb therapy was independent of IL-1R or IL-17Ra signaling. Finally, we investigated whether immunostimulatory approaches with antibodies against programmed death-1 (PD-1) or 41BB (CD137) could be used to capitalize on the immune-mediated effects of trastuzumab. We demonstrate that anti-PD-1 or anti-CD137 mAb can significantly improve the therapeutic activity of anti-ErbB-2 mAb in immunocompetent mice.

A critical role for granzymes in antigen cross-presentation through regulating phagocytosis of killed tumor cells.

Granzymes A and B (GrAB) are known principally for their role in mediating perforin-dependent death of virus-infected or malignant cells targeted by CTL. In this study, we show that granzymes also play a critical role as inducers of Ag cross-presentation by dendritic cells (DC). This was demonstrated by the markedly reduced priming of naive CD8(+) T cells specific for the model Ag OVA both in vitro and in vivo in response to tumor cells killed in the absence of granzymes. Reduced cross-priming was due to impairment of phagocytosis of tumor cell corpses by CD8α(+) DC but not CD8α(-) DC, demonstrating the importance of granzymes in inducing the exposure of prophagocytic "eat-me" signals on the dying target cell. Our data reveal a critical and previously unsuspected role for granzymes A and B in dictating immunogenicity by influencing the mode of tumor cell death and indicate that granzymes contribute to the efficient generation of immune effector pathways in addition to their well-known role in apoptosis induction.

Anti-CD73 antibody therapy inhibits breast tumor growth and metastasis.

Extracellular adenosine is a potent immunosuppressor that accumulates during tumor growth. We performed proof-of-concept studies investigating the therapeutic potential and mechanism of action of monoclonal antibody (mAb)-based therapy against CD73, an ecto-enzyme overexpressed on breast-cancer cells that catalyzes the dephosphorylation of adenosine monophosphates into adenosine. We showed that anti-CD73 mAb therapy significantly delayed primary 4T1.2 and E0771 tumor growth in immune-competent mice and significantly inhibited the development of spontaneous 4T1.2 lung metastases. Notably, anti-CD73 mAb therapy was essentially dependent on the induction of adaptive anti-tumor immune responses. Knockdown of CD73 in 4T1.2 tumor cells confirmed the tumor-promoting effects of CD73. In addition to its immunosuppressive effect, CD73 enhanced tumor-cell chemotaxis, suggesting a role for CD73-derived adenosine in tumor metastasis. Accordingly, administration of adenosine-5'-N-ethylcarboxamide to tumor-bearing mice significantly enhanced spontaneous 4T1.2 lung metastasis. Using selective adenosine-receptor antagonists, we showed that activation of A2B adenosine receptors promoted 4T1.2 tumor-cell chemotaxis in vitro and metastasis in vivo. In conclusion, our study identified tumor-derived CD73 as a mechanism of tumor immune escape and tumor metastasis, and it also established the proof of concept that targeted therapy against CD73 can trigger adaptive anti-tumor immunity and inhibit metastasis of breast cancer.