Detection of PD-L1-Expressing Myeloid Cell Clusters in the Hyaluronan-Enriched Stroma in Tumor Tissue and Tumor-Draining Lymph Nodes.

Expression of the transmembrane protein PD-L1 is frequently upregulated in cancer. Because PD-L1-expressing cells can induce apoptosis or anergy of T lymphocytes through binding to the PD1 receptor, the PD-L1-mediated inhibition of activated PD1+ T cells is considered a major pathway for tumor immune escape. However, the mechanisms that regulate the expression of PD-L1 in the tumor microenvironment are not fully understood. Analysis of organotypic tumor tissue slice cultures, obtained from mice with implanted syngeneic tumors (MBT2 bladder tumors in C3H mice, Renca kidney, and CT26 colon tumors in BALB/c mice), as well as from patients with cancer, revealed that tumor-associated hyaluronan (HA) supports the development of immunosuppressive PD-L1+ macrophages. Using genetically modified tumor cells, we identified epithelial tumor cells and cancer-associated mesenchymal fibroblast-like cells as a major source of HA in the tumor microenvironment. These HA-producing tumor cells, and particularly the vimentin-positive fibroblast-like cells of bone marrow origin, directly interact with tumor-recruited myeloid cells to form large stromal congregates/clusters that are highly enriched for both HA and PD-L1. Furthermore, similar cell clusters composed of HA-producing fibroblast-like cells and PD-L1+ macrophages were detected in tumor-draining, but not in distant, lymph nodes. Collectively, our findings indicate that the formation of multiple large HA-enriched stromal clusters that support the development of PD-L1-expressing APCs in the tumor microenvironment and draining lymph nodes could contribute to the immune escape and resistance to immunotherapy in cancer.

Mechanisms of immune evasion in bladder cancer.

With the introduction of multiple new agents, the role of immunotherapy is rapidly expanding across all malignancies. Bladder cancer is known to be immunogenic and is responsive to immunotherapy including intravesical BCG and immune checkpoint inhibitors. Multiple trials have addressed the role of checkpoint inhibitors in advanced bladder cancer, including atezolizumab, avelumab, durvalumab, nivolumab and pembrolizumab (all targeting the PD1/PD-L1 pathway). While these trials have demonstrated promising results and improvements over existing therapies, less than half of patients with advanced disease demonstrate clinical benefit from checkpoint inhibitor therapy. Recent breakthroughs in cancer biology and immunology have led to an improved understanding of the influence of the tumor microenvironment on the host's immune system. It appears that tumors promote the formation of highly immunosuppressive microenvironments preventing generation of effective anti-tumor immune response through multiple mechanisms. Therefore, reconditioning of the tumor microenvironment and restoration of the competent immune response is essential for achieving optimal efficacy of cancer immunotherapy. In this review, we aim to discuss the major mechanisms of immune evasion in bladder cancer and highlight novel pathways and molecular targets that may help to attenuate tumor-induced immune tolerance, overcome resistance to immunotherapy and improve clinical outcomes.

COX2/mPGES1/PGE2 pathway regulates PD-L1 expression in tumor-associated macrophages and myeloid-derived suppressor cells.

In recent years, it has been established that programmed cell death protein ligand 1 (PD-L1)-mediated inhibition of activated PD-1+ T lymphocytes plays a major role in tumor escape from immune system during cancer progression. Lately, the anti-PD-L1 and -PD-1 immune therapies have become an important tool for treatment of advanced human cancers, including bladder cancer. However, the underlying mechanisms of PD-L1 expression in cancer are not fully understood. We found that coculture of murine bone marrow cells with bladder tumor cells promoted strong expression of PD-L1 in bone marrow-derived myeloid cells. Tumor-induced expression of PD-L1 was limited to F4/80+ macrophages and Ly-6C+ myeloid-derived suppressor cells. These PD-L1-expressing cells were immunosuppressive and were capable of eliminating CD8 T cells in vitro. Tumor-infiltrating PD-L1+ cells isolated from tumor-bearing mice also exerted morphology of tumor-associated macrophages and expressed high levels of prostaglandin E2 (PGE2)-forming enzymes microsomal PGE2 synthase 1 (mPGES1) and COX2. Inhibition of PGE2 formation, using pharmacologic mPGES1 and COX2 inhibitors or genetic overexpression of PGE2-degrading enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH), resulted in reduced PD-L1 expression. Together, our study demonstrates that the COX2/mPGES1/PGE2 pathway involved in the regulation of PD-L1 expression in tumor-infiltrating myeloid cells and, therefore, reprogramming of PGE2 metabolism in tumor microenvironment provides an opportunity to reduce immune suppression in tumor host.

Calcium Oxalate Stone Fragment and Crystal Phagocytosis by Human Macrophages.

PURPOSE: In murine and human hyperoxaluric conditions macrophages can be seen surrounding renal calcium oxalate crystal deposits. We hypothesized that macrophages have a role in degrading and destroying these deposits. We investigated the inflammatory response and phagocytic mechanisms when macrophages were exposed to human kidney stones and inorganic crystals. MATERIALS AND METHODS: Human monocytes were differentiated into resting, fully differentiated macrophages by treatment with recombinant human macrophage colony-stimulating factor (M-CSF) or GM-CSF (granulocyte M-CSF) for 6 days. After confirming phenotype by flow cytometry the macrophages were exposed for 20 hours to fragments of sterile human calcium oxalate stones or calcium oxalate crystals. Crystal uptake was determined, and supernatant cytokine and chemokine profiles were analyzed using antibody arrays. Quantitative reverse transcriptase-polymerase chain reaction was done to validate mRNA profile expression. RESULTS: Under direct vision fluorescence microscopy activated human macrophages were noted to surround stone fragments and synthesized crystals, and destroy them in a step-by-step process that involved clathrin mediated endocytosis and phagocytosis. An inflammatory cascade was released by macrophages, including the chemokines chemokine ligand (CCL)2, CCL3, interleukin (IL)-1 receptor antagonist (IL-1ra), complement component C5/C5a and IL-8. Response patterns to stone and crystal material depended on macrophage phenotype and activation status. CONCLUSIONS: In our in vitro study macrophages differentiated with M-CSF showed greater ability to phagocytize crystal deposits than those treated with GM-CSF. Following clathrin mediated endocytosis macrophages released a number of cytokines that are crucial for the inflammatory immune response. This suggests that tissue macrophages have an important role in preventing kidney stone disease by removing and digesting interstitial renal crystal deposits.

Tissue Slice Culture and Analysis of Tumor-Associated Hyaluronan in Urothelial Carcinoma.

Hyaluronan is a major component of the extracellular matrix in both normal and tumor tissue. Many solid cancers, including bladder cancer, are characterized by deregulated hyaluronan metabolism. It is postulated that the deregulated metabolism in cancer tissue is characterized by elevated hyaluronan synthesis and degradation. This results in the accumulation of small hyaluronan fragments in the tumor microenvironment which promotes cancer-related inflammation, stimulates tumor cell proliferation and angiogenesis, and contributes to immune-associated immune suppression. For a better understanding of the complex mechanisms of hyaluronan metabolism in cancer, it has been proposed to use precision-cut tissue slice cultures prepared using freshly excised cancer tissue. Here we describe the protocol for establishing tissue slice cultures and analysis of tumor-associated hyaluronan in human urothelial carcinoma.

Hyaluronan Metabolism in Urologic Cancers.

Hyaluronan (HA) is one of the major components of the extracellular matrix in tumor tissue. Recent reports have made it clear that the balance of HA synthesis and degradation is critical for tumor progression. HA is synthesized on the cytoplasmic surface of the plasma membrane by hyaluronan synthases (HAS) and extruded into the extracellular space. Excessive HA production in cancer is associated with enhanced HA degradation in the tumor microenvironment, leading to the accumulation of HA fragments with small molecular weight. These perturbations in both HA synthesis and degradation may play important roles in tumor progression. Recently, it has become increasingly clear that small HA fragments can induce a variety of biological events, such as angiogenesis, cancer-promoting inflammation, and tumor-associated immune suppression. Progression of urologic malignancies, particularly of prostate and bladder cancers, as well as of certain types of kidney cancer show markedly perturbed metabolism of tumor-associated HA. This review highlights the recent research findings regarding HA metabolism in tumor microenvironments with a special focus on urologic cancers. It also will discuss the potential implications of these findings for the development of novel therapeutic interventions for the treatment of prostate, bladder, and kidney cancers.

Circulating and tumor-infiltrating myeloid cell subsets in patients with bladder cancer.

Both cancer-related inflammation and tumor-induced immune suppression are associated with expansion of myeloid cell subsets including myeloid-derived suppressor cells. However, little known regarding characteristics of myeloid cells in patients with bladder cancer. In this study, we analyzed myeloid cells from peripheral blood (PBMC) and tumor tissue that were collected from patients with superficial noninvasive and invasive urothelial carcinomas. Our results demonstrate that PBMC from bladder cancer patients contain two major CD11b myeloid cell subsets: granulocyte-type CD15(high) CD33(low) cells and monocyte-type CD15(low) CD33(high) cells. The number of circulating granulocytic but not monocytic myeloid cells in cancer patients was markedly increased when compared to healthy individuals. Both myeloid cell subsets from cancer patients were highly activated and produced substantial amounts of proinflammatory chemokines/cytokines including CCL2, CCL3, CCL4, G-CSF, IL-8 and IL-6. Granulocytic myeloid cells were able to inhibit in vitro T cell proliferation through induction of CD4(+) Foxp3(+) T regulatory cells. Analysis of bladder cancer tissues revealed that tumors were infiltrated with monocyte-macrophage CD11b(+) HLA-DR(+) and granulocytic CD11b(+) CD15(+) HLA-DR(-) myeloid cells. Collectively, this study identifies myeloid cell subsets in patients with bladder cancer. We demonstrate that these highly activated inflammatory myeloid cells represent a source of multiple chemokines/cytokines and may contribute to inflammation and immune dysfunction in bladder cancer.

Deregulated hyaluronan metabolism in the tumor microenvironment drives cancer inflammation and tumor-associated immune suppression.

Hyaluronan (HA) is known to be a prominent component of the extracellular matrix in tumors, and many solid cancers are characterized by aberrant HA metabolism resulting in increased production in tumor tissue. HA has been implicated in regulating a variety of cellular functions in tumor cells and tumor-associated stromal cells, suggesting that altered HA metabolism can influence tumor growth and malignancy at multiple levels. Importantly, increased HA production in cancer is associated with enhanced HA degradation due to high levels of expression and activity of hyaluronidases (Hyal). Understanding the complex molecular and cellular mechanisms involved in abnormal HA metabolism and catabolism in solid cancers could have important implications for the design of future cancer therapeutic approaches. It appears that extensive crosstalk between immune cells and HA-enriched stroma contributes to tumor growth and progression in several ways. Specifically, the interaction of tumor-recruited Hyal2-expressing myeloid-derived suppressor cells (MDSCs) of bone marrow origin with HA-producing cancer-associated fibroblasts and epithelial tumor cells results in enhanced HA degradation and accumulation of small pro-inflammatory HA fragments, which further drives cancer-related inflammation. In addition, hyaluronan-enriched stroma supports the transition of tumor-recruited Hyal2+MDSCs to the PD-L1+ tumor-associated macrophages leading to the formation of an immunosuppressive and tolerogenic tumor microenvironment. In this review, we aim to discuss the contribution of tumor-associated HA to cancer inflammation, angiogenesis, and tumor-associated immune suppression. We also highlight the recent findings related to the enhanced HA degradation in the tumor microenvironment.

High Levels of PD-L1+ and Hyal2+ Myeloid-derived Suppressor Cells in Renal Cell Carcinoma.

Renal cell carcinoma (RCC) patients frequently have increased number of immunosuppressive myeloid cells in circulation. High number of myeloid-derived suppressor cells (MDSCs) in the blood are associated with immune suppression as well as with cancer-related inflammation which drives the mobilization of myeloid cells to tumor tissue. Here, we show that peripheral blood from a previously untreated RCC patient has increased the number of monocytic CD33+CD11b+ MDSCs, which also co-expressed PD-L1 and membrane-bound enzyme hyaluronidase 2 (Hyal2). PD-L1 expression is associated with immune suppression, whereas expression of Hyal2 is associated with inflammation, because Hyal2+ myeloid cells can degrade the extracellular hyaluronan (HA), leading to the accumulation of pro-inflammatory HA fragments with low molecular weight. These findings implicate the potential involvement of monocytic MDSCs in both tumor-associated immune suppression and cancer-related inflammation. Analysis of organotypic tumor-tissue slice cultures prepared from cancer tissue of the same patient revealed the significant presence of PD-L1+ HLA-DR+ macrophage-like or dendritic cell-like antigen-presenting cells in tumor stroma. Interestingly, stroma-associated PD-L1+ cells frequently have intracellular hyaluronan. Collectively, data presented in this study suggest that the interplay between tumor-recruited myeloid cells and stromal HA may contribute to the inflammation and immune tolerance in kidney cancer.

Altered expression of 15-hydroxyprostaglandin dehydrogenase in tumor-infiltrated CD11b myeloid cells: a mechanism for immune evasion in cancer.

Many cancers are known to produce high amounts of PGE(2), which is involved in both tumor progression and tumor-induced immune dysfunction. The key enzyme responsible for the biological inactivation of PGE(2) in tissue is NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH). It is well established that cancer cells frequently show down-regulated expression of 15-PGDH, which plays a major role in catabolism of the PGE(2). Here we demonstrate that tumor-infiltrated CD11b cells are also deficient for the 15-PGDH gene. Targeted adenovirus-mediated delivery of 15-PGDH gene resulted in substantial inhibition of tumor growth in mice with implanted CT-26 colon carcinomas. PGDH-mediated antitumor effect was associated with attenuated tumor-induced immune suppression and substantially reduced secretion of immunosuppressive mediators and cytokines such as PGE(2), IL-10, IL-13, and IL-6 by intratumoral CD11b cells. We show also that introduction of 15-PGDH gene in tumor tissue is sufficient to redirect the differentiation of intratumoral CD11b cells from immunosuppressive M2-oriented F4/80(+) tumor-associated macrophages (TAM) into M1-oriented CD11c(+) MHC class II-positive myeloid APCs. Notably, the administration of the 15-PGDH gene alone demonstrated a significant therapeutic effect promoting tumor eradication and long-term survival in 70% of mice with preestablished tumors. Surviving mice acquired antitumor T cell-mediated immune response. This study for the first time demonstrates an important role of the 15-PGDH in regulation of local antitumor immune response and highlights the potential to be implemented to enhance the efficacy of cancer therapy and immunotherapy.

Mechanism regulating reactive oxygen species in tumor-induced myeloid-derived suppressor cells.

Myeloid-derived suppressor cells (MDSC) are a major component of the immune suppressive network described in cancer and many other pathological conditions. Recent studies have demonstrated that one of the major mechanisms of MDSC-induced immune suppression is mediated by reactive oxygen species (ROS). However, the mechanism of this phenomenon remained unknown. In this study, we observed a substantial up-regulation of ROS by MDSC in all of seven different tumor models and in patients with head and neck cancer. The increased ROS production by MDSC is mediated by up-regulated activity of NADPH oxidase (NOX2). MDSC from tumor-bearing mice had significantly higher expression of NOX2 subunits, primarily p47(phox) and gp91(phox), compared with immature myeloid cells from tumor-free mice. Expression of NOX2 subunits in MDSC was controlled by the STAT3 transcription factor. In the absence of NOX2 activity, MDSC lost the ability to suppress T cell responses and quickly differentiated into mature macrophages and dendritic cells. These findings expand our fundamental understanding of the biology of MDSC and may also open new opportunities for therapeutic regulation of these cells in cancer.

Acute Kidney Injury-Induced Systemic Inflammation and Risk of Kidney Cancer Formation.

In this issue of Cancer Research, Zhou and colleagues investigate the role of acute kidney injury (AKI) and AKI-associated systemic inflammation in the development of kidney cancer. They demonstrate a positive association between the formation of clear-cell renal cell carcinoma and AKI induced by ischemia-reperfusion injury in genetically modified mice. In parallel with the emergence of kidney tumors, mice with ischemic injury develop systemic inflammation associated with tissue infiltration by neutrophils and fibroblasts and upregulated expression of several inflammatory factors, with CXCL1 displaying the highest levels of upregulation. Accordingly, blockade of CXCL1-mediated signaling inhibited the emergence of kidney tumors in mice subjected to ischemic kidney injury. The study provides evidence for a new experimental approach to prevent the formation of clear-cell renal cell carcinoma and reduce kidney cancer incidence through modulation of the AKI-induced inflammatory response using inhibitors of CXC/CXCR2 axis. As the incidence of kidney cancer continues to increase, new treatment strategies for this devastating disease are urgently needed. Zhou and colleagues provide preclinical proof of concept for a new therapeutic strategy and address an unmet need for this difficult to prevent and treat cancer disease.See related article by Zhou et al., p. 2690.

Hyal2 Expression in Tumor-Associated Myeloid Cells Mediates Cancer-Related Inflammation in Bladder Cancer.

The increased presence of myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAM) in tumor tissue has been extensively reported. However, their role in the regulation of hyaluronan (HA) metabolism in the tumor microenvironment has not been established. Here we describe a novel function of tumor-associated myeloid cells related to the enhanced breakdown of extracellular HA in human bladder cancer tissue, leading to the accumulation of small HA fragments with molecular weight (MW) <20 kDa. Increased fragmentation of extracellular HA and accumulation of low molecular weight HA (LMW-HA) in tumor tissue was associated with elevated production of multiple inflammatory cytokines, chemokines, and angiogenic factors. The fragmentation of HA by myeloid cells was mediated by the membrane-bound enzyme hyaluronidase 2 (Hyal2). Increased numbers of Hyal2+CD11b+ myeloid cells were detected in the tumor tissue as well as in the peripheral blood of patients with bladder cancer. Coexpression of CD33 suggested that these cells belong to monocytic myeloid-derived suppressor cells. The HA-degrading function of Hyal2-expressing MDSCs could be enhanced by exposure to tumor-conditioned medium, and IL1ß was identified as one of the factors involved in the stimulation of Hyal2 activity. CD44-mediated signaling played an important role in the regulation of HA-degrading activity of Hyal2-expressing myeloid cells, as the engagement of CD44 receptor with specific mAb triggered translocation of Hyal2 enzyme to the cellular surface and stimulated secretion of IL1ß. Taken together, this work identifies Hyal2-expressing tumor-associated myeloid cells as key players in the accumulation of LMW-HA in the tumor microenvironment and cancer-related inflammation and angiogenesis. SIGNIFICANCE: This study identifies Hyal2-expressing tumor-associated myeloid cells of monocyte-macrophage lineage as contributors to hyaluronan degradation in bladder cancer tissue, leading to accumulation of inflammatory and proangiogenic low molecular weight hyaluronan fragments.

Generation of antigen-presenting cells from tumor-infiltrated CD11b myeloid cells with DNA demethylating agent 5-aza-2'-deoxycytidine.

Tumor-recruited CD11b myeloid cells, including myeloid-derived suppressor cells, play a significant role in tumor progression, as these cells are involved in tumor-induced immune suppression and tumor neovasculogenesis. On the other hand, the tumor-infiltrated CD11b myeloid cells could potentially be a source of immunostimulatory antigen-presenting cells (APCs), since most of these cells represent common precursors of both dendritic cells and macrophages. Here, we investigated the possibility of generating mature APCs from tumor-infiltrated CD11b myeloid cells. We demonstrate that in vitro exposure of freshly excised mouse tumors to DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (decitabine, AZA) results in selective elimination of tumor cells, but, surprisingly it also enriches CD45(+) tumor-infiltrated cells. The majority of "post-AZA" surviving CD45(+) tumor-infiltrated cells were represented by CD11b myeloid cells. A culture of isolated tumor-infiltrated CD11b cells in the presence of AZA and GM-CSF promoted their differentiation into mature F4/80/CD11c/MHC class II-positive APCs. These tumor-derived myeloid APCs produced substantially reduced amounts of immunosuppressive (IL-13, IL-10, PGE(2)), pro-angiogenic (VEGF, MMP-9) and pro-inflammatory (IL-1beta, IL-6, MIP-2) mediators than their precursors, freshly isolated tumor-infiltrated CD11b cells. Vaccinating naïve mice with ex vivo generated tumor-derived APCs resulted in the protection of 70% mice from tumor outgrowth. Importantly, no loading of tumor-derived APC with exogenous antigen was needed to stimulate T cell response and induce the anti-tumor effect. Collectively, our results for the first time demonstrate that tumor-infiltrated CD11b myeloid cells can be enriched and differentiated in the presence of DNA demethylating agent 5-aza-2'-deoxycytidine into mature tumor-derived APCs, which could be used for cancer immunotherapy.

Bcl-2 mediated modulation of vascularization in prostate cancer xenografts.

PURPOSE: We previously demonstrated that Bcl-2 overexpression enhances the radiation resistance of PC-3 human prostate cancer cells and xenografts by inhibiting apoptosis, increasing proliferation, and promoting angiogenesis. To further elucidate the relationship between Bcl-2 expression and the angiogenic potential of PC-3-Bcl-2 cells, tumorigenicity, angiogenesis, and lymphangiogenesis were evaluated and compared in a Bcl-2 overexpressing clone in vitro and in vivo. EXPERIMENTAL DESIGN: Human prostate cancer cells over expressing Bcl-2 were studied in vitro and in vivo to determine the angiogenic and lymphangiogenic properties of these cells. RESULTS: Increased Bcl-2 expression enhanced the tumorigenicity of prostate cancer xenografts. It also enhanced the expression and secretion of key angiogenic and lymphangiogenic factors that stimulated the synthesis of CD31-positive blood vessels and LYVE-1 positive lymphatics. Specifically, the increased angiogenic and lymphangiogenic potential correlated with increased serum levels of basic fibroblast growth factor (bFGF), interleukin 8 (CXCL8), and matrix metalloproteinase (MMP 9). In vitro analysis demonstrated that Bcl-2 expressing tumor cells secreted bFGF and vascular endothelial growth factor (VEGF) into culture supernatants. Microarray analysis of Bcl-2 expressing PC-3 cells demonstrated increased transcription of genes involved in metabolism, such as interleukins, growth factors, tumor necrosis factors (TNF) family members, and peptidases. CONCLUSIONS: Together, these results demonstrate that Bcl-2 can regulate tumoral angiogenesis and lymphangiogenesis and suggest that therapy targeted at Bcl-2 expression, angiogenesis, and lymphangiogenesis may synergistically modulate tumor growth and confirm that Bcl-2 is a pivotal target for cancer therapy.

Effects of CXCR4 antagonist CTCE-9908 on prostate tumor growth.

BACKGROUND: Recent reports have linked the survival-promoting effect of CXCR4 to the up regulation of Bcl-2 protein expression. MATERIALS AND METHODS: To further elucidate the relationship between Bcl-2 and CXCR4, tumorigenicity was evaluated in in vitro and in vivo models following treatment with CTCE-9908, a CXCR4 antagonist peptide. RESULTS: In vitro, CTCE-9908 inhibited cellular proliferation in PC-3-Bcl-2 and PC-3-Neo cell lines Furthermore in our xenograft model, CTCE-9908 delivered via daily intraperitoneal injections resulted in a statistically significant reduction in tumor size compared to control (396 + 205 mm(3) vs. 1,010 + 215 mm(3) respectively, p < 0.05) in the Bcl-2 expressing tumors. This reduction was associated with knockdown of VEGF, inhibition of angiogenesis and lymphangiogenesis, and induction of apoptosis. CTCE-9908 therapy was also associated with a marked reduction in intra-tumoral host cells expressing VEGFR1 and CD11b myeloid-derived suppressor cells (MDSC). CONCLUSION: These data show that CXCR4 antagonists represent a valuable addition to the cancer therapeutic arsenal. Such agents may have beneficial synergistic dual-effects in reducing tumor cell proliferation directly, and indirectly through perturbation of the tumor microenvironment. Further studies of the novel CTCE-9908 compound in prostate and other solid tumor inhibition are warranted. Prostate 69: 1460-1469, 2009. (c) 2009 Wiley-Liss, Inc.

Reversal of myeloid cell-mediated immunosuppression in patients with metastatic renal cell carcinoma.

PURPOSE: Tumor-induced immunosuppression remains a significant obstacle that limits the efficacy of biological therapy for renal cell carcinoma. Here we evaluate the role of CD33 myeloid-derived suppressor cells (MDSC) in the regulation of T-cell responses in renal cell carcinoma patients. We also examine effect of all-trans-retinoic acid (ATRA) on MDSC-mediated immune suppression. EXPERIMENTAL DESIGN: CD33-positive myeloid cells were isolated from the peripheral blood of renal cell carcinoma patients with magnetic beads and tested in vitro for their ability to inhibit T-cell responses. T-cell function was evaluated using ELISPOT and CTL assays. RESULTS: MDSC isolated from renal cell carcinoma patients, but not from healthy donors, were capable of suppressing antigen-specific T-cell responses in vitro through the secretion of reactive oxygen species and nitric oxide upon interaction with CTL. MDSC-mediated immune suppression and IFN-gamma down-regulation was reversible in vitro by exposing cells to the reactive oxygen species inhibitors. Moreover, ATRA was capable of abrogating MDSC-mediated immunosuppression and improving T-cell function by direct differentiation into antigen-presenting cell precursors. CONCLUSIONS: These results may have significant implications regarding the future design of active immunotherapy protocols that may include differentiation agents as part of a multimodal approach to renal cell carcinoma immunotherapy.

Reversal of tumor-mediated immunosuppression.

Therapeutic cancer vaccines, one form of active immunotherapy, have long been under investigation; consequently, several vaccine-based strategies have now moved from the bench to the clinical arena. Despite their tremendous promise, current vaccine strategies have shown only limited success in clinical settings, even in renal cell carcinoma (RCC), a prototypical malignancy for the application of immunotherapy. There is ample evidence that, especially in RCC, multiple immunosuppressive mechanisms exist that considerably dampen antitumor responses and weaken the activity of current immunotherapeutic regimens. Therefore, it will be necessary to reverse tumor-mediated immunosuppression before immunotherapies can successfully be applied. Recent insights into the nature and characteristics of the regulatory elements of the immune system have provided new opportunities to enhance vaccine-mediated antitumor immunity and, thereby, increase the chance for improving patient outcome. These new insights represent important considerations for the future design and application of more effective cancer vaccines against RCC and other cancers.

Calcium Oxalate Differentiates Human Monocytes Into Inflammatory M1 Macrophages.

Purpose: A number of hyperoxaluric states have been associated with calcium oxalate (CaOx) deposits in the kidneys. In animal models of stone disease, these crystals interact with circulating monocytes that have migrated into the kidney as part of innate immunity. Similarly, macrophages surround CaOx crystals in kidneys of patients excreting high levels of oxalate. We investigate the effect of this exposure and subsequent human immunological response in vitro. Materials and methods: Primary human monocytes were collected from healthy donors and exposed to CaOx, potassium oxalate, and zinc oxalate (ZnOx). Cytokine production was measured with a multiplex ELISA. Quantitative reverse transcription-polymerase chain reaction was done to validate the mRNA profile expression. M1 macrophage phenotype was confirmed with immunofluorescence microscopy. Results: Both primary monocytes and THP-1 cells, a human monocytic cell line, respond strongly to CaOx crystals in a dose-dependent manner producing TNF-α, IL-1ß, IL-8, and IL-10 transcripts. Exposure to CaOx followed by 1 h with LPS had an additive effect for cytokine production compared to LPS alone, however, LPS followed by CaOx led to significant decrease in cytokine production. Supernatants taken from monocytes were previously exposed to CaOx crystals enhance M2 macrophage crystal phagocytosis. CaOx, but not potassium or ZnOx, promotes monocyte differentiation into inflammatory M1-like macrophages. Conclusion: In our in vitro experiment, human monocytes were activated by CaOx and produced inflammatory cytokines. Monocytes recognized CaOx crystals through a specific mechanism that can enhance or decrease the innate immune response to LPS. CaOx promoted M1 macrophage development. These results suggest that monocytes have an important role promoting CaOx-induced inflammation.