Disruption of CCR5-dependent homing of regulatory T cells inhibits tumor growth in a murine model of pancreatic cancer

Treg cells in different forms of uterine cancer

Recently, studies involving uterine cervical cancer and uterine corpus cancer have been reported from many institutes. The presence of regulatory T cells (Treg cells) in human uterine cancer is crucial for maintaining immunological homeostasis. To improve treatment strategies, I will be reviewing recent studies in the field. This work will discuss the central role that Treg cells play in the development of uterine cancer, which makes these cells a key missing component in current cancer immunotherapy.

Tumor-infiltrating monocytic myeloid-derived suppressor cells mediate CCR5-dependent recruitment of regulatory T cells favoring tumor growth

Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of myeloid cells in cancer patients and tumor-bearing mice that potently inhibits T cell responses. During tumor progression, MDSCs accumulate in several organs, including the tumor tissue. So far, tumor-infiltrating MDSC subpopulations remain poorly explored. In this study, we performed global gene expression profiling of mouse tumor-infiltrating granulocytic and monocytic (MO-MDSC) subsets compared with MDSCs from peripheral blood. RMA-S lymphoma-infiltrating MO-MDSCs not only produced high levels of NO and arginase-1, but also greatly increased levels of chemokines comprising the CCR5 ligands CCL3, CCL4, and CCL5. MO-MDSCs isolated from B16 melanoma and from skin tumor-bearing ret transgenic mice also expressed high levels of CCL3, CCL4, and CCL5. Expression of CCR5 was preferentially detected on regulatory T cells (Tregs). Accordingly, tumor-infiltrating MO-MDSCs directly attracted high numbers of Tregs via CCR5 in vitro. Intratumoral injection of CCL4 or CCL5 increased tumor-infiltrating Tregs, and deficiency of CCR5 led to their profound decrease. Moreover, in CCR5-deficient mice, RMA-S and B16 tumor growth was delayed emphasizing the importance of CCR5 in the control of antitumor immune responses. Overall, our data demonstrate that chemokines secreted by tumor-infiltrating MO-MDSCs recruit high numbers of Tregs revealing a novel suppressive role of MDSCs with potential clinical implications for the development of cancer immunotherapies.

CCR5 gene polymorphism is a genetic risk factor for radiographic severity of rheumatoid arthritis

The chemokine receptor [C-C chemokine receptor 5 (CCR5)] is expressed on diverse immune effecter cells and has been implicated in the pathogenesis of rheumatoid arthritis (RA). This study sought to determine whether single-nucleotide polymorphisms (SNPs) in the CCR5 gene and their haplotypes were associated with susceptibility to and severity of RA. Three hundred fifty-seven patients with RA and 383 healthy unrelated controls were recruited. Using a pyrosequencing assay, we examined four polymorphisms -1118 CTAT(ins) (/del) (rs10577983), 303 A>G (rs1799987), 927 C>T (rs1800024), and 4838 G>T (rs1800874) of the CCR5 gene, which were distributed over the promoter region as well as the 5' and 3' untranslated regions. No significant difference in the genotype, allele, and haplotype frequencies of the four selected SNPs was observed between RA patients and controls. CCR5 polymorphisms of -1118 CTAT(del) (P = 0.012; corrected P = 0.048) and 303 A>G (P = 0.012; corrected P = 0.048) showed a significant association with radiographic severity in a recessive model, and, as a result of multivariate logistic regression analysis, were found to be an independent predictor of radiographic severity. When we separated the erosion score from the total Sharp score, the statistical significance of CCR5 polymorphisms showed an increase; -1118 CTAT(ins) (/del) (P = 0.007; corrected P = 0.028) and 303 A>G (P = 0.007; corrected P = 0.028). Neither SNPs nor haplotypes of the CCR5 gene showed a significant association with joint space narrowing score. These results indicate that genetic polymorphisms of CCR5 are an independent risk factor for radiographic severity denoted by modified Sharp score, particularly joint erosion in RA.

Tumor-infiltrating regulatory T cells delineated by upregulation of PD-1 and inhibitory receptors

Foxp3(+) regulatory T (T(reg)) cells are dominant suppressor cells which regulate conventional T (T(conv)) cells. Inside tumor microenvironment, T(reg) cells have been known to become potent in suppressing T(conv) cell responses, thereby enabling tumor cells to circumvent immune response. However, the underlying mechanism by which tumor-infiltrating T(reg) cells display enhanced suppressive function is still unresolved. To understand characteristics and function of tumor-infiltrating T(reg) cells as well as T(conv) cells in the tumor site, we analyzed their phenotypes either within tumor burden or at distant site of tumor using both heterotopic and orthotopic mouse cancer models. Compared to CD8(+) T cells at distant site of tumor, tumor-infiltrating CD8(+) T cells dramatically upregulated programmed death 1 (PD-1) and other inhibitory receptors, thereby being more exhausted functionally. Tumor-infiltrating CD4(+) T cells also expressed higher level of PD-1 than CD4(+) T cells at distant site of tumor but very surprisingly, upregulation of PD-1 occurred in CD4(+)Foxp3(+) T(reg) as well as CD4(+)Foxp3(-) T(conv) cells. Moreover, tumor infiltrating T(reg) cells upregulated other inhibitory receptors such as T cell immunoglobulin mucin 3 (TIM-3), cytotoxic T lymphocyte antigen-4 (CTLA-4), glucocorticoid-induced tumor necrosis factor receptor (GITR), and lymphocyte activation gene-3 (LAG-3). These results suggest that upregulation of PD-1 and other inhibitory receptors on tumor-infiltrating T(reg) cells is related with their enhanced suppressive function.

The role of inflammatory cells in fostering pancreatic cancer cell growth and invasion

The pancreatic ductal adenocarcinoma (PDAC) microenvironment accommodates a variety of cell types and a plethora of complex interactions between tumor cells, host cells and extracellular matrix (ECM) components. Here we review the role of inflammatory cells, in particular mast cells, myeloid-derived suppressor cells, macrophages, T regulatory cells, T helper cells and neutrophils. The picture that emerges is that of a tumor microenvironment, in which the immune response is actively suppressed, and inflammatory cells contribute in a variety of ways to tumor progression.

Upregulation of C-X-C chemokine receptor type 1 expression is associated with late-stage gastric adenocarcinoma

Chemokine receptors play multiple roles in the development and progression of various tumor types. The aim of this study was to examine C-X-C chemokine receptor type 1 (CXCR1) protein expression in gastric adenocarcinoma and to investigate the clinical implications of CXCR1 upregulation. Expression of CXCR1 protein in 83 specimens of sporadic gastric adenocarcinoma and their corresponding non-neoplastic mucosa obtained by gastrectomy was assayed using immunohistochemistry. The intensity of immunostaining in tumor tissue was considered strong when tumor tissue staining was more intense than in the corresponding non-neoplastic mucosa; the intensity was null when staining was weaker in the tumor than in the corresponding non-neoplastic mucosa; and the intensity was weak when staining was similar in both tissues. Microvascular density in tumor tissue and its corresponding non-neoplastic mucosa was measured using monoclonal antibody against CD34. A strong correlation was observed between elevated CXCR1 protein expression and tumor stage (P<0.05). T stage, N stage and overall stage positively correlated with CXCR1 protein expression. Microvascular density was higher in tumors with strong CXCR1 protein expression, but the correlation with CXCR1 was not linear (P=0.07). Multiple logistic regression analyses showed that, compared to no or weak expression, overexpression of CXCR1 protein was a significant risk factor for high N stage (N2, N3). These results indicate that CXCR1 may be considered as a new and promising target for gastric adenocarcinoma therapy.

Deficiency of C-C chemokine receptor 5 suppresses tumor development via inactivation of NF-κB and upregulation of IL-1Ra in melanoma model

To evaluate the relevance of C-C chemokine receptor type 5 (CCR5) expression and tumor development, we compared melanoma growth in CCR5 knockout (CCR5^−/−) mice and wild type (CCR5^+/+) mice. CCR5^−/− mice showed reduced tumor volume, tumor weight, and increased survival rate when compared to CCR5^+/+ mice. We investigated the activation of NF-κB since it is an implicated transcription factor in the regulation of genes involving cell growth, apoptosis, and tumor growth. Significant inhibition of DNA binding activity of NF-κB, and translocation of p50 and p65 into the nucleus through the inhibition of phosphorylation of IκB was found in the melanoma tissues of CCR5^−/− mice compared to melanoma tissues of CCR5^+/+ mice. NF-κB target apoptotic protein expression, such as cleaved caspase-3, cleaved PARP, and Bax, was elevated, whereas the survival protein expression levels, such as Bcl-2, C-IAP1, was decreased in the melanoma tissues of CCR5^−/− mice. Interestingly, we found that the level of IL-1Ra, a tumor growth suppressive cytokine, was significantly elevated in tumor tissue and spleen of CCR5^−/− mice compared to the level in CCR5^+/+ mice. Moreover, infiltration of CD8⁺ cytotoxic T cell and CD57⁺ natural killer cells was significantly increased in melanoma tumor and spleen tissue of CCR5^−/− mice compared to that of CCR5^+/+ mice. Therefore, these results showed that CCR5 deficiency caused apoptotic cell death of melanoma through inhibition of NF-κB and upregulation of IL-1Ra.

Pancreatic ductal adenocarcinoma: a review of immunologic aspects

With the continued failures of both early diagnosis and treatment options for pancreatic cancer, it is now time to comprehensively evaluate the role of the immune system on the development and progression of pancreatic cancer. It is important to develop strategies that harness the molecules and cells of the immune system to treat this disease. This review will focus primarily on the role of immune cells in the development and progression of pancreatic ductal adenocarcinoma and to evaluate what is known about the interaction of immune cells with the tumor microenvironment and their role in tumor growth and metastasis. We will conclude with a brief discussion of therapy for pancreatic cancer and the potential role for immunotherapy. We hypothesize that the role of the immune system in tumor development and progression is tissue specific. Our hope is that better understanding of this process will lead to better treatments for this devastating disease.

Control of transplant tolerance and intragraft regulatory T cell localization by myeloid-derived suppressor cells and CCL5

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature cells that are believed to inhibit immune responses in the contexts of cancer and organ transplantation, in association with regulatory T cells (Treg). However, the way in which MDSC cooperate with Treg remains elusive. In this study, we used DNA microarrays to analyze gene expression in blood-derived MDSC from rat recipients of kidney allografts. We found CCL5 (Rantes), a chemotactic C-C motif 5 chemokine, to be strongly downregulated after treatment with a tolerizing regimen. The amount of CCL5 protein was also lower in the plasma of tolerant recipients, whereas intragraft CCL5 was unchanged. Because CCL5 is chemotactic for Treg, we hypothesized that a gradient of CCL5 between the graft and peripheral blood might contribute to the intragraft localization of Treg in tolerant animals. To test this hypothesis, we treated tolerant rat recipients of kidney allografts with recombinant rat CCL5 to restore normal plasma concentrations. This led to a strong reduction in intragraft Treg monitored by immunohistofluorescence and by quantitative real-time PCR measurement of Foxp3 mRNA. Ultimately, this treatment led to an increase in serum creatinine concentrations and to kidney graft rejection after about a month. The kidney function of syngeneic grafts was not affected by a similar administration of CCL5. These data highlight the contribution of MDSC to the establishment of a graft-to-periphery CCL5 gradient in tolerant kidney allograft recipients, which controls recruitment of Treg to the graft where they likely contribute to maintaining tolerance.

Bone marrow-derived proangiogenic cells in pancreatic cancer

Tumor-derived signals systemically induce an angiogenic switch that allows cancer cells to survive and grow. However, the vascular network in tumors is not well organized and fails to meet metabolic needs to maintain tissue homeostasis, resulting in significant hypoxia. Among various tumors, pancreatic ductal adenocarcinoma (PDAC) typically develops in an unusually disordered microenvironment, which contributes to its highly aggressive behavior. Since anti-vascular endothelial growth factor (VEGF) (Avastin) has failed to demonstrate a survival benefit in PDAC, we need to re-visit the basic biology of this disease and understand what makes it so refractory to the anti-angiogenic approaches that are clinically effective in other neoplasms. To address this issue, we specifically focused on the process of neovascularization where bone marrow-derived cells (BMDCs) play a role during pancreatic tumorigenesis. We have identified subsets of BMDCs that regulate key processes during development of the neovessels through paracrine Hedgehog signaling. Considering the importance of systemic responses occurring in tumor bearing hosts, we are currently using genetically engineered mice, which spontaneously develop PDAC, Pdx1-Cre;LSL-Kras(G12D);p53(lox/+) strain, to clarify critical events that can trigger aberrant angiogenesis in pancreatic cancer. These studies allow us to provide insights into the cellular and molecular mechanisms of pancreatic tumorigenesis and have an implication for the design of therapies against this difficult disease.

Targeting regulatory T cells

Cancers express tumor-associated antigens that should elicit immune response to antagonize the tumor growth, but spontaneous immune rejection of established cancer is rare, suggesting an immunosuppressive environment hindering host antitumor immunity. Among the specific and active tumor-mediated mechanisms, CD4(+)CD25(high) T regulatory cells (Treg) are important mediators of active immune evasion in cancer. In this review, we will discuss Treg subpopulations and the mechanisms of their suppressive functions. Treg depletion improves endogenous antitumor immunity and the efficacy of active immunotherapy in animal models for cancer, suggesting that inhibiting Treg function could also improve the limited successes of human cancer immunotherapy. We will also discuss specific strategies for devising effective cancer immunotherapy targeting Treg.

Regulatory T cells in human ovarian cancer

Multiple layers of suppressive components including regulatory T (T(Reg)) cells, suppressive antigen-presenting cells, and inhibitory cytokines form suppressive networks in the ovarian cancer microenvironment. It has been demonstrated that as a major suppressive element, T(Reg) cells infiltrate tumor, interact with several types of immune cells, and mediate immune suppression through different molecular and cellular mechanisms. In this paper, we focus on human ovarian cancer and will discuss the nature of T(Reg) cells including their subsets, trafficking, expansion, and function. We will briefly review the development of manipulation of T(Reg) cells in preclinical and clinical settings.

Regulatory T cell migration during an immune response

CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells migrate into both inflammatory sites and draining lymph nodes (LNs) during an immune response, and have unique and overlaping functions in each location. Current studies suggest that Treg cells in draining LNs and inflamatory sites may not simply be a division of labor, but rather Treg cells migrate in a coordinated fashion between peripheral tissues and draining LNs. Trafficking between inflammatory sites and draining LNs is not only crucial for Treg cells to act, but also for them to acquire optimal immune regulatory activities. Furthermore, recent work has revealed that T helper (Th)1, Th2 and Th17 cell master transcription factors control Treg cell function by regulating genes important for Treg cell migration and suppression, and consequently affect disease pathogenesis.

Tumor-derived chemokine CCL5 enhances TGF-β-mediated killing of CD8(+) T cells in colon cancer by T-regulatory cells

Chemokine CCL5/RANTES is highly expressed in cancer where it contributes to inflammation and malignant progression. In this study, we show that CCL5 plays a critical role in immune escape in colorectal cancer. We found that higher levels of CCL5 expression in human and murine colon tumor cells correlated with higher levels of apoptosis of CD8+ T cells and infiltration of T-regulatory cells (T(reg)). In mouse cells, RNA interference (RNAi)-mediated knockdown of CCL5 delayed tumor growth in immunocompetent syngeneic hosts but had no effect on tumor growth in immunodeficient hosts. Reduced tumor growth was correlated with a reduction in T(reg) infiltration and CD8(+) T-cell apoptosis in tumors. Notably, we found that CCL5 enhanced the cytotoxicity of T(reg) against CD8(+) T cells. We also found tumor growth to be diminished in mice lacking CCR5, a CCL5 receptor, where a similar decrease in both T(reg) cell infiltration and CD8(+) T-cell apoptosis was noted. TGF-β signaling blockade diminished apoptosis of CD8(+) T cells, implicating TGF-β as an effector of CCL5 action. In support of this concept, CCL5 failed to enhance the production of TGF-β by CCR5-deficient T(reg) or to enhance their cytotoxic effects against CD8(+) T cells. CCR5 signaling blockade also diminished the in vivo suppressive capacity of T(reg) in inhibiting the antitumor responses of CD8(+) T cells, in the same way as CCL5 signaling blockade. Together, our findings establish that CCL5/CCR5 signaling recruits T(reg) to tumors and enhances their ability to kill antitumor CD8(+) T cells, thereby defining a novel mechanism of immune escape in colorectal cancer.

Optimal population of FoxP3+ T cells in tumors requires an antigen priming-dependent trafficking receptor switch

FoxP3⁺ T cells populate tumors and regulate anti-tumor immunity. The requirement for optimal population of FoxP3⁺ regulatory T cells in tumors remains unclear. We investigated the migration requirement and stability of tumor-associated FoxP3⁺ T cells. We found that only memory, but not naïve, FoxP3⁺ T cells are highly enriched in tumors. Almost all of the tumor-infiltrating FoxP3⁺ T cells express Helios, an antigen associated either with thymus-generated FoxP3⁺ T cells or activated T cells in the periphery. The tumor-infiltrating FoxP3⁺ T cells largely lack CD62L and CCR7, two trafficking receptors required for T cell migration into secondary lymphoid tissues. Instead, the tumor infiltrating FoxP3⁺ T cells highly express memory/tumor-associated CCR8 and CXCR4. Antigen priming is required for induction of this trafficking receptor phenotype in FoxP3⁺ T cells and only antigen primed, but not antigen-inexperienced naive, FoxP3⁺ T cells can efficiently migrate into tumors. While the migration of FoxP3⁺ T cells into tumors was a readily detectable event, generation of induced FoxP3⁺ T cells within tumors was unexpectedly inefficient. Genetic marking of current and ex-FoxP3⁺ T cells revealed that tumor-infiltrating FoxP3⁺ T cells are highly stable and do not readily convert back to FoxP3⁻ T cells. Taken together, our results indicate that population of tumors with thymus-generated FoxP3⁺ T cells requires an antigen priming-dependent trafficking receptor switch in lymphoid tissues.

Pancreatic adenocarcinoma induces bone marrow mobilization of myeloid-derived suppressor cells which promote primary tumor growth

PURPOSE

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immunosuppressive cells that are upregulated in cancer. Little is known about the prevalence and importance of MDSC in pancreas adenocarcinoma (PA).

EXPERIMENTAL DESIGN

Peripheral blood, bone marrow, and tumor samples were collected from pancreatic cancer patients, analyzed for MDSC (CD15(+)CD11b(+)) by flow cytometry and compared to cancer-free controls. The suppressive capacity of MDSC (CD11b(+)Gr-1(+)) and the effectiveness of MDSC depletion were assessed in C57BL/6 mice inoculated with Pan02, a murine PA, and treated with placebo or zoledronic acid, a potent aminobisphosphonate previously shown to target MDSC. The tumor microenvironment was analyzed for MDSC (Gr1(+)CD11b(+)), effector T cells, and tumor cytokine levels.

RESULTS

Patients with PA demonstrated increased frequency of MDSC in the bone marrow and peripheral circulation which correlated with disease stage. Normal pancreas tissue showed no MDSC infiltrate, while human tumors avidly recruited MDSC. Murine tumors similarly recruited MDSC that suppressed CD8(+) T cells in vitro and accelerated tumor growth in vivo. Treatment with zoledronic acid impaired intratumoral MDSC accumulation resulting in delayed tumor growth rate, prolonged median survival, and increased recruitment of T cells to the tumor. This was associated with a more robust type 1 response with increased levels of IFN-γ and decreased levels of IL-10.

CONCLUSIONS

MDSC are important mediators of tumor-induced immunosuppression in pancreatic cancer. Inhibiting MDSC accumulation with zoledronic acid improves the host anti-tumor response in animal studies suggesting that efforts to block MDSC may represent a novel treatment strategy for pancreatic cancer.

CCL5 neutralization restricts cancer growth and potentiates the targeting of PDGFRβ in colorectal carcinoma

Increased CCL5 levels are markers of an unfavourable outcome in patients with melanoma, breast, cervical, prostate, gastric or pancreatic cancer. Here, we have assessed the role played by CCL5/CCR5 interactions in the development of colon cancer. To do so, we have examined a number of human colorectal carcinoma clinical specimens and found CCL5 and its receptors over-expressed within primary as well as liver and pulmonary metastases of patients compared to healthy tissues. In vitro, CCL5 increased the growth and migratory responses of colon cancer cells from both human and mouse origins. In addition, systemic treatment of mice with CCL5-directed antibodies reduced the extent of development of subcutaneous colon tumors, of liver metastases and of peritoneal carcinosis. Consistently, we found increased numbers of CD45-immunoreactive cells within the stroma of the remaining lesions as well as at the interface with the healthy tissue. In contrast, selective targeting of CCR5 through administration of TAK-779, a CCR5 antagonist, only partially compromised colon cancer progression. Furthermore, CCL5 neutralization rendered the tumors more sensitive to a PDGFRβ-directed strategy in mice, this combination regimen offering the greatest protection against liver metastases and suppressing macroscopic peritoneal carcinosis. Collectively, our data demonstrate the involvement of CCL5 in the pathogenesis of colorectal carcinoma and point to its potential value as a therapeutic target.

Targeting regulatory T cells in cancer

Infiltration of tumors by regulatory T cells confers growth and metastatic advantages by inhibiting antitumor immunity and by production of receptor activator of NF-κB (RANK) ligand, which may directly stimulate metastatic propagation of RANK-expressing cancer cells. Modulation of regulatory T cells can enhance the efficacy of cancer immunotherapy. Strategies include depletion, interference with function, inhibition of tumoral migration, and exploitation of T-cell plasticity. Problems with these strategies include a lack of specificity, resulting in depletion of antitumor effector T cells or global interruption of regulatory T cells, which may predispose to autoimmune diseases. Emerging technologies, such as RNA interference and tetramer-based targeting, may have the potential to improve selectivity and efficacy.

Pancreatic cancer alters human CD4+ T lymphocyte function: a piece in the immune evasion puzzle

OBJECTIVES

To verify whether the dysregulation of CD4 T cells concurs in worsening the outcome of pancreatic cancer, we compared the effects of pancreatic cancer and other gastrointestinal cancer cell-conditioned media on the (1) proliferation, migration, and differentiation of CD4 T cells and (2) expansion of CD4 memory (CD45RO), naive (CD45RA), activated (CD69), and regulatory (CD25) subsets.

METHODS

After culture of CD4 T cells in control, pancreatic (BxPC3, Capan1, MiaPaCa2), or gastrointestinal cancer (AGS, HepG2, HT29) cell-conditioned media, we evaluated proliferation, migration, interferon γ (IFNγ) production, and CD45RA, CD45RO, CD69, and CD25 membrane expression in control and conditioned CD4 T cells.

RESULTS

Only pancreatic cancer-conditioned media (1) inhibited CD4 T-cell proliferation (P < 0.001) and migration under human stromal cell-derived factor-α chemotaxis (P < 0.001) and (2) induced CD4 T-cell IFNγ production (P < 0.05) and the expansion of the CD69-positive subset (P < 0.001) with respect to the control, with no changes being found in the CD45RA, CD45RO, and CD25 subsets.

CONCLUSIONS

The in vitro findings achieved in the present study demonstrate that pancreatic cancer cells inhibit CD4 T-cell proliferation and migration, induce IFNγ production, and favor a CD69 subset expansion, suggesting that CD4 T cells play an important role in pancreatic cancer immune evasion.

How to improve the immunogenicity of chemotherapy and radiotherapy

Chemotherapy or radiotherapy could induce various tumor cell death modalities, releasing tumor-derived antigen as well as danger signals that could either be captured for triggering antitumor immune response or ignored. Exploring the interplay among therapeutic drugs, tumor cell death and the immune cells should improve diagnostic, prognostic, predictive, and therapeutic management of tumor. We summarized some of the cell death-derived danger signals and the mechanism for host to sense and response to cell death in the tumor microenvironment. Based on the recent clinical or experimental findings, several strategies have been suggested to improve the immunogenicity of cell death and augment antitumor immunity.

Expression of chemokine receptor CCR5 correlates with the presence of hepatic molecular metastases in K-ras positive human colorectal cancer

BACKGROUND

Molecular metastases are precursors of postoperative recurrence, detected by molecular-biological tools. Chemokines and their receptors contribute to dissemination and local immune recognition. A strong expression of the chemokine receptor CCR5 is associated with non-metastatic colorectal cancer and increased CD8+ T-cell infiltration. The aim of this study was to analyze whether CCR5 expression correlates with the presence of hepatic molecular metastases (MM).

METHODS

Ninety-three patients undergoing elective surgery for colorectal cancer were assessed. The K-ras mutation status was defined by PCR-RFLP, and the CCR5 expression status was analyzed by CCR5-specific reverse transcription (RT-PCR) analysis. Liver biopsy samples had been intra-operatively taken to screen for MM. MM were detected by K-ras-specific PCR-RFLP and nested CK20/GCC RT-PCR. Prevalence of MM was correlated with CCR5 expression status.

RESULTS

Human colorectal cancer harboured K-ras mutations in 53% (codon 12: 47%; codon 13: 6%) of cases. Among K-ras mutants, MM were detected in 27-53% of patients, dependent on the technique applied (K-ras-specific PCR-RFLP assay vs. nested CK20/GCC RT-PCR approach (P = 0.004)). CCR5 expression of K-ras mutants ranged from absent (23/49: 47%), weak (17/49: 35%), intermediate (4/49: 8%) to strong (5/49: 10%). MM were found in 30% of CCR5 negative and in 23% of CCR5 positive cancer patients by the K-ras-specific PCR-RFLP assay. The nested CK20/GCC RT-PCR assay detected MM in 87% of CCR5 negative and in 27% of CCR5 positive colorectal cancer patients (P = 0.00002).

CONCLUSION

Thus, CCR5 expression of the primary cancer might be a valuable biomarker indicating the absence of hepatic molecular metastases.

Immunotherapeutic modulation of the suppressive liver and tumor microenvironments

The liver is an immunologically unique organ, consisting of resident hematopoietic and parenchymal cells which often contribute to a relatively tolerant microenvironment. It is also becoming increasingly clear that tumor-induced immunosuppression occurs via many of the same cellular mechanisms which contribute to the tolerogenic liver microenvironment. Myeloid cells, consisting of dendritic cells (DC), macrophages and myeloid derived suppressor cells (MDSC), have been implicated in providing a tolerogenic liver environment and immune dysfunction within the tumor microenvironment which can favor tumor progression. As we increase our understanding of the biological mechanisms involved for each phenotypic and/or functionally distinct leukocyte subset, immunotherapeutic strategies can be developed to overcome the inherent barriers to the development of improved strategies for the treatment of liver disease and tumors. In this review, we discuss the principal myeloid cell-based contributions to immunosuppression that are shared between the liver and tumor microenvironments. We further highlight immune-based strategies shown to modulate immunoregulatory cells within each microenvironment and enhance anti-tumor responses.

The suppressive tumor microenvironment: a challenge in cancer immunotherapy

In this review, we introduce the changing public perception of vaccines and immunotherapy in cancer treatments. We discuss the roles that different immunosuppressive cells play in the tumor microenvironment. Tumor associated macrophages (TAMs) and M1 and M2 macrophage phenotypes are discussed in depth. Additionally, the role that myeloid derived suppressor cells (MDSC) and T regulatory cells (Tregs) play in the tumor microenvironment is addressed. Highlighted are examples of therapies used against each suppressive cell type, which vary from the hypothetical to the ineffective; the inefficient to the successful. A variety of treatments have been tried to combat this fundamental problem, indeed the cause that allows cancerous mutated cells to survive, multiply and overtake the body. Efficient methods to disable each particular suppressive type of cell have been introduced; this review summarizes the discussion with a table to guide future development. We see gene therapy as the most innovative and flexible method to lead the charge to specifically modifying the tumor microenvironment.

An aberrant thymus in CCR5-/- mice is coupled with an enhanced adaptive immune response in fungal infection

CCR5 is a potent mediator of regulatory T cell (Treg) chemotaxis. In murine histoplasmosis, mice lacking CCR5 or endogenous CCL4 have a reduced number of Tregs in the lungs, which results in accelerated resolution of infection. In this study, we demonstrate that CCR5 controls the outcome of Histoplasma capsulatum infection by dictating thymic and lymph node egress of Tregs. Mice lacking CCR5 or treated with a mAb to CCL4 had more Tregs in the thymus prior to and during infection. Thymic accumulation was associated with diminished transcription of the sphingosine 1-phosphate 1 receptor and Krüppel-like factor 2, both of which regulate thymic and lymph node emigration of T cells. The significance of CCR5 in Treg egress was demonstrated by generating mixed bone marrow chimeras. Chimeric mice had an increased proportion of CCR5(-/-) Tregs in the thymus and lymph nodes and a decreased proportion of Tregs in the lungs prior to and during H. capsulatum infection. Hence, CCR5 signaling regulates pathogen persistence in murine histoplasmosis by regulating Tregs exiting from the thymus and lymph nodes and, consequently, their subsequent homing in the periphery.

Potential targets for pancreatic cancer immunotherapeutics

Pancreatic adenocarcinoma is the fourth leading cause of cancer death with an overall 5-year survival of less than 5%. As there is ample evidence that pancreatic adenocarcinomas elicit antitumor immune responses, identification of pancreatic cancer-associated antigens has spurred the development of vaccination-based strategies for treatment. While promising results have been observed in animal tumor models, most clinical studies have found only limited success. As most trials were performed in patients with advanced pancreatic cancer, the contribution of immune suppressor mechanisms should be taken into account. In this article, we detail recent work in tumor antigen vaccination and the recently identified mechanisms of immune suppression in pancreatic cancer. We offer our perspective on how to increase the clinical efficacy of vaccines for pancreatic cancer.

Regulatory T cells in colorectal cancer: from biology to prognostic relevance

Regulatory T cells (Tregs) were initially described as "suppressive" lymphocytes in the 1980s. However, it took almost 20 years until the concept of Treg-mediated immune control in its present form was finally established. Tregs are obligatory for self-tolerance and defects within their population lead to severe autoimmune disorders. On the other hand Tregs may promote tolerance for tumor antigens and even hamper efforts to overcome it. Intratumoral and systemic accumulation of Tregs has been observed in various types of cancer and is often linked to worse disease course and outcome. Increase of circulating Tregs, as well as their presence in mesenteric lymph nodes and tumor tissue of patients with colorectal cancer de facto suggests a strong involvement of Tregs in the antitumor control. This review will focus on the Treg biology in view of colorectal cancer, means of Treg accumulation and the controversies regarding their prognostic significance. In addition, a concise overview will be given on how Tregs and their function can be targeted in cancer patients in order to bolster an inherent immune response and/or increase the efficacy of immunotherapeutic approaches.

An ISCOM vaccine combined with a TLR9 agonist breaks immune evasion mediated by regulatory T cells in an orthotopic model of pancreatic carcinoma

Vaccines based on immune stimulatory complexes (ISCOM) induce T-cell responses against tumor antigen (Ag). However, immune responses are impaired in pancreatic cancer patients. We investigated the efficacy of an ISCOM vaccine in a murine pancreatic carcinoma model. Panc02 cells expressing OVA as a model Ag were induced subcutaneously or orthotopically in the pancreas of C57BL/6 mice. Treatment consisted of an OVA containing ISCOM vaccine, either used alone or in combination with the TLR9 agonist CpG. The ISCOM vaccine effectively induced Ag-specific CTL capable of killing tumor cells. However, in mice with established tumors CTL induction by the vaccine was inefficient and did not affect tumor growth. Lack of efficacy correlated with increased numbers of Treg. Depletion of Treg with anti-CD25 mAb restored CTL induction and prolonged survival. Adding low-dose CpG to the ISCOM vaccine reduced Treg numbers, enhanced CTL responses and induced regression of pancreatic tumors in a CD8(+) T cell-dependent manner. Mice cured from the primary tumor mounted a memory T-cell response against wild-type Panc02 tumors, indicative of epitope spreading. Combining ISCOM vaccines with TLR agonists is a promising strategy for breaking tumor immune evasion and deserves further evaluation for the treatment of pancreatic carcinoma.

Chemokine expression from oncolytic vaccinia virus enhances vaccine therapies of cancer

Tumor vaccines can induce robust immune responses targeting tumor antigens in the clinic, but antitumor effects have been disappointing. One reason for this is ineffective tumor infiltration of the cytotoxic T lymphocytes (CTLs) produced. Oncolytic viruses are capable of selectively replicating within tumor tissue and can induce a strong immune response. We therefore sought to determine whether these therapies could be rationally combined such that modulation of the tumor microenvironment by the viral therapy could help direct beneficial CTLs induced by the vaccine. As such, we examined the effects of expressing chemokines from oncolytic vaccinia virus, including CCL5 (RANTES), whose receptors are expressed on CTLs induced by different vaccines, including type-1-polarized dendritic cells (DC1). vvCCL5, an oncolytic vaccinia virus expressing CCL5, induced chemotaxis of lymphocyte populations in vitro and in vivo, and displayed improved safety in vivo. Interestingly, enhanced therapeutic benefits with vvCCL5 in vivo correlated with increased persistence of the viral agent exclusively within the tumor. When tumor-bearing mice were both vaccinated with DC1 and treated with vvCCL5 a further significant enhancement in tumor response was achieved which correlated with increased levels of tumor infiltrating lymphocytes. This approach therefore represents a novel means of combining biological therapies for cancer treatment.

The immunoregulatory mechanisms of carcinoma for its survival and development

The immune system in patients detects and eliminates tumor cells, but tumors still progress persistently. The mechanisms by which tumor cells survive under the pressure of immune surveillance are not fully understood. This review is to present the evidence from clinical studies, showing a significant correlation of clinicopathological features of carcinoma with: (1) the loss of classical human leukocyte antigen class I, (2) the up-regulation of non-classical human leukocyte antigen class I, pro-apoptotic Fas ligand and receptor-binding cancer antigen expressed on SiSo cells I, and (3) the formation of immunosuppressive microenvironment by up-regulation of transforming growth factor-beta, Galectin-1, inhibitory ligand B7s, indoleamine 2,3-dioxygenase and arginase, as well as by recruitment of tumor-induced myeloid-derived suppressor cells and regulatory T cells. All of these factors may together protect carcinoma cells from the immune-cytotoxicity.

Modified vaccinia Ankara expressing survivin combined with gemcitabine generates specific antitumor effects in a murine pancreatic carcinoma model

Survivin is overexpressed by 70-80% of pancreatic cancers, and is associated with resistance to chemotherapy and a poor prognosis. Gemcitabine has been a standard treatment for patients with advanced pancreatic cancer for a decade. Recent reports have demonstrated that gemcitabine treatment attenuates the tumor-suppressive environment by eliminating CD11b(+)/Gr-1(+) myeloid-derived suppressor cells (MDSCs). We hypothesize that a cancer vaccine targeting survivin can achieve enhanced efficacy when combined with gemcitabine. In this study, we tested this hypothesis using modified vaccinia Ankara (MVA) expressing full-length murine survivin. The poorly immunogenic mouse pancreas adenocarcinoma cell line, Pan02, which expresses murine survivin and is syngeneic to C57BL/6, was used for this study. Immunization with MVA-survivin resulted in a modest therapeutic antitumor effect on established Pan02 tumors. When administered with gemcitabine, MVA-survivin immunization resulted in significant tumor regression and prolonged survival. The enhanced vaccine efficacy was associated with decreased CD11b(+)/Gr-1(+) MDSCs. To analyze the survivin-specific immune response to MVA-survivin immunization, we utilized a peptide library of 15mers with 11 residues overlapping from full-length murine survivin. Splenocytes from mice immunized with MVA-survivin produced intracellular γ-interferon in response to in vitro stimulation with the overlapping peptide library. Increased survivin-specific CD8(+) T cells that specifically recognized the Pan02 tumor line were seen in mice treated with MVA-survivin and gemcitabine. These data suggest that vaccination with MVA-survivin in combination with gemcitabine represents an attractive strategy to overcome tumor-induced peripheral immune tolerance, and this effect has potential for clinical benefit in pancreatic cancer.

Regulatory T cells: overcoming suppression of T-cell immunity

Regulatory T cells inhibit cellular immunity and represent an obstacle for the development of cancer immunotherapy. The understanding of Treg cellular biology has exponentially increased during the last 10 years, driven primarily by elegant in vivo studies of mouse models systems and in vitro studies of human cells. Numerous clinical strategies are under active investigation to achieve Treg depletion or inhibition in patients with cancer, including low-dose cyclophosphamide and interleukin-2 or anti-interleukin-2R immunotoxins. To date, only modest results have been reported in patients. Our preliminary data suggest that the antihuman CD25 monoclonal daclizumab may be useful as an alternative approach for in vivo Treg depletion, but the mechanism of action of this effect remains to be elucidated. Certain immune modulatory agents may indirectly affect Tregs in patients with cancer but not necessarily in the desired direction for the therapeutic setting. More sophisticated techniques that have become available for Treg analysis in patients will assist in this important translational effort.

Regulatory T-cell trafficking: from thymic development to tumor-induced immune suppression

Regulatory T cells (Tregs) have become a priority for many investigators in immunology due to their potent immunosuppressive and tolerogenic effects. While Treg activity is required for normal immune homeostasis, dysregulation of their numbers can induce autoimmunity or aid in the pathogenesis of disease. Therefore, great effort has been made to understand the mechanisms by which Tregs accumulate in different areas of the body. Like other lymphocytes, Tregs migrate in response to a network of chemotactic stimuli involving chemokines, chemokine receptors, integrins, and their corresponding ligands. However, many of these stimuli are exclusive to Tregs, inducing their migration while leaving conventional populations unaffected. It is these selective stimuli that result in increased ratios of Tregs among conventional effector populations, leading to changes in immune suppression and homeostasis. This review explores selective Treg trafficking during thymic Treg development, migration to secondary lymphoid tissues and emigration into the periphery during homeostatic conditions, inflammation, and the tumor microenvironment, placing emphasis on stimuli that selectively recruits Tregs to target locations.

Methyl gallate exhibits potent antitumor activities by inhibiting tumor infiltration of CD4+CD25+ regulatory T cells

CD4(+)CD25(+) regulatory T (Treg) cells play crucial roles in the host response to tumors. Increasing evidence supports the existence of elevated numbers of Treg cells in solid tumors and hematologic malignancies. In this study, the effects of methyl gallate on Treg cells were examined. Methyl gallate inhibited Treg cell-suppressive effects on effector CD4(+) T cells and Treg migration toward tumor environment. The expression of Treg surface markers including CTLA-4, CCR4, CXCR4, and glucocorticoid-induced TNFR was significantly suppressed upon methyl gallate treatment. Furthermore, forkhead box P3 (Foxp3) expression was also significantly decreased by methyl gallate, suggesting that the suppressive effects of methyl gallate on Treg were medicated by decrease of Treg-specific transcription factor Foxp3. In tumor-bearing hosts, methyl gallate treatment substantially reduced tumor growth and prolonged the survival rate. In contrast, nu/nu mice did not show decreased tumor progression in response to methyl gallate. In addition, in tumor-bearing Treg-depleted mice, tumor growth and the survival rates were not changed by methyl gallate treatment, strongly suggesting that the main therapeutic target of methyl gallate in tumor suppression was related to modulation of the CD4(+)CD25(+) Treg cell functions. In the spleen of tumor-bearing mice, methyl gallate treatment induced a significant decrease in the CD4(+)CD25(+)Foxp3(high) Treg cell population. Especially, the number of tumor-infiltrating CD25(+)Foxp3(high) Treg cells was significantly lower in methyl gallate-treated mice. These results suggest that methyl gallate can be used to reverse immune suppression and as a potentially useful adjunct for enhancing the efficacy of immune-based cancer therapy.

The molecular mechanisms of traditional Chinese medicine ZHENG syndromes on pancreatic tumor growth

BACKGROUND

Traditional Chinese medicine (TCM) syndromes (ZHENG in Chinese) are the abstraction from the comprehensive analysis of clinical information gained by the four main diagnostic TCM methods: observation, listening, questioning, and pulse analyses. Proper TCM diagnosis is the most important principle to guide the prescribing of Chinese herbs.

OBJECTIVE

To evaluate the specific effect of TCM ZHENG on tumor growth and to examine the molecular mechanisms underlying ZHENG and tumor growth.

METHODS

The authors established subcutaneous tumor models of pancreatic cancer ZHENG syndromes of Damp heat (Shi-Re) and Spleen deficiency (Pi-Xu). Tissue samples of the subcutaneous transplanted tumors from each model were studied versus control tumors. CCR5 and CXCR4 proteins in these tissues were assayed by immunohistochemical staining. The expression of CCR5/CCL5/CCL4/CCL3 and CXCR4/SDF-1 mRNA was investigated by reverse transcriptase-polymerase chain reaction (RT-PCR). SDF-1, CCL4, CCL5, and CCL3, which are ligands of CXCR4 and CCR5, were examined by ELISA.

RESULTS

The study found that tumor models with different ZHENG were successfully established in each group; the tumor growth of Shi-Re group was slower than that of the control group. It was found that there was a significant difference in CCR5 mRNA expression levels among the Pi-Xu, Shi-Re, and control groups. The results of immunohistochemistry staining revealed that the positive rate of CCR5 protein in Shi-Re group, Pi-Xu group, and control group was 25.00%, 53.33%, 83.33%, respectively. The Shi-Re group expressed the lowest levels of CCL5 and CCL4.

CONCLUSION

The results of the study suggest that the existence of TCM ZHENG may influence the tumor growth in pancreatic cancer, which might be mediated by the expression of CCR5/CCL5/CCL4. This finding may lead to the development of TCM ZHENG as a prognostic indicator in pancreatic tumor growth.

The role of IL-1beta in reduced IL-7 production by stromal and epithelial cells: a model for impaired T-cell numbers in the gut during HIV-1 infection

OBJECTIVES

Interleukin (IL)-7 is a key cytokine in T-cell homeostasis. Stromal cells, intestinal epithelial cells and keratinocytes are known to produce this cytokine. The mechanisms and cellular factors regulating IL-7 production are still unclear. We assessed whether IL-1beta and interferon (IFN)-gamma, cytokines produced during inflammatory conditions, may impact on IL-7 production.

DESIGN

We used human intestinal epithelial cells (DLD-1 cell line) and bone marrow stromal cells (HS27 cell line), known to produce IL-7; IL-7 production was evaluated at the mRNA and protein levels. To assess whether treatment of HS27 cells with IL-1beta and/or IFN-gamma leads to changes in the gene expression of cytokines, Toll-like receptors (TLRs) and chemokines, we analysed gene expression profiles using the whole-genome microarray Human Gene 1.0 ST.

RESULTS

We found that IFN-gamma enhanced the expression of IL-7 mRNA (P < 0.001) in both cell lines. IL-1beta treatment led to a significant down-regulation (P < 0.001) of IL-7 mRNA expression in both cell lines. The IL-7 concentration in supernatants collected from treated DLD-1 and HS27 cell cultures reflected the trend of IL-7 mRNA levels. The gene profiles revealed dramatic changes in expression of cytokines and their receptors (IL-7/IL-7R alpha; IL-1alpha,IL-1beta/IL-1R1; IFN-gamma/IFN-gammaR1), of IFN regulatory factors (IRF-1 and 2), of TLRs and of important chemo-attractants for T cells. The microarray results were verified by additional methods.

CONCLUSIONS

Our results are discussed in the setting of inflammation and T-cell survival in the gut compartment during HIV-1 infection where stromal and epithelial cells may produce factors that contribute to impaired IL-7 homeostasis and homing of T cells.

CCR5 dictates the equilibrium of proinflammatory IL-17+ and regulatory Foxp3+ T cells in fungal infection

CCR5 is a chemotactic mediator for inflammatory cells as well as regulatory T cells (Tregs). In this study, we investigated the role of CCR5 during infection with the fungal pathogen Histoplasma capsulatum. Mice lacking CCR5 or treated with an mAb to CCL4 had impaired infiltration of inflammatory cells to the lungs. Despite displaying an elevated fungal burden prior to activation of an adaptive immune response, CCL4-neutralized and CCR5(-/-) mice resolved infection more efficiently than controls. Accelerated fungal clearance was associated with a reduced number of Tregs in the lungs. Impaired trafficking was not solely responsible for the paucity of Tregs in the lungs, as proliferation of both CD4(+) T cells and Tregs was diminished in CCR5(-/-) lungs during infection. A reduced number of Tregs in CCR5(-/-) lungs was associated with a selective increase of Th17 cytokines, and neutralization of IL-17 increased Treg proliferation and consequently fungal burden in CCR5(-/-) mice. Thus, CCR5 dictates pathogen persistence by tightly regulating the balance between Treg and Th17 cells in H. capsulatum infection.

CCR5 signaling suppresses inflammation and reduces adverse remodeling of the infarcted heart, mediating recruitment of regulatory T cells

Myocardial infarction triggers an inflammatory reaction that is involved in cardiac remodeling. Cardiac repair is dependent on regulatory mechanisms that suppress inflammation and prevent excessive matrix degradation. Chemokine induction in the infarcted heart mediates recruitment of leukocyte subsets with distinct properties. We demonstrate that signaling through the CC chemokine receptor 5 (CCR5) prevents uncontrolled postinfarction inflammation and protects from adverse remodeling by recruiting suppressive mononuclear cells. CCR5 and its ligands macrophage inflammatory protein (MIP)-1alpha and MIP-1beta were markedly induced in the infarcted mouse myocardium. In addition, almost 40% of the mononuclear cells infiltrating the infarct expressed CCR5. CCR5(-/-) mice exhibited marked upregulation of proinflammatory cytokine and chemokine expression in the infarct. In wild-type infarcts CCR5+ mononuclear cells had anti-inflammatory properties, expressing higher levels of IL-10 than CCR5- cells. In contrast, mononuclear cells isolated from CCR5(-/-) infarcts had reduced IL-10 expression. Moreover, enhanced inflammation in the absence of CCR5 was associated with impaired recruitment of CD4+/foxp3+ regulatory T cells (Tregs). The CCR5+ Treg subset exhibited increased IL-10 expression, reflecting potent anti-inflammatory activity. Accentuated inflammation in CCR5(-/-) infarcts was associated with increased matrix metalloproteinase (MMP) expression, reduced TIMP levels, and enhanced MMP-2 and MMP-9 activity, resulting in worse cardiac dilation. These results suggest that CCR5-mediated Treg recruitment may restrain postinfarction inflammation, preventing excessive matrix degradation and attenuating adverse remodeling.

Regulatory T cells in cancer

At the present time, regulatory T cells (Tregs) are an integral part of immunology but the route from discovery of "suppressive" lymphocytes in the 1980s to the current established concept of Tregs almost 20 years later has been a rollercoaster ride. Tregs are essential for maintaining self-tolerance as defects in their compartment lead to severe autoimmune diseases. This vitally important function exists alongside the detrimental effects on tumor immunosurveillance and antitumor immunity. Beginning with the identification of CD4(+)CD25(+) Tregs in 1995, the list of Treg subsets, suppressive mechanisms, and knowledge about their various origins is steadily growing. Increase in Tregs within tumors and circulation of cancer patients, observed in early studies, implied their involvement in pathogenesis and disease progression. Several mechanisms, ranging from proliferation to specific trafficking networks, have been identified to account for their systemic and/or local accumulation. Since various immunotherapeutic approaches are being utilized for cancer therapy, various strategies to overcome the antagonistic effects exerted by Tregs are being currently explored. An overview on the biology of Tregs present in cancer patients, their clinical impact, and methods for modulating them is given in this review. Despite the extensive studies on Tregs in cancer many questions still remain unanswered. Even the paradigm that Tregs generally are disadvantageous for the control of malignancies is now under scrutiny. Insight into the specific role of Tregs in different types of neoplasias is the key for targeting them in a way that is beneficial for the clinical outcome.

Low expression of chemokine receptor CCR5 in human colorectal cancer correlates with lymphatic dissemination and reduced CD8+ T-cell infiltration

BACKGROUND

Chemokines and their receptors have been proposed to distinctly contribute to tumor growth, dissemination, and local immune escape. The aim of this study was to evaluate the relevance of the chemokine receptor CCR5 expression for the progression of human colorectal cancer.

METHODS

CCR5 expression was assessed by RT-PCR analysis in 103 colorectal cancer patients. Intensity of CCR5 expression was correlated with both tumor and patient characteristics. Infiltration of tumor margins with CD8(+) T cells in the context of CCR5 expression was analyzed by immunohistochemistry in additional 18 colorectal cancer specimens.

RESULTS

Human colorectal cancer revealed variable intensities of CCR5 expression ranging from absent (48/103: 47%), weak (30/103: 29%), intermediate (13/103: 13%), to strong (12/103: 12%). Absent or weak CCR5 expression was significantly associated with advanced UICC stages (P=0.02) and lymphatic metastasis (P=0.05). In addition, CCR5 expression positively correlated with CD8(+) T-cell infiltration in tumor margins (P=0.001).

CONCLUSION

In summary, intermediate and strong CCR5 expression was significantly associated with nonmetastatic colorectal cancer and increased CD8(+) T-cell infiltration.

T regulatory cells, the evolution of targeted immunotherapy

T regulatory cells are able to suppress anti-tumour immunity in pre-clinical models and in patients. This review highlights the important discoveries in Treg immunology critical to the evolution of targeted immunotherapy. We also describe the therapeutic applications that are currently being assessed and their future potential.

Biology and clinical observations of regulatory T cells in cancer immunology

This review specifically examines the role of regulatory T cells (Tregs) in cancer in both mice and the clinic. Due to the rapid refinement of the definition of Tregs and their heterogeneity, emphasis is given to research findings over the past three years. For clarity, this review is broadly divided into three short sections that outline the basic biology of Tregs - (1) Treg lineage and development, (2) Treg subsets, and (3) mechanisms of Treg-mediated immune suppression; followed by two more comprehensive sections that cover; (4) clinical observations of Tregs and cancer, and (5) modifications of Treg biology as cancer immunotherapies. The latter two sections discuss the measurement of function and frequency of Treg in model systems and clinical trials and possible ways to interfere with Treg-mediated immune suppression with the focus on recent pre-clinical and clinical findings.

The role of regulatory T cells in cancer

There has been an explosion of literature focusing on the role of regulatory T (Treg) cells in cancer immunity. It is becoming increasingly clear that Treg cells play an active and significant role in the progression of cancer, and have an important role in suppressing tumor-specific immunity. Thus, there is a clear rationale for developing clinical strategies to diminish their regulatory influences, with the ultimate goal of augmenting antitimor immunity. Therefore, manipulation of Treg cells represent new strategies for cancer treatment. In this Review, I will summarize and review the explosive recent studies demonstrating that Treg cells are increased in patients with malignancies and restoration of antitumor immunity in mice and humans by depletion or reduction of Treg cells. In addition, I will discuss both the prognostic value of Treg cells in tumor progression in tumor-bearing hosts and the rationale for strategies for therapeutic vaccination and immunotherapeutic targeting of Treg cells with drugs and microRNA.

CCR5 is involved in resolution of inflammation in proteoglycan-induced arthritis

OBJECTIVE

CCR5 and its ligands (CCL3, CCL4, and CCL5) may play a role in inflammatory cell recruitment into the joint. However, it was recently reported that CCR5 on T cells and neutrophils acts as a decoy receptor for CCL3 and CCL5 to assist in the resolution of inflammation. The aim of this study was to determine whether CCR5 functions as a proinflammatory or antiinflammatory mediator in arthritis, by examining the role of CCR5 in proteoglycan (PG)-induced arthritis (PGIA).

METHODS

Arthritis was induced by immunizing wild-type (WT) and CCR5-deficient (CCR5(-/-)) BALB/c mice with human PG in adjuvant. The onset and severity of PGIA were monitored over time. Met-RANTES was used to block CCR5 in vivo. Arthritis was transferred to SCID mice, using spleen cells from arthritic WT and CCR5(-/-) mice. The expression of cytokines and chemokines was measured by enzyme-linked immunosorbent assay.

RESULTS

In CCR5(-/-) mice and WT mice treated with the CCR5 inhibitor Met-RANTES, exacerbated arthritis developed late in the disease course. The increase in arthritis severity in CCR5(-/-) mice correlated with elevated serum levels of CCL5. However, exacerbated arthritis was not intrinsic to the CCR5(-/-) lymphoid cells, because the arthritis that developed in SCID mouse recipients was similar to that in WT and CCR5(-/-) mice. CCR5 expression in the SCID mouse was sufficient to clear CCL5, because serum levels of CCL5 were the same in SCID mouse recipients receiving cells from either WT or CCR5(-/-) mice.

CONCLUSION

These data demonstrate that CCR5 is a key player in controlling the resolution of inflammation in experimental arthritis.

Pancreatic cancer cells activate CCL5 expression in mesenchymal stromal cells through the insulin-like growth factor-I pathway

Mesenchymal stromal cells (MSCs) have a critical role in cancer progression and metastasis. Despite extensive studies of the physiological responses in cancer cells, the molecular mechanisms regulating gene expression in MSCs by cancer cells remain undefined. Here we demonstrate that CC chemokine ligand 5 (CCL5) expression was increased in MSCs co-cultured with pancreatic cancer cells (PCCs), and this activation was dependent on extracellular insulin-like growth factor (IGF-I). Moreover, CCL5 induction in MSCs was required for the activation of IGF-I pathway in PCCs. These results reveal a link between the IGF-I pathway in PCCs and CCL5 pathway in MSCs through the interaction of those cells.

Soluble MHC-peptide complexes: tools for the monitoring of T cell responses in clinical trials and basic research

Soluble MHC-peptide complexes, commonly known as tetramers, allow the detection and isolation of antigen-specific T cells. Although other types of soluble MHC-peptide complexes have been introduced, the most commonly used MHC class I staining reagents are those originally described by Altman and Davis. As these reagents have become an essential tool for T cell analysis, it is important to have a large repertoire of such reagents to cover a broad range of applications in cancer research and clinical trials. Our tetramer collection currently comprises 228 human and 60 mouse tetramers and new reagents are continuously being added. For the MHC II tetramers, the list currently contains 21 human (HLA-DR, DQ and DP) and 5 mouse (I-A(b)) tetramers. Quantitative enumeration of antigen-specific T cells by tetramer staining, especially at low frequencies, critically depends on the quality of the tetramers and on the staining procedures. For conclusive longitudinal monitoring, standardized reagents and analysis protocols need to be used. This is especially true for the monitoring of antigen-specific CD4+ T cells, as there are large variations in the quality of MHC II tetramers and staining conditions. This commentary provides an overview of our tetramer collection and indications on how tetramers should be used to obtain optimal results.

Monocytes promote tumor cell survival in T-cell lymphoproliferative disorders and are impaired in their ability to differentiate into mature dendritic cells

A variety of nonmalignant cells present in the tumor microenvironment promotes tumorigenesis by stimulating tumor cell growth and metastasis or suppressing host immunity. The role of such stromal cells in T-cell lymphoproliferative disorders is incompletely understood. Monocyte-derived cells (MDCs), including professional antigen-presenting cells such as dendritic cells (DCs), play a central role in T-cell biology. Here, we provide evidence that monocytes promote the survival of malignant T cells and demonstrate that MDCs are abundant within the tumor microenvironment of T cell-derived lymphomas. Malignant T cells were observed to remain viable during in vitro culture with autologous monocytes, but cell death was significantly increased after monocyte depletion. Furthermore, monocytes prevent the induction of cell death in T-cell lymphoma lines in response to either serum starvation or doxorubicin, and promote the engraftment of these cells in nonobese diabetic/severe combined immunodeficient mice. Monocytes are actively recruited to the tumor microenvironment by CCL5 (RANTES), where their differentiation into mature DCs is impaired by tumor-derived interleukin-10. Collectively, the data presented demonstrate a previously undescribed role for monocytes in T-cell lymphoproliferative disorders.