Regulatory-T-cell inhibition versus depletion: the right choice in cancer immunotherapy

Prostate cancer, tumor immunity and a renewed sense of optimism in immunotherapy

The recent FDA approval of the first therapeutic vaccine against prostate cancer has revitalized the public interest in the fields of cancer immunology and immunotherapy. Yet, clinical results are modest. A reason for this limited success may reside in the capacity of the tumor to convert inflammation in a tumor-promoting condition and eventually escape immune surveillance. Here we present the main known interactions between the prostate tumor and the immune system, showing how the malignancy can dodge the immune system by also exerting several immunosuppressive mechanisms. We also discuss experimental and clinical strategies proposed to counteract cancer immune evasion and emphasize the importance of implementing appropriate murine models like the transgenic adenocarcinoma of the mouse prostate model for investigating the biology of prostate cancer and novel immunotherapy approaches against it.

Brain cancer immunoediting: novel examples provided by immunotherapy of malignant gliomas

A number of studies in murine models have suggested that the immune system may edit different tumors by forcing their expression profiles so that they escape immune reactions and proliferate. Glioblastoma (GB), the most frequent and aggressive primary brain tumor, provides a good example of this, thanks to the production of numerous immunosuppressive molecules (with TGF-β being of paramount importance), downregulation of the MHC complex and deregulation of the potential for antigen presentation by the surrounding microglia. Given that surgery, radiotherapy and chemotherapy with available protocols have limited effects on the survival of GB patients, different immunotherapy strategies have been developed, based on the use of dendritic cells, antibodies and peptide vaccination. Presently, bevacizumab, a humanized anti-VEGF antibody, provides the most successful example for immune-based treatment of GB, however, its action is limited in time, as the often tumor relapses due to still undefined immunoediting mechanisms. Altered function of EGF receptor-driven pathways is common in GB and is most frequently due to the presence of a deleted form named EGFRvIII, providing a unique cancer epitope that has been targeted by immunotherapy. A recent trial of GB immunotherapy based on vaccination with the EGFRvIII peptide has shown clinical benefit: interestingly most GBs at relapse were negative for EGFRvIII expression, a relevant, direct example of cancer immunoediting. Investigations on the mechanisms of GB immunoediting will lead to an increased understanding of the biology of this malignancy and hopefully provide novel therapeutic targets.

The ambiguity in immunology

In the present article, we discuss the various ambiguous aspects of the immune system that render this complex biological network so highly flexible and able to defend the host from different external invaders. This ambiguity stems mainly from the property of the immune system to be both protective and harmful. Immunity cannot be fully protective without producing a certain degree of damage (immunopathology) to the host. The balance between protection and tissue damage is, therefore, critical for the establishment of immune homeostasis and protection. In this review, we will consider as ambiguous, various immunological tactics including: (a) the opposing functions driving immune responses, immune-regulation, and contra-regulation, as well as (b) the phenomenon of chronic immune activation as a result of a continuous cross-presentation of apoptotic T cells by dendritic cells. All these plans participate principally to maintain a state of chronic low-level inflammation during persisting infections, and ultimately to favor the species survival.

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.

A role for T-bet-mediated tumour immune surveillance in anti-IL-17A treatment of lung cancer

Lung cancer is the leading cause of cancer deaths worldwide. The cytokine interleukin-17A supports tumour vascularization and growth, however, its role in lung cancer is unknown. Here we show, in the lungs of patients with lung adenocarcinoma, an increase in interleukin-17A that is inversely correlated with the expression of T-bet and correlated with the T regulatory cell transcription factor Foxp3. Local targeting of interleukin-17A in experimental lung adenocarcinoma results in a reduction in tumour load, local expansion of interferon-γ-producing CD4(+) T cells and a reduction in lung CD4(+)CD25(+)Foxp3(+) regulatory T cells. T-bet((-/-)) mice have a significantly higher tumour load compared with wild-type mice. This is associated with the local upregulation of interleukin-23 and induction of interleukin-17A/interleukin-17R-expressing T cells infiltrating the tumour. Local anti-interleukin-17A antibody treatment partially improves the survival of T-bet((-/-)) mice. These results suggest that local anti-interleukin-17A antibody therapy could be considered for the treatment of lung tumours.

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.

The dendritic cell-regulatory T lymphocyte crosstalk contributes to tumor-induced tolerance

Tumor cells commonly escape from elimination by innate and adaptive immune responses using multiple strategies among which is the active suppression of effector immune cells. Regulatory T lymphocytes (Treg) and tolerogenic dendritic cells play essential roles in the establishment and persistence of cancer-induced immunosuppression. Differentiating dendritic cells (DCs) exposed to tumor-derived factors may be arrested at an immature stage becoming inept at initiating immune responses and may induce effector T-cell anergy or deletion. These tolerogenic DCs, which accumulate in patients with different types of cancers, are also involved in the generation of Treg. In turn, Treg that expand during tumor progression contribute to the immune tolerance of cancer by impeding DCs' ability to orchestrate immune responses and by directly inhibiting antitumoral T lymphocytes. Herein we review these bidirectional communications between DCs and Treg as they relate to the promotion of cancer-induced tolerance.

Epithelial nuclear factor-κB signaling promotes lung carcinogenesis via recruitment of regulatory T lymphocytes

The mechanisms by which chronic inflammatory lung diseases, particularly chronic obstructive pulmonary disease (COPD), confer enhanced risk for lung cancer are not well defined. To investigate whether nuclear factor (NF)-κB, a key mediator of immune and inflammatory responses, provides an interface between persistent lung inflammation and carcinogenesis, we utilized tetracycline-inducible transgenic mice expressing, constitutively active IκB kinase β in airway epithelium (IKTA mice). Intraperitoneal injection of ethyl carbamate (urethane) or 3-methylcholanthrene (MCA) and butylated hydroxytoluene (BHT) was used to induce lung tumorigenesis. Doxycycline-treated IKTA mice developed chronic airway inflammation and markedly increased numbers of lung tumors in response to urethane, even when transgene expression (and therefore epithelial NF-κB activation) was begun after exposure to carcinogen. Studies using a separate tumor initiator/promoter model (MCA+BHT) indicated that NF-κB functions as an independent tumor promoter. Enhanced tumor formation in IKTA mice was preceded by increased proliferation and reduced apoptosis of alveolar epithelium, resulting in increased formation of premalignant lesions. Investigation of inflammatory cells in lungs of IKTA mice revealed a substantial increase in macrophages and lymphocytes, including functional CD4+/CD25+/FoxP3+ regulatory T lymphocytes (Tregs). Importantly, Treg depletion using repetitive injections of anti-CD25 antibodies limited excessive tumor formation in IKTA mice. At 6 weeks following urethane injection, antibody-mediated Treg depletion in IKTA mice reduced the number of premalignant lesions in the lungs in association with an increase in CD8 lymphocytes. Thus, persistent NF-κB signaling in airway epithelium facilitates carcinogenesis by sculpting the immune/inflammatory environment in the lungs.

Chemokine nitration prevents intratumoral infiltration of antigen-specific T cells

Blocking CCL2 nitration in tumors promoted CD8⁺ influx and reduced tumor growth and prolonged survival in mice when combined with adoptive cell therapy.

Tumor-promoted constraints negatively affect cytotoxic T lymphocyte (CTL) trafficking to the tumor core and, as a result, inhibit tumor killing. The production of reactive nitrogen species (RNS) within the tumor microenvironment has been reported in mouse and human cancers. We describe a novel RNS-dependent posttranslational modification of chemokines that has a profound impact on leukocyte recruitment to mouse and human tumors. Intratumoral RNS production induces CCL2 chemokine nitration and hinders T cell infiltration, resulting in the trapping of tumor-specific T cells in the stroma that surrounds cancer cells. Preconditioning of the tumor microenvironment with novel drugs that inhibit CCL2 modification facilitates CTL invasion of the tumor, suggesting that these drugs may be effective in cancer immunotherapy. Our results unveil an unexpected mechanism of tumor evasion and introduce new avenues for cancer immunotherapy.

A CCR4 antagonist combined with vaccines induces antigen-specific CD8+ T cells and tumor immunity against self antigens

Regulatory T cells (Tregs) may impede cancer vaccine efficacy in hematologic malignancies and cancer. CCR4 antagonists, an emergent class of Treg inhibitor, have been shown to block recruitment of Tregs mediated by CCL22 and CCL17. Our aim was to demonstrate the ability of a CCR4 antagonist (a small chemical molecule identified in silico) when combined with vaccines to break peripheral tolerance controlled by Tregs, a prerequisite for the induction of CD8(+) T cells against self Ags. Immunization of transgenic or normal mice expressing tumor-associated self Ags (Her2/neu, OVA, gp100) with a CCR4 antagonist combined with various vaccines led to the induction of effector CD8(+) T cells and partial inhibition of tumor growth expressing self Ags in both prophylactic and therapeutic settings. The CCR4 antagonist was more efficient than cyclophosphamide to elicit anti-self CD8(+) T cells. We also showed that the population of Tregs expressing CCR4 corresponded to memory (CD44(high)) and activated (ICOS(+)) Tregs, an important population to be targeted to modulate Treg activity. CCR4 antagonist represents a competitive class of Treg inhibitor able to induce functional anti-self CD8(+) T cells and tumor growth inhibition when combined with vaccines. High expression of CCR4 on human Tregs also supports the clinical development of this strategy.

Clinical significance of tumor-infiltrating FOXP3+ T cells in patients with ocular adnexal mucosa-associated lymphoid tissue lymphoma

We evaluated the association between tumor-infiltrating FOXP3+ T cells and clinical outcomes in patients with ocular adnexal lymphoma of mucosa-associated lymphoid tissue type (OAML). Pretreatment formalin-fixed paraffin-embedded tissues from 42 patients with OAML were stained with 236A/E7 anti-FOXP3 murine monoclonal antibody as well as CD3, CD4 and CD8 antibodies. The amount of FOXP3+ T cells was numerically quantified using an image analysis program. Front-line treatments were as follows: combination chemotherapy (n = 25); radiotherapy (n = 9); doxycycline (n = 6); and wait and see (n = 2). Complete response (CR) was observed in 20 (50%) of 40 evaluable patients. Median progression-free survival (PFS) was 50 months. A high number of FOXP3+ T cells (n = 21, ≥ 180/0.58 mm(2)) showed a higher CR rate (33%vs 71%, P = 0.013) and tendency towards prolonged PFS (48 vs 67 months, P = 0.110). In the combination chemotherapy group, a high number of FOXP3+ T cells was significantly associated with a higher CR rate (29%vs 82%, P = 0.008) and prolonged PFS (17 vs 79 months, P = 0.003). A high number of tumor-infiltrating FOXP3+ T cells correlates with a favorable clinical outcome in OAML patients.

Sustained suppression by Foxp3+ regulatory T cells is vital for infectious transplantation tolerance

A new genetic mouse model demonstrates the necessity of Foxp3⁺ T reg cells for infectious tolerance.

A paradigm shift in immunology has been the recent discovery of regulatory T cells (T reg cells), of which CD4⁺Foxp3⁺ cells are proven as essential to self-tolerance. Using transgenic B6.Foxp3^hCD2 mice to isolate and ablate Foxp3⁺ T reg cells with an anti-hCD2 antibody, we show for the first time that CD4⁺Foxp3⁺ cells are crucial for infectious tolerance induced by nonablative anti–T cell antibodies. In tolerant animals, Foxp3⁺ T reg cells are constantly required to suppress effector T cells still capable of causing tissue damage. Tolerated tissue contains T cells that are capable of rejecting it, but are prevented from doing so by therapeutically induced Foxp3⁺ T reg cells. Finally, Foxp3⁺ cells have been confirmed as the critical missing link through which infectious tolerance operates in vivo. Peripherally induced Foxp3⁺ cells sustain tolerance by converting naive T cells into the next generation of Foxp3⁺ cells. Empowering Foxp3⁺ regulatory T cells in vivo offers a tractable route to avoid and correct tissue immunopathology.

Clinical outcome of patients with various advanced cancer types vaccinated with an optimized cryptic human telomerase reverse transcriptase (TERT) peptide: results of an expanded phase II study

BACKGROUND

TERT (telomerase reverse transcriptase) plays a critical role in tumor cell growth and survival. In an expanded phase II study, we evaluated the immunological and clinical responses to the TERT-targeting Vx-001 vaccine in patients with advanced solid tumors.

METHODS

HLA-A*0201-positive patients received two subcutaneous injections of the optimized TERT(572Y) peptide followed by four injections of the native TERT(572) peptide, every 3 weeks. Peptide-specific immune responses were evaluated by enzyme-linked immunosorbent spot at baseline, and after the second and the sixth vaccinations.

RESULTS

Fifty-five patients were enrolled and 34 (62%) completed the six vaccinations. A TERT-specific T-cell immune response was observed in 55% and 70% of patients after the second and the sixth vaccinations, respectively. The disease control rate (DCR) was 36% [95% confidence interval (CI) 24% to 49%], including one complete and one partial response. Immunologically responding patients had a better clinical outcome than nonresponders [DCR: 44% versus 14% (P = 0.047); progression-free survival (PFS): 5.2 versus 2.2 months (P = 0.0001) and overall survival: 20 versus 10 months (P = 0.041)]. Multivariate analysis revealed that the immunological response was an independent variable associated with increased PFS (hazard ratio = 3.35; 95% CI 1.7-6.7).

CONCLUSION

Vx-001 vaccine was well tolerated and induced a TERT-specific immunological response, which was significantly correlated with improved clinical outcome.

Alterations in regulatory T-cells: rediscovered pathways in immunotoxicology

In addition to the effector T-cells subsets, T-cells can also differentiate into cells that play a suppressive or regulatory role in adaptive immune responses. The cell types currently identified as regulatory T-cells (T(regs)) include natural or thymic-derived T(regs), T-cells which express Foxp3(+)CD25(+)CD4(+) and can suppress immune responses to autoreactive T-cells, as well as inducible T(regs), that are generated from naïve T-cells in the periphery after interaction with antigens presented by dendritic cells. Inducible T(regs) include T(H)3 cells, T(r)1 cells, and Foxp3(+)-inducible T(regs). T(regs) have been shown to be critical in the maintenance of immune responses and T-cell homeostasis. These cells play an important role in suppressing responses to self-antigens and in controlling inappropriate responses to non-self-antigens, such as commensal bacteria or food in the gut. For example, depletion of CD4(+)CD25(+) T(regs) from mice resulted in the development of multi-organ autoimmune diseases. CD4(+)CD25(+) T(regs) and/or IL-10-producing T(r)1 cells are capable of suppressing or attenuating T(H)2 responses to allergens. Moreover, adoptive transfer of CD4(+)CD25(+) T(regs) from healthy to diseased animals resulted in the prevention or cure of certain autoimmune diseases, and was able to induce transplantation tolerance. Clinical improvement seen after allergen immunotherapy for allergic diseases such as rhinitis and asthma is associated with the induction of IL-10- and TGFβ-producing T(r)1 cells as well as FoxP3-expressing IL-10 T-cells, with resulting suppression of the T(H)2 cytokine milieu. Activation, expansion, or suppression of CD4(+)CD25(+) T(regs) in vivo by xenobiotics, including drugs, may therefore represent a relevant mechanism underlying immunotoxicity, including immunosuppression, allergic asthma, and autoimmune diseases.

Demethylation of the FOXP3 gene in human melanoma cells precludes the use of this epigenetic mark for quantification of Tregs in unseparated melanoma samples

The human suppressive T cells that stably express transcription factor FOXP3, or regulatory T cells (Tregs), are thought to suppress antitumor immune responses. The most specific marker for human Tregs is the demethylation of CpG dinucleotides located in the first intron of FOXP3 (FOXP3i1). FOXP3i1 is completely methylated in other hematopoietic cells, including nonsuppressive T cells that transiently express FOXP3 after activation. Previously, we and others reported estimations of the frequency of Tregs in the blood of melanoma patients using a FOXP3i1 methylation-specific qPCR assay. Here, we attempted to quantify Tregs inside tumor samples using this assay. However, we found demethylated FOXP3i1 sequences in the melanoma cells themselves. This demethylation was not associated with substantial FOXP3 mRNA or protein expression, even though the demethylation extended to the promoter and terminal regions of the gene in some melanoma cells. Our results imply that analyzing Treg frequencies by quantification of demethylated FOXP3i1 will require that tumor-infiltrating T cells be separated from melanoma cells.

Neem leaf glycoprotein inhibits CD4+CD25+Foxp3+ Tregs to restrict murine tumor growth

Background: The presence of Tregs in tumors is associated with compromised tumor-specific immune responses and has a clear negative impact on survival of cancer patients. Thus, downregulation of Tregs is considered as a promising cancer immunotherapeutic approach. We have reported previously that neem leaf glycoprotein (NLGP) prophylaxis restricts tumor growth in mice by immune activation. In continuation, here, involvement of NLGP in the modulation of Tregs in association with tumor growth restriction is investigated. Results: NLGP downregulates CD4+CD25+Foxp3+ Tregs within tumors. NLGP-mediated downregulation of CCR4 along with its ligand CCL22 restricts Treg migration at the tumor site. NLGP is not apoptotic to Tregs but significantly downregulates the expression of Foxp3, CTLA4 and GITR. It also reverses the functional impairment of T-effector cells by Tregs, in terms of IFN-γ secretion, cellular proliferation and tumor cell cytotoxicity. NLGP also facilitates reconditioning of tumor microenvironment (hostile) by increasing IFN-γ and IL-12 but decreasing IL-10, TGF-β, VEGF and IDO, creating an antitumor niche. Interaction between Foxp3, p-NFATc3 and p-Smad2/3, needed for successful Treg function, is also inhibited by NLGP. Conclusion: All of these coordinated events might result in inhibition of Treg associated-tumor growth and therefore increased survivability of mice having NLGP treatment before or/and after tumor inoculation. Thus, the possibility of NLGP being an excellent tool as a T-cell anergy breaker by abrogating the suppressor functions of Tregs in cancer needs to be explored further in the clinic.

Purification and kinetic characterization of human indoleamine 2,3-dioxygenases 1 and 2 (IDO1 and IDO2) and discovery of selective IDO1 inhibitors

Indoleamine 2,3-dioxygenase (IDO1) catalyzes the first step in tryptophan breakdown along the kynurenine pathway. Therapeutic inhibition of IDO1 is receiving much attention due to its proposed role in the pathogenesis of several diseases including cancer, hypotension and neurodegenerative disorders. A related enzyme, IDO2 has recently been described. We report the first purification and kinetic characterization of human IDO2 using a facile l-tryptophan consumption assay amenable to high throughput screening. We found that the K(m) of human IDO2 for l-tryptophan is much higher than that of IDO1. We also describe the identification and characterization of a new IDO1 inhibitor compound, Amg-1, by high throughput screening, and compare the inhibition profiles of IDO1 and IDO2 with Amg-1 and previously described compounds. Our data indicate that human IDO1 and IDO2 have different kinetic parameters and different inhibition profiles. Docking of Amg-1 and related analogs to the known structure of IDO1 and to homology-modeled IDO2 suggests possible rationales for the different inhibition profiles of IDO1 and IDO2.

A Role for PPARgamma in the Regulation of Cytokines in Immune Cells and Cancer

Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated transcription factor and a member of the nuclear receptor superfamily. PPARγ and its ligands appear to serve diverse biological functions. In addition to the well-studied effects of PPARγ on metabolism and cellular differentiation, abundant evidence suggests that PPARγ is an important regulator of the immune system and cancers. Since cytokines are not only key modulators of inflammation with pro- and anti-inflammatory functions but they also can either stimulate or inhibit tumor growth and progression, this review summarizes the role for PPARγ in the regulation of cytokine production and cytokine-mediated signal transduction pathways in immune cells and cancer.

CXCL12/CXCR4 blockade induces multimodal antitumor effects that prolong survival in an immunocompetent mouse model of ovarian cancer

The chemokine CXCL12 and its receptor CXCR4 are expressed widely in human cancers, including ovarian cancer, in which they are associated with disease progression at the levels of tumor cell proliferation, invasion, and angiogenesis. Here, we used an immunocompetent mouse model of intraperitoneal papillary epithelial ovarian cancer to show that modulation of the CXCL12/CXCR4 axis in ovarian cancer has multimodal effects on tumor pathogenesis associated with induction of antitumor immunity. siRNA-mediated knockdown of CXCL12 in BR5-1 cells that constitutively express CXCL12 and CXCR4 reduced cell proliferation in vitro, and tumor growth in vivo. Similarly, treatment of BR5-1-derived tumors with AMD3100, a selective CXCR4 antagonist, resulted in increased tumor apoptosis and necrosis, reduction in intraperitoneal dissemination, and selective reduction of intratumoral FoxP3(+) regulatory T cells (Treg). Compared with controls, CXCR4 blockade greatly increased T-cell-mediated antitumor immune responses, conferring a significant survival advantage to AMD3100-treated mice. In addition, the selective effect of CXCR4 antagonism on intratumoral Tregs was associated with both higher CXCR4 expression and increased chemotactic responses to CXCL12, a finding that was also confirmed in a melanoma model. Together, our findings reinforce the concept of a critical role for the CXCL12/CXCR4 axis in ovarian cancer pathogenesis, and they offer a definitive preclinical validation of CXCR4 as a therapeutic target in this disease.

Cisplatin pretreatment enhances anti-tumor activity of cytokine-induced killer cells

AIM: To investigate whether cisplatin (DDP) enhances the anti-tumor activity of cytokine- induced killer (CIK) cells in a murine colon adenocarcinoma model.

METHODS: Tumor size and weight served as indicators of therapeutic response. Immunohistochemistry was performed to observe intratumoral lymphocyte infiltration and tumor microvessel density. Changes in the percentage of regulatory T (Treg) cells within the spleens of tumor-bearing mice preconditioned with DDP were monitored using flow cytometry.

RESULTS: A marked T cell-dependent, synergistic anti-tumor effect of the combined therapy was observed (1968 ± 491 mm³ vs 3872 ± 216 mm³; P = 0.003). Preconditioning chemotherapy with DDP augmented the infiltration of CD3+ T lymphocytes into the tumor mass and reduced the percentage of both intratumoral and splenic Treg cells.

CONCLUSION: Preconditioning with DDP markedly enhances the efficacy of adoptively transferred CIK cells, providing a potential clinical modality for the treatment of patients with colorectal cancer.

Antigen localization controls T cell-mediated tumor immunity

Effective antitumor immunotherapy requires the identification of suitable target Ags. Interestingly, many of the tumor Ags used in clinical trials are present in preparations of secreted tumor vesicles (exosomes). In this study, we compared T cell responses elicited by murine MCA101 fibrosarcoma tumors expressing a model Ag at different localizations within the tumor cell in association with secreted vesicles (exosomes), as a nonsecreted cell-associated protein, or as secreted soluble protein. Remarkably, we demonstrated that only the tumor-secreting vesicle-bound Ag elicited a strong Ag-specific CD8(+) T cell response, CD4(+) T cell help, Ag-specific Abs, and a decrease in the percentage of immunosuppressive regulatory T cells in the tumor. Moreover, in a therapeutic tumor model of cryoablation, only in tumors secreting vesicle-bound Ag could Ag-specific CD8(+) T cells still be detected up to 16 d after therapy. We concluded that the localization of an Ag within the tumor codetermines whether a robust immunostimulatory response is elicited. In vivo, vesicle-bound Ag clearly skews toward a more immunogenic phenotype, whereas soluble or cell-associated Ag expression cannot prevent or even delay outgrowth and results in tumor tolerance. This may explain why particular immunotherapies based on these vesicle-bound tumor Ags are potentially successful. Therefore, we conclude that this study may have significant implications in the discovery of new tumor Ags suitable for immunotherapy and that their location should be taken into account to ensure a strong antitumor immune response.

Recruitment of regulatory T cells is correlated with hypoxia-induced CXCR4 expression, and is associated with poor prognosis in basal-like breast cancers

Introduction

Basal-like breast cancers behave more aggressively despite the presence of a dense lymphoid infiltrate. We hypothesised that immune suppression in this subtype may be due to T regulatory cells (Treg) recruitment driven by hypoxia-induced up-regulation of CXCR4 in Treg.

Methods

Immunoperoxidase staining for FOXP3 and CXCL12 was performed on tissue microarrays from 491 breast cancers. The hypoxia-associated marker carbonic anhydrase IX (CA9) and double FOXP3/CXCR4 staining were performed on sections from a subset of these cancers including 10 basal-like and 11 luminal cancers matched for tumour grade.

Results

High Treg infiltration correlated with tumour CXCL12 positivity (OR 1.89, 95% CI 1.22 to 2.94, P = 0.004) and basal phenotype (OR 3.14, 95% CI 1.08 to 9.17, P = 0.004) in univariate and multivariate analyses. CXCL12 positivity correlated with improved survival (P = 0.005), whereas high Treg correlated with shorter survival for all breast cancers (P = 0.001), luminal cancers (P < 0.001) and basal-like cancers (P = 0.040) that were confirmed in a multivariate analysis (OR 1.61, 95% CI 1.02 to 2.53, P = 0.042). In patients treated with hormone therapy, high Treg were associated with a shorter survival in a multivariate analysis (OR 1.78, 95% CI 1.01 to 3.15, P = 0.040). There was a tendency for luminal cancers to show CXCL12 expression (102/138, 74%) compared to basal-like cancers (16/27, 59%), which verged on statistical significance (P = 0.050). Up-regulation of CXCR4 in Treg correlated with the basal-like phenotype (P = 0.029) and tumour hypoxia, as indicated by CA9 expression (P = 0.049).

Conclusions

Our data show that in the setting of hypoxia and CXCR4 up-regulation in Treg, CXCL12 expression may have the negative consequence of enhancing Treg recruitment and suppressing the anti-tumour immune response.

Noncanonical K27-linked polyubiquitination of TIEG1 regulates Foxp3 expression and tumor growth

Earlier, we demonstrated the essential role of Kruppel-like transcription factor, TIEG1, in TGF-β-induced regulatory T cell (Treg) development. In this article, we demonstrate that IL-6, which promotes Th17 development, abrogated TIEG1 nuclear translocation and inhibited TGF-β-induced Treg development. Tyrosine kinase Tyk2-mediated phosphorylation of TIEG1 at Tyr179 promoted noncanonical K-27-linked polyubiquitination, which inhibited TIEG1 nuclear translocation. To test the role of TIEG1-regulated Treg/Th17 development in antitumor immunity, we analyzed TRAMP-C2 tumor growth in TIEG1(-/-) mice. The defective Treg development and elevated Th17 response resulted in enhanced immune reactivity in the tumor and inhibition of TRAMP-C2 tumor growth in TIEG1(-/-) mice. Thus, our results uncovered a novel regulatory mechanism that modulates Tregs and may regulate tumor progression.

CD103 is a hallmark of tumor-infiltrating regulatory T cells

Regulatory T cells (Treg) mediate tolerance towards self-antigens by suppression of innate and adaptive immunity. In cancer patients, tumor-infiltrating FoxP3+ Treg suppress local anti-tumor immune responses and are often associated with poor prognosis. Markers that are selectively expressed on tumor-infiltrating Treg may serve as targets for immunotherapy of cancer. Here we show that CD103, an integrin mediating lymphocyte retention in epithelial tissues, is expressed at high levels on tumor-infiltrating FoxP3+ Treg in several types of murine cancer. In the CT26 model of colon cancer up to 90% of the intratumoral FoxP3+ cells expressed CD103 compared to less than 20% in lymphoid organs. CD103+ Treg suppressed T effector cell activation more strongly than CD103(neg) Treg. Expression of CD103 on Treg closely correlated with intratumoral levels of transforming growth factor β (TGF-β) and could be induced in a TGF-β-dependent manner by tumor cell lines. In vivo, gene silencing of TGF-β reduced the frequency of CD103+ Treg, demonstrating that CD103 expression on tumor-infiltrating Treg is driven by intratumoral TGF-β. Functional blockade of CD103 using a monoclonal antibody did however not reduce the number of intratumoral Treg, indicating that CD103 is not involved in homing or retention of FoxP3+ cells in the tumor tissue. In conclusion, expression of CD103 is a hallmark of Treg that infiltrate TGF-β-secreting tumors. CD103 thus represents an interesting target for selective depletion of tumor-infiltrating Treg, a strategy that may help to improve anti-cancer therapy.

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.

The bone marrow stroma in hematological neoplasms--a guilty bystander

In the setting of hematological neoplasms, changes in the bone marrow (BM) stroma might arise from pressure exerted by the neoplastic clone in shaping a supportive microenvironment, or from chronic perturbation of the BM homeostasis. Under such conditions, alterations in the composition of the BM stroma can be profound, and could emerge as relevant prognostic factors. In this Review, we delineate the multifaceted contribution of the BM stroma to the pathobiology of several hematological neoplasms, and discuss the impact of stromal modifications on the natural course of these diseases. Specifically, we highlight the involvement of BM stromal components in lymphoid and myeloid malignancies, and present the most relevant processes responsible for remodeling the BM stroma. The role of bystander BM stromal elements in the setting of hematological neoplasms is discussed, strengthening the rationale for treatment strategies that target the BM stroma.

Prostatectomy restores the maturation competence of blood dendritic cell precursors and reverses the abnormal expansion of regulatory T lymphocytes

OBJECTIVE

To verify the presence of deviated dendritic cell (DC) precursors and of suppressor lymphocytes (Treg) in tumor bearing prostate cancer (PCa) patients and to monitor the corrective effect of tumor ablation.

METHODS

Monocytes isolated from the blood of patients before and 1 month after prostatectomy were allowed to reach complete maturation (mDC) ex vivo in a clinical grade two-step process. T-regulatory cells were identified in the lymphocyte cell fraction by the CD4(+)CD25(high)FoxP3(+)/CD4(+)CD25(high)CD127(low/-) phenotype.

RESULTS

Despite loss of the monocytes marker CD14, cytokine-matured DCs of tumor bearing patients expressed lower levels of the costimulatory molecule CD80 and of the maturation markers CD83 and CCR7 compared to mDC of normal subjects (NS, P = 0.001, 0.001, and 0.008, respectively). Prostatectomy restored CD80, CD83, and CCR7 expression to values not different from those of NS (P = 0.15, 0.60, and 0.71) and significantly higher than those of the pre-surgery state (CD83, P = 0.0003 and CCR7, P = 0.002). The frequency of Tregs, identified as either CD4 + CD25(high)FoxP3(+) or CD4(+)CD25(high)CD127(low/-), was significantly higher in pre-surgery patients than in NS (P = 0.0001 and 0.0003) and significant recovery of the CD4(+)CD25(high)CD127(low/-) (P = 0.0005) was observed after surgery.

CONCLUSIONS

The presence of defective DC precursors and suppressor lymphocytes in the tumor-bearing, but not tumor-free stage, positions the latter as the ideal setting for clinical success of PCa vaccine therapy.

Human FoxP3(+)CD4(+) regulatory T cells: their knowns and unknowns

Human regulatory T cells (Tregs) expressing the transcription factor FoxP3 play indispensable roles for the maintenance of immunological self-tolerance and immune homeostasis. In this review, we discuss immunological characteristics of human FoxP3(+) Tregs and to what extent they are similar to or different from the murine counterparts. We also discuss important issues that remain to be addressed in the field to better understand the pathophysiology of autoimmune disease and to build solid basis for immunotherapies targeting FoxP3(+) Tregs.

A tritherapy combination of a fusion protein vaccine with immune-modulating doses of sequential chemotherapies in an optimized regimen completely eradicates large tumors in mice

Tumor-induced immunosuppression plays a critical role in both impeding tumor-specific immune responses and limiting the effects of cancer immunotherapy. Analyses of regulatory cells recruited during the growth of the E7-expressing tumor, TC-1, revealed a high percentage of regulatory T cells (Tregs) as well as myeloid-derived suppressor cells (MDSCs) in spleens and tumors. In this study, we proposed that treatment with immune-modulating doses of cyclophosphamide (CTX) and all-trans retinoic acid (ATRA) would result in a beneficial tumor microenvironment with the suppression of Tregs and MDSCs and, thus, enhance the effect of a human papillomavirus protein vaccine. Our results showed that CTX preconditioning and persistent ATRA treatment along with the vaccine achieved long-term survival and induced long-term memory responses. However, the effect of the antitumor response sharply declined when the tritherapy was initiated after the optimal therapeutic time. The more intensive regimen could rescue the effect of the tritherapy accompanied by the decreased percentage of Tregs and MDSCs in spleens and tumors. Besides, a favorable host environment was created by the reduced secretion of interleukin-10 and 6 and vascular endothelial growth factor (VEGF) in the tumor niche and decreased the expression of phosphorylation-signal transducer and activator of transcription 3 of TC-1 tumors. Our data shed light on the immune-modulating doses of sequential chemoimmunotherapeutic strategy targeting not only the tumor but also its microenvironment, which suggests a potential clinical benefit for the immunotherapy of HPV-associated malignancies.

2011: the immune hallmarks of cancer

Ten years after the publication of the position paper “The hallmarks of cancer” (Hanahan and Weinberg Cell 100:57–70, 2000), it has become increasingly clear that mutated cells on their way to giving rise to a tumor have also to learn how to thrive in a chronically inflamed microenvironment, evade immune recognition, and suppress immune reactivity. Genetic and molecular definition of these three immune hallmarks of cancer offers the opportunity to learn how to deploy specific countermeasures to reverse the situation in favor of the immune system and, eventually, the patient. This new information could be channeled to address what seem to be the three major hallmarks for the immune control of cancer progression: effective procedures to activate immune reactivity; characterization of not-disposable oncoantigens; and counteraction of immune suppression.

TLR1/TLR2 agonist induces tumor regression by reciprocal modulation of effector and regulatory T cells

Using TLR agonists in cancer treatment can have either beneficial or detrimental effects. Therefore, it is important to determine their effect on the tumor growth and understand the underlying mechanisms in animal tumor models. In this study, we report a general immunotherapeutic activity of a synthetic bacterial lipoprotein (BLP), a TLR1/TLR2 agonist, on established lung carcinoma, leukemia, and melanoma in mice. Systemic treatment of 3LL tumor-bearing mice with BLP, but not LPS, led to a dose-dependent tumor regression and a long-lasting protective response against tumor rechallenge. The BLP-mediated tumor remission was neither mediated by a direct tumoricidal activity nor by innate immune cells, because it lacked therapeutic effect in immunodeficient SCID mice. Instead, BLP treatment reduced the suppressive function of Foxp3(+) regulatory T cells (Tregs) and enhanced the cytotoxicity of tumor-specific CTL in vitro and in vivo. Furthermore, adoptive cotransfer of BLP-pretreated but not untreated CTL and Tregs from wild-type but not from TLR2(-/-) mice was sufficient to restore antitumor immunity in SCID mice by reciprocally modulating Treg and CTL function. These results demonstrate that the TLR1/TLR2 agonist BLP may have a general tumor therapeutic property involving reciprocal downregulation of Treg and upregulation of CTL function. This property may play an important role in the development of novel antitumor strategies.

Basic concepts of inflammation and its role in carcinogenesis

While the normal inflammatory cascade is self-limiting and crucial for host protection against invading pathogens and in the repair of damaged tissue, a wealth of evidence suggests that chronic inflammation is the engine driving carcinogenesis. Over a period of almost 150 years the link between inflammation and cancer development has been well established. In this chapter we discuss the fundamental concepts and mechanisms behind normal inflammation as it pertains to wound healing. We further discuss the association of inflammation and its role in carcinogenesis, highlighting the different stages of cancer development, namely tumour initiation, promotion and progression. With both the innate and adaptive arms of the immune system being central to the inflammatory process, we examine the role of a number of immune effectors in contributing to the carcinogenic process. In addition, we highlight the influences of host genetics in altering cancer risk.

Frequency of circulating Tregs with demethylated FOXP3 intron 1 in melanoma patients receiving tumor vaccines and potentially Treg-depleting agents

PURPOSE

Regulatory T cells (Tregs) are thought to inhibit antitumor immune responses, and their depletion could therefore have a synergistic effect with therapeutic cancer vaccines. We investigated the impact of three medications on blood Treg frequency in vaccinated cancer patients.

EXPERIMENTAL DESIGN

To date, the most specific marker for human Tregs is demethylation in the DNA that encodes the transcription factor FOXP3. Thus, we used a FOXP3 methylation-specific quantitative PCR assay (MS-qPCR) to measure Treg frequencies in the peripheral blood mononuclear cells (PBMCs) of melanoma patients. The patients participated in three clinical trials that combined tumor vaccines with potential Treg-depleting agents: low-dose cyclophosphamide, anti-CD25 monoclonal antibody daclizumab, and the IL-2/diphtheria toxin fusion protein denileukin diftitox.

RESULTS

In the nine control patients, blood Treg frequencies varied over time; there was a 46% reduction in one patient. In treated patients, a more than 2-fold decrease in Tregs was observed in one out of 11 patients receiving cyclophosphamide and in four out of 13 receiving daclizumab, but there was no such Treg decrease in any of the six patients who received denileukin diftitox. As a positive control, a more than 2-fold increase in blood Tregs was detected in four out of nine patients who were treated with interleukin-2.

CONCLUSIONS

We used a MS-qPCR method that detects Tregs but not other activated T lymphocytes; however, none of the Treg-depleting strategies that we tested led, in the majority of patients, to a conservative 50% reduction in blood Tregs.

Regulatory T cells predict the time to initial treatment in early stage chronic lymphocytic leukemia

BACKGROUND

Early stage chronic lymphocytic leukemia is characterized by a highly variable course of disease. Because it is believed that regulatory T cells (T(regs) ) are potent suppressors of antitumor immunity, the authors hypothesized that increased T(regs) may favor disease progression.

METHODS

T(reg) levels (cluster of differentiation 3 [CD3]-positive, [CD4]-positive, CD25-positive, and CD127-negative) in peripheral blood from 102 patients were analyzed by flow cytometry. Statistical analysis was used to evaluate correlations with clinical data.

RESULTS

The relative T(reg) numbers in CD4-positive T cells were significantly greater in patients with chronic lymphocytic leukemia compared with the numbers in a control group of 170 healthy individuals (P = .001). Patients were divided into 2 groups using a median T(reg) value of 9.7% (the percentage of CD4-positive T cells). Patients with higher T(reg) levels had a significantly shorter time to initial treatment (median, 5.9 years) compared with patients who had lower T(reg) levels (median, 11.7 years; log-rank P = .019). Furthermore, T(reg) levels (the percentage of CD4-positive T cells) had significant prognostic power to predict the time to initial treatment in univariate analysis (P = .023) and in multivariate Cox regression analysis that included the variables Rai stage, immunoglobulin heavy-chain variable region gene mutational status, chromosomal aberrations, and CD38 expression (P = .028).

CONCLUSIONS

Higher T(reg) levels had significant and independent prognostic power for predicting the time to initial treatment in patients with low to intermediate stage chronic lymphocytic leukemia.

Depletion of regulatory T cells facilitates growth of established tumors: a mechanism involving the regulation of myeloid-derived suppressor cells by lipoxin A4

Regulatory T cells (Tregs) are thought to facilitate tumor development by suppressing protective antitumor immune responses. However, recent clinical and laboratory studies show that Tregs are a favorable element against cancer. In this study, we provide evidence that Tregs have both promoting and inhibiting effects on tumors, depending on the stage of tumor development. By using 0.5 mg cyclophosphamide, we constructed a murine liver cancer model in which Tregs were continuously and selectively depleted. Under such conditions, we found that tumor growth was inhibited at early stages but accelerated later on. Analysis of the tumor microenvironment disclosed that long-term Treg depletion by 0.5 mg cyclophosphamide treatment induced Gr-1(+)CD11b(+) myeloid-derived suppressor cells (MDSCs). Ablation of MDSCs by anti-Gr-1 Ab blocked Treg depletion-induced promotion of tumor growth. Furthermore, lipoxygenases 5 and 12, two enzymes participating in the biosynthesis of the lipid anti-inflammatory mediator lipoxin A(4), were upregulated or downregulated by Treg depletion or adoptive transfer. Correspondingly, the levels of lipoxin A(4) were increased or decreased. Lipoxin A(4) thus regulated the induction of MDSCs in response to Treg depletion. These findings suggest that Tregs may play different roles at different stages of tumor growth: promoting early and inhibiting late tumor growth. Our study also suggests that the interplay among Tregs, MDSCs, and lipoxin A(4) tunes the regulation of tumor-associated inflammation.

CD4+CD25+ regulatory T cell depletion improves the graft-versus-tumor effect of donor lymphocytes after allogeneic hematopoietic stem cell transplantation

Donor T cells play a pivotal role in the graft-versus-tumor effect after allogeneic hematopoietic stem cell transplantation. Regulatory T cells (T(reg)s) may reduce alloreactivity, the major component of the graft-versus-tumor effect. In the setting of donor lymphocyte infusion after hematopoietic stem cell transplantation, we postulated that T(reg) depletion could improve alloreactivity and likewise the graft-versus-tumor effect of donor T cells. The safety and efficacy of T(reg)-depleted donor lymphocyte infusion was studied in 17 adult patients with malignancy relapse after hematopoietic stem cell transplantation. All but one had previously failed to respond to at least one standard donor lymphocyte infusion, and none had experienced graft-versus-host disease. Two of the 17 patients developed graft-versus-host disease after their first T(reg)-depleted donor lymphocyte infusion and experienced a long-term remission of their malignancy. Four of the 15 patients who did not respond after a first T(reg)-depleted donor lymphocyte infusion received a second T(reg)-depleted donor lymphocyte infusion combined with lymphodepleting chemotherapy aimed to also eliminate recipient T(reg)s. All four developed acute-like graft-versus-host disease that was associated with a partial or complete and durable remission. In the whole cohort, graft-versus-host disease induction through T(reg) depletion was associated with improved survival. These results suggest that T(reg)-depleted donor lymphocyte infusion is a safe, feasible approach that induces graft-versus-host or graft-versus-tumor effects in alloreactivity-resistant patients. In patients not responding to this approach, the combination of chemotherapy-induced lymphodepletion of the recipient synergizes with the effect of T(reg)-depleted donor lymphocyte infusion. These findings offer a rational therapeutic approach for cancer cellular immunotherapy.

Significant anti-tumour activity of adoptively transferred T cells elicited by intratumoral dendritic cell vaccine injection through enhancing the ratio of CD8(+) T cell/regulatory T cells in tumour

We have shown that immunization with dendritic cells (DCs) pulsed with hepatitis B virus core antigen virus-like particles (HBc-VLP) packaging with cytosine-guanine dinucleotide (CpG) (HBc-VLP/CpG) alone were able to delay melanoma growth but not able to eradicate the established tumour in mice. We tested whether, by modulating the vaccination approaches and injection times, the anti-tumour activity could be enhanced. We used a B16-HBc melanoma murine model not only to compare the efficacy of DC vaccine immunized via footpads, intravenously or via intratumoral injections in treating melanoma and priming tumour-specific immune responses, but also to observe how DC vaccination could improve the efficacy of adoptively transferred T cells to induce an enhanced anti-tumour immune response. Our results indicate that, although all vaccination approaches were able to protect mice from developing melanoma, only three intratumoral injections of DCs could induce a significant anti-tumour response. Furthermore, the combination of intratumoral DC vaccination and adoptive T cell transfer led to a more robust anti-tumour response than the use of each treatment individually by increasing CD8(+) T cells or the ratio of CD8(+) T cell/regulatory T cells in the tumour site. Moreover, the combination vaccination induced tumour-specific immune responses that led to tumour regression and protected surviving mice from tumour rechallenge, which is attributed to an increase in CD127-expressing and interferon-γ-producing CD8(+) T cells. Taken together, these results indicate that repeated intratumoral DC vaccination not only induces expansion of antigen-specific T cells against tumour-associated antigens in tumour sites, but also leads to elimination of pre-established tumours, supporting this combined approach as a potent strategy for DC-based cancer immunotherapy.

Regulatory T-cell number is increased in chronic lymphocytic leukemia patients and correlates with progressive disease

Regulatory T-cells (Treg) actively maintain immunological self-tolerance and play a significant role in the progression of cancer. Treg cell numbers have been evaluated in 80 patients with previously untreated chronic lymphocytic leukemia (CLL) and in 40 normal healthy volunteers. Treg cells are higher in CLL patients than in controls and correlate with disease status (more advanced clinical stage, peripheral blood B-cell lymphocytosis, absolute CD38+ B-cell number, and more elevated LDH levels). No correlation was found with ZAP-70 expression, IgVH mutational status and cytogenetic abnormalities. This data shows that Treg cell number is abnormal in CLL patients.

Transient depletion of CD4(+) T cells augments IL-21-based immunotherapy of disseminated neuroblastoma in syngeneic mice

IL-21 is a member of the IL-2 cytokine family, produced by CD4+ T cells. We previously showed that immunotherapy (IT) with IL-21-transduced neuroblastoma cells (Neuro2a/IL-21) cured 33% of syngeneic mice bearing systemic NB. Here, we studied whether the removal of Treg cells could potentiate the therapeutic efficacy of Neuro2a/IL-21 vaccine. The administration of anti-CD25 mAb, which targets Treg cells, slightly potentiated the effect of vaccine IT (50% cure rate), but anti-CD4 mAb had a more potent effect leading to 80% cure rate. Anti-CD25 mAb, indeed, only partially depleted CD4+CD25+FoxP3+ Treg cells, whereas anti-CD4 mAb was more effective in this respect, leading to 90% depletion of Treg cells. In mice receiving vaccine+anti-CD4 mAb, which developed systemic immunity to NB, CD4+ T cells counts completely recovered in 90 days. Depletion of CD8+ T cells abrogated the effect of the combined IT, indicating a predominant role of these cells in driving the immune response. In addition, CD8+ T cells from cured mice coinjected with Neuro2a/parental cells (pc) in NOD-SCID mice completely inhibited tumor growth. Spleen cells from mice receiving Neuro2a/IL-21 vaccination showed increased expression of IFN-alpha2, -beta1 and -gamma mRNA. Moreover, mice receiving vaccine therapy alone or vaccine+anti-CD4 mAb showed increased IFN-gamma serum levels and IFN-gamma-producing CD8+ T cells were found in spleen cells. In conclusion, anti-CD4 mAb potentiated IL-21-based IT by removing Treg cells and/or their precursors and other potentially immune-suppressive CD4+ cell subsets, thus allowing the development of an IL-21-driven CD8+ T cell response, which mediates NB rejection.

B7-H1-dependent sex-related differences in tumor immunity and immunotherapy responses

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) are immunopathogenic in cancers by impeding tumor-specific immunity. B7-homologue 1 (B7-H1) (CD274) is a cosignaling molecule with pleiotropic effects, including hindering antitumor immunity. In this study, we demonstrate sex-dependent, B7-H1-dependent differences in tumor immunity and response to immunotherapy in a hormone-independent cancer, murine B16 melanoma. Antitumor immunity was better in B7-H1(-/-) females versus males as a result of reduced regulatory T cell function in the B7-H1(-/-) females, and clinical response following B7-H1 blockade as tumor immunotherapy was significantly better in wild-type females than in males, owing to greater B7-H1 blockade-mediated reduction of Treg function in females. Wild-type female Tregs expressed significantly lower B7-H1 versus males but were insensitive to estrogen in vitro. Female B7-H1(-/-) Tregs were exquisitely sensitive to estrogen-mediated functional reduction in vitro, suggesting that B7-H1 effects occur before terminal Treg differentiation. Immune differences were independent of known B7-H1 ligands. Sex-dependent immune differences are seldom considered in designing immune therapy or interpreting immunotherapy treatment results. Our data demonstrate that sex is an important variable in tumor immunopathogenesis and immunotherapy responses through differential Treg function and B7-H1 signaling.

Characterization of cytokine-induced myeloid-derived suppressor cells from normal human peripheral blood mononuclear cells

Tumor immune tolerance can derive from the recruitment of suppressor cell populations, including myeloid-derived suppressor cells (MDSCs). In cancer patients, increased MDSCs correlate with more aggressive disease and a poor prognosis. Expression of 15 immune factors (TGFbeta, IL-1beta, IL-4, IL-6, IL-10, GM-CSF, M-CSF, IDO, fms-related tyrosine kinase 3 ligand, c-kit ligand, inducible NO synthase, arginase-1, TNF-alpha, cyclo-oxygenase 2, vascular endothelial growth factor [VEGF]) by MDSC-inducing human solid tumor cell lines was evaluated by RT-PCR. Based upon these data, cytokine mixtures were then tested for their ability to generate suppressive CD33(+) cells from healthy donor PBMCs in vitro by measuring their ability to inhibit the proliferation of, and IFN-gamma production by, fresh autologous human T cells after CD3/CD28 stimulation. Induced MDSCs were characterized with respect to their morphology, surface phenotype, and gene expression profile. MDSC-inducing cancer cell lines demonstrated multiple pathways for MDSC generation, including overexpression of IL-6, IL-1beta, cyclo-oxygenase 2, M-CSF, and IDO. CD33(+) cells with potent suppressive capacity were best generated in vitro by GM-CSF and IL-6, and secondarily by GM-CSF + IL-1beta, PGE(2), TNF-alpha, or VEGF. Characterization studies of cytokine-induced suppressive cells revealed CD33(+)CD11b(+)CD66b(+)HLA-DR(low)IL-13R alpha2(int) large mononuclear cells with abundant basophilic cytoplasm. Expression of inducible NO synthase, TGFbeta, NADPH oxidase, VEGF, and/or arginase-1 was also upregulated, and Transwell studies showed suppression of autologous T cells to be contact dependent. Suppressive CD33(+) cells generated from PBMCs by GM-CSF and IL-6 were consistent with human MDSCs. This study suggests that these cytokines are potential therapeutic targets for the inhibition of MDSC induction in cancer patients.

Trends in cancer immunotherapy

Modulation of the immune system for therapeutic ends has a long history, stretching back to Edward Jenner's use of cowpox to induce immunity to smallpox in 1796. Since then, immunotherapy, in the form of prophylactic and therapeutic vaccines, has enabled doctors to treat and prevent a variety of infectious diseases, including cholera, poliomyelitis, diphtheria, measles and mumps. Immunotherapy is now increasingly being applied to oncology. Cancer immunotherapy attempts to harness the power and specificity of the immune system for the treatment of malignancy. Although cancer cells are less immunogenic than pathogens, the immune system is capable of recognizing and eliminating tumor cells. However, tumors frequently interfere with the development and function of immune responses. Thus, the challenge for cancer immunotherapy is to apply advances in cellular and molecular immunology and develop strategies that effectively and safely augment antitumor responses.