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

DNA methylation changes and inflammaging in aging-associated diseases

Aging as an inevitable phenomenon is associated with pervasive changes in physiological functions. There is a relationship between aging and the increase of several chronic diseases. Most age-related disorders are accompanied by an underlying chronic inflammatory state, as demonstrated by local infiltration of inflammatory cells and greater levels of proinflammatory cytokines in the bloodstream. Within inflammaging, many epigenetic events, especially DNA methylation, change. During the aging process, due to aberrations of DNA methylation, biological processes are disrupted, leading to the emergence or progression of a variety of human diseases, including cancer, neurodegenerative disorders, cardiovascular disease and diabetes. The focus of this review is on DNA methylation, which is involved in inflammaging-related activities, and how its dysregulation leads to human disorders.

The Nitrogen Mustards

The nitrogen mustards are powerful cytotoxic and lymphoablative agents and have been used for more than 60 years. They are employed in the treatment of cancers, sarcomas, and hematologic malignancies. Cyclophosphamide, the most versatile of the nitrogen mustards, also has a place in stem cell transplantation and the therapy of autoimmune diseases. Adverse effects caused by the nitrogen mustards on the central nervous system, kidney, heart, bladder, and gonads remain important issues. Advances in analytical techniques have facilitated the investigation of the pharmacokinetics of the nitrogen mustards, especially the oxazaphosphorines, which are prodrugs requiring metabolic activation. Enzymes involved in the metabolism of cyclophosphamide and ifosfamide are very polymorphic, but a greater understanding of the pharmacogenomic influences on their activity has not yet translated into a personalized medicine approach. In addition to damaging DNA, the nitrogen mustards can act through other mechanisms, such as antiangiogenesis and immunomodulation. The immunomodulatory properties of cyclophosphamide are an area of current exploration. In particular, cyclophosphamide decreases the number and activity of regulatory T cells, and the interaction between cyclophosphamide and the intestinal microbiome is now recognized as an important factor. New derivatives of the nitrogen mustards continue to be assessed. Oxazaphosphorine analogs have been synthesized in attempts to both improve efficacy and reduce toxicity, with varying degrees of success. Combinations of the nitrogen mustards with monoclonal antibodies and small-molecule targeted agents are being evaluated. SIGNIFICANCE STATEMENT: The nitrogen mustards are important, well-established therapeutic agents that are used to treat a variety of diseases. Their role is continuing to evolve.

IFNα Augments Clinical Efficacy of Regulatory T-cell Depletion with Denileukin Diftitox in Ovarian Cancer

PURPOSE

Immunotherapy treats some cancers, but not ovarian cancer. Regulatory T cells (Tregs) impede anti-ovarian cancer immunity but effective human Treg-directed treatments are lacking. We tested Treg depletion with denileukin diftitox (DD) ± IFNα as ovarian cancer immunotherapy.

PATIENTS AND METHODS

Mice with syngeneic ID8 ovarian cancer challenge were treated with DD, IFNα, or both. The phase 0/I trial tested one dose-escalated DD infusion for functional Treg reduction, safety, and tolerability. The phase II trial added IFNα2a to DD if DD alone failed clinically.

RESULTS

DD depleted Tregs, and improved antitumor immunity and survival in mice. IFNα significantly improved antitumor immunity and survival with DD. IFNα did not alter Treg numbers or function but boosted tumor-specific immunity and reduced tumor Treg function with DD by inducing dendritic cell IL6. DD alone was well tolerated, depleted functional blood Tregs and improved immunity in patients with various malignancies in phase 0/I. A patient with ovarian cancer in phase 0/I experienced partial clinical response prompting a phase II ovarian cancer trial, but DD alone failed phase II. Another phase II trial added pegylated IFNα2a to failed DD, producing immunologic and clinical benefit in two of two patients before a DD shortage halt. DD alone was well tolerated. Adding IFNα increased toxicities but was tolerable, and reduced human Treg numbers in blood, and function through dendritic cell-induced IL6 in vitro.

CONCLUSIONS

Treg depletion is clinically useful but unlikely alone to cure ovarian cancer. Rational treatment agent combinations can salvage clinical failure of Treg depletion alone, even when neither single agent provides meaningful clinical benefit.

Comprehensive analysis of current approaches to inhibit regulatory T cells in cancer

CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Treg) have emerged as a dominant T cell population inhibiting anti-tumor effector T cells. Initial strategies used for Treg-depletion (cyclophosphamide, anti-CD25 mAb…) also targeted activated T cells, as they share many phenotypic markers. Current, ameliorated approaches to inhibit Treg aim to either block their function or their migration to lymph nodes and the tumor microenvironment. Various drugs originally developed for other therapeutic indications (anti-angiogenic molecules, tyrosine kinase inhibitors,etc) have recently been discovered to inhibit Treg. These approaches are expected to be rapidly translated to clinical applications for therapeutic use in combination with immunomodulators.

Trial watch: Chemotherapy with immunogenic cell death inducers

The long-established notion that apoptosis would be immunologically silent, and hence it would go unnoticed by the immune system, if not tolerogenic, and hence it would actively suppress immune responses, has recently been revisited. In some instances, indeed, cancer cells undergo apoptosis while emitting a spatiotemporally-defined combination of signals that renders them capable of eliciting a long-term protective antitumor immune response. Importantly, only a few anticancer agents can stimulate such an immunogenic cell death. These include cyclophosphamide, doxorubicin and oxaliplatin, which are currently approved by FDA for the treatment of multiple hematologic and solid malignancies, as well as mitoxantrone, which is being used in cancer therapy and against multiple sclerosis. In this Trial Watch, we will review and discuss the progress of recent (initiated after January 2008) clinical trials evaluating the off-label use of cyclophosphamide, doxorubicin, oxaliplatin and mitoxantrone.

MicroRNA-21-Enriched Exosomes as Epigenetic Regulators in Melanomagenesis and Melanoma Progression: The Impact of Western Lifestyle Factors

DNA mutation-induced activation of RAS-BRAF-MEK-ERK signaling associated with intermittent or chronic ultraviolet (UV) irradiation cannot exclusively explain the excessive increase of malignant melanoma (MM) incidence since the 1950s. Malignant conversion of a melanocyte to an MM cell and metastatic MM is associated with a steady increase in microRNA-21 (miR-21). At the epigenetic level, miR-21 inhibits key tumor suppressors of the RAS-BRAF signaling pathway enhancing proliferation and MM progression. Increased MM cell levels of miR-21 either result from endogenous upregulation of melanocytic miR-21 expression or by uptake of miR-21-enriched exogenous exosomes. Based on epidemiological data and translational evidence, this review provides deeper insights into environmentally and metabolically induced exosomal miR-21 trafficking beyond UV-irradiation in melanomagenesis and MM progression. Sources of miR-21-enriched exosomes include UV-irradiated keratinocytes, adipocyte-derived exosomes in obesity, airway epithelium-derived exosomes generated by smoking and pollution, diet-related exosomes and inflammation-induced exosomes, which may synergistically increase the exosomal miR-21 burden of the melanocyte, the transformed MM cell and its tumor environment. Several therapeutic agents that suppress MM cell growth and proliferation attenuate miR-21 expression. These include miR-21 antagonists, metformin, kinase inhibitors, beta-blockers, vitamin D, and plant-derived bioactive compounds, which may represent new options for the prevention and treatment of MM.

A unique thymus-derived regulatory T cell subset associated with systemic lupus erythematosus

Background

Foxp3 is a marker for regulatory T cells (Treg cells), but recent studies have shown the plasticity and heterogeneity of CD4⁺Foxp3⁺ T cells. This study aimed to examine the phenotype and function of circulating CD4⁺Foxp3⁺ T cells in patients with systemic lupus erythematosus (SLE).

Methods

We enrolled 47 patients with SLE, 31 with organ-specific autoimmune diseases (15 with multiple sclerosis and 16 with primary immune thrombocytopenia), and 19 healthy subjects. Peripheral blood mononuclear cells were used to evaluate the proportion and phenotype of CD4⁺Foxp3⁺ cells using multicolor flow cytometry, the status of the Treg-specific demethylated region (TSDR) of the foxp3 gene by methylation-specific polymerase chain reaction, and the immunoregulatory function of CD4⁺CD25⁺ cells by allogeneic mixed lymphocyte reaction. Immunohistochemistry of renal biopsy specimens obtained from 6 patients with lupus nephritis and 5 with IgA nephropathy was conducted to detect IL-17A-expressing CD4⁺Foxp3⁺ cells.

Results

CD4⁺Foxp3⁺ T cells were increased in SLE patients compared with organ-specific autoimmune disease controls or healthy controls. Circulating CD4⁺Foxp3⁺ T cells were correlated with the disease activity of SLE. The increased CD4⁺Foxp3⁺ T cells in active SLE patients were mainly derived from thymus-derived Treg (tTreg) cells, as determined by a demethylated TSDR status, and represented a unique phenotype, upregulated expression of CD49d, CD161, and IL-17A, with immunosuppressive ability comparable to that of healthy controls. Finally, CD4⁺Foxp3⁺IL-17A⁺ cells were infiltrated into the renal biopsy specimens of patients with active lupus nephritis.

Conclusions

A unique tTreg subset with dichotomic immunoregulatory and T helper 17 phenotypes is increased in the circulation of SLE patients and may be involved in the pathogenic process of SLE.

T-Regulatory Cells In Tumor Progression And Therapy

Regulatory T cells (Tregs) are important members of the immune system regulating the host responses to infection and neoplasms. Tregs prevent autoimmune disorders by protecting the host-cells from an immune response, related to the peripheral tolerance. However, tumor cells use Tregs as a shield to protect themselves against anti-tumor immune response. Thus, Tregs are a hurdle in achieving the complete potential of anti-cancer therapies including immunotherapy. This has prompted the development of novel adjuvant therapies that obviate their negative effects thereby enhancing the therapeutic efficacy. Our earlier studies have shown the efficacy of the glycolytic inhibitor, 2-deoxy-D-glucose (2-DG) by reducing the induced Tregs pool and enhance immune stimulation as well as local tumor control. These findings have suggested its potential for enhancing the efficacy of immunotherapy, besides radiotherapy and chemotherapy. This review provides a brief account of the current status of Tregs as a component of the immune-biology of tumors and various preclinical and clinical strategies pursued to obviate the limitations imposed by them in achieving therapeutic efficacy.

Tumor infiltrating lymphocytes in malignant melanoma - allies or foes?

This is an overview of current problematics regarding the role of tumor infiltrating lymphocytes (TILs) in malignant melanomas. Various and often conflicting data have been published, correlating tumor type, stage, prognosis, as well as sex and age of patients. This is partly due to heterogeneity in scaling systems and unstandardized TILs grading but also due to changes of tumor-host interactions. Melanomas are an immunologically heterogeneous group with variability of TILs, where distinct gene expression patterns were found in tumors with absent, and/or non- brisk TIL grade versus brisk TIL grade. However, the presence of TILs alone appears to be inadequate for implicating them as immunologically functional. Further characterisation of TIL phenotype and function is warranted. This especially concerns, evaluation of TILs of the suppressor phenotype but rather than as a prognostic factor, more for prediction of targeted immunotherapy.

Tbet-positive regulatory T cells accumulate in oropharyngeal cancers with ongoing tumor-specific type 1 T cell responses

Regulatory T cells (Tregs) may comprise different subsets allowing them to efficiently suppress different types of effector T cells. In this study, we show that high numbers of both conventional and Tbet co-expressing Foxp3^hi Tregs accumulate in human papilloma virus (HPV)-driven oropharyngeal squamous cell carcinoma (OPSCC). The infiltration of Tbet+ Foxp3+ Tregs was strongly correlated with a concomitant tumor-specific and conventional type 1-oriented intratumoral T cell infiltrate. Both conventional CD4+CD25+CD127–Foxp3^hi Tregs and their Tbet^hi counterparts exhibited an activated phenotype, co-expressed high levels of CTLA4 and Helios and exhibited a maximally demethylated Foxp3 gene locus TSDR, indicating their full capacity to impede a type 1 effector T cell response. Interestingly, while the prognostic value of conventional Tregs was neutral, a high intratumoral frequency of Tbet+ Tregs was associated with prolonged disease-specific survival, most likely because their presence reflected high numbers of effector T cells. The presence of these Tbet+ Tregs may in part explain why a dense type 1-oriented immune infiltrate in OPSCC is not enough to fully control tumor growth.

Filaggrin null mutations are associated with altered circulating Tregs in atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with a complex pathogenesis. Although regulatory T cells (Tregs) have previously been studied in AD, their role remains controversial, likely owing to patient heterogeneity. Thus, we recruited adult AD patients and age‐matched healthy controls, and assessed their filaggrin (FLG) genotype, serum IgE level, and eczema area and severity index (EASI). We found increased proportions of all circulating Treg subpopulations in AD patients. Moreover, we show positive correlations between circulating Tregs and serum IgE FLG null mutations limited the expansion of both memory and effector Tregs and enhanced that of recently thymus‐emigrated Tregs. Furthermore, proportions of circulating Th2‐ or Th17‐Tregs but not Th1‐Tregs were increased in AD patients, and accentuated by FLG null mutations, thereby mimicking the immune deviation observed in Th cell populations. Moreover, ICOS⁺ Tregs showed reduced production of interleukin‐10, suggesting impaired immunosuppression in AD. The level of demethylation of FOXP3i1, which reflects the stability of FOXP3 expression, was similar in the blood and skin of AD patients and healthy controls. Overall, these results show that Tregs may participate into AD pathogenesis and that FLG null mutations exert further modifications on specific subpopulations of circulating Tregs.

Ontogeny of Tumor-associated CD4+CD25+Foxp3+ T-regulatory Cells

The critical contribution of CD4+CD25+Foxp3+ T-regulatory cells (Treg) to immune suppression in the tumor microenvironment is well-established. Whereas the mechanisms that drive the generation and accumulation of Treg in tumors have been an active area of study, the information on their origin and population dynamics remains limited. In this review, we discuss the ontogeny of tumor-associated Treg in light of the recently identified lineage markers.

Phase II Study of Autologous Monocyte-Derived mRNA Electroporated Dendritic Cells (TriMixDC-MEL) Plus Ipilimumab in Patients With Pretreated Advanced Melanoma

Purpose

Autologous monocyte-derived dendritic cells (DCs) electroporated with synthetic mRNA (TriMixDC-MEL) are immunogenic and have antitumor activity as a monotherapy in patients with pretreated advanced melanoma. Ipilimumab, an immunoglobulin G1 monoclonal antibody directed against the cytotoxic T-lymphocyte-associated protein 4 receptor that counteracts physiologic suppression of T-cell function, improves the overall survival of patients with advanced melanoma. This phase II study investigated the combination of TriMixDC-MEL and ipilimumab in patients with pretreated advanced melanoma.

Patients and Methods

Thirty-nine patients were treated with TriMixDC-MEL (4 × 106 cells administered intradermally and 20 × 106 cells administered intravenously) plus ipilimumab (10 mg/kg every 3 weeks for a total of four administrations, followed by maintenance therapy every 12 weeks in patients who remained progression free). Six-month disease control rate according to the immune-related response criteria served as the primary end point.

Results

The 6-month disease control rate was 51% (95% CI, 36% to 67%), and the overall tumor response rate was 38% (including eight complete and seven partial responses). Seven complete responses and one partial tumor response are ongoing after a median follow-up time of 36 months (range, 22 to 43 months). The most common treatment-related adverse events (all grades) consisted of local DC injection site skin reactions (100%), transient post–DC infusion chills (38%) and flu-like symptoms (84%), dermatitis (64%), hepatitis (13%), hypophysitis (15%), and diarrhea/colitis (15%). Grade 3 or 4 immune-related adverse events occurred in 36% of patients. There was no grade 5 adverse event.

Conclusion

The combination of TriMixDC-MEL and ipilimumab is tolerable and results in an encouraging rate of highly durable tumor responses in patients with pretreated advanced melanoma.

Combination of nanoparticle-based therapeutic vaccination and transient ablation of regulatory T cells enhances anti-viral immunity during chronic retroviral infection

Background

Regulatory T cells (Tregs) have been shown to limit anti-viral immunity during chronic retroviral infection and to restrict vaccine-induced T cell responses. The objective of the study was to assess whether a combinational therapy of nanoparticle-based therapeutic vaccination and concomitant transient ablation of Tregs augments anti-viral immunity and improves virus control in chronically retrovirus-infected mice. Therefore, chronically Friend retrovirus (FV)-infected mice were immunized with calcium phosphate (CaP) nanoparticles functionalized with TLR9 ligand CpG and CD8⁺ or CD4⁺ T cell epitope peptides (GagL_85–93 or Env gp70_123–141) of FV. In addition, Tregs were ablated during the immunization process. Reactivation of CD4⁺ and CD8⁺ effector T cells was analysed and the viral loads were determined.

Results

Therapeutic vaccination of chronically FV-infected mice with functionalized CaP nanoparticles transiently reactivated cytotoxic CD8⁺ T cells and significantly reduced the viral loads. Transient ablation of Tregs during nanoparticle-based therapeutic vaccination strongly enhanced anti-viral immunity and further decreased viral burden.

Conclusion

Our data illustrate a crucial role for CD4⁺ Foxp3⁺ Tregs in the suppression of anti-viral T cell responses during therapeutic vaccination against chronic retroviral infection. Thus, the combination of transient Treg ablation and therapeutic nanoparticle-based vaccination confers robust and sustained anti-viral immunity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-016-0258-9) contains supplementary material, which is available to authorized users.

Comparative Analysis of Protocols to Induce Human CD4+Foxp3+ Regulatory T Cells by Combinations of IL-2, TGF-beta, Retinoic Acid, Rapamycin and Butyrate

Regulatory T cells (Tregs) suppress other immune cells and are critical mediators of peripheral tolerance. Therapeutic manipulation of Tregs is subject to numerous clinical investigations including trials for adoptive Treg transfer. Since the number of naturally occurring Tregs (nTregs) is minute, it is highly desirable to develop a complementary approach of inducing Tregs (iTregs) from naïve T cells. Mouse studies exemplify the importance of peripherally induced Tregs as well as the applicability of iTreg transfer in different disease models. Yet, procedures to generate iTregs are currently controversial, particularly for human cells. Here we therefore comprehensively compare different established and define novel protocols of human iTreg generation using TGF-β in combination with other compounds. We found that human iTregs expressed several Treg signature molecules, such as Foxp3, CTLA-4 and EOS, while exhibiting low expression of the cytokines Interferon-γ, IL-10 and IL-17. Importantly, we identified a novel combination of TGF-β, retinoic acid and rapamycin as a robust protocol to induce human iTregs with superior suppressive activity in vitro compared to currently established induction protocols. However, iTregs generated by these protocols did not stably retain Foxp3 expression and did not suppress in vivo in a humanized graft-versus-host-disease mouse model, highlighting the need for further research to attain stable, suppressive iTregs. These results advance our understanding of the conditions enabling human iTreg generation and may have important implications for the development of adoptive transfer strategies targeting autoimmune and inflammatory diseases.

Monoclonal antibodies against GARP/TGF-β1 complexes inhibit the immunosuppressive activity of human regulatory T cells in vivo

Regulatory T cells (Tregs) are essential to prevent autoimmunity, but excessive Treg function contributes to cancer progression by inhibiting antitumor immune responses. Tregs exert contact-dependent inhibition of immune cells through the production of active transforming growth factor-β1 (TGF-β1). On the Treg cell surface, TGF-β1 is in an inactive form bound to membrane protein GARP and then activated by an unknown mechanism. We demonstrate that GARP is involved in this activation mechanism. Two anti-GARP monoclonal antibodies were generated that block the production of active TGF-β1 by human Tregs. These antibodies recognize a conformational epitope that requires amino acids GARP137-139 within GARP/TGF-β1 complexes. A variety of antibodies recognizing other GARP epitopes did not block active TGF-β1 production by Tregs. In a model of xenogeneic graft-versus-host disease in NSG mice, the blocking antibodies inhibited the immunosuppressive activity of human Tregs. These antibodies may serve as therapeutic tools to boost immune responses to infection or cancer via a mechanism of action distinct from that of currently available immunomodulatory antibodies. Used alone or in combination with tumor vaccines or antibodies targeting the CTLA4 or PD1/PD-L1 pathways, blocking anti-GARP antibodies may improve the efficiency of cancer immunotherapy.

FOXP3+ Tregs: heterogeneous phenotypes and conflicting impacts on survival outcomes in patients with colorectal cancer

The tumor microenvironment composites a mixture of immune lymphoid cells, myeloid cells, stromal cells with complex cytokines, as well as numerous lymphovascular vessels. Colorectal cancer (CRC) is a common malignancy and one of the leading causes of tumor-related death in the United States and worldwide. The immune status in the tumor microenvironment contributes to the survival of a patient with CRC. Regulatory T cells (Tregs) are considered a key factor in immune escape and immunotherapy failure among cancer patients. The transcription factor forkhead box P3 (FOXP3) is a crucial intracellular marker and also a key developmental and functional factor for CD4+CD25+ Tregs. Tregs are correlated with survival in various human neoplasms, and elevated proportions of Tregs are usually associated with unfavorable clinical outcomes. However, the role of Tregs in CRC remains controversial. High densities of tumor-infiltrating Tregs in CRC patients are reported to be correlated with worse or better outcomes. And Tregs may not be predictive of prognosis after resection of the primary tumor. The exact explanations for these discordant results remain unclear. The heterogeneous instincts of cell phenotype, gene expression, and functional activities of Tregs may partly contribute this contrasting result. Furthermore, the lack of a robust marker for identifying Tregs or due to the different techniques applied is also account. The Treg-specific demethylated region (TSDR) was recently reported to be a specific epigenetic marker for natural Tregs (nTregs), which can stably express FOXP3. The FOXP3-TSDR demethylation assay may be an promising technique for CRC-related nTregs studies.

Lysosomal-associated Transmembrane Protein 4B (LAPTM4B) Decreases Transforming Growth Factor β1 (TGF-β1) Production in Human Regulatory T Cells

Production of active TGF-β1 is one mechanism by which human regulatory T cells (Tregs) suppress immune responses. This production is regulated by glycoprotein A repetitions predominant (GARP), a transmembrane protein present on stimulated Tregs but not on other T lymphocytes (Th and CTLs). GARP forms disulfide bonds with proTGF-β1, favors its cleavage into latent inactive TGF-β1, induces the secretion and surface presentation of GARP·latent TGF-β1 complexes, and is required for activation of the cytokine in Tregs. We explored whether additional Treg-specific protein(s) associated with GARP·TGF-β1 complexes regulate TGF-β1 production in Tregs. We searched for such proteins by yeast two-hybrid assay, using GARP as a bait to screen a human Treg cDNA library. We identified lysosomal-associated transmembrane protein 4B (LAPTM4B), which interacts with GARP in mammalian cells and is expressed at higher levels in Tregs than in Th cells. LAPTM4B decreases cleavage of proTGF-β1, secretion of soluble latent TGF-β1, and surface presentation of GARP·TGF-β1 complexes by Tregs but does not contribute to TGF-β1 activation. Therefore, LAPTM4B binds to GARP and is a negative regulator of TGF-β1 production in human Tregs. It may play a role in the control of immune responses by decreasing Treg immunosuppression.

Brain Tumor Immunotherapy: What have We Learned so Far?

High grade glioma is a rare brain cancer, incurable in spite of modern neurosurgery, radiotherapy, and chemotherapy. Novel approaches are in research, and immunotherapy emerges as a promising strategy. Clinical experiences with active specific immunotherapy demonstrate feasibility, safety and most importantly, but incompletely understood, prolonged long-term survival in a fraction of the patients. In relapsed patients, we developed an immunotherapy schedule and we categorized patients into clinically defined risk profiles. We learned how to combine immunotherapy with standard multimodal treatment strategies for newly diagnosed glioblastoma multiforme patients. The developmental program allows further improvements related to newest scientific insights. Finally, we developed a mode of care within academic centers to organize cell-based therapies for experimental clinical trials in a large number of patients.

Tissue resident regulatory T cells: novel therapeutic targets for human disease

Over the past decade, the ability of regulatory T cells (Tregs) to suppress multiple types of immune cells has received tremendous attention. Mounting evidence has revealed that tissue resident Tregs control non-immunological processes of their target tissues and contribute to a plethora of human diseases. The identification of novel tissue-specific Tregs has highlighted their heterogeneity and complexity. This review summarizes the recent findings for visceral adipose tissue CD4+Foxp3+ regulatory T cells (VAT Tregs), muscle Tregs, bone Tregs and skin memory Tregs, with a focus on their unique functions in local tissues. This interpretation of the roles of tissue-specific Tregs and of their involvement in disease progression provides new insight into the discovery of potential therapeutic targets of human diseases.

A phase I clinical trial combining dendritic cell vaccination with adoptive T cell transfer in patients with stage IV melanoma

Adoptive transfer of in vitro-expanded tumor-infiltrating lymphocytes (TIL) has shown great clinical benefit in patients with malignant melanoma. TIL therapy itself has little side effects, but conditioning chemo- or radiotherapy and postinfusion interleukin 2 (IL-2) injections are associated with severe adverse advents. We reasoned that combining TIL infusion with dendritic cell (DC) vaccination could circumvent the need for conditioning and IL-2 support and thus represent a milder treatment approach. Eight patients with stage IV melanoma were enrolled in the MAT01 study, consisting of vaccination with autologous tumor-lysate-loaded DC, followed by TIL infusion. Six of eight patients were treated according to protocol, while one patient received only TIL and one only DC. Treatments were well tolerated with a single grade 3 adverse event. The small study size precludes analysis of clinical responses, though interestingly one patient showed a complete remission and two had stable disease. Analysis of the infusion products revealed that mature DC were generated in all cases. TIL after expansion were CD3+ T cells, dominated by effector memory CD8+ cytotoxic T cells. Analysis of the T cell receptor repertoire revealed presence of highly dominant clones in most infusion products, and many of these could be detected in the circulation for weeks after T cell transfer. Here, we report the first combination of DC vaccination and TIL infusion in malignant melanoma. This combined treatment was safe and feasible, though after evaluating both clinical and immunological parameters, we expect that administration of lymphodepleting chemotherapy and IL-2 will likely increase treatment efficacy.

Selective inhibition of regulatory T cells by targeting the PI3K-Akt pathway

Despite the strides that immunotherapy has made in mediating tumor regression, the clinical effects are often transient, and therefore more durable responses are still needed. The temporary nature of the therapy-induced immune response can be attributed to tumor immune evasion mechanisms, mainly the effect of suppressive immune cells and, in particular, regulatory T cells (Treg). Although the depletion of Tregs has been shown to be effective in enhancing immune responses, selective depletion of these suppressive cells without affecting other immune cells has not been very successful, and new agents are sought. We found that PI3K-Akt pathway inhibitors selectively inhibit Tregs with minimal effect on conventional T cells (Tconv). Our results clearly show selective in vitro inhibition of activation (as represented by a decrease in downstream signaling) and proliferation of Tregs in comparison with Tconvs when treated with different Akt and PI3K inhibitors. This effect has been observed in both human and murine CD4 T cells. In vivo treatment with these inhibitors resulted in a significant and selective reduction in Tregs in both naïve and tumor-bearing mice. Furthermore, these PI3K-Akt inhibitors led to a significant therapeutic antitumor effect, which was shown to be Treg dependent. Here, we report the use of PI3K-Akt pathway inhibitors as potent agents for the selective depletion of suppressive Tregs. We show that these inhibitors are able to enhance the antitumor immune response and are therefore promising clinical reagents for Treg depletion.

Higher FOXP3-TSDR demethylation rates in adjacent normal tissues in patients with colon cancer were associated with worse survival

BACKGROUND

The influence of natural regulatory T cells (nTregs) on the patients with colon cancer is unclear. Demethylated status of the Treg-specific demethylated region (TSDR) of the FOXP3 gene was reported to be a potential biomarker for the identification of nTregs.

METHODS

The demethylation rate of the TSDR (TSDR-DMR) was calculated by using methylation-specific quantitative polymerase chain reaction (MS-qPCR) assay. The expression of TSDR-DMR and FOXP3 mRNA was investigated in various colorectal cancer cell lines. A total of 130 colon carcinoma samples were utilized to study the DMR at tumor sites (DMRT) and adjacent normal tissue (DMRN). The correlations between DMRs and clinicopathological variables of patients with colon cancer were studied.

RESULTS

The TSDR-DMRs varied dramatically among nTregs (97.920 ± 0.466%) and iTregs (3.917 ± 0.750%). Significantly, DMRT (3.296 ± 0.213%) was higher than DMRN (1.605 ± 0.146%) (n = 130, p = 0.000). Higher DMRN levels were found in female patients (p = 0.001) and those with distant metastases (p = 0.017), and were also associated with worse recurrence-free survival in non-stage IV patients (low vs. high, p = 0.022). However, further Cox multivariate analysis revealed that the FOXP3-TSDR status does not have prognostic value.

CONCLUSION

MS-qPCR assays of FOXP3-TSDR can efficiently distinguish nTregs from non-nTregs. Abnormal recruitment of nTregs occurs in the local tumor microenvironment. Infiltration of tissue-resident nTregs may have a negative role in anti-tumor effects in patients with colon cancer; however, this role is limited and complicated.

Intralesional treatment of stage III metastatic melanoma patients with L19-IL2 results in sustained clinical and systemic immunologic responses

L19-IL2 is a recombinant protein comprising the cytokine IL2 fused to the single-chain monoclonal antibody L19. In previous studies, intralesional injection with IL2 has shown efficacy for the locoregional treatment of cutaneous/subcutaneous metastases in patients with advanced melanoma. The objectives of this study were to investigate whether (i) intralesional delivery of a targeted form of IL2 would yield similar results, with reduction of injection frequency and treatment duration; and (ii) systemic immune responses were induced by the local treatment. Patients with stage IIIB/IIIC melanoma and cutaneous/subcutaneous injectable metastases received weekly intratumoral injections of L19-IL2 at a maximum dose of 10 MIU/week for 4 consecutive weeks. Tumor response was evaluated 12 weeks after the first treatment. Twenty-four of 25 patients were evaluable for therapy-induced responses. A complete response (CR) by modified immune-related response criteria (irRC) of all treated metastases was achieved in 6 patients (25%), with long-lasting responses in most cases (5 patients for ≥24 months). Objective responses were documented in 53.9% of all index lesions [44.4% CR and 9.5% partial responses (by irRC)], and 36.5% of these remained stable, while 9.5% progressed. Toxicity was comparable with that of free IL2, and no serious adverse events were recorded. A significant temporary increase of peripheral regulatory T cells and natural killer cells, sustained increase of absolute CD4(+) lymphocytes, and decrease of myeloid-derived suppressor cells were observed upon treatment. Finally, we recorded encouraging data about the progression time to distant metastases and overall survival.

Monitoring the frequency and function of regulatory T cells and summary of the approaches currently used to inhibit regulatory T cells in cancer patients

Regulatory T cells (Treg) are a subset of T lymphocytes that in humans represent less than the 10 % of circulating CD4(+) T cells. Treg are specialized in the inhibition of the immune responses and play a crucial role in the maintenance of immunological tolerance. Several lines of evidence clearly documented the role of Treg in restraining antitumor immune responses. For this reason, antitumor immunotherapy approaches have been recently associated with drug treatments aimed at depleting Treg or blocking their functions. A summary of the currently used in vivo approaches to limit Treg expansion in cancer patients is here provided.A comprehensive phenotypic and functional monitoring of Treg is crucial for the precise assessment of the effects that these different drug treatments exert on Treg. In this chapter, we will provide guidelines for an accurate ex vivo identification of human Treg. Due to the phenotypic and functional heterogeneity, intrinsic plasticity, and the lack of a unique marker exclusively expressed by human Treg, the clear-cut identification of this T cell subset requires the expert usage of multiparametric flow cytometry analysis (FACS). In this view, a combination of phenotypic and functional assessment of Treg is mandatory. In this chapter, we will describe the most reliable methods to identify and monitor the modulation of human Treg in patients undergoing immunological or drug-based treatments. Protocols to measure ex vivo the suppressive functions of Treg are also provided.

Transcriptional control of regulatory T cells

Regulatory T cells (Tregs) constitute unique T cell lineage that plays a key role for immunological tolerance. Tregs are characterized by the expression of the forkhead box transcription factor Foxp3, which acts as a lineage-specifying factor by determining the unique suppression profile of these immune cells. Here, we summarize the recent progress in understanding how Foxp3 expression itself is epigenetically and transcriptionally controlled, how the Treg-specific signature is achieved and how unique properties of Treg subsets are defined by other transcription factors. Finally, we will discuss recent studies focusing on the molecular targeting of Tregs to utilize the specific properties of this unique cell type in therapeutic settings.

GARP is regulated by miRNAs and controls latent TGF-β1 production by human regulatory T cells

GARP is a transmembrane protein present on stimulated human regulatory T lymphocytes (Tregs), but not on other T lymphocytes (Th cells). It presents the latent form of TGF-β1 on the Treg surface. We report here that GARP favors the cleavage of the pro-TGF-β1 precursor and increases the amount of secreted latent TGF-β1. Stimulated Tregs, which naturally express GARP, and Th cells transfected with GARP secrete a previously unknown form of latent TGF-β1 that is disulfide-linked to GARP. These GARP/TGF-β1 complexes are possibly shed from the T cell surface. Secretion of GARP/TGF-β1 complexes was not observed with transfected 293 cells and may thus be restricted to the T cell lineage. We conclude that in stimulated human Tregs, GARP not only displays latent TGF-β1 at the cell surface, but also increases its secretion by forming soluble disulfide-linked complexes. Moreover, we identified six microRNAs (miRNAs) that are expressed at lower levels in Treg than in Th clones and that target a short region of the GARP 3’ UTR. In transfected Th cells, the presence of this region decreased GARP levels, cleavage of pro-TGF-β1, and secretion of latent TGF-β1.

Denileukin diftitox (ONTAK) induces a tolerogenic phenotype in dendritic cells and stimulates survival of resting Treg

ONTAK blocks DC maturation by coreceptor downmodulation and inhibition of Stat3 phosphorylation to induce a tolerogenic phenotype. ONTAK kills activated CD4 T cells but stimulates antiapoptosis in resting Treg by engagement and stimulation through CD25.

Convergences and divergences of thymus- and peripherally derived regulatory T cells in cancer

The expansion of regulatory T cells (T_reg) is a common event characterizing the vast majority of human and experimental tumors and it is now well established that T_reg represent a crucial hurdle for a successful immunotherapy. T_reg are currently classified, according to their origin, into thymus-derived T_reg (tT_reg) or peripherally induced T_reg (pT_reg) cells. Controversy exists over the prevalent mechanism accounting for T_reg expansion in tumors, since both tT_reg proliferation and de novo pT_reg differentiation may occur. Since tT_reg and pT_reg are believed as preferentially self-specific or broadly directed to non-self and tumor-specific antigens, respectively, the balance between tT_reg and pT_reg accumulation may impact on the repertoire of antigen specificities recognized by T_reg in tumors. The prevalence of tT_reg or pT_reg may also affect the outcome of immunotherapies based on tumor-antigen vaccination or T_reg depletion. The mechanisms dictating pT_reg induction or tT_reg expansion/stability are a matter of intense investigation and the most recent results depict a complex landscape. Indeed, selected T_reg subsets may display peculiar characteristics in terms of stability, suppressive function, and cytokine production, depending on microenvironmental signals. These features may be differentially distributed between pT_reg and tT_reg and may significantly affect the possibility of manipulating T_reg in cancer therapy. We propose here that innovative immunotherapeutic strategies may be directed at diverting unstable/uncommitted T_reg, mostly enriched in the pT_reg pool, into tumor-specific effectors, while preserving systemic immune tolerance ensured by self-specific tT_reg.

Immune evasion in acute myeloid leukemia: current concepts and future directions

Immune responses generated against malignant cells have the potential to inhibit tumor growth, or even eliminate transformed cells before a tumor forms. However, immune tolerance mechanisms that normally protect healthy tissues from autoimmune damage pose a formidable barrier to the development of effective anti-tumor immunity. Because malignant cells are derived from self-tissues, the majority of defined tumor antigens are either shared or aberrantly expressed self-proteins. Eliciting productive T cell responses against such proteins is challenging, as most high-affinity, self-reactive T cells are purged during thymic selection. Some T cells capable of tumor antigen recognition escape thymic deletion, but are functionally inhibited by peripheral tolerance mechanisms which limit their ability to attack a developing malignancy. Alternatively, some tumors express antigens derived from mutated self-proteins, viral proteins or self proteins expressed only during embryonic development. These antigens are recognized by the immune system as foreign and could be recognized by a relatively large number of peripheral T cells. Even in this scenario, tumors evade otherwise effective T cell responses by employing potent immunosuppressive mechanisms within their local environment. In the setting for solid malignancies, such as melanoma, a growing number of putative immune evasion mechanisms have been characterized. However, acute myeloid leukemia (AML) is a systemic disease, and the pathways it exploits to subvert the host immune response may be quite different than those of a solid tumor. Much remains unknown regarding the immune escape mechanisms promoted by AML, and whether efforts to thwart tolerance may influence the progression of this disease. Here, we review current concepts of immune evasion in AML, and speculate how potentially effective immunotherapeutic strategies might be developed to reverse immune tolerance in leukemia patients in the future.

Natural and induced T regulatory cells in cancer

CD4+Foxp3+ T regulatory (Treg) cells control many facets of immune responses ranging from autoimmune diseases, to inflammatory conditions, and cancer in an attempt to maintain immune homeostasis. Natural Treg (nTreg) cells develop in the thymus and constitute a critical arm of active mechanisms of peripheral tolerance particularly to self antigens. A growing body of knowledge now supports the existence of induced Treg (iTreg) cells which may derive from a population of conventional CD4+ T cells. The fork-head transcription factor (Foxp3) typically is expressed by natural CD4+ Treg cells, and thus serves as a marker to definitively identify these cells. On the contrary, there is less consensus on what constitutes iTreg cells as their precise definition has been somewhat elusive. This is in part due to their distinct phenotypes which are shaped by exposure to certain inflammatory or "assault" signals stemming from the underlying immune disorder. The "policing" activity of Treg cells tends to be uni-directional in several pathological conditions. On one end of the spectrum, Treg cell suppressive activity is beneficial by curtailing T cell response against self-antigens and allergens thus preventing autoimmune diseases and allergies. On the other end however, their inhibitory roles in limiting immune response against pseudo-self antigens as in tumors often culminates into negative outcomes. In this review, we focus on this latter aspect of Treg cell immunobiology by highlighting the involvement of nTreg cells in various animal models and human tumors. We further discuss iTreg cells, relationship with their natural counterpart, and potential co-operation between the two in modulating immune response against tumors. Lastly, we discuss studies focusing on these cells as targets for improving anti-tumor immunity.

Natural and induced T regulatory cells in cancer

CD4+Foxp3+ T regulatory (Treg) cells control many facets of immune responses ranging from autoimmune diseases, to inflammatory conditions, and cancer in an attempt to maintain immune homeostasis. Natural Treg (nTreg) cells develop in the thymus and constitute a critical arm of active mechanisms of peripheral tolerance particularly to self antigens. A growing body of knowledge now supports the existence of induced Treg (iTreg) cells which may derive from a population of conventional CD4+ T cells. The fork-head transcription factor (Foxp3) typically is expressed by natural CD4+ Treg cells, and thus serves as a marker to definitively identify these cells. On the contrary, there is less consensus on what constitutes iTreg cells as their precise definition has been somewhat elusive. This is in part due to their distinct phenotypes which are shaped by exposure to certain inflammatory or “assault” signals stemming from the underlying immune disorder. The “policing” activity of Treg cells tends to be uni-directional in several pathological conditions. On one end of the spectrum, Treg cell suppressive activity is beneficial by curtailing T cell response against self-antigens and allergens thus preventing autoimmune diseases and allergies. On the other end however, their inhibitory roles in limiting immune response against pseudo-self antigens as in tumors often culminates into negative outcomes. In this review, we focus on this latter aspect of Treg cell immunobiology by highlighting the involvement of nTreg cells in various animal models and human tumors. We further discuss iTreg cells, relationship with their natural counterpart, and potential co-operation between the two in modulating immune response against tumors. Lastly, we discuss studies focusing on these cells as targets for improving anti-tumor immunity.

Therapeutic opportunities for manipulating T(Reg) cells in autoimmunity and cancer

Forkhead box P3 (FOXP3)-expressing regulatory T (T(Reg)) cells have a pivotal role in the regulation of immune responses and in the maintenance of immunological self-tolerance. These cells have emerged as attractive targets for strategies that allow the steering of immune responses in desired directions - arming the immune system to destroy infected cells and cancer cells or downregulating it to limit tissue destruction in autoimmunity. Efforts to understand the generation, activation and function of T(Reg) cells should permit the development of therapeutics for reprogramming the immune system. In this Review, we discuss insights into the generation of T(Reg) cells, their involvement in disease and the molecular basis of the dominant tolerance exerted by FOXP3(+) T(Reg) cells that could permit their safe and specific manipulation in humans.

Methylation of FOXP3 in regulatory T cells is related to the severity of coronary artery disease

OBJECTIVES

Regulatory T (Treg) cells have been shown to play a protective role in experimental atherosclerosis. However, it is unclear whether Tregs can protect from rupture of vulnerable plaque in patients with atherosclerosis. Demethylation of the DNA encoding the transcription factor forkhead box P3 (FOXP3) was found to be essential for the stable maintenance of the suppressive properties of Tregs. We aimed to evaluate Treg levels in patients with acute coronary syndrome (ACS) using a method based on Treg-specific DNA demethylation within the FOXP3 gene.

METHODS AND RESULTS

Peripheral blood was collected to determine Treg levels by PCR-based DNA methylation analysis. We found that Treg levels were decreased in patients with ACS compared with normal coronary controls. The decrease in Tregs was associated with the severity of the ACS. Furthermore, up-regulation of DNA-methyltransferases was detected in CD4(+)CD25(+) Tregs obtained from ACS patients as compared to those from normal coronary controls. A dose-dependent increase in the methylation of the Treg-specific demethylated region in FOXP3 was observed in cultures of PBMCs with ox-LDL. Moreover, the ox-LDL-induced Treg effects could be restored by loading (-)-epigallocatechin-3-gallate, a methyltransferase inhibitor. Treatment of CD4(+)CD25(+) Tregs with ox-LDL resulted in a 41% increase in the methylation of FOXP3, a 66% of reduction in FOXP3 mRNA expression, and an increase in the expression of DNA methyltransferase 3a as well as 3b.

CONCLUSIONS

Our data demonstrate that reduction in Treg cells is associated with ACS in atherosclerotic patients. Epigenetic suppression of FOXP3 might lead to down-regulation of Treg cells, and in turn increase the risk of ACS.

Low-dose temozolomide before dendritic-cell vaccination reduces (specifically) CD4+CD25++Foxp3+ regulatory T-cells in advanced melanoma patients

BACKGROUND

In cancer immunotherapy, dendritic cells (DCs) play a fundamental role in the dialog between innate and adaptive immune response, but several immunosuppressive mechanisms remain to be overcome. For example, a high number of CD4+CD25++Foxp3+ regulatory T-cells (Foxp3+Tregs) have been observed in the peripheral blood and tumor microenvironment of cancer patients. On the basis of this, we conducted a study on DC-based vaccination in advanced melanoma, adding low-dose temozolomide to obtain lymphodepletion.

METHODS

Twenty-one patients were entered onto our vaccination protocol using autologous DCs pulsed with autologous tumor lysate and keyhole limpet hemocyanin. Patients received low-dose temozolomide before vaccination and 5 days of low-dose interleukin-2 (IL-2) after vaccination. Circulating Foxp3+Tregs were evaluated before and after temozolomide, and after IL-2.

RESULTS

Among the 17 evaluable patients we observed 1 partial response (PR), 6 stable disease (SD) and 10 progressive disease (PD). The disease control rate (PR+SD = DCR) was 41% and median overall survival was 10 months. Temozolomide reduced circulating Foxp3+Treg cells in all patients. A statistically significant reduction of 60% was observed in Foxp3+Tregs after the first cycle, whereas the absolute lymphocyte count decreased by only 14%. Conversely, IL-2 increased Foxp3+Treg cell count by 75.4%. Of note the effect of this cytokine, albeit not statistically significant, on the DCR subgroup led to a further 33.8% reduction in Foxp3+Treg cells.

CONCLUSIONS

Our results suggest that the combined immunological therapy, at least as far as the DCR subgroup is concerned, effectively reduced the number of Foxp3+Treg cells, which exerted a blunting effect on the growth-stimulating effect of IL-2. However, this regimen, with its current modality, would not seem to be capable of improving clinical outcome.

Revisiting immune-based therapies for aggressive follicular cell-derived thyroid cancers

BACKGROUND

With our growing understanding of the immune system and mechanisms employed by tumors to evade destruction, the field of cancer immunotherapy has been revitalized. Concurrent inflammation has long been associated with follicular cell-derived thyroid cancer (FDTC). In the last decade, much research has focused on characterizing the tumor-associated immune response in patients with FDTC.

SUMMARY

Mast cells, natural killer cells, macrophages, dendritic cells, B cells, and T cells have been identified within FDTC-associated immune infiltrate. Collectively, these findings suggest that the immune response to FDTC is compromised and may even promote tumor progression. A more thorough characterization of the tumor-associated immune response in FDTC may lead to the development of immune-based adjuvant therapies for patients with aggressive disease.

CONCLUSIONS

Immune-based therapies could provide essential alternatives to patients that cannot be treated surgically, those with recurrent or persistent lymph node metastases, and those with anaplastic thyroid cancer.

Effects of cyclophosphamide and IL-2 on regulatory CD4+ T cell frequency and function in melanoma patients vaccinated with HLA-class I peptides: impact on the antigen-specific T cell response

The frequency and function of regulatory T cells (Tregs) were studied in stage II–III melanoma patients who were enrolled in a phase II randomized trial of vaccination with HLA-A*0201-modified tumor peptides versus observation. The vaccinated patients received low-dose cyclophosphamide (CTX) and low-dose interleukin-2 (IL-2). Tregs were analyzed in the lymph nodes (LNs) of stage III patients who were undergoing complete lymph node dissection and in peripheral blood mononuclear cells (PBMCs) collected before vaccination and at different time points during the vaccination period. The LNs of the vaccinated patients, which were surgically removed after two rounds of vaccination and one dose of CTX, displayed a low frequency of Tregs and a less immunosuppressive environment compared with those of the untreated patients. The accurate time-course analysis of the PBMCs of patients enrolled in the vaccination arm indicated a limited and transient modulation in the frequencies of Tregs in PBMCs collected after low-dose CTX administration and a strong Treg boost in those PBMCs collected after low-dose IL-2 administration. However, a fraction of the IL-2-boosted Tregs was functionally modulated to a Th-1-like phenotype in the vaccinated patients. Moreover, low-dose IL-2 promoted the concomitant expansion of conventional activated CD4⁺ T cells. Despite the amplification of Tregs, IL-2 administration maintained or further increased the number of antigen-specific CD8⁺ T cells that were induced by vaccination as demonstrated by the ex vivo human leukocyte antigen-multimer staining and IFN-γ ELISpot assays. Our study suggests that the use of CTX as a Treg modulator should be revised in terms of the administration schedule and of patients who may benefit from this drug treatment. Despite the Treg expansion that was observed in this study, low-dose IL-2 is not detrimental to the functional activities of vaccine-primed CD8⁺ T cell effectors when used in the inflammatory environment of vaccination.

The role of E3 ubiquitin ligase Cbl proteins in interleukin-2-induced Jurkat T-cell activation

Interleukin- (IL-) 2 is the major growth factor for T-cell activation and proliferation. IL-2 has multiple functions in the regulation of immunological processes. Although most studies focus on T-cell immunomodulation, T-cell activation by IL-2 is the foundation of priming the feedback loop. Here, we investigated the effect of MAPK/ERK and PI3K/Akt signaling pathways on IL-2-induced cell activation and the regulatory mechanisms of upstream ubiquitin ligase Cbl-b and c-Cbl. Morphological analysis of Jurkat T cells was performed by cytospin preparations with Wright-Giemsa stain. CD25 expression on Jurkat T cells was determined by flow cytometry. Changes in cell activation proteins such as p-ERK, ERK, p-Akt, Akt, and ubiquitin ligase Casitas B-cell Lymphoma (Cbl) proteins were analyzed by western blot. Following IL-2-induced activation of Jurkat T cells, p-ERK expression was upregulated, while there was no change in p-Akt, ERK, or Akt expression. Thus, the MAPK/ERK signaling pathway, but not PI3K/Akt, was involved in IL-2-induced T-cell activation. Either using PD98059 (a specific inhibitor for p-ERK) or depletion of ERK with small interfering RNA (siRNA) reduced the expression of CD25. This study also showed that ubiquitin ligase proteins Cbl-b and c-Cbl might be involved in IL-2-induced Jurkat T-cell activation by negatively regulating the MAPK/ERK signaling pathway.

Influence of pharmacological immunomodulatory agents on CD4(+)CD25(high)FoxP3(+) T regulatory cells in humans

T regulatory cells (Tregs) play a critical role in the immunologic tolerance to the graft in transplantation. Thus, due to their immunosuppressive capability, ex vivo expanded Tregs may be used as a cellular therapy and an attractive novel strategy to control chronic rejection and eliminate need for lifelong pharmacological immunosuppression. Since Treg therapy is still in its infancy, initially Tregs still need to be applied in combination with pharmacological agents to prevent rejection. Fortunately, some of the medications have been shown to enhance the function and number of Tregs. In the clinic, different immunosuppressive regimens are used for individual patients for different types of organ transplantation. In this review, we present the most commonly used pharmacological agents for immunosuppression and discuss how they affect the Treg population. It is extremely difficult to dissect the effect of single agent on Tregs population in clinical settings since usually the combination of several medications is applied at the same time for graft protection. Nevertheless, experimental and clinical data indicate that thymoglobulin as immunosuppressive induction and mTOR inhibitors as immunosuppressive maintenance agents have the most beneficial effect on Treg population in the blood. Among supplemental agents promoting Tregs, anti-TNFα preparations have been in clinical use (in autoimmune diseases) for many years, so they are optimal candidates for testing in transplant settings in combination with Treg based cellular therapy.

Depletion of Tregs in vivo: a promising approach to enhance antitumor immunity without autoimmunity

Evaluation of: Rech AJ, Mick R, Martin S et al. CD25 blockade depletes and selectively reprograms regulatory T cells in concert with immunotherapy in cancer patents. Sci. Transl. Med. 4(134), 134ra62 (2012). Tregs are involved in the maintenance of immunological self-tolerance. Recent studies have revealed that Tregs suppress antitumor immunity and that they are major obstacles for cancer immunotherapy. Various approaches have been carried out to cancel immunological suppression by Tregs in clinical settings; however, side effects such as autoimmunity occurred and expected antitumor effects were not achieved. In a recent study, Rech et al. evaluated daclizumab, a US FDA-approved humanized anti-CD25 antibody, for regulation of Treg cells in a peptide vaccination trial of breast cancer patients. Daclizumab caused long-lasting depletion of CD25+ Tregs, reprogramming of CD25+ Tregs, and enhancement of antipeptide immune response. Of note, major autoimmune responses were not observed in daclizumab-treated patients. This study provides a possible safe and promising approach to regulate Tregs in cancer vaccine therapy.

Induced and natural regulatory T cells in human cancer

INTRODUCTION

Evidence suggests that FOXP3(+)CD25(high)CD4(+) regulatory T cells (Treg) which accumulate in cancer may have beneficial or unfavorable effects on prognosis. The presence in tumor-associated inflammatory infiltrates of two subsets of Treg with distinct phenotypic and functional profiles might explain these conflicting observations.

AREAS COVERED

Human inducible (i) Treg arising by tumor-driven conversion of conventional CD4(+) T cells are highly suppressive, therapy-resistant Treg which down-regulate anti-tumor immune responses, promoting tumor growth. Natural (n) Treg, normally responsible for maintaining peripheral tolerance, control cancer-associated inflammation, which favors tumor progression. This division of labor between nTreg and iTreg is not absolute, and overlap may be common. Nevertheless, iTreg play a critical and major role in cancer and cancer therapy. The tumor microenvironment determines the type, frequency and suppression levels of accumulating Treg.

EXPERT OPINION

In cancer, a selective removal or silencing of iTreg and not of nTreg should be a therapeutic goal. However, the implementation of this challenging strategy requires further studies of cellular and molecular crosstalk among immune cells in the tumor microenvironment.

Dynamics of T-cell infiltration during the course of ovarian cancer: the gradual shift from a Th17 effector cell response to a predominant infiltration by regulatory T-cells

The type of immune cells that are present within the tumor microenvironment can play a crucial role in the survival of patients. However, little is known about the dynamics of the tumor-infiltrating immune cells during disease progression. We studied the immune cells that infiltrated the tumor tissues of ovarian cancer patients at different stages of disease. The early stages of development of ovarian carcinomas were characterized by a strong Th17 immune response, whereas in stage II patients, recruitment of high numbers of Th1 cells was observed. In disseminated tumors (Stages III-IV), we detected a dominant population of Helios(+) activated regulatory T cells (Tregs) along with high numbers of monocytes/macrophages and myeloid dendritic cells (mDCs). Tumor-infiltrating Tregs had markedly lower expression of CCR4 than circulating Tregs, and the numbers of tumor-infiltrating Tregs significantly correlated with the levels of CCL22 in ovarian tumor cell culture supernatants, suggesting their recruitment via a CCR4/CCL22 interaction. CCL22 was mainly produced by tumor cells, monocytes/macrophages and mDCs in the primary ovarian tumors, and its expression markedly increased in response to IFNγ. Taken together, the specific recruitment of Tregs, probably triggered by inflammatory stimuli, leads to a significant immune suppression in the advanced stages of ovarian cancer.

The role of the adenosinergic pathway in immunosuppression mediated by human regulatory T cells (Treg)

Tumor-induced dysfunction of immune cells is a common problem in cancer. Tumors induce immune suppression by many different mechanisms, including accumulation of regulatory T cells (Treg). Adaptive Treg (Tr1) generated in the tumor microenvironment express CD39 and CD73 ectonucleotidases, produce adenosine and are COX2+PGE2+. Adenosine and PGE2 produced by Tr1 or tumor cells bind to their respective receptors on the surface of T effector cells (Teff) and cooperate in up-regulating cytosolic 3'5'-cAMP levels utilizing adenylyl cyclase isoform 7 (AC-7). In Teff, increased cAMP mediates suppression of anti-tumor functions. Treg, in contrast to Teff, seem to require high cAMP levels for mediating suppression. This differential requirement of Treg and Teff for cAMP offers an opportunity for pharmacologic interventions using selected inhibitors of the adenosine/PGE2 pathways. Blocking of adenosine/PGE2 production by Tr1 or blocking binding of these factors to their receptors on T cells or inhibition of cAMP synthesis in Teff all represent novel therapeutic strategies that used in combination with conventional therapies could restore anti-tumor functions of Teff . At the same time, these inhibitors could disarm Tr1 cells by depriving them of the factors promoting their generation and activity or by down-regulating 3'5'-cAMP levels. Thus, the pharmacologic control of Treg-Teff interactions offers a novel strategy for restoration of anti-tumor Teff functions and silencing of Treg. Used in conjunction with anti-cancer drugs or with immune therapies, this strategy has a potential to improve therapeutic effects by preventing or reversing tumor-induced immune suppression.