Anette Sundstedt

Role for IL-10 in Suppression Mediated by Peptide-Induced Regulatory T Cells In Vivo

Regulatory CD4+ T cells were induced in the Tg4 TCR transgenic mouse specific for the N-terminal peptide (Ac1-9) of myelin basic protein by intranasal administration of a high-affinity MHC-binding analog (Ac1-9[4Y]). Peptide-induced tolerant cells (PItol) were anergic, failed to produce IL-2, but responded to Ag by secretion of IL-10. PItol cells were predominantly CD25− and CTLA-4+ and their anergic state was reversed by addition of IL-2 in vitro. PItol cells suppressed the response of naive Tg4 cells both in vitro and in vivo. The in vitro suppression mediated by these cells was not reversed by cytokine neutralization and was cell-cell contact-dependent. However, suppression of proliferation and IL-2 production by PItol cells in vivo was abrogated by neutralization of IL-10. These results emphasize an important role for IL-10 in the function of peptide-induced regulatory T cells in vivo and highlight the caution required in extrapolating mechanisms of T regulatory cell function from in vitro studies.

Persistent antigenic stimulation alters the transcription program in T cells, resulting in antigen-specific tolerance

Repetitive antigen stimulation induces peripheral T cell tolerance in vivo. It is not known, however, whether multiple stimulations merely suppress T cell activation or, alternatively, change the transcriptional program to a distinct, tolerant state. In this study, we have discovered that STAT3 and STAT5 were activated in response to antigen stimulation in vivo, in marked contrast to the suppression of AP‐1, NF‐κB and NFAT. In addition, a number of transcription factors were induced in tolerant T cells following antigen challenge in vivo, including T‐bet, Irf‐1 and Egr‐2. The altered transcription program in tolerant cells associates closely with the suppression of cell cycle progression and IL‐2 production, as well as with the induction of IL‐10. Studies of T‐bet and Egr‐2 show that the function of T‐bet in peptide treatment‐induced regulatory T cells is not associated with Th1 differentiation, but correlates with the suppression of IL‐2, whereas expression of Egr‐2 led to an up‐regulation of the cell cycle inhibitors p21cip1 and p27kip. Our results demonstrate a balanced transcription program regulated by different transcription factors for T cell activation and/or tolerance during antigen‐induced T cell responses. Persistent antigen stimulation can induce T cell tolerance by changing the balance of transcription factors.

Superantigen-induced regulatory T cells display different suppressive functions in the presence or absence of natural CD4+CD25+ regulatory T cells in vivo.

Repeated exposures to both microbial and innocuous Ags in vivo have been reported to both eliminate and tolerize T cells after their initial activation and expansion. The remaining tolerant T cells have been shown to suppress the response of naive T cells in vitro. This feature is reminiscent of natural CD4+CD25+ regulatory T cells. However, it is not known whether the regulatory function of in vivo-tolerized T cells is similar to the function of natural CD4+CD25+ regulatory T cells. In this study, we demonstrate that CD4+CD25+ as well as CD4+CD25− T cells isolated from mice treated with superantigen three consecutive times to induce tolerance were functionally comparable to natural CD4+CD25+ regulatory T cells, albeit more potent. The different subpopulations of in vivo-tolerized CD4+ T cells efficiently down-modulated costimulatory molecules on dendritic cells, and their suppressive functions were strictly cell contact dependent. Importantly, we demonstrate that conventional CD4+CD25− T cells could also be induced to acquire regulatory functions by the same regimen in the absence of natural regulatory T cells in vivo, but that such regulatory cells were functionally different.

Tasquinimod modulates suppressive myeloid cells and enhances cancer immunotherapies in murine models

Shen, Sundstedt, and colleagues show in murine models that tasquinimod enhanced the antitumor effects of SurVaxM tumor vaccine for prostate cancer and of 5T4Fab-SEA tumor-targeted superantigen for melanoma by inhibiting the accumulation and function of tumor-infiltrating suppressive myeloid cells. A major barrier for cancer immunotherapy is the presence of suppressive cell populations in patients with cancer, such as myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAM), which contribute to the immunosuppressive microenvironment that promotes tumor growth and metastasis. Tasquinimod is a novel antitumor agent that is currently at an advanced stage of clinical development for treatment of castration-resistant prostate cancer. A target of tasquinimod is the inflammatory protein S100A9, which has been demonstrated to affect the accumulation and function of tumor-suppressive myeloid cells. Here, we report that tasquinimod provided a significant enhancement to the antitumor effects of two different immunotherapeutics in mouse models of cancer: a tumor vaccine (SurVaxM) for prostate cancer and a tumor-targeted superantigen (TTS) for melanoma. In the combination strategies, tasquinimod inhibited distinct MDSC populations and TAMs of the M2-polarized phenotype (CD206+). CD11b+ myeloid cells isolated from tumors of treated mice expressed lower levels of arginase-1 and higher levels of inducible nitric oxide synthase (iNOS), and were less immunosuppressive ex vivo, which translated into a significantly reduced tumor-promoting capacity in vivo when these cells were coinjected with tumor cells. Tumor-specific CD8+ T cells were increased markedly in the circulation and in tumors. Furthermore, T-cell effector functions, including cell-mediated cytotoxicity and IFNγ production, were potentiated. Taken together, these data suggest that pharmacologic targeting of suppressive myeloid cells by tasquinimod induces therapeutic benefit and provide the rationale for clinical testing of tasquinimod in combination with cancer immunotherapies. Cancer Immunol Res; 3(2); 136–48. ©2014 AACR.

IL-2 Overcomes the Unresponsiveness but Fails to Reverse the Regulatory Function of Antigen-Induced T Regulatory Cells

Intranasal administration of peptide Ac1–9[4Y], based on the N-terminal epitope of myelin basic protein, can induce CD4+ T cell tolerance, and suppress experimental autoimmune encephalomyelitis induction. The peptide-induced regulatory T (PI-TReg) cells failed to produce IL-2, but expressed IL-10 in response to Ag and could suppress naive T cell responses in vitro. Analysis of Jak-STAT signaling pathways revealed that the activation of Jak1, STAT3, and STAT5 were induced in tolerant T cells after Ag stimulation in vivo. In addition, the expression of suppressor of cytokine signaling 3 was induced in tolerant T cells, suggesting that cytokines regulate the tolerant state of the PI-TReg cells. Stimulation of PI-TReg cells in vitro with IL-10 induced Jak1 and STAT3 activation, but not STAT5, suggesting that IL-10 is important, but not the only cytokine involved in the development of T cell tolerance. Although IL-2 expression was deficient, stimulation with IL-2 in vitro induced Jak1 and STAT5 activation in PI-TReg cells, restored their proliferative response to antigenic stimulation, and abrogated PI-TReg-mediated suppression in vitro. However, the addition of IL-2 could not suppress IL-10 expression, and the IL-2 gene remained inactive. After withdrawal of IL-2, the PI-TReg cells regained their nonproliferative state and suppressive ability. These results underline the ability of the immune system to maintain tolerance to autoantigens, but at the same time having the ability to overcome the suppressive phenotype of tolerant T cells by cytokines, such as IL-2, during the protective immune response to infection.

Intranasal peptide-induced peripheral tolerance: the role of IL-10 in regulatory T cell function within the context of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a T cell-mediated autoimmune disease commonly employed as a model for multiple sclerosis. Extensive studies have demonstrated that EAE may be prevented or ameliorated by the intranasal administration of soluble peptides representing encephalitogenic epitopes. There is increasing evidence that this peptide administration may function via the generation of regulatory cells. The mechanism of action of these cells remains controversial and it seems likely that it may vary between experimental models. At present the majority of work on regulatory cells has centred on characterising naturally occurring regulators, or those generated artificially ex vivo, and less is known about induced regulatory cells produced following peptide administration. This report aims to briefly outline the evidence for the existence of natural regulatory T cells and to introduce the sub-types of induced regulatory T cells now recognised. In several of these regulatory cell systems investigated to date, interleukin-10 (IL-10) has been shown to be important in cell function. This has not been directly investigated in a model employing peptide therapy to induce peripheral tolerance, hence the purpose of this study was to investigate the role of IL-10 in the generation of these regulatory cells. This work has employed both a TCR transgenic mouse system, for predominantly in vitro studies of cell function, and an IL-10 knock-out mouse strain to investigate in vivo disease protection. The results summarised in this report demonstrate that IL-10 is fundamentally important in the generation of disease protection following intranasal peptide therapy.

Natural and Induced Regulatory T Cells

Abstract: Mucosal antigen delivery can induce tolerance, as shown by suppression of subsequent responses to antigen. Our previous work showed that both intranasal and oral routes of antigen delivery were effective but indicated that the intranasal route might be more reliable. Intranasal peptide administration induced cells that could mediate bystander suppression of responses to associated antigenic epitopes. Here, we discuss further investigation into the nature of intranasal, peptide‐induced tolerance. Cells from mice treated with intranasal peptide became anergic and shut down secretion of cytokines such as IL‐2, but still secreted IL‐10. This latter cytokine was required for suppression of immune responses in vivo even though suppression of responses in vitro was IL‐10 independent. Intranasal peptide induced a subset of CD25−, CTLA‐4+ regulatory cells that suppressed naive cell function in vitro and in vivo. We provide evidence that these cells arise from CD25− precursors and differentiate independently from natural CD25+ regulatory cells. IL‐10‐secreting regulatory cells are also found in the peripheral blood of humans and can be induced by soluble peptide administration. This route of tolerance induction offers promise as a means of antigen‐specific immunotherapy of allergic and autoimmune conditions in humans.

Antigen-Induced IL-10+ Regulatory T Cells Are Independent of CD25+ Regulatory Cells for Their Growth, Differentiation, and Function

Recent studies have emphasized the importance of T cells with regulatory/suppressor properties in controlling autoimmune diseases. A number of different types of regulatory T cells have been described with the best characterized being the CD25+ population. In addition, it has been shown that regulatory T cells can be induced by specific Ag administration. In this study, we investigate the relationship between peptide-induced, CD4+ regulatory T cells and naturally occurring CD4+CD25+ cells derived from the Tg4 TCR-transgenic mouse. Peptide-induced cells were FoxP3− and responded to Ag by secreting IL-10, whereas CD25+ cells failed to secrete this cytokine. Both cell types were able to suppress the proliferation of naive lymphocytes in vitro although with distinct activation sensitivities. Depletion of CD25+ cells did not affect the suppressive properties of peptide-induced regulators. Furthermore, peptide-induced regulatory/suppressor T cells could be generated in RAG−/−, TCR-transgenic mice that do not spontaneously generate CD25+ regulatory cells. These results demonstrate that these natural and induced regulatory cells fall into distinct subsets.

The role of cytokines in immunological tolerance: potential for therapy

Current immunosuppression protocols, although often effective, are nonspecific and therefore hazardous. Consequently, immunological tolerance that is antigen specific and does not globally depress the patients immune system has become one of the Holy Grails of immunology. Since the discovery that cytokines have immunomodulatory effects, extensive research has investigated the potential of these molecules to induce and maintain specific immunological tolerance in the context of transplantation, allergy and autoimmunity. In this article, we review the possible mechanisms by which cytokines can modulate the immune response and the animal models that frequently confound the theory that a single cytokine, or group of cytokines, can induce tolerance in a predictable manner. Finally, we discuss the role of cytokines at a paracrine level, particularly in the context of inducing and maintaining antigen-specific, regulatory T cells with the clinical potential to suppress specific immune responses.

Combining tumor-targeted superantigens with interferon-alpha results in synergistic anti-tumor effects

In this study we explored the possibility of improving the anti-tumor potency of tumor-targeted superantigens (TTS) by combination treatment with interferon-alpha (IFN-alpha). TTS utilizes the powerful T cell activating property of the superantigen staphylococcal enterotoxin A (SEA) in fusion with an anti-tumor Fab-fragment to target this T cell activity against tumor cells. TTS fusion proteins have shown anti-tumor efficacy in a number of experimental tumor models including the B16 mouse melanoma transfected with a human tumor-associated antigen recognized by the C215 monoclonal antibody. IFN-alpha is approved for the treatment of solid tumors such as renal cell carcinoma and malignant melanoma and exerts immunomodulatory effects, which make it an appropriate candidate to combine with immunotherapy against cancer. Here we report that daily administration of IFN-alpha (20 000 U i.p.) enhances and sustains CD8+ T cell activation induced by the TTS C215Fab-SEA (10 microg i.v.) in C57Bl/6 mice, as reflected by increased and prolonged cell-mediated cytotoxicity against tumor cells ex vivo as well as by augmented serum IFN-gamma levels. C215Fab-SEA synergized with IFN-alpha in reducing the number of lung tumors in B16-C215 melanoma bearing mice as compared to mono therapy. In a long term tumor survival experiment, the prolonged median survival time of the combination treatment was 3.5 and 7.7 times the prolonged median survival times of C215Fab-SEA and IFN-alpha monotherapies, respectively. Hence, the combination treatment provoked synergistic anti-tumor effects as measured by the number of lung tumors and markedly prolonged survival. The enhanced therapeutic efficacy correlated with a striking and sustained increase of CD8- and perforin-expressing tumor-infiltrating cells. These results suggest significant potential of combining TTS with IFN-alpha for human cancer therapy.