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.

Members of the suppressor of cytokine signaling (SOCS) family were discovered as negative regulators of cytokine signaling by inhibition of the Janus kinase–signal transducer and activator of transcription (Jak-STAT) pathway. Among them, cytokine-induced Src homology 2 (SH2) protein (CIS) was found to inhibit the interleukin 3– and erythropietin-mediated STAT5 signaling pathway. However, involvement of SOCS proteins in other signaling pathways is still unknown. This study shows that the expression of CIS is selectively induced in T cells after T cell receptor (TCR) stimulation. In transgenic mice, with selective expression of CIS in CD4 T cells, elevated CIS strongly promotes TCR-mediated proliferation and cytokine production in vitro, and superantigen-induced T cell activation in vivo. Forced expression of CIS also prolongs survival of CD4 T cells after TCR activation. Molecular events immediately downstream from the TCR are not changed in CIS-expressing CD4 T cells, but activation of mitogen-activated protein (MAP) kinase pathways by TCR stimulation is significantly enhanced. Together with the increased MAP kinase activation, a direct interaction of CIS and protein kinase Cθ was also demonstrated. These results suggest that CIS is one of the important regulators of TCR-mediated T cell activation. The functions of CIS, enhancing TCR signaling and inhibiting cytokine signaling, may be important in the regulation of immune response and homeostasis.

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-jB 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 p21 cip1 and p27 kip . 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.See accompanying commentary http://www.dx

A major barrier for cancer immunotherapy is the presence of suppressive cell populations in cancer patients, 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 co-injected 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.