gammadelta T cells are important contributors to innate immunity against cancer, but their regulatory role in controlling immune responses remains largely unknown. Here we report that a dominant gammadelta1 T cell population among lymphocytes infiltrating breast tumors possessed a potent ability to suppress naive and effector T cell responses and to block the maturation and function of dendritic cells. Adoptive cotransfer experiments demonstrated their in vivo suppressive activity. However, their immunosuppressive activity could be reversed by human Toll-like receptor (TLR) 8 ligands both in vitro and in vivo. siRNA-mediated knockdown experiments revealed that MyD88, TRAF6, IKKalpha IKKbeta, and p38alpha molecules in gammadelta1 cells were required for these cells to respond to TLR8 ligands, whereas TAK1, JNK, and ERK molecules did not appear to be involved in functional regulation. These results provide new insights into the regulatory mechanisms of tumor-specific gammadelta T cells and identify a unique TLR8 signaling pathway linking to their functional regulation.

Regulatory T cells play an important role in the maintenance of immunological self-tolerance by suppressing immune responses against autoimmune diseases and cancer. Little is known, however, about the nature of the physiological target antigens for CD4(+) regulatory T (Treg) cells. Here we report the identification of the LAGE1 protein as a ligand for tumor-specific CD4(+) Treg cell clones generated from the tumor-infiltrating lymphocytes (TILs) of cancer patients. Phenotypic and functional analyses demonstrated that they were antigen-specific CD4(+) Treg cells expressing CD25 and GITR molecules and possessing suppressive activity on the proliferative response of naive CD4(+) T cells to anti-CD3 antibody stimulation. Ligand-specific activation and cell-cell contact were required for TIL102 Treg cells to exert suppressive activity on CD4(+) effector cells. These findings suggest that the presence of tumor-specific CD4(+) Treg cells at tumor sites may have a profound effect on the inhibition of T cell responses against cancer.

Prostate cancer is the most common cancer among men in the United States and the second most common malignant cause of male deaths in the United States. There is currently no effective therapy for late-stage disease, whereas surgery or radiation therapy is the only choice for early-stage disease. Immunotherapy affords a promising approach to the treatment of various types of cancer, including prostate cancer (1 -5). Although peptide-or dendritic cell -based vaccines can induce antigenspecific immune responses, objective clinical responses remain infrequent and transient (3,6). A possible explanation is that tumor cells may create an immunosuppressive environment in cancer patients. Thus, a better understanding of the interaction between tumor-infiltrating immune cells and cancer cells is critical to efforts to devise strategies that would enhance the therapeutic efficacy of immunologic interventions.Recent studies indicate that preexisting CD4 + regulatory T (Treg) cells at tumor sites may pose major obstacles to effective cancer immunotherapy, as these cells have a potent ability to suppress host immune responses (7 -9). Indeed, increased proportions of CD4 + CD25 + Treg cells in the total CD4 + T-cell populations have been documented in patients with different types of cancers, including lung, breast, and ovarian tumors (10 -12). Our recent findings further show the presence of antigen-specific CD4 + Treg cells at tumor sites, where they induce antigen-specific and local immune tolerance (7,8). The removal or elimination of Treg cell populations with anti-CD25 monoclonal antibody (mAb) treatment results in effective rejection of transplanted tumors in animal models (13), further suggesting a functional role for these Treg cells in tumor progression and immunosuppression.Because Treg cell -mediated immunosuppression exists at tumor sites, a new strategy for depletion of Treg cells or reversal of the suppressive function of Treg cells will be important in efforts to induce antigen-specific effector T cells. Thus, we recently showed that Toll-like receptor 8 (TLR8) ligands can specifically reverse the suppressive function of both antigen-specific and

IntroductionRegulatory T (Treg) cells play a central role in controlling immune tolerance and homeostasis of the immune system, preventing autoimmune diseases, and limiting chronic inflammatory diseases. 1,2 However, Treg cells can also inhibit effective immune responses against cancer and various pathogen infections. [3][4][5] Therefore, it is critical to better define the suppressive mechanisms used by Treg cells in order to develop effective approaches for their clinical manipulation for therapeutic intervention. Significant progress has been made in delineating the molecules and mechanisms that Treg cells use to mediate suppression. [6][7][8] These mechanisms include suppression by inhibitory cytokines and secreted molecules, 9 by cytolysis or apoptosis of target cells, [10][11][12] by consumption of limiting growth factors and metabolic disruption, [12][13][14] and/or by affecting dendritic cell functions. 15 The majority of previous studies were performed in animal models, so whether these mechanisms are also used by human Treg cells is still under investigation. In addition, the fate and function of responder T cells suppressed by Treg cells is unclear.Cellular senescence was described initially more than 40 years ago in human fibroblasts with limited passages in cell culture. 16 It is now well known that senescent cells have permanent cell-cycle arrest but remain viable and metabolically active and possess unique transcriptional profiles and gene-regulation signatures. 17 There are 2 major categories of cellular senescence: replicative senescence (also known as telomere-dependent senescence) [18][19][20] and premature senescence (also known as extrinsic senescence or telomere-independent senescence). 17,[21][22][23] Recent studies suggest that replicative senescence also occurs in the human immune system. Accumulation of senescent CD8 ϩ T cells has been found in persons during normal aging, in younger persons with chronic viral infections, and in patients with certain types of cancers. [24][25][26][27] Senescent CD8 ϩ T cells show functional changes and have defective killing abilities due to the loss of perforin and granzyme or have defects in signaling of granule exocytosis. 28,29 Furthermore, senescent CD8 ϩ T cells have negative regulatory functions that reduce the effects of immunization and vaccinations and prolong the survival of allografts. 26,30 Improved understanding of the molecular mechanisms used in the generation of senescent T cells and their functional alterations will open new avenues to restoring T-cell function and will help in the design of novel vaccines for infectious diseases and cancers.In the present study, we explored the suppressive mechanisms used by human Treg cells and investigated the fate of Treg-treated responder T cells and found that treatment with CD4 ϩ CD25 hi naturally occurring Treg cells can induce naive/effector T-cell senescence. We further identified the molecular signaling that controls the process of T-cell senescence and characterized these senescent T cells....

Although Th17 cells play critical roles in the pathogenesis of many inflammatory and autoimmune diseases, their prevalence among tumor-infiltrating lymphocytes (TILs) and function in human tumor immunity remains largely unknown. We have recently demonstrated high percentages of Th17 cells in TILs from ovarian cancer patients, but the mechanisms of accumulation of these Th17 cells in the tumor microenvironment are still unclear. In this study, we further showed elevated Th17 cell populations in the TILs obtained from melanoma and breast and colon cancers, suggesting that development of tumor-infiltrating CD4+ Th17 cells may be a general feature in cancer patients. We then demonstrated that tumor microenvironmental RANTES and MCP-1 secreted by tumor cells and tumor-derived fibroblasts mediate the recruitment of Th17 cells. In addition to their recruitment, we found that tumor cells and tumor-derived fibroblasts produce a proinflammatory cytokine milieu as well as provide cell–cell contact engagement that facilitates the generation and expansion of Th17 cells. We also showed that inflammatory TLR and nucleotide oligomerization binding domain 2 signaling promote the attraction and generation of Th17 cells induced by tumor cells and tumor-derived fibroblasts. These results identify Th17 cells as an important component of human TILs, demonstrate mechanisms involved in the recruitment and regulation of Th17 cells in tumor microenvironments, and provide new insights relevant for the development of novel cancer immunotherapeutic approaches.