NKG2D receptor regulates human effector T-cell cytokine production

Although innate immune signals shape the activation of naive T cells, it is unclear how innate signals influence effector T-cell function. This study determined the effects of stimulating the NKG2D receptor in conjunction with the TCR on human effector CD8(+) T cells. Stimulation of CD8(+) T cells through CD3 and NKG2D simultaneously or through a chimeric NKG2D receptor, which consists of NKG2D fused to the intracellular region of CD3ζ, activated β-catenin and increased expression of β-catenin-induced genes, whereas T cells stimulated through the TCR or a combination of the TCR and CD28 did not. Activation by TCR and NKG2D prevented expression and production of anti-inflammatory cytokines IL-10, IL-9, IL-13, and VEGF-α in a β-catenin- and PPARγ- dependent manner. NKG2D stimulation also modulated the cytokine secretion of T cells activated simultaneously through CD3 and CD28. These data indicate that activating CD8(+) T cells through the NKG2D receptor along with the TCR modulates signal transduction and the production of anti-inflammatory cytokines. Thus, human effector T cells alter their function depending on which innate receptors are engaged in conjunction with the TCR complex.     

ITK and IL-15 support two distinct subsets of CD8+ T cells

CD8(+) T cells are commonly divided into na?ve CD44(lo)CD122(lo) and "memory phenotype" CD44(hi)CD122(hi) cells. Here we show data suggesting that these two cell populations represent independent CD8(+) T cell subsets. Whereas IL-15(-/-) mice lack CD44(hi)CD122(hi) CD8(+) T cells, mice deficient in the kinase ITK lack CD44(lo)CD122(lo) cells among CD8(+) T cells. The same defects were observed during thymus development. CD44(hi)CD122(hi) cells were found among double-positive thymocytes and increased in frequency during CD8 development in wild-type mice. At the mature stage, IL-15(-/-) mice harbored virtually no CD44(hi)CD122(hi) CD8(+) thymocytes. In contrast, ITK(-/-) mice lacked CD44(lo)CD122(lo) CD8(+) cells at this stage. We generated mice with genetic deletions in both IL-15 and ITK and observed a severe reduction of all CD8(+) T cells. The two CD44(lo)CD122(lo) and CD44(hi)CD122(hi) CD8(+) T cell subsets differed in the periphery in that natural killer (NK) receptor expression was found only on CD44(hi)CD122(hi) CD8(+) T cells. This expression was paralleled by their ability to respond to both T cell receptor and NK receptor engagements. In contrast, CD44(lo)CD122(lo) CD8(+) T cells mounted stronger responses to T cell receptor stimulation but failed to recognize NK receptor ligands. Thus, whereas ITK-dependent CD44(lo)CD122(lo) CD8(+) T cells appear to represent conventional CD8(+) T cells, IL-15-dependent CD44(hi)CD122(hi) CD8(+) T cells may have functions in both adaptive and innate immunity.     

RAG-dependent peripheral T cell receptor diversification in CD8+ T lymphocytes

Rearrangement of T cell receptor (TCR) genes is driven by transient expression of V(D)J recombination-activating genes (RAGs) during lymphocyte development. Immunological dogma holds that T cells irreversibly terminate RAG expression before exiting the thymus, and that all of the progeny arising from mature T cells express the parental TCRs. When single pancreatic islet-derived, NRP-A7 peptide-reactive CD8(+) T cells from nonobese diabetic (NOD) mice were repeatedly stimulated with peptide-pulsed dendritic cells, daughter T cells reexpressed RAGs, lost their ability to bind to NRP-A7K(d) tetramers, ceased to transcribe tetramer-specific TCR genes, and, instead, expressed a vast array of other TCR rearrangements. Pancreatic lymph node (PLN) CD8(+) T cells from animals expressing a transgenic NRP-A7-reactive TCR transcribed and translated RAGs in vivo and displayed endogenous TCRs on their surface. RAG reexpression also occurred in the PLN CD8(+) T cells of wild-type NOD mice and could be induced in the peripheral CD8(+) T cells of nondiabetes-prone TCR-transgenic B10.H2(g7) mice by stimulation with peptide-pulsed dendritic cells. In contrast, reexpression of RAGs could not be induced in the CD8(+) T cells of B6 mice expressing an ovalbumin-specific, K(b)-restricted TCR, or in the CD8(+) T cells of NOD mice expressing a lymphocytic choriomeningitis virus-specific, D(b)-restricted TCR. Extra-thymic reexpression of the V(D)J recombination machinery in certain CD8(+) T cell subpopulations, therefore, enables further diversification of the peripheral T cell repertoire.     

Delineation of antigen-specific and antigen-nonspecific CD8(+) memory T-cell responses after cytokine-based cancer immunotherapy

Memory T cells exhibit tremendous antigen specificity within the immune system and accumulate with age. Our studies reveal an antigen-independent expansion of memory, but not naive, CD8(+) T cells after several immunotherapeutic regimens for cancer resulting in a distinctive phenotype. Signaling through T-cell receptors (TCRs) or CD3 in both mouse and human memory CD8(+) T cells markedly up-regulated programmed death-1 (PD-1) and CD25 (IL-2 receptor α chain), and led to antigen-specific tumor cell killing. In contrast, exposure to cytokine alone in vitro or with immunotherapy in vivo did not up-regulate these markers but resulted in expanded memory CD8(+) T cells expressing NKG2D, granzyme B, and possessing broadly lytic capabilities. Blockade of NKG2D in mice also resulted in significantly diminished antitumor effects after immunotherapy. Treatment of TCR-transgenic mice bearing nonantigen expressing tumors with immunotherapy still resulted in significant antitumor effects. Human melanoma tissue biopsies obtained from patients after topically applied immunodulatory treatment resulted in increased numbers of these CD8(+) CD25(-) cells within the tumor site. These findings demonstrate that memory CD8(+) T cells can express differential phenotypes indicative of adaptive or innate effectors based on the nature of the stimuli in a process conserved across species.     

CD4+NKG2D+ T cells in Crohn's disease mediate inflammatory and cytotoxic responses through MICA interactions

BACKGROUND & AIMS: Crohn's disease (CD) is an inflammatory bowel disease characterized by uncontrolled immune responses to bacterial flora, with excessive activation of T lymphocytes. MICA is a stress-induced major histocompatibility complex-related molecule expressed on normal intestinal epithelial cells (IECs) and recognized by the NKG2D-activating receptor on CD8(+) T cells, gammadelta T cells, and natural killer cells. We examined the role of MICA-NKG2D interactions in the activation of T lymphocytes in CD. METHODS: MICA expression was analyzed by flow cytometry on IECs isolated from patients with active inflammatory bowel disease and controls. NKG2D expression and function were analyzed on lamina propria and peripheral blood lymphocytes. RESULTS: MICA expression was significantly increased on IECs in CD, with higher expression in macroscopically involved areas. A subset of CD4(+) T cells expressing NKG2D was increased in the lamina propria from patients with CD compared with controls and patients with ulcerative colitis. CD4(+)NKG2D(+) T cells with a Th1 cytokine profile and expressing perforin were increased in the periphery and in the mucosa in CD. CD4(+)NKG2D(+) T-cell clones were functionally active through MICA-NKG2D interactions, producing interferon-gamma and killing targets expressing MICA. IECs from patients with CD had the ability to expand this subset in vitro. CD4(+)NKG2D(+) lamina propria lymphocytes from patients with CD highly expressed interleukin-15R alpha, and interleukin-15 increased NKG2D and DAP10 expression in CD4(+)NKG2D(+) T-cell clones. CONCLUSIONS: These findings highlight the role of MICA-NKG2D in the activation of a unique subset of CD4(+) T cells with inflammatory and cytotoxic properties in CD.     

Gamma c cytokines condition the progressive differentiation of CD4+ T cells

After their initial antigen encounter in the secondary lymphoid organs, activated T cells must receive additional signals in the peripheral tissues to fully differentiate. Here, we provide evidence that gamma(c) cytokines are critical during this process. Using the Marilyn (Ml) T cell antigen receptor (TCR) transgenic model, we show that male skin grafts are tolerated in the absence of gamma(c), but that Ml CD4(+) T cells proliferate normally in response to antigen, traffic to the graft site and recruit an inflammatory response [including natural killer (NK) cells, neutrophils, and macrophages] that is independent of T cell gamma(c) expression. Whereas wild-type T cells demonstrate a progressive differentiation phenotype from the spleen to the tissues, skin-infiltrating effector T cells (CD44(hi)CD62L(lo)) from gamma(c)(-) mice were phenotypically abnormal with reduced ICOS, NKG2D, granzyme B, and IFN-gamma expression. These defects could be mapped to deficiencies in IL-2 and, surprisingly, IL-15. These results define a late checkpoint in T cell differentiation in the tissues where gamma(c) cytokines, including IL-15, authenticate CD4(+) T cell effector functions.     

Class I MHC molecules on hematopoietic cells can support intrathymic positive selection of T cell receptor transgenic T cells.

The identity of cells that mediate positive selection of CD8(+) T cells was investigated in two T cell receptor (TCR) transgenic systems. Irradiated beta(2)-microglobulin mutant mice or mice with mutations in both the K(b) and D(b) genes were repopulated with fetal liver cells from class I(+) TCR transgenic mice. In the case of the 2C TCR, mature transgene-expressing CD8(+) T cells appeared in the thymuses of the chimeras and in larger numbers in the peripheral lymphoid organs. These CD8(+) T cells were functional, exhibited a naive, resting phenotype, and were mostly thymus-dependent. Their development depended on donor cell class I expression. These results establish that thymic hematopoietic cells can direct positive selection of CD8(+) T cells expressing a conventional TCR. In contrast, no significant development of HY (male antigen)-TCR(+) CD8(+) T cells was observed in class I(+) into class I-deficient chimeras. These data suggest that successful positive selection directed by hematopoietic cells depends on specific properties of the TCR or its thymic ligands. The possibility that hematopoietic cell-induced, positive selection occurs only with TCRs that exhibit relatively high avidity interactions with selecting ligands in the thymus is discussed.     

Role of NKG2D signaling in the cytotoxicity of activated and expanded CD8+ T cells

Activating and expanding T cells using T-cell receptor (TCR) cross-linking antibodies and interleukin 2 (IL-2) results in potent cytotoxic effector cells capable of recognizing a broad range of malignant cell targets, including autologous leukemic cells. The mechanism of target cell recognition has previously been unknown. Recent studies show that ligation of NKG2D on natural killer (NK) cells directly induces cytotoxicity, whereas on T cells it costimulates TCR signaling. Here we demonstrate that NKG2D expression is up-regulated upon activation and expansion of human CD8+ T cells. Antibody blocking, redirected cytolysis, and small interfering RNA (siRNA) studies using purified CD8+ T cells demonstrate that cytotoxicity against malignant target cells occurs through NKG2D-mediated recognition and signaling and not through the TCR. Activated and expanded CD8+ T cells develop cytotoxicity after 10 to 14 days of culture, coincident with the expression of the adapter protein DAP10. T cells activated and expanded in low (30 U/mL) and high (300 U/mL) concentrations of IL-2 both up-regulated NKG2D expression equally, but only cells cultured in high-dose IL-2 expressed DAP10 and were cytotoxic. Collectively these results establish that NKG2D triggering accounts for the majority of major histocompatibility complex (MHC)-unrestricted cytotoxicity of activated and expanded CD8+ T cells, likely through DAP10-mediated signaling.     

Antigen presentation by keratinocytes directs autoimmune skin disease

The antigen-presenting cells that initiate and maintain MHC class II-associated organ-specific autoimmune diseases are poorly defined. We now describe a new T cell antigen receptor (TCR) transgenic (Tg) model of inflammatory skin disease in which keratinocytes activate and are the primary target of autoreactive CD4(+) T cells. We previously generated keratin 14 (K14)-A(beta)b mice expressing MHC class II only on thymic cortical epithelium. CD4(+) T cells from K14-A(beta)b mice fail to undergo negative selection and thus have significant autoreactivity. The TCR genes from an autoreactive K14-A(beta)b CD4 hybridoma were cloned to produce a TCR Tg mouse, 2-2-3. 2-2-3 TCR Tg cells are negatively selected in WT C57BL6 mice but not in 2-2-3K14-A(beta)b mice. Interestingly, a significant number of mice that express both the K14-A(beta)b transgene and the autoreactive 2-2-3 TCR spontaneously develop inflammatory skin disease with mononuclear infiltrates, induction of MHC class II expression on keratinocytes, and T helper 1 cytokines. Disease can be induced by skin inflammation but not solely by activation of T cells. Thus, cutaneous immunopathology can be directed through antigen presentation by tissue-resident keratinocytes to autoreactive TCR Tg CD4(+) cells.     

T cell receptor dynamism of mucosal and systemic CD4+ T cells in the course of an immune response to Escherichia coli heat-labile enterotoxin

The changes in T cell receptor (TCR) Vbeta expression, use, and clonality in mice orally challenged with Escherichia coli heat-labile enterotoxin (LT) were assessed. Use of the TCR Vbeta family and clonality were significantly changed at the single-cell level. In Peyer's patches of treated mice, use of TCR Vbeta6, Vbeta8, and Vbeta14 increased in CD4(+)CD44(+) T cells, compared with use in nontreated mice. On the other hand, use of TCR Vbeta1 and Vbeta8 was enhanced in splenic CD4(+)CD44(+) T cells. Intraepithelial lymphocytes isolated from LT-challenged mice showed expanded clonality (e.g., Vbeta1, Vbeta2, Vbeta9, and Vbeta18) and altered TCR Vbeta use (e.g., Vbeta15, Vbeta16, and Vbeta17). These findings reveal that oral administration of LT has distinct effects on mucosal versus systemic alphabeta T cells for induction of CD4(+) T cells with selected Vbeta use. This most likely reflects the function of LT as a mucosal modulator.     

Dual-functional capability of CD3+CD56+ CIK cells, a T-cell subset that acquires NK function and retains TCR-mediated specific cytotoxicity

CD3(+)CD56(+) cytokine-induced killer (CIK) cells display a potent cytolytic activity. The adhesion molecule lymphocyte function-associated antigen-1 plays a crucial role in binding as well as in cytolytic activity of CIK cells against tumor target cells expressing the corresponding ligands. CIK cells express activating natural killer (NK) receptors, including NKG2D, DNAX accessory molecule-1 (DNAM-1), and low levels of NKp30. Cell signaling not only through TCR/CD3 but also through NKG2D, DNAM-1, and NKp30 leads to CIK cell activation resulting in granule exocytosis, cytokine secretion, and cytotoxicity. Antibody blocking experiments showed that DNAM-1, NKG2D, and NKp30 are involved in the TCR-independent tumor cell recognition and killing. Anti-CMV-specific CIK cells could be expanded in standard CIK cultures and mediate both specific, MHC-restricted recognition and TCR-independent NK-like cytolytic activity against leukemic cell lines or fresh leukemic blasts. Antibody blocking of lymphocyte function-associated antigen-1 and DNAM-1 led to significant reduction of both CTL and NK-cell functions, whereas blocking of NKG2D and NKp30 only inhibited NK-like cytotoxicity. Their dual-effector function suggests that CIK cells, when used in a clinical setting, may control both neoplastic relapses and viral infections, 2 frequently associated complications in patients who received a transplant.     

CTLA-4 dysregulation of self/tumor-reactive CD8+ T-cell function is CD4+ T-cell dependent

Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) maintains peripheral tolerance by suppressing T-cell activation and proliferation but its precise role in vivo remains unclear. We sought to elucidate the impact of CTLA-4 expression on self/tumor-reactive CD8(+) T cells by using the glycoprotein (gp) 100-specific T-cell receptor (TCR) transgenic mouse, pmel-1. pmel-1 CLTA-4(-/-) mice developed profound, accelerated autoimmune vitiligo. This enhanced autoimmunity was associated with a small but highly activated CD8(+) T-cell population and large numbers of CD4(+) T cells not expressing the transgenic TCR. Adoptive transfer of pmel-1 CLTA-4(-/-) CD8(+) T cells did not mediate superior antitumor immunity in the settings of either large established tumors or tumor challenge, suggesting that the mere absence of CTLA-4-mediated inhibition on CD8(+) T cells did not directly promote enhancement of their effector functions. Removal of CD4(+) T cells by crossing the pmel-1 CLTA-4(-/-) mouse onto a Rag-1(-/-) background resulted in the complete abrogation of CD8(+) T-cell activation and autoimmune manifestations. The effects of CD4(+) CLTA-4(-/-) T cells were dependent on the absence of CTLA-4 on CD8(+) T cells. These results indicated that CD8(+) CLTA-4(-/-) T-cell-mediated autoimmunity and tumor immunity required CD4(+) T cells in which the function was dysregulated by the absence of CTLA-4-mediated negative costimulation.     

High- and low-affinity single-peptide/MHC ligands have distinct effects on the development of mucosal CD8αα and CD8αβ T lymphocytes

In this study, we compared the influence of two peptides on the selection of CD8alphaalpha and CD8alphabeta intraepithelial lymphocytes (IELs) of the intestine, which develop by a unique and partially thymus-independent process. Mice were used in which all T cells carried one transgenic T cell antigen receptor (TCR) (F5), and in which only well defined transgenic peptides were presented by H-2Db. The first peptide, for which the F5 TCR has a high affinity, derives from the influenza virus nucleoprotein (NP68). The second peptide, NP34, is an antagonistic variant of NP68 and is recognized by the F5 TCR with low affinity. To avoid presentation of endogenous peptides or production of T cells carrying alternative TCRs, F5 TCR transgenic mice were generated that were deficient for Tap-1 and Rag-1. In these mice, no CD3(+)CD8(+) cells were found in lymph nodes, spleen, or intestine. Introduction of transgenes encoding either NP34 or NP68 along with an endoplasmic reticulum signal sequence enabled Tap-1-independent expression of each peptide in these mice. Positive selection of F5TCR+CD8(+) thymocytes was not rescued by these transgenic peptides. However, the high-affinity NP68 peptide induced maturation of CD8alphaalpha IEL, whereas the low-affinity NP34 peptide stimulated development of both CD8alphabeta and CD8alphaalpha IEL, but in smaller numbers. When both peptides were present, CD8alphabeta T cells failed to develop and the number of CD8alphaalpha IELs was lower than in mice carrying the NP68 transgene alone. These data demonstrate that single ligands with a high or low affinity for TCR are capable of inducing or inhibiting the maturation of alternative subsets of IELs.     

T cells from epicutaneously immunized mice are prone to T cell receptor revision

Epicutaneous immunization of T cell receptor (TCR) transgenic (Tg) mice whose CD4(+) T cells are specific for the Ac1-11 fragment of myelin basic protein (MBP) with Ac1-11 elicits T cells with dominant suppressor/regulatory activity that confers protection against Ac1-11-induced experimental autoimmune encephalomyelitis. We now report that such disease-resistant MBP TCR Tg mice also harbor a sizeable fraction of peripheral CD4(+) T cells lacking surface expression of the Tg TCR beta chain and expressing diverse, endogenously rearranged TCR beta chains. Ex vivo incubation at physiological temperature caused the loss of neo-beta-chain expression and reversion to the MBP alphabeta TCR(+) phenotype. The presence of recombination activating gene 1 and 2 proteins in CD4(+) T cells with revised TCRs was consistent with effective V(D)J recombination activity. The emergence of these cells did not depend on the thymic compartment. We conclude that in mice epicutaneously immunized with an autoantigen, peripheral specific T cells are susceptible to multiple mechanisms of tolerance.     

4-1BB regulates NKG2D costimulation in human cord blood CD8+ T cells

Ligation of NKG2D, a potent costimulatory receptor, can be either beneficial or detrimental to CD8(+) cytotoxic T cell (CTL) responses. Factors for these diverse NKG2D effects remain elusive. In this study, we demonstrate that 4-1BB, another costimulatory receptor, is an essential regulator of NKG2D in CD8(+) T cells. Costimulation of NKG2D caused down-modulation of NKG2D, but induced 4-1BB expression on the cell surface, even in the presence of TGF-beta1, which inhibits 4-1BB expression. Resulting NKG2D(-)4-1BB(+) cells were activated but still in an immature state with low cytotoxic activity. However, subsequent 4-1BB costimulation induced cytotoxic activity and restored down-modulated NKG2D. The cytotoxic activity and NKG2D expression induced by 4-1BB on NKG2D(+)4-1BB(+) cells were refractory to TGF-beta1 down-modulation. Such 4-1BB effects were enhanced by IL-12. In contrast, in the presence of IL-4, 4-1BB effects were abolished because IL-4 down-modulated NKG2D and 4-1BB expression in cooperation with TGF-beta1, generating another CD8(+) T-cell type lacking both NKG2D and 4-1BB. These NKG2D(-)4-1BB(-) cells were inert and unable to gain cytotoxic activity. Our results suggest that 4-1BB plays a critical role in protecting NKG2D from TGF-beta1-mediated down-modulation. Co-expression of NKG2D and 4-1BB may represent an important biomarker for defining competency of tumor infiltrating CD8(+) T cells.     

Tpl2 and ERK transduce antiproliferative T cell receptor signals and inhibit transformation of chronically stimulated T cells

The protein kinase encoded by the Tpl2 protooncogene plays an obligatory role in the transduction of Toll-like receptor and death receptor signals in macrophages, B cells, mouse embryo fibroblasts, and epithelial cells in culture and promotes inflammatory responses in animals. To address its role in T cell activation, we crossed the T cell receptor (TCR) transgene 2C, which recognizes class I MHC presented peptides, into the Tpl2(-/-) genetic background. Surprisingly, the TCR2C(tg/tg)/Tpl2(-/-) mice developed T cell lymphomas with a latency of 4-6 months. The tumor cells were consistently TCR2C(+)CD8(+)CD4(-), suggesting that they were derived either from chronically stimulated mature T cells or from immature single positive (ISP) cells. Further studies showed that the population of CD8(+) ISP cells was not expanded in the thymus of TCR2C(tg/tg)/Tpl2(-/-) mice, making the latter hypothesis unlikely. Mature peripheral T cells of Tpl2(-/-) mice were defective in ERK activation and exhibited enhanced proliferation after TCR stimulation. The same cells were defective in the induction of CTLA4, a negative regulator of the T cell response, which is induced by TCR signals via ERK. These findings suggest that Tpl2 functions normally in a feedback loop that switches off the T cell response to TCR stimulation. As a result, Tpl2, a potent oncogene, functions as a tumor suppressor gene in chronically stimulated T cells.     

Expansion of a unique CD57⁺NKG2Chi natural killer cell subset during acute human cytomegalovirus infection

During human CMV infection, there is a preferential expansion of natural killer (NK) cells expressing the activating CD94-NKG2C receptor complex, implicating this receptor in the recognition of CMV-infected cells. We hypothesized that NK cells expanded in response to pathogens will be marked by expression of CD57, a carbohydrate antigen expressed on highly mature cells within the CD56(dim)CD16(+) NK cell compartment. Here we demonstrate the preferential expansion of a unique subset of NK cells coexpressing the activating CD94-NKG2C receptor and CD57 in CMV(+) donors. These CD57(+)NKG2C(hi) NK cells degranulated in response to stimulation through their NKG2C receptor. Furthermore, CD57(+)NKG2C(hi) NK cells preferentially lack expression of the inhibitory NKG2A receptor and the inhibitory KIR3DL1 receptor in individuals expressing its HLA-Bw4 ligand. Moreover, in solid-organ transplant recipients with active CMV infection, the percentage of CD57(+)NKG2C(hi) NK cells in the total NK cell population preferentially increased. During acute CMV infection, the NKG2C(+) NK cells proliferated, became NKG2C(hi), and finally acquired CD57. Thus, we propose that CD57 might provide a marker of "memory" NK cells that have been expanded in response to infection.     

Mononuclear myeloid-derived "suppressor" cells express RAE-1 and activate natural killer cells

Myeloid-derived suppressor cells (MDSCs) accumulate in cancer patients and tumor-bearing mice and potently suppress T-cell activation. In this study, we investigated whether MDSCs regu-late natural killer (NK)-cell function. We discovered that mononuclear Gr-1(+)CD11b(+)F4/80(+) MDSCs isolated from RMA-S tumor-bearing mice do not suppress, but activate NK cells to produce high amounts of IFN-gamma. Gr-1(+)CD11b(+)F4/80(+) MDSCs isolated from tumor-bearing mice, but not myeloid cells from naive mice, expressed the ligand for the activating receptor NKG2D, RAE-1. NK-cell activation by MDSCs depended partially on the interaction of NKG2D on NK cells with RAE-1 on MDSCs. NK cells eliminated Gr-1(+)CD11b(+)F4/80(+) MDSCs in vitro and upon adoptive transfer in vivo. Finally, depletion of Gr-1(+) cells that comprise MDSCs confirmed their protective role against the NK-sensitive RMA-S lymphoma in vivo. Our study reveals that MDSCs do not suppress all aspects of antitumor immune responses and defines a novel, unexpected activating role of MDSCs on NK cells. Thus, our results have great impact on the design of immune therapies against cancer aiming at the manipulation of MDSCs.     

CD4(+)CD25(+) T-cell development is regulated by at least 2 distinct mechanisms.

It has recently been shown that CD4(+)CD25(+) T cells are immunoregulatory T cells that prevent CD4(+) T-cell-mediated organ-specific autoimmune diseases. In this study, the regulatory mechanism of CD4(+)CD25(+) T-cell development were investigated using T-cell receptor (TCR) transgenic mice. It was found that CD4(+)CD25(+) T cells preferentially expressed the endogenous TCRalpha chain in DO10(+) TCR transgenic mice compared with CD4(+)CD25(-) T cells. Moreover, it was found that CD4(+)CD25(+) thymocytes were severely decreased in DO10(+) TCR-alpha(-/-) mice in positively selecting and negatively selecting backgrounds, whereas CD4(+)CD25(-) thymocytes efficiently developed by transgenic TCR in DO10(+) TCR-alpha(-/-) mice in positively selecting backgrounds, indicating that the appropriate affinity of TCR to major histocompatibility complex (MHC) for the development of CD4(+)CD25(+) thymocytes is different from that of CD4(+)CD25(-) thymocytes and that a certain TCR-MHC affinity is required for the development of CD4(+)CD25(+) thymocytes. Finally, it was found that, in contrast to thymus, CD4(+)CD25(+) T cells were readily detected in spleen of DO10(+) TCR-alpha(-/-) mice in positively selecting backgrounds and that splenic CD4(+)CD25(+) T cells, but not CD4(+)CD25(+) thymocytes, were significantly decreased in B-cell-deficient mice, suggesting that B cells may control the peripheral pool of CD4(+)CD25(+) T cells. Together, these results indicate that the development of CD4(+)CD25(+) T cells in thymus and the homeostasis of CD4(+)CD25(+) T cells in periphery are regulated by distinct mechanisms.