TCR transgenic CD8+ T cells activated in the presence of TGFbeta express FoxP3 and mediate linked suppression of primary immune responses and cardiac allograft rejection

Intestinal cDC1 drive cross-tolerance to epithelial-derived antigen via induction of FoxP3+CD8+ Tregs

Although CD8⁺ T cell tolerance to tissue-specific antigen (TSA) is essential for host homeostasis, the mechanisms underlying peripheral cross-tolerance and whether they may differ between tissue sites remain to be fully elucidated. Here, we demonstrate that peripheral cross-tolerance to intestinal epithelial cell (IEC)-derived antigen involves the generation and suppressive function of FoxP3⁺CD8⁺ T cells. FoxP3⁺CD8⁺ T_reg generation was dependent on intestinal cDC1, whose absence led to a break of tolerance and epithelial destruction. Mechanistically, intestinal cDC1-derived PD-L1, TGFβ, and retinoic acid contributed to the generation of gut-tropic CCR9⁺CD103⁺FoxP3⁺CD8⁺ T_regs Last, CD103-deficient CD8⁺ T cells lacked tolerogenic activity in vivo, indicating a role for CD103 in FoxP3⁺CD8⁺ T_reg function. Our results describe a role for FoxP3⁺CD8⁺ T_regs in cross-tolerance in the intestine for which development requires intestinal cDC1.

Suppression of Chlamydial Pathogenicity by Nonspecific CD8+ T Lymphocytes

Chlamydia trachomatis, a leading infectious cause of tubal infertility, induces upper genital tract pathology, such as hydrosalpinx, which can be modeled with Chlamydia muridarum infection in mice. Following C. muridarum inoculation, wild-type mice develop robust hydrosalpinx, but OT1 mice fail to do so because their T cell receptors are engineered to recognize a single ovalbumin epitope (OVA457-462). These observations have demonstrated a critical role of Chlamydia-specific T cells in chlamydial pathogenicity. In the current study, we have also found that OT1 mice can actively inhibit chlamydial pathogenicity. First, depletion of CD8+ T cells from OT1 mice led to the induction of significant hydrosalpinx by Chlamydia, indicating that CD8+ T cells are necessary to inhibit chlamydial pathogenicity. Second, adoptive transfer of CD8+ T cells from OT1 mice to CD8 knockout mice significantly reduced chlamydial induction of hydrosalpinx, demonstrating that OT1 CD8+ T cells are sufficient for attenuating chlamydial pathogenicity in CD8 knockout mice. Finally, CD8+ T cells from OT1 mice also significantly inhibited hydrosalpinx development in wild-type mice following an intravaginal inoculation with Chlamydia Since T cells in OT1 mice are engineered to recognize only the OVA457-462 epitope, the above observations have demonstrated a chlamydial antigen-independent immune mechanism for regulating chlamydial pathogenicity. Further characterization of this mechanism may provide information for developing strategies to reduce infertility-causing pathology induced by infections.

Indoleamine 2,3-dioxgenase-transfected mesenchymal stem cells suppress heart allograft rejection by increasing the production and activity of dendritic cells and regulatory T cells

Expression of indoleamine 2,3-dioxygenase (IDO) in mesenchymal stem cells (MSC) is thought to contribute to MSC-mediated immunosuppression. A lentiviral-based transgenic system was used to generate bone marrow stem cells (BMSC) which stably expressed IDO (IDO-BMSCs). Coculture of IDO-BMSCs with dendritic cells (DC) or T cells was used to evaluate the immunomodulatory effect of IDO-BMSCs. A heterotopic heart transplant model in rats was used to evaluate allograft rejection after IDO-BMSC treatment. Mechanisms of IDO-BMSC-mediated immunosuppression were investigated by evaluating levels of proinflammatory and anti-inflammatory cytokines, and production of Tregs. A significant decrease in DC marker-positive cells and a significant increase in Tregs were observed in IDO-BMSC cocultured. Treatment of transplanted rats with IDO-BMSCs was associated with significantly prolonged graft survival. Compared with the control groups, transplanted animals treated with IDO-BMSCs had a (1) significantly higher ejection fraction and fractional shortening, (2) significantly lower expression of CD86, CD80, and MHCII, and significantly higher expression in CD274, and Tregs, and (3) significantly higher levels of interleukin-10 (IL-10), transforming growth factor beta-1 (TGF-β1), TGF-β2, and TGF-β3, and significantly lower levels of IL-2 and interferon gamma. Our results expand our understanding of the molecular mechanisms underlying suppression of heart allograft rejection via IDO-expressing BMSCs.

Cancer Cell-targeted and Activatable Photoimmunotherapy Spares T Cells in a 3D Coculture Model

Photodynamic therapy (PDT) is an established therapeutic modality that uses nonionizing near-infrared light to activate photocytotoxicity of endogenous or exogenous photosensitizers (PSs). An ongoing avenue of cancer research involves leveraging PDT to stimulate antitumor immune responses; however, these effects appear to be best elicited in low-dose regimens that do not provide significant tumor reduction using conventional, nonspecific PSs. The loss of immune enhancement at higher PDT doses may arise in part from indiscriminate damage to local immune cell populations, including tumor-infiltrating T cells. We previously introduced "tumor-targeted, activatable photoimmunotherapy" (taPIT) using molecular-targeted and cell-activatable antibody-PS conjugates to realize precision tumor photodamage with microscale fidelity. Here, we investigate the immune cell sparing effect provided by taPIT in a 3D model of the tumor immune microenvironment. We report that high-dose taPIT spares 25% of the local immune cell population, five times more than the conventional PDT regimen, in a 3D coculture model incorporating epithelial ovarian cancer cells and T cells. These findings suggest that the enhanced selectivity of taPIT may be utilized to achieve local tumor reduction with sparing of intratumor effector immune cells that would otherwise be lost if treated with conventional PDT.

An immunogenic phenotype in paternal antigen-specific CD8+ T cells at embryo implantation elicits later fetal loss in mice

Central to pregnancy success is a state of T cell tolerance to paternal antigens, which is initiated at conception. The role and regulation of specific phenotypes of CD8⁺ T cells in mediating pregnancy tolerance is not clear. This study aimed to investigate the impact on pregnancy outcome of altering the cytokine environment during maternal CD8⁺ T cell priming in early pregnancy. Transgenic Act-mOVA male mice were mated to C57BL/6 (B6) females to generate fetuses expressing ovalbumin (OVA) as a model paternal antigen. OVA-reactive CD8⁺ OT-I T cells were activated in vitro with OVA in the presence of either transforming growth factor-β1 (TGFB1) plus interleukin-10 (IL10), or IL2, to mimic normal or dysregulated uterine conditions, respectively, and transferred into pregnant mice on gestational day 3.5. OT-I T cells activated with TGFB1 and IL10, like naive OT-I T cells, did not alter embryo implantation or fetal viability. In contrast, OT-I T cells activated with IL2 caused extensive fetal loss manifesting in mid-gestation. IL2-activated OT-I T cells expressed less FOXP3 and higher interferon-γ (IFNG) than cells activated with TGFB1 and IL10. Fetal loss did not occur in females mated with B6 males, demonstrating the antigen specificity of fetal loss, and was not abrogated by maternal genetic C1q deficiency indicating a mechanism independent of antibody-mediated cytotoxicity. These data indicate that alternative phenotypes generated in maternal CD8⁺ T cells at the time of priming with paternal antigens can impact pregnancy outcome, such that inappropriate activation of CD8⁺ T cells before implantation is capable of causing antigen-specific fetal loss later in pregnancy.

Natural Killer T Cells Contribute to Neutrophil Recruitment and Ocular Tissue Damage in a Model of Intraocular Tumor Rejection

PURPOSE

Immune privilege of the eye protects the nonregenerative ocular tissues from innate and adaptive immune-mediated inflammation. In the case of intraocular tumors, immune privilege can be arrested to allow for immune-mediated rejection. Activation of innate immune cells can contribute to necrosis of the intraocular tumor and bystander ocular tissue. Identifying the cellular components of the innate immune system that contribute to ocular destruction, but are not needed for tumor rejection, provides insights into the immunopathological sequelae in intraocular tumor rejection.

METHODS

Wild-type (WT), Jα18 knockout (KO) mice lacking type I natural killer T (NKT) cells, and CD1d KO mice lacking all NKT cells, were used to identify the role of type II NKT cells in intraocular tumor rejection immunopathology.

RESULTS

CD1d KO mice had significantly lowered rates of necrotic eye destruction during tumor rejection compared to WT or Jα18 KO mice. Transcriptome and protein analyses revealed that CD1d KO mice had significantly lower expression of CXCL3 compared to WT or Jα18 KO mice, and this was associated with decreased neutrophil recruitment. The presence of type II NKT cells in WT or Jα18 KO mice led to increased CXCL3, which attracted neutrophils to the intraocular tumor and culminated in destruction of the eye.

CONCLUSIONS

We found that type II NKT cells are critical in initiating a damaging inflammatory antitumor response involving the recruitment of neutrophils that compromises the integrity of the eye. Loss of type II NKT cells or depleting neutrophils allows for a productive intraocular tumor response that converts the rejection phenotype to preserve the eye.

Allospecific Tregs Expanded After Anergization Remain Suppressive in Inflammatory Conditions but Lack Expression of Gut-homing Molecules

Cell therapy with antigen-specific regulatory T-cells (Treg) has great potential to selectively control unwanted immune responses after allogeneic stem-cell or solid organ transplantation and in autoimmune diseases. Ex vivo allostimulation with costimulatory blockade (alloanergization) of human T-cells expands populations of alloantigen-specific Treg, providing a cellular strategy to control donor T-cell alloresponses causing graft-versus-host disease after allogeneic hematopoietic stem-cell transplantation. Crucially, it is not known if Treg expanded in this way are stable in proinflammatory conditions encountered after transplantation, or if they possess capacity to migrate to key target organs. Using an in vitro model to functionally characterize human Treg expanded after alloanergization, we now show that these cells remain potently allosuppressive in the presence of relevant exogenous inflammatory signals. Expanded allospecific Treg retained expression of molecules conferring migratory capacity to several organs but small intestine-specific chemotaxis was markedly impaired, in keeping with the preponderance of gut graft-versus-host disease in previous clinical studies using this strategy. Importantly, impaired gut-specific chemotaxis could be partially corrected by pharmacological treatment. These findings will facilitate more effective application of this cellular approach to limit T-cell alloresponses after hematopoietic stem-cell transplantation and the wider application of the strategy to other clinical settings.

Advances on Non-CD4 + Foxp3+ T Regulatory Cells: CD8+, Type 1, and Double Negative T Regulatory Cells in Organ Transplantation

The overwhelming body of research on T regulatory cells (Treg) has focused on CD4 + CD25 + Foxp3+ T cells. However, recent years have witnessed a resurgence in interest in CD4 - CD8+, CD4 - CD8- (double negative [DN]), and CD4 + Foxp3- type 1 Treg (Tr1) Treg and their role in controlling autoimmune diseases and in promoting the survival of organ allografts and xenografts. CD8+ and DN Treg can arise spontaneously (natural Treg) or can be induced in situ. Both CD8+ and DN Treg have been shown to enhance the survival of organ allografts and xenografts. Additionally, both can suppress alloimmune responses by contact-dependent mechanisms by either inducing apoptosis or mediating direct cytolysis of effector T cells. CD8+, DN, and Tr1 Treg can also act in a contact-independent manner by elaborating soluble immunosuppressive factors, such as TGF-β and IL-10. Applying CD8+, DN, and Tr1 Treg for enhancing the survival of organ allografts and xenografts is still in its infancy but holds significant potential. Furthermore, there is a need for a more comprehensive understanding of how current immunosuppressive therapies applied to organ transplantations affect the wide array of Treg populations.

Microparticulate β-glucan vaccine conjugates phagocytized by dendritic cells activate both naïve CD4 and CD8 T cells in vitro

Microparticulate β-glucan (MG) conjugated to vaccine antigen has been shown to serve as an effective adjuvant in vivo. To further study antigen presentation by MG:vaccine conjugates, bone marrow-derived dendritic cells (BMDC) were treated with MG conjugated to ovalbumin (OVA), then interacted with splenocytes from DO11.10 transgenic mice expressing an OVA peptide-specific T cell receptor. BMDC treated with MG:OVA induced significantly higher numbers of activated (CD25+CD69+) OVA-specific CD4+ T cells than BMDC treated with OVA alone. BMDC treated with MG:OVA upregulated CD86 and CD40 expression as well as MG alone, indicating that conjugation of OVA does not alter the immunostimulatory capacity of MG. Activation of CD8+ OVA-specific OT-1 cells showed that MG:OVA is also capable of enhancing cross-presentation by BMDC to CD8+ cytotoxic T cells. These results show that MG acts as an adjuvant to enhance antigen presentation by dendritic cells to naïve, antigen-specific CD4 and CD8 T cells.

Memory of tolerance and induction of regulatory T cells by erythrocyte-targeted antigens

New approaches based on induction of antigen-specific immunological tolerance are being explored for treatment of autoimmunity and prevention of immunity to protein drugs. Antigens associated with apoptotic debris are known to be processed tolerogenically in vivo. Our group is exploring an approach toward antigen-specific tolerization using erythrocyte-binding antigens, based on the premise that as the erythrocytes circulate, age and are cleared, the erythrocyte surface-bound antigen payload will be cleared tolerogenically along with the eryptotic debris. Here, we characterized the phenotypic signatures of CD8+ T cells undergoing tolerance in response to soluble and erythrocyte-targeted antigen. Signaling through programmed death-1/programmed death ligand-1 (PD-1/PD-L1), but not through cytotoxic T lymphocyte antigen 4 (CTLA4), was shown to be required for antigen-specific T cell deletion, anergy and expression of regulatory markers. Generation of CD25+FOXP3+ regulatory T cells in response to erythrocyte-targeted antigens but not soluble antigen at an equimolar dose was observed, and these cells were required for long-term maintenance of immune tolerance in both the CD4+ and CD8+ T cell compartments. Evidence of infectious tolerance was observed, in that tolerance to a one antigenic epitope was able to regulate responses to other epitopes in the same protein antigen.

Phenotypic and functional characteristic of a newly identified CD8+ Foxp3- CD103+ regulatory T cells

TGF-β and Foxp3 expressions are crucial for the induction and functional activity of CD4(+)Foxp3(+) regulatory T (iTreg) cells. Here, we demonstrate that although TGF-β-primed CD8(+) cells display much lower Foxp3 expression, their suppressive capacity is equivalent to that of CD4(+) iTreg cells, and both Foxp3(-) and Foxp3(+) CD8+ subsets have suppressive activities in vitro and in vivo. CD8(+)Foxp3(-) iTreg cells produce little IFN-γ but almost no IL-2, and display a typical anergic phenotype. Among phenotypic markers expressed in CD8(+)Foxp3(-) cells, we identify CD103 expression particularly crucial for the generation and function of this subset. Moreover, IL-10 and TGF-β signals rather than cytotoxicity mediate the suppressive effect of this novel Treg population. Therefore, TGF-β can induce both CD8(+)Foxp3(-) and CD8(+)Foxp3(+) iTreg subsets, which may represent the unique immunoregulatory means to treat autoimmune and inflammatory diseases.

Participation of T regulatory cells in equine recurrent airway obstruction

Recurrent airway obstruction (RAO) is an equine immune-mediated disease with a high incidence worldwide. The aim of this work was to contribute to the understanding of RAO pathogenesis by studying T cells bearing regulatory markers in peripheral blood (PB) and in bronchoalveolar lavage fluid (BALF) recovered from the same group of susceptible horses before and after exposure to moldy hay, which has been shown to induce RAO signology in our horse herd. With this purpose, mononuclear cells were obtained from the BALF and PB from horses before and after antigenic challenge and were stained with fluorochrome-conjugated antibodies against CD4, CD25 and Foxp3 and subsequently analyzed by flow cytometry. The results indicated that the percentage of CD4+, Foxp3+ cells clearly increased in PB and BALF obtained from horses with RAO. In addition, the percentage of CD4+, CD25(high) cells was greatly augmented in BALF of RAO positive horses compared with a baseline. No changes were observed in the PB compartment. The percentage of CD4+, CD25(high), Foxp3+ cells in BALF increased in horses with active disease compared to horses in remission; this cell population also does not show changes in the PB compartment when RAO positive and RAO negative horses were compared. On the other hand, when the percentage of CD4, Foxp3 positive cells were compared with the percentage of CD4+, CD25(high) cells, the numbers were very similar. This observation was true for PB and BALF cells from non exposed horses as well as horses exposed to antigen. In all the experimental situations studied, the population expressing all of the markers CD4+, CD25(high), Foxp3+ represent only a minor percentage of CD4+, CD25(high) or CD4+, Foxp3 subpopulations; therefore, an significant number of CD4+, CD25(high), Foxp3- and CD4+, CD25(null), Foxp3+ cells must exist. Finally, we conclude that horses with RAO show an airway accumulation of T cells bearing regulatory markers that probably are modulating the course of this disease, and that these T cells may be involved in the resolution of immune-mediated bronchial inflammation.

Therapeutic polyclonal human CD8+ CD25+ Fox3+ TNFR2+ PD-L1+ regulatory cells induced ex-vivo

We report that polyclonal CD8regs generated in one week ex-vivo with anti-CD3/28 beads and cytokines rapidly developed suppressive activity in vitro sustained by TGF-β. In immunodeficient mice, these CD8regs demonstrated a markedly protective, IL-10 dependent activity against a xeno-GVHD. They expressed IL-2Rα/β, Foxp3, TNFR2, and the negative co-stimulatory receptors CTLA-4, PD-1, PD-L1 and Tim-3. Suppressive activity in vitro correlated better with TNFR2 and PD-L1 than Foxp3. Blocking studies suggested that TNF enhanced PD-L1 expression and the suppressive activity of the CD8regs generated. Unlike other polyclonal CD4 and CD8 Tregs, these CD8regs preferentially targeted allogeneic T cells, but they lacked cytotoxic activity against them even after sensitization. Unlike CD4regs, these CD8regs could produce IL-2 and proliferate while inhibiting target cells. If these CD8regs can persist in foreign hosts without impairing immune surveillance, they could serve as a practical remission-inducing product for the treatment of autoimmune diseases, graft-versus-host disease, and allograft rejection.

Donor bone marrow-derived T cells inhibit GVHD induced by donor lymphocyte infusion in established mixed allogeneic hematopoietic chimeras

Delayed administration of donor lymphocyte infusion (DLI) to established mixed chimeras has been shown to achieve anti-tumor responses without graft-vs.-host disease (GVHD). Herein we show that de novo donor BM-derived T cells that are tolerant of the recipients are important in preventing GVHD in mixed chimeras receiving delayed DLI. Mixed chimeras lacking donor BM-derived T cells developed significantly more severe GVHD than those with donor BM-derived T cells after DLI, even though both groups had comparable levels of total T cells at the time of DLI. Post-DLI depletion of donor BM-derived T cells in mixed chimeras, as late as 20 days after DLI, also provoked severe GVHD. Although both CD4 and CD8 T cells contributed to the protection, the latter were significantly more effective, suggesting that inhibition of GVHD was not mainly mediated by CD4 regulatory T cells. The lack of donor BM-derived T cells was associated with markedly increased accumulation of DLI-derived alloreactive T cells in parenchymal GVHD target tissues. Thus, donor BM-derived T cells are an important factor in determining the risk of GVHD and therefore, offer a potential therapeutic target for preventing and ameliorating GVHD in the setting of delayed DLI in established mixed chimeras.

Influence of CD8+ T regulatory cells on intraocular tumor development

The interior of the eye, or uvea, is a site of immune privilege where certain immune responses are attenuated or completely excluded to protect non-regenerating tissues essential for vision. One consequence of this immunoregulation is compromised immune mediated elimination of intraocular tumors. For example, certain murine tumor cell lines which are rejected by host immune responses when transplanted in the skin grow progressively when placed in the anterior chamber (a.c.) of the eye. Progressive ocular tumor growth occurs despite induction of tumor-specific CD8+ T cell responses capable of eliminating a subsequent tumor challenge in the skin or opposite eye. Why these CD8+ T effectors fail to eliminate established ocular tumors is not known. It is well appreciated that growth of tumors in the a.c. induces the generation of immunosuppressive CD8+ T regulatory (Treg) cells. However, the contribution of CD8+ Treg in ocular tumor progression remains unclear. Several studies indicate that these CD8+ Treg target responding CD4+ T cells to inhibit their induction of macrophage-dependent delayed type hypersensitivity (DTH) responses to tumor antigens (Ags). However, induction of tumor-specific CD4+ T cell responses does not assure intraocular tumor elimination. This review is focused on how CD8+ Treg could influence the tumoricidal activity of ocular tumor-specific CD8+ T effector cells.

Common gamma chain cytokines promote rapid in vitro expansion of allo-specific human CD8+ suppressor T cells

Human CD8⁺ regulatory T cells, particularly the CD8⁺CD28⁻ T suppressor cells, have emerged as an important modulator of alloimmunity. Understanding the conditions under which these cells are induced and/or expanded would greatly facilitate their application in future clinical trials. In the current study, we develop a novel strategy that combines common gamma chain (γc) cytokines IL-2, IL-7 and IL-15 and donor antigen presenting cells (APCs) to stimulate full HLA-mismatched allogeneic human CD8⁺ T cells which results in significant expansions of donor-specific CD8⁺CD28⁻ T suppressor cells in vitro. The expanded CD8⁺CD28⁻ T cells exhibit increased expressions of CTLA-4, FoxP3, and CD25, while down-regulate expressions of CD56, CD57, CD127, and perforin. Furthermore, these cells suppress proliferation of CD4⁺ T cells in a contact-dependent and cytokine-independent manner. Interestingly, the specificity of suppression is restricted by the donor HLA class I antigens but promiscuous to HLA class II antigens, providing a potential mechanism for linked suppression. Taken together, our results demonstrate a novel role for common γc cytokines in combination with donor APCs in the expansion of donor-specific CD8⁺CD28⁻ T suppressor cells, and represent a robust strategy for in vitro generation of such cells for adoptive cellular immunotherapy in transplantation.

Immune amplification of murine CD8 suppressor T cells induced via an immune-privileged site: quantifying suppressor T cells functionally

Background

CD8⁺ suppressor T cells exert antigen-specific suppression of the expression of hypersensitivity by activated T cells. Therefore, CD8⁺ suppressor T cells serve a major regulatory role for the control of active immunity. Accordingly, the number and/or activity of CD8⁺ suppressor T cells should be influenced by an immune response to the antigen. To test this hypothesis we used an adoptive transfer assay that measures the suppression of the expression of delayed-type hypersensitivity (DTH) by CD8⁺ suppressor T cells to quantify the antigen-specific suppression of DTH by these suppressor T cells.

Methods

Suppressor T cells were induced in the spleens of mice by the injection of antigen into the anterior chamber of an eye. Following this injection, the mice were immunized by the same antigen injected into the anterior chamber. Spleen cells recovered from these mice (AC-SPL cells) were titrated in an adoptive transfer assay to determine the number of AC-SPL cells required to effect a 50% reduction of antigen-induced swelling (Sw50) in the footpad of immunized mice challenged by antigen.

Results

Suppression of the expression of DTH is proportional to the number of AC-SPL cells injected into the site challenged by antigen. The number of AC-SPL cells required for a 50% reduction in DTH-induced swelling is reduced by injecting a cell population enriched for CD8⁺ AC-SPL cells. Immunizing the mice receiving intracameral antigen to the same antigen decreases the RSw50 of AC-SPL cells required to inhibit the expression of DTH.

Conclusions

The results provide the first quantitative demonstration that the numbers of antigen-specific splenic CD8⁺ suppressor T cells are specifically amplified by antigen during an immune response.

CD8⁺ Foxp3⁺ tumor infiltrating lymphocytes accumulate in the context of an effective anti-tumor response

The composition of tumor infiltrating lymphocytes (TIL) is heterogeneous. In addition, the ratio of various subpopulations in the tumor microenvironment is highly dependent on the nature of the host's immune response. Here, we characterize Foxp3-expressing CD8(+) T cells in the tumor that demonstrate effector function and accumulate in the context of an effective anti-tumor response. CD8(+) Foxp3(+) T cells are induced in TIL in regressing tumors of FVB/N mice treated with a GM-CSF secreting HER-2/neu targeted whole cell vaccine. Foxp3 expression in tumor antigen-specific CD8 T cells is restricted to the tumor microenvironment and influenced by cues in the tumor. Interestingly, Foxp3(+) and Foxp3(-) CD8(+) T cells have similar IFN-γ production and antigen-specific degranulation after stimulation with RNEU(420-429) , the immunodominant HER-2/neu (neu) epitope in this model. Adoptive transfer studies, using RNEU((420-429)) -specific effector T cells into neu-N mice (a model that results in immune tolerance to neu), confirm that CD8(+) Foxp3(+) T cells are present in tumors only if there is an existing pool of tumor-rejecting effector T cells. CD8(+) Foxp3(+) TILs mark the presence of tumor-rejecting antigen-specific T cells and their accumulation serves as a marker for an effective T cell response.

PPAR-γ agonist rosiglitazone protects peritoneal membrane from dialysis fluid-induced damage

Exposure to non-physiological solutions during peritoneal dialysis (PD) produces structural alterations to the peritoneal membrane and ultrafiltration dysfunction. The high concentration of glucose and glucose degradation products in standard PD fluids induce a local diabetic environment, which leads to the formation of advanced glycation end products (AGEs) that have an important role in peritoneal membrane deterioration. Peroxisome proliferator-activated receptor γ (PPAR-γ) agonists are used to treat type II diabetes and they have beneficial effects on inflammation, fibrosis, and angiogenesis. Hence, we evaluated the efficacy of the PPAR-γ agonist rosiglitazone (RSG) in ameliorating peritoneal membrane damage in a mouse PD model, and we analyzed the mechanisms underlying the protection offered by RSG. Exposure of the peritoneum to PD fluid resulted in AGEs accumulation, an inflammatory response, the loss of mesothelial cell monolayer and invasion of the compact zone by mesothelial cells, fibrosis, angiogenesis, and functional impairment of the peritoneum. Administration of RSG diminished the accumulation of AGEs, preserved the mesothelial monolayer, decreased the number of invading mesothelial cells, reduced fibrosis and angiogenesis, and improved peritoneal function. Interestingly, instead of reducing the leukocyte recruitment, RSG administration enhanced this process and specifically, the recruitment of CD3+ lymphocytes. Furthermore, RSG treatment augmented the levels of the anti-inflammatory cytokine interleukin (IL)-10 and increased the recruitment of CD4+ CD25+ FoxP3+ cells, suggesting that regulatory T cells mediated the protection of the peritoneal membrane. In cell-culture experiments, RSG did not prevent or reverse the mesothelial to mesenchymal transition, although it decreased mesothelial cells apoptosis. Accordingly, RSG appears to produce pleiotropic protective effects on the peritoneal membrane by reducing the accumulation of AGEs and inflammation, and by preserving the mesothelial cells monolayer, highlighting the potential of PPAR-γ activation to ameliorate peritoneal deterioration in PD patients.

Identification of regulatory Foxp3+ invariant NKT cells induced by TGF-beta

Invariant NKT (iNKT) cells were shown to prevent the onset of experimental autoimmune encephalomyelitis in mice following administration of their specific TCR agonist alpha-galactosylceramide. We found that this protection was associated with the emergence of a Foxp3(+) iNKT cell population in cervical lymph nodes. We demonstrate that the differentiation of these cells is critically dependent on TGF-beta in both mice and humans. Moreover, in vivo generation of Foxp3(+) iNKT cells was observed in the TGF-beta-rich environment of the murine gut. Foxp3(+) iNKT cells displayed a phenotype similar to that of Foxp3(+) regulatory T cells, and they suppress through a contact-dependent, glucocorticoid-induced TNFR-mediated mechanism. Nevertheless, Foxp3(+) iNKT cells retain distinctive NKT cell characteristics, such as promyelocytic leukemia zinc finger protein expression and preferential homing to the liver following adoptive transfer, where they stably maintained Foxp3 expression. Our data thus unveil an unexpected capacity of iNKT cells to acquire regulatory functions that may contribute to the establishment of immunological tolerance.

IL-17 promotes tumor development through the induction of tumor promoting microenvironments at tumor sites and myeloid-derived suppressor cells

The role of immune responses in tumor development is a central issue for tumor biology and immunology. IL-17 is an important cytokine for inflammatory and autoimmune diseases. Although IL-17-producing cells are detected in cancer patients and tumor-bearing mice, the role of IL-17 in tumor development is controversial, and mechanisms remain to be fully elucidated. In the current study, we found that the development of tumors was inhibited in IL-17R-deficient mice. A defect in IFN-gammaR increased tumor growth, whereas tumor growth was inhibited in mice that were deficient in both IL-17R and IFN-gammaR compared with wild-type animals. Further experiments showed that neutralization of IL-17 by Abs inhibited tumor growth in wild-type mice, whereas systemic administration of IL-17 promoted tumor growth. The IL-17R deficiency increased CD8 T cell infiltration, whereas it reduced the infiltration of myeloid-derived suppressor cells (MDSCs) in tumors. In contrast, administration of IL-17 inhibited CD8 T cell infiltration and increased MDSCs in tumors. Further analysis indicated that IL-17 was required for the development and tumor-promoting activity of MDSCs in tumor-bearing mice. These data demonstrate that IL-17-mediated responses promote tumor development through the induction of tumor-promoting microenvironments at tumor sites. IL-17-mediated regulation of MDSCs is a primary mechanism for its tumor-promoting effects. The study provides novel insights into the role of IL-17 in tumor development and has major implications for targeting IL-17 in treatment of tumors.

IL-6 positively regulates Foxp3+CD8+ T cells in vivo

Although recent studies have identified regulatory roles for Foxp3(+)CD8(+) T cells, the mechanisms that induce their development and underlie their functions in vivo have not been elucidated. Here, we show that IL-6 positively regulates the Foxp3(+)CD8(+) T-cell development and function. The Foxp3(+)CD8(+) T cells that differentiated in vitro in the presence of IL-6 suppressed autoimmune colitis and arthritis in vivo. Moreover, Foxp3(+)CD8(+) T cells that developed in vivo in the presence of enhanced IL-6 signaling suppressed the development of a spontaneous T(h)17 cell-mediated autoimmune arthritis. Thus, we concluded that Foxp3(+)CD8(+) T cells develop in response to IL-6 and regulate chronic inflammation in T(h)17 cell-mediated F759 autoimmune arthritis. These results suggested that Foxp3(+)CD8(+) T cells may develop in response to IL-6 under certain inflammatory conditions in vivo and may regulate some other chronic inflammation diseases.

Translational mini-review series on Th17 cells: induction of interleukin-17 production by regulatory T cells

Uncommitted (naive) CD4(+) T helper cells (Thp) can be induced to differentiate to specific lineages according to the local cytokine milieu, towards T helper type 1 (Th1), Th2, Th17 and regulatory T cell (T(reg)) phenotypes in a mutually exclusive manner. Each phenotype is characterized by unique signalling pathways and expression of specific transcription factors, notably T-bet for Th1, GATA-3 for Th2, forkhead box P3 (FoxP3) for T(regs) and receptor-related orphan receptor (ROR)alpha and RORgammat for Th17 cells. T(regs) and Th17 cells have been demonstrated to arise from common precursors in a reciprocal manner based on exposure to transforming growth factor (TGF)-beta or TGF-beta plus interleukin (IL)-6 and carry out diametrically opposing functions, namely suppression or propagation of inflammation, respectively. However, while epigenetic modifications in Th1 and Th2 differentiated cells prevents their conversion to other phenotypes, Th17 cells generated in vitro using TGF-beta and IL-6 are unstable and can convert to other phenotypes, especially Th1, both in vitro and in vivo. T(regs) are generated from naive precursors both in the thymus (natural, nT(regs)) and in the periphery (induced, iT(regs)). The highly suppressive function of T(regs) enables them to control many inflammatory diseases in animals and makes them particularly attractive candidates for immunotherapy in humans. The stability of the T(reg) phenotype is therefore of paramount importance in this context. Recent descriptions of T(reg) biology have suggested that components of pathogens or inflammatory mediators may subvert the suppressive function of T(regs) in order to allow propagation of adequate immune responses. Unexpectedly, however, a number of groups have now described conversion of T(regs) to the Th17 phenotype induced by appropriate inflammatory stimuli. These observations are particularly relevant in the context of cell therapy but may also explain some of the dysregulation seen in autoimmune diseases. In this paper, we review T(reg) to Th17 conversion and propose some potential mechanisms for this phenomenon.

Cutting Edge: Tumor-specific CD8+ T cells infiltrating prostatic tumors are induced to become suppressor cells

We previously reported that naive, tumor-specific CD8(+) (TcR-I) T cells transferred into prostate tumor-bearing mice traffic to the prostate where they become tolerized. We now report that TcR-I cells suppress the proliferation of naive T cells. This suppression is mediated at least in part by secreted factors, and the suppressive activity can be blocked by Abs directed against TGF-beta. We further report that TcR-I cells must infiltrate the prostate to acquire suppressive activity. Delivery of tumor-specific CD4(+) T cells prevents the conversion of TcR-I cells into suppressor cells. Taken together, our findings may have critical implications for sustaining T cell responsiveness during immunotherapy, as the development of suppressor cells in the tumor microenvironment may eliminate the potency of T cells primed in the periphery or delivered during adoptive immunotherapy.

Treating autoimmune disease by targeting CD8(+) T suppressor cells

Current treatments for autoimmune disease are hampered by the non-specificity of immunomodulatory interventions, having to accept broad suppression of immunoresponsiveness with potentially serious side effects, such as infection or malignancy. The development of antigen-specific approaches, downregulating pathogenic immune responses while maintaining protective immunity, would be a major step forward. One possible approach involves the targeting of physiological regulatory mechanisms, such as inhibitory CD8 T cells that are now recognized to fine-tune many aspects of immune responses. CD8 T suppressor (Ts) cells may directly inhibit other T cells or condition antigen-presenting cells in such a way that immune amplification steps are dampened. The promise of CD8 Ts cells lies in their potential to disrupt host-injurious immune responses in a targeted fashion. For therapeutic purposes, such CD8 Ts cells could either be generated in vitro and transferred into the host or their numbers and activity could be modulated by treating the patient with established or novel immunomodulators. Emerging evidence shows that several subsets of CD8 Ts cells exist. While there is still considerable uncertainty about the molecular mechanisms through which CD8 Ts cells can reset immune responses to protect the host, their potential diagnostic and therapeutic use is intriguing and has generated renewed interest.

IL-23 drives pathogenic IL-17-producing CD8+ T cells

IL-17-producing CD8(+) T cells (Tc17) appear to play a role in a range of conditions, such as autoimmunity and cancer. Thus far, Tc17 cells have been only marginally studied, resulting in a paucity of data on their biology and function. We demonstrate that Tc17 and Th17 cells share similar developmental characteristics, including the previously unknown promoting effect of IL-21 on Tc17 cell differentiation and IL-23-dependent expression of IL-22. Both STAT1 and STAT4 are required for optimal development of Tc17 cells and maximal secretion of cytokines. Tc17 cells are cytotoxic, and they can be either pathogenic or nonpathogenic upon adoptive transfer in the model of autoimmune diabetes. Tc17 cells treated with TGF-beta1 plus IL-6 are not diabetogenic, whereas IL-23-treated cells potently induce the disease. IL-17A and IL-17F are necessary but not sufficient for diabetes induction by Tc17 cells. Tc17 cells treated with TGF-beta1 plus IL-6 or IL-23 likely differ in pathogenicity due to their disparate capacity to attract other immune cells and initiate inflammation.

T cell sensitivity to TGF-beta is required for the effector function but not the generation of splenic CD8+ regulatory T cells induced via the injection of antigen into the anterior chamber

The introduction of antigen into the anterior chamber (AC) of the eye induces the production of antigen-specific splenic CD8⁺ regulatory T cells (AC-SPL cells) that suppress a delayed-type hypersensitivity (DTH) reaction in immunized mice. Because the generation of these regulatory T cells is also induced by exposure to transforming growth factor (TGF)-β and antigen or F4/80⁺ cells exposed to TGF-β and antigen in vitro, we investigated (i) whether these cells are produced in dominant negative receptor for transforming growth factor β receptor type II (dnTGFβRII) or Cbl-b^−/− mice whose T cells are resistant to TGF-β, (ii) whether DTH is suppressed by wild type (WT) CD8⁺ AC-SPL cells in Cbl-b^−/− and dnTGFβRII mice and (iii) the effect of antibodies to TGF-β on the suppression of DTH by CD8⁺ AC-SPL cells. DnTGFβRII immunized and Cbl-b^−/− mice produced splenic CD8⁺ regulatory cells after the intracameral injection of antigen and immunization. The suppression of a DTH reaction by CD8⁺ AC-SPL cells in WT mice was blocked by the local inclusion of antibodies to TGF-β when WT splenic CD8⁺ AC-SPL cells were injected into the DTH reaction site. Moreover, the DTH reaction in immunized dnTGFβRII and Cbl-b^−/− mice was not suppressed by the transfer of WT CD8⁺ AC-SPL cells to the site challenged with antigen. In aggregate, these observations suggest that T cell sensitivity to TGF-β is not an obligate requirement for the in vivo induction of CD8⁺ AC-SPL T cells but the suppression of an in vivo DTH reaction by CD8⁺ AC-SPL cells is dependent on TGF-β.

Diversity in the contribution of interleukin-10 to T-cell-mediated immune regulation

Recent progress in our understanding of mechanisms by which the immunosuppressive cytokine interleukin-10 (IL-10) participates in an ever-increasing diversity of T-cell lineages to maintain immune homeostasis has broadened the framework for defining regulatory and effector T cells and has blurred the lines between them. In this review, we highlight established and emerging roles for IL-10 produced by distinct CD4(+) T-cell lineages that underlie its non-redundant role in curbing immune responses to the intestinal microbiota at steady state and its role to limit T-cell-driven inflammation in responses to pathogens.

Prevention of allograft rejection by amplification of Foxp3(+)CD4(+)CD25(+) regulatory T cells

CD4(+)CD25(+) T cells were identified originally as potent suppressors of autoimmunity and were later termed "natural regulatory T cells" or nTreg cells. Subsequently, a transcription factor called forkhead box protein 3 (Foxp3) was identified to be a critical regulator for Treg differentiation and function. Foxp3(+)CD4(+)CD25(+) Treg cells have been increasingly documented to suppress allograft rejection and to mediate allograft tolerance in transplantation. In this article, the authors review current approaches for amplification of allo-specific Foxp3(+)CD4(+)CD25(+) Treg cells for prevention of allograft rejection and induction of allo-specific transplant tolerance.

The suppression of hypersensitivity by ocular-induced CD8(+) T cells requires compatibility in the Qa-1 haplotype

The injection of antigen into the anterior chamber (AC, intracameral injection)2 of a murine eye induces the generation of splenic CD8⁺ regulatory T cells (AC-SPL cells) that effect the antigen-specific suppression of a Delayed-Type Hypersensitivity (DTH) reaction. Here we show (i) for the first time that the local antigen-specific suppression of DTH-induced swelling in immunized mice by either an intracameral injection of antigen or by the direct injection of CD8⁺ AC-SPL cells into an antigen-challenged site is associated with an absence of infiltrated mononuclear cells, (ii) the local antigen-specific suppression of the DTH reaction by CD8⁺ AC-SPL cells requires compatibility between the Qa-1 but not H2 antigen haplotype of the immunized recipient and the injected AC-SPL regulatory T cells, (iii) The suppression of the DTH reaction by CD8⁺ AC-SPL cells requires the expression of Qa-1 but not H2 antigens and is not due to bystander suppression.

Murine CD8+ regulatory T lymphocytes: the new era

Regulatory T lymphocytes unequivocally play a major role in the maintenance of immunologic homeostasis. The first descriptions of regulatory T lymphocytes concerned CD8(+) cells, but this field was brought into discredit when some of its central tenets turned out to be erroneous. CD4(+) regulatory T cells took over and, with the help of newly developed molecular tools, rapidly were phenotypically and functionally characterized. We now know that these cells control a large variety of immune responses. However some observations of in vitro or in vivo immune regulation could not be explained with CD4(+) regulatory T cell activity and depended on the action of a variety of CD8(+) T cell populations. In recent years, substantial progress has been made in the phenotypic and functional characterization of CD8(+) regulatory T cells. These cells play a role in the control of intestinal immunity, immunopathology, and autoimmunity, as well as in immune privilege of the eye, in oral tolerance, and in prevention of graft-versus-host disease and graft-rejection. The suppressor effector mechanisms used by these cells are in part shared with CD4(+) regulatory T cells and in part unique to this population. We here review the current literature on naturally occurring and experimentally induced murine CD8(+) regulatory T-cell populations.

CD8+ suppressor T cells resurrected

This review focuses on the role of antigen-specific T cells that mediate active inhibition of immune responses over the past 35 years since their initial description. The field has experienced several changes in the accepted paradigm of such suppressor/regulatory T cells, from initial indications that such cells were CD8(+), to the view that such cells did not exist, to the identification of the transcription factor Foxp3 as a key orchestrator of inhibitory function. Although most Foxp3(+) cells in a resting animal are CD4(+)CD25(+) cells, Foxp3 expression and inhibitory function can be induced by antigens in the periphery by selective cytokine conditions, particularly TGF-beta. Such induced T cells occur within both the CD4 and the CD8 T-cell lineages and appear to mediate suppression by inhibiting the costimulatory activity of antigen-presenting cells and the production of inhibitory cytokines. Recent data generated by analysis of TCR Tg T cells that do not select many Foxp3-positive cells during thymic development are reviewed, emphasizing the pattern of "linked suppression" and focus of the relative potency of different mechanisms of suppression.

Splenic CD8+ T cells secrete TGF-beta1 to exert suppression in mice with anterior chamber-associated immune deviation

Background CD8+ regulatory T cells (Treg) have been considered to be involved in a model of ocular-induced tolerance, known as anterior chamber-associated immune deviation (ACAID). The mechanisms of suppression by CD8+ T cells in ACAID remain only poorly understood. TGF-beta1 is considered as an inhibitory cytokine for immunosuppression in some models. The production of TGF-beta1 by CD8+ T cells in ACAID, and whether CD8+ T cells exert suppression through TGF-beta1, is unknown. Methods The suppressive effect of CD8+ T cells in ACAID mice was determined by a local adoptive transfer (LAT) assay. The production of TGF-beta1 by CD8+ T cells was measured by enzyme-linked immunosorbent assay (ELISA). Anti-TGF-beta1 antibodies were used in the LAT assay to test if they could block the inhibitory effect of CD8+ T cells. Results CD8+ T cells from ACAID mice were shown to block the delayed-type hypersensitivity (DTH) response in an antigen-specific manner in a LAT assay. These CD8+ T cells secreted TGF-beta1, and their suppression could partially be blocked by anti-TGF-beta1 antibodies. Conclusions Our study confirms that CD8+ T cells from ACAID mice possess inhibitory properties. This population exerts part of its suppressive function via the production of TGF-beta1.

CD8+ regulatory T cells are responsible for GAD-IgG gene-transferred tolerance induction in NOD mice

Our previous studies demonstrated that lipopolysaccharide (LPS)-stimulated splenocytes, retrovirally transduced with a glutamate decarboxylate 65 (GAD) and immunoglobulin G (IgG) fusion construct, can protect non-obese diabetic (NOD) mice from diabetes by inducing GAD-specific tolerance, and also that there are increased numbers of CD4(+) regulatory T cells (Tregs) in GAD-IgG-treated NOD mice. However, little is known about the role of CD8(+) Tregs in GAD-IgG gene-transferred tolerance induction in NOD mice. Here, we found that GAD-IgG-transduced splenocytes induced an increase in the number of CD8(+) Foxp3(+) Tregs in vitro. Using a T-cell depletion assay, we found that, compared with undepleted groups, NOD recipients transfused with CD8(-) or CD8(-) CD25(-) GAD-IgG-transduced splenocytes showed a decrease in the percentage of CD8(+) Foxp3(+) T cells, a high incidence of diabetes, serious insulitis, GAD-specific hyperresponsiveness at both the cellular and humoral levels, and changes in cytokine expression. These results indicate that CD8(+) Tregs, which were induced in vitro by GAD-IgG-transduced splenocytes, were also responsible for GAD-IgG gene-transferred tolerance induction in NOD mice.

Immune regulation and control of regulatory T cells by OX40 and 4-1BB

The TNFR family members OX40 (CD134) and 4-1BB (CD137) have been found to play major roles as costimulatory receptors for both CD4 and CD8 T cells. In particular, in many situations, they can control proliferation, survival, and cytokine production, and hence are thought to dictate accumulation of protective T cells during anti-viral and anti-tumor responses and pathogenic T cells during autoimmune reactions. As opposed to simply controlling the activity of naïve, effector, and memory T cells, recent data have suggested that both molecules are also instrumental in controlling the generation and activity of so-called regulatory or suppressor T cells (Treg), perhaps in both positive and negative manners. Part of the action on Treg might function to further promote protective or pathogenic T cells, but alternate activities of OX40 and 4-1BB on Treg are also being described that suggest that there might be control by these molecules at multiple levels that will alter the biological outcome when these receptors are ligated. This review specifically focuses on recent studies of regulatory T cells, and regulatory or suppressive activity, that are modulated by OX40 or 4-1BB.

Special regulatory T-cell review: Suppressors regulated but unsuppressed

The rise-and-fall and reincarnation of suppressor T cells is reviewed from the perspective of a participant in the field.

Foxp3 transcription-factor-dependent and -independent regulation of the regulatory T cell transcriptional signature

The CD4(+)CD25(+) lineage of regulatory T (Treg) cells plays a key role in controlling immune and autoimmune responses and is characterized by a unique transcriptional signature. The transcription factor Foxp3 had been thought to determine the Treg cell lineage, a hypothesis challenged by recent observations. We have performed a cross-sectional analysis of the Treg cell signature in Treg-like cells generated under a number of conditions, with or without Foxp3, to delineate the elements that can be ascribed to T cell activation, interleukin-2, transforming growth factor-beta (TGF-beta) signaling, or Foxp3 itself. These influences synergized to determine many of the signature's components. Much of the Treg cell signature was not ascribable to Foxp3 because it contained gene clusters that are coregulated with, but not transactivated by, Foxp3. Thus, a higher level of regulation upstream of Foxp3 determines the lineage, distinct from elements downstream of Foxp3 that are essential for its regulatory properties.

Antigen, in the Presence of TGF-β, Induces Up-Regulation of FoxP3gfp+ in CD4+ TCR Transgenic T Cells That Mediate Linked Suppression of CD8+ T Cell Responses

CD4(+)CD25(+) regulatory T cells (Tregs) inhibit immune responses to a variety of Ags, but their specificity and mechanism of suppression are controversial. This controversy is largely because many studies focused on natural Tregs with undefined specificities and suppression has frequently been measured on polyclonal T cell responses. To address the issue of specificity further, we have bred K(d)-specific, CD4(+) TCR (TCR75) transgenic mice to Foxp3(gfp) knockin reporter mice to permit sorting of Tregs with a known specificity. Foxp3(gfp).TCR75 mice did not express significant numbers of natural FoxP3(+) Tregs expressing the TCR75 transgenes, but FoxP3 expression was induced by stimulating with K(d) plus TGF-beta. The resulting GFP(+) TCR75 cells were anergic, whereas the GFP(-) TCR75 cells proliferated upon restimulation with K(d) peptide. Yet both exhibited severely reduced expression of intracellular IFN-gamma and TNF-alpha upon restimulation. GFP(+), but not GFP(-), TCR75 T cells suppressed responses by naive TCR75 T cells and by nontransgenic spleen cells stimulated with anti-CD3. GFP(+) TCR75 cells also inhibited polyclonal C57BL/6 anti-K(d) CTL responses if the APC expressed K(d) and both MHC class I and class II, and responses by OT1 T cells to B6.K(d).OVA but not B6.K(d) plus OVA expressing APC, demonstrating linked-suppression of CD8 responses. Thus, Tregs exhibit a greater degree of specificity in vitro than previously appreciated. The observation that Tregs and responder T cells must recognize the same APC provides a mechanistic explanation for the observation that Tregs must be in direct contact with effector T cells to suppress their responses.

CD8+ T cell-mediated suppression of autoimmunity in a murine lupus model of peptide-induced immune tolerance depends on Foxp3 expression

Systemic lupus erythematosus is an autoimmune disease caused by autoantibodies, including IgG anti-DNA. New Zealand Black/New Zealand White F(1) female mice, a model of spontaneous polygenic systemic lupus erythematosus, tolerized with an artificial peptide (pConsensus) based on anti-DNA IgG sequences containing MHC class I and class II T cell determinants, develop regulatory CD4+CD25+ T cells and CD8+ inhibitory T cells (CD8+ Ti), both of which suppress autoantibody production. CD8+ Ti inhibit primarily via secretion of TGF-beta. In the present study, we show that the inhibitory function of CD8+ T cells from tolerized mice is sustained for up to 8 wk and at all times depends on expression of Foxp3. Both CD28-positive and CD28-negative CD8+ T cells contain inhibitory cells, but the expression of mRNA for Foxp3 and for TGF-beta is higher and lasts longer in the CD28- subset. In vitro addition of TGF-beta (in the presence of IL-2) induces Foxp3 expression in a dose-response manner. Gene inhibition or blockade with small interfering RNA of Foxp3 abrogates the ability of the CD8+ Ti to inhibit anti-DNA production and the proliferation of CD4+ Th cells. Moreover, a significant correlation between expression of Foxp3 and ability of CD8+ Ti to secrete TGF-beta is observed. Therefore, CD8+ Ti in this system of tolerance are similar to CD4+CD25+ regulatory T cells in their dependence on expression of Foxp3, and there may be a bidirectional Foxp3/TGF-beta autocrine loop that determines the ability of the CD8+ T cells to control autoimmunity.

Soluble Ig-like transcript 3 inhibits tumor allograft rejection in humanized SCID mice and T cell responses in cancer patients

Attempts to enhance patients' immune responses to malignancies have been largely unsuccessful. We now describe an immune-escape mechanism mediated by the inhibitory receptor Ig-like transcript 3 (ILT3) that may be responsible for such failures. Using a humanized SCID mouse model, we demonstrate that soluble and membrane ILT3 induce CD8(+) T suppressor cells and prevent rejection of allogeneic tumor transplants. Furthermore, we found that patients with melanoma, and carcinomas of the colon, rectum, and pancreas produce the soluble ILT3 protein, which induces the differentiation of CD8(+) T suppressor cells and impairs T cell responses in MLC. These responses are restored by anti-ILT3 mAb or by depletion of soluble ILT3 from the serum. Immunohistochemical staining of biopsies from the tumors and metastatic lymph nodes suggests that CD68(+) tumor-associated macrophages represent the major source of soluble ILT3. Alternative splicing, resulting in the loss of the ILT3 transmembrane domain, may contribute to the release of ILT3 in the circulation. These data suggest that ILT3 depletion or blockade is crucial to the success of immunotherapy in cancer. In contrast, the inhibitory activity of soluble ILT3 on T cell alloreactivity in vitro and in vivo suggests the potential usefulness of rILT3 for immunosuppressive treatment of allograft recipients or patients with autoimmune diseases.

Anti-CD25 treatment and FOXP3-positive regulatory T cells in heart transplantation

The interleukin-2 receptor alpha chain (IL-2Ra, CD25) plays a major part in shaping the dynamics of T cell populations following immune activation, due to its role in T cell proliferation and survival. Strategies to blunt the effector responses in transplantation have been developed by devising pharmaceutical agents to block the IL-2 pathways. However, such strategies could adversely affect the CD25(+)FOXP3(+)T regulatory (T reg) populations which also rely on intereukin-2 signaling for survival. The present study shows that a cohort of heart allograft recipients treated with Daclizumab (a humanized anti-CD25 antibody) display FOXP3 expression patterns consistent with functional T regulatory cell populations. High levels of FOXP3 were observed to correlate with lower incidence of and recovery from acute rejection, as well as lower levels of anti-donor HLA antibody production. Therefore, T reg populations appear fully functional in patients treated with Daclizumab, even when 5 doses were administered. By comparison, patients treated with fewer doses or no Daclizumab had a higher incidence of acute rejection, antibody production and graft failure. Therefore, our data indicates that Daclizumab treatment does not interfere with the generation of regulatory T cells and has a beneficial effect on heart allograft survival.

The role of T helper 17 (Th17) and regulatory T cells (Treg) in human organ transplantation and autoimmune disease

Uncommitted (naive) murine CD4+ T helper cells (Thp) can be induced to differentiate towards T helper 1 (Th1), Th2, Th17 and regulatory (Treg) phenotypes according to the local cytokine milieu. This can be demonstrated most readily both in vitro and in vivo in murine CD4+ T cells. The presence of interleukin (IL)-12 [signalling through signal transduction and activator of transcription (STAT)-4] skews towards Th1, IL-4 (signalling through STAT-6) towards Th2, transforming growth factor (TGF)-beta towards Treg and IL-6 and TGF-beta towards Th17. The committed cells are characterized by expression of specific transcription factors, T-bet for Th1, GATA-3 for Th2, forkhead box P3 (FoxP3) for Tregs and RORgammat for Th17 cells. Recently, it has been demonstrated that the skewing of murine Thp towards Th17 and Treg is mutually exclusive. Although human Thp can also be skewed towards Th1 and Th2 phenotypes there is as yet no direct evidence for the existence of discrete Th17 cells in humans nor of mutually antagonistic development of Th17 cells and Tregs. There is considerable evidence, however, both in humans and in mice for the importance of interferon (IFN)-gamma and IL-17 in the development and progression of inflammatory and autoimmune diseases (AD). Unexpectedly, some models of autoimmunity thought traditionally to be solely Th1-dependent have been demonstrated subsequently to have a non-redundant requirement for Th17 cells, notably experimental allergic encephalomyelitis and collagen-induced arthritis. In contrast, Tregs have anti-inflammatory properties and can cause quiescence of autoimmune diseases and prolongation of transplant function. As a result, it can be proposed that skewing of responses towards Th17 or Th1 and away from Treg may be responsible for the development and/or progression of AD or acute transplant rejection in humans. Blocking critical cytokines in vivo, notably IL-6, may result in a shift from a Th17 towards a regulatory phenotype and induce quiescence of AD or prevent transplant rejection. In this paper we review Th17/IL-17 and Treg biology and expand on this hypothesis.