Specific elimination of effector memory CD4+ T cells due to enhanced Fas signaling complex formation and association with lipid raft microdomains

Elimination of autoreactive CD4⁺ T cells through the death receptor Fas/CD95 is an important mechanism of immunological self-tolerance. Fas deficiency results in systemic autoimmunity, yet does not affect the kinetics of T-cell responses to acute antigen exposure or infection. Here we show that Fas and TCR-induced apoptosis are largely restricted to CD4⁺ T cells with an effector memory phenotype (effector memory T cells (T_EM)), whereas central memory and activated naïve CD4⁺ T cells are relatively resistant to both. Sensitivity of T_EM to Fas-induced apoptosis depends on enrichment of Fas in lipid raft microdomains, and is linked to more efficient formation of the Fas death-inducing signaling complex. These results explain how Fas can cull T cells reactive against self-antigens without affecting acute immune responses. This work also identifies Fas-induced apoptosis as a possible immunotherapeutic strategy to eliminate T_EM linked to the pathogenesis of a number of autoimmune diseases.     

The role of CD4 T cell help for CD8 CTL activation

CD4 T cells play an important role in the initiation and persistence of CD8 T cells responses. In this review, we report on and evaluate the mechanisms by which CD4 T cells contribute to activation of CD8 T cells and the signal pathways of the down-streaming events after CD4 T cell help.     

CD4 T cell dependent tumor immunity stimulated by dendritic cell based vaccine

CD8 CTLs have been accountable for the major effector cells responsible for the rejection of tumor cells. And CD40 signaling and IL-12 have been shown to be the essential pathways involved in the activation process. Immunizing mice with dendritic cells transduced with an adenovirus expressing the human melanoma antigen gp100, an immunization strategy of xenoimmunization, stimulated potent tumor protection dependent on effective CD4 T cells in the absence of CD8 T cells. Further studies revealed that neither CD40 signaling nor IL-12 was indispensable for the activation of dendritic and CD4 T cells in this model. Stimulation of effective antitumor immunity targeting the self-antigen did not elicit autoimmunity. The implications of this study were discussed.     

GITR ligand-costimulation activates effector and regulatory functions of CD4+ T cells

Engagement of glucocorticoid-induced TNFR-related protein (GITR) enables the costimulation of both CD25⁻CD4⁺ effector (Teff) and CD25⁺CD4⁺ regulatory (Treg) cells; however, the effects of GITR-costimulation on Treg function remain controversial. In this study, we examined the effects of GITR ligand (GITRL) binding on the respective functions of CD4⁺ T cells. GITRL-P815 transfectants efficiently augmented anti-CD3-induced proliferation and cytokine production by Teff cells. Proliferation and IL-10 production in Treg were also enhanced by GITRL transfectants when exogenous IL-2 and stronger CD3 stimulation was provided. Concomitant GITRL-costimulation of Teff and Treg converted the anergic state of Treg into a proliferating state, maintaining and augmenting their function. Thus, GITRL-costimulation augments both effector and regulatory functions of CD4⁺ T cells. Our results suggest that highly activated and increased ratios of Treg reverse the immune-enhancing effects of GITRL-costimulation in Teff, which may be problematic for therapeutic applications using strong GITR agonists.     

Splenic dendritic cell subsets prime and boost CD8 T cells and are involved in the generation of effector CD8 T cells

The ability of the dendritic cell (DC) subsets, CD8alpha+ and CD8alpha- DCs, to initiate a CD8 T cell response or to activate memory CD8 T cells and generate effector CD8 T cells has been controversial. In this study, we analyse the capacity of splenic DC subsets to induce CD8 T cell responses to a CD8 T cell epitope (pb9) of a malaria antigen. The administration of peptide-pulsed CD8alpha- or CD8alpha+ DCs primes and boosts a primed CD8 T cell response against the malaria epitope. In vitro, depletion of CD11c(+) DCs from mouse splenocytes, immunised with recombinant vaccinia virus Ankara (MVA) expressing pb9 epitope, significantly reduced the generation of pb9-specific IFNgamma producing effector CD8 T cells, indicating that splenic DCs are involved in the development of pb9-specific IFNgamma producing effector cells. Taken together, this result shows that both DC subsets have the ability to prime and boost CD8 T cell responses and are involved in the activation of memory CD8 T cells.     

Regulatory T cells constrain the TCR repertoire of antigen‐stimulated conventional CD4 T cells

To analyze the potential role of Tregs in controlling the TCR repertoire breadth to a non‐self‐antigen, a TCRβ transgenic mouse model (EF4.1) expressing a limited, yet polyclonal naïve T‐cell repertoire was used. The response of EF4.1 mice to an I‐Ab‐associated epitope of the F‐MuLV envelope protein is dominated by clones expressing a Vα2 gene segment, thus allowing a comprehensive analysis of the TCRα repertoire in a relatively large cohort of mice. Control and Treg‐depleted EF4.1 mice were immunized, and the extent of the Vα2‐bearing, antigen‐specific TCR repertoire was characterized by high‐throughput sequencing and spectratyping analysis. In addition to increased clonal expansion and acquisition of effector functions, Treg depletion led to the expression of a more diverse TCR repertoire comprising several private clonotypes rarely observed in control mice or in the pre‐immune repertoire. Injection of anti‐CD86 antibodies in vivo led to a strong reduction in TCR diversity, suggesting that Tregs may influence TCR repertoire diversity by modulating costimulatory molecule availability. Collectively, these studies illustrate an additional mechanism whereby Tregs control the immune response to non‐self‐antigens.     

A tolerogenic semimature dendritic cells induce effector T-cell hyporesponsiveness by activation of antigen-specific CD4+CD25+ T regulatory cells that promotes skin allograft survival in mice

Semimature dendritic cells (smDCs) can induce autoimmune tolerance by activation of host antigen-specific CD4⁺CD25⁺ regulatory T (Treg) cells. We hypothesized that donor smDCs injected into recipients would induce effector T-cell hyporesponsiveness by activating CD4⁺CD25⁺Treg cells, and promote skin allograft survival. Myeloid smDCs were derived from C57BL/6J mice (donors) in vitro. BALB/c mice (recipients) were injected with smDCs to generate antigen-specific CD4⁺CD25⁺Treg cells in vivo. Allograft survival was prolonged when BALB/c recipients received either C57BL/6J smDCs prior to grafting or C57BL/6J smDC-derived CD4⁺CD25⁺Treg cells post-grafting, and skin flaps from these grafts showed the highest IL-10 production regardless of rapamycin treatments. Our findings confirm that smDCs constitute an independent subgroup of DCs that play a key role for inducing CD4⁺CD25⁺Treg cells to express high IL-10 levels, which induce hyporesponsiveness of effector T cells. Pre-treating recipients with donor smDCs may have potential for transplant tolerance induction.     

CD40 ligation restores cytolytic T lymphocyte response and eliminates fibrosarcoma in the peritoneum of mice lacking CD4+ T cells

Absence of CD4⁺ T cell help has been suggested as a mechanism for failed anti-tumor cytotoxic T lymphocytes (CTL) response. We examined the requirement for CD4⁺ T cells to eliminate an immunogenic murine fibrosarcoma (6132A) inoculated into the peritoneal cavity. Immunocompetent C3H mice eliminated both single and repeat intraperitoneal (IP) inoculums, and developed high frequency of 6132A-specific interferon-γ (IFNγ)-producing CTL in the peritoneal cavity. Adoptive transfer of peritoneal exudate cells (PEC) isolated from control mice, protected SCID mice from challenge with 6132A. In contrast, CD4 depleted mice had diminished ability to eliminate tumor and succumbed to repeat IP challenges. Mice depleted of CD4⁺ T cells lacked tumor-specific IFNγ producing CTL in the peritoneal cavity. Adoptive transfer of PEC from CD4 depleted mice failed to protect SCID mice from 6132A. However, splenocytes isolated from same CD4 depleted mice prevented tumor growth in SCID mice, suggesting that 6132A-specific CTL response was generated, but was not sustained in the peritoneum. Treating CD4 depleted mice with agonist anti-CD40 antibody, starting on days 3 or 8 after initiating tumor challenge, led to persistence of 6132A-specific IFNγ producing CTL in the peritoneum, and eliminated 6132A tumor. The findings suggest that CTL can be activated in the absence of CD4⁺ T cells, but CD4⁺ T cells are required for a persistent CTL response at the tumor site. Exogenous stimulation through CD40 can restore tumor-specific CTL activity to the peritoneum and promote tumor clearance in the absence of CD4⁺ T cells.Supported in part by grants from Children’s Hospital of Wisconsin Foundation, Society of University Surgeons Foundation, Florence and Marshall Schwid Foundation, Elsa Pardee Foundation, Kathy Duffy Fogarty Fund of the Greater Milwaukee Foundation (JS) and NIH grant RO1-CA-37156 (HS); Andrew Lodge and Ping Yu have contributed equally to this work.     

CD137 signaling interferes with activation and function of CD4+CD25+ regulatory T cells in induced tolerance to experimental autoimmune thyroiditis

Experimental autoimmune thyroiditis (EAT), a model for Hashimoto's thyroiditis, is a T cell-mediated disease inducible with mouse thyroglobulin (mTg). Pretreatment with mTg, however, can induce CD4+ T cell-mediated tolerance to EAT. We demonstrate that CD4+CD25+ regulatory cells are critical for the tolerance induction, as in vivo depletion of CD25+ cells abrogated established tolerance, and CD4+CD25+ cells from tolerized mice suppressed mTg-responsive cells in vitro. Importantly, administration of an agonistic CD137 monoclonal antibody (mAb) inhibited tolerance development, and the mediation of established tolerance. CD137 mAb also inhibited the suppression of mTg-responsive cells by CD4+CD25+ cells in vitro. Signaling through CD137 likely resulted in enhancement of the responding inflammatory T cells, as anti-CD137 did not enable CD4+CD25+ T cells to proliferate in response to mTg in vitro.     

Engagement of CD44 up-regulates Fas Ligand expression on T cells leading to activation-induced cell death

Activation-induced cell death (AICD) plays a pivotal role in self-tolerance by deleting autoreactive T cells, but a defect of AICD results in expansion of autoreactive T cells and is deeply involved in the pathogenesis of rheumatoid arthritis. Although the process of AICD is mainly mediated by Fas Ligand (FasL)/Fas signaling, it remains unclear what induces FasL expression on T cells. In the present study, we found that CD44 was the most potent stimulator of FasL expression on human peripheral T cells. CD44 cross-linking rapidly up-regulated FasL expression on the T cell surface by delivery from the cytoplasm without new FasL protein synthesis. This up-regulation of FasL was mediated by activation of a tyrosine kinase, IP3 receptor-dependent Ca²⁺ mobilization and actin cytoskeletal rearrangements. Furthermore, AICD induced by CD3 restimulation was inhibited by hyaluronidase as well as by soluble Fas, indicating an interaction between membrane-bound hyaluronan and the cell surface CD44 was involved in the up-regulation of FasL expression on T cells and subsequent AICD. We therefore propose that the engagement of CD44 on T cells can eliminate autoreactive T cells by expression of FasL and FasL-mediated AICD. Grant support: Scientific Research by the Ministry of Health, Labor and Welfare of Japan, the Ministry of Education, Culture, Sports, Science and Technology of Japan and University of Occupational and Environmental Health, Japan.     

CD4+CD25+调节性T细胞的外周维持

CD4 CD25 调节性T细胞作为一种抑制性T细胞功能亚群,在维持机体的免疫自稳和免疫耐受方面发挥了关键作用。该作用的发挥与其外周细胞库的维持密切相关。新近的研究显示CD4 CD25 调节性T细胞主要通过两种机制来维持其外周细胞库,一些功能分子参与其中。     

Ability of CD8(+) T cell anti-feline immunodeficiency virus activity correlated with peripheral CD4(+) T cell counts and plasma viremia

In the host defense mechanism against feline immunodeficiency virus (FIV) infection, CD8(+) T cells specifically attack virus-infected cells and suppress the replication of the virus in a non-cytolytic manner by secreting soluble factors. In this study, we measured CD8(+) T cell anti-FIV activity in 30 FIV-infected cats. We investigated its relationship with the number of peripheral blood lymphocytes, particularly the CD4(+) T cell and CD8(+) T cell counts, and the relationship between anti-FIV activity and the number of T cells of CD8alpha(+)beta(lo) and CD8alpha(+)beta(-) phenotypes. A clearly significant correlation was observed between anti-FIV activity and the number of CD4(+) T cells. A weaker anti-FIV activity was associated with a greater decrease in the number of CD4(+) T cells. However, there was no significant correlation between anti-FIV activity and the number of B or CD8(+) T cells. Compared with SPF cats, FIV-infected cats had significantly higher CD8alpha(+)beta(lo) T cell and CD8alpha(+)beta(-) T cell counts, but, no significant correlation was observed between these cell counts and anti-FIV activity. This anti-FIV activity significantly correlated with plasma viremia, which was detected in cats with a weak anti-FIV activity. These results suggest that the anti-FIV activity of CD8(+) T cells plays an important role in plasma viremia and the maintenance of CD4(+) T cells in the body. It is unlikely that CD8alpha(+)beta(lo) or CD8alpha(+)beta(-) T cells appearing after FIV infection represent a phenotype of CD8(+) cells with anti-FIV activity.     

CD98hc regulates the development of experimental colitis by controlling effector and regulatory CD4 T cells

CD4⁺ T cell activation is controlled by signaling through the T cell receptor in addition to various co-receptors, and is also affected by their interactions with effector and regulatory T cells in the microenvironment. Inflammatory bowel diseases (IBD) are caused by the persistent activation and expansion of auto-aggressive CD4⁺ T cells that attack intestinal epithelial cells. However, the molecular basis for the persistent activation of CD4⁺ T cells in IBD remains unclear. In this study, we investigated how the CD98 heavy chain (CD98hc, Slc3a2) affected the development of colitis in an experimental animal model. Transferring CD98hc-deficient CD4⁺CD25⁻ T cells into Rag2^−/− mice did not cause colitis accompanied by increasing Foxp3⁺ inducible regulatory T cells. By comparison, CD98hc-deficient naturally occurring regulatory T cells (nTregs) had a decreased capability to suppress colitis induced by CD4⁺CD25⁻ T cells, although CD98hc-deficient mice did not have a defect in the development of nTregs. Blocking CD98hc with an anti-CD98 blocking antibody prevented the development of colitis. Our results indicate that CD98hc regulates the expansion of autoimmune CD4⁺ T cells in addition to controlling nTregs functions, which suggests the CD98hc as an important target molecule for establishing strategies for treating colitis.     

A unique unresponsive CD4+ T cell phenotype post TCR antagonism

The functional outcomes of the T cell’s interaction with the peptide:MHC complex can be dramatically altered by the introduction of a single amino acid substitution. Previous studies have described the varied effects of these altered peptide ligands (APL) on T cell responses. These outcomes of T cell interaction with an APL include the induction of clonal unresponsiveness (anergy) and inhibition of T cell responses (antagonism). The phenotype of peptide-induced anergy, i.e. low proliferation and low IL-2 production, has been extensively described, and a number of groups have demonstrated antagonism. However, the response of T cells to an agonist ligand after encountering an antagonistic stimulus has not been previously characterized. Here, we show that T cells post-antagonism fail to proliferate but produce large quantities of IL-2 upon stimulation with their wild type ligand. This unique phenotype is not due to differences in IL-2 receptor expression or rates of apoptosis, and cannot be overcome by the addition of recombinant IL-2. The response of CD4 T cells to agonist stimulation after encountering an antagonist is a novel phenotype, and is distinct from previously described forms of anergy.     

T helper 1 effector memory CD4+ T cells protect the skin from poxvirus infection

1. Download : Download high-res image (224KB)
2. Download : Download full-size image

     

CD4+CD25+ suppressor T cells regulate pathogen induced inflammation and disease

A key suppressor role has recently been ascribed to the natural CD4+CD25+ regulatory T cells (Treg), the removal of which leads to the development of autoimmune disease and aggravated pathogen-induced inflammation in otherwise normal hosts. The repertoire of antigen specificities of Treg is as broad as that of naive T cells, recognizing both self and non-self antigens, enabling Treg to control a broad range of immune responses. Although widely acknowledged to play a role in the maintenance of self-tolerance, recent studies indicate that Treg can be activated and expanded against bacterial, viral and parasite antigens in vivo. Such pathogen-specific Treg can prevent infection-induced immunopathology but may also increase the load of infection and prolong pathogen persistence by suppressing protective immune responses. This review discusses the role of Treg in the prevention of exaggerated inflammation favoring chronicity in bacterial or fungal infections and latency in viral infections. Special attention is given to the role of Treg in the modulation of gastric inflammation induced by Helicobacter pylori infection. Findings in both experimentally infected mice and humans with natural infection indicate that Treg are important in protecting the H. pylori-infected host against excessive gastric inflammation and disease symptoms but on the negative side promote bacterial colonization at the gastric and duodenal mucosa which may increase the risk in H. pylori-infected individuals to develop duodenal ulcers.     

Neoantigen-driven B cell and CD4 T follicular helper cell collaboration promotes anti-tumor CD8 T cell responses

1. Download : Download high-res image (168KB)
2. Download : Download full-size image

     

CD4<Superscript>+</Superscript> T-cell recognition of human 5T4 oncofoetal antigen: implications for initial depletion of CD25<Superscript>+</Superscript> T cells

Background The human 5T4 (h5T4) oncofoetal antigen is expressed by a wide variety of human carcinomas including colorectal, ovarian, gastric and renal, but rarely on normal tissues. Its restricted expression on tumour tissues as well as its association with tumour progression and bad prognosis has driven the development of a MVA-based vaccine (TroVax) which has been tested in several early phase clinical trials and these studies have led to the start of a phase III trial in renal cell carcinoma patients. We have recently shown that CD8⁺ T cells recognizing h5T4 can be generated in the absence of CD4⁺ T cells from peripheral blood lymphocytes of human healthy individuals. Results We report the existence and expansion of human CD4⁺ T cells against h5T4 by stimulation with autologous monocyte-derived dendritic cells infected with a replication defective adenovirus encoding the h5T4 cDNA (Ad-h5T4). The h5T4-specific T-cell responses in normal individuals are enhanced by initial depletion of CD25⁺ cells (putative T regulatory cells) prior to the in vitro stimulation. We have identified a novel h5T4-derived 15-mer peptide recognized by CD4⁺ T cells in HLA-DR4 positive healthy individuals. Interestingly, CD4⁺ T cells spontaneously recognizing a different 5T4 epitope restricted by HLA-DR were identified in tumour-infiltrating lymphocytes isolated from a regressing renal cell carcinoma lung metastasis. Conclusion Our data show that CD4⁺ T cells recognizing h5T4 can be expanded and detected in healthy individuals and a renal cell carcinoma patient. Such h5T4-specific CD4⁺ T cells boosted or induced by vaccination could act to modulate both cell or antibody mediated anti-tumour responses. This work was supported by Cancer Research UK.