Contraction Of CD8 Research Articles

Exhaustion of Human Dendritic Cells Results in a Switch from the IL-15R/IL-15- to IL-2R/IL-2-driven Expansion of Antigen-specific CD8+ T Cells

Abstract Maturation of dendritic cell (DC) is considered to be crucial for their ability to promote clonal expansion of antigen-specific T cells. Here, we show that the ability to expand human antigen-specific CD8+ T cells is a feature of specialized “effector” DCs at early stages of maturation, and it is suppressed in “exhausted” DCs at late stages of maturation and in DCs matured in the conditions of chronic inflammation. Effector DCs, at early stages of maturation induced by TLR ligands and interferons, express membrane IL-15Rα/IL-15 complex, which promotes highly efficient and IL-2/IL-2Rα-independent expansion of MART-1-specific IL-15Rαhigh CD8+ T cells and cooperates with DC-produced IL-12p70 in inducing poly-functional CTL phenotype. In sharp contrast, exhausted DCs which lack membrane IL-15Rα/IL-15 complex, utilize a significantly less efficient IL-2Rα/IL-2 trans-presentation pathway to co-stimulate CD8+ T cells. The currently-reported switch from the IL-15Rα/IL-15- to IL-2Rα/IL-2 costimulatory pathway in exhausted DCs helps to understand the role of inflammation in clonal expansion and contraction of CD8+ T cells at different stages of immune responses and helps to design improved modes of immunotherapy of cancer and chronic infections.

Intrinsic role of FoxO3a in the contraction of CD8+ T cell response (110.14)

Abstract CD8+ T cells undergo rapid expansion during infection with intracellular pathogens, which is followed by swift and massive culling of primed CD8+ T cells. The mechanisms that govern the massive contraction of primed CD8+ T cells are not clear. We show that the transcription factor Foxo3a plays a key role in the contraction, not expansion, of CD8+ T cell response against Listeria monocytogenes (LM). FoxO3a-mutant OVA-specific CD8+ T cells isolated during peak of response displayed reduced expression of pro-apoptotic molecules BIM and PUMA, and underwent reduced apoptosis during contraction phase in comparison to WT cells. A higher number of memory precursor effector cells (MPECs) were detectable in FoxO3a-mutant mice compared to WT mice during contraction phase. Furthermore, FoxO3a-mutant OVA-specific CD8+ T cells upon transfer into normal mice underwent highly reduced contraction. These results show for the first time that FoxO3a acts in a cell intrinsic manner to promote the culling of primed CD8+T cells during the contraction phase.

Orchestration of B and T cell responses in health and disease by common gamma chain family cytokines with a focus on IL-21

Members of a subfamily of the type 1 four-helix-bundle cytokines with receptors sharing the common gamma (cγ) chain including IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21 have distinct activities on the differentiation of effector, memory, and regulatory T cells [1,2]. Furthermore, IL-2, IL-4, and IL-21 serve distinct roles in control of B cell development and differentiation to antibody producing cells. We and others recently reported that both IL-2 and IL-21 are essential for maintenance of CD8 T cells and control of chronic viral infection, while both cytokines are dispensable for expansion and contraction of CD8 T cells during acute and resolved viral infection [3-7]. While IL-21 has been implicated in cross-regulation of Th17 cells and inducible regulatory T cells (Treg) in vitro, development of Th17 and Treg cells and consequently organ-related autoimmune disease remain unaffected in IL-21R-deficient mice in vivo [8,9]. In contrast, we now found that IL-21 can potently inhibit proliferation and function of inducible and natural Treg cells in models of T cell transfer colitis, viral infection, and asthma. Increased numbers of Tregs in IL-21R-deficient mice offer an explanation for suppression of Th2-mediated asthma and susceptibility to chronic viral infection described in the knockout mice [5,10]. Furthermore, the importance of IL-21 for B cell and antibody responses has been well established. Recently, it has been suggested that IL-21 is crucial for development of T follicular helper cells (Tfh) and defective B cell responses in IL-21R-deficient mice are due to the absence of Tfh cells. However, we found that germinal center development and antibody responses were severely impaired in mice that lack IL-21R specifically on B cells suggesting that IL-21 regulates germinal center responses in a B cell intrinsic manner [11]. In addition, we have shown that requirement of IL-21 for a B cell response is overcome by immunization with particulate antigens containing TLR7/8 ligands (such as viral RNS). These data demonstrate that innate pathogen patterns (PAMPs) and Th cell derived signals co-operate in the induction of optimal IgG responses. Interestingly, in contrast to follicular B cell responses, IL-21 has been shown to negatively regulate marginal zone (MZ) B-cell survival and antibody production to Streptococous pneumonia [12].

Caspase-3 Is Transiently Activated without Cell Death during Early Antigen Driven Expansion of CD8+ T Cells In Vivo

BackgroundCD8+ T cell responses develop rapidly during infection and are swiftly reduced during contraction, wherein >90% of primed CD8+ T cells are eliminated. The role of apoptotic mechanisms in controlling this rapid proliferation and contraction of CD8+ T cells remains unclear. Surprisingly, evidence has shown non-apoptotic activation of caspase-3 to occur during in vitro T-cell proliferation, but the relevance of these mechanisms to in vivo CD8+ T cell responses has yet to be examined.Methods and FindingsWe have evaluated the activity of caspase-3, a key downstream inducer of apoptosis, throughout the entirety of a CD8+ T cell response. We utilized two infection models that differ in the intensity, onset and duration of antigen-presentation and inflammation. Expression of cleaved caspase-3 in antigen specific CD8+ T cells was coupled to the timing and strength of antigen presentation in lymphoid organs. We also observed coordinated activation of additional canonical apoptotic markers, including phosphatidylserine exposure. Limiting dilution analysis directly showed that in the presence of IL7, very little cell death occurred in both caspase-3hi and caspase-3low CD8+ T cells. The expression of active caspase-3 peaked before effector phenotype (CD62Llow) CD8+ T cells emerged, and was undetectable in effector-phenotype cells. In addition, OVA-specific CD8+ cells remained active caspase-3low throughout the contraction phase.ConclusionsOur results specifically implicate antigen and not inflammation in driving activation of apoptotic mechanisms without cell death in proliferating CD8+ T cells. Furthermore, the contraction of CD8+ T cell response following expansion is likely not mediated by the key downstream apoptosis inducer, caspase-3.

IL-15 protects antigen-specific CD8+ T cell contraction after Mycobacterium bovis bacillus Calmette-Guérin infection

We reported previously that IL-15 plays a critical role in protecting effector CD8(+) T cells from apoptosis during the contraction phase following acute infection with Listeria monocytogenes by inducing antiapoptotic molecules. In the present study, we examined the effects of in vivo administration of rIL-15 on contraction of CD8(+) T cells after chronic infection with Mycobacterium bovis BCG and on the efficacy of BCG vaccination against Mycobacterium tuberculosis infection. Antigen-specific CD8(+) T cells reached an expansion peak at approximately Day 21, followed by a contraction after inoculation with rBCG expressing OVA. In vivo administration of rIL-15 from Days 22 to 42 after BCG inoculation inhibited apoptosis of effector CD8(+) T cells by up-regulating their Bcl-2 expression, resulting in a significant increase of antigen-specific memory CD8(+) T cells producing IFN-gamma. However, the IL-15 treatment did not elicit improved efficacy of BCG vaccination against M. tuberculosis. These results suggest that IL-15 plays a critical role in protecting activated CD8(+) T cells from apoptosis during the contraction phase following BCG inoculation, although IL-15 administration alone at the contraction phase might not be sufficient to protect the efficient memory T cell responses against subsequent infection with M. tuberculosis.

Mutation in the Fas Pathway Impairs CD8+ T Cell Memory

Fas death pathway is important for lymphocyte homeostasis, but the role of Fas pathway in T cell memory development is not clear. We show that whereas the expansion and contraction of CD8+ T cell response against Listeria monocytogenes were similar for wild-type (WT) and Fas ligand (FasL) mutant mice, the majority of memory CD8+ T cells in FasL mutant mice displayed an effector memory phenotype in the long-term in comparison with the mainly central memory phenotype displayed by memory CD8+ T cells in WT mice. Memory CD8+ T cells in FasL mutant mice expressed reduced levels of IFN-gamma and displayed poor homeostatic and Ag-induced proliferation. Impairment in CD8+ T cell memory in FasL mutant hosts was not due to defective programming or the expression of mutant FasL on CD8+ T cells, but was caused by perturbed cytokine environment in FasL mutant mice. Although adoptively transferred WT memory CD8+ T cells mediated protection against L. monocytogenes in either the WT or FasL mutant hosts, FasL mutant memory CD8+ T cells failed to mediate protection even in WT hosts. Thus, in individuals with mutation in Fas pathway, impairment in the function of the memory CD8+ T cells may increase their susceptibility to recurrent/latent infections.

IL-21 Induces Apoptosis of Antigen-Specific CD8+ T Lymphocytes

IL-21, a member of the common gamma-chain family of cytokines, has pleiotropic effects on T, B, and NK cells. We found that IL-21 and the prototype common gamma-chain cytokine IL-2 can stimulate proliferation and cytokine secretion by Ag-specific rhesus monkey CD8+ T cells. However, unique among the members of this family of cytokines, we found that IL-21 drives these cells to apoptosis by down-regulation of Bcl-2. These findings suggest that IL-21 may play an important role in the contraction of CD8+ T cell responses.

Delayed Expansion and Contraction of CD8+ T Cell Response during Infection with VirulentSalmonella typhimurium

Ag presentation to CD8(+) T cells often commences immediately after infection, which facilitates their rapid expansion and control of infection. Subsequently, the primed cells undergo rapid contraction. We report that this paradigm is not followed during infection with virulent Salmonella enterica, serovar Typhimurium (ST), an intracellular bacterium that replicates within phagosomes of infected cells. Although susceptible mice die rapidly (approximately 7 days), resistant mice (129 x 1SvJ) harbor a chronic infection lasting approximately 60-90 days. Using rOVA-expressing ST (ST-OVA), we show that T cell priming is considerably delayed in the resistant mice. CD8(+) T cells that are induced during ST-OVA infection undergo delayed expansion, which peaks around day 21, and is followed by protracted contraction. Initially, ST-OVA induces a small population of cycling central phenotype (CD62L(high)IL-7Ralpha(high)CD44(high)) CD8(+) T cells. However, by day 14-21, majority of the primed CD8(+) T cells display an effector phenotype (CD62L(low)IL-7Ralpha(low)CD44(high)). Subsequently, a progressive increase in the numbers of effector memory phenotype cells (CD62L(low)IL-7Ralpha(high)CD44(high)) occurs. This differentiation program remained unchanged after accelerated removal of the pathogen with antibiotics, as majority of the primed cells displayed an effector memory phenotype even at 6 mo postinfection. Despite the chronic infection, CD8(+) T cells induced by ST-OVA were functional as they exhibited killing ability and cytokine production. Importantly, even memory CD8(+) T cells failed to undergo rapid expansion in response to ST-OVA infection, suggesting a delay in T cell priming during infection with virulent ST-OVA. Thus, phagosomal lifestyle may allow escape from host CD8(+) T cell recognition, conferring a survival advantage to the pathogen.

A Murine Model of Bone Marrow Failure Mediated by Disparity in Minor Histocompatibility Antigens.

Destruction of hematopoietic cells in aplastic anemia and other hematologic diseases is mediated in most patients by effector cells of the immune system. We have developed a mouse model of immune-mediated bone marrow failure which employs parental lymph node cell infusion into F1 recipients, resulting in bone marrow hypercellularity, pancytopenia, and death from infection and bleeding, without other organ involvement by graft-versus-host disease (Bloom, ML et al. Exp. Hematol . 32:1163, 2004; Chen, J et al. Blood 104:1671, 2004). Because major histocompatibility antigens are not the targets in acquired aplastic anemia, we now have developed a model of murine marrow failure based on disparity of minor histocompatibility antigens. Lymph node cells from C57BL/6 mice were infused into sublethally-irradiated, MHC-matched, C.B10-H2b/LilMce recipients. Animals developed severe pancytopenia and marrow hypoplasia within two-three weeks. CD8+ T lymphocytes were expanded in the blood and infiltrated bone marrow, becoming detectable at day 7 and reaching peak levels at days 10–12. There were no inflammatory responses observed in the skin, intestines, or other visceral organs by gross or microscopic pathological examination. In our experiments we observed a time-dependent expansion followed by contraction of CD8+ T cells specific for a minor histocompatibility antigen H60 as measured by flowcytometry using an H60-specific tetramer. H60 is an antigen peptide derived from a glycoprotein, a known ligand for stimulatory NKG2D receptors, and is immunodominant over other minor antigens in stem cell transplantation. The proportion of H60-specific CD8+ T cells was strongly negatively correlated with peripheral blood white cell, neutrophil, and platelet counts. Isolated H60-specific T-cells from bone marrow of affected animals induced apoptosis in vitro of normal C57BL/6 bone marrow cells in co-culture. The degree of apoptosis was further increased by addition of CD4 T-cells from same affected donors, suggesting a helper lymphocyte effect. The role of H60-specific T cells was demonstrated in further transplant experiments. Infusion of 5 × 106 C57BL/6 lymph node cells that had been depleted of H60-specific T cells was unable to induce marrow failure in C.B10 recipients, while the same number of cells with the addition of 20–90 × 103 H60-specific CD8+ T cells led to thrombocytopenia and leucopenia in recipients. H60-specific T cells thus appear to be key effectors, responsible at least for the initiation of marrow cell destruction. Mice could be treated with cyclosporine at 50 mg/g/day for five days, if treatments were begun at the time of lymph node cell infusion. Immunosuppressive therapy abolished H60-specific CD8+ T cell expansion and attenuated the development of peripheral pancytopenia, effectively rescuing animals. In conclusion, we demonstrate in this model of immune-mediated bone marrow failure that a single clone of peptide-specific T-cells is capable of efficient marrow destruction and the production of aplastic anemia.

Role of Tumor Necrosis Factor Receptors in Regulating CD8 T-Cell Responses during Acute Lymphocytic Choriomeningitis Virus Infection

The role of tumor necrosis factor (TNF) in regulating various phases of the antiviral T-cell response is incompletely understood. Additionally, despite strong evidence ascribing a role for TNF in protecting against T-cell-dependent autoimmunity, the underlying mechanisms are still obscure. To address these issues, we have investigated the role of tumor necrosis factor receptors (TNFRs) I (p55R) and II (p75R) in regulating CD8 T-cell responses to lymphocytic choriomeningitis virus (LCMV) with wild-type, p55R-deficient (p55(-/-)), p75R-deficient (p75(-/-)), and p55R- and p75R-deficient (DKO) mice. Loss of p55R increased the number of memory CD8 T cells to only one of the two immunodominant epitopes, and p75R deficiency had a minimal impact on the T-cell response to LCMV. Strikingly, deficiency of both p55R and p75R had a more dramatic effect on the LCMV-specific CD8 T-cell response; in the DKO mice, as a sequel to enhanced expansion and a reduction in contraction of CD8 T cells, there was a substantial increase in the number of memory CD8 T cells (specific to the two immunodominant epitopes). While the majority of LCMV-specific memory CD8 T cells in wild-type mice were CD62Lhi CCR7hi (central memory), a major proportion of memory CD8 T cells in DKO mice were CD62Llo CCR7hi. TNFR deficiency did not affect the proliferative renewal of memory CD8 T cells. Taken together, these data suggested that TNFRs p55R and p75R have overlapping roles in downregulating CD8 T-cell responses and establishment of immune homeostasis during an acute viral infection.

Antioxidant treatment reduces expansion and contraction of antigen-specific CD8+ T cells during primary but not secondary viral infection.

During many viral infections, antigen-specific CD8(+) T cells undergo large-scale expansion. After viral clearance, the vast majority of effector CD8(+) T cells undergo apoptosis. Previous studies have implicated reactive oxygen intermediates (ROI) in lymphocyte apoptosis. The purpose of the experiments presented here was to determine the role of ROI in the expansion and contraction of CD8(+) T cells in vivo during a physiological response such as viral infection. Mice were infected with lymphocytic choriomeningitis virus (LCMV) and treated with Mn(III)tetrakis(4-benzoic acid)porphyrin chloride (MnTBAP), a metalloporphyrin-mimetic compound with superoxide dismutase activity, from days 0 to 8 postinfection. At the peak of CD8(+)-T-cell response, on day 8 postinfection, the numbers of antigen-specific cells were 10-fold lower in MnTBAP-treated mice than in control mice. From days 8 to 30, a contraction phase ensued where the numbers of antigen-specific CD8(+) T cells declined 25-fold in vehicle-treated mice compared to a 3.5-fold decrease in MnTBAP-treated mice. Differences in contraction appeared to be due to greater proliferation in drug-treated mice. By day 38, the numbers of antigen-specific CD8(+) memory T cells were equivalent for the two groups. The administration of MnTBAP during secondary viral infection had no effect on the expansion of antigen-specific CD8(+) secondary effector T cells. These data suggest that ROI production is critical for the massive expansion and contraction of antigen-specific CD8(+) T cells during primary, but not secondary, viral infection.

Antigen-Driven Expansion and Contraction of CD8+-Activated T Cells in Primary EBV Infection

The origin of the increased numbers of CD8+ atypical lymphocytes, expressing activated markers such as HLA-DR or CD45RO, in the peripheral blood of patients with infectious mononucleosis (IM) has been debated. Using a recently developed assay to detect intracellular accumulation of IFN-gamma in EBV-reactive T cells by FACS, we have demonstrated that 34-54% of HLA-DR+/CD8+ and 34-60% of CD45RO+/CD8+ T cells in the PBMCs of febrile patients suffering from IM are EBV-specific. The EBV-specific CD8+ T cell counts in the PBMCs of four febrile patients suffering from IM ranged between 2,260 and 8,200/microl, decreasing to 5.1% and 7.9% of the counts in the first samples over 10 days in two donors. The decline of CD8+ T cell subpopulations, namely HLA-DR+, CD45RO+, and EBV-specific T cells, was in parallel with the drop in the EBV genome load. These data indicate that the Ag-driven expansion of CD8+ T cells and subsequent contraction with the Ag decline in vivo in humans is effective for clearing virus-infected cells with minimal disturbance of the homeostasis of the immune system.