CD4 memory T cells divide poorly in response to antigen because of their cytokine profile

Immunological memory is a hallmark of adaptive immunity, and understanding T cell memory will be central to the development of effective cell-mediated vaccines. The characteristics and functions of CD4 memory cells have not been well defined. Here we demonstrate that the increased size of the secondary response is solely a consequence of the increased antigen-specific precursor frequency within the memory pool. Memory cells proliferated less than primary responding cells, even within the same host. By analyzing the entry of primary and memory cells into the cell cycle, we found that the two populations proliferated similarly until day 5; after this time, fewer of the reactivated memory cells proliferated. At this time, fewer of the reactivated memory cells made IL-2 than primary responding cells, but more made IFNγ. Both these factors affected the low proliferation of the memory cells, because either exogenous IL-2 or inhibition of IFNγ increased the proliferation of the memory cells

IL-2 receptor γ chain cytokines differentially regulate human CD8+CD127+ and CD8+CD127− T cell division and susceptibility to apoptosis

Expression of IL-7 receptor α (CD127) is associated with naive and memory (i.e. non-effector) CD8+ T cell phenotypes. Effector CD8+ T cells are predominantly CD127− and most die by apoptosis. Therefore, CD127 appears to be a marker for CD8+ T cell differentiation, yet its role in CD8+ T cell survival and memory development is unclear. To address this, we investigated the cell death and cell division of isolated CD8+CD127+ and CD8+CD127− T cells in response to common IL-2 receptor γ chain (γC) cytokines other than IL-7. We show here that (i) memory cells (CD127+CD45RA−) divide frequently in response to either IL-2, -4 or -15; (ii) IL-2 and -15 enhance cell division in effector–memory-like cells (CD127−CD45RA+) while IL-4 enhances the cell division of effector cells (CD127−CD45RA−); (iii) CD8+CD127+ T cells are more sensitive to the anti-apoptotic effects of IL-2 or IL-15 than CD8+CD127− T cells and (iv) CD8+CD127+ T cell produce more Bcl-2 in response to IL-2 or IL-15 compared with CD8+CD127− T cells. Therefore, CD8+CD127+ and CD8+CD127− T cells differ in their responsiveness to cell division and anti-apoptotic signals from IL-2, -4 and -15. This suggests a role for γC cytokines in the pathogenesis of diseases in which CD127 expression is altered on CD8+ T cells such as in progressive viral infections and cancer

GeorgeOral Immunization of Rhesus Macaques with Adenoviral HIV Vaccines Using Enteric-coated Capsules

Targeted delivery of vaccine candidates to the gastrointestinal (GI) tract holds potential for mucosal immunization, particularly against mucosal pathogens like the human immunodeficiency virus (HIV). Among the different strategies for achieving targeted release in the GI tract, namely the small intestine, pH sensitive enteric coating polymers have been shown to protect solid oral dosage forms from the harsh digestive environment of the stomach and dissolve relatively rapidly in the small intestine by taking advantage of the luminal pH gradient. We developed an enteric polymethacrylate formulation for coating hydroxy-propyl-methyl-cellulose (HPMC) capsules containing lyophilized Adenoviral type 5 (Ad5) vectors expressing HIV-1 gag and a string of six highly-conserved HIV-1 envelope peptides representing broadly cross-reactive CD4+ and CD8+ T cell epitopes. Oral immunization of rhesus macaques with these capsules primed antigen-specific mucosal and systemic immune responses and subsequent intranasal delivery of the envelope peptide cocktail using a mutant cholera toxin adjuvant boosted cellular immune responses including, antigen-specific intracellular IFN-γ-producing CD4+ and CD8+ effector memory T cells in the intestine. These results suggest that the combination of oral adenoviral vector priming followed by intranasal protein/peptide boosting may be an effective mucosal HIV vaccination strategy for targeting viral antigens to the GI tract and priming systemic and mucosal immunity

Persistence of tumor-infiltrating CD8 T cells is tumor-dependent but antigen-independent

How tumor-infiltrating lymphocytes (TILs) that are tumor-specific but functionally tolerant persist in the antigen-expressing tumor tissue is largely unknown. We have previously developed a modified TRansgenic Adenocarcinoma of the Mouse Prostate (TRAMP) model where prostate cancer cells express the T-cell epitope SIYRYYGL (SIY) recognized by CD8 T cells expressing the 2C T-cell receptor (TCR) (referred to as TRP-SIY mice). In TRP-SIY mice, activated 2C T cells rapidly become tolerant following infiltration into the prostate tumor. In this study, we show that tolerant 2C T cells persist in the prostate tumor of TRP-SIY mice by proliferating slowly in a tumor-dependent, but antigen-, interleukin (IL)-7- and IL-15-independent manner. We also show that disappearance of 2C T cells from the lymphoid organs of TRP-SIY mice are due to antigen-induced T-cell contraction rather than altered trafficking or generalized T-cell depletion in the mice. Finally, we show that clonal T cells unreactive to SIY are equally capable of persisting in the prostate tumor. These findings suggest that while functional tolerance of TILs is induced by antigen, persistence of tolerant TILs in the tumor tissue is mediated by a novel mechanism: slow proliferation independent of antigen and homeostatic cytokines. These results also allow CD8 T-cell survival in the tumor environment to be compared with T-cell survival in chronic infection

Absence of Both IL-7 and IL-15 Severely Impairs the Development of CD8+ T Cell Response against Toxoplasma gondii

CD8+ T cells play an essential role in the protection against both acute as well as chronic Toxoplasma gondii infection. Although the role of IL-15 has been reported to be important for the development of long-term CD8+ T cell immunity against the pathogen, the simultaneous roles played by both IL-15 and related γ-chain family cytokine IL-7 in the generation of this response during acute phase of infection has not been described. We demonstrate that while lack of IL-7 or IL-15 alone has minimal impact on splenic CD8+ T cell maturation or effector function development during acute Toxoplasmosis, absence of both IL-7 and IL-15 only in the context of infection severely down-regulates the development of a potent CD8+ T cell response. This impairment is characterized by reduction in CD44 expression, IFN-γ production, proliferation and cytotoxicity. However, attenuated maturation and decreased effector functions in these mice are essentially downstream consequences of reduced number of antigen-specific CD8+ T cells. Interestingly, the absence of both cytokines did not impair initial CD8+ T cell generation but affected their survival and differentiation into memory phenotype IL-7Rαhi cells. Significantly lack of both cytokines severely affected expression of Bcl-2, an anti-apoptotic protein, but minimally affected proliferation. The overarching role played by these cytokines in eliciting a potent CD8+ T cell immunity against T. gondii infection is further evidenced by poor survival and high parasite burden in anti IL-7 treated IL-15−/− mice. These studies demonstrate that the two cytokines, IL-7 and IL-15, are exclusively important for the development of protective CD8+ T cell immune response against T. gondii. To the best of our knowledge this synergism between IL-7 and IL-15 in generating an optimal CD8+ T cell immunity against intracellular parasite or any other infectious disease model has not been previously reported

TSC1/2 Signaling Complex Is Essential for Peripheral Naïve CD8+ T Cell Survival and Homeostasis in Mice

The PI3K-Akt-mTOR pathway plays crucial roles in regulating both innate and adaptive immunity. However, the role of TSC1, a critical negative regulator of mTOR, in peripheral T cell homeostasis remains elusive. With T cell-specific Tsc1 conditional knockout (Tsc1 KO) mice, we found that peripheral naïve CD8+ T cells but not CD4+ T cells were severely reduced. Tsc1 KO naïve CD8+ T cells showed profound survival defect in an adoptive transfer model and in culture with either stimulation of IL-7 or IL-15, despite comparable CD122 and CD127 expression between control and KO CD8+ T cells. IL-7 stimulated phosphorylation of Akt(S473) was diminished in Tsc1 KO naïve CD8+T cells due to hyperactive mTOR-mediated feedback suppression on PI3K-AKT signaling. Furthermore, impaired Foxo1/Foxo3a phosphorylation and increased pro-apoptotic Bim expression in Tsc1 KO naïve CD8+T cells were observed upon stimulation of IL-7. Collectively, our study suggests that TSC1 plays an essential role in regulating peripheral naïve CD8+ T cell homeostasis, possible via an mTOR-Akt-FoxO-Bim signaling pathway

Tissue Specific Deletion of Inhibitor of Kappa B Kinase 2 with OX40-Cre Reveals the Unanticipated Expression from the OX40 Locus in Skin Epidermis

NF-κB signalling plays an essential role in T cell activation and generation of regulatory and memory populations in vivo. In the present study, we aimed to investigate the role of NF-κB signalling in post-activation T cells using tissue specific ablation of inhibitor of kappa-B kinase 2 expression, an important component of the inhibitor of kappa-B kinase complex in canonical NF-κB signalling. The OX40 antigen is expressed on activated T cells. Therefore, we used previously described mouse strain expressing Cre recombinase from the endogenous OX40 locus. Ablation of IKK2 expression using OX40Cre mice resulted in the development of an inflammatory response in the skin epidermis causing wide spread skin lesions. The inflammatory response was characterised by extensive leukocytic infiltrate in skin tissue, hyperplasia of draining lymph nodes and widespread activation in the T cell compartment. Surprisingly, disease development did not depend on T cells but was rather associated with an unanticipated expression of Cre in skin epidermis, and activation of the T cell compartment did not require Ikbk2 deletion in T cells. Employment of Cre reporter strains revealed extensive Cre activity in skin epidermis. Therefore, development of skin lesions was rather more likely explained by deletion of Ikbk2 in skin keratinocytes in OX40Cre mice

IL-2 Mediates CD4+ T Cell Help in the Breakdown of Memory-Like CD8+ T Cell Tolerance under Lymphopenic Conditions

Background: Lymphopenia results in the proliferation and differentiation of naïve T cells into memory-like cells in the apparent absence of antigenic stimulation. This response, at least in part due to a greater availability of cytokines, is thought to promote anti-self responses. Although potentially autoreactive memory-like CD8 + T cells generated in a lymphopenic environment are subject to the mechanisms of peripheral tolerance, they can induce autoimmunity in the presence of antigen-specific memory-like CD4 + T helper cells. Methodology/Principal Findings: Here, we studied the mechanisms underlying CD4 help under lymphopenic conditions in transgenic mice expressing a model antigen in the beta cells of the pancreas. Surprisingly, we found that the self-reactivity mediated by the cooperation of memory-like CD8 + and CD4 + T cells was not abrogated by CD40L blockade. In contrast, treatment with anti-IL-2 antibodies inhibited the onset of autoimmunity. IL-2 neutralization prevented the CD4-mediated differentiation of memory-like CD8 + T cells into pathogenic effectors in response to self-antigen cross-presentation. Furthermore, in the absence of helper cells, induction of IL-2 signaling by an IL-2 immune complex was sufficient to promote memory-like CD8 + T cell self-reactivity. Conclusions/Significance: IL-2 mediates the cooperation of memory-like CD4 + and CD8 + T cells in the breakdown of crosstolerance, resulting in effector cytotoxic T lymphocyte differentiation and the induction of autoimmune disease

A CD8+ T cell transcription signature predicts prognosis in autoimmune disease.

Autoimmune diseases are common and debilitating, but their severe manifestations could be reduced if biomarkers were available to allow individual tailoring of potentially toxic immunosuppressive therapy. Gene expression-based biomarkers facilitating such tailoring of chemotherapy in cancer, but not autoimmunity, have been identified and translated into clinical practice. We show that transcriptional profiling of purified CD8(+) T cells, which avoids the confounding influences of unseparated cells, identifies two distinct subject subgroups predicting long-term prognosis in two autoimmune diseases, antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), a chronic, severe disease characterized by inflammation of medium-sized and small blood vessels, and systemic lupus erythematosus (SLE), characterized by autoantibodies, immune complex deposition and diverse clinical manifestations ranging from glomerulonephritis to neurological dysfunction. We show that the subset of genes defining the poor prognostic group is enriched for genes involved in the interleukin-7 receptor (IL-7R) pathway and T cell receptor (TCR) signaling and those expressed by memory T cells. Furthermore, the poor prognostic group is associated with an expanded CD8(+) T cell memory population. These subgroups, which are also found in the normal population and can be identified by measuring expression of only three genes, raise the prospect of individualized therapy and suggest new potential therapeutic targets in autoimmunity

Impact of the TCR Signal on Regulatory T Cell Homeostasis, Function, and Trafficking

Signaling through the T cell antigen receptor (TCR) is important for the homeostasis of naïve and memory CD4+ T cells. The significance of TCR signaling in regulatory T (Treg) cells has not been systematically addressed. Using an Ox40-cre allele that is prominently expressed in Treg cells, and a conditional null allele of the gene encoding p56Lck, we have examined the importance of TCR signaling in Treg cells. Inactivation of p56Lck resulted in abnormal Treg homeostasis characterized by impaired turnover, preferential redistribution to the lymph nodes, loss of suppressive function, and striking changes in gene expression. Abnormal Treg cell homeostasis and function did not reflect the involvement of p56Lck in CD4 function because these effects were not observed when CD4 expression was inactivated by Ox40-cre.The results make clear multiple aspects of Treg cell homeostasis and phenotype that are dependent on a sustained capacity to signal through the TCR