The decision between T cell activation and tolerance is governed by the spatial and temporal integration of diverse molecular signals and events occurring downstream of TCR and costimulatory or ...coinhibitory receptor engagement. The PI3K-protein kinase B (PKB; also known as Akt) signaling pathway is a central axis in mediating proximal signaling events of TCR and CD28 engagement in T cells. Perturbation of the PI3K-PKB pathway, or the loss of negative regulators of T cell activation, such as the E3 ubiquitin ligase Cbl-b, have been reported to lead to increased susceptibility to autoimmunity. In this study, we further examined the molecular pathway linking PKB and Cbl-b in murine models. Our data show that the protein kinase GSK-3, one of the first targets identified for PKB, catalyzes two previously unreported phosphorylation events at Ser
and Ser
of Cbl-b. GSK-3 inactivation by PKB abrogates phosphorylation of Cbl-b at these two sites and results in reduced Cbl-b protein levels. We further show that constitutive activation of PKB in vivo results in a loss of tolerance that is mediated through the downregulation of Cbl-b. Altogether, these data indicate that the PI3K-PKB-GSK-3 pathway is a novel regulatory axis that is important for controlling the decision between T cell activation and tolerance via Cbl-b.
CD8
T cells can be polarized into several different subsets as defined by the cytokines they produce and the transcription factors that govern their differentiation. Here, we identified the ...polarizing conditions to induce an IL22-producing CD8
Tc22 subset, which is dependent on IL6 and the aryl hydrocarbon receptor transcription factor. Further characterization showed that this subset was highly cytolytic and expressed a distinct cytokine profile and transcriptome relative to other subsets. In addition, polarized Tc22 were able to control tumor growth as well as, if not better than, the traditional IFNγ-producing Tc1 subset. Tc22s were also found to infiltrate the tumors of human patients with ovarian cancer, comprising up to approximately 30% of expanded CD8
tumor-infiltrating lymphocytes (TIL). Importantly, IL22 production in these CD8
TILs correlated with improved recurrence-free survival. Given the antitumor properties of Tc22 cells, it may be prudent to polarize T cells to the Tc22 lineage when using chimeric antigen receptor (CAR)-T or T-cell receptor (TCR) transduction-based immunotherapies.
Although toll-like receptor (TLR) signals are critical for promoting antigen presenting cell maturation, it remains unclear how stimulation via different TLRs influence dendritic cell (DC) function ...and the subsequent adaptive response in vivo. Furthermore, the relationship between TLR-induced cytokine production by DCs and the consequences on the induction of a functional immune response is not clear. We have established a murine model to examine whether TLR3 or TLR4 mediated DC maturation has an impact on the cytokines required to break tolerance and induce T-cell-mediated autoimmunity. Our study demonstrates that IL-12 is not absolutely required for the induction of a CD8 T-cell-mediated tissue specific immune response, but rather the requirement for IL-12 is determined by the stimuli used to mature the DCs. Furthermore, we found that IFNα is a critical pathogenic component of the cytokine milieu that circumvents the requirement for IL-12 in the induction of autoimmunity. These studies illustrate how different TLR stimuli have an impact on DC function and the induction of immunity.
Regulatory T cells (Treg) are an integral component of the adaptive immune system that negatively affect antitumor immunity. Here, we investigated the role of the E3 ubiquitin ligase casitas ...B-lineage lymphoma-b (Cbl-b) in establishing CD8+ T-cell resistance to Treg-mediated suppression to enhance antitumor immunity. Transcriptomic analyses suggested that Cbl-b regulates pathways associated with cytokine signaling and cellular proliferation. We showed that the hypersecretion of IFNγ by Cbl-b-deficient CD8+ T cells selectively attenuated CD8+ T-cell suppression by Tregs. Although IFNγ production by Cbl-b-deficient T cells contributed to phenotypic alterations in Tregs, the cytokine did not attenuate the suppressive function of Tregs. Instead, IFNγ had a profound effect on CD8+ T cells by directly upregulating interferon-stimulated genes and modulating T-cell activation. In murine models of adoptive T-cell therapy, Cbl-b-deficient T cells elicited superior antitumor immune response. Furthermore, Cbl-b-deficient CD8+ T cells were less susceptible to suppression by Tregs in the tumor through the effects of IFNγ. Collectively, this study demonstrates that the hypersecretion of IFNγ serves as a key mechanism by which Cbl-b-deficient CD8+ T cells are rendered resistant to Tregs. See related Spotlight by Wolf and Baier, p. 370.
Regulatory T (Treg) cells are crucial for maintaining peripheral tolerance and controlling T-cell responses. The generation of Treg in the thymus requires TCR triggering and CD28 costimulation. ...Engagement of these receptors induces a number of signalling pathways, including the activation of NF-κB via PKCθ and the Bcl-10/CARMA1/MALT complex. Previous studies have shown that PKCθ, Bcl-10 and CARMA1 are important for Treg development. It is unclear, however, whether different members of the NF-κB family contribute to Treg development or homeostasis. In this study, we show that Treg numbers are reduced in the absence of c-Rel but not NF-κB1 (p50). Furthermore, using mixed bone marrow chimeras from WT and KO animals, we demonstrate that the requirement for PKCθ, Bcl-10 and c-Rel is T-cell intrinsic, and cannot be rescued by the presence of WT cells. Therefore, c-Rel and NF-κB1 have differential roles in Treg development.
The signaling adaptor TNFR-associated factor 1 (TRAF1) is specifically lost from virus-specific CD8 T cells during the chronic phase of infection with HIV in humans or lymphocytic choriomeningitis ...virus (LCMV) clone 13 in mice. In contrast, TRAF1 is maintained at higher levels in virus-specific T cells of HIV controllers or after acute LCMV infection. TRAF1 expression negatively correlates with programmed death 1 expression and HIV load and knockdown of TRAF1 in CD8 T cells from viral controllers results in decreased HIV suppression ex vivo. Consistent with the desensitization of the TRAF1-binding co-stimulatory receptor 4-1BB, 4-1BBL-deficient mice have defects in viral control early, but not late, in chronic infection. TGFβ induces the posttranslational loss of TRAF1, whereas IL-7 restores TRAF1 levels. A combination treatment with IL-7 and agonist anti-4-1BB antibody at 3 wk after LCMV clone 13 infection expands T cells and reduces viral load in a TRAF1-dependent manner. Moreover, transfer of TRAF1(+) but not TRAF1(-) memory T cells at the chronic stage of infection reduces viral load. These findings identify TRAF1 as a potential biomarker of HIV-specific CD8 T cell fitness during the chronic phase of disease and a target for therapy.
The manipulation of T cell metabolism to enhance anti-tumor activity is an area of active investigation. Here, we report that activating the amino acid starvation response in effector CD8+ T cells ...ex vivo using the general control non-depressible 2 (GCN2) agonist halofuginone (halo) enhances oxidative metabolism and effector function. Mechanistically, we identified autophagy coupled with the CD98-mTOR axis as key downstream mediators of the phenotype induced by halo treatment. The adoptive transfer of halo-treated CD8+ T cells into tumor-bearing mice led to robust tumor control and curative responses. Halo-treated T cells synergized in vivo with a 4-1BB agonistic antibody to control tumor growth in a mouse model resistant to immunotherapy. Importantly, treatment of human CD8+ T cells with halo resulted in similar metabolic and functional reprogramming. These findings demonstrate that activating the amino acid starvation response with the GCN2 agonist halo can enhance T cell metabolism and anti-tumor activity.
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•Arginine (arg) withdrawal activates the GCN2 pathway in CD8+ T cells•Activation of GCN2 increases oxidative metabolism and effector function in CD8+ T cells•Halofuginone (halo) induces the same phenotype as arg withdrawal in CD8+ T cells•Halo enhances the efficacy of CD8+ T cells in models of adoptive cell therapy
The impact of GCN2 signaling on the function and metabolism of activated CD8+ T cells was unclear. St. Paul et al. demonstrate that activation of GCN2 in CD8+ T cells results in increased oxidative metabolism and anti-tumor activity. Targeting GCN2 can be a new avenue to enhance cancer immunotherapy.
Autoimmune diseases may develop because of defective maturation, activation, differentiation and function of regulatory T cells. Previous studies have shown that exposure to donor antigen activates ...peripheral TCRαβ+CD3+CD4–CD8–NK1.1–, double‐negative (DN) T cells, which specifically suppress anti‐donor T cells and enhance survival of skin and heart grafts from allogeneic and xenogeneic donors. However, the role of DN T cells in preventing T cell‐mediated autoimmune disease is unknown. Here, we analyzed the ability of DN T cells to recognize peptides expressed on self MHC and to suppress peptide‐reactive CD8+ T cells, using the P14 mouse model that expresses a transgenic TCR specific for gp33 peptide presented on self MHC class I‐Db. We found that injection of gp33 peptide resulted in increased DN and decreased CD8+ T cell numbers in the lymph nodes when compared to untreated mice. Injection of gp33, but not TCR‐non‐specific AV peptide, increased expression of T cell activation markers on DN T cells. Moreover, gp33‐activated DN T cells suppressed proliferation of syngeneic CD8+ T cells via killing activated CD8+ T cells in an antigen‐specific fashion in vitro. Furthermore, transferring gp33‐activated DN T cells inhibited the development of autoimmune diabetes, suggesting that DN T cells may provide a novel therapy for T cell‐mediated autoimmune diseases.
The T cell costimulatory molecule CD28 is important for T cell survival, yet both the signaling pathways downstream of CD28 and the apoptotic pathways they antagonize remain poorly understood. Here ...we demonstrate that CD4(+) T cells from CD28-deficient mice show increased susceptibility to Fas-mediated apoptosis via a phosphatidylinositol 3-kinase (PI3K)-dependent pathway. Protein kinase B (PKBalpha/Akt1) is an important serine/threonine kinase that promotes survival downstream of PI3K signals. To understand how PI3K-mediated signals downstream of CD28 contribute to T cell survival, we examined Fas-mediated apoptosis in T cells expressing an active form of PKBalpha. Our data demonstrate that T cells expressing active PKB are resistant to Fas-mediated apoptosis in vivo and in vitro. PKB transgenic T cells show reduced activation of caspase-8, BID, and caspase-3 due to impaired recruitment of procaspase-8 to the death-inducing signaling complex (DISC). Similar alterations are seen in T cells from mice which are haploinsufficient for PTEN, a lipid phosphatase that regulates phosphatidylinositol-3,4,5-trisphosphate (PIP(3)) and influences PKBalpha activity. These findings provide a novel link between CD28 and an important apoptosis pathway in vivo, and demonstrate that PI3K/PKB signaling prevents apoptosis by inhibiting DISC assembly.
The p53-induced protein with a death domain, PIDD, was identified as a p53 target gene whose main role is to execute apoptosis in a p53-dependent manner. To investigate the physiological role of PIDD ...in apoptosis, we generated PIDD-deficient mice. Here, we report that, although PIDD expression is inducible upon DNA damage, PIDD-deficient mice undergo apoptosis normally not only in response to DNA damage, but also in response to various p53-independent stress signals and to death receptor (DR) engagement. This indicates that PIDD is not required for DNA damage-, stress-, and DR-induced apoptosis. Also, in the absence of PIDD, both caspase-2 processing and activation occur in response to DNA damage. Our findings demonstrate that PIDD does not play an essential role for all p53-mediated or p53-independent apoptotic pathways.
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