An interleukin-21-interleukin-10-STAT3 pathway is critical for functional maturation of memory CD8+ T cells

Antigen-specific culture of memory-like CD8 T cells for adoptive immunotherapy

Cytotoxic T cells typically are expanded ex vivo in culture with IL2 for adoptive immunotherapy. This culture period leads to a differentiated phenotype and acquisition of effector function, as well as a loss of in vivo proliferative capability and antitumor efficacy. Here, we report antigen-specific and polyclonal expansion of cytotoxic T cells in a cocktail of cytokines and small molecules that leads to a memory-like phenotype in mouse and human cells even during extended culture, leading to enhanced in vivo expansion and tumor control in mice.

T cell-intrinsic role of IL-6 signaling in primary and memory responses

Innate immune recognition is critical for the induction of adaptive immune responses; however the underlying mechanisms remain incompletely understood. In this study, we demonstrate that T cell-specific deletion of the IL-6 receptor α chain (IL-6Rα) results in impaired Th1 and Th17 T cell responses in vivo, and a defect in Tfh function. Depletion of Tregs in these mice rescued the Th1 but not the Th17 response. Our data suggest that IL-6 signaling in effector T cells is required to overcome Treg-mediated suppression in vivo. We show that IL-6 cooperates with IL-1β to block the suppressive effect of Tregs on CD4⁺ T cells, at least in part by controlling their responsiveness to IL-2. In addition, although IL-6Rα-deficient T cells mount normal primary Th1 responses in the absence of Tregs, they fail to mature into functional memory cells, demonstrating a key role for IL-6 in CD4⁺ T cell memory formation.

DOI:http://dx.doi.org/10.7554/eLife.01949.001

The human body's ability to defend itself against pathogens relies on two distinct but connected systems: the innate and the adaptive immune systems. Innate immune cells survey their environment and use receptors located on their surface to distinguish between molecules that are harmless and molecules that stem from pathogens. When the cells of the innate immune system detect a pathogen, they secrete signaling molecules to alert adaptive immune cells to the invaders. Both sets of immune cells then mount a coordinated attack that usually kills the pathogen.

The adaptive immune system also produces memory cells that retain information about the pathogen: this allows the organism to mount a fast and efficient immune response the next time the same type of pathogen strikes. However, it is not completely understood how the innate immune system communicates with the adaptive immune system to allow these processes to take place.

One of the signaling molecules involved in the communication between different types of immune cells is a protein called Interleukin 6 (IL-6). This protein must be produced in order to trigger the immune response: however, many immune cells are able to recognize and respond to IL-6, so it has been difficult to study its impact on specific cell types.

Nish et al. have now investigated the effects of IL-6 on T cells, one of the main types of adaptive immune cell, by creating mice with T cells that are not able to recognize IL-6. The detection of pathogens by innate immune cells normally has several effects: the population of T cells increases; the T cells produce daughter cells—T helper cells—that support innate immune cells in killing pathogens; and memory cells are formed. Nish et al. find that these responses are impaired in the mutant mice.

To understand why, Nish et al. turn to T regulatory cells; these are adaptive immune cells that control the strength of the immune response. These experiments show that when T cells are ‘blind’ to IL-6, they are more sensitive to the action of T regulatory cells, and this disturbs the delicate balance between the stimulation and inhibition of the immune system. Nish et al. go on to show that IL-6 works together with another signaling molecule, Interleukin 1, to regulate how the T cells respond. The work helps to explain how the adaptive immune system mounts an immune response against pathogens but not against the host's own tissues.

DOI:http://dx.doi.org/10.7554/eLife.01949.002

Graded levels of IRF4 regulate CD8+ T cell differentiation and expansion, but not attrition, in response to acute virus infection

In response to acute virus infections, CD8(+) T cells differentiate to form a large population of short-lived effectors and a stable pool of long-lived memory cells. The characteristics of the CD8(+) T cell response are influenced by TCR affinity, Ag dose, and the inflammatory cytokine milieu dictated by the infection. To address the mechanism by which differences in TCR signal strength could regulate CD8(+) T cell differentiation, we investigated the transcription factor, IFN regulatory factor 4 (IRF4). We show that IRF4 is transiently upregulated to differing levels in murine CD8(+) T cells, based on the strength of TCR signaling. In turn, IRF4 controls the magnitude of the CD8(+) T cell response to acute virus infection in a dose-dependent manner. Modest differences in IRF4 expression dramatically influence the numbers of short-lived effector cells at the peak of the infection, but have no impact on the kinetics of the infection or on the rate of T cell contraction. Furthermore, the expression of key transcription factors such as T cell factor 1 and Eomesodermin are highly sensitive to graded levels of IRF4. In contrast, T-bet expression is less dependent on IRF4 levels and is influenced by the nature of the infection. These data indicate that IRF4 is a key component that translates the strength of TCR signaling into a graded response of virus-specific CD8(+) T cells.

Assessing the role of STAT3 in DC differentiation and autologous DC immunotherapy in mouse models of GBM

Cellular microenvironments, particularly those found in tumors, elicit a tolerogenic DC phenotype which can attenuate immune responses. Central to this process is the STAT3-mediated signaling cascade. As a transcription factor and oncogene, STAT3 promotes the expression of genes which allow tumor cells to proliferate, migrate and evade apoptosis. More importantly, activation of STAT3 in tumor infiltrating immune cells has been shown to be responsible, in part, for their immune-suppressed phenotype. The ability of STAT3 to orchestrate a diverse set of immunosuppressive instructions has made it an attractive target for cancer vaccines. Using a conditional hematopoietic knockout mouse model of STAT3, we evaluated the impact of STAT3 gene ablation on the differentiation of dendritic cells from bone marrow precursors. We also assessed the impact of STAT3 deletion on phagocytosis, maturation, cytokine secretion and antigen presentation by GM-CSF derived DCs in vitro. In addition to in vitro studies, we compared the therapeutic efficacy of DC vaccination using STAT3 deficient DCs to wild type counterparts in an intracranial mouse model of GBM. Our results indicated the following pleiotropic functions of STAT3: hematopoietic cells which lacked STAT3 were unresponsive to Flt3L and failed to differentiate as DCs. In contrast, STAT3 was not required for GM-CSF induced DC differentiation as both wild type and STAT3 null bone marrow cells gave rise to similar number of DCs. STAT3 also appeared to regulate the response of GM-CSF derived DCs to CpG. STAT3 null DCs expressed high levels of MHC-II, secreted more IL-12p70, IL-10, and TNFα were better antigen presenters in vitro. Although STAT3 deficient DCs displayed an enhanced activated phenotype in culture, they elicited comparable therapeutic efficacy in vivo compared to their wild type counterparts when utilized in vaccination paradigms in mice bearing intracranial glioma tumors.

TLR4 ligands lipopolysaccharide and monophosphoryl lipid a differentially regulate effector and memory CD8+ T Cell differentiation

Vaccines formulated with nonreplicating pathogens require adjuvants to help bolster immunogenicity. The role of adjuvants in Ab production has been well studied, but how they influence memory CD8(+) T cell differentiation remains poorly defined. In this study we implemented dendritic cell-mediated immunization to study the effects of commonly used adjuvants, TLR ligands, on effector and memory CD8(+) T cell differentiation in mice. Intriguingly, we found that the TLR4 ligand LPS was far more superior to other TLR ligands in generating memory CD8(+) T cells upon immunization. LPS boosted clonal expansion similar to the other adjuvants, but fewer of the activated CD8(+) T cells died during contraction, generating a larger pool of memory cells. Surprisingly, monophosphoryl lipid A (MPLA), another TLR4 ligand, enhanced clonal expansion of effector CD8(+) T cells, but it also promoted their terminal differentiation and contraction; thus, fewer memory CD8(+) T cells formed, and MPLA-primed animals were less protected against secondary infection compared with those primed with LPS. Furthermore, gene expression profiling revealed that LPS-primed effector cells displayed a stronger pro-memory gene expression signature, whereas the gene expression profile of MPLA-primed effector cells aligned closer with terminal effector CD8(+) T cells. Lastly, we demonstrated that the LPS-TLR4-derived "pro-memory" signals were MyD88, but not Toll/IL-1R domain-containing adapter inducing IFN-β, dependent. This study reveals the influential power of adjuvants on the quantity and quality of CD8(+) T cell memory, and that attention to adjuvant selection is crucial because boosting effector cell expansion may not always equate with more memory T cells or greater protection.

Interleukin-21: a double-edged sword with therapeutic potential

Interleukin-21 is a cytokine with broad pleiotropic actions that affect the differentiation and function of lymphoid and myeloid cells. Since its discovery in 2000, a tremendous amount has been learned about its biological actions and the molecular mechanisms controlling IL-21-mediated cellular responses. IL-21 regulates both innate and adaptive immune responses, and it not only has key roles in antitumour and antiviral responses but also exerts major effects on inflammatory responses that promote the development of autoimmune diseases and inflammatory disorders. Numerous studies have shown that enhancing or inhibiting the action of IL-21 has therapeutic effects in animal models of a wide range of diseases, and various clinical trials are underway. The current challenge is to understand how to specifically modulate the actions of IL-21 in the context of each specific immune response or pathological situation. In this Review, we provide an overview of the basic biology of IL-21 and discuss how this information has been - and can be - exploited therapeutically.

Id2 represses E2A-mediated activation of IL-10 expression in T cells

Interleukin-10 (IL-10) is a key immunoregulatory cytokine that functions to prevent inflammatory and autoimmune diseases. Despite the critical role for IL-10 produced by effector CD8(+) T cells during pathogen infection and autoimmunity, the mechanisms regulating its production are poorly understood. We show that loss of the inhibitor of DNA binding 2 (Id2) in T cells resulted in aberrant IL-10 expression in vitro and in vivo during influenza virus infection and in a model of acute graft-versus-host disease (GVHD). Furthermore, IL-10 overproduction substantially reduced the immunopathology associated with GVHD. We demonstrate that Id2 acts to repress the E2A-mediated trans-activation of the Il10 locus. Collectively, our findings uncover a key regulatory role of Id2 during effector T cell differentiation necessary to limit IL-10 production by activated T cells and minimize their suppressive activity during the effector phase of disease control.

STAT3, STAT4, NFATc1, and CTCF regulate PD-1 through multiple novel regulatory regions in murine T cells

Programmed death-1 (PD-1) is a crucial negative regulator of CD8 T cell development and function, yet the mechanisms that control its expression are not fully understood. Through a nonbiased DNase I hypersensitivity assay, four novel regulatory regions within the Pdcd1 locus were identified. Two of these elements flanked the locus, bound the transcriptional insulator protein CCCTC-binding factor, and interacted with each other, creating a potential regulatory compartmentalization of the locus. In response to T cell activation signaling, NFATc1 bound to two of the novel regions that function as independent regulatory elements. STAT binding sites were identified in these elements as well. In splenic CD8 T cells, TCR-induced PD-1 expression was augmented by IL-6 and IL-12, inducers of STAT3 and STAT4 activity, respectively. IL-6 or IL-12 on its own did not induce PD-1. Importantly, STAT3/4 and distinct chromatin modifications were associated with the novel regulatory regions following cytokine stimulation. The NFATc1/STAT regulatory regions were found to interact with the promoter region of the Pdcd1 gene, providing a mechanism for their action. Together these data add multiple novel distal regulatory regions and pathways to the control of PD-1 expression and provide a molecular mechanism by which proinflammatory cytokines, such as IL-6 or IL-12, can augment PD-1 expression.

IFN-λ exerts opposing effects on T cell responses depending on the chronicity of the virus infection

IFN-λ induces an antiviral state in many cell types and may contribute to the overall inflammatory environment after infection. Either of these effects may influence adaptive immune responses, but the role of type 3 IFNs in the development of primary and memory T cell responses to infection has not been evaluated. In this study, we examined T cell responses to acute or persistent lymphocytic choriomeningitis virus infection in IFN-λR1-deficient mice. Following acute infection, we find that IFN-λR1-deficient mice produced normal levels of IFN, robust NK cell responses, but greater than normal CD4+ and CD8+ T cell responses compared with wild type BALB/c mice. There were more T cells that were IL-7R(hi) and, correspondingly, the IFN-λR-deficient mice showed a 2- to 3-fold increase in memory T cell number. The inhibitory effect of IFN-λR expression was independent of direct cytokine signaling into T cells. In contrast with acute infection, the IFN-λR-deficient mice generated markedly diminished T cell responses and had greater weight loss compared with wild type mice when confronted with a highly disseminating variant of lymphocytic choriomeningitis virus. These data indicate that IFN-λR limits T cell responses and memory after transient infection but augments T cell responses during persisting infection. Thus, the immune-regulatory functions for IFN-λR are complex and vary with the overall inflammatory environment.

Mir-155, a central modulator of T-cell responses

The activation of T cells is a tightly regulated process that has evolved to maximize protective immune responses to pathogens while minimizing damage to self-tissues. A delicate balance of cell-intrinsic, costimulatory, and transcriptional pathways as well as micro-environmental cues such as local cytokines controls the magnitude and nature of T-cell responses in vivo. The discovery of functional small noncoding RNAs called micro-RNAs (miRNAs) has introduced new mechanisms that contribute to the regulation of protein translation and cellular responses to stimuli. miRNAs are short (approximately 22 bp) RNA species, which bind to mRNAs and suppress translation. Due to their short length and imperfect base pairing requirements, each miRNA has the potential to regulate various pathways through the translational inhibition of multiple mRNAs. The human and mouse genomes each encode hundreds of miRNAs, and studying the function of miRNAs has led to the realization that they play important roles in diverse biological processes from development and cancer to immunity. This review focuses on the function of mir-155 in T cells and the impact of this miRNA on autoimmunity, tumor immunity, and pathogen-induced immunity.

Transcription factor STAT3 and type I interferons are corepressive insulators for differentiation of follicular helper and T helper 1 cells

Follicular helper T (Tfh) cells are required for the establishment of T-dependent B cell memory and high affinity antibody-secreting cells. We have revealed herein opposing roles for signal transducer and activator of transcription 3 (STAT3) and type I interferon (IFN) signaling in the differentiation of Tfh cells following viral infection. STAT3-deficient CD4(+) T cells had a profound defect in Tfh cell differentiation, accompanied by decreased germinal center (GC) B cells and antigen-specific antibody production during acute infection with lymphocytic choriomeningitis virus. STAT3-deficient Tfh cells had strikingly increased expression of a number of IFN-inducible genes, in addition to enhanced T-bet synthesis, thus adopting a T helper 1 (Th1) cell-like effector phenotype. Conversely, IFN-αβ receptor blockade restored Tfh and GC B cell phenotypes in mice containing STAT3-deficient CD4(+) T cells. These data suggest mutually repressive roles for STAT3 and type I IFN signaling pathways in the differentiation of Tfh cells following viral infection.

STAT3 is a central regulator of lymphocyte differentiation and function

Signalling in lymphocytes through cytokine receptors is critical for their development, activation and differentiation into effector cells that mediate protection against pathogens and provide the host with protective immunological memory. The essential role of cytokine signalling has been established not only by the generation and examination of gene-targeted mice, but also 'Experiments of Nature' whereby monogenic mutations cause primary immunodeficient conditions characterised by impaired immunity to infectious diseases due to compromised lymphocyte function. Mutations in STAT3 cause autosomal dominant hyper-IgE syndrome. Here, we will review how the study of STAT3-deficient individuals has revealed non-redundant functions of STAT3 and specific cytokines in human lymphocyte biology, and have delineated mechanisms underlying the distinct clinical features of autosomal dominant hyper-IgE syndrome.

SOCS3, a Major Regulator of Infection and Inflammation

In this review, we describe the role of suppressor of cytokine signaling-3 (SOCS3) in modulating the outcome of infections and autoimmune diseases as well as the underlying mechanisms. SOCS3 regulates cytokine or hormone signaling usually preventing, but in some cases aggravating, a variety of diseases. A main role of SOCS3 results from its binding to both the JAK kinase and the cytokine receptor, which results in the inhibition of STAT3 activation. Available data also indicate that SOCS3 can regulate signaling via other STATs than STAT3 and also controls cellular pathways unrelated to STAT activation. SOCS3 might either act directly by hampering JAK activation or by mediating the ubiquitination and subsequent proteasome degradation of the cytokine/growth factor/hormone receptor. Inflammation and infection stimulate SOCS3 expression in different myeloid and lymphoid cell populations as well as in diverse non-hematopoietic cells. The accumulated data suggest a relevant program coordinated by SOCS3 in different cell populations, devoted to the control of immune homeostasis in physiological and pathological conditions such as infection and autoimmunity.

Early Decision: Effector and Effector Memory T Cell Differentiation in Chronic Infection

As effector memory T cells (Tem) are the predominant population elicited by chronic parasitic infections, increasing our knowledge of their function, survival and derivation, as phenotypically and functionally distinct from central memory and effector T cells will be critical to vaccine development for these diseases. In some infections, memory T cells maintain increased effector functions, however; this may require the presence of continued antigen, which can also lead to T cell exhaustion. Alternatively, in the absence of antigen, only the increase in the number of memory cells remains, without enhanced functionality as central memory. In order to understand the requirement for antigen and the potential for longevity or protection, the derivation of each type of memory must be understood. A thorough review of the data establishes the existence of both memory (Tmem) precursors and effector T cells (Teff) from the first hours of an immune response. This suggests a new paradigm of Tmem differentiation distinct from the proposition that Tmem only appear after the contraction of Teff. Several signals have been shown to be important in the generation of memory T cells, such as the integrated strength of “signals 1-3” of antigen presentation (antigen receptor, co-stimulation, cytokines) as perceived by each T cell clone. Given that these signals integrated at antigen presentation cells have been shown to determine the outcome of Teff and Tmem phenotypes and numbers, this decision must be made at a very early stage. It would appear that the overwhelming expansion of effector T cells and the inability to phenotypically distinguish memory T cells at early time points has masked this important decision point. This does not rule out an effect of repeated stimulation or chronic inflammatory milieu on populations generated in these early stages. Recent studies suggest that Tmem are derived from early Teff, and we suggest that this includes Tem as well as Tcm. Therefore, we propose a testable model for the pathway of differentiation from naïve to memory that suggests that Tem are not fully differentiated effector cells, but derived from central memory T cells as originally suggested by Sallusto et al. in 1999, but much debated since.

Essential role of IL-10/STAT3 in chronic stress-induced immune suppression

Stress can either enhance or suppress immune functions depending on a variety of factors such as duration of stressful condition. Chronic stress has been demonstrated to exert a significant suppressive effect on immune function. However, the mechanisms responsible for this phenomenon remain to be elucidated. Here, male C57BL/6 mice were placed in a 50-ml conical centrifuge tube with multiple punctures to establish a chronic restraint stress model. Serum IL-10 levels, IL-10 production by the splenocytes, and activation of STAT3 in the mouse spleen were assessed. We demonstrate that IL-10/STAT3 axis was remarkably activated following chronic stress. Moreover, TLR4 and p38 MAPK play a pivotal role in the activation of IL-10/STAT3 signaling cascade. Interestingly, blocking antibody against IL-10 receptor and inhibition of STAT3 by STAT3 inhibitor S3I-201 attenuates stress-induced lymphocyte apoptosis. Inhibition of IL-10/STAT3 dramatically inhibits stress-induced reduction in IL-12 production. Furthermore, disequilibrium of Th1/Th2 cytokine balance caused by chronic stress was also rescued by blocking IL-10/STAT3 axis. These results yield insight into a new mechanism by which chronic stress regulates immune functions. IL-10/STAT3 pathway provides a novel relevant target for the manipulation of chronic stress-induced immune suppression.

Re-adapting T cells for cancer therapy: from mouse models to clinical trials

Adoptive T-cell therapy involves the isolation, expansion, and reinfusion of T lymphocytes with a defined specificity and function as a means to eradicate cancer. Our research has focused on specifying the requirements for tumor eradication with antigen-specific T cells and T cells transduced to express a defined T-cell receptor (TCR) in mouse models and then translating these strategies to clinical trials. Our design of T-cell-based therapy for cancer has reflected efforts to identify the obstacles that limit sustained effector T-cell activity in mice and humans, design approaches to enhance T-cell persistence, develop methods to increase TCR affinity/T-cell functional avidity, and pursue strategies to overcome tolerance and immunosuppression. With the advent of genetic engineering, a highly functional population of T cells can now be rapidly generated and tailored for the targeted malignancy. Preclinical studies in faithful and informative mouse models, in concert with knowledge gained from analyses of successes and limitations in clinical trials, are shaping how we continue to develop, refine, and broaden the applicability of this approach for cancer therapy.

Vaccinated C57BL/6 mice develop protective and memory T cell responses to Coccidioides posadasii infection in the absence of interleukin-10

High concentrations of lung tissue-associated interleukin-10 (IL-10), an anti-inflammatory and immunosuppressive cytokine, correlate with susceptibility of mice to Coccidioides spp. infection. In this study, we found that macrophages, dendritic cells, neutrophils, and both CD8(+) and CD4(+) T cells recruited to Coccidioides posadasii-infected lungs of nonvaccinated and vaccinated mice contributed to the production of IL-10. The major IL-10-producing leukocytes were CD8(+) T cells, neutrophils, and macrophages in lungs of nonvaccinated mice, while both Foxp3(+) and Foxp3(-) subsets of IL-10(+) CD4(+) T cells were significantly elevated in vaccinated mice. Profiles of the recruited leukocytes in lungs revealed that only CD4(+) T cells were significantly increased in IL-10(-/-) knockout mice compared to their wild-type counterparts. Furthermore, ex vivo recall assays showed that CD4(+) T cells isolated from vaccinated IL-10(-/-) mice compared to vaccinated wild-type mice produced significantly higher amounts of IL-2, gamma interferon (IFN-γ), IL-4, IL-6, and IL-17A in the presence of a coccidioidal antigen, indicating that IL-10 suppresses Th1, Th2, and Th17 immunity to Coccidioides infection. Analysis of absolute numbers of CD44(+) CD62L(-) CD4(+) T effector memory T cells (TEM) and IFN-γ- and IL-17A-producing CD4(+) T cells in the lungs of Coccidioides-infected mice correlated with better fungal clearance in nonvaccinated IL-10(-/-) mice than in nonvaccinated wild-type mice. Our results suggest that IL-10 suppresses CD4(+) T-cell immunity in nonvaccinated mice during Coccidioides infection but does not impede the development of a memory response nor exacerbate immunopathology of vaccinated mice over at least a 4-month period after the last immunization.

Stemness of T cells and the hematopoietic stem cells: fate, memory, niche, cytokines

Stem cells are able to generate both cells that differentiate and cells that remain undifferentiated but potentially have the same developmental program. The prolonged duration of the protective immune memory for infectious diseases such as polio, small pox, and measles, suggested that memory T cells may have stem cell properties. Understanding the molecular basis for the life-long persistence of memory T cells may be useful to project targeted therapies for immune deficiencies and infectious diseases and to formulate vaccines. In the last decade evidence from different laboratories shows that memory T cells may share self-renewal pathways with bone marrow hematopoietic stem cells. In stem cells the intrinsic self-renewal activity, which depends on gene expression, is known to be modulated by extrinsic signals from the environment that may be tissue specific. These extrinsic signals for stemness of memory T cells include cytokines such as IL-7 and IL-15 and there are other cytokine signals for maintaining the cytokine signature (TH1, TH2, etc.) of memory T cells. Intrinsic and extrinsic pathways that might be common to bone marrow hematopoietic stem cells and memory T lymphocytes are discussed and related to self-renewal functions.

Antigen availability determines CD8⁺ T cell-dendritic cell interaction kinetics and memory fate decisions

T cells are activated by antigen (Ag)-bearing dendritic cells (DCs) in lymph nodes in three phases. The duration of the initial phase of transient, serial DC-T cell interactions is inversely correlated with Ag dose. The second phase, characterized by stable DC-T cell contacts, is believed to be necessary for full-fledged T cell activation. Here we have shown that this is not the case. CD8⁺ T cells interacting with DCs presenting low-dose, short-lived Ag did not transition to phase 2, whereas higher Ag dose yielded phase 2 transition. Both antigenic constellations promoted T cell proliferation and effector differentiation but yielded different transcriptome signatures at 12 hr and 24 hr. T cells that experienced phase 2 developed long-lived memory, whereas conditions without stable contacts yielded immunological amnesia. Thus, T cells make fate decisions within hours after Ag exposure, resulting in long-term memory or abortive effector responses, correlating with T cell-DCs interaction kinetics.

Interferon-dependent IL-10 production by Tregs limits tumor Th17 inflammation

The capacity of IL-10 and Tregs in the inflammatory tumor microenvironment to impair anticancer Th1 immunity makes them attractive targets for cancer immunotherapy. IL-10 and Tregs also suppress Th17 activity, which is associated with poor prognosis in several cancers. However, previous studies have overlooked their potential contribution to the regulation of pathogenic cancer-associated inflammation. In this study, we investigated the origin and function of IL-10–producing cells in the tumor microenvironment using transplantable tumor models in mice. The majority of tumor-associated IL-10 was produced by an activated Treg population. IL-10 production by Tregs was required to restrain Th17-type inflammation. Accumulation of activated IL-10+ Tregs in the tumor required type I IFN signaling but not inflammatory signaling pathways that depend on TLR adapter protein MyD88 or IL-12 family cytokines. IL-10 production limited Th17 cell numbers in both spleen and tumor. However, type I IFN was required to limit Th17 cells specifically in the tumor microenvironment, reflecting selective control of tumor-associated Tregs by type I IFN. Thus, the interplay of type I IFN, Tregs, and IL-10 is required to negatively regulate Th17 inflammation in the tumor microenvironment. Therapeutic interference of this network could therefore have the undesirable consequence of promoting Th17 inflammation and cancer growth.

IL-27 receptor signaling regulates memory CD4+ T cell populations and suppresses rapid inflammatory responses during secondary malaria infection

Interleukin-27 (IL-27) is known to control primary CD4(+) T cell responses during a variety of different infections, but its role in regulating memory CD4(+) T responses has not been investigated in any model. In this study, we have examined the functional importance of IL-27 receptor (IL-27R) signaling in regulating the formation and maintenance of memory CD4(+) T cells following malaria infection and in controlling their subsequent reactivation during secondary parasite challenge. We demonstrate that although the primary effector/memory CD4(+) T cell response was greater in IL-27R-deficient (WSX-1(-/-)) mice following Plasmodium berghei NK65 infection than in wild-type (WT) mice, there were no significant differences in the size of the maintained memory CD4(+) T population(s) at 20 weeks postinfection in the spleen, liver, or bone marrow of WSX-1(-/-) mice compared with WT mice. However, the composition of the memory CD4(+) T cell pool was slightly altered in WSX-1(-/-) mice following clearance of primary malaria infection, with elevated numbers of late effector memory CD4(+) T cells in the spleen and liver and increased production of IL-2 in the spleen. Crucially, WSX-1(-/-) mice displayed significantly enhanced parasite control compared with WT mice following rechallenge with homologous malaria parasites. Improved parasite control in WSX-1(-/-) mice during secondary infection was associated with elevated systemic production of multiple inflammatory innate and adaptive cytokines and extremely rapid proliferation of antigen-experienced T cells in the liver. These data are the first to demonstrate that IL-27R signaling plays a role in regulating the magnitude and quality of secondary immune responses during rechallenge infections.

Lineage relationship of effector and memory T cells

Adaptive immunity is characterized by the ability to form long-lived immunological memory. Upon re-exposure to antigen, memory T cells respond more rapidly and robustly than naïve T cells, providing better clearance of pathogens. Recent reviews have reinforced the text-book view that memory T cells arise from effector cells. Although this notion is teleologically appealing, emerging data are more consistent with a model where naïve cells directly develop into memory cells without transitioning through an effector stage. A clear understanding of the lineage relationships between memory and effector cells has profound implications for the design of vaccines and for the development of effective T cell-based therapies.

Determinants of the extent and duration of STAT3 signaling

Multiple molecular mechanisms have been identified that are responsible for the deregulation of the quantitative aspects of JAK-STAT signaling. These mechanisms enhance the extent and the duration of, e.g., STAT3 activation and have profound consequences on the phenotypes of the affected cells. The fine tuning of STAT3 signaling is required to maintain its physiological functions and its deregulation is associated with diverse pathological states. Deregulation can be exerted by the gain of function of components mediating the activation of STAT3 or the loss of function of molecules involved in the deactivation steps of STAT3. Gain of function mutations can involve tyrosine kinases that phosphorylate STAT3, mutations in cytokine and growth factor receptors causing their ligand independent activation, mutations in STAT3 that enhance and prolong its tyrosine phosphorylation and the autocrine or paracrine production and secretion of cytokines, most notably IL-6. Diminished deactivation of phosphorylated STAT3 can be due to the reduced expression of tyrosine phosphatases, inactivating mutations in these enzymes, silencing or functional inactivation of SOCS molecules, post-transcriptional inhibition of PIAS3 expression or deletion mutations in the lymphocyte adaptor protein, LNK. STAT3 variants that exhibit autonomous transactivation potential have been detected in 40% of patients with T-cell large granular lymphocytic leukemia in clonally expanded CD8⁺ T cells. These patients also were preferentially affected by neutropenia and rheumatoid disorders and the results suggest that activating STAT3 mutations in T lymphocytes could be a cause of autoimmune diseases.

Cell-intrinsic IL-27 and gp130 cytokine receptor signaling regulates virus-specific CD4⁺ T cell responses and viral control during chronic infection

The outcome of chronic viral infections, which affect millions of people worldwide, is greatly dependent on CD4⁺ T cells. Here we showed that T cell-specific ablation of the common interleukin-6 (IL-6) family receptor, gp130, profoundly compromised virus-specific CD4⁺ T cell survival, T follicular helper responses, and IL-21 production at late stages of chronic lymphocytic choriomeningitis virus (LCMV) infection. These effects were cell intrinsic for CD4⁺ T cells and were accompanied by a reduction of CD8⁺ T cells, antibodies, and a severe failure in viral control. We identified IL-27 as a gp130 cytokine that promoted antiviral CD4⁺ T cell accumulation in vivo and that rapidly induced IL-21 ex vivo. Furthermore, IL-27R was critical for control of persistent LCMV in vivo. These results reveal that gp130 cytokines (particularly IL-27) are key regulators of CD4⁺ T cell responses during an established chronic viral infection, empowering both humoral and cytotoxic immunity.

The transcription factor Interferon Regulatory Factor 4 is required for the generation of protective effector CD8+ T cells

Robust cytotoxic CD8(+) T-cell response is important for immunity to intracellular pathogens. Here, we show that the transcription factor IFN Regulatory Factor 4 (IRF4) is crucial for the protective CD8(+) T-cell response to the intracellular bacterium Listeria monocytogenes. IRF4-deficient (Irf4(-/-)) mice could not clear L. monocytogenes infection and generated decreased numbers of L. monocytogenes-specific CD8(+) T cells with impaired effector phenotype and function. Transfer of wild-type CD8(+) T cells into Irf4(-/-) mice improved bacterial clearance, suggesting an intrinsic defect of CD8(+) T cells in Irf4(-/-) mice. Following transfer into wild-type recipients, Irf4(-/-) CD8(+) T cells became activated and showed initial proliferation upon L. monocytogenes infection. However, these cells could not sustain proliferation, produced reduced amounts of IFN-γ and TNF-α, and failed to acquire cytotoxic function. Forced IRF4 expression in Irf4(-/-) CD8(+) T cells rescued the defect. During acute infection, Irf4(-/-) CD8(+) T cells demonstrated diminished expression of B lymphocyte-induced maturation protein-1 (Blimp-1), inhibitor of DNA binding (Id)2, and T-box expressed in T cells (T-bet), transcription factors programming effector-cell generation. IRF4 was essential for expression of Blimp-1, suggesting that altered regulation of Blimp-1 contributes to the defects of Irf4(-/-) CD8(+) T cells. Despite increased levels of B-cell lymphoma 6 (BCL-6), Eomesodermin, and Id3, Irf4(-/-) CD8(+) T cells showed impaired memory-cell formation, indicating additional functions for IRF4 in this process. As IRF4 governs B-cell and CD4(+) T-cell differentiation, the identification of its decisive role in peripheral CD8(+) T-cell differentiation, suggests a common regulatory function for IRF4 in adaptive lymphocytes fate decision.

The role of IL-27 in the induction of anti-tumor cytotoxic T lymphocyte response

Cytotoxic T lymphocyte (CTL) response is a critical component of the immune response to tumors, therefore optimal induction of CTL responses to tumor antigens is highly desired for developing efficient cancer immunotherapy. IL-27 is a member of the IL-12 family of cytokines that is comprised of an IL-12 p40-related protein subunit, EBV-induced gene 3 (EBI3), and a p35-related subunit, p28. IL-27 functions through IL-27R and has been shown to have potent anti-tumor activity via activation of a variety of immune components, including anti-tumor CD8(+) T cell responses. However, the exact mechanisms of how IL-27 enhances anti-tumor CD8(+) T cell responses are not fully understood. In this paper we mainly discuss the evidences that suggest novel mechanisms by which IL-27 enhances anti-tumor CTL responses, including IL-27 inhibition of activation-induced cell death; the phenotypes of IL-27-stimulated CTLs; IL-27-induced CTL IL-10/IL-21 production and IL-27-mediated suppression of regulatory T cell responses. These evidences suggest that IL-27 may have a great potential to be utilized in boosting anti-tumor CTL responses in human cancer patients.

Antigen and transforming growth factor Beta receptors contribute to long term functional and phenotypic heterogeneity of memory CD8 T cells

Pathogen-specific CD8 T cells provide a mechanism for selectively eliminating host cells that are harboring intracellular pathogens. The pathogens are killed when lytic molecules are injected into the cytoplasm of the infected cells and begin an apoptotic cascade. Activated CD8 T cells also release large quantities of pro-inflammatory cytokines that stimulate other immune cells in the local vicinity. As the alveoli are extraordinarily sensitive to cytokine induced damage, multiple layers of immune regulation limit the activities of immune cells that enter the lungs. These mechanisms include receptor-mediated signaling pathways in CD8 T cells that respond to peptide antigens and transforming growth factor β. Both pathways influence the functional and phenotypic properties of long-lived CD8 T cells populations in peripheral and lymphoid tissues.

Signal transducer and activator of transcription 3 (STAT3) mutations underlying autosomal dominant hyper-IgE syndrome impair human CD8(+) T-cell memory formation and function

BACKGROUND

The capacity of CD8(+) T cells to control infections and mediate antitumor immunity requires the development and survival of effector and memory cells. IL-21 has emerged as a potent inducer of CD8(+) T-cell effector function and memory development in mouse models of infectious disease. However, the role of IL-21 and associated signaling pathways in protective CD8(+) T-cell immunity in human subjects is unknown.

OBJECTIVE

We sought to determine which signaling pathways mediate the effects of IL-21 on human CD8(+) T cells and whether defects in these pathways contribute to disease pathogenesis in patients with primary immunodeficiencies caused by mutations in components of the IL-21 signaling cascade.

METHODS

Human primary immunodeficiencies resulting from monogenic mutations provide a unique opportunity to assess the requirement for particular molecules in regulating human lymphocyte function. Lymphocytes from patients with loss-of-function mutations in signal transducer and activator of transcription 1 (STAT1), STAT3, or IL-21 receptor (IL21R) were used to assess the respective roles of these genes in human CD8(+) T-cell differentiation in vivo and in vitro.

RESULTS

Mutations in STAT3 and IL21R, but not STAT1, led to a decrease in multiple memory CD8(+) T-cell subsets in vivo, indicating that STAT3 signaling, possibly downstream of IL-21R, regulates the memory cell pool. Furthermore, STAT3 was important for inducing the lytic machinery in IL-21-stimulated naive CD8(+) T cells. However, this defect was overcome by T-cell receptor engagement.

CONCLUSION

The IL-21R/STAT3 pathway is required for many aspects of human CD8(+) T-cell behavior but in some cases can be compensated by other signals. This helps explain the relatively mild susceptibility to viral disease observed in STAT3- and IL-21R-deficient subjects.

The cup runneth over: lessons from the ever-expanding pool of primary immunodeficiency diseases

A recent surge in newly described primary immunodeficiencies (PIDs) has highlighted new physiological and pathophysiological pathways that affect the immune system. Furthermore, the study of individuals with PIDs has substantially improved our understanding of basic cellular and signalling pathways in host defence and immune regulation. Single-gene defects can lead to disease manifestations that range from extremely narrow infectious phenotypes to remarkably broad multisystem effects. Hypomorphic or hypermorphic gene mutations often occur in human diseases; when coupled with the fact that humans are exposed to naturally encountered antigens and pathogens, this helps to make the case that the study of immunological diseases in humans should be at the forefront of basic immunological research.

Nicotine inhibits memory CTL programming

Nicotine is the main tobacco component responsible for tobacco addiction and is used extensively in smoking and smoking cessation therapies. However, little is known about its effects on the immune system. We confirmed that multiple nicotinic receptors are expressed on mouse and human cytotoxic T lymphocytes (CTLs) and demonstrated that nicotinic receptors on mouse CTLs are regulated during activation. Acute nicotine presence during activation increases primary CTL expansion in vitro, but impairs in vivo expansion after transfer and subsequent memory CTL differentiation, which reduces protection against subsequent pathogen challenges. Furthermore, nicotine abolishes the regulatory effect of rapamycin on memory CTL programming, which can be attributed to the fact that rapamycin enhances expression of nicotinic receptors. Interestingly, naïve CTLs from chronic nicotine-treated mice have normal memory programming, which is impaired by nicotine during activation in vitro. In conclusion, simultaneous exposure to nicotine and antigen during CTL activation negatively affects memory development.

FoxO1 controls effector-to-memory transition and maintenance of functional CD8 T cell memory

During a T cell response, naive CD8 T cells differentiate into effector cells. Subsequently, a subset of effector cells termed memory precursor effector cells further differentiates into functionally mature memory CD8 T cells. The transcriptional network underlying this carefully scripted process is not well understood. In this study, we report that the transcription factor FoxO1 plays an integral role in facilitating effector-to-memory transition and functional maturation of memory CD4 and CD8 T cells. We find that FoxO1 is not required for differentiation of effector cells, but in the absence of FoxO1, memory CD8 T cells displayed features of senescence and progressive attrition in polyfunctionality, which in turn led to impaired recall responses and poor protective immunity. These data suggest that FoxO1 is essential for maintenance of functional CD8 T cell memory and protective immunity. Under competing conditions in bone marrow chimeric mice, FoxO1 deficiency did not perturb clonal expansion or effector differentiation. Instead, FoxO1-deficient memory precursor effector cells failed to survive and form memory CD8 T cells. Mechanistically, FoxO1 deficiency perturbed the memory CD8 T cell transcriptome, characterized by pronounced alterations in the expression of genes that encode transcription factors (including Tcf7), effector molecules, cell cycle regulators, and proteins that regulate fatty acid, purine, and pyramidine metabolism and mitochondrial functions. We propose that FoxO1 is a key regulator that reprograms and steers the differentiation of effector cells to functionally competent memory cells. These findings have provided fundamental insights into the mechanisms that regulate the quality of CD8 T cell memory to intracellular pathogens.

CD8(+) T-cell effector function and transcriptional regulation during HIV pathogenesis

A detailed understanding of the immune response to human immunodeficiency virus (HIV) infection is needed to inform prevention and therapeutic strategies that aim to contain the acquired immunodeficiency syndrome (AIDS) pandemic. The cellular immune response plays a critical role in controlling viral replication during HIV infection and will likely need to be a part of any vaccine approach. The qualitative feature of the cellular response most closely associated with immunological control of HIV infection is CD8(+) T-cell cytotoxic potential, which is responsible for mediating the elimination of infected CD4(+) T cells. Understanding the underlying mechanisms involved in regulating the elicitation and maintenance of this kind of effector response can provide guidance for vaccine design. In this review, we discuss the evidence for CD8(+) T cells as correlates of protection, the means by which their antiviral capacity is evaluated, and transcription factors responsible for their function, or dysfunction, during HIV infection.

Transcriptional regulation of effector and memory CD8+ T cell fates

Immunity to intracellular pathogens and cancer relies on the generation of robust CD8(+) T cell effector responses as well as the establishment of immunological memory. During a primary immune response CD8(+) T cells experience diverse extracellular environmental cues and cell-cell interactions that trigger downstream transcriptional programs ultimately guiding a CD8(+) T cell to undertake either an effector or a memory cell fate. Here, we discuss our current understanding of the signaling pathways and transcriptional networks that regulate effector and memory commitment in CD8(+) T lymphocytes.

Pegylated IL-10 induces cancer immunity: the surprising role of IL-10 as a potent inducer of IFN-γ-mediated CD8(+) T cell cytotoxicity

Recently, the development of several strategies based on immunotherapy has raised hopes for a more promising way to treat cancer patients. Here, we describe how interleukin (IL)-10, a seemingly unlikely candidate, stimulates the immune system in a particularly efficacious way. IL-10, an omnipotent anti-inflammatory cytokine, delivers an equally potent immune stimulation in the context of CD8(+) T cells and tumor immunity. By activation of tumor-resident, tumor-specific CD8(+) T cells, pegylated IL-10 can induce rejection of large and metastasizing tumors in mice. Here, we summarize the mechanisms of action of IL-10, the reasons why the mechanisms may be crucial for the treatment of cancer patients, and the rationale for applying pegylated IL-10 in the clinic.

Id2-mediated inhibition of E2A represses memory CD8+ T cell differentiation

The transcription factor inhibitor of DNA binding (Id)2 modulates T cell fate decisions, but the molecular mechanism underpinning this regulation is unclear. In this study we show that loss of Id2 cripples effector differentiation and instead programs CD8(+) T cells to adopt a memory fate with increased Eomesodermin and Tcf7 expression. We demonstrate that Id2 restrains CD8(+) T cell memory differentiation by inhibiting E2A-mediated direct activation of Tcf7 and that Id2 expression level mirrors T cell memory recall capacity. As a result of the defective effector differentiation, Id2-deficient CD8(+) T cells fail to induce sufficient Tbx21 expression to generate short-lived effector CD8(+) T cells. Our findings reveal that the Id2/E2A axis orchestrates T cell differentiation through the induction or repression of downstream transcription factors essential for effector and memory T cell differentiation.

Transferred WT1-reactive CD8+ T cells can mediate antileukemic activity and persist in post-transplant patients

Relapse remains a leading cause of death after allogeneic hematopoietic cell transplantation (HCT) for patients with high-risk leukemias. The potentially beneficial donor T cell-mediated graft-versus-leukemia (GVL) effect is often mitigated by concurrent graft-versus-host disease (GVHD). Providing T cells that can selectively target Wilms tumor antigen 1 (WT1), a transcription factor overexpressed in leukemias that contributes to the malignant phenotype, represents an opportunity to promote antileukemic activity without inducing GVHD. HLA-A*0201-restricted WT1-specific donor-derived CD8 cytotoxic T cell (CTL) clones were administered after HCT to 11 relapsed or high-risk leukemia patients without evidence of on-target toxicity. The last four treated patients received CTL clones generated with exposure to interleukin-21 (IL-21) to prolong in vivo CTL survival, because IL-21 can limit terminal differentiation of antigen-specific T cells generated in vitro. Transferred cells exhibited direct evidence of antileukemic activity in two patients: a transient response in one patient with advanced progressive disease and the induction of a prolonged remission in a patient with minimal residual disease (MRD). Additionally, three treated patients at high risk for relapse after HCT survive without leukemia relapse, GVHD, or additional antileukemic treatment. CTLs generated in the presence of IL-21, which were transferred in these latter three patients and the patient with MRD, all remained detectable long-term and maintained or acquired in vivo phenotypic and functional characteristics associated with long-lived memory CD8 T cells. This study supports expanding efforts to immunologically target WT1 and provides insights into the requirements necessary to establish potent persistent T cell responses.

Disparate roles for STAT5 in primary and secondary CTL responses

IL-2 signals during the primary response to infection are essential in shaping CD8(+) T cell fate decisions. How CD8(+) T cells integrate IL-2 signals in the development of functional memory is not well understood. Because IL-2 induces potent activation of the STAT5 transcription factor, we tested the role of STAT5 in CD8(+) memory T cell differentiation and function using a model system in which STAT5 activity is inducibly abrogated upon CD8(+) T cell activation. We report that STAT5 activity is broadly important for the expansion and effector function of all effector CTL subsets. After pathogen clearance, STAT5 was required for the survival of effector phenotype memory CTLs during the contraction phase. However, despite its role in supporting full primary CD8(+) T cell expansion, and unlike IL-2, STAT5 activity is not required for the development of memory CD8(+) T cells capable of robust secondary expansion upon rechallenge. Our findings highlight differential requirements for survival signals between primary and secondary effector CTL, and demonstrate that IL-2-dependent programming of memory CD8(+) T cells capable of secondary expansion and secondary effector differentiation is largely STAT5 independent.

The smallest unit: effector and memory CD8(+) T cell differentiation on the single cell level

CD8⁺ T cell immune responses provide immediate protection against primary infection and durable memory capable of rapidly fighting off re-infection. Immediate protection and lasting memory are implemented by phenotypically and functionally distinct T cell subsets. While it is now widely accepted that these diverge from a common source of naïve T cells (T_n), the developmental relation and succession of effector and memory T cell subsets is still under intense debate. Recently, a distinct memory T cell subset has been suggested to possess stem cell-like features, sparking the hope to harness its capacity for self-renewal and diversification for successful therapy of chronic infections or malignant diseases. In this review we highlight current developmental models of memory generation, T cell subset diversification and T cell stemness. We discuss the importance of single cell monitoring techniques for adequately mapping these developmental processes and take a brief look at signaling components active in the putative stem cell-like memory T cell compartment.

Anti-viral CD8 T cells and the cytokines that they love

Viral infections cause an immunological disequilibrium that provokes CD8 T cell responses. These cells play critical roles in purging acute infections, limiting persistent infections, and conferring life-long protective immunity. At every stage of the response anti-viral CD8 T cells are sensitive to signals from cytokines. Initially cytokines operate as immunological warning signs that inform of the presence of an infection, and also influence the developmental choices of the responding cells. Later during the course of the response other sets of cytokines support the survival and maintenance of the differentiated anti-viral CD8 T cells. Although many cytokines promote virus-specific CD8 T cells, other cytokines can suppress their activities and thus favor viral persistence. In this review we discuss how select cytokines act to regulate anti-viral CD8 T cells throughout the response and influence the outcome of viral infections.

Metabolic switching and fuel choice during T-cell differentiation and memory development

Clearance or control of pathogens or tumors usually requires T-cell-mediated immunity. As such, understanding the mechanisms that govern the function, maintenance, and persistence of T cells will likely lead to new treatments for controlling disease. During an immune response, T-cell development is marked by striking changes in metabolism. There is a growing appreciation that these metabolic changes underlie the capacity of T cells to perform particular functions, and this has led to a recent focus on the idea that the manipulation of cellular metabolism can be used to shape adaptive immune responses. Although interest in this area has grown in the last few years, a full understanding of the metabolic control of T-cell functions, particularly during an immune response in vivo, is still lacking. In this review, we first provide a basic overview of metabolism in T cells, and then we focus on recent studies providing new or updated insights into the regulation of metabolic pathways and how they underpin T-cell differentiation and memory T-cell development.

Protecting and rescuing the effectors: roles of differentiation and survival in the control of memory T cell development

Vaccines, arguably the single most important intervention in improving human health, have exploited the phenomenon of immunological memory. The elicitation of memory T cells is often an essential part of successful long-lived protective immunity. Our understanding of T cell memory has been greatly aided by the development of TCR Tg mice and MHC tetrameric staining reagents that have allowed the precise tracking of antigen-specific T cell responses. Indeed, following acute infection or immunization, naïve T cells undergo a massive expansion culminating in the generation of a robust effector T cell population. This peak effector response is relatively short-lived and, while most effector T cells die by apoptosis, some remain and develop into memory cells. Although the molecular mechanisms underlying this cell fate decision remain incompletely defined, substantial progress has been made, particularly with regards to CD8(+) T cells. For example, the effector CD8(+) T cells generated during a response are heterogeneous, consisting of cells with more or less potential to develop into full-fledged memory cells. Development of CD8(+) T cell memory is regulated by the transcriptional programs that control the differentiation and survival of effector T cells. While the type of antigenic stimulation and level of inflammation control effector CD8(+) T cell differentiation, availability of cytokines and their ability to control expression and function of Bcl-2 family members governs their survival. These distinct differentiation and survival programs may allow for finer therapeutic intervention to control both the quality and quantity of CD8(+) T cell memory. Effector to memory transition of CD4(+) T cells is less well characterized than CD8(+) T cells, emerging details will be discussed. This review will focus on the recent progress made in our understanding of the mechanisms underlying the development of T cell memory with an emphasis on factors controlling survival of effector T cells.

Id2 influences differentiation of killer cell lectin-like receptor G1(hi) short-lived CD8+ effector T cells

CD8(+) T cells play a crucial role in the clearance of intracellular pathogens through the generation of cytotoxic effector cells that eliminate infected cells and long-lived memory cells that provide enhanced protection against reinfection. We have previously shown that the inhibitor of E protein transcription factors, Id2, is necessary for accumulation of effector and memory CD8(+) T cells during infection. In this study, we show that CD8(+) T cells lacking Id2 did not generate a robust terminally differentiated killer cell lectin-like receptor G1 (KLRG1)(hi) effector population, but displayed a cell-surface phenotype and cytokine profile consistent with memory precursors, raising the question as to whether loss of Id2 impairs the differentiation and/or survival of effector memory cells. We found that deletion of Bim rescued Id2-deficient CD8(+) cell survival during infection. However, the dramatic reduction in KLRG1(hi) cells caused by loss of Id2 remained in the absence of Bim, such that Id2/Bim double-deficient cells form an exclusively KLRG1(lo)CD127(hi) memory precursor population. Thus, we describe a role for Id2 in both the survival and differentiation of normal CD8(+) effector and memory populations.

IL-27 enhances the survival of tumor antigen-specific CD8+ T cells and programs them into IL-10-producing, memory precursor-like effector cells

IL-27 is a member of the IL-12 family of cytokines that is comprised of an IL-12 p40-related protein subunit, EBV-induced gene 3, and a p35-related subunit, p28. IL-27 functions through IL-27R and has been shown to have potent antitumor activity via activation of a variety of cellular components, including antitumor CD8(+) T-cell responses. However, the exact mechanisms of how IL-27 enhances antitumor CD8(+) T-cell responses remain unclear. Here we show that IL-27 significantly enhances the survival of activated tumor antigen-specific CD8(+) T cells in vitro and in vivo, and programs tumor antigen-specific CD8(+) T cells into memory precursor-like effector cells, characterized by upregulation of Bcl-6, SOCS3, Sca-1, and IL-10. While STAT3 activation and the CTL survival-enhancing effects can be independent of CTL IL-10 production, we show here that IL-27-induced CTL IL-10 production contributes to memory precursor cell phenotype induction, CTL memory, and tumor rejection. Thus, IL-27 enhances antitumor CTL responses via programming tumor antigen-specific CD8(+) T cells into a unique memory precursor type of effector cells characterized by a greater survival advantage. Our results have important implications for designing immunotherapy against human cancer.

Differential effects of γc cytokines on postselection differentiation of CD8 thymocytes

The primary consequence of positive selection is to render thymocytes responsive to cytokines and chemokines expressed in the thymic medulla. In the present study, our main objective was to discover which cytokines could support the differentiation of positively selected thymocytes. To this end, we have developed an in vitro model suitable for high-throughput analyses of positive selection and CD8 T-cell differentiation. The model involves coculture of TCRhiCD5intCD69− double-positive (DP) thymocytes with peptide-pulsed OP9 cells and γc-cytokines. We report that IL-4, IL-7, and IL-21 have nonredundant effects on positively selected DP thymocytes. IL-7 signaling phosphorylates STAT5 and ERK; induces Foxo1, Klf2, and S1pr1; and supports the differentiation of classic CD8 T cells. IL-4 activates STAT6 and ERK and supports the differentiation of CD8intPD-L1hiCD44hiEOMES+ innate CD8 T cells. IL-21 is produced by thymic epithelial cells and the IL-21 receptor-α is strongly induced on DP thymocytes undergoing positive selection. IL-21 signaling phosphorylates STAT3 and STAT5, but not ERK, and does not support CD8 T-cell differentiation. However, IL-21 has a unique ability to up-regulate BCL-6, expand DP thymocytes undergoing positive selection, and increase the production of mature T cells. Our data suggest that injection of recombinant IL-21 might enhance thymic output in subjects with age- or disease-related thymic atrophy.

Decisions on the road to memory

A fundamental property of the adaptive immune system is the ability to generate antigen-specific memory, which protects against repeated infections with the same pathogens and determines the success of vaccination. Immune memory is built up alongside a response providing direct protection during the course of a primary immune response. For CD8 T cells, this involves the generation of two distinct types of effector cells. Short lived effector cells (SLECs) confer immediate protection, but contribute little to the memory repertoire. Memory precursor effector cells (MPECs) have the ability to respond to survival signals and develop into memory cells. These two types of cells can be distinguished on the basis of surface markers and express distinct genetic programs. A single naive CD8 T cell can give rise to both MPEC and SLEC daughter cells. This may involve an initial asymmetric division or depend on later instructive signals acting on equipotent daughter cells. Strong inflammatory signals favor the generation of SLECs and weaker inflammation favors the generation of MPECs. A distinguishing feature of MPECs is their ability to persist when most effector cells die. This survival depends on signals from the IL-7 receptor, which induce expression of anti-apoptotic factors. MPECs are therefore characterized by expression of the IL-7 receptor as well as the CCR7 chemokine receptor, which allows homing to areas in lymphoid organs where IL-7 is produced. Critical for persistence of MPECs is further their responsiveness to myeloid cell derived IL-15, which instructs these cells to switch their metabolic programs from glycolysis associated with rapid proliferation to fatty acid oxidation required during a more resting state. As the mechanisms determining generation of immunological memory are unraveled, opportunities will emerge for the improvement of vaccination strategies.