Broad programming by IL-2 receptor signaling for extended growth to multiple cytokines and functional maturation of antigen-activated T cells

Interleukin-2 signaling in the regulation of T cell biology in autoimmunity and cancer

Interleukin-2 (IL-2) is a critical cytokine for T cell peripheral tolerance and immunity. Here, we review how IL-2 interaction with the high-affinity IL-2 receptor (IL-2R) supports the development and homeostasis of regulatory T cells and contributes to the differentiation of helper, cytotoxic, and memory T cells. A critical element for each T cell population is the expression of CD25 (Il2rα), which heightens the receptor affinity for IL-2. Signaling through the high-affinity IL-2R also reinvigorates CD8+ exhausted T (Tex) cells in response to checkpoint blockade. We consider the molecular underpinnings reflecting how IL-2R signaling impacts these various T cell subsets and the implications for enhancing IL-2-dependent immunotherapy of autoimmunity, other inflammatory disorders, and cancer.

Disruption of CISH promotes the antitumor activity of human T cells and decreases PD-1 expression levels

Tumor cells and the immunosuppressive tumor microenvironment suppress the antitumor activity of T cells through immune checkpoints, including the PD-L1/PD-1 axis. Cytokine-inducible SH2-containing protein (CISH), a member of the suppressor of cytokine signaling (SOCS) family, inhibits JAK-STAT and T cell receptor (TCR) signaling in T and natural killer (NK) cells. However, its role in the regulation of immune checkpoints in T cells remains unclear. In this study, we ablated CISH in T cells with CRISPR-Cas9 and found that the sensitivity of T cells to TCR and cytokine stimulation was increased. In addition, chimeric antigen receptor T cells with CISH deficiency exhibited longer survival and higher cytokine secretion and antitumor activity. Notably, PD-1 expression was decreased in activated CISH-deficient T cells in vitro and in vivo. The level of FBXO38, a ubiquitination-regulating protein that reduces PD-1 expression, was elevated in activated T cells after CISH ablation. Hence, this study reveals a mechanism by which CISH promotes PD-1 expression by suppressing the expression of FBXO38 and proposes a new strategy for augmenting the therapeutic effect of CAR-T cells by inhibiting CISH.

Pre-Clinical Autoimmunity in Lupus Relatives: Self-Reported Questionnaires and Immune Dysregulation Distinguish Relatives Who Develop Incomplete or Classified Lupus From Clinically Unaffected Relatives and Unaffected, Unrelated Individuals

Systemic lupus erythematosus (SLE) is propelled by pathogenic autoantibody (AutoAb) and immune pathway dysregulation. Identifying populations at risk of reaching classified SLE is essential to curtail inflammatory damage. Lupus blood relatives (Rel) have an increased risk of developing SLE. We tested factors to identify Rel at risk of developing incomplete lupus (ILE) or classified SLE vs. clinically unaffected Rel and healthy controls (HC), drawing from two unique, well characterized lupus cohorts, the lupus autoimmunity in relatives (LAUREL) follow-up cohort, consisting of Rel meeting <4 ACR criteria at baseline, and the Lupus Family Registry and Repository (LFRR), made up of SLE patients, lupus Rel, and HC. Medical record review determined ACR SLE classification criteria; study participants completed the SLE portion of the connective tissue disease questionnaire (SLE-CSQ), type 2 symptom questions, and provided samples for assessment of serum SLE-associated AutoAb specificities and 52 plasma immune mediators. Elevated SLE-CSQ scores were associated with type 2 symptoms, ACR scores, and serology in both cohorts. Fatigue at BL was associated with transition to classified SLE in the LAUREL cohort (p≤0.01). Increased levels of BLyS and decreased levels of IL-10 were associated with type 2 symptoms (p<0.05). SLE-CSQ scores, ACR scores, and accumulated AutoAb specificities correlated with levels of multiple inflammatory immune mediators (p<0.05), including BLyS, IL-2Rα, stem cell factor (SCF), soluble TNF receptors, and Th-1 type mediators and chemokines. Transition to SLE was associated with increased levels of SCF (p<0.05). ILE Rel also had increased levels of TNF-α and IFN-γ, offset by increased levels of regulatory IL-10 and TGF-β (p<0.05). Clinically unaffected Rel (vs. HC) had higher SLE-CSQ scores (p<0.001), increased serology (p<0.05), and increased inflammatory mediator levels, offset by increased IL-10 and TGF-β (p<0.01). These findings suggest that Rel at highest risk of transitioning to classified SLE have increased inflammation coupled with decreased regulatory mediators. In contrast, clinically unaffected Rel and Rel with ILE demonstrate increased inflammation offset with increased immune regulation, intimating a window of opportunity for early intervention and enrollment in prevention trials.

Microwave ablation of primary breast cancer inhibits metastatic progression in model mice via activation of natural killer cells

Surgery is essential for controlling the symptoms and complications of stage IV breast cancer. However, locoregional treatment of primary tumors often results in distant progression, including lung metastasis, the most common type of visceral metastasis. As a minimally invasive thermal therapy, microwave ablation (MWA) has been attempted in the treatment of breast cancer, but the innate immune response after MWA has not yet been reported. Using two murine models of stage IV breast cancer, we found that MWA of primary breast cancer inhibited the progression of lung metastasis and improved survival. NK cells were activated after MWA of the primary tumor and exhibited enhanced cytotoxic functions, and the cytotoxic pathways of NK cells were activated. Depletion experiments showed that NK cells but not CD4+ or CD8+ T cells played a pivotal role in prolonging survival. Then, we found that compared with surgery or control treatment, MWA of the primary tumor induced completely different NK-cell-related cytokine profiles. Macrophages were activated after MWA of the primary tumor and produced IL-15 that activated NK cells to inhibit the progression of metastasis. In addition, MWA of human breast cancer stimulated an autologous NK-cell response. These results demonstrate that MWA of the primary tumor in metastatic breast cancer inhibits metastatic progression via the macrophage/IL-15/NK-cell axis. MWA of the primary tumor may be a promising treatment strategy for de novo stage IV breast cancer, although further substantiation is essential for clinical testing.

PTPN2 phosphatase deletion in T cells promotes anti-tumour immunity and CAR T-cell efficacy in solid tumours

Although adoptive T-cell therapy has shown remarkable clinical efficacy in haematological malignancies, its success in combating solid tumours has been limited. Here, we report that PTPN2 deletion in T cells enhances cancer immunosurveillance and the efficacy of adoptively transferred tumour-specific T cells. T-cell-specific PTPN2 deficiency prevented tumours forming in aged mice heterozygous for the tumour suppressor p53. Adoptive transfer of PTPN2-deficient CD8+ T cells markedly repressed tumour formation in mice bearing mammary tumours. Moreover, PTPN2 deletion in T cells expressing a chimeric antigen receptor (CAR) specific for the oncoprotein HER-2 increased the activation of the Src family kinase LCK and cytokine-induced STAT-5 signalling, thereby enhancing both CAR T-cell activation and homing to CXCL9/10-expressing tumours to eradicate HER-2+ mammary tumours in vivo. Our findings define PTPN2 as a target for bolstering T-cell-mediated anti-tumour immunity and CAR T-cell therapy against solid tumours.

Daclizumab: Mechanisms of Action, Therapeutic Efficacy, Adverse Events and Its Uncovering the Potential Role of Innate Immune System Recruitment as a Treatment Strategy for Relapsing Multiple Sclerosis

Daclizumab (DAC) is a humanized, monoclonal antibody that blocks CD25, a critical element of the high-affinity interleukin-2 receptor (IL-2R). DAC HYP blockade of CD25 inhibits effector T cell activation, regulatory T cell expansion and survival, and activation-induced T-cell apoptosis. Because CD25 blockade reduces IL-2 consumption by effector T cells, it increases IL-2 bioavailability allowing for greater interaction with the intermediate-affinity IL-2R, and therefore drives the expansion of CD56^bright natural killer (NK) cells. Furthermore, there appears to be a direct correlation between CD56^bright NK cell expansion and DAC HYP efficacy in reducing relapses and MRI evidence of disease activity in patients with RMS in phase II and phase III double-blind, placebo- and active comparator-controlled trials. Therapeutic efficacy was maintained during open-label extension studies. However, treatment was associated with an increased risk of rare adverse events, including cutaneous inflammation, autoimmune hepatitis, central nervous system Drug Reaction with Eosinophilia Systemic Symptoms (DRESS) syndrome, and autoimmune Glial Fibrillary Acidic Protein (GFAP) alpha immunoglobulin-associated encephalitis. As a result, DAC HYP was removed from clinical use in 2018. The lingering importance of DAC is that its use led to a deeper understanding of the underappreciated role of innate immunity in the potential treatment of autoimmune disease.

Role of the EHD Family of Endocytic Recycling Regulators for TCR Recycling and T Cell Function

T cells use the endocytic pathway for key cell biological functions, including receptor turnover and maintenance of the immunological synapse. Some of the established players include the Rab GTPases, the SNARE complex proteins, and others, which function together with EPS-15 homology domain-containing (EHD) proteins in non-T cell systems. To date, the role of the EHD protein family in T cell function remains unexplored. We generated conditional EHD1/3/4 knockout mice using CD4-Cre and crossed these with mice bearing a myelin oligodendrocyte glycoprotein-specific TCR transgene. We found that CD4⁺ T cells from these mice exhibited reduced Ag-driven proliferation and IL-2 secretion in vitro. In vivo, these mice exhibited reduced severity of experimental autoimmune encephalomyelitis. Further analyses showed that recycling of the TCR-CD3 complex was impaired, leading to increased lysosomal targeting and reduced surface levels on CD4⁺ T cells of EHD1/3/4 knockout mice. Our studies reveal a novel role of the EHD family of endocytic recycling regulatory proteins in TCR-mediated T cell functions.

Inducible T Cell Kinase Regulates the Acquisition of Cytolytic Capacity and Degranulation in CD8+ CTLs

Patients with mutations in inducible T cell kinase (ITK) are susceptible to viral infections, particularly EBV, suggesting that these patients have defective function of CD8⁺ CTLs. In this study, we evaluated the effects of ITK deficiency on cytolysis in murine CTLs deficient in ITK, and both human and murine cells treated with an ITK inhibitor. We find that ITK deficiency leads to a global defect in the cytolysis of multiple targets. The absence of ITK both affected CTL expansion and delayed the expression of cytolytic effectors during activation. Furthermore, absence of ITK led to a previously unappreciated intrinsic defect in degranulation. Nonetheless, these defects could be overcome by early or prolonged exposure to IL-2, or by addition of IL-12 to cultures, revealing that cytokine signaling could restore the acquisition of effector function in ITK-deficient CD8⁺ T cells. Our results provide new insight into the effect of ITK and suboptimal TCR signaling on CD8⁺ T cell function, and how these may contribute to phenotypes associated with ITK deficiency.

Microwave ablation combined with OK-432 induces Th1-type response and specific antitumor immunity in a murine model of breast cancer

Background

Minimally invasive therapies, such as microwave ablation (MWA), are widely used for the treatment of solid tumors. Previous studies suggest that MWA is feasible for the treatment of small breast cancer, and thermal ablation may induce adaptive antitumor immunity. However, the induced immune responses are mostly weak, and the immunomodulation effects of MWA in breast cancer are unclear. Immunostimulant OK-432 can induce tumor-specific T-cell responses and may augment the immunity induced by MWA.

Methods

We treated 4T1 breast cancer bearing BALB/c mice with MWA, OK-432, MWA plus OK-432, or left without treatment. Survival time was evaluated with the Kaplan–Meyer method comparing survival curves by log-rank test. On day 25 after ablation, surviving mice received tumor rechallenge, and the rechallenged tumor volumes were calculated every 5 days. Immunohistochemistry and flow cytometry were used to evaluate the T-cell immune responses in ablated tissues and spleens. The tumor-specific immunity was assessed by enzyme-linked immunospot assays. Besides, the cytokine patterns were identified from enzyme-linked immunosorbent assay.

Results

Microwave ablation plus OK-432 resulted in longer survival than single treatment and protect most surviving mice from tumor rechallenge. Both local and systemic T-cell responses were induced by MWA and were further enhanced by subsequent administration of OK-432. Moreover, the combination of MWA and OK-432 induced stronger tumor-specific immune responses than MWA alone. In addition, OK-432 and MWA synergistically promoted the production of Th1-type but not Th2-type cytokines, and polarized T-cell responses to Th1-dominant state.

Conclusions

The T-cell immune responses were activated by MWA in breast cancer. Furthermore, the combination of MWA and OK-432 induced Th1-type response and elicited specific antitumor immunity.

Substance P mediates pro-inflammatory cytokine release form mesenteric adipocytes in Inflammatory Bowel Disease patients

BACKGROUND & AIMS

Substance P (SP), neurokinin-1 receptors (NK-1Rs) are expressed in mesenteric preadipocytes and SP binding activates proinflammatory signalling in these cells. We evaluated the expression levels of SP (Tac-1), NK-1R (Tacr-1), and NK-2R (Tacr-2) mRNA in preadipocytes isolated from patients with Inflammatory Bowel Disease (IBD) and examined their responsiveness to SP compared to control human mesenteric preadipocytes. The Aim of our study is to investigate the effects of the neuropeptide SP on cytokine expression in preadipocytes of IBD vs control patients and evaluate the potential effects of these cells on IBD pathophysiology via SP-NK-R interactions.

METHODS

Mesenteric fat was collected from control, Ulcerative colitis (UC) and Crohn's disease (CD) patients (n=10-11 per group). Preadipocytes were isolated, expanded in culture and exposed to substance P. Colon biopsies were obtained from control and IBD patients.

RESULTS

Tacr-1 and -2 mRNA were increased in IBD preadipocytes compared to controls, while Tac-1 mRNA was increased only in UC preadipocytes. SP differentially regulated the expression of inflammatory mediators in IBD preadipocytes compared to controls. Disease-dependent responses to SP were also observed between UC and CD preadipocytes. IL-17A mRNA expression and release increased after SP treatment in both CD and UC preadipocytes, while IL-17RA mRNA increased in colon biopsies from IBD patients.

CONCLUSIONS

Preadipocyte SP-NK-1R interactions during IBD may participate in IBD pathophysiology. The ability of human preadipocytes to release IL-17A in response to SP together with increased IL-17A receptor in IBD colon opens the possibility of a fat-colonic mucosa inflammatory loop that may be active during IBD.

CD4 T-cell memory generation and maintenance

Immunologic memory is the adaptive immune system's powerful ability to remember a previous antigen encounter and react with accelerated vigor upon antigen re-exposure. It provides durable protection against reinfection with pathogens and is the foundation for vaccine-induced immunity. Unlike the relatively restricted immunologic purview of memory B cells and CD8 T cells, the field of CD4 T-cell memory must account for multiple distinct lineages with diverse effector functions, the issue of lineage commitment and plasticity, and the variable distribution of memory cells within each lineage. Here, we discuss the evidence for lineage-specific CD4 T-cell memory and summarize the known factors contributing to memory-cell generation, plasticity, and long-term maintenance.

PTPN2 restrains CD8⁺ T cell responses after antigen cross-presentation for the maintenance of peripheral tolerance in mice

Antigen cross-presentation by dendritic cells is crucial for priming cytotoxic CD8(+) T cells to invading pathogens and tumour antigens, as well as mediating peripheral tolerance to self-antigens. The protein tyrosine phosphatase N2 (PTPN2) attenuates T cell receptor (TCR) signalling and tunes CD8(+) T cell responses in vivo. In this study we have examined the role of PTPN2 in the maintenance of peripheral tolerance after the cross-presentation of pancreatic β-cell antigens. The transfer of OVA-specific OT-I CD8(+) T cells (C57BL/6) into RIP-mOVA recipients expressing OVA in pancreatic β-cells only results in islet destruction when OVA-specific CD4(+) T cells are co-transferred. Herein we report that PTPN2-deficient OT-I CD8(+) T cells transferred into RIP-mOVA recipients acquire CTL activity and result in β cell destruction and the development of diabetes in the absence of CD4(+) help. These studies identify PTPN2 as a critical mediator of peripheral T cell tolerance limiting CD8(+) T cell responses after the cross-presentation of self-antigens. Our findings reveal a mechanism by which PTPN2 SNPs might convert a tolerogenic CD8(+) T cell response into one capable of causing the destruction of pancreatic β-cells. Moreover, our results provide insight into potential approaches for enhancing T cell-mediated immunity and/or T cell adoptive tumour immunotherapy.

The potential for genetically altered microglia to influence glioma treatment

Diffuse and unstoppable infiltration of brain and spinal cord tissue by neoplastic glial cells is the single most important therapeutic problem posed by the common glioma group of tumors: astrocytoma, oligoastrocytoma, oligodendroglioma, their malignant variants and glioblastoma. These neoplasms account for more than two thirds of all malignant central nervous system tumors. However, most glioma research focuses on an examination of the tumor cells rather than on host-specific, tumor micro-environmental cells and factors. This can explain why existing diffuse glioma therapies fail and why these tumors have remained incurable. Thus, there is a great need for innovation. We describe a novel strategy for the development of a more effective treatment of diffuse glioma. Our approach centers on gaining control over the behavior of the microglia, the defense cells of the CNS, which are manipulated by malignant glioma and support its growth. Armoring microglia against the influences from glioma is one of our research goals. We further discuss how microglia precursors may be genetically enhanced to track down infiltrating glioma cells.

ICOS-expressing lymphocytes promote resolution of CD8-mediated lung injury in a mouse model of lung rejection

Acute rejection, a common complication of lung transplantation, may promote obliterative bronchiolitis leading to graft failure in lung transplant recipients. During acute rejection episodes, CD8(+) T cells can contribute to lung epithelial injury but the mechanisms promoting and controlling CD8-mediated injury in the lung are not well understood. To study the mechanisms regulating CD8(+) T cell-mediated lung rejection, we used a transgenic model in which adoptively transferred ovalbumin (OVA)-specific cytotoxic T lymphocytes (CTL) induce lung injury in mice expressing an ovalbumin transgene in the small airway epithelium of the lungs (CC10-OVA mice). The lung pathology is similar to findings in humans with acute lung transplant. In the presence of an intact immune response the inflammation resolves by day 30. Using CC10-OVA.RAG(-/-) mice, we found that CD4(+) T cells and ICOS(+/+) T cells were required for protection against lethal lung injury, while neutrophil depletion was not protective. In addition, CD4(+)Foxp3 (+) ICOS(+) T cells were enriched in the lungs of animals surviving lung injury and ICOS(+/+) Tregs promoted survival in animals that received ICOS(-/-) T cells. Direct comparison of ICOS(-/-) Tregs to ICOS(+/+) Tregs found defects in vitro but no differences in the ability of ICOS(-/-) Tregs to protect from lethal lung injury. These data suggest that ICOS affects Treg development but is not necessarily required for Treg effector function.

The basis of distinctive IL-2- and IL-15-dependent signaling: weak CD122-dependent signaling favors CD8+ T central-memory cell survival but not T effector-memory cell development

Recent work suggests that IL-2 and IL-15 induce distinctive levels of signaling through common receptor subunits and that such varied signaling directs the fate of Ag-activated CD8(+) T cells. In this study, we directly examined proximal signaling by IL-2 and IL-15 and CD8(+) T cell primary and memory responses as a consequence of varied CD122-dependent signaling. Initially, IL-2 and IL-15 induced similar p-STAT5 and p-S6 activation, but these activities were only sustained by IL-2. Transient IL-15-dependent signaling is due to limited expression of IL-15Rα. To investigate the outcome of varied CD122 signaling for CD8(+) T cell responses in vivo, OT-I T cells were used from mouse models where CD122 signals were attenuated by mutations within the cytoplasmic tail of CD122 or intrinsic survival function was provided in the absence of CD122 expression by transgenic Bcl-2. In the absence of CD122 signaling, generally normal primary response occurred, but the primed CD8(+) T cells were not maintained. In marked contrast, weak CD122 signaling supported development and survival of T central-memory (T(CM)) but not T effector-memory (T(EM)) cells. Transgenic expression of Bcl-2 in CD122(-/-) CD8(+) T cells also supported the survival and persistence of T(CM) cells but did not rescue T(EM) development. These data indicate that weak CD122 signals readily support T(CM) development largely through providing survival signals. However, stronger signals, independent of Bcl-2, are required for T(EM) development. Our findings are consistent with a model whereby low, intermediate, and high CD122 signaling support T(CM) memory survival, T(EM) programming, and terminal T effector cell differentiation, respectively.

Regulation of CD4+ T-cell contraction during pathogen challenge

Signals orchestrating productive CD4+ T-cell responses are well documented; however, the regulation of contraction of CD4+ T-cell effector populations following the resolution of primary immune responses is not well understood. While distinct mechanisms of T-cell death have been defined, the relative importance of discrete death pathways during the termination of immune responses in vivo remains unclear. Here, we review the current understanding of cell-intrinsic and -extrinsic variables that regulate contraction of CD4+ T-cell effector populations through multiple pathways that operate both initially during T-cell priming and later during the effector phase. We discuss the relative importance of antigen-dependent and -independent mechanisms of CD4+ T-cell contraction during in vivo responses, with a special emphasis on influenza virus infection. In this model, we highlight the roles of greater differentiation and presence in the lung of CD4+ effector T cells, as well as their polarization to particular T-helper subsets, in maximizing contraction. We also discuss the role of autocrine interleukin-2 in limiting the extent of contraction, and we point out that these same factors regulate contraction during secondary CD4+ T-cell responses.

The IL-2 defect in systemic lupus erythematosus disease has an expansive effect on host immunity

IL-2 production is decreased in systemic lupus erythematosus (SLE) patients and affects T cell function and other aspects of host immunity. Transcription factors regulating IL-2 production behave aberrantly in SLE T cells. In addition to IL-2 dysregulation, other IL-2 family members (IL-15 and IL-21) are abnormally expressed in SLE. Decreased IL-2 production in SLE patients leads to many immune defects such as decreased T_reg production, decreased activation-induced cell death (AICD), and decreased cytotoxicity. IL-2 deficiency results in systemic dysregulation of host immune responses in patients suffering from SLE disease.

The transcriptional control of the perforin locus

SUMMARY

Natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) use cytotoxic granules containing perforin and granzymes to lyse infected or malignant host cells, thereby providing immunity to intracellular microbes and tumors. Perforin is essential for cytotoxic granule-mediated killing. Perforin expression is regulated transcriptionally and correlates tightly with the development of cells that can exhibit cytotoxic activity. Although a number of genes transcribed by T cells and NK cells have been studied, the cell-specificity of perforin gene expression makes it an ideal model system in which to clarify the transcriptional mechanisms that guide the development and activation of cytotoxic lymphocytes. In this review, we discuss what is known about perforin expression and its regulation, then elaborate on recent studies that utilized chromosome transfer and bacterial artificial chromosome transgenics to define a comprehensive set of cis-regulatory regions that control transcription of the human PRF1 gene in a near-physiologic context. In addition, we compare the human and murine Prf1 loci and discuss how transcription factors known to be important for driving CTL differentiation might also directly regulate the cis-acting domains that control Prf1. Our review emphasizes how studies of PRF1/Prf1 gene transcription can illuminate not only the mechanisms of cytotoxic lymphocyte differentiation but also some basic principles of transcriptional regulation.

Interleukin-2 and inflammation induce distinct transcriptional programs that promote the differentiation of effector cytolytic T cells

Interleukin(IL)-2 and inflammation regulate effector and memory cytolytic T-lymphocyte (CTL) generation during infection. We demonstrate a complex interplay between IL-2 and inflammatory signals during CTL differentiation. IL-2 stimulation induced the transcription factor eomesodermin (Eomes), upregulated perforin (Prf1) transcription, and repressed re-expression of memory CTL markers Bcl6 and IL-7Ralpha. Binding of Eomes and STAT5 to Prf1 cis-regulatory regions correlated with transcriptional initiation (increased recruitment of RNA polymerase II to the Prf1 promoter). Inflammation (CpG, IL-12) enhanced expression of IL-2Ralpha and the transcription factor T-bet, but countered late Eomes and perforin induction while preventing IL-7Ralpha repression by IL-2. After infection of mice with lymphocytic choriomeningitis virus, IL-2Ralpha-deficient effector CD8(+) T cells expressed more Bcl6 but less perforin and granzyme B, formed fewer KLRG-1(+) and T-bet-expressing CTL, and killed poorly. Thus, inflammation influences both effector and memory CTL differentiation, whereas persistent IL-2 stimulation promotes effector at the expense of memory CTL development.

Allogeneic T regulatory cell-mediated transplantation tolerance in adoptive therapy depends on dominant peripheral suppression and central tolerance

T regulatory cells (Tregs) represent agents to mediate tolerance to allografts so that the use of immunosuppressive drugs is avoided. In this regard, we previously demonstrated that the adoptive transfer of allogeneic Tregs into IL-2Rbeta(-/-) mice prevented autoimmunity and led to allograft tolerance. Here, we investigated the requirements and mechanisms that favor this long-lasting tolerance. The most potent tolerance required exact matching of all alloantigens between the adoptively transferred allogeneic Tregs and allogeneic skin grafts, but tolerance to such allografts that lacked expression of major histocompatibility complex class I or II molecules also occurred. Thus, Tregs are not required to directly recognize major histocompatibility complex class II alloantigens to suppress skin transplant rejection. Depletion of allogeneic Tregs substantially, but not completely, abrogated this form of tolerance. However, thymocytes from allogeneic Treg adoptively transferred IL-2Rbeta(-/-) mice did not reject the corresponding allogeneic skin graft in secondary Scid recipients. Consistent with a requirement for a deletional mechanism in this IL-2Rbeta(-/-) model, a small number of wild-type T cells readily abrogated the immune tolerant state. Collectively, these findings indicate that full tolerance induction is largely dependent on substantial Treg-mediated suppression and thymic deletion of alloreactive T cells and may represent general conditions for Treg-mediated transplantation tolerance.

CD27 sustains survival of CTLs in virus-infected nonlymphoid tissue in mice by inducing autocrine IL-2 production

Immunity to infections relies on clonal expansion of CD8+ T cells, their maintenance as effector CTLs, and their selection into a memory population. These processes rely on delivery of survival signals to activated CD8+ T cells. We here reveal the mechanism by which costimulatory CD27-CD70 interactions sustain survival of CD8+ effector T cells in infected tissue. By unbiased genome-wide gene expression analysis, we identified the Il2 gene as the most prominent CD27 target gene in murine CD8+ T cells. In vitro, CD27 directed IL-2 expression and promoted clonal expansion of primed CD8+ T cells exclusively by IL-2-dependent survival signaling. In mice intranasally infected with influenza virus, Cd27-/- CD8+ effector T cells displayed reduced IL-2 production, accompanied by impaired accumulation in lymphoid organs and in the lungs, which constitute the tissue effector site. Reconstitution of Cd27-/- CD8+ T cells with the IL2 gene restored their accumulation to wild-type levels in the lungs, but it did not rescue their accumulation in lymphoid organs. Competition experiments showed that the IL-2 produced under the control of CD27 supported effector CD8+ T cell survival in the lungs in an autocrine manner. We conclude that CD27 signaling directs the IL-2 production that is reportedly essential to sustain survival of virus-specific CTLs in nonlymphoid tissue.

Modeling the role of IL-2 in the interplay between CD4+ helper and regulatory T cells: assessing general dynamical properties

Mathematical models accounting for well-known evidences relating to the dynamics of interleukin 2, helper and regulatory T cells are presented. These models extend an existent model (the so-called cross-regulation model of immunity), by assuming IL-2 as the growth factor produced by helper cells, but used by both helper and regulatory cells to proliferate and survive. Two model variants, motivated by current literature, are explored. The first variant assumes that regulatory cells suppress helper cells by limiting IL-2 production and consuming the available IL-2; i.e. they just trigger competition for IL-2. The second model variant adds to the latter competitive mechanism the direct inhibition of helper cells activation by regulatory cells. The extended models retain key dynamical features of the cross-regulation model. But such reasonable behavior depends on parameter constraints, which happen to be realistic and lead to interesting biological discussions. Furthermore, the introduction of IL-2 in these models breaks the local/specific character of interactions, providing new properties to them. In the extended models, but not in the cross-regulation model, the response triggered by an antigen affects the response to other antigens in the same lymph node. The first model variant predicts an unrealistic coupling of the immune reactions to all the antigens in the lymph node. In contrast, the second model variant allows the coexistent of concomitant tolerant and immune responses to different antigens. The IL-2 derived from an ongoing immune reaction reinforces tolerance to other antigens in the same lymph node. Overall the models introduced here are useful extensions of the cross-regulation formalism. In particular, they might allow future studies of the effect of different IL-2 modulation therapies on CD4+ T cell dynamics.

Cell cycle progression following naive T cell activation is independent of Jak3/common gamma-chain cytokine signals

T cell proliferation following activation is an essential aspect of the adaptive immune response. Multiple factors, such as TCR signaling, costimulation, and signals from cytokines, each contribute to determine the magnitude of T cell expansion. In this report, we examine in detail the role of Jak3/common gamma-chain-dependent cytokines in promoting cell cycle progression and proliferation of naive T cells. Using naive CD4+ T cells from Jak3-deficient mice and wild-type CD4+ T cells treated with a small molecule inhibitor of Jak3, we find that these cytokine signals are not required for proliferation; instead, they are important for the survival of activated T cells. In addition, we show that the percentage of cells entering the cell cycle and the percentage of cells in each round of cell division are comparable between Jak3-deficent and wild-type T cells. Furthermore, cell cycle progression and the regulated expression of key cell cycle proteins are independent of Jak3/common gamma-chain cytokine signals. These findings hold true over a wide range of TCR signal strengths. However, when CD28 costimulatory signals, but not TCR signals, are limiting, Jak3-dependent cytokine signals become necessary for the proliferation of naive T cells. Because CD28 signaling has been found to be dispensable for autoreactive T cell responses, these data suggest the potential for interfering with autoimmune T cell responses by inhibition of Jak3 signaling.

A low interleukin-2 receptor signaling threshold supports the development and homeostasis of T regulatory cells

Interleukin-2 receptor (IL-2R) signaling is essential for T regulatory (Treg) cell development and homeostasis. Here, we show that expression of IL-2Rbeta chains that lack tyrosine residues important for the association of the adaptor Shc and the transcription factor STAT5 in IL-2Rbeta-deficient mice resulted in production of a normal proportion of natural Treg cells that suppressed severe autoimmunity related with deficiency in IL-2 or IL-2R. These mutant IL-2Rbeta chains supported suboptimal and transient STAT5 activation that upregulate the transcription factor Foxp3 to normal amounts in natural, but not induced, Treg cells. Nevertheless, gene expression profiling revealed many targets in peripheral natural Treg cells that were IL-2 dependent and a substantial overlap between the Treg cell IL-2-dependent gene program and the Treg cell transcriptional signature. Collectively, these findings demonstrate that a critical, and perhaps minor, subset of IL-2-dependent targets is indexed to a low IL-2R signaling threshold and that a substantial proportion of the Treg cell gene program is regulated by IL-2.

The IL-2/CD25 pathway determines susceptibility to T1D in humans and NOD mice

Although the interleukin-2 (IL-2)/IL-2R signaling pathway has been the focus of numerous studies, certain aspects of its molecular regulation are not well characterized, especially in non-T cells, and a more complete understanding of the pathway is necessary to discern the functional basis of the genetic association between the IL-2-IL-21 and IL-2RA/CD25 gene regions and T1D in humans. Genetic variation in these regions may promote T1D susceptibility by influencing transcription and/or splicing and, hence, IL-2 and IL-2RA/CD25 expression at the protein level in different immune cell subsets; thus, there is a need to establish links between the genetic variation and immune cell phenotypes and functions in humans, which can be further investigated and validated in mouse models. The detection and characterization of genetically determined immunophenotypes should aid in elucidating disease mechanisms and may enable future monitoring of disease initiation and progression in prediabetic subjects and of responses to therapeutic intervention.

A function for IL-7R for CD4+CD25+Foxp3+ T regulatory cells

The IL-2/IL-2R interaction is important for development and peripheral homeostasis of T regulatory (Treg) cells. IL-2- and IL-2R-deficient mice are not completely devoid of Foxp3+ cells, but rather lack population of mature CD4+CD25+Foxp3high Treg cells and contain few immature CD4+CD25-Foxp3low T cells. Interestingly, common gamma chain (gammac) knockout mice have been shown to have a near complete absence of Foxp3+ Treg cells, including the immature CD25-Foxp3low subset. Therefore, other gammac-cytokine(s) must be critically important during thymic development of CD4+CD25+Foxp3+ Treg cells apart from the IL-2. The present study was undertaken to determine whether the gammac-cytokines IL-7 or IL-15 normally contribute to expression of Foxp3 and Treg cell production. These studies revealed that mice double deficient in IL-2Rbeta and IL-7Ralpha contained a striking lack in the CD4+Foxp3+ population and the Treg cell defect recapitulated the gammac knockout mice. In the absence of IL-7R signaling, IL-15/IL-15R interaction is dispensable for the production of CD4+CD25+Foxp3+ Treg cells, indicating that normal thymic Treg cell production likely depends on signaling through both IL-2 and IL-7 receptors. Selective thymic reconstitution of IL-2Rbeta in mice double deficient in IL-2Rbeta and IL-7Ralpha established that IL-2Rbeta is dominant and sufficient to restore production of Treg cells. Furthermore, the survival of peripheral CD4+Foxp3low cells in IL-2Rbeta-/- mice appears to depend upon IL-7R signaling. Collectively, these data indicate that IL-7R signaling contributes to Treg cell development and peripheral homeostasis.

Interleukin 2: from immunostimulation to immunoregulation and back again

Interleukin 2 (IL-2) was one of the first cytokines to be discovered. However, the complex role of IL-2 and its receptor in the regulation of immune responses is only now emerging. This review explores the various signals triggered by IL-2 and discusses their translation into biological function. A model is outlined that accommodates the seemingly contradictory functions of IL-2, and explains how one cytokine can be an essential T-cell growth and differentiation factor and yet also be indispensable to maintain peripheral tolerance.

The biology of interleukin-2

Much data support an essential role for interleukin (IL)-2 in immune tolerance. This idea is much different from the early paradigm in which IL-2 is central for protective immune responses. This change in thinking occurred when a T regulatory cell defect was shown to be responsible for the lethal autoimmunity associated with IL-2/IL-2R deficiency. This realization allowed investigators to explore immune responses in IL-2-nonresponsive mice rendered autoimmune-free. Such studies established that IL-2 sometimes contributes to optimal primary immune responses, but it is not mandatory. Emerging findings, however, suggest an essential role for IL-2 in immune memory. Here, the current understanding of the dual role of IL-2 in maintaining tolerance and contributing to immunity in vivo is reviewed with some emphasis on T regulatory cell production and homeostasis. Also discussed are implications of this new appreciation concerning the immunobiology of IL-2 with respect to targeting IL-2 or its receptor in immunotherapy.

Signaling by small GTPases in the immune system

The Ras superfamily consists of over 50 low-molecular-weight proteins that cycle between an inactive guanosine diphosphate-bound state and an active guanosine triphosphate (GTP)-bound state. They are involved in a variety of signal transduction pathways that regulate cell growth, intracellular trafficking, cell migration, and apoptosis. Several methods have been devised to measure the activation state of Ras proteins, defined as the percent of Ras molecules in the active GTP-bound state. We have previously developed a quantitative biochemical method that can be applied to animal and human tissues and have used it to measure the activation state of Ras, Rap1, Rheb, and Rho proteins in cultured cells and in animal and human tumors. Ras, Rac, and Rho all play roles in regulating the functions of T and B lymphocytes and dendritic cells, and these proteins are clearly important in maintaining normal immune system function.

OX40-mediated differentiation to effector function requires IL-2 receptor signaling but not CD28, CD40, IL-12Rbeta2, or T-bet

Ag-specific CD4 T cells transferred into unirradiated Ag-bearing recipients proliferate, but survival and accumulation of proliferating cells is not extensive and the donor cells do not acquire effector functions. We previously showed that a single costimulatory signal delivered by an agonist Ab to OX40 (CD134) promotes accumulation of proliferating cells and promotes differentiation to effector CD4 T cells capable of secreting IFN-gamma. In this study, we determined whether OX40 costimulation requires supporting costimulatory or differentiation signals to drive acquisition of effector T cell function. We report that OX40 engagement drives effector T cell differentiation in the absence of CD28 and CD40 signals. Two important regulators of Th1 differentiation, IL-12R and T-bet, also are not required for acquisition of effector function in CD4 T cells responsive to OX40 stimulation. Finally, we show that CD25-deficient CD4 T cells produce little IFN-gamma in the presence of OX40 costimulation compared with wild type, suggesting that IL-2R signaling is required for efficient OX40-mediated differentiation to IFN-gamma secretion.

AFP-specific CD4+ helper T-cell responses in healthy donors and HCC patients

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, and is often diagnosed at an advanced stage. We have investigated alpha-fetoprotein (AFP) as a tumor-associated antigen for HCC. We identified major histocompatibility complex class I-restricted peptide epitopes derived from AFP and studied CD8 T-cell responses in vivo and in vitro in ongoing immunotherapy studies. Helper T cells are of critical importance in shaping the immune response; therefore, we investigated the frequency and function of AFP-specific CD4 T cells in the general population and among HCC patients. CD4 T-cell responses were assessed by direct ex vivo multicytokine enzyme-linked immunospot assay and by measurement of cytokine levels using a multicytokine assay. Our analysis indicates that healthy donors have very low frequencies of AFP-specific CD4 T-cell responses, which are of TH1 type, detectable ex vivo. In contrast, these T cells were either reduced or eliminated in HCC patients at advanced stages of disease. To better activate these cells, we compared the stimulatory capacity of both AFP protein-fed and AdVhAFP-engineered dendritic cells (DC). Healthy donors have CD4 T-cell responses, which were activated in response to AFP protein-fed DC whereas HCC patients do not demonstrate significant responses to AFP protein. AdVhAFP-transduced DC were capable of activating higher frequency TH1 CD4 responses to AFP in both healthy donors and AFP-positive HCC patients. Importantly, CD4 T-cell cytokine expression profiles were skewed towards interleukin-2 and interferon-gamma production when activated by adenovirally engineered DC, which has therapeutic implications for vaccination efforts.

Function of the IL-2R for Thymic and Peripheral CD4+CD25+ Foxp3+ T Regulatory Cells

IL-2 contributes to the production, function, and homeostasis of CD4+CD25+ T(reg) cells. However, it remains uncertain whether IL-2 is essential for the development of T(reg) cells in the thymus, their homeostasis in the periphery, or both. The present study was undertaken to investigate the contribution of IL-2 during thymic T(reg) cell development and its maintenance in peripheral immune tissue. Relying on genetic mouse models where IL-2R signaling was either completely blocked or selectively inhibited in peripheral CD4+CD25+ T(reg) cells, we show that the IL-2/IL-2R interaction is active in the thymus at the earliest stage of the development of T(reg) cells to promote their expansion and to up-regulate Foxp3 and CD25 to normal levels. Furthermore, CD4+CD25+Foxp3+ T(reg) cells with impaired IL-2-induced signaling persist in the periphery and control autoimmunity without constant thymic output. These peripheral T(reg) cells with poor responsiveness to IL-2 exhibited slower growth and extended survival in vivo, somewhat lower suppressive activity, and poor IL-2-dependent survival in vitro. Mixed thymic and bone marrow chimeric mice showed that wild-type-derived T(reg) cells were substantially more effective in populating peripheral immune tissue than T(reg) cells with impaired IL-2 signaling. Collectively, these data support the notion that normally IL-2 is a dominant mechanism controlling the number of thymic and peripheral T(reg) cells.

Cytokine-dependent Blimp-1 expression in activated T cells inhibits IL-2 production

After Ag activation of naive T cells in vitro, extensive growth and differentiation into effector cells depend upon IL-2. DNA microarray analysis was used to identify IL-2-dependent molecules regulating this process. In this study, we show that the transcriptional repressor B lymphocyte-induced maturation protein 1 (Blimp-1) is expressed by a cytokine-dependent pathway in activated T lymphocytes. IL-2 production by activated CD4(+) and CD8(+) T cells inversely correlated with Blimp-1 levels as higher IL-2 production was associated with lower Blimp-1 expression. Furthermore, ectopic expression of Blimp-1 by activated T cells inhibited IL-2 production but enhanced granzyme B and CD25 expression. Collectively, these findings indicate that there is a negative feedback regulatory loop in activated T cells such that IL-2 inhibits its own production through induction of Blimp-1 while promoting an effector cell phenotype.

All-trans retinoic acid stimulates IL-2-mediated proliferation of human T lymphocytes: early induction of cyclin D3

Vitamin A is established as an important immune regulator, but the mechanisms whereby vitamin A regulates T cell biology are poorly defined. In this study, we show that an active metabolite of vitamin A, all-trans retinoic acid (RA), potently stimulates T cell proliferation by modulating IL-2-mediated signaling downstream of IL-2R and independent of the induction of IL-2. Thus, at concentrations as low as 0.1 nM, RA enhanced the division of normal human T lymphocytes that were simultaneously stimulated with anti-CD3 mAbs and saturating concentrations of IL-2. At the optimal concentration of RA (50 nM), a 3-fold increase in T cell proliferation was observed. The induced proliferation was preceded by increased phosphorylation of the retinoblastoma protein and enhanced G1- to S-phase progression. Interestingly, the promitogenic effect of RA was found to be particularly directed toward increased expression of cyclin D3 at both the mRNA and protein level. Furthermore, the stimulatory effect of RA on cyclin D3 expression as well as on cell proliferation was completely abolished in the presence of the JAK inhibitor AG-490 or blocking IL-2R alpha mAbs, and RA also enhanced cyclin D3 expression and T cell proliferation in the presence of IL-2 alone. Finally, we showed that the proliferative effect of RA was mimicked by agonists of the retinoic acid receptor (RAR) and completely inhibited by a RAR-selective antagonist. In conclusion, our results indicate that RA, via RAR, stimulates IL-2-induced signaling in a JAK-dependent manner to enhance cyclin D3 expression and thereby promote T cell proliferation.

Donor-specific Cytotoxic Hyporesponsiveness Associated With High Interleukin-10 Messenger RNA Expression in Cardiac Allograft Patients

BACKGROUND

After transplantation, CD4+CD25+FOXP3+ and interleukin (IL) 10-producing regulatory cells might regulate immune responses toward donor antigens. In this study, we determined whether cardiac allograft recipients show donor-specific hyporesponsiveness and studied the underlying mechanisms.

METHODS

We analyzed the donor-specific T-cell responses by mixed lymphocyte reactions and limiting dilution assays to define whether cardiac allograft recipients (n = 21) show proliferative and cytotoxic hyporesponsiveness to donor antigens long after transplantation (range, 1.5-7 years). The mechanisms controlling immune responses, that is, FOXP3+/GITR+ T cells, and IL-10-producing cells, were studied by quantitative real-time polymerase chain reaction.

RESULTS

In the presence of a proliferative response to donor antigens, no cytotoxic responsiveness could be measured in a number of patients in the absence (73%) and presence of exogenous IL-2 (29%), IL-15 (31%), and IL-15 plus IL2Ralpha blockade (88%). Overall, the cytotoxic response to donor cells was significantly lower than the reactivity to third-party cells after the addition of IL-2 (p = 0.004) and IL-15 plus IL2Ralpha blockade (p < 0.001). After donor stimulation, the peripheral blood mononuclear cells expressed higher messenger RNA (mRNA) levels of IL-10, but not of FOXP3 or GITR, than after third-party stimulation (p = 0.003). Moreover, the IL-10 mRNA expression was inversely correlated with the donor-specific cytotoxic responsiveness (p = 0.01).

CONCLUSIONS

A significant proportion of patients showed donor-specific cytotoxic hyporesponsiveness long after heart transplantation, which was associated with high mRNA levels of IL-10 but not of FOXP3 or GITR. This observation suggests that IL-10-producing cells participate in the donor-specific cytotoxic hyporeactivity.

Differential regulation of T-cell growth by IL-2 and IL-15

Although interleukin 2 (IL-2) and IL-15 signal through the common gamma chain (γc) and through IL-2 receptor β–chain (CD122) subunits, they direct distinct physiologic and immunotherapeutic responses in T cells. The present study provides some insight into why IL-2 and IL-15 differentially regulate T-cell function by revealing that these cytokines are strikingly distinct in their ability to control protein synthesis and T-cell mass. IL-2 and IL-15 are shown to be equivalent mitogens for antigen-stimulated CD8+ T cells but not for equivalent growth factors. Antigen-primed T cells cannot autonomously maintain amino acid incorporation or de novo protein synthesis without exogenous cytokine stimulation. Both IL-2 and IL-15 induce amino acid uptake and protein synthesis in antigen-activated T cells; however, the IL-2 response is strikingly more potent than the IL-15 response. The differential action of IL-2 and IL-15 on amino acid uptake and protein synthesis is explained by temporal differences in signaling induced by these 2 cytokines. Hence, the present results show that cytokines that are equivalent mitogens can have different potency in terms of regulating protein synthesis and cell growth.

Control of CD4 + T‐cell memory by cytokines and costimulators

During T-cell priming, cytokines and costimulatory molecules provide important signals that determine the magnitude and quality of the response. Although the functions of defined cytokines and costimulators in the primary T-cell response are well characterized, much less is known about how these factors contribute to memory T-cell development and survival. Since memory cells are thought to be long-lived progeny of the primary response, it is conceivable that the same signals shaping initial T-cell expansion and differentiation also contribute to memory generation. Here, we review evidence and show novel data on the role of the cytokines interleukin-2 (IL-2) and IL-7 and the costimulator CD28 in CD4+ memory T-cell development. We emphasize that transient IL-2 and CD28 signals during priming imprint a long-lasting survival advantage in primed T cells, thus contributing to the persistence of a memory population. The requirement for IL-2 and CD28 signals is not linked to promoting T-cell division and expansion but most likely due to their capacity to (i) promote effector cell differentiation; (ii) induce survival proteins, and, as we discuss in more detail; (iii) program expression of receptors for 'memory survival factors' such as IL-7. Studies exploring the therapeutic potential of these insights are also discussed.

STAT5-mediated signals sustain a TCR-initiated gene expression program toward differentiation of CD8 T cell effectors

Poorly functional effector CD8 T cells are generated in some pathological situations, including responses to weakly antigenic tumors. To identify the molecular bases for such defective differentiation, we monitored gene expression in naive monoclonal CD8 T cells during responses to TCR ligands of different affinity. We further evaluated whether responses to weak Ags may be improved by addition of cytokines. Transient gene expression was observed for a cluster of genes in response to the weak TCR agonist. Strikingly, gene expression was stabilized by low dose IL-2. This IL-2-sustained gene cluster encoded notably transcripts for CD25, cytolytic effector molecules (granzyme B) and TNF-R family costimulatory molecules (glucocorticoid-induced TNF-R (GITR), OX40, and 4-1BB). IL-2-enhanced surface expression or function was also demonstrated in vivo for these genes. A constitutive active form of STAT5 mimicked the IL-2 effect by sustaining transcripts for the same gene cluster. Consistent with this, under conditions of low avidity TCR engagement and IL-2 treatment, endogenous STAT5 binding to 4-1BB and granzyme B promoters was demonstrated by chromatin immunoprecipitation. This study highlights those genes for which IL-2, via STAT5 activation, acts as a stabilizer of gene regulation initiated by TCR signals, contributing to the development of a complete CD8 T cell effector program.

OX40 (CD134) engagement drives differentiationof CD4+ T cells to effector cells

Naive, CD4+ T cells proliferate extensively but fail to differentiate when they are transferred into unirradiated recipients that express alloantigen or transgenic antigen on all MHC class II+ cells. Addition of an agonist antibody to OX40 (CD134), a costimulatory TNF receptor family member expressed on activated CD4+ T cells, enables the proliferating T cells to accumulate as differentiated effector cells and kill the host animals. The donor T cells from anti-OX40-treated animals express high levels of IL-2R alpha (CD25) and acquire the ability to secrete IFN-gamma when stimulated with IL-12 and IL-18. OX40 promotes differentiation by 48 h in T cell priming, before changes in Bcl-2 expression or cell recovery become apparent. We found that a Bcl-2 transgene or deficiency in Fas or TNFR1 failed to influence accumulation of differentiated donor cells, and found larger changes in expression of cytokine and cytokine receptor genes than in survival genes. Accumulation of differentiated CD4+ effector T cells is initiated directly through OX40, but some OX40-deficient donor cells can gain effector function as bystanders to OX40+/+ cells. Taken together, these data suggest that CD4+ T cell differentiation to effector function is an important effect of OX40 engagement under conditions of ubiquitous antigen presentation.

IL-2 production by dendritic cells is not critical for the activation of cognate and innate effectors in draining lymph nodes

Dendritic cells (DC) are unique antigen-presenting cells capable of triggering NK cell effector functions and priming naive T cells in vivo. Microbial stimulation induces early IL-2 production by mouse DC. Previous reports demonstrated that IL-2 is enriched at the site of DC/T cell interaction and promotes allogeneic T cell proliferation. However, the direct role of DC-derived IL-2 in the differentiation of cytotoxic T lymphocytes and in NK cell triggering in vivo has not been investigated. Lipopolysaccharide (LPS) stimulation of mouse bone marrow-derived DC results in early IL-2 production unless IL-4 is introduced in DC cultures. Here we show that IL-2 produced by LPS-activated DC is dispensable for cognate T cell responses since IL-2 loss of function DC elicit OVA-specific Tc1 effector and memory lymphocytes in draining lymph nodes in a setting where ex vivo cultured DC do not transfer antigens to host DC. Moreover, adoptively transferred IL-2 loss of function DC maintain their capacity to trigger NK cell proliferation/recruitment in lymph nodes. Therefore, immediate inducible IL-2 production by DC following microbial infection might play a regulatory role at ports of entry rather than in secondary lymphoid organs.

IL-2 responsiveness of CD4 and CD8 lymphocytes: further investigations with human IL-2Rbeta transgenic mice

Responsiveness to IL-2 varies from one lympho-mononuclear subset to another. NK lymphocytes and monocytes spontaneously respond to IL-2 whereas it is generally accepted that T and B lymphocytes need to be activated to fully acquire this competence. To further investigate this phenomenon, we studied human IL-2Rbeta (hIL-2Rbeta) transgenic mice constitutively expressing heterospecific, intermediate-affinity IL-2R (hIL-2Rbeta/mouse IL-2Rgamma(c)). We noted that the B lymphocytes and monocytes from spleens of these hIL-2Rbeta transgenic animals failed to grow when cultured in IL-2-containing medium. Under the same experimental conditions, CD4 lymphocytes survived, again without growth, whereas CD8 lymphocytes and NK cells were able to proliferate and develop potent LAK cytotoxicity. The properties of these CD4 and CD8 lymphocytes were then compared after purification. Both subsets expressed functional IL-2R able to induce global protein phosphorylation and, more precisely, signal transducer and activation of transcription 5 and Erk phosphorylation. Therefore, the differential growth potential of these CD4 and CD8 lymphocytes cannot be explained by the lack of IL-2R-dependent early signaling events. When the entrance of purified CD4 and CD8 lymphocytes into the cell cycle was analyzed, we found that the CD4 lymphocytes were unable to enter the G1 phase in the absence of anti-CD3 stimulation. This correlates with the effect of IL-2 on cyclin-dependent kinase inhibitor p27(kip1). In CD4 lymphocytes, IL-2 does not affect p27(kip1) expression. But in CD8 lymphocytes, IL-2 down-modulates p27(kip1). These results indicate that, aside from IL-2R expression and function, IL-2 responsiveness is also controlled by lineage-specific mechanisms.

The quantal theory of how the immune system discriminates between "self and non-self"

In the past 50 years, immunologists have accumulated an amazing amount of information as to how the immune system functions. However, one of the most fundamental aspects of immunity, how the immune system discriminates between self vs. non-self, still remains an enigma. Any attempt to explain this most intriguing and fundamental characteristic must account for this decision at the level of the whole immune system, but as well, at the level of the individual cells making up the immune system. Moreover, it must provide for a molecular explanation as to how and why the cells behave as they do. The "Quantal Theory", proposed herein, is based upon the "Clonal Selection Theory", first proposed by Sir McFarland Burnet in 1955, in which he explained the remarkable specificity as well as diversity of recognition of everything foreign in the environment. The "Quantal Theory" is built upon Burnet's premise that after antigen selection of cell clones, a proliferative expansion of the selected cells ensues. Furthermore, it is derived from experiments which indicate that the proliferation of antigen-selected cell clones is determined by a quantal, "all-or-none", decision promulgated by a critical number of cellular receptors triggered by the T Cell Growth Factor (TCGF), interleukin 2 (IL2). An extraordinary number of experiments reported especially in the past 20 years, and detailed herein, indicate that the T cell Antigen Receptor (TCR) behaves similarly, and also that there are several critical numbers of triggered TCRs that determine different fates of the T cells. Moreover, the fates of the cells appear ultimately to be determined by the TCR triggering of the IL2 and IL2 receptor (IL2R) genes, which are also expressed in a very quantal fashion. The "Quantal Theory" states that the fundamental decisions of the T cell immune system are dependent upon the cells receiving a critical number of triggered TCRs and IL2Rs and that the cells respond in an all-or-none fashion. The "Quantal Theory" accounts fully for the development of T cells in the thymus, and such fundamental cellular fates as both "positive" and "negative" selection, as well as the decision to differentiate into a "Regulatory T cell" (T-Reg). In the periphery, the "Quantal Theory" accounts for the decision to proliferate or not in response to the presence of an antigen, either non-self or self, or to differentiate into a T-Reg. Since the immune system discriminates between self and non-self antigens by the accumulated number of triggered TCRs and IL2Rs, therapeutic manipulation of the determinants of these quantal decisions should permit new approaches to either enhance or dampen antigen-specific immune responses.

Ginsenoside Rg1 enhances CD4(+) T-cell activities and modulates Th1/Th2 differentiation

Panax ginseng is commonly used as a tonic medicine in Asian countries such as Korea, China, and Japan. It has been reported that ginsenoside Rg1 in P. ginseng increases the proportion of T helper (Th) cells among the total number of T cells and promotes IL-2 gene expression in murine splenocytes. This implies that ginsenoside Rg1 increases the immune activity of CD4(+) T cells, however, the exact mechanism remains unknown. The present study elucidated the direct effect of Rg1 on helper T-cell activities and on Th1/Th2 lineage development. The results demonstrated that ginsenoside Rg1 had no mitogenic effects on unstimulated CD4(+) T cells, but augmented CD4(+) T-cell proliferation upon activation with anti-CD3/anti-CD28 antibodies in a dose-dependent manner. Rg1 also enhanced the expression of cell surface protein CD69 on CD4(+) T cells. In Th0 condition, ginsenoside Rg1 increases the expression of IL-2 mRNA, and enhances the expression of IL-4 mRNA on CD4(+) T cells, suggesting that Rg1 prefers to induce Th2 lineage development. In addition, ginsenoside Rg1 increases IL-4 secretion in CD4(+) T cells under Th2 skewed condition, while decreasing IFN-gamma secretion of cells in Th1 polarizing condition. Thus, Rg1 enhances Th2 lineage development from the naïve CD4(+) T cell both by increasing Th2 specific cytokine secretion and by repressing Th1 specific cytokine production. Therefore, these results suggest that ginsenoside Rg1 is a desirable agent for enhancing CD4(+) T-cell activity, as well as the correction of Th1-dominant pathological disorders.

Chung-Yeul-Gue-Soup-Sa-Gan-Tang, traditional Korean medicine, enhances CD4(+) T cell activities and modulates Th1/Th2 lineage development

Chung-Yeul-Gue-Soup-Sa-Gan-Tang (CYT), a traditional Korea herbal medicine, has been widely used in Korea for the treatment of various immunological disorders, including allergic asthma. In this study, CYT was examined in vitro and tested for possible immunological effects. The results demonstrated that CYT had no mitogenic effects on unstimulated CD4(+) T cells, but rather increased CD4(+) T cell proliferation upon activation with anti-CD3/CD28 antibody. Under the Th0 condition, CYT also enhanced expression of interleukin (IL)-2 in purified murine CD4(+) T cells assayed by real-time PCR, suggesting that CYT moderately increases the activity of helper T cells upon T cell receptor ligation under the neutral condition. However, the Th1 cells were overpopulated following CYT treatment under the Th1 condition, while Th2 cells were under-populated in the Th2 driven condition. In addition, under Th1/Th2-skewed conditions, the levels of IL-4 were considerably decreased, while the expression of T-bet and interferon-gamma were increased with CYT treatment. Thus, CYT enhances Th1 lineage development from naive CD4(+) T cells both by increasing Th1 specific cytokine secretion and repressing Th2 specific cytokine production. These results suggest that CYT is a desirable agent for the correction of Th2 dominant pathological disorders.

Synthetic peptides mapping to epitopes of the extracellular domain of the interleukin-2 receptor beta-chain to inhibit T-cell activation

Expression of the high-affinity IL-2 receptor (IL-2R) on the surface of activated T cells makes it an attractive target for selective inhibition of alloreactive T cells in organ transplantation. IL-2 binds to its receptor via the extracellular domain of the beta-chain. In this study we synthesized synthetic peptides that map to epitopes of this domain and tested their ability to inhibit the activation and proliferation of mitogen-stimulated peripheral-blood T cells. Solid-phase synthesis was applied to create three oligopeptides of primary structures corresponding to the epitopes M(107)-E(118), Y(178)-Q(199), and E(190)-Q(199) of the extracellular domain of the IL-2Rbeta-chain. A nonhomologous peptide served as control. Peripheral-blood mononuclear cells isolated from 16 healthy volunteers (median age 41 years, range 26 to 56 years) were cultured with various concentrations of peptides and the mitogen phytohemagglutinin (PHA). The inhibitory effect of the peptides on cell proliferation was evaluated by automated cell counting and colorimetric proliferation assays. Cell activation was assessed by immunophenotyping using antibodies directed toward CD4, CD25, or CD69. The amount of IL-2 in culture supernates was measured by enzyme-linked immunoassay. Cultures in the presence of the peptide M(107)-E(118) (500 nmol/L) inhibited PHA-induced T-cell proliferation by 38%, and IL-2 secretion by 57%. Immunophenotyping confirmed suppression of activated T cells. Peptides Y(178)-Q(199) and E(190)-Q(199) inhibited proliferation, but failed to significantly affect IL-2 secretion. The control peptide showed no effect on the activation parameters. Our data indicate that the M(107)-E(118) peptide has promise for organ transplantation therapy.

IL-2 induces a competitive survival advantage in T lymphocytes

The acquisition of long-term survival potential by activated T lymphocytes is essential to ensure the successful development of a memory population in the competitive environment of the lymphoid system. The factors that grant competitiveness for survival to primed T cells are poorly defined. We examined the role of IL-2 signals during priming of CD4(+) T cells in the induction of a long-lasting survival program. We show that Ag-induced cycling of CD4(+) IL-2(-/-) T cells is independent of IL-2 in vitro. However, IL-2(-/-) T cells failed to accumulate in large numbers and develop in effector cells when primed in the absence of IL-2. More importantly, Ag-activated IL-2(-/-) T cells were unable to survive for prolonged periods of time after adoptive transfer in unmanipulated, syngeneic mice. IL-2(-/-) T cells exposed to IL-2 signals during priming, however, acquired a robust and long-lasting survival advantage over cells that cycled in the absence of IL-2. Interestingly, this IL-2-induced survival program was required for long-term persistence of primed IL-2(-/-) T cells in an intact lymphoid compartment, but was unnecessary in a lymphopenic environment. Therefore, IL-2 enhances competitiveness for survival in CD4(+) T cells, thereby facilitating the development of a memory population.

Tolerance, not immunity, crucially depends on IL-2

Interleukin-2 (IL-2) was identified based on its potent T-cell growth-factor activity and is widely considered to be a key cytokine in T-cell-dependent immune responses. However, the main non-redundant activity of this cytokine centres on the regulation of T-cell tolerance, and recent studies indicate that a failure in the production of CD4(+)CD25(+) regulatory T cells is the underlying cause of autoimmunity in the absence of IL-2. In marked contrast to the importance of IL-2 in peripheral T-cell tolerance, T-cell immunity is readily elicited to various agents in the absence of IL-2 in vivo. Here, we discuss these findings and, in particular, the action of IL-2 on regulatory T cells and effector cells, and the targeting of IL-2 and/or the IL-2 receptor in clinical settings.