Interleukin 2 leads to dose-dependent expression of the alpha chain of the IL-2 receptor on CD25-negative T lymphocytes in the absence of exogenous antigenic stimulation

A Novel Whole Tissue Explant Model of Hidradenitis Suppurativa

Hidradenitis Suppurativa (HS) is a relatively common and highly morbid inflammatory skin disease. Due to our relatively limited understanding of HS's pathogenesis, there are currently insufficient treatment options available, and many patients' medical needs are not being met. This is partly due to a scarcity of ex vivo human assays and animal models that accurately recapitulate the disease. To address this deficit, we have developed a whole-tissue explant model of HS to examine its pathogenic mechanisms and the efficacy of potential treatments within intact human tissue. We measured cytokine protein and RNA within whole tissue maintained in an agar-media solution, finding that IL-6 and IL-8 concentrations trended upwards in both HS explants and healthy controls, while IL-17A, IL-1β, and TNF-α exhibited increases in HS tissue alone. We also show that the explants were responsive to treatment with both dexamethasone and IL-2. Not only do our results show that this model effectively delivers treatments throughout the explants, but they also elucidate which cytokines are related to the explant process regardless of tissue state and which are related to HS tissue specifically, laying the groundwork for future implementations of this model.

Impact of in vitro HIV infection on human thymic regulatory T cell differentiation

Background

The differentiation and function of immunosuppressive regulatory T cells (Tregs) is dictated by the master transcription factor FoxP3. During HIV infection, there is an increase in Treg frequencies in the peripheral blood and lymphoid tissues. This accentuates immune dysfunction and disease progression. Expression of FoxP3 by thymic Tregs (tTregs) is partially controlled by TGF-β. This cytokine also contributes to Treg development in the peripheral blood and lymphoid tissues. Although TGF-β mediates lymphoid tissue fibrosis and peripheral Treg differentiation in HIV-infected individuals, its role in the induction and maintenance of Tregs within the thymus during HIV infection remains unclear.

Methods

Thymocytes were isolated from fresh human thymic tissues obtained from pediatric patients undergoing cardiac surgery. Infection by both R5- and X4-tropic HIV-1 strains and TGF-β treatment of human thymocytes was performed in an in vitro co-culture model with OP9-DL1 cells expressing Notch ligand delta-like 1 without T cell receptor (TCR) activation.

Results

Despite high expression of CCR5 and CXCR4 by tTregs, FoxP3 +  CD3highCD8- thymocytes were much less prone to in vitro infection with R5- and X4-tropic HIV strains compared to FoxP3-CD3highCD8- thymocytes. As expected, CD3highCD4+ thymocytes, when treated with TGF-β1, upregulated CD127 and this treatment resulted in increased FoxP3 expression and Treg differentiation, but did not affect the rate of HIV infection. FoxP3 expression and Treg frequencies remained unchanged following in vitro HIV infection alone or in combination with TGF-β1.

Conclusion

FoxP3 expression and tTreg differentiation is not affected by in vitro HIV infection alone or the combination of in vitro HIV infection and TGF-β treatment.

Themis is indispensable for IL-2 and IL-15 signaling in T cells

To perform their antiviral and antitumor functions, T cells must integrate signals both from the T cell receptor (TCR), which instruct the cell to remain quiescent or become activated, and from cytokines that guide cellular proliferation and differentiation. In mature CD8⁺ T cells, Themis has been implicated in integrating TCR and cytokine signals. We investigated whether Themis plays a direct role in cytokine signaling in mature T cells. Themis was required for IL-2- and IL-15-driven CD8⁺ T cell proliferation both in mice and in vitro. Mechanistically, we found that Themis promoted the activation of the transcription factor Stat and mechanistic target of rapamycin signaling downstream of cytokine receptors. Metabolomics and stable isotope tracing analyses revealed that Themis deficiency reduced glycolysis and serine and nucleotide biosynthesis, demonstrating a receptor-proximal requirement for Themis in triggering the metabolic changes that enable T cell proliferation. The cellular, metabolic, and biochemical defects caused by Themis deficiency were corrected in mice lacking both Themis and the phosphatase Shp1, suggesting that Themis mediates IL-2 and IL-15 receptor-proximal signaling by restraining the activity of Shp1. Together, these results not only shed light on the mechanisms of cytokine signaling but also provide new clues on manipulating T cells for clinical applications.

Continuous Modeling of T CD4 Lymphocyte Activation and Function

T CD4+ cells are central to the adaptive immune response against pathogens. Their activation is induced by the engagement of the T-cell receptor by antigens, and of co-stimulatory receptors by molecules also expressed on antigen presenting cells. Then, a complex network of intracellular events reinforce, diversify and regulate the initial signals, including dynamic metabolic processes that strongly influence both the activation state and the differentiation to effector cell phenotypes. The regulation of cell metabolism is controlled by the nutrient sensor adenosine monophosphate-activated protein kinase (AMPK), which drives the balance between oxidative phosphorylation (OXPHOS) and glycolysis. Herein, we put forward a 51-node continuous mathematical model that describes the temporal evolution of the early events of activation, integrating a circuit of metabolic regulation into the main routes of signaling. The model simulates the induction of anergy due to defective co-stimulation, the CTLA-4 checkpoint blockade, and the differentiation to effector phenotypes induced by external cytokines. It also describes the adjustment of the OXPHOS-glycolysis equilibrium by the action of AMPK as the effector function of the T cell develops. The development of a transient phase of increased OXPHOS before induction of a sustained glycolytic phase during differentiation to the Th1, Th2 and Th17 phenotypes is shown. In contrast, during Treg differentiation, glycolysis is subsequently reduced as cell metabolism is predominantly polarized towards OXPHOS. These observations are in agreement with experimental data suggesting that OXPHOS produces an ATP reservoir before glycolysis boosts the production of metabolites needed for protein synthesis, cell function, and growth.

Engineered Cytokine Signaling to Improve CAR T Cell Effector Function

Adoptive immunotherapy with T cells genetically modified to express chimeric antigen receptors (CARs) is a promising approach to improve outcomes for cancer patients. While CAR T cell therapy is effective for hematological malignancies, there is a need to improve the efficacy of this therapeutic approach for patients with solid tumors and brain tumors. At present, several approaches are being pursued to improve the antitumor activity of CAR T cells including i) targeting multiple antigens, ii) improving T cell expansion/persistence, iii) enhancing homing to tumor sites, and iv) rendering CAR T cells resistant to the immunosuppressive tumor microenvironment (TME). Augmenting signal 3 of T cell activation by transgenic expression of cytokines or engineered cytokine receptors has emerged as a promising strategy since it not only improves CAR T cell expansion/persistence but also their ability to function in the immunosuppressive TME. In this review, we will provide an overview of cytokine biology and highlight genetic approaches that are actively being pursued to augment cytokine signaling in CAR T cells.

IL-2 contributes to cirrhosis-associated immune dysfunction by impairing follicular T helper cells in advanced cirrhosis

BACKGROUND & AIMS

Patients with decompensated cirrhosis suffer from recurrent infections and inadequate responses to prophylactic vaccinations. However, many patients present with hypergammaglobulinemia (HGG), indicating a sustained ability to generate antibody responses. As follicular T helper (Tfh) cells are central facilitators of humoral immunity, we hypothesized that Tfh cell responses may be altered in advanced liver disease and we aimed to identify the mechanisms underlying any such alterations.

METHODS

Tfh, regulatory T (Treg) cells, B cells, circulating cytokines and immunoglobulins were analyzed in cohorts of patients with compensated (n = 37) and decompensated cirrhosis (n = 82) and in non-cirrhotic controls (n = 45). Intrahepatic T cells were analyzed in 8 decompensated patients. The influence of IL-2 on Tfh cell function was evaluated in vitro, including Tfh cell cloning and T cell-B cell co-cultures with clones and primary tonsil-derived Tfh cells.

RESULTS

Tfh cell frequencies were reduced in patients with decompensated cirrhosis, with phenotypic signatures indicative of increased IL-2 signaling. Soluble IL-2 receptor (sCD25) was elevated in these patients and CD4 T cells were more responsive to IL-2 signaling, as characterized by STAT5 phosphorylation. IL-2 exposure in vitro diminished the Tfh phenotype and resulted in impaired Tfh helper function in co-culture experiments with naïve B cells. Tfh cells were barely detectable in cirrhotic livers. IL-2 signatures on Tfh cells in decompensated patients correlated with immunoglobulin levels, which were found to be associated with improved survival.

CONCLUSIONS

Tfh cell impairment represents a previously underestimated feature of cirrhosis-associated immune dysfunction that is driven by IL-2. The presence of HGG in decompensated patients predicts an intact Tfh cell compartment and is associated with a favorable outcome.

LAY SUMMARY

Patients with advanced cirrhosis often fail to generate protective immunity after prophylactic vaccinations and suffer from recurring infections that are associated with high mortality. Follicular T helper (Tfh) cells are specialized CD4 T cells that enable the emergence of antibody responses against microbial pathogens. This report demonstrates that Tfh cells are impaired in patients with advanced cirrhosis due to interleukin-2 signaling, a cytokine that is known to impair the generation of Tfh cells.

Human Mesenchymal Stem Cells Overexpressing Interleukin 2 Can Suppress Proliferation of Neuroblastoma Cells in Co-Culture and Activate Mononuclear Cells In Vitro

High-dose recombinant interleukin 2 (IL2) therapy has been shown to be successful in renal cell carcinoma and metastatic melanoma. However, systemic administration of high doses of IL2 can be toxic, causing capillary leakage syndrome and stimulating pro-tumor immune response. One of the strategies to reduce the systemic toxicity of IL2 is the use of mesenchymal stem cells (MSCs) as a vehicle for the targeted delivery of IL2. Human adipose tissue-derived MSCs were transduced with lentivirus encoding IL2 (hADSCs-IL2) or blue fluorescent protein (BFP) (hADSCs-BFP). The proliferation, immunophenotype, cytokine profile and ultrastructure of hADSCs-IL2 and hADSCs-BFP were determined. The effect of hADSCs on activation of peripheral blood mononuclear cells (PBMCs) and proliferation and viability of SH-SY5Y neuroblastoma cells after co-culture with native hADSCs, hADSCs-BFP or hADSCs-IL2 on plastic and Matrigel was evaluated. Ultrastructure and cytokine production by hADSCs-IL2 showed modest changes in comparison with hADSCs and hADSCs-BFP. Conditioned medium from hADSC-IL2 affected tumor cell proliferation, increasing the proliferation of SH-SY5Y cells and also increasing the number of late-activated T-cells, natural killer (NK) cells, NKT-cells and activated T-killers. Conversely, hADSC-IL2 co-culture led to a decrease in SH-SY5Y proliferation on plastic and Matrigel. These data show that hADSCs-IL2 can reduce SH-SY5Y proliferation and activate PBMCs in vitro. However, IL2-mediated therapeutic effects of hADSCs could be offset by the increased expression of pro-oncogenes, as well as the natural ability of hADSCs to promote the progression of some tumors.

An Integrative Network Modeling Approach to T CD4 Cell Activation

The adaptive immune response is initiated by the interaction of the T cell antigen receptor/CD3 complex (TCR) with a cognate peptide bound to a MHC molecule. This interaction, along with the activity of co-stimulatory molecules and cytokines in the microenvironment, enables cells to proliferate and produce soluble factors that stimulate other branches of the immune response for inactivation of infectious agents. The intracellular activation signals are reinforced, amplified and diversified by a complex network of biochemical interactions, and includes the activity of molecules that modulate the activation process and stimulate the metabolic changes necessary for fulfilling the cell energy demands. We present an approach to the analysis of the main early signaling events of T cell activation by proposing a concise 46-node hybrid Boolean model of the main steps of TCR and CD28 downstream signaling, encompassing the activity of the anergy factor Ndrg1, modulation of activation by CTLA-4, and the activity of the nutrient sensor AMPK as intrinsic players of the activation process. The model generates stable states that reflect the overcoming of activation signals and induction of anergy by the expression of Ndrg1 in the absence of co-stimulation. The model also includes the induction of CTLA-4 upon activation and its competition with CD28 for binding to the co-stimulatory CD80/86 molecules, leading to stable states that reflect the activation arrest. Furthermore, the model integrates the activity of AMPK to the general pathways driving differentiation to functional cell subsets (Th1, Th2, Th17, and Treg). Thus, the network topology incorporates basic mechanism associated to activation, regulation and induction of effector cell phenotypes. The model puts forth a conceptual framework for the integration of functionally relevant processes in the analysis of the T CD4 cell function.

A role for cell-autocrine interleukin-2 in regulatory T-cell homeostasis

Activated T-cells make both interleukin-2 (IL2) and its high-affinity receptor component CD25. Regulatory CD4 T-cells (Treg cells) do not make IL2, and the IL2-CD25 circuit is considered a paracrine circuit crucial in their generation and maintenance. Yet, all T-cells are capable of making IL2 at some stage during differentiation, making a cell-intrinsic autocrine circuit additionally possible. When we re-visited experiments with mixed bone marrow chimeras using a wide range of ratios of wild-type (WT) and IL2-/- genotype progenitors, we found that, as expected, thymic Treg cells were almost equivalent between WT and IL2-/- genotypes at ratios with WT prominence. However, at WT-limiting ratios, the IL2-/- genotype showed lower thymic Treg frequencies, indicating a role for cell-intrinsic autocrine IL2 in thymic Treg generation under IL2-limiting conditions. Further, peripheral IL2-/- naive CD4 T-cells showed poor conversion to inducible Tregs (pTregs) both in vivo and in vitro, again indicating a significant role for cell-intrinsic autocrine IL2 in their generation. Peripherally, the IL2-/- genotype was less prominent at all WT:IL2-/- ratios among both thymic Tregs (tTregs) and pTregs, adoptively transferred IL2-/- Tregs showed poorer survival than WT Tregs did, and RNA-seq analysis of WT and IL2-/- Tregs showed interesting differences in the T-cell receptor and transforming growth factor-beta-bone morphogenetic protein-JNK pathways between them, suggesting a non-titrating role for cell-intrinsic autocrine IL2 in Treg programming. These data indicate that cell-intrinsic autocrine IL2 plays significant roles in Treg generation and maintenance.

An Optimized Full-Length FLT3/CD3 Bispecific Antibody Demonstrates Potent Anti-leukemia Activity and Reversible Hematological Toxicity

FLT3 (FMS-like tyrosine kinase 3), expressed on the surface of acute myeloid leukemia (AML) blasts, is a promising AML target, given its role in the development and progression of leukemia, and its limited expression in tissues outside the hematopoietic system. Small molecule FLT3 kinase inhibitors have been developed, but despite having clinical efficacy, they are effective only on a subset of patients and associated with high risk of relapse. A durable therapy that can target a wider population of AML patients is needed. Here, we developed an anti-FLT3-CD3 immunoglobulin G (IgG)-based bispecific antibody (7370) with a high affinity for FLT3 and a long half-life, to target FLT3-expressing AML blasts, irrespective of FLT3 mutational status. We demonstrated that 7370 has picomolar potency against AML cell lines in vitro and in vivo. 7370 was also capable of activating T cells from AML patients, redirecting their cytotoxic activity against autologous blasts at low effector-to-target (E:T) ratio. Additionally, under our dosing regimen, 7370 was well tolerated and exhibited potent efficacy in cynomolgus monkeys by inducing complete but reversible depletion of peripheral FLT3⁺ dendritic cells (DCs) and bone marrow FLT3⁺ stem cells and progenitors. Overall, our results support further clinical development of 7370 to broadly target AML patients.

Differential Interleukin-2 Transcription Kinetics Render Mouse but Not Human T Cells Vulnerable to Splicing Inhibition Early after Activation

T cells are nodal players in the adaptive immune response against pathogens and malignant cells. Alternative splicing plays a crucial role in T cell activation, which is analyzed mainly at later time points upon stimulation. Here we have discovered a 2-h time window early after stimulation where optimal splicing efficiency or, more generally, gene expression efficiency is crucial for successful T cell activation. Reducing the splicing efficiency at 4 to 6 h poststimulation significantly impaired murine T cell activation, which was dependent on the expression dynamics of the Egr1-Nab2-interleukin-2 (IL-2) pathway. This time window overlaps the time of peak IL-2 de novo transcription, which, we suggest, represents a permissive time window in which decreased splicing (or transcription) efficiency reduces mature IL-2 production, thereby hampering murine T cell activation. Notably, the distinct expression kinetics of the Egr1-Nab2-IL-2 pathway between mouse and human render human T cells refractory to this vulnerability. We propose that the rational temporal modulation of splicing or transcription during peak de novo expression of key effectors can be used to fine-tune stimulation-dependent biological outcomes. Our data also show that critical consideration is required when extrapolating mouse data to the human system in basic and translational research.

IL-27 gene therapy induces depletion of Tregs and enhances the efficacy of cancer immunotherapy

Tumor-induced expansion of Tregs is a significant obstacle to cancer immunotherapy. However, traditional approaches to deplete Tregs are often inefficient, provoking autoimmunity. We show here that administration of IL-27-expressing recombinant adeno-associated virus (AAV-IL-27) significantly inhibits tumor growth and enhances T cell responses in tumors. Strikingly, we found that AAV-IL-27 treatment causes rapid depletion of Tregs in peripheral blood, lymphoid organs, and - most pronouncedly - tumor microenvironment. AAV-IL-27-mediated Treg depletion is dependent on IL-27 receptor and Stat1 in Tregs and is a combined result of CD25 downregulation in Tregs and inhibition of IL-2 production by T cells. In combination with a GM-CSF vaccine, AAV-IL-27 treatment not only induced nearly complete tumor rejection, but also resulted in amplified neoantigen-specific T cell responses. AAV-IL-27 also dramatically increased the efficacy of anti-PD-1 therapy, presumably due to induction of PD-L1 in T cells and depletion of Tregs. Importantly, AAV-IL-27 therapy did not induce significant adverse events, partially due to its induction of IL-10. In a plasmacytoma mouse model, we found that IL-10 was required for AAV-IL-27-mediated tumor rejection. Thus, our study demonstrates the potential of AAV-IL-27 as an independent cancer therapeutic and as an efficient adjuvant for cancer immunotherapy.

Critical role of OX40 signaling in the TCR-independent phase of human and murine thymic Treg generation

Regulatory T cells (Tregs) play a pivotal role in immune-tolerance, and loss of Treg function can lead to the development of autoimmunity. Natural Tregs generated in the thymus substantially contribute to the Treg pool in the periphery, where they suppress self-reactive effector T cells (Teff) responses. Recently, we showed that OX40L (TNFSF4) is able to drive selective proliferation of peripheral Tregs independent of canonical antigen presentation (CAP-independent) in the presence of low-dose IL-2. Therefore, we hypothesized that OX40 signaling might be integral to the TCR-independent phase of murine and human thymic Treg (tTreg) development. Development of tTregs is a two-step process: Strong T-cell receptor (TCR) signals in combination with co-signals from the TNFRSF members facilitate tTreg precursor selection, followed by a TCR-independent phase of tTreg development in which their maturation is driven by IL-2. Therefore, we investigated whether OX40 signaling could also play a critical role in the TCR-independent phase of tTreg development. OX40^-/- mice had significantly reduced numbers of CD25^-Foxp3^low tTreg precursors and CD25⁺Foxp3⁺ mature tTregs, while OX40L treatment of WT mice induced significant proliferation of these cell subsets. Relative to tTeff cells, OX40 was expressed at higher levels in both murine and human tTreg precursors and mature tTregs. In ex vivo cultures, OX40L increased tTreg maturation and induced CAP-independent proliferation of both murine and human tTregs, which was mediated through the activation of AKT-mTOR signaling. These novel findings show an evolutionarily conserved role for OX40 signaling in tTreg development and proliferation, and might enable the development of novel strategies to increase Tregs and suppress autoimmunity.

Viral Escape Mutant Epitope Maintains TCR Affinity for Antigen yet Curtails CD8 T Cell Responses

T cells have the remarkable ability to recognize antigen with great specificity and in turn mount an appropriate and robust immune response. Critical to this process is the initial T cell antigen recognition and subsequent signal transduction events. This antigen recognition can be modulated at the site of TCR interaction with peptide:major histocompatibility (pMHC) or peptide interaction with the MHC molecule. Both events could have a range of effects on T cell fate. Though responses to antigens that bind sub-optimally to TCR, known as altered peptide ligands (APL), have been studied extensively, the impact of disrupting antigen binding to MHC has been highlighted to a lesser extent and is usually considered to result in complete loss of epitope recognition. Here we present a model of viral evasion from CD8 T cell immuno-surveillance by a lymphocytic choriomeningitis virus (LCMV) escape mutant with an epitope for which TCR affinity for pMHC remains high but where the antigenic peptide binds sub optimally to MHC. Despite high TCR affinity for variant epitope, levels of interferon regulatory factor-4 (IRF4) are not sustained in response to the variant indicating differences in perceived TCR signal strength. The CD8+ T cell response to the variant epitope is characterized by early proliferation and up-regulation of activation markers. Interestingly, this response is not maintained and is characterized by a lack in IL-2 and IFNγ production, increased apoptosis and an abrogated glycolytic response. We show that disrupting the stability of peptide in MHC can effectively disrupt TCR signal strength despite unchanged affinity for TCR and can significantly impact the CD8+ T cell response to a viral escape mutant.

Circulating rotavirus-specific T cells have a poor functional profile

Frequencies of circulating T cells producing IFN-γ, TNF-α, and IL-2, and percentages of T cells proliferating after stimulation with rotavirus (RV), tetanus toxoid, and influenza were evaluated in PBMC derived from healthy adults and children. In addition, the potential anergic state of RV-specific T cells was analyzed by stimulation of PBMC with RV antigen in the presence of three anergy inhibitors (rIL-2, rIL-12, or DGKα-i). The quality and magnitude of RV-T cell responses were significantly lower than those of tetanus toxoid and influenza antigens. RV-CD4 T cell response was enriched in monofunctional IFN-γ(+) cells, while influenza-CD4 and tetanus toxoid-CD4 T cell responses were enriched in multifunctional T cells. Moreover, rIL-2--unlike rIL-12 or DGKα-i--increased the frequencies of RV-CD4 TNF-α(+), CD4 IFN-γ(+), and CD8 IFN-γ(+) cells. Thus, circulating RV-T cells seem to have a relatively poor functional profile that may be partially reversed in vitro by the addition of rIL-2.

Patients with T⁺/low NK⁺ IL-2 receptor γ chain deficiency have differentially-impaired cytokine signaling resulting in severe combined immunodeficiency

X-linked severe combined immunodeficiency (X-SCID) leads to a T(-) NK(-) B(+) immunophenotype and is caused by mutations in the gene encoding the IL-2 receptor γ-chain (IL2RG). IL2RG(R222C) leads to atypical SCID with a severe early onset phenotype despite largely normal NK- and T-cell numbers. To address this discrepancy, we performed a detailed analysis of T, B, and NK cells, including quantitative STAT phosphorylation and functional responses to the cytokines IL-2, IL-4, IL-15, and IL-21 in a patient with the IL2RG(R222C) mutation. Moreover, we identified nine additional unpublished patients with the same mutations, all with a full SCID phenotype, and confirmed selected immunological observations. T-cell development was variably affected, but led to borderline T-cell receptor excision circle (TREC) levels and a normal repertoire. T cells showed moderately reduced proliferation, failing enhancement by IL-2. While NK-cell development was normal, IL-2 enhancement of NK-cell degranulation and IL-15-induced cytokine production were absent. IL-2 or IL-21 failed to enhance B-cell proliferation and plasmablast differentiation. These functional alterations were reflected by a differential impact of IL2RG(R222C) on cytokine signal transduction, with a gradient IL-4<IL-2/IL-15<IL-21. Thus, IL2RG(R222C) causes a consistently severe clinical phenotype that is not predicted by the variable and moderate impairment of T-cell immunity or TREC analysis.

Cytokine therapies in HIV-1 infection: present and future

Since the introduction of highly active antiretroviral therapy (HAART), HIV-related deaths have declined dramatically in the developed world. However, HAART is neither able to eradicate the virus nor are its immunomodulatory effects sufficient to effect complete control of the virus. In addition, the long-term use of HAART is complicated by drug-related toxicities and compliance issues, both of which impact upon the development of viral resistance. The failure of structured treatment interruption strategies in those with chronic HIV-infection combined with the above limitations, has prompted renewed interest in immunotherapy. Cytokines and therapeutic vaccination have been proposed as HAART-adjunctive and HAART-sparing treatments in HIV-infection, and the current and future role of cytokine therapy in this disease will be the subject of this review.

Influence of serum and soluble CD25 (sCD25) on regulatory and effector T-cell function in hepatocellular carcinoma

Our previous studies showed that high levels of soluble CD25 (sCD25) in the serum of patients with hepatocellular carcinoma (HCC) correlated with blunted effector T-cells (Teff) responses, tumour burden and poor survival. Understanding the interactions between Teff, CD4+CD25+ regulatory T cells (Treg) and soluble factors can identify novel therapeutic targets. In this study, we characterize the mechanisms by which HCC serum and sCD25 mediate suppression of Teff and evaluate the effect of sCD25 on the suppression assays with normal healthy control cells (NHC) at a 1:1 Treg to Teff cell ratio to determine whether sCD25 has any impact on Treg suppression. HCC serum and sCD25 suppressed Teff proliferation and downregulated CD25 expression on HCC Teff in a dose-dependent fashion with sCD25 doses above 3000 pg/ml. Treg from HCC and cirrhosis patients suppressed proliferation of target CD4+CD25- Teff in serum-free medium (SFM). HCC Treg showed a higher degree of suppression than cirrhosis-derived Treg. In contrast, Treg from NHC did not suppress target Teff in SFM. However, isolated Treg from all three study subjects (HCC, cirrhosis and NHC) suppressed CD4+CD25- Teff in serum conditions or in the presence of sCD25 in the range 6000-12,000 pg/ml. In conclusion, downregulation of CD25 cell surface expression on Teff is part of the overall suppressive mechanism of sCD25 and HCC serum on Teff responses. The observed sCD25 and HCC serum-mediated suppression is further influenced via novel immune-inhibitory interaction between CD4+CD25+ Treg and sCD25.

In vivo expansion of naive and activated CD4+CD25+FOXP3+ regulatory T cell populations in interleukin-2-treated HIV patients

HIV-1 infection is characterized by a progressive decline in CD4(+) T cells leading to a state of profound immunodeficiency. IL-2 therapy has been shown to improve CD4(+) counts beyond that observed with antiretroviral therapy. Recent phase III trials revealed that despite a sustained increase in CD4(+) counts, IL-2-treated patients did not experience a better clinical outcome [Abrams D, et al. (2009) N Engl J Med 361(16):1548-1559]. To explain these disappointing results, we have studied phenotypic, functional, and molecular characteristics of CD4(+) T cell populations in IL-2-treated patients. We found that the principal effect of long-term IL-2 therapy was the expansion of two distinct CD4(+)CD25(+) T cell populations (CD4(+)CD25(lo)CD127(lo)FOXP3(+) and CD4(+)CD25(hi)CD127(lo)FOXP3(hi)) that shared phenotypic markers of Treg but could be distinguished by the levels of CD25 and FOXP3 expression. IL-2-expanded CD4(+)CD25(+) T cells suppressed proliferation of effector cells in vitro and had gene expression profiles similar to those of natural regulatory CD4(+)CD25(hi)FOXP3(+) T cells (Treg) from healthy donors, an immunosuppressive T cell subset critically important for the maintenance of self-tolerance. We propose that the sustained increase of the peripheral Treg pool in IL-2-treated HIV patients may account for the unexpected clinical observation that patients with the greatest expansion of CD4(+) T cells had a higher relative risk of clinical progression to AIDS.

Plasmodium falciparum-mediated induction of human CD25Foxp3 CD4 T cells is independent of direct TCR stimulation and requires IL-2, IL-10 and TGFbeta

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) regulate disease-associated immunity and excessive inflammatory responses, and numbers of CD4(+)CD25(+)Foxp3(+) Tregs are increased during malaria infection. The mechanisms governing their generation, however, remain to be elucidated. In this study we investigated the role of commonly accepted factors for Foxp3 induction, TCR stimulation and cytokines such as IL-2, TGFbeta and IL-10, in the generation of human CD4(+)CD25(+)Foxp3(+) T cells by the malaria parasite Plasmodium falciparum. Using a co-culture system of malaria-infected red blood cells (iRBCs) and peripheral blood mononuclear cells from healthy individuals, we found that two populations of Foxp3(hi) and Foxp3(int) CD4(+)CD25(hi) T cells with a typical Treg phenotype (CTLA-4(+), CD127(low), CD39(+), ICOS(+), TNFRII(+)) were induced. Pro-inflammatory cytokine production was confined to the Foxp3(int) subset (IFNgamma, IL-4 and IL-17) and inversely correlated with high relative levels of Foxp3(hi) cells, consistent with Foxp3(hi) CD4 T cell-mediated inhibition of parasite-induced effector cytokine T cell responses. Both Foxp3(hi) and Foxp3(int) cells were derived primarily from proliferating CD4(+)CD25(-) T cells with a further significant contribution from CD25(+)Foxp3(+) natural Treg cells to the generation of the Foxp3(hi) subset. Generation of Foxp3(hi), but not Foxp3(int), cells specifically required TGFbeta1 and IL-10. Add-back experiments showed that monocytes expressing increased levels of co-stimulatory molecules were sufficient for iRBC-mediated induction of Foxp3 in CD4 T cells. Foxp3 induction was driven by IL-2 from CD4 T cells stimulated in an MHC class II-dependent manner. However, transwell separation experiments showed that direct contact of monocytes with the cells that acquire Foxp3 expression was not required. This novel TCR-independent and therefore antigen-non specific mechanism for by-stander CD4(+)CD25(hi)Foxp3(+) cell induction is likely to reflect a process also occurring in vivo as a consequence of immune activation during malaria infection, and potentially a range of other infectious diseases.

IL-15 acts as a potent inducer of CD4(+)CD25(hi) cells expressing FOXP3

IL-15 is a member of the gamma chain-dependent cytokines and known to affect innate and CD8(+) adaptive immune responses. Despite a growing interest in the use of IL-15 as an immunotherapeutic agent, the broad spectrum of immunoregulatory functions exerted by IL-15 has not been fully elucidated. Here, we demonstrate that IL-15 increases expression of CD25 and forkhead box transcription factor P3 (FOXP3), a master transcriptional regulator of regulatory T cells, in human peripheral CD4(+)CD25(-) T cells in the absence of antigenic stimulation. Comparisons involving IL-2 and IL-7 revealed that the induction of CD25(hi) and FOXP3 expression was most prominent with IL-15 and IL-2. More modest effects were seen with IL-7. Despite levels of FOXP3 expression comparable to that of conventional regulatory T cells, cytokine-induced CD4(+)CD25(hi)FOXP3(+) cells exerted only weak suppressor activity. Thus, the current study has demonstrated that IL-15 acts as a potent inducer of CD4(+)CD25(hi)FOXP3(+) cells in the periphery, and suggests a potential role for IL-15 in blunting immune activation. This study has provided further insights into the pleiotropic nature of IL-15 beyond the regulation of CD8(+) T cells.

Effects of Intravenous Immunoglobulins on Peripheral Blood Mononuclear Cell Activation in Vitro

The therapeutic effects of intravenous immunoglobulins (IVIGs) on different chronic inflammatory and autoimmune diseases is well appreciated, though clinical studies with high-evidence levels are largely missing. Similar to the broad spectrum of diseases and their underlying etiopathogenic background, the mechanisms of action seem heterogenous and multifold. Several studies addressing in vitro and in vivo effects of IVIG on various immunological parameters have been described with partly contradictory results. In this study immunoglobulins and stabilizers present in commercial IVIG preparations were studied in regard to the in vitro proliferation and cytokine production of peripheral blood mononuclear cells when stimulated with phytohemagglutinin (PHA), interleukin 2, and tetanus toxoid. Whereas the immunoglobulins stimulate the proliferation of PBMCs and decrease IFNgamma secretion, stabilizers of IVIG seem to inhibit the proliferation of PBMCs while increasing the secretion of IFN gamma. These effects have to be taken into account when balancing the impact of IVIG dosage and infusion intervals and relating them to clinical side effects and therapeutic efficacy.

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.

Compatibility of porcine and human interleukin 2: implications for xenotransplantation

BACKGROUND

Xenotransplantation provides a possible solution to the severe shortage of allogeneic organ donors. The pig, which shares many physiological similarities with humans, makes it an optimal species for preclinical experimentation and clinical applications. Interleukin 2 (IL2) is a potent growth factor secreted primarily by T helper lymphocytes and it is vital to the cellular expansion required for a productive immune response and the development and peripheral expansion of CD4+CD25+ regulatory T cells. Therefore, it is essential to understand of the compatibility of IL2 between pigs and humans.

METHODS

We first compared the cDNA and protein sequences and the crystal structures of human and porcine IL2 and IL2 receptors, respectively. The effect of IL2 to induce T cell proliferation was determined by 3H-thymidine incorporation and cell cycle detection.

RESULTS

Porcine IL2 induced very limited proliferation of human lymphocytes while it functioned well on porcine lymphocytes. Human IL2 had remarkably reduced effects on porcine lymphocytes whereas it worked well on human lymphocytes.

CONCLUSION

Our present study showed that the interaction of IL2 and IL2R across species might have defects. Together with the wide physiological functions of IL2, our data indicated that physiological disorders could be caused by the poor function of xenogeneic donor IL2 on host cells in full hematopoietic chimera. Our data suggested an additional potential advantage for the mixed xenogeneic chimeras.

Reduced Secondary Cytokine Induction by BAY 50-4798, a High-Affinity Receptor-Specific Interleukin-2 Analog

Recombinant interleukin-2 (IL-2) (aldesleukin, Proleukin, Chiron, Emeryville, CA) is approved for treatment of cancer patients and under investigation in HIV-infected individuals. However, treatment with aldesleukin is associated with toxicity, which may be due to its elicitation of inflammatory mediators from cells that express the intermediate-affinity IL-2 receptor. BAY 50-4798, a novel IL-2 analog, is a selective agonist for the high-affinity receptor. It induces the proliferation of activated T cells with a potency similar to that of aldesleukin but has reduced activity on cells expressing the intermediate-affinity receptor. In the current study, we compared cytokine responses elicited in peripheral blood mononuclear cell (PBMC) cultures stimulated with BAY 50-4798 or aldesleukin. BAY 50-4798 induced approximately 5-fold lower mean levels of endogenous IL-2 than aldesleukin, and at least 50% lower levels of proinflammatory cytokines, such as tumor necrosis fctor-alpha (TNF-alpha), IL-1beta, IL-6, and interferon-gamma (IFN-gamma). Furthermore, statistically significant reductions in the levels of IL-5, IL-8, IL-10, IL-13, and granulocyte-macrophage colony-stimulating factor (GM-CSF) were observed in response to BAY 50-4798. These findings increase our understanding of the biologic action of BAY 50-4798 and suggest a mechanism by which it may exhibit better safety than aldesleukin in humans.

In vivo expansion of CD4CD45RO-CD25 T cells expressing foxP3 in IL-2-treated HIV-infected patients

Administration of IL-2 to HIV-infected patients leads to expansion of a unique subset of CD4CD45ROCD25 cells. In this study, the origin, clonality, and function of these cells were investigated. Analysis of TCR excision circles revealed that the CD4CD45ROCD25 cells were the product of peripheral expansion but remained polyclonal as determined by TCR repertoire analysis. Phenotypically, these cells were distinct from naturally occurring Tregs; they exhibited intermediate features, between those of memory and naive cells, and had lower susceptibility to apoptosis than CD45ROCD25 or memory T cells. Studies of intracellular cytokine production and proliferation revealed that cytokine-expanded naive CD25 cells had low IL-2 production and required costimulation for proliferation. Despite elevated expression of forkhead transcription factor P3 (foxP3), they exerted only weak suppression compared with CD45ROCD25 cells (Tregs). In summary, in vivo IL-2 administration to HIV-infected patients leads to peripheral expansion of a population of long-lived CD4CD45ROCD25 cells that express high levels of foxP3 but exert weak suppressive function. These CD4CD25 cytokine-expanded naive cells, distinct from antigen-triggered cells and Tregs, play a role in the maintenance of a state of low turnover and sustained expansion of the CD4 T cell pool.

BAY 50-4798, a novel, high-affinity receptor-specific recombinant interleukin-2 analog, induces dose-dependent increases in CD25 expression and proliferation among unstimulated, human peripheral blood mononuclear cells in vitro

Interleukin-2 administration induces CD4 T cell expansion in HIV-infected patients, however, toxicity can limit dosing. BAY 50-4798 is a recombinant IL-2 analog with >1000-fold specificity for the high-affinity IL-2 receptor. The effects of this compound on unstimulated human PBMC were evaluated. PBMC from HIV(-) and HIV(+) donors were cultured in vitro with incremental doses of BAY 50-4798 or aldesleukin. CD25 expression and proliferation were evaluated with flow cytometry. Cytokine levels were measured by ELISA in culture supernatants. BAY 50-4798 induced dose-dependent increases in CD25 expression and proliferation of T cells, NK, and B cells and showed selectivity for CD4 T cells expressing CD25. Induction of pro-inflammatory cytokines was also dose-dependent and was observed at the concentrations of BAY 50-4798 with the highest biologic activity. These data suggest that BAY 50-4798 can induce proliferation of unstimulated T cells but loss of T cell selectivity and induction of pro-inflammatory cytokines occur at concentrations exerting the highest biologic activity.

Long-term effects of intermittent interleukin 2 therapy in patients with HIV infection: characterization of a novel subset of CD4+/CD25+ T cells

The long-term immunologic effects of intermittent interleukin 2 (IL-2) therapy were evaluated in a cross-sectional study by comparing 3 groups: HIV-seronegative volunteers, HIV-infected (HIV+) patients receiving highly active antiretroviral therapy (HAART), and HIV+ patients receiving HAART and intermittent IL-2. Whole-blood immunophenotyping was performed to study expression of the IL-2 receptor chains on T lymphocytes and natural killer cells and to further characterize CD4+/CD25+ T cells. Increased CD25 expression, especially in CD4+ T cells but also in CD8+ T cells, without increases in expression of the β and γ chains of the IL-2 receptor was detected in the IL-2 group. Up to 79% of naive CD4+ T cells (median, 61%) from patients in the IL-2 group expressed CD25, and the number of naive CD4+/CD25+ T cells correlated positively with both the total and naive CD4+ T-cell counts. A discrete population of CD45 double intermediate RA+/RO+CD4+ cells was also preferentially expanded in the IL-2 group, and the number of these cells strongly correlated with the total CD4+ count. Despite increases in CD25 expression, T lymphocytes from patients treated with IL-2 did not have increased expression of early (CD69) or late (CD95) activation markers or evidence of recent proliferation (Ki67). Both CD4+/CD25+ and CD4+/CD25− cells from IL-2–treated HIV+ patients proliferated in response to mitogens, specific antigens, and T-cell-receptor–mediated stimuli. Thus, intermittent administration of IL-2 in HIV+ patients leads to preferential expansion of a unique subset of CD4+ T cells that may represent a critical population in T-cell homeostasis.

Long-term effects of intermittent interleukin 2 therapy in patients with HIV infection: characterization of a novel subset of CD4+/CD25+ T cells

The long-term immunologic effects of intermittent interleukin 2 (IL-2) therapy were evaluated in a cross-sectional study by comparing 3 groups: HIV-seronegative volunteers, HIV-infected (HIV+) patients receiving highly active antiretroviral therapy (HAART), and HIV+ patients receiving HAART and intermittent IL-2. Whole-blood immunophenotyping was performed to study expression of the IL-2 receptor chains on T lymphocytes and natural killer cells and to further characterize CD4+/CD25+ T cells. Increased CD25 expression, especially in CD4+ T cells but also in CD8+ T cells, without increases in expression of the β and γ chains of the IL-2 receptor was detected in the IL-2 group. Up to 79% of naive CD4+ T cells (median, 61%) from patients in the IL-2 group expressed CD25, and the number of naive CD4+/CD25+ T cells correlated positively with both the total and naive CD4+ T-cell counts. A discrete population of CD45 double intermediate RA+/RO+CD4+ cells was also preferentially expanded in the IL-2 group, and the number of these cells strongly correlated with the total CD4+ count. Despite increases in CD25 expression, T lymphocytes from patients treated with IL-2 did not have increased expression of early (CD69) or late (CD95) activation markers or evidence of recent proliferation (Ki67). Both CD4+/CD25+ and CD4+/CD25− cells from IL-2–treated HIV+ patients proliferated in response to mitogens, specific antigens, and T-cell-receptor–mediated stimuli. Thus, intermittent administration of IL-2 in HIV+ patients leads to preferential expansion of a unique subset of CD4+ T cells that may represent a critical population in T-cell homeostasis.

Role of anti-interleukin-2 receptor antibodies in kidney transplantation

From the early 1960s, the mainstay of immunosuppression for kidney transplantation has been corticosteroids. Since then, many new drugs have been developed to maintain the renal allograft. Current maintenance immunosuppression commonly consists of corticosteroids, antiproliferative agents and calcineurin inhibitors (e.g. cyclosporin). More recently, antihuman antibodies, either monoclonal or polyclonal, have been developed to use for induction at the time of transplantation or to treat rejection. With the advances in molecular technology, a new class of antihuman antibodies [the anti-interleukin-2 receptor (IL-2R) antibodies] has emerged that incorporate a murine antigen-binding site on to a human immunoglobulin backbone. Such methodology creates antihuman antibodies with high affinity for the epitope and with prolonged serum antibody half-lives. Interleukin-2 and its receptor are central to lymphocyte activation and are the main targets of calcineurin inhibitors. In addition, the anti-IL-2R antibodies inhibit a key target in immune activation. Daclizumab and basiliximab have been shown to significantly reduce the incidence of acute rejection in kidney transplantation. Since these anti-IL-2R antibodies are well tolerated and since calcineurin inhibitors are intrinsically nephrotoxic, anti-IL-2R antibodies have been used in an attempt to avoid cyclosporin after transplantation. Data from clinical trials seem to indicate that the addition of an anti-IL-2R antibody is not sufficient to warrant complete withdrawal of calcineurin inhibitors for more than a very short period after transplantation. A more promising role for anti-IL-2R antibodies may be in renal transplant recipients with delayed graft function (DGF). Recent data on the use of either low-dose calcineurin inhibitors or sirolimus (rapamycin) in conjunction with the anti-IL-2R antibodies for patients with DGF showed no increased risk of acute rejection. Long-term graft survival with use of these low-dose calcineurin inhibitor protocols has yet to be established.

Prospects for IL-16 in the treatment of AIDS

IL-16 is a multi-functional cytokine that uses CD4 as a receptor to signal diverse biological activities by target cells including T-lymphocytes, monocytes and eosinophils. IL-16 has been shown to repress HIV-1 infection in lymphocytes and monocytic cells and it is active against both laboratory and naturally acquired virus isolates. In lymphocytes, the repressive effect of IL-16 occurs at the level of virus transcription, while it appears to inhibit viral entry in monocytic cells. Clinical studies comparing serum IL-16 levels with the state of HIV-1 disease suggest that this cytokine is a functionally significant endogenous antiviral factor. The antiviral activity of IL-16 may be of therapeutic benefit in HIV/AIDS but its greatest potential is for immune reconstitution. Stimulation of CD4+ T-cells with IL-16 primes cells to respond to IL-2, by upregulating the expression of IL-2 receptor p75 (CD25). Co-treatment of peripheral blood mononuclear cells (PBMC) with IL-16 plus IL-2 (or IL-15) in vitro selectively expands the population of CD4+ T-cells. Clinical trials of recombinant IL-2 have already shown promise in HIV/AIDS. In combination with IL-16, the beneficial effects of IL-2 may be augmented and specifically targeted to CD4+ T-cells. Thus, IL-16 shows considerable promise as an agent for the biological therapy of HIV/AIDS.