IL-18 has pleotropic effects on the activation of T cells during antigen presentation. We investigated the effects of human IL-18 on the engraftment and function of human T cell subsets in xenograft mouse models. IL-18 enhanced the engraftment of human CD8+ effector T cells and promoted the development of xenogeneic graft versus host disease (GVHD). In marked contrast, IL-18 had reciprocal effects on the engraftment of CD4+CD25+Foxp3+ regulatory T cells (Tregs) in the xenografted mice. Adoptive transfer experiments indicated that IL-18 prevented the suppressive effects of Tregs on the development of xenogeneic GVHD. The IL-18 results were robust as they were observed in two different mouse strains. In addition, the effects of IL-18 were systemic as IL-18 promoted engraftment and persistence of human effector T cells and decreased Tregs in peripheral blood, peritoneal cavity, spleen and liver. In vitro experiments indicated that the expression of the IL-18Rα was induced on both CD4 and CD8 effector T cells and Tregs, and that the duration of expression was less sustained on Tregs. These preclinical data suggest that human IL-18 may have use as an adjuvant for immune reconstitution after cytotoxic therapies, and to augment adoptive immunotherapy, donor leukocyte infusions, and vaccine strategies.
Citation: Carroll RG, Carpenito C, Shan X, Danet-Desnoyers G, Liu R, et al. (2008) Distinct Effects of IL-18 on the Engraftment and Function of Human Effector CD8+ T Cells and Regulatory T Cells. PLoS ONE 3(9): e3289. doi:10.1371/journal.pone.0003289
Editor: Derya Unutmaz, New York University School of Medicine, United States of America
Received: July 24, 2008; Accepted: August 27, 2008; Published: September 26, 2008
Copyright: © 2008 Carroll et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was supported by research funding from GlaxoSmithKline to CHJ. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: Z.L.J. is an employee of GlaxoSmithKline; the other authors have no competing financial interests to declare.
Initially isolated from macrophages as a potent interferon-γ (IFN-γ)-inducing factor , , Interleukin-18 (IL-18) is a multifunctional cytokine affecting both innate and adaptive immune responses , . IL-18 is produced as an inactive precursor (pro-IL-18), which is activated by proteolytic cleavage, primarily by caspase-1 , . Pro-IL-18 is produced by multiple cell types, including macrophages , dendritic cells , vascular endothelial cells , and intestinal epithelial cells .
Numerous effector functions have been attributed to IL-18. Perhaps the best characterized of these is IL-18's context-dependent induction of Th1 or Th2 CD4 T cell polarization . In the presence of IL-12, IL-18 drives the Th1 polarization of activated CD4+ T cells. However, in the absence of IL-12 (or in the presence of IL-2 or IL-4), IL-18 promotes IgE expression and Th2 differentiation. More recently, IL-18 has been demonstrated, in synergy with IL-23, to drive TH17 cell polarization , . IL-18 also exerts multiple effects on NK cells, including increased cytoxicity , and in synergy with IL-2, promotion of NK cell expansion and IFNγ production . Given its widespread immune-augmenting functions, it is not surprising that IL-18 has been evaluated in numerous animal models of cancer. For example, IL-18 enhances the efficacy of DNA vaccines directed against prostate-specific antigen  or Fos-related antigen . Additionally, IL-18 augments the efficacy of DC-based vaccines ,  as well as whole-cell tumor vaccines . However, IL-18 has also been reported to enhance tumor progression (reviewed in ). For example, tumor-produced IL-18 induces Fas ligand expression in melanoma cells, possibly resulting in escape from NK cell-mediated immune surveillance . Furthermore, IL-18 has been shown to increase the invasiveness of myeloid leukemia lines .
IL-18 has also been implicated in multiple autoimmune-associated pathologies (reviewed in ). For example, high levels of IL-18 are found in the synovial fluid of rheumatoid arthritis patients , and alleviation of rheumatoid arthritis symptoms is associated with a decrease in IL-18 levels . Paradoxically, given its' proinflammatory properties, IL-18 is well tolerated and safe in humans . In contrast, IL-12 is toxic at doses three orders of magnitude lower .
The rationale for the present study was to determine if IL-18 might present a less toxic alternative to IL-12 as an adjunct for cancer adoptive transfer immunotherapy. In the study described herein, we demonstrate that IL-18 administration resulted in increased engraftment of CD8+ human T cells. Concurrently, IL-18 administration resulted in a decrease in human CD4+CD25+FoxP3+ regulatory T cells (Tregs). Furthermore, we find that IL-18 augmented xenogeneic GVHD, and overrode the suppressive effect of Tregs in vivo. Our findings indicate that by simultaneously affecting both CD8+ T cells and Tregs, IL-18 may alter the set point of an immune response, underscoring the potential utility of IL-18 as an adjuvant in cancer therapy.
All animal experiments were approved by the University of Pennsylvania Institutional Animal Care and Use Committee. NOD/scid/β2microglobulinnull (NOD/scid/β2mnull)  and NOD/scid/IL-2rγnull (NOG)  mice were purchased from the Jackson Laboratory. Animals were bred in the Animal Services Unit of the University of Pennsylvania. The mice were housed under specific pathogen-free conditions in microisolator cages and given unrestricted access to autoclaved food and acidified water. Animals of both sexes were used for experiments at 6–9 weeks of age.
Cells and Animal Injections
Peripheral blood mononuclear cells (PBMCs) were obtained by leukapheresis of healthy volunteer donors by the University of Pennsylvania Human Immunology Core. All specimens were collected under a University Institutional Review Board-approved protocol, and informed consent was obtained from each donor. Cells were injected intraperitoneally into non-irradiated host animals as described in the individual experiments.
Recombinant human IL-18 (SB-485232) and pegylated human IL-18 (GSK-189720) were prepared as previously described at GlaxoSmithKline . Subcutaneous injections of 15 µg/animal were performed daily for the recombinant product and twice weekly for the pegylated product, taking into consideration the increased persistence of the pegylated IL-18.
Animals were sacrificed by CO2 asphyxiation. Peripheral blood was obtained by cardiac puncture, and the spleen, liver, lung, and gut were isolated and portions were fixed in 4% paraformaldehyde. Liver leukocytes were separated by Ficoll density gradient centrifugation and splenocytes were prepared by mechanical disassociation. Cells were retrieved from the peritoneal cavity by PBS lavage.
Mouse tissues were fixed in 4% paraformaldehyde and embedded in paraffin. 5–6 µm sections were cut for immunohistochemical staining. Following deparaffinization and high temperature antigen unmasking procedures, sections were incubated with murine monoclonal antibodies to human CD25 (Clone 4C9 [Vector], 1:100), or Foxp3 (Clone236A/E7 [AbCam], 1:40). Sections were then incubated with biotinylated secondary antibody (goat anti-mouse IgG [Vector]) and signal was localized using 3,3′-diaminobenzidine tetrahydrochloride (DAB, [Vector]) as the chromogen. Hematoxylin was used for counterstaining. Positively stained cells were quantified with Metamorph software (Universal Imaging Corporation) using the Manual Count option. Quantification was performed in a blinded manner. For each organ, at least 8 fields per animal were tabulated.
After euthanasia, peripheral blood, peritoneal cavity washings, spleen, and liver were obtained from euthanized animals. Single cell suspensions were stained with conjugated anti-human lymphocyte surface markers (CD45, clones H130 or 2D1, CD4, clone SK3, CD8, clone SK1 or 3B5, and CD25, clone M-A251, all from BD Pharmingen) and Foxp3 (Clone 206D, Biolegend). Cell populations were analyzed using either LSRII or FACSCalibur flow cytometers (Becton Dickinson) and Flowjo software (Tree Star). Human lymphocytes were initially identified by gating on the human CD45+ population within the live gate, and human lymphocyte subsets were further defined within this population. The absolute number of human cells was determined using TruCount tubes (BD Biosciences) or a Multisizer 3 (Beckman Coulter).
Adoptive Transfer of Ex Vivo Expanded Tregs
Human CD4+CD25high cells were isolated from PBMCs using magnetic beads (Miltenyi Biotech) as described . Gamma-irradiated (100 Gy) K562-based antigen presenting cells modified to express CD64, CD86 and OX40L  were used to stimulate purified populations of CD4+CD25high cells, which were expanded ex vivo in the presence of 300 U/ml IL-2 (Chiron) and 100 ng/ml Rapamycin (Calbiochem) . After one growth cycle (approximately 14–21 days), the cells were harvested and used for injection as described in the text.
In Vitro Suppression Assay
Following harvest of expanded T cells (Tregs and control CD4 cells), varying numbers of Tregs were plated in 100 µl of X-VIVO 15+10% human AB serum in round bottom 96 well plates (Corning Incorporated, Corning, NY). Frozen autologous PBMCs were thawed, CFSE-labeled, and resuspended in culture medium at 1×107/ml. Anti-CD3 beads (Invitrogen) were added at a ratio of 1 bead per cell. 100 µl of PBMC cell suspension (1×106 cells) was added to individual wells in a 96 well plate. CFSE-labeled PBMCs without CD3 beads (and lacking Tregs) were used as negative controls; CFSE-labeled PBMC stimulated with anti-CD3 beads (no Tregs) were used as positive controls. Where indicated, the suppression assay was performed in the presence of 500 ng/ml recombinant human IL-18. The cultures were harvested four days later and stained with APC-conjugated anti-CD8 (BD Pharmingen). Data were acquired on a FACSCalibur flow cytometer using Cell Quest Pro software and analyzed using FlowJo software. Quantitative analysis of Treg suppression capacity was performed by gating on CD8+ CFSE+ cells .
All results were expressed as means±standard deviation. Unless otherwise indicated, the statistical significance of differences between groups was evaluated by two-sample t tests assuming equal variance or the Mann-Whitney rank sum test. Survival data were analyzed by lifetable methods using log rank analysis performed using SysStat (Systat Software, Inc.).
In preliminary experiments we evaluated recombinant human IL-18 at doses from 1 to 100 µg/mouse/day for anti-tumor effects in xenografted mice (data not shown), and 15 µg was chosen as a daily dose based on tolerability and efficacy, and because this dose is less than the equivalent maximum tolerated dose that has been established in monkeys and humans , . The effects of IL-18 were tested on human T cell subsets using two humanized mouse models , . Initially, we determined if IL-18 directly affected the engraftment of human T cells in NOD/scid/β2mnull mice. These mice, in addition to lacking mature B and T cells, have reduced levels of NK cells compared to NOD/scid mice . When NOD/scid/β2mnull mice were injected intraperitoneally with PBMC, human CD45 positive cells were recovered from peripheral blood, liver and spleen. Daily subcutaneous injections of IL-18 caused a substantial increase in the number of human leukocytes recovered from the blood, liver and spleens of the mice (Fig. 1A). However, the leukocyte promoting effect of IL-18 was entirely attributable to increased engraftment of CD8+ T cells, as the number of CD4+ T cells was not increased by IL-18 (Fig. 1B and 1C). No NK cells or B cells were observed at this time point (data not shown).
Figure 1. Human IL-18 Promotes Systemic Increases in Human CD8 T Cell Numbers in NOD/scid/β2mnull mice injected with human PBMCs.
NOD/scid/β2mnull mice were injected intraperitoneally with 5×107 human PBMCs and 24 hours later, a three week course of daily subcutaneous injections of 15 µg recombinant human IL-18 was initiated. At the end of the injection time course, the animals were sacrificed, peripheral blood was collected, and liver and spleen homogenates were prepared. Human cell populations were detected by flow cytometry. Absolute cell numbers in the peripheral blood were determined using Tru-Count tubes; absolute cell numbers from spleen and liver were determined using a Coulter Multisizer 3. The mean±s.d. is shown for (A) human CD45+ cells, (B) human CD4+ cells, and (C) human CD8+ cells. Open bars represent values from mock-treated animals; filled bars represent values from IL-18 treated animals. These data are a representative single experiment of seven different experiments. Asterisks indicate significant differences between mock- and IL-18-treated animals (n = 6 to 10 mice/group; p<0.05).doi:10.1371/journal.pone.0003289.g001
As is shown below, we observed that the IL-18 treated mice developed xenogeneic GVHD more rapidly than mice engrafted with PBMC only. We first considered the hypothesis that the IL-18-mediated increase in human CD8+ cells could account for this. However, an alternative hypothesis was also considered, that decreased engraftment with regulatory T cells could also account for this, because others have shown that regulatory T cell numbers and function can influence the onset and severity of xenogeneic GVHD , . Although IL-18 did not influence the total number of CD4 cells (Fig. 1B), there were significant decreases in regulatory T cells in the IL-18 treated mice, as judged by CD25 and FoxP3 expression (Fig. 2). The percentage and absolute number of CD4+CD25+ cells was decreased in all organs and tissues examined, i.e. blood, spleen, liver, and peritoneal cavity (Fig. 2A and 2B).
Figure 2. Human IL-18 Mediates a Decrease in Tregs in NOD/scid/β2mnull mice Injected with Human PBMCs.
5×107 PBMCs were transferred into NOD/scid /β2Mnull mice. The day following cell injection, a three week course of subcutaneous huIL-18 injections was initiated. Animals in the experiment depicted in panel A received twice-weekly doses of 15 µg pegylated human IL-18, while the animals in the experiments depicted in panel B received daily doses of 15 µg recombinant human IL-18. (A) At the end of IL-18 treatment, cells isolated from the peripheral blood, peritoneal cavity, spleen and liver were stained with antibodies to human CD45, CD4, and CD25 and analyzed by flow cytometry. The mean percentage of CD+CD25+ cells from each tissue is depicted. Filled bars represent values obtained from IL-18-treated animals; open bars represent values obtained from mock-treated animals. (B) Paraffin sections from the spleens of mock- or IL-18-treated animals were reacted with antibodies specific for human CD25 or Foxp3 . Antibody-reactive cells per 400X field were enumerated blindly, and the mean±s.d. depicted. Solid bars depict sections from IL-18-treated animals, while open bars represent sections from mock-treated animals. The experiment in panel A was performed 2 times, and the experiment in panel B was performed 6 times. Asterisks indicate significant differences between mock- and IL-18-treated animals (n = 8/group; p<0.05).doi:10.1371/journal.pone.0003289.g002
It was possible that the distinct effects of IL-18 on human lymphocyte subsets were due to relative efficiencies of engraftment for effector and regulatory subsets in the NOD/scid/β2mnull mice. To test this possibility, PBMCs were transferred into NOD/scid/IL-2rγnull (NOG) mice. This strain is highly permissive to human hematopoietic stem cell engraftment . In NOG mice injected with PMBC, the mice treated with IL-18 had consistently elevated numbers of human CD45+ cells in the peripheral blood, and this increase was entirely accounted for by increased numbers of CD8+ cells (Fig. 3A) as was the case for NOD/scid/β2Mnull mice. The NOG mice also had reciprocal decreases in CD4+CD25+Foxp3+ cells in the blood (Fig. 3B) and all tissues examined (data not shown). The IL-18 mediated decrease in CD4+CD25+FoxP3+ cells was not due to decreased recovery of the cells, as tissue sections examined by immunohistochemistry also documented consistent decreases in cells that stained for Foxp3 (data not shown). Furthermore, as shown in Fig. 3C, the CD8:Treg ratios in the peripheral blood of individual animals were markedly increased by IL-18 treatment.
Figure 3. The Human IL-18-Mediated Decrease in Tregs is Not Restricted to NOD/scid/β2mnull Mice.
NOD/scid/IL-2rγnull (NOG) mice were injected with 5×106 human PBMCs, and 24 hours later, a three week course of daily subcutaneous injections of 15 µg recombinant human IL-18 was initiated. The absolute numbers of human CD8+ cells (A) and CD4+CD25+Foxp3+ cells (B) in the peripheral blood were determined using TruCount tubes. Values from individual mice are depicted. (C) The ratio of CD8 cell number to CD4+25+Foxp3+ cell number for each animal in panels A and B is plotted on a log scale. In panels A and B, asterisks (*) indicate significant differences between mock- and IL-18-treated animals (n = 6 to 8/group; p<0.05). In panel C, asterisks (**) indicate p<0.001.doi:10.1371/journal.pone.0003289.g003
To assess the effects of IL-18 treatment on human T cell differentiation in NOG mice after IL-18 treatment, peripheral blood and spleen were examined by flow cytometry (Fig. 4). There were only minor effects of IL-18 on the fraction of T cells with a central memory (CD27+CD28+) phenotype, and the modest effects were different in blood and spleen. There was only a slight effect of IL-18 on the appearance of T cells with a senescent or effector memory phenotype (CD28+CD57+ or CD27+CD57+).
Figure 4. Effects of Human IL-18 on CD8 T Cell Differentiation in NOG mice.
NOG mice were injected intraperitoneally with 5×106 human PBMCs, and beginning 1 day later, were injected with 15 µg recombinant human IL-18 daily for three weeks. Spleen tissue and peripheral blood were collected and analyzed for the presence of different CD8+ T cell subsets by flow cytometry. Cell populations were initially gated on human CD45 and human CD8. Filled bars represent values mean±s.d. obtained from IL-18-treated animals; open bars represent values obtained from mock-treated animals. The data in this figure represent results from one of two independent experiments. Asterisks indicate significant differences between mock- and IL-18-treated animals (p<0.05).doi:10.1371/journal.pone.0003289.g004
As was mentioned above, we observed that both the NOD/scid/β2Mnull and NOG mouse strains had earlier onset and more severe xenogeneic GVHD after PBMC engraftment and human IL-18 treatment (Fig. 5). Clinical appearance and examination of weight curves revealed that IL-18 treated mice had more significant manifestations of GVHD as indicated by lethargy, hunched posture, generalized erythema, and a progressive reduction in mean weights from pretransplant levels (data not shown). Pathologic examination revealed that the IL-18 treated mice had more severe tissue infiltration and inflammation of the lung, liver and gastrointestinal tracts (Supplemental Fig. S1 and S2).
Figure 5. Human IL-18 Accelerates Xenogeneic GVHD in NOG mice.
5×106 PBMC were transferred into NOG mice on day 0, and IL-18 or PBS injected daily starting on day 1. On the x-axis are days after transfer of cells. On the y-axis is the proportion of recipients surviving (n = 8/group; P<.02).doi:10.1371/journal.pone.0003289.g005
To address the mechanisms for these observations, we used an adoptive transfer model of effector and regulatory T cells that we and others have developed –. PBMCs were subjected to immunoaffinity bead separation to obtain CD4+25high cells and PBMC depleted of CD4+25high cells. The CD4+25high cells at baseline were >70% Foxp3+, and these cells were expanded using K562 cells expressing CD64, CD86, and OX40L in the presence of IL-2 and rapamycin as described . NOG mice were injected with PBMC plus enriched CD4+CD25− effector cells, or with PBMC plus ex vivo-expanded CD4+25+ Tregs. IL-18 treatment in vivo accelerated GVHD lethality in mice engrafted with PBMC plus enriched CD4+CD25− effector cells, or with PBMC plus ex vivo expanded CD4+25+ cells (Fig. 6A and B). In contrast, most mice engrafted with PBMC and ex vivo expanded Tregs had long term survival. The mice were monitored for engraftment of CD8+ T cells by periodic measurements of absolute CD8+ T cell numbers in peripheral blood using the Trucount assay (Fig. 6C–E). Mice engrafted with PBMC and CD4+ effector cells had a progressive increase in the number of circulating CD8+ T cells. Previous studies have shown that human Tregs prevent the expansion of the presumably xenoreactive CD8+ T cells in mice . We found that ex vivo expanded Tregs also prevented the expansion of CD8+ T cells in the mice. However, IL-18 treatment resulted in a striking increase in the numbers of CD8+ T cells in mice engrafted with either PBMCs and CD4+ effectors or with PBMCs and Tregs. In fact, all IL-18-treated animals were sacrificed early due to acute GVHD symptoms (Fig. 6E and data not shown). Thus, in the presence of IL-18, Tregs failed to control CD8+ T cell proliferation. However, the Kaplan-Meier curves show a significant difference between each of the 4 groups, indicating that Tregs have an effect even in the face of IL18 treatment.
Figure 6. Effect of Human IL-18 on Treg-Induced Delay of Xenogeneic GVHD in NOG Mice.
NOG mice were injected with 2×107 Treg-depleted human PBMCs supplemented with either 4 million autologous CD4+CD25− T cells (“CD4 T cells”) or 4 million autologous, ex vivo-expanded CD4+CD25+ cells (“Tregs”). One cohort of each group received daily injections of 15 µg recombinant human IL-18 for three weeks. Human cell engraftment in the peripheral blood was measured 11, 22, and 30 days post-injection. The animals were followed until the onset of xenogeneic GVHD. (A) Experimental overview. (B) Kaplan-Meier Survival Analysis (Log-Rank) of the indicated cohorts of mice. The Holm-Sidak method for multiple comparisons (significance level 0.05) was performed, and showed significant differences between all groups. (C–E) Peripheral blood levels of human CD8+ T cells were measured at Day 11 (C), Day 22 (D), and Day 30 (E) post-injection. Note that all IL-18-treated animals are not represented in panel E due to their death from acute GVHD.doi:10.1371/journal.pone.0003289.g006
Because IL-18 was able to override some of the effects of the Tregs as indicated by the findings of increased CD8+ T cells in mice given adoptively transferred Tregs, we next evaluated the effects of IL-18 on Treg function in vitro. We found that the addition of IL-18 to culture medium did not affect the population doubling rate of Tregs in vitro after anti-CD3/CD28 stimulation, in the presence or absence of IL-2 (data not shown). Furthermore, IL-18 did not affect the suppressive function of ex vivo expanded Tregs (Fig. 7) or the expression of Foxp3 (data not shown). Finally, the upregulation of IL-18Rα did not differ between CD4+25− or CD4+25+ T cells in culture after activation using a variety of stimulation conditions. However, it is notable that the expression of IL-18Rα was not sustained on the regulatory T cells after day 3 in culture, in contrast to bulk CD4 and CD8 T cell subsets (Fig. 8).
Figure 7. Human IL-18 Does Not Prevent Treg Suppressive Function in Vitro.
Purified Tregs were expanded ex vivo for 18 days, and then tested in an in vitro suppression assay. Autologous PBMCs were labeled with CFSE and stimulated using anti-CD3 Ab coated beads and mixed with either no Tregs (top panel) or expanded Tregs at the indicated ratio (Treg:PBMC) in the presence or absence of recombinant human IL-18 (500 ng/ml). Histograms show the expansion of CD8+ cells on day 4 of culture.doi:10.1371/journal.pone.0003289.g007
Figure 8. Rapid Down Regulation of IL18-Rα on Tregs Following Cell Activation.
Purified populations of Tregs, as well as bulk CD4 and CD8 cells, were activated with either αCD3/αCD28 beads, PHA (5 µg/ml), or PHA+recombinant human IL-18 (500 ng/ml). IL-18Rα expression was measured by flow cytometry. IL-18Rα MFI on effector CD4 cells (A), Tregs (B) and effector CD8 cells (C) is plotted before stimulation and 1, 2, and 3 days following stimulation.doi:10.1371/journal.pone.0003289.g008
This study demonstrates that in immune-deficient mice engrafted with human PBMCs, human IL-18 administration exerts opposite effects upon two human cell populations: CD8+ T cell numbers are increased, while CD4+CD25+FoxP3+ Treg cell numbers are markedly decreased. The altered ratio of effector to Treg engraftment was functionally important as judged by the accelerated onset and severity of xenogeneic GVHD in the recipient mice. These effects were unexpected because we are not aware of studies with mouse IL-18 that have revealed differential effects of IL-18 on regulatory and effector T cells , .
Our studies revealed several potential mechanisms for the effects of IL-18. IL-18 can cause the expansion of mouse NK cells , but has not been reported to directly mediate the expansion of T cells. Consistent with this, we were unable to demonstrate a direct effect of IL-18 on the expansion of human effector or regulatory T cells in vitro. However, we found that the expression of the IL-18Rα subunit was more prolonged on effector T cells than Tregs, providing a potential mechanism to explain the reciprocal effects that we observed in vivo on the effects of IL-18 on effector T cells and Tregs. There may be important species specific differences in the biology of IL-18 on human and mouse T cells . In the mouse, IL-18 has a protective effect on CD4(+)-mediated acute GVHD , and blockade of IL-18 accelerates acute GVHD-related mortality in mice . Recent studies in the mouse indicate that IL18 has a role in promoting an IFN-γ dependent positive regulation of memory CD8 T cell proliferation . Recent studies with human cells indicate that the interaction of IL-18 treated NK cells and DCs induces maturation of DCs that subsequently promote Th1 and IFN-γ secretion . Together, the above studies are consistent with our findings, and suggest a mechanism that IL-18 promotes engraftment of CD8 cells in the mice at the expense of regulatory T cells, leading to increased memory CD8 cells and increased xenogeneic GVHD.
A complete mechanistic understanding of the effects mediated by IL-18 is not yet available from the present findings. It is still not clear which T cell subsets are preferentially expanded during IL-18 therapy in the mice, although we found some selective effects on subsets of CD8 T cells in Figure 4. We do not yet know if CD8 T cells need to be activated in order to be regulated by IL-18. Similarly, we do not yet know if CD4 T cells need to be present for the IL-18 effects on CD8 cells. Our data in Figure 6 suggest that the effects on CD8 T cells and Tregs are independent.
IL-18 has been proposed to have a role in a number of inflammatory and autoimmune disorders in mice and man . In mice, IL-18 may have a role in lupus nephritis . In humans, IL-18 over-expression has been reported in rheumatoid arthritis, sarcoidosis, adult-onset Still's disease, vasculitis, lupus, urticaria and histiocytosis , –. Tregs have been reported to be decreased or to have decreased functional activity in a number of autoimmune disorders , and it is possible that an imbalance of Tregs and effector T cells due to differential IL-18 signaling contributes to the loss of tolerance.
Depletion of Tregs in tumor bearing mice enhances the response to immunotherapy . A high ratio of effector CD8 T cells to Tregs in the tumor microenvironment has been shown to be a favorable prognostic feature in patients with ovarian cancer , . An increase in the ratio of CD8+ T effector to regulatory cells in syngeneic mouse tumor models and in humans with cancer correlates with responses to immunotherapies , . Thus, the ability of IL-18 to increase the ratio of effector CD8+ T cells to Tregs may have important implications for therapeutic vaccines and adoptive transfer strategies .
The ability of IL-18 to increase the ratio of effector CD8+ T cells to Tregs may have important implications for therapeutic vaccines and cancer therapy. Depletion of Tregs in tumor bearing mice enhances the response to immunotherapy . A high ratio of effector CD8 T cells to Tregs in the tumor microenvironment has been shown to be a favorable prognostic feature in patients with ovarian cancer , . Furthermore, an increase in the ratio of CD8+ T effector to regulatory cells in syngeneic mouse tumor models and in humans with cancer correlates with responses to immunotherapies , .
Our findings may have important implications for cancer therapy due to the immunosuppressive tumor microenvironment. Cancer patients have increased tumor infiltrating Tregs , and in many cases, CD8+ CTLs from the tumor environment are dysfunctional , . Recently, it has become more widely appreciated that successful immunotherapy requires neutralization of the immunosuppressive features of the tumor microenvironment, in particular Tregs . Thus, by inhibiting Tregs and promoting conventional T cells, human IL-18 may have potential to restore immunocompetence in cancer patients, and thereby augment the effects of cytotoxic and biologic therapies, in order to provoke and maintain an effective anti-tumor immune response. Finally, IL-18 may have potential to augment the anti-tumor effects of donor leukocyte infusions by promoting effector T cells at the expense of regulatory T cell expansion.
Photomicrographs of lung and liver tissue sections taken from animals after xenogeneic GVHD induction. 10 million PBMC were transferred into NOG recipient mice followed by daily injections of IL-18 (15 µg) or PBS. Animals were euthanized on day 20 when recipients of PBMC and IL-18 were moribund. Sections were stained with hematoxylin and eosin. Left: Lung sections taken from PBMC or PBMC+IL-18 recipients, demonstrating severe inflammation and lymphocytic infiltration in IL-18 recipients. Right: Liver sections demonstrating marked periportal lymphocytic infiltrates in IL-18 recipients.
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Photomicrographs of gut tissue sections taken from animals after xenogeneic GVHD induction. Sections were obtained from the animals described above in Suppl. Fig. S1. Left: low magnification. Middle: higher magnification. Right: highest magnification.
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We thank Ella Ofori, Laura Pell and Michelle Kanther for expert technical assistance.
Conceived and designed the experiments: RGC SMA GC JLR CHJ. Performed the experiments: RGC CC XS GDD RL TG SJ. Analyzed the data: RGC CC XS GDD TG JLR ZLJ SJ. Contributed reagents/materials/analysis tools: ZLJ. Wrote the paper: RGC CHJ.
- 1. Okamura H, Tsutsi H, Komatsu T, Yutsudo M, Hakura A, et al. (1995) Cloning of a new cytokine that induces IFN-gamma production by T cells. Nature 378: 88–91.
- 2. Ushio S, Namba M, Okura T, Hattori K, Nukada Y, et al. (1996) Cloning of the cDNA for human IFN-gamma-inducing factor, expression in Escherichia coli, and studies on the biologic activities of the protein. J Immunol 156: 4274–4279.
- 3. Nakanishi K, Yoshimoto T, Tsutsui H, Okamura H (2001) Interleukin-18 regulates both Th1 and Th2 responses. Annu Rev Immunol 19: 423–474.
- 4. Gracie JA, Robertson SE, McInnes IB (2003) Interleukin-18. J Leukoc Biol 73: 213–224.
- 5. Gu Y, Kuida K, Tsutsui H, Ku G, Hsiao K, et al. (1997) Activation of interferon-gamma inducing factor mediated by interleukin-1beta converting enzyme. Science 275: 206–209.
- 6. Ghayur T, Banerjee S, Hugunin M, Butler D, Herzog L, et al. (1997) Caspase-1 processes IFN-gamma-inducing factor and regulates LPS-induced IFN-gamma production. Nature 386: 619–623.
- 7. Stoll S, Jonuleit H, Schmitt E, Muller G, Yamauchi H, et al. (1998) Production of functional IL-18 by different subtypes of murine and human dendritic cells (DC): DC-derived IL-18 enhances IL-12-dependent Th1 development. Eur J Immunol 28: 3231–3239.
- 8. Gerdes N, Sukhova GK, Libby P, Reynolds RS, Young JL, et al. (2002) Expression of interleukin (IL)-18 and functional IL-18 receptor on human vascular endothelial cells, smooth muscle cells, and macrophages: implications for atherogenesis. J Exp Med 195: 245–257.
- 9. Takeuchi M, Nishizaki Y, Sano O, Ohta T, Ikeda M, et al. (1997) Immunohistochemical and immuno-electron-microscopic detection of interferon-gamma-inducing factor (“interleukin-18”) in mouse intestinal epithelial cells. Cell Tissue Res 289: 499–503.
- 10. Mathur AN, Chang HC, Zisoulis DG, Kapur R, Belladonna ML, et al. (2006) T-bet is a critical determinant in the instability of the IL-17-secreting T-helper phenotype. Blood 108: 1595–1601.
- 11. Mathur AN, Chang HC, Zisoulis DG, Stritesky GL, Yu Q, et al. (2007) Stat3 and Stat4 direct development of IL-17-secreting Th cells. J Immunol 178: 4901–4907.
- 12. Tsutsui H, Nakanishi K, Matsui K, Higashino K, Okamura H, et al. (1996) IFN-gamma-inducing factor up-regulates Fas ligand-mediated cytotoxic activity of murine natural killer cell clones. J Immunol 157: 3967–3973.
- 13. Son YI, Dallal RM, Mailliard RB, Egawa S, Jonak ZL, et al. (2001) Interleukin-18 (IL-18) synergizes with IL-2 to enhance cytotoxicity, interferon-gamma production, and expansion of natural killer cells. Cancer Res 61: 884–888.
- 14. Marshall DJ, Rudnick KA, McCarthy SG, Mateo LR, Harris MC, et al. (2006) Interleukin-18 enhances Th1 immunity and tumor protection of a DNA vaccine. Vaccine 24: 244–253.
- 15. Luo Y, Zhou H, Mizutani M, Mizutani N, Liu C, et al. (2005) A DNA vaccine targeting Fos-related antigen 1 enhanced by IL-18 induces long-lived T-cell memory against tumor recurrence. Cancer Res 65: 3419–3427.
- 16. Tatsumi T, Gambotto A, Robbins PD, Storkus WJ (2002) Interleukin 18 gene transfer expands the repertoire of antitumor Th1-type immunity elicited by dendritic cell-based vaccines in association with enhanced therapeutic efficacy. Cancer Res 62: 5853–5858.
- 17. Tanaka F, Hashimoto W, Robbins PD, Lotze MT, Tahara H (2002) Therapeutic and specific antitumor immunity induced by co-administration of immature dendritic cells and adenoviral vector expressing biologically active IL-18. Gene Ther 9: 1480–1486.
- 18. Xu B, Dong CY, Zhang F, Lin YM, Wu KF, et al. (2007) Synergistic antileukemia effect of combinational gene therapy using murine beta-defensin 2 and IL-18 in L1210 murine leukemia model. Gene Ther 14: 1181–1187.
- 19. Vidal-Vanaclocha F, Mendoza L, Telleria N, Salado C, Valcarcel M, et al. (2006) Clinical and experimental approaches to the pathophysiology of interleukin-18 in cancer progression. Cancer Metastasis Rev 25: 417–434.
- 20. Cho D, Song H, Kim YM, Houh D, Hur DY, et al. (2000) Endogenous interleukin-18 modulates immune escape of murine melanoma cells by regulating the expression of Fas ligand and reactive oxygen intermediates. Cancer Res 60: 2703–2709.
- 21. Zhang B, Wu KF, Cao ZY, Rao Q, Ma XT, et al. (2004) IL-18 increases invasiveness of HL-60 myeloid leukemia cells: up-regulation of matrix metalloproteinases-9 (MMP-9) expression. Leuk Res 28: 91–95.
- 22. Boraschi D, Dinarello CA (2006) IL-18 in autoimmunity: review. Eur Cytokine Netw 17: 224–252.
- 23. Gracie JA, Forsey RJ, Chan WL, Gilmour A, Leung BP, et al. (1999) A proinflammatory role for IL-18 in rheumatoid arthritis. J Clin Invest 104: 1393–1401.
- 24. Pittoni V, Bombardieri M, Spinelli FR, Scrivo R, Alessandri C, et al. (2002) Anti-tumour necrosis factor (TNF) alpha treatment of rheumatoid arthritis (infliximab) selectively down regulates the production of interleukin (IL) 18 but not of IL12 and IL13. Ann Rheum Dis 61: 723–725.
- 25. Robertson MJ, Mier JW, Logan T, Atkins M, Koon H, et al. (2006) Clinical and biological effects of recombinant human interleukin-18 administered by intravenous infusion to patients with advanced cancer. Clin Cancer Res 12: 4265–4273.
- 26. Leonard JP, Sherman ML, Fisher GL, Buchanan LJ, Larsen G, et al. (1997) Effects of single-dose interleukin-12 exposure on interleukin-12-associated toxicity and interferon-gamma production. Blood 90: 2541–2548.
- 27. Christianson SW, Greiner DL, Hesselton RA, Leif JH, Wagar EJ, et al. (1997) Enhanced human CD4+ T cell engraftment in beta2-microglobulin-deficient NOD-scid mice. J Immunol 158: 3578–3586.
- 28. Shultz LD, Lyons BL, Burzenski LM, Gott B, Chen X, et al. (2005) Human lymphoid and myeloid cell development in NOD/LtSz-scid IL2R gamma null mice engrafted with mobilized human hemopoietic stem cells. J Immunol 174: 6477–6489.
- 29. Kirkpatrick RB, McDevitt PJ, Matico RE, Nwagwu S, Trulli SH, et al. (2003) A bicistronic expression system for bacterial production of authentic human interleukin-18. Protein Expr Purif 27: 279–292.
- 30. Basu S, Golovina T, Mikheeva T, June CH, Riley JL (2008) Foxp3 Mediated Induction of Pim 2 Allows Human T Regulatory Cells to Preferentially Expand in Rapamycin. J Immunol in press.
- 31. Suhoski MM, Golovina TN, Aqui NA, Tai VC, Varela-Rohena A, et al. (2007) Engineering artificial antigen-presenting cells to express a diverse array of co-stimulatory molecules. Mol Ther 15: 981–988.
- 32. Herzyk DJ, Soos JM, Maier CC, Gore ER, Narayanan PK, et al. (2002) Immunopharmacology of recombinant human interleukin-18 in non-human primates. Cytokine 20: 38–48.
- 33. Trenado A, Sudres M, Tang Q, Maury S, Charlotte F, et al. (2006) Ex vivo-expanded CD4+CD25+ immunoregulatory T cells prevent graft-versus-host-disease by inhibiting activation/differentiation of pathogenic T cells. J Immunol 176: 1266–1273.
- 34. Mutis T, van Rijn RS, Simonetti ER, Aarts-Riemens T, Emmelot ME, et al. (2006) Human regulatory T cells control xenogeneic graft-versus-host disease induced by autologous T cells in RAG2-/-gammac-/- immunodeficient mice. Clin Cancer Res 12: 5520–5525.
- 35. Hoffmann P, Eder R, Kunz-Schughart LA, Andreesen R, Edinger M (2004) Large-scale in vitro expansion of polyclonal human CD4(+)CD25high regulatory T cells. Blood 104: 895–903.
- 36. Hoffmann P, Ermann J, Edinger M, Fathman CG, Strober S (2002) Donor-type CD4(+)CD25(+) regulatory T cells suppress lethal acute graft-versus-host disease after allogeneic bone marrow transplantation. J Exp Med 196: 389–399.
- 37. Godfrey WR, Ge YG, Spoden DJ, Levine BL, June CH, et al. (2004) In vitro expanded human CD4+CD25+ T regulatory cells markedly inhibit allogeneic dendritic cell stimulated MLR cultures. Blood 104: 453–461.
- 38. Taylor PA, Lees CJ, Blazar BR (2002) The infusion of ex vivo activated and expanded CD4(+)CD25(+) immune regulatory cells inhibits graft-versus-host disease lethality. Blood 99: 3493–3499.
- 39. Dinarello CA (1999) IL-18: A TH1-inducing, proinflammatory cytokine and new member of the IL-1 family. J Allergy Clin Immunol 103: 11–24.
- 40. Logan TF, Robertson MJ (2006) Interleukins 18 and 21: biology, mechanisms of action, toxicity, and clinical activity. Curr Oncol Rep 8: 114–119.
- 41. June CH, Blazar BR (2006) Clinical application of expanded CD4+25+ cells. Semin Immunol 18: 78–88.
- 42. Zeiser R, Zambricki EA, Leveson-Gower D, Kambham N, Beilhack A, et al. (2007) Host-derived interleukin-18 differentially impacts regulatory and conventional T cell expansion during acute graft-versus-host disease. Biol Blood Marrow Transplant 13: 1427–1438.
- 43. Reddy P, Teshima T, Kukuruga M, Ordemann R, Liu C, et al. (2001) Interleukin-18 regulates acute graft-versus-host disease by enhancing Fas-mediated donor T cell apoptosis. J Exp Med 194: 1433–1440.
- 44. Iwai Y, Hemmi H, Mizenina O, Kuroda S, Suda K, et al. (2008) An IFN-γ-IL-18 Signaling Loop Accelerates Memory CD8+ T Cell Proliferation. PLoS ONE 3: e2404.
- 45. Agaugue S, Marcenaro E, Ferranti B, Moretta L, Moretta A (2008) Human natural killer cells exposed to IL-2, IL-12, IL-18 or IL-4 differently modulate priming of naive T cells by monocyte-derived dendritic cells. Blood Jun 25 [Epub ahead of print].
- 46. Dinarello CA (2007) Interleukin-18 and the pathogenesis of inflammatory diseases. Semin Nephrol 27: 98–114.
- 47. Calvani N, Tucci M, Richards HB, Tartaglia P, Silvestris F (2005) Th1 cytokines in the pathogenesis of lupus nephritis: the role of IL-18. Autoimmun Rev 4: 542–548.
- 48. Dai SM, Shan ZZ, Xu H, Nishioka K (2007) Cellular targets of interleukin-18 in rheumatoid arthritis. Ann Rheum Dis 66: 1411–1418.
- 49. Greene CM, Meachery G, Taggart CC, Rooney CP, Coakley R, et al. (2000) Role of IL-18 in CD4+ T lymphocyte activation in sarcoidosis. J Immunol 165: 4718–4724.
- 50. Tedeschi A, Lorini M, Suli C, Asero R (2007) Serum interleukin-18 in patients with chronic ordinary urticaria: association with disease activity. Clin Exp Dermatol 32: 568–570.
- 51. Efthimiou P, Kontzias A, Ward CM, Ogden NS (2007) Adult-onset Still's disease: can recent advances in our understanding of its pathogenesis lead to targeted therapy? Nat Clin Pract Rheumatol 3: 328–335.
- 52. Hultgren O, Andersson B, Hahn-Zoric M, Almroth G (2007) Serum concentration of interleukin-18 is up-regulated in patients with ANCA-associated vasculitis. Autoimmunity 40: 529–531.
- 53. Lin YJ, Wan L, Sheu JJ, Huang CM, Lin CW, et al. (2008) A/C polymorphism in the interleukin-18 coding region among Taiwanese systemic lupus erythematosus patients. Lupus 17: 124–127.
- 54. Takada H, Ohga S, Mizuno Y, Suminoe A, Matsuzaki A, et al. (1999) Oversecretion of IL-18 in haemophagocytic lymphohistiocytosis: a novel marker of disease activity. Br J Haematol 106: 182–189.
- 55. Viglietta V, Baecher-Allan C, Weiner HL, Hafler DA (2004) Loss of functional suppression by CD4(+)CD25(+) regulatory T cells in patients with multiple sclerosis. Journal of Experimental Medicine 199: 971–979.
- 56. Sutmuller RP, van Duivenvoorde LM, van Elsas A, Schumacher TN, Wildenberg ME, et al. (2001) Synergism of cytotoxic T lymphocyte-associated antigen 4 blockade and depletion of CD25(+) regulatory T cells in antitumor therapy reveals alternative pathways for suppression of autoreactive cytotoxic T lymphocyte responses. J Exp Med 194: 823–832.
- 57. Zhang L, Conejo-Garcia JR, Katsaros D, Gimotty PA, Massobrio M, et al. (2003) Intratumoral T cells, recurrence, and survival in epithelial ovarian cancer. N Engl J Med 348: 203–213.
- 58. Sato E, Olson SH, Ahn J, Bundy B, Nishikawa H, et al. (2005) Intraepithelial CD8+ tumor-infiltrating lymphocytes and a high CD8+/regulatory T cell ratio are associated with favorable prognosis in ovarian cancer. Proc Natl Acad Sci U S A 102: 18538–18543.
- 59. Hodi FS, Butler M, Oble DA, Seiden MV, Haluska FG, et al. (2008) Immunologic and clinical effects of antibody blockade of cytotoxic T lymphocyte-associated antigen 4 in previously vaccinated cancer patients. Proc Natl Acad Sci U S A 105: 3005–3010.
- 60. Quezada SA, Peggs KS, Curran MA, Allison JP (2006) CTLA4 blockade and GM-CSF combination immunotherapy alters the intratumor balance of effector and regulatory T cells. J Clin Invest 116: 1935–1945.
- 61. June CH (2007) Principles of adoptive T cell cancer therapy. J Clin Invest 117: 1204–1212.
- 62. Woo EY, Chu CS, Goletz TJ, Schlienger K, Coukos G, et al. (2001) Regulatory CD4+CD25+ T cells in tumors from patients with early-stage non small cell lung cancer and late-stage ovarian cancer. Cancer Res 61: 4766–4772.
- 63. Gajewski TF, Meng Y, Blank C, Brown I, Kacha A, et al. (2006) Immune resistance orchestrated by the tumor microenvironment. Immunol Rev 213: 131–145.
- 64. Zou W (2005) Immunosuppressive networks in the tumour environment and their therapeutic relevance. Nat Rev Cancer 5: 263–274.
- 65. Curiel TJ (2007) Tregs and rethinking cancer immunotherapy. J Clin Invest 117: 1167–1174.