Administration Of Interleukin-15 Research Articles

Interleukin-15 modulates the response of cortical neurons to ischemia

ObjectiveStroke is a major cause of death and disability in the United States. Current acute stroke therapy consists of clot-dissolving drugs, catheter-based interventions and physical rehabilitation. To date, there are no therapies that directly enhance neuronal survival after a stroke. Previous work from our lab demonstrated that Interleukin-15 (IL-15) peptide could rescue cardiomyocytes subjected to hypoxia. We sought to extend these findings to cortical neurons since IL-15 has been implicated to have an important role in neuronal homeostasis. MethodsWe have evaluated the effect of IL-15 peptide on primary cortical neurons derived from embryonic rats in vitro under conditions of anoxia and glucose deprivation, and in vivo following middle cerebral artery occlusion. ResultsIL-15 administration rescued neuronal cells subjected to anoxia coupled with glucose deprivation (AGD), as well as with reoxygenation. A hallmark of stroke is the ischemic microenvironment and associated oxidative stress, which results in DNA damage and ER stress, both of which contribute to neuronal cell damage and death. The expression of anoxia, ER stress, and DNA damage factors/markers was evaluated via western blot and correlated with the cellular survival effects of IL-15 in vitro. In addition, IL-15 effect of alleviating ER stress and increasing cell survival was also observed in vivo. InterpretationOur data indicate, for the first time, that administration of the pleiotropic factor IL-15 reduces neuronal cell death during AGD, which correlates with modulation of multiple cellular stress pathways.

Interleukin-15 enhances proinflammatory T-cell responses in patients with MS and EAE.

ObjectiveWe posit that interleukin-15 (IL-15) is a relevant contributor to MS pathobiology as this cytokine is elevated in the CNS and periphery of patients with MS. We aim to investigate (1) the impact of IL-15 on T lymphocytes from patients with MS and (2) the in vivo role of IL-15 using the experimental autoimmune encephalomyelitis (EAE) mouse model.MethodsWe compared the impact of IL-15 on T lymphocytes obtained from untreated patients with MS (relapsing-remitting, secondary progressive, and primary progressive) to cells from age/sex-matched healthy controls (HCs) using multiparametric flow cytometry and in vitro assays. We tested the effects of peripheral IL-15 administration after EAE disease onset in C57BL/6 mice.ResultsIL-15 triggered STAT5 signaling in an elevated proportion of T cells from patients with MS compared with HCs. This cytokine also enhanced the production of key proinflammatory cytokines (interferon γ, granulocyte-macrophage colony-stimulating factor [GM-CSF], IL-17, and tumor necrosis factor) by T cells from both MS and controls, but these effects were more robust for the production of IL-17 and GM-CSF in T-cell subsets from patients with MS. At the peak of EAE disease, the proportion of CD4+ and CD8+ T cells expressing CD122+, the key signaling IL-15 receptor chain, was enriched in the CNS compared with the spleen. Finally, peripheral administration of IL-15 into EAE mice after disease onset significantly aggravated clinical scores and increased the number of inflammatory CNS-infiltrating T cells long term after stopping IL-15 administration.ConclusionsOur results underscore that IL-15 contributes to the amplification of T-cell inflammatory properties after disease onset in both MS and EAE.

Phase 1 Study of Subcutaneous Recombinant Human (rh) Interleukin-15 and Intravenous Alemtuzumab in Patients with Rrelapsed/Refractory T-Cell Lymphoma

BACKGROUND: Interleukin-15 (IL-15) is a member of the 4-α helix bundle family of cytokines. Administration of single-agent IL-15 to patients with cancer produced substantial increases and activation of natural killer (NK) cells and CD8+ T cells, but no clinical responses. Subsequent studies showed that IL-15 enhances the efficacy of anti-tumor monoclonal antibodies that work through antibody-dependent cell cytotoxicity, a process mediated by NK cells. In the MET-1 xenograft mouse model, the combination of IL-15 and the anti-CD52 antibody alemtuzumab led to significantly more durable responses than each agent by itself. Here we report the final results of the phase I trial of IL-15 and alemtuzumab in patients with relapsed and refractory T-cell lymphoma (NCT02689453). METHODS: In this phase I single-center trial IL-15 was given subcutaneously 5 days per week for 2 weeks in a standard 3+3 dose escalation scheme (DL1: 0.5μg/kg, DL2: 1μg/kg, DL3: 2μg/kg), followed by alemtuzumab 30mg intravenously three times weekly for 4 weeks. Primary endpoints were type and frequency of adverse events and the maximum tolerated dose of IL-15. RESULTS: A total of eleven patients (pts) were treated at DL1 (3), DL2 (4) and DL3 (4). Seven pts had acute adult T-cell leukemia (ATL), two had chronic ATL, and two had peripheral T-cell lymphoma not otherwise specified (PTCL-NOS). There were no dose-limiting toxicities through the maximum planned dose of 2μg/kg/day. Two pts both with acute subtype ATL were unable to complete treatment due to rapidly progressive disease early in their treatment course, but there was no evidence tumor simulation or expansion of circulating ATL cell numbers during the period of IL-15 administration Hematologic AEs included lymphopenia (all 11 pts, 7 with grade 3/4), neutropenia (8 pts, 2 with grade 3), anemia (10 pts, 1 with grade 3), and thrombocytopenia (4 pts, 1 with grade 3). The most common non-hematologic AEs were infusion-related reactions experienced by 10 of the 11 pts during alemtuzumab infusion, and urticaria (4, pts, 2 with grade 3, both of whom at MTD). Two pts had incidental findings of a catheter-associated thrombus and pulmonary emboli, necessitating institution of prophylactic anticoagulation for subsequent pts after which no additional thromboembolic events were seen. Infectious adverse events included one case each of CMV reactivation without end-org involvement, HSV reactivation, Zoster, bacterial sinusitis, and cellulitis (in a patient with ATL and skin involvement), all grade 2. There was no evidence of graft versus host disease in two pts with previous allogeneic stem cell transplantation, and there were no serious adverse events attributable to IL-15. Administration of IL-15 resulted in a median 2.1-fold increase (range 1.2-3.4) in absolute lymphocyte count, 2.5-fold (1-5.9) increase in the number of circulating CD8+ T cells, and 7.2-fold (1.1-17.1) increase in NK cells across all dose levels (Figure 1A). At the MTD, the median ALC, CD8+ T cell, and NK cell increases were 2, 2.1, and 15.3-fold respectively. The overall response rate was 45% with 2/11 complete responses (CR) and 3/11 partial responses (PR) (Figure 1B). Notably, all pts with leukemic disease attained CR in the blood (Figure 1C), with varying response in other compartments. A patient with acute ATL had a CR at first restaging but developed central nervous system relapse after four weeks; this remained the only site of disease until the patient's death 8 months later. A patient with PTCL-NOS had a delayed response, with a PR at 3 and CR at 5 months which was ongoing at 12-month follow-up. Two pts with chronic ATL had PRs which lasted 10 and 4 months, and a patient with acute ATL had a PR at first restaging which was ongoing at the end of treatment. In all pts, response was correlated with normalization of serum LDH and soluble CD25. Analysis of peripheral blood mononuclear cells from responders and non-responders using single-cell RNA-seq is under way and will be presented. CONCLUSION: Combination of IL-15 and alemtuzumab was safe at all dose levels administered with no evidence of treatment related disease stimulation. The contribution of IL-15 to the known clinical efficacy of alemtuzumab in relapsed/refractory T-cell malignancies needs to be assessed in a randomized trial. Further evaluation of IL-15 in the post-allogeneic transplant setting, particularly prior to donor lymphocyte infusion, is also planned. Disclosures No relevant conflicts of interest to declare. OffLabel Disclosure: alemtuzumab for T-cell lymphoma

GVHD prevents NK-cell–dependent leukemia and virus-specific innate immunity

AbstractAllogeneic bone marrow transplantation (allo-BMT) is a curative therapy for hematological malignancies, but is associated with significant complications, principally graft-versus-host disease (GVHD) and opportunistic infections. Natural killer (NK) cells mediate important innate immunity that provides a temporal bridge until the reconstruction of adaptive immunity. Here, we show that the development of GVHD after allo-BMT prevented NK-cell reconstitution, particularly within the maturing M1 and M2 NK-cell subsets in association with exaggerated activation, apoptosis, and autophagy. Donor T cells were critical in this process by limiting the availability of interleukin 15 (IL-15), and administration of IL-15/IL-15Rα or immune suppression with rapamycin could restore NK-cell reconstitution. Importantly, the NK-cell defect induced by GVHD resulted in the failure of NK-cell–dependent in vivo cytotoxicity and graft-versus-leukemia effects. Control of cytomegalovirus infection after allo-BMT was also impaired during GVHD. Thus, during GVHD, donor T cells compete with NK cells for IL-15 thereby inducing profound defects in NK-cell reconstitution that compromise both leukemia and pathogen-specific immunity.

Fewer circulating natural killer cells 28 days after double cord blood transplantation predicts inferior survival and IL-15 response

AbstractNatural killer (NK) cell immune reconstitution after double umbilical cord blood transplantation (dUCBT) is rapid and thought to be involved in graft-versus-leukemia (GvL) reactions. To investigate the role of NK cell recovery on clinical outcomes, the absolute number of NK cells at day 28 after dUCBT was determined, and patients with low numbers of NK cells had inferior 2-year disease-free survival (hazard ratio 1.96; P = .04). A detailed developmental and functional analysis of the recovering NK cells was performed to link NK recovery and patient survival. The proportion of NK cells in each developmental stage was similar for patients with low, medium, and high day 28 NK cell numbers. As compared with healthy controls, patients posttransplant showed reduced NK functional responses upon K562 challenge (CD107a, interferon-γ, and tumor necrosis factor-α); however, there were no differences based on day 28 NK cell number. Patients with low NK numbers had 30% less STAT5 phosphorylation in response to exogenous interleukin-15 (IL-15) (P = .04) and decreased Eomes expression (P = .025) compared with patients with high NK numbers. Decreased STAT5 phosphorylation and Eomes expression may be indicative of reduced sensitivity to IL-15 in the low NK cell group. Incubation of patient samples with IL-15 superagonist (ALT803) increased cytotoxicity and cytokine production in all patient groups. Thus, clinical interventions, including administration of IL-15 early after transplantation, may increase NK cell number and function and, in turn, improve transplantation outcomes.

New Interleukin-15 Superagonist (IL-15 SA) Significantly Enhances Graft-Versus-Tumor Activity After Allogeneic Hematopoietic Stem Cell Transplantation

Interleukin-15 (IL-15) is a pleiotropic cytokine, which plays various roles in the innate and adaptive immune system, including the development, activation, homing and survival of immune effector cells. IL-15 has been previously shown to increase CD8+ T and NK cells number and function in normal mice and recipients of stem cell transplantation. However, obstacles remain in using IL-15 therapeutically, specifically its low potency and short in vivo half-life. To overcome this, a new IL-15 mutant (IL-15N72D, J. Immunol, 2009; 183:3598) has been developed, with increased biological activity. Co-expressing IL-15N72D, in conjunction with IL-15RαSu/Fc produced a biologically active and highly potent IL-15 superagonist complex (IL-15SA, also known as ALT-803, Cytokine, 2011; 56:804). We evaluated the effects of IL-15-SA on immune reconstitution and graft-versus-tumor (GVT) activity in recipients of allogeneic hematopoietic stem cell transplantation (HSCT). Lethally irradiated BALB/c recipients were transplanted with T-cell depleted (TCD) bone marrow (BM) cells from B6 mice. IL-15 SA was administered via IP injection in two doses on days +17 and +24 after transplant. Animals were sacrificed at day 28. Administration of IL-15 significantly increased the numbers of CD8+ T cells and NK cells. IL-15 SA also augmented interferon-γ secretion from CD8+ T cells. We observed similar activity in B6CBA→CB6F1 transplant model. Interestingly IL-15 SA upregulates NKG2D and CD107a expression on CD8+ T cells. IL-15 SA administration also specifically increased slow-proliferative CD8+ T-cell proliferation in conjunction with robust IFN-γ and TNF-α secretion in CD8+ T cells in recipients of CFSE (carboxyfluorescein succinimidyl ester) labeled-T-cell infusion, whereas there was no effect on CD4+ T-cell proliferation. We then tested the anti-tumor activity of IL-15 SA in three different tumor models; murine mastocytoma (P815), murine B cell lymphoma (A20) and murine renal cell carcinoma (Renca). We found that IL-15 SA administration enhanced GVT activity against P815 and A20 in recipients of allogeneic HSCT though this activity required a low-dose T cell infusion with HSCT. Interestingly, augmented GVT activity against to Renca after IL-15 SA administration in recipients of allogeneic HSCT did not require T cell infusion.We conclude that IL-15 SA is a very potent cytokine complex for enhancing CD8+ and NK cell reconstitution and function after HSCT, which would be a candidate for post-transplant immunotherapy. Disclosures:Wong:Altor Bioscience: Employment.

Abstract 3506: IL-15 or IL-15/IL-15Rα complexes activates natural killer cells and enhances anti-GD2 monoclonal antibody-mediated antibody-dependent cellular cytotoxicity in vitro and in vivo

Abstract Antibody-dependent cellular cytotoxicity (ADCC) plays an important role in the efficacy of therapeutic anti-cancer monoclonal antibodies (mAbs). Natural killer (NK) cell is the major effector lymphocytes in mediating ADCC through Fc ≤ receptor (FcαR). Indeed, the use of cytokine such as IL2 and GM-CSF to improve the mAbs-mediated ADCC has been studied. Recently, interleukin-15 (IL-15) or IL-15/IL-15 receptor ≤ (IL-15Rβ) complexes have been shown to enhance the cytotoxicity of NK cells but their effects on ADCC mediated by NK cells have not been well-investigated. Here, we evaluated the effects of in vivo stimulation with IL-15 or IL-15/IL-15Rα complexes on the ADCC activity of NK cells mediated by anti-GD2 mAb (14G2a). Fresh DX5+ NK cells from PBS-treated mice were ineffective in inducing 14G2a-coated apoptosis of a relatively NK cell-resistant lymphoma, EL4, with 19.6% and 17.3% for EL4+14G2a compared with EL4, respectively. Upon daily injection of murine IL-15 for 3 or 5 days, a significant and persistent ADCC activity of NK cells (49.0∼50.8%, P < 0.001) was observed from day 3 to 5. In addition, a single administration of IL-15/IL-15Rα complexes on day 0 induced a peak ADCC activity at day 2 (59.8%, P < 0.001) and then slightly decreased at day 3 (37.8%, P < 0.001). Moreover, IL-15 or IL-15/IL-15Rα complexes-induced ADCC activities of NK cells could be eliminated by NKG2D blockade. FACS analysis of murine splenocytes showed that IL-15 or IL-15/IL-15Rα complexes administrations significantly increased the percentage of FcαR-positive NK cells from resting stage 75% to 85% and 92%, respectively, and also slightly enhanced the surface expression of FcαR on NK cells. Furthermore, IL-15/IL-15Rα complexes rapidly induced the expression of CD69 on FcαR-expressed NK cells from 14.5% to 92.6% at 24h, followed by returning to baseline at day 3. However, sustained IL-15 treatment maintained the expression of CD69 on FcαR-positive NK cells but the maximal expression of CD69 was only 52.5% at day 5. These results demonstrated that IL-15 and IL-15/IL-15Rα complexes exhibit different potency or time kinetics on the activation of FcαR-expressing NK cells. Based on these in vitro data, we evaluated the in vivo anti-cancer efficacy of 14G2a in syngeneic EL4 murine model in combination with timed sequential treatments of IL-15 or IL-15/IL-15Rα complexes. Both sustained IL-15 or IL-15/IL-15Rα complexes effectively and equally prolonged the survival of EL4-bearing mice compared with 14G2a only (P <0.001). In conclusion, these data show that IL-15 or IL-15/IL-15Rα complexes may enhance the therapeutic potential of anti-glycan or other therapeutic mAbs currently used clinically for patients with malignancies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3506. doi:1538-7445.AM2012-3506

Simultaneous Blockade of Multiple Immune System Inhibitory Checkpoints Enhances Antitumor Activity Mediated by Interleukin-15 in a Murine Metastatic Colon Carcinoma Model

Interleukin 15 (IL-15) is a promising cytokine for immunotherapy of cancer due to its ability to stimulate the immunity of natural killer, B, and T cells. Its effectiveness, however, may be limited by inhibitory checkpoints and pathways that can attenuate immune responses. Finding strategies to abrogate these negative regulators and enhance the efficacy of IL-15 is a critical challenge. In a preclinical study, we evaluated IL-15 combined with antibodies to block the negative immune regulators cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed death ligand 1 (PD-L1) in a metastatic murine CT26 colon carcinoma model. IL-15 treatment resulted in a significant prolongation of survival in mice with metastatic tumor. Administration of IL-15, however, also increased expression of PD-1 on the surface of CD8(+) T cells including CD8(+)CD44(high) memory phenotype T cells. Moreover, IL-15 also increased the secretion of the immunosuppressive cytokine, IL-10. Combining IL-15 with anti-PD-L1 and anti-CTLA-4 (multiple immune checkpoint blockade) exhibited greater CTL killing and IFNγ secretion. Moreover, this combination resulted in a significant reduction in surface expression of PD-1 on CD8(+) T cells, a decrease in IL-10 secretion, and led to significantly longer survival of tumor-bearing animals compared with mice treated with IL-15 alone or combined singularly with anti-PD-L1 or anti-CTLA-4. Combining the immune stimulatory properties of IL-15 with the simultaneous removal of 2 critical immune system inhibitory checkpoints, we showed enhancement of immune responses leading to increased antitumor activity.

IL-15 in HIV infection: pathogenic or therapeutic potential?

Recent studies have shown that interleukin-15 (IL-15) is produced during acute HIV and SIV infection, and may impact viremia and viral set point. This is further supported by the findings that administration of IL-15 during acute SIV infection dramatically increases viral set point. Although the role of intrinsic IL-15 during chronic infection is much less defined, in vivo administration of IL-15 does not increase viral replication in SIV-infected animals. Recent data also suggest that IL-15 acts, not only on CD8+ T cells and natural killer cells, but also on effector memory CD4+ T cells. IL-15 clearly expands very different CD4+ T cell subpopulations than IL-2 in SIV-infected animals, and may be useful for the restoration of effector memory CD4+ Tcells that are depleted early in HIV and SIV infection. Understanding IL-15's role in SIV infection may help us to design novel therapeutic approaches to HIV infection.

Coadministration of Interleukins 7 and 15 with Bacille Calmette‐Guérin Mounts Enduring T Cell Memory Response againstMycobacterium tuberculosis

The bacille Calmette-Guérin (BCG) vaccine renders protection against tuberculosis in childhood but not in adulthood. This may be due to its failure to induce long-lasting memory T cells. T cell memory is dependent on crucial cytokine signals during the priming phases. Therefore, coadministering the BCG vaccine with cytokines may improve its efficacy. A combination of the cytokines interleukin 7 (IL-7) and interleukin 15 (IL-15) or a combination of the cytokines interleukin 1 (IL-1), interleukin 6 (IL-6), and tumor necrosis factor alpha (TNF-alpha), which are known to influence memory T cell generation, were administered along with BCG to mice. The animals were rested for a period of 240 d before they were challenged with Mycobacterium tuberculosis. Five weeks later, they were killed to study the T cell memory response. Administration of IL-7 and IL-15, but not IL-1, IL-6, and TNF-alpha, with BCG resulted in an improved CD4 and CD8 T cell memory response. Mice injected with BCG supplemented with IL-7 and IL-15 showed enhanced T cell proliferation, T helper 1-type cytokine production, and an increased pool of multifunctional M. tuberculosis-specific memory T cells. Furthermore, there was a statistically significant reduction in the mycobacterial burden in the lungs. Our results indicate that supplementation of the BCG vaccine with IL-7 and IL-15 would substantially improve its efficacy by enhancing the T cell memory response.

In Vivo Administration of Interleukin 15 (IL-15) Safely Promotes the Survival and Proliferation of Adoptively Transferred Antigen-Specific T Cell Clones

The adoptive transfer of antigen-specific CD8+ cytotoxic T lymphocytes (CTL) that have been expanded in vitro is a promising treatment for human malignancies and infections. Interleukin (IL)-2 is frequently administered to support the in vivo survival of transferred T cells, but causes systemic toxicity when given in high doses and promotes the expansion of CD4+ regulatory T cells, which can inhibit antitumor immunity. IL-15, like IL-2, belongs to the four α-helix bundle family of cytokines and shares functional activities with IL-2, including binding to the IL-2 receptor (R) β and γc signaling components and promoting the proliferation of activated T cells in vitro. Despite the similar structure and in vitro function of IL-2 and IL-15, mice deficient in IL-15 or IL-15Rα have a marked reduction in natural killer (NK) cells, NKT cells, and CD8+ memory cells, whereas mice deficient in IL-2 or IL-2Rα have lymphoid hyperplasia and autoimmunity. Because of its critical role in the maintenance of T cell memory, IL-15 is an attractive alternative to IL-2 for augmenting adoptively transferred T cell immunity in humans. We administered IL-15 subcutaneously to nonhuman primates and evaluated toxicity, immunological effects, and peak and trough plasma levels. After establishing a safe regimen of IL-15 dosing, we evaluated the ability of IL-15 to support the survival of adoptively transferred CD8+ effector T cell (TE) clones in vivo.Results: IL-15 was administered subcutaneously to five macaques at doses ranging from 2.5 – 15 μg/kg, given either daily or every 3 days, respectively. The animals were monitored for clinical toxicity and plasma levels. Peripheral blood T cell subsets were enumerated at intervals and evaluated for phenotype and expression of Ki-67, a nuclear antigen expressed by cells undergoing proliferation. Daily administration of high-dose IL-15 resulted in a pronounced increase in the absolute numbers and Ki-67-expression of CD8+ T cells and NK cells, respectively, and preferentially expanded CD8+CD95+CCR7− effector memory (TEM) and CD8+CD95+CCR7+ central memory T cells (TCM). However, daily IL-15 in doses of 5 – 15 μg/kg was associated with accumulation of IL-15 in serum, and caused toxicities that were reversible when IL-15 was discontinued. By contrast, intermittent IL-15 treatment every 3 days was safe and induced only a moderate increase in NK cells, CD8+ TEM and TCM, and enhanced expression of Ki-67 in these cell subsets. This coincided with an increase of the absolute number of cytomegalovirus (CMV)-specific CD8+ T cells in the peripheral blood, but total numbers of CD4+ FoxP3+ T cells were not increased with IL-15. We then examined the ability of IL-15 administered every 3 – 4 days for 3 weeks to support the in vivo persistence of TCM-derived CMV-specific CD8+ TE clones that were marked to express a truncated macaque CD19 surface molecule and transferred to the animals without prior lymphodepletion. As previously reported, CD8+ TE clones derived from TCM precursors survive in vitro in low-doses of IL-15 in the absence of T cell receptor stimulation, persist long term in vivo after transfer and revert to the memory pool (Berger et al, JCI 2008, 118:294). In comparison with animals that received CD8+ T cells alone in which transferred T cells persisted at a stable level of 0.2 – 0.8% of circulating CD8+ cells, the administration of IL-15 after T cell transfer resulted in the establishment of a high-level T cell response (10 – 15% of CD8+ T cells; >100 cells/μL) that persisted for >6 months after IL-15 was discontinued. The CD19+CD8+ TE clones re-acquired a memory T cell phenotype in vivo and expressed bcl-2, bcl-xL and Ki-67 comparable to endogenous CD8+ T cells. The transferred cells were present in large numbers in bone marrow and lymph node samples obtained on day 14 and day 56 after infusion suggesting that they efficiently occupied niches of T cell memory. This data in a large animal model predictive of clinical translation demonstrates that IL-15 can be safely administered, exerts a profound immunologic effect, and dramatically augments the long-term survival of ex vivo expanded antigen-specific CD8+ CTL clones after adoptive transfer without promoting in vivo expansion of CD4+ Foxp3+ regulatory cells. Thus, IL-15 may be a safer and more effective alternative to IL-2 and/or lymphodepletion to support the in vivo persistence of adoptively transferred tumor or virus-specific T cells in human immunotherapy.

107: Murine natural killer dendritic cells (NKDC) expanded in interleukin-15 (IL-15) exhibit potent antitumor responses in vivo

Objective: NKDC are a novel subtype of dendritic cells (DC) with natural killer (NK) cell properties, as they can lyse tumor cells, present antigen to T cells and secrete IFN-γ. IL-15 is known to be an important regulator of NK cell ontogeny. We hypothesized that IL-15 is also essential for the development, survival, and proliferation of NKDC. Methods: Splenocytes from IL-15−/− and wild type B6 mice were analyzed via flow cytometry for NK cells and NKDC. IL-15−/− mice were treated with i.p. administration of exogenous IL-15 (1 μg/day) and splenocytes were analyzed at serial time points.

Interleukin-15 increases hepatic regenerative activity

Interleukin-15 (IL-15) is expressed in many organs. It generally inhibits apoptosis and increases cellular proliferation and differentiation. However, IL-15's roles in liver are unknown. We aimed to determine if IL-15 influences hepatic integrity and regenerative activity. Expression of IL-15 and its receptors was evaluated in several liver injury models, primary hepatocytes, and two liver cell lines. Effects of IL-15 on viability, proliferation, and apoptosis were assessed in cultured liver cells, and also in the livers of healthy mice. IL-15 and its receptors are expressed constitutively in healthy livers, and ligand expression is induced in injured livers. Cultured primary hepatocytes and liver cell lines express IL-15 and its receptors. Administration of IL-15 has minimal effects on cultured liver cells, but significantly up-regulates oval cell accumulation, cyclin mRNA expression, and mature hepatocyte replication in healthy mice. These effects are associated with focal hepatic inflammation and increased expression of TNF-alpha and IFN-gamma, but not with increased cell death or aminotransferase release. IL-15 expression increases during liver injury and IL-15 treatment induces a wound healing-type response in healthy adult mice. These findings suggest that IL-15 may contribute to regenerative activity in damaged liver.

Interleukin-15 stimulates adiponectin secretion by 3T3-L1 adipocytes: Evidence for a skeletal muscle-to-fat signaling pathway

Interleukin-15 (IL-15) is a cytokine which is highly expressed in skeletal muscle tissue, and which has anabolic effects on skeletal muscle protein dynamics both in vivo and in vitro. Additionally, administration of IL-15 to rats and mice inhibits white adipose tissue deposition. To determine if the action of IL-15 on adipose tissue is direct, the capacity of cultured murine 3T3-L1 preadipocytes and adipocytes to respond to IL-15 was examined. IL-15 administration inhibited lipid accumulation in differentiating 3T3-L1 preadipocytes, and stimulated secretion of the adipocyte-specific hormone adiponectin by differentiated 3T3-L1 adipocytes. The latter observation constitutes the first report of a cytokine or growth factor which stimulates adiponectin production. IL-15 mRNA expression by cultured 3T3-L1 adipogenic cells and C2C12 murine skeletal myogenic cells was also examined. Quantitative real-time PCR indicated IL-15 mRNA was expressed by C2C12 skeletal myogenic cells, and was upregulated more than 10-fold in differentiated skeletal myotubes compared to undifferentiated myoblasts. In contrast, 3T3-L1 cells expressed little or no IL-15 mRNA at either the undifferentiated preadipocyte or differentiated adipocyte stages. These findings provide support for the hypothesis that IL-15 functions in a muscle-to-fat endocrine axis which modulates fat:lean body composition and insulin sensitivity.

Interleukin-15 is able to suppress the increased DNA fragmentation associated with muscle wasting in tumour-bearing rats

Administration of interleukin-15 (IL-15) to rats bearing the Yoshida AH-130 ascites hepatoma (a tumour that induces an important cachectic response) resulted in a significant reduction of muscle wasting, both measured as muscle weight and as protein content of different types of skeletal muscle. In addition, the administration of the cytokine completely reversed the increased DNA fragmentation observed in skeletal muscle of tumour-bearing animals. Concerning the mechanism(s) involved in the anti-apoptotic effects of IL-15 on skeletal muscle, the administration of the cytokine resulted in a considerable decrease in both R1 (43%) and R2 (64%) TNF-α receptors (TNFRs), and therefore it may be suggested that IL-15 decreases apoptosis by affecting TNF-α signalling. Formation of NO could be the signalling event associated with the activation of apoptosis in muscle of tumour-bearing rats; indeed, administration of IL-15 decreased the inducible nitric oxide synthase protein levels by 73%, suggesting that NO formation and muscle apoptosis during tumour growth are related. In conclusion, IL-15 seems to be able to reduce/suppress protein loss and apoptosis related to muscle wasting during cancer cachexia in experimental animals.

Overexpression of Interleukin-15 Induces Skeletal Muscle Hypertrophy in Vitro: Implications for Treatment of Muscle Wasting Disorders

Interleukin-15 (IL-15) is a novel anabolic factor for skeletal muscle which inhibits muscle wasting associated with cancer (cachexia) in a rat model. To develop a cell culture system in which the mechanism of the anabolic action of IL-15 on skeletal muscle could be examined, the mouse C2 skeletal myogenic cell line was transduced with a retroviral expression vector for IL-15 and compared to sister cells transduced with a control vector. Overexpression of IL-15 induced fivefold higher levels of sarcomeric myosin heavy chain and α-actin accumulation in differentiated myotubes. Secreted factors from IL-15-overexpressing myogenic cells, but not from control cells, induced increased myofibrillar protein accumulation in cocultured control myotubes. IL-15 overexpression induced a hypertrophic myotube morphology similar to that described for cultured myotubes which overexpressed the well-characterized anabolic factor insulin-like growth factor-I (IGF-I). However, in contrast to IGF-I, the hypertrophic action of IL-15 on skeletal myogenic cells did not involve stimulation of skeletal myoblast proliferation or differentiation. IL-15 induced myotube hypertrophy at both low and high IGF-I concentrations. Furthermore, in contrast to IGF-I, which stimulated only protein synthesis under these culture conditions, IL-15 both stimulated protein synthesis and inhibited protein degradation in cultured skeletal myotubes. These findings indicate that IL-15 action on skeletal myogenic cells is distinct from that of IGF-I. Due to the ability of IGF-I to stimulate cell division and its association with several forms of cancer, controversy exists concerning the advisability of treating cachexia or age-associated muscle wasting with IGF-I. Administration of IL-15 or modulation of the IL-15 signaling pathway may represent an alternative strategy for maintaining skeletal muscle mass under these conditions.

Effect of CD40 ligand and other immunomodulators on Pneumocystis carinii infection in rat model

The corticosteroid-treated animal is well established as an experimental model for the study ofPneumocystis carinii pneumonitis (PCP). Latent or acquired infection with P. carinii in the murine lung progresses to fatal pneumonitis when the host is profoundly immunocompromized. In this study the effects of five immunomodulators; recombinant CD40 ligand (CD40L), bryostatin 1, recombinant FLT3 ligand (FLT3L), recombinant granulocyte colony-stimulating factor (G-CSF) and recombinant interleukin-15 (IL-15) were investigated against PCP in a dexamethasone immunosuppressed Sprague–Dawley rat model. The majority of rats (70%) treated with CD40L at the onset of dexamethasone immunosuppression were protected against PCP. When CD40L was given after 10 days of immunosuppression, only 40% of the rats resolved the infection. However, 95% of the control animals developed PCP. Immunosuppressed rats treated with bryostatin 1, an immune activator had a partial (50%) protection against P. carinii infection. In contrast, daily administration of FLT3L, IL-15 or G-CSF provided no protection against P. carinii infection.