Interleukin 15 as a promising candidate for tumor immunotherapy

Antibody fusions with immunomodulatory proteins for cancer therapy

The potential of immunomodulatory proteins, in particular cytokines, for cancer therapy is well recognized, but hampered by the toxicity associated with their systemic application. In order to address this problem, targeted delivery by antibody fusion proteins has been early proposed and their development intensively pursued over the last decade. Here, factors influencing the selection and modification of cytokines and antibody formats for this approach are being discussed, indicating current developments and translational advances in the field.

Understanding of molecular mechanisms in natural killer cell therapy

Cancer cells and the immune system are closely related and thus influence each other. Although immune cells can suppress cancer cell growth, cancer cells can evade immune cell attack via immune escape mechanisms. Natural killer (NK) cells kill cancer cells by secreting perforins and granzymes. Upon contact with cancer cells, NK cells form immune synapses to deliver the lethal hit. Mature NK cells are differentiated from hematopoietic stem cells in the bone marrow. They move to lymph nodes, where they are activated through interactions with dendritic cells. Interleukin-15 (IL-15) is a key molecule that activates mature NK cells. The adoptive transfer of NK cells to treat incurable cancer is an attractive approach. A certain number of activated NK cells are required for adoptive NK cell therapy. To prepare these NK cells, mature NK cells can be amplified to obtain sufficient numbers of NK cells. Alternatively, NK cells can be differentiated and amplified from hematopoietic stem cells. In addition, the selection of donors is important to achieve maximal efficacy. In this review, we discuss the overall procedures and strategies of NK cell therapy against cancer.

Combined therapy with CTL cells and oncolytic adenovirus expressing IL-15-induced enhanced antitumor activity

Addition of immunoregulation factor to an oncolytic adenovirus being constructed is a developmental step in tumor gene therapy; however, cytokine IL-15 has not been frequently used as a potential cancer therapy agent. Here, we constructed an E2F-1 promoter oncolytic adenovirus based on type 5 adenovirus, which induces viral replication and proliferation in targeted tumor cells. We inserted the IL-15 gene into the E3 region of the model and found that human IL-15 expressing oncolytic adenovirus (Ad-E2F/IL15) shows a more intense antitumor effect than simple oncolytic viruses (Ad-E2F) do. Precisely because IL-15 can activate natural killer (NK) cells, CD8(+)T cells, and other immune cells, in antitumor therapy, Ad-E2F/IL15 was used in combination with cytotoxic T lymphocytes (CTL) to create a virus that can induce IL-15 gene expression while lysing tumors and stimulating the activity and function of adoptive immune cells. The therapeutic effect of this therapy is clearly stronger than that of a single application of oncolytic viruses or CTL, and hence, it could be a potential new tumor therapy.

IL-15 suppresses colitis-associated colon carcinogenesis by inducing antitumor immunity

IL-15 regulates the development, survival, and proliferation of multiple innate and adaptive immune cells and plays a dual role, inducing both tumor cell growth and antitumor immunity. However, the role of IL-15 in inflammation-induced cancer remains unclear. To explore this, we have compared the colon carcinoma burden of Il15^-/- and Il15rα ^-/- mice with wild type (WT) mice after induction of colitis-associated colon carcinogenesis utilizing the AOM/DSS model. Compared to WT mice, Il15^-/- but not Il15rα ^-/- mice showed reduced survival, along with higher tumor incidence, colon weight, and tumor size. This suggests that low affinity IL-15 signaling via the shared IL-2Rβ/γc decreases the risk for developing colitis-associated cancer. CD11c-Il15 mice, in which IL-15 expression is reconstituted in Il15^-/- mice under the control of the CD11c-promoter, showed that selective reconstitution of IL-15 in antigen-presenting cells restored the CD8⁺ T and NK cell compartments, serum levels of IFNγ, G-CSF, IL-10, and CXCL1 and reduced tumor burden. After demonstrating IL-15 expression in human colorectal cancer (CRC) cells in situ, we investigated the role of this cytokine in the modulation of key colonic oncogenic pathways in the tumor. While these pathways were found to be unaltered in the absence of IL-15, tumor transcriptome analysis showed that the loss of IL-15 upregulates key inflammatory mediators associated with colon cancer progression, such as IL-1β, IL-22, IL-23, Cxcl5, and Spp1. These findings provide evidence that IL-15 suppresses colitis-associated colon carcinogenesis through regulation of antitumor cytotoxicity, and modulation of the inflammatory tumor micromilieu.

Functional network pipeline reveals genetic determinants associated with in situ lymphocyte proliferation and survival of cancer patients

The tumor microenvironment is host to a complex network of cytokines that contribute to shaping the intratumoral immune reaction. Chromosomal gains and losses, coupled with expression analysis, of 59 cytokines and receptors and their functional networks were investigated in colorectal cancers. Changes in local expression for 13 cytokines were shown. Metastatic patients exhibited an increased frequency of deletions of cytokines from chromosome 4. Interleukin 15 (IL15) deletion corresponded with decreased IL15 expression, a higher risk of tumor recurrence, and reduced patient survival. Decreased IL15 expression affected the local proliferation of B and T lymphocytes. Patients with proliferating B and T cells at the invasive margin and within the tumor center had significantly prolonged disease-free survival. These results delineate chromosomal instability as a mechanism of modulating local cytokine expression in human tumors and underline the major role of IL15. Our data provide further mechanisms resulting in changes of specific immune cell densities within the tumor, and the importance of local active lymphocyte proliferation for patient survival.

Myxoma virus expressing a fusion protein of interleukin-15 (IL15) and IL15 receptor alpha has enhanced antitumor activity

Myxoma virus, a rabbit poxvirus, can efficiently infect various types of mouse and human cancer cells. It is a strict rabbit-specific pathogen, and is thought to be safe as a therapeutic agent in all non-rabbit hosts tested including mice and humans. Interleukin-15 (IL15) is an immuno-modulatory cytokine with significant potential for stimulating anti-tumor T lymphocytes and NK cells. Co-expression of IL15 with the α subunit of IL15 receptor (IL15Rα) greatly enhances IL15 stability and bioavailability. Therefore, we engineered a new recombinant myxoma virus (vMyx-IL15Rα-tdTr), which expresses an IL15Rα-IL15 fusion protein plus tdTomato red fluorescent reporter protein. Permissive rabbit kidney epithelial (RK-13) cells infected with vMyx-IL15Rα-tdTr expressed and secreted the IL15Rα-IL15 fusion protein. Functional activity was confirmed by demonstrating that the secreted fusion protein stimulated proliferation of cytokine-dependent CTLL-2 cells. Multi-step growth curves showed that murine melanoma (B16-F10 and B16.SIY) cell lines were permissive to vMyx-IL15Rα-tdTr infection. In vivo experiments in RAG1-/- mice showed that subcutaneous B16-F10 tumors treated with vMyx-IL15Rα-tdTr exhibited attenuated tumor growth and a significant survival benefit for the treated group compared to the PBS control and the control viruses (vMyx-IL15-tdTr and vMyx-tdTr). Immunohistological analysis of the subcutaneous tumors showed dramatically increased infiltration of NK cells in vMyx-IL15Rα-tdTr treated tumors compared to the controls. In vivo experiments with immunocompetent C57BL/6 mice revealed a strong infiltrate of both NK cells and CD8+ T cells in response to vMyx-IL15Rα-tdTr, and prolonged survival. We conclude that delivery of IL15Rα-IL15 in a myxoma virus vector stimulates both innate and adaptive components of the immune system.

Positive and negative regulation by NK cells in cancer

Our understanding of NK biology has expanded immensely since the initial discovery of natural killer cells in 1975. New studies have uncovered various levels of immune regulation both on and by unique subsets of NK cells, which go well beyond simple receptor-ligand interactions between NK cells and target cancer cells. Distinct suppressor and effector populations of NK cells have been delineated in both viral and tumor models. Interactions between NK cells and dendritic cells, T cells, and B cells also dramatically alter the overall immune response to cancer. To exploit the diverse functional abilities of NK cell subsets for cancer immunotherapies, it is important to understand NK cell biology and NK regulator mechanisms.

Simultaneous dissection and comparison of IL-2 and IL-15 signaling pathways by global quantitative phosphoproteomics

Common γ-chain family of cytokines (IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21, where IL stands for interleukin) are key regulators of the immune homeostasis that exhibit pleiotropic biological activities and even sometimes redundant roles as a result of the utilization of the same receptor subunit. However, they also exert distinct functions that make each of them to be indispensable. For instance, all family members can act as T-cell growth factors; however, we found that IL-15 but not IL-7 can replace IL-2 to promote and sustain the proliferation of Kit225T cells. In addition to the γ-chain, IL-2 and IL-15 share the β-chain, which creates the paradox of how they can trigger diverse phenotypes despite signaling through the same receptors. To investigate this paradigm, we combined SILAC with enrichment of tyrosine-phosphorylated proteins and peptides followed by mass spectrometric analysis to quantitatively assess the signaling networks triggered downstream IL-2/IL-2R and IL-15/IL-15R. This study confirmed that the transduction pathways initiated by both cytokines are highly similar and revealed that the main signaling branches, JAK/STAT, RAS/MAPK and PI3K/AKT, were nearly equivalently activated in response to both ILs. Despite that, our study revealed that receptor internalization rates differ in IL-2- and IL-15-treated cells indicating a discrete modulation of cytokine signaling. All MS data have been deposited in the ProteomeXchange with identifier PXD001129 (http://proteomecentral.proteomexchange.org/dataset/PXD001129).

Interleukin-15: new kid on the block for antitumor combination therapy

Interleukin (IL)-15 is one of the most promising molecules to be used in antitumor immune therapy, as it is able to stimulate the main killer cells of both the innate and adaptive immune system. Although this cytokine can be used as a stand-alone immunotherapeutic agent, IL-15 will probably be most efficient in combination with other strategies to overcome high tumor burden, immune suppression of the tumor microenvironment and/or the short half-life of IL-15. In this review, we will discuss the combination strategies with IL-15 that have been tested to date in different animal tumor models, which include chemotherapy, other immunostimulatory cytokines, targeted therapy, adoptive cell transfer and gene therapy. In addition, we give an overview of IL-15 combination therapies that are currently tested in clinical studies to treat patients with hematological or advanced solid tumors.

The IL-2 cytokine family in cancer immunotherapy

The use of cytokines from the IL-2 family (also called the common γ chain cytokine family) such as interleukin (IL)-2, IL-7, IL-15, and IL-21 to activate the immune system of cancer patients is one of the most important areas of current cancer immunotherapy research. The infusion of IL-2 at low or high doses for multiple cycles in patients with metastatic melanoma and renal cell carcinoma was the first successful immunotherapy for cancer proving that the immune system could completely eradicate tumor cells under certain conditions. The initial clinical success observed in some IL-2-treated patients encouraged further efforts focused on developing and improving the application of other IL-2 family cytokines (IL-4, IL-7, IL-9, IL-15, and IL-21) that have unique biological effects playing important roles in the development, proliferation, and function of specific subsets of lymphocytes at different stages of differentiation with some overlapping effects with IL-2. IL-7, IL-15, and IL-21, as well as mutant forms or variants of IL-2, are now also being actively pursued in the clinic with some measured early successes. In this review, we summarize the current knowledge on the biology of the IL-2 cytokine family focusing on IL-2, IL-15 and IL-21. We discuss the similarities and differences between the signaling pathways mediated by these cytokines and their immunomodulatory effects on different subsets of immune cells. Current clinical application of IL-2, IL-15 and IL-21 either as single agents or in combination with other biological agents and the limitation and potential drawbacks of these cytokines for cancer immunotherapy are also described. Lastly, we discuss the future direction of research on these cytokines, such as the development of new cytokine mutants and variants for improving cytokine-based immunotherapy through differential binding to specific receptor subunits.

Dysregulation of interferon regulatory factors impairs the expression of immunostimulatory molecules in hepatitis C virus genotype 1-infected hepatocytes

BACKGROUND

IL-7 and IL-15 are produced by hepatocytes and are critical for the expansion and function of CD8 T cells. IL-15 needs to be presented by IL-15Rα for efficient stimulation of CD8 T cells.

METHODS

We analysed the hepatic levels of IL-7, IL-15, IL-15Rα and interferon regulatory factors (IRF) in patients with chronic hepatitis C (CHC) (78% genotype 1) and the role of IRF1 and IRF2 on IL-7 and IL-15Rα expression in Huh7 cells with or without hepatitis C virus (HCV) replicon.

RESULTS

Hepatic expression of both IL-7 and IL-15Rα, but not of IL-15, was reduced in CHC. These patients exhibited decreased hepatic IRF2 messenger RNA levels and diminished IRF2 staining in hepatocyte nuclei. We found that IRF2 controls basal expression of both IL-7 and IL-15Rα in Huh7 cells. IRF2, but not IRF1, is downregulated in cells with HCV genotype 1b replicon and this was accompanied by decreased expression of IL-7 and IL-15Rα, a defect reversed by overexpressing IRF2. Treating Huh7 cells with IFNα plus oncostatin M increased IL-7 and IL-15Rα mRNA more intensely than either cytokine alone. This effect was mediated by strong upregulation of IRF1 triggered by the combined treatment. Induction of IRF1, IL-7 and IL-15Rα by IFNα plus oncostatin M was dampened in replicon cells but the combination was more effective than either cytokine alone.

CONCLUSIONS

HCV genotype 1 infection downregulates IRF2 in hepatocytes attenuating hepatocellular expression of IL-7 and IL-15Rα. Our data reveal a new mechanism by which HCV abrogates specific T-cell responses and point to a novel therapeutic approach to stimulate anti-HCV immunity.

Feasibility of Applying Helper-Dependent Adenoviral Vectors for Cancer Immunotherapy

Adenoviruses (Ads) infect a broad range of tissue types, and derived vectors have been extensively used for gene therapy. Helper-dependent Ad vectors (HDAds), devoid of viral coding sequences, allow for insertion of large or multiple transgenes in a single vector and have been preclinically used for the study of genetic disorders. However, the clinical application of Ad vectors including HDAds for genetic disorders has been hampered by an acute toxic response. This characteristic, while disadvantageous for gene replacement therapy, could be strategically advantageous for the activation of an immune response if HDAds were used as an adjunct treatment in cancer. Cancer treatments including immunotherapy are frequently limited by the inhibitory environment produced by both tumors and their stroma, each of which express numerous inhibitory molecules. Hence, multiple inhibitory mechanisms must be overcome for development of anti-tumor immunity. The large coding capacity of HDAds can accommodate multiple immune modulating transgenes that could produce a combined effect to overcome tumor-derived inhibition and ensure intratumoral effector T-cell proliferation and function. In this review, we discuss the potential advantages of HDAds to cancer immunotherapy based on potent host immune responses to Ads.

Characterization of the CD40L/Oncostatin M/Oncostatin M receptor axis as an antiviral and immunostimulatory system disrupted in chronic HCV infection

BACKGROUND & AIMS

Oncostatin M (OSM) is an inflammatory cytokine which interacts with a heterodimeric receptor formed by gp130 and either OSMRβ or LIFR. Here we have analysed OSM and its receptors in livers with chronic hepatitis C (CHC) and studied the factors that regulate this system.

METHODS

OSM, OSM receptors and OSM-target molecules were studied by immunohistochemistry and/or qPCR analysis in livers from CHC patients and controls. We determined the production of OSM by CD40L-stimulated antigen presenting cells (APC) and its biological effects on HuH7 cells containing HCV replicon (HuH7 Core-3').

RESULTS

OSM was upregulated in livers with CHC and its production was mapped to CD11c+ cells. OSM levels correlated directly with inflammatory activity and CD40L expression. In vitro studies showed that OSM is released by APC upon interaction with activated CD4+ T cells in a CD40L-dependent manner. Culture of HuH7 Core-3' cells with supernatant from CD40L-stimulated APC repressed HCV replication and induced IL-7 and IL-15Rα. These effects were dampened by antibodies blocking OSM or gp130 and by silencing OSMRβ. In CHC livers OSMRβ and LIFR were significantly downregulated and their values correlated with those of OSM-induced molecules. Experiments in HuH7 cells showed that impaired STAT3 signaling and exposure to TGFβ1, two findings in CHC, are factors involved in repressing OSMRβ and LIFR, respectively.

CONCLUSIONS

OSM is a cytokine possessing vigorous antiviral and immunostimulatory properties which is released by APC upon interaction with CD40L present on activated CD4+ T cells. In livers with CHC, OSM is overexpressed but its biological activity appears to be hampered because of downregulation of its receptor subunits.

IL-15 deficient tax mice reveal a role for IL-1α in tumor immunity

IL-15 is recognized as a promising candidate for tumor immunotherapy and has been described as both a promoter of cancer and a promoter of anti-cancer immunity. IL-15 was discovered in cells transformed by HTLV-1, the etiologic agent of adult T cell leukemia/lymphoma (ATL) and the human retrovirus that carries the Tax oncogene. We have developed the TAX-LUC mouse model of ATL in which Tax expression drives both malignant transformation and luciferase expression, enabling non-invasive imaging of tumorigenesis in real time. To identify the role of IL-15 in spontaneous development of lymphoma in vivo, an IL-15^−/− TAX-LUC strain was developed and examined. The absence of IL-15 resulted in aggressive tumor growth and accelerated mortality and demonstrated that IL-15 was not required for Tax-mediated lymphoma but was essential for anti-tumor immunity. Further analysis revealed a unique transcriptional profile in tumor cells that arise in the absence of IL-15 that included a significant increase in the expression of IL-1α and IL-1α-regulated cytokines. Moreover, anti-IL-1α antibodies and an IL-1 receptor antagonist (Anakinra) were used to interrogate the potential of IL-1α targeted therapies in this model. Taken together, these findings identify IL-15 and IL-1α as therapeutic targets in lymphoma.

The activation of TLR7 regulates the expression of VEGF, TIMP1, MMP2, IL-6, and IL-15 in Hela cells

Toll-like receptors (TLRs) play important roles in activation of immunoreaction and tumor development. Toll-like receptor 7 (TLR7), one of the TLRs binding with single-stranded RNA, activates intracellular pathways and stimulates the release of proinflammatory cytokines, chemokines. In this study, we investigated the impact of the TLR7-signaling pathway on the expression of vascular endothelial growth factor (VEGF), matrix metalloproteinase 2 (MMP2), tissue inhibitor of metalloproteinase 1 (TIMP1), interleukin 6 (IL-6), and interleukin 15 (IL-15), which have been testified to refer to the immunomodulating and tumor progression. We confirmed that the TLR7 was expressed by Hela cells, despite the abundance was weak. Gardiquimod, one of the TLR7 ligands, can promote these five genes expression in varying degrees. After stimulating with gardiquimod, the expression of the IL-15V1, 3 increased about 4.5 times on RNA level, the other expression was only up-regulated about 2 times. We also discovered that gardiquimod could activate the MAPK/ERK- and PI3K/AKT-signaling pathways, and the specific inhibitors studies indicate that, the effect of gardiquimod on these genes expression is mainly or partially dependent on the activation of these two signaling pathways. To sum up, the activation of TLR7 signaling pathway may modulate some genes expression in Hela cells and may contribute to the pathogenesis of the cervical cancer.

Dendritic cell-specific delivery of Flt3L by coronavirus vectors secures induction of therapeutic antitumor immunity

Efficacy of antitumor vaccination depends to a large extent on antigen targeting to dendritic cells (DCs). Here, we assessed antitumor immunity induced by attenuated coronavirus vectors which exclusively target DCs in vivo and express either lymphocyte- or DC-activating cytokines in combination with a GFP-tagged model antigen. Tracking of in vivo transduced DCs revealed that vectors encoding for Fms-like tyrosine kinase 3 ligand (Flt3L) exhibited a higher capacity to induce DC maturation compared to vectors delivering IL-2 or IL-15. Moreover, Flt3L vectors more efficiently induced tumor-specific CD8⁺ T cells, expanded the epitope repertoire, and provided both prophylactic and therapeutic tumor immunity. In contrast, IL-2- or IL-15-encoding vectors showed a substantially lower efficacy in CD8⁺ T cell priming and failed to protect the host once tumors had been established. Thus, specific in vivo targeting of DCs with coronavirus vectors in conjunction with appropriate conditioning of the microenvironment through Flt3L represents an efficient strategy for the generation of therapeutic antitumor immunity.

Intricacies for posttranslational tumor-targeted cytokine gene therapy

The safest and most effective cytokine therapies require the favorable accumulation of the cytokine in the tumor environment. While direct treatment into the neoplasm is ideal, systemic tumor-targeted therapies will be more feasible. Electroporation-mediated transfection of cytokine plasmid DNA including a tumor-targeting peptide-encoding sequence is one method for obtaining a tumor-targeted cytokine produced by the tumor-bearing patient's tissues. Here, the impact on efficacy of the location of targeting peptide, choice of targeting peptide, tumor histotype, and cytokine utilization are studied in multiple syngeneic murine tumor models. Within the same tumor model, the location of the targeting peptide could either improve or reduce the antitumor effect of interleukin (IL)12 gene treatments, yet in other tumor models the tumor-targeted IL12 plasmid DNAs were equally effective regardless of the peptide location. Similarly, the same targeting peptide that enhances IL12 therapies in one model fails to improve the effect of either IL15 or PF4 for inhibiting tumor growth in the same model. These interesting and sometimes contrasting results highlight both the efficacy and personalization of tumor-targeted cytokine gene therapies while exposing important aspects of these same therapies which must be considered before progressing into approved treatment options.

Recombinant human IL-15 trans-presentation by B leukemic cells from chronic lymphocytic leukemia induces autologous NK cell proliferation leading to improved anti-CD20 immunotherapy

Recombinant human IL-15 (rhIL-15) is one of the most promising cytokines for antitumor immunotherapy. In physiology IL-15 trans-presentation by accessory cells leads to pleiotropic activities, including activation of immune cells, such as NK cells. NK cells are largely involved in Ab-dependent cellular cytotoxicity mediated by therapeutic mAbs, such as rituximab, in chronic lymphocytic leukemia (CLL). Nevertheless, in CLL, Ab-dependent cellular cytotoxicity is relatively impaired by the low E:T ratio (NK/B leukemic cells). Thus, any strategy leading to an increase in NK cell number and activation status can offer new strategies for CLL treatment. To this end, we evaluated the effect of rhIL-15 on autologous NK cell stimulation in CLL samples. We show that rhIL-15 induces NK cell activation and proliferation, leading to improved B leukemic cell depletion. This phenomenon is significantly increased in the presence of anti-CD20 mAbs. In addition, the greater effect of obinutuzumab versus rituximab suggests a cooperative role between rhIL-15 signaling and CD16 signaling in the induction of NK cell proliferation. Moreover, rhIL-15-induced proliferation of autologous NK cells is strictly dependent on their interaction with B leukemic cells, identified in this study as new accessory cells for rhIL-15 trans-presentation. Thus, rhIL-15 is able to promote NK cell-based activity in Ab immunotherapy of CLL.

Immunotherapeutic applications of IL-15

IL-15 is a member of the IL-2 family of cytokines, which play a fundamental role in innate and adaptive immune responses. IL-15 has pleiotropic immune-enhancing activities, as it stimulates NK, T and NKT cell proliferation, survival and effector functions. In view of these properties, IL-15 is regarded as a good candidate for cancer immunotherapy. This possibility is reinforced by its low toxicity and efficacy in preclinical tumor models. The use of IL-15 to boost the immune response in HIV infection has also been proposed, although further studies are required to establish potential risks and benefits. Clinical trials of IL-15 have been initiated in cancer patients and in HIV vaccination and will elucidate the potential of IL-15-based immunotherapy. The purpose of this review is to provide an update on the potential applications of IL-15 in cancer immunotherapy and HIV infection.

IL15 levels on day 7 after hematopoietic cell transplantation predict chronic GVHD

Chronic GVHD (cGVHD) is an important complication of allogeneic hematopoietic cell transplantation (HCT). As preemptive therapy might be efficacious if administered early post transplant, we set out to determine whether cGVHD can be predicted from the serum level of a biomarker on day 7 or 28. In a discovery cohort of 153 HCT recipients conditioned with BU, fludarabine and rabbit antithymocyte globulin (ATG), we determined serum levels of B-cell-activating factor, vascular endothelial growth factor, soluble TNF-α receptor 1, soluble IL2 receptor α, IL5, IL6, IL7, IL15, γ-glutamyl transpeptidase, cholinesterase, total protein, urea and ATG. Patients with low levels of IL15 (<30.6 ng/L) on day 7 had 2.7-fold higher likelihood of developing significant cGVHD (needing systemic immunosuppressive therapy) than patients with higher IL15 levels (P<0.001). This was validated in a validation cohort of 105 similarly-treated patients; those with low IL15 levels had 3.7-fold higher likelihood of developing significant cGVHD (P=0.001). Low IL15 was not associated with relapse; it trended to be associated with acute GVHD and was associated with low infection rates. In conclusion, low IL15 levels on day 7 are predictive of cGVHD, and thus could be useful in guiding preemptive therapy.

IL-7 and IL-15 instruct the generation of human memory stem T cells from naive precursors

Long-living memory stem T cells (T(SCM)) with the ability to self-renew and the plasticity to differentiate into potent effectors could be valuable weapons in adoptive T-cell therapy against cancer. Nonetheless, procedures to specifically target this T-cell population remain elusive. Here, we show that it is possible to differentiate in vitro, expand, and gene modify in clinically compliant conditions CD8(+) T(SCM) lymphocytes starting from naive precursors. Requirements for the generation of this T-cell subset, described as CD62L(+)CCR7(+)CD45RA(+)CD45R0(+)IL-7Rα(+)CD95(+), are CD3/CD28 engagement and culture with IL-7 and IL-15. Accordingly, T(SCM) accumulates early after hematopoietic stem cell transplantation. The gene expression signature and functional phenotype define this population as a distinct memory T-lymphocyte subset, intermediate between naive and central memory cells. When transplanted in immunodeficient mice, gene-modified naive-derived T(SCM) prove superior to other memory lymphocytes for the ability to expand and differentiate into effectors able to mediate a potent xenogeneic GVHD. Furthermore, gene-modified T(SCM) are the only T-cell subset able to expand and mediate GVHD on serial transplantation, suggesting self-renewal capacity in a clinically relevant setting. These findings provide novel insights into the origin and requirements for T(SCM) generation and pave the way for their clinical rapid exploitation in adoptive cell therapy.

IL-15 augments TCR-induced CD4+ T cell expansion in vitro by inhibiting the suppressive function of CD25 High CD4+ T cells

Due to its critical role in NK cell differentiation and CD8⁺ T cell homeostasis, the importance of IL-15 is more firmly established for cytolytic effectors of the immune system than for CD4⁺ T cells. The increased levels of IL-15 found in several CD4⁺ T cell-driven (auto-) immune diseases prompted us to examine how IL-15 influences murine CD4⁺ T cell responses to low dose TCR-stimulation in vitro. We show that IL-15 exerts growth factor activity on both CD4⁺ and CD8⁺ T cells in a TCR-dependent and Cyclosporin A-sensitive manner. In CD4⁺ T cells, IL-15 augmented initial IL-2-dependent expansion and once IL-15Rα was upregulated, IL-15 sustained the TCR-induced expression of IL-2/15Rβ, supporting proliferation independently of secreted IL-2. Moreover, IL-15 counteracts CD4⁺ T cell suppression by a gradually expanding CD25^HighCD4⁺ T cell subset that expresses Foxp3 and originates from CD4⁺CD25⁺ Tregs. These in vitro data suggest that IL-15 may dramatically strengthen the T cell response to suboptimal TCR-triggering by overcoming an activation threshold set by Treg that might create a risk for autoimmune pathology.

Generation of natural killer cells from hematopoietic stem cells in vitro for immunotherapy

Natural killer (NK) cells are part of the innate immune system and are an alluring option for immunotherapy due to their ability to kill infected cells or cancer cells without prior sensitization. Throughout the past 20 years, different groups have been able to reproduce NK cell development in vitro, and NK cell ontogeny studies have provided the basis for the establishment of protocols to produce NK cells in vitro for immunotherapy. Here, we briefly discuss NK cell development and NK cell immunotherapy approaches. We review the factors needed for NK cell differentiation in vitro, which stem cell sources have been used, published protocols, challenges and future directions for Good Manufacturing Practice protocols.

Age-dependent changes in innate immune phenotype and function in rhesus macaques (Macaca mulatta)

Aged individuals are more susceptible to infections due to a general decline in immune function broadly referred to as immune senescence. While age-related changes in the adaptive immune system are well documented, aging of the innate immune system remains less well understood, particularly in nonhuman primates. A more robust understanding of age-related changes in innate immune function would provide mechanistic insight into the increased susceptibility of the elderly to infection. Rhesus macaques have proved a critical translational model for aging research, and present a unique opportunity to dissect age-dependent modulation of the innate immune system. We examined age-related changes in: (i) innate immune cell frequencies; (ii) expression of pattern recognition receptors (PRRs) and innate signaling molecules; (iii) cytokine responses of monocytes and dendritic cells (DC) following stimulation with PRR agonists; and (iv) plasma cytokine levels in this model. We found marked changes in both the phenotype and function of innate immune cells. This included an age-associated increased frequency of myeloid DC (mDC). Moreover, we found toll-like receptor (TLR) agonists lipopolysaccharide (TLR4), fibroblast stimulating ligand-1 (TLR2/6), and ODN2006 (TLR7/9) induced reduced cytokine responses in aged mDC. Interestingly, with the exception of the monocyte-derived TNFα response to LPS, which increased with age, TNFα, IL-6, and IFNα responses declined with age. We also found that TLR4, TLR5, and innate negative regulator, sterile alpha and TIR motif containing protein (SARM), were all expressed at lower levels in young animals. By contrast, absent in melanoma 2 and retinoic acid-inducible gene I expression was lowest in aged animals. Together, these observations indicate that several parameters of innate immunity are significantly modulated by age and contribute to differential immune function in aged macaques.

Interleukin-12: clinical usage and molecular markers of cancer susceptibility

The last decade has seen the emergence of immunomodulators as therapeutic agents in cancer treatment. Interleukins (ILs) are a category of small cell-signaling molecules that organize communication and interaction between immune cells and therefore they could be used as perfect immunomodulators. IL-12 is a promising candidate for cancer immunotherapy since it plays a major role in development of antitumor immune response. Numerous studies report that IL-12 promotes an effective destruction of cancer cells both in vivo and in vitro. In addition, IL-12 has anti-angiogenic activity and it is able to dramatically decrease tumor-supportive activities of tumor-associated macrophages. The first part of the review is devoted to immunobiology of IL-12. Signaling pathways of IL-12 as well as clinical trials of this cytokine are discussed. The second part of the review is concerned on the inherited variations in IL-12A and IL-12B genes that could modulate cancer susceptibility, and as a consequence, possess predictive, therapeutic, or prognostic significance. It is known that functional single nucleotide polymorphisms (SNPs) in IL-12A and IL-12B genes may dramatically affect on protein expression level, or alter its functions, which may lead to immune disorders, autoimmune diseases, and eventually contribute to cancer occurrence. The list of genetic polymorphisms for further investigations might include the following: IL-12B_+1188A/C (rs3212227), IL-12A_+277G/A (rs568408), IL-12A_-798T/A (rs582054), IL-12A_-504T/G (rs190533), IL-12A_-1148T/C (rs2243123), and IL-12B_+16974 A/C. Perhaps, some of these SNPs may become an attractive target for oncogenomics and possibly could be used in programs of early cancer diagnosis as well as cancer prevention in the nearest future.

Differential effects of denileukin diftitox IL-2 immunotoxin on NK and regulatory T cells in nonhuman primates

Denileukin diftitox (DD), a fusion protein comprising IL-2 and diphtheria toxin, was initially expected to enhance antitumor immunity by selectively eliminating regulatory T cells (Tregs) displaying the high-affinity IL-2R (α-β-γ trimers). Although DD was shown to deplete some Tregs in primates, its effects on NK cells (CD16(+)CD8(+)NKG2A(+)CD3(-)), which constitutively express the intermediate-affinity IL-2R (β-γ dimers) and play a critical role in antitumor immunity, are still unknown. To address this question, cynomolgus monkeys were injected i.v. with two doses of DD (8 or 18 μg/kg). This treatment resulted in a rapid, but short-term, reduction in detectable peripheral blood resting Tregs (CD4(+)CD45RA(+)Foxp3(+)) and a transient increase in the number of activated Tregs (CD4(+)CD45RA(-)Foxp3(high)), followed by their partial depletion (50-60%). In contrast, all NK cells were deleted immediately and durably after DD administration. This difference was not due to a higher binding or internalization of DD by NK cells compared with Tregs. Coadministration of DD with IL-15, which binds to IL-2Rβ-γ, abrogated DD-induced NK cell deletion in vitro and in vivo, whereas it did not affect Treg elimination. Taken together, these results show that DD exerts a potent cytotoxic effect on NK cells, a phenomenon that might impair its antitumoral properties. However, coadministration of IL-15 with DD could alleviate this problem by selectively protecting potentially oncolytic NK cells, while allowing the depletion of immunosuppressive Tregs in cancer patients.

Small cell lung cancer tumour cells induce regulatory T lymphocytes, and patient survival correlates negatively with FOXP3+ cells in tumour infiltrate

Small cell lung cancer (SCLC) kills at least one person every 2 hr in the United Kingdom. Some patients do relatively well but most have rapidly progressive disease. There is no effective treatment and overall 2-year survival is less than 5%. Patients with SCLC have poorly understood local and systemic immune defects and can be immunocompromised. As CD4(+) T lymphocytes coordinate and regulate immunity, a better understanding of interactions between SCLC tumour cells and CD4(+) T cells may lead to effective molecular immunotherapy. We show that some, but not all, SCLC tumour cell lines secrete molecules that induce IL-10 secretion by and de novo differentiation of functional CD4(+)CD25(+)FOXP3(+)CD127(lo)Helios(-) regulatory T (Treg) cells in healthy blood lymphocytes. FOXP3(+) T cells were found in SCLC tumour biopsies, and patients with higher ratios of FOXP3(+) cells in tumour infiltrates have a worse survival rate. The inhibitory effect of SCLC tumour cells was not affected by blocking IL-10 receptor or TGF-β signalling but was partially reversed by blocking IL-15, which is reported to be involved in human Treg cells induction. IL-15 was secreted by SCLC cells that inhibited CD4(+) T-cell proliferation and was present in SCLC biopsy tumour cells. These novel findings demonstrate that SCLC tumour cells can induce CD4(+) T-cell-mediated immunosuppression. This gives a potential mechanism by which SCLC tumour cells may downregulate local and systemic immune responses and contribute to poor patient survival. Our data suggest that IL-15 and Treg cells are potential new therapeutic targets to improve immune response and patient survival in SCLC.

An antibody fusion protein for cancer immunotherapy mimicking IL-15 trans-presentation at the tumor site

Cytokines driving the immune response are powerful tools for cancer immunotherapy, but their application is generally limited by severe systemic toxicity. Targeted approaches by means of antibody-cytokine fusion proteins might enable focus on the cytokine activity to the tumor site, thereby reducing unwanted side effects. Here, we investigated the possibility to improve the efficiency of interleukin (IL)-15 presentation in a targeted approach by the incorporation of an IL-15Rα chain fragment, mimicking physiologic trans-presentation. Therefore, an antibody cytokine fusion protein (scFv_RD_IL-15) composed of an antibody moiety targeting the tumor stromal fibroblast activation protein (FAP), an extended IL-15Rαsushi domain (RD) and IL-15 was generated, exhibiting antibody-mediated specific binding and cytokine activity in soluble and targeted form. Comparative analysis with a corresponding antibody fusion protein devoid of RD (scFv_IL-15) showed for scFv_RD_IL-15 in solution enhanced stimulatory activity on Mo7e (IL-15Rβγ) cells and reduced proliferation response on CTLL-2 (IL-15Rαβγ) cells, while in FAP-targeted, that is, membrane-bound form, comparable proliferation of CTLL-2 (IL-15Rαβγ) cells was obtained. In addition, scFv_RD_IL-15 achieved in its soluble and target-bound form stronger proliferation and cytotoxicity on unstimulated and activated T cells, respectively. Furthermore, in vivo analysis in a lung metastasis tumor mouse model revealed a superior antitumor effect for scFv_RD_IL-15 in comparison with that obtained by an untargeted or RD missing version of IL-15 fusion protein. Thus, tumor-directed trans-presentation of IL-15 in association with RD in form of an antibody fusion protein seems to be a promising approach to further improve the antitumor effect of IL-15.

Interleukin-15 plays a central role in human kidney physiology and cancer through the γc signaling pathway

The ability of Interleukin-15 (IL-15) to activate many immune antitumor mechanisms renders the cytokine a good candidate for the therapy of solid tumors, particularly renal cell carcinoma. Although IL-15 is being currently used in clinical trials, the function of the cytokine on kidney's components has not been extensively studied; we thus investigated the role of IL-15 on normal and tumor renal epithelial cells. Herein, we analyzed the expression and the biological functions of IL-15 in normal renal proximal tubuli (RPTEC) and in their neoplastic counterparts, the renal clear cell carcinomas (RCC). This study shows that RPTEC express a functional heterotrimeric IL-15Rαβγc complex whose stimulation with physiologic concentrations of rhIL-15 is sufficient to inhibit epithelial mesenchymal transition (EMT) commitment preserving E-cadherin expression. Indeed, IL-15 is not only a survival factor for epithelial cells, but it can also preserve the renal epithelial phenotype through the γc-signaling pathway, demonstrating that the cytokine possess a wide range of action in epithelial homeostasis. In contrast, in RCC in vitro and in vivo studies reveal a defect in the expression of γc-receptor and JAK3 associated kinase, which strongly impacts IL-15 signaling. Indeed, in the absence of the γc/JAK3 couple we demonstrate the assembly of an unprecedented functional high affinity IL-15Rαβ heterodimer, that in response to physiologic concentrations of IL-15, triggers an unbalanced signal causing the down-regulation of the tumor suppressor gene E-cadherin, favoring RCC EMT process. Remarkably, the rescue of IL-15/γc-dependent signaling (STAT5), by co-transfecting γc and JAK3 in RCC, inhibits EMT reversion. In conclusion, these data highlight the central role of IL-15 and γc-receptor signaling in renal homeostasis through the control of E-cadherin expression and preservation of epithelial phenotype both in RPTEC (up-regulation) and RCC (down-regulation).

Characterization of recombinant human IL-15 deamidation and its practical elimination through substitution of asparagine 77

PURPOSE

The use of recombinant human interleukin (rhIL)-15 as a potential therapeutic immune modulator and anticancer agent requires pure, stable preparations. However, purified rhIL-15 preparations readily accumulated heterogeneities. We sought to improve rhIL-15 stability through process, formulation, and targeted amino acid changes.

METHODS

The solution state of rhIL-15 versus buffer composition and temperature was studied using SEC and IEX methods. rhIL-15 deamidation was confirmed using RP-HPLC/ESI-MS, enzymatic labeling, and peptide mapping. Deamidation kinetics were measured versus buffer composition and pH using RP-HPLC. Deamidation-resistant rhIL-15 variants (N77A, N77S, N77Q, G78A, and [N71S/N72A/N77A]) were produced in E. coli, then assayed for T-cell culture expansion potency and deamidation resistance.

RESULTS

Adding 20% ethanol to buffers or heating at ≥32°C dispersed rhIL-15 transient pairs, improving purification efficiencies. Asparagine 77 deamidated rapidly at pH 7.4 with activation energy of 22.9 kcal per mol. Deamidation in citrate buffer was 17-fold slower at pH 5.9 than at pH 7.4. Amino acid substitutions at N77 or G78 slowed deamidation ≥23-fold. rhIL-15 variants N77A and (N71S/N72A/N77A) were active in a CTLL-2 proliferation assay equivalent to unsubstituted rhIL-15.

CONCLUSIONS

The N77A and (N71S/N72A/N77A) rhIL-15 variants are resistant to deamidation and remain potent, thus providing enhanced drug substances for clinical evaluation.

Interleukin-15 supports generation of highly potent clinical-grade natural killer cells in long-term cultures for targeting hematological malignancies

OBJECTIVE

Interleukin (IL)-15 is a promising novel cytokine for natural killer (NK) cell activation and survival. We studied the effects of IL-15 compared to IL-2 on NK cells in long-term cultures for clinical translation.

MATERIALS AND METHODS

CD56(+)CD3(-) NK cells were expanded with IL-2 or IL-15 for 2 to 4 weeks within lymphokine-activated killer (LAK) cell cultures (LAK-NK) in serum-enriched AIM V or CellGro Stem Cell Growth Medium (SCGM). Cell growth, viability, and NK cell content were monitored and cytotoxicity assessed in a flow cytometric cytotoxicity assay.

RESULTS

IL-15 (100-1000 U/mL) could replace IL-2 (1000 U/mL) in AIM V cultures to achieve efficient LAK cell expansion. However, IL-15-stimulated LAK cells exceeded cytotoxicity of IL-2-stimulated LAK cells against K562, notably at later culture points. In the powerful CellGro SCGM, LAK cells expanded over 28 days an average of 905-fold ± 320-fold standard error of the mean (SEM) for IL-2 (500 U/mL) and 484-fold ± 98-fold SEM for IL-15 (500 U/mL), and NK cells within such LAK cultures expanded an average of 2320-fold ± 975-fold SEM for IL-2 and 1084-fold ± 309-fold SEM for IL-15. Importantly, such IL-15-activated LAK-NK cells retained enhanced cytotoxicity at later culture points against K562 as well. IL-15-stimulated effectors were also highly cytotoxic against hematological targets MOLT-4 and KU812 and nontoxic against autologous nonmalignant cells. Interestingly, IL-15-LAK-NK cells showed overall significant upregulation of the main activating and inhibitory NK cell receptors after long-term cytokine stimulation.

CONCLUSIONS

Our results demonstrate the potential for IL-15 to support large-scale expansion of clinical-grade LAK-NK effectors, which could retain enhanced longer-term potency and preserve activation receptors in therapy of hematological malignancies. Protocols are readily clinically translatable.