Interleukin-2 and interleukin-15: immunotherapy for cancer

Global transcriptional analysis delineates the differential inflammatory response interleukin-15 elicits from cultured human T cells

OBJECTIVE

Interleukin 15 (IL)-15 controls proliferation and survival of T cells, but its effects and the underlying cellular regulation are not well understood. Previous studies have focused on its effects on short-term T-cell cultures. In view of the potential problems associated with using IL-2 alone in adoptive immunotherapy protocols, we investigated the impact of IL-15 on T-cell cultures and the global transcriptional effects it elicits in such cultures.

MATERIALS AND METHODS

DNA microarrays and flow cytometry were used to examine the differential effect of 20 ng/mL IL-15 on primary serum-free T-cell cultures activated and cultured in the presence of IL-2. Quantitative reverse transcriptase polymerase chain reaction confirmed select microarray data.

RESULTS

IL-15 significantly increased ex vivo expansion of primary human T cells over the entire 11-day expansions without affecting viability. The 1133 genes were consistently differentially expressed among three donor samples. Ontological analysis demonstrated that IL-15 increases expression of genes involved in inflammatory response (e.g., tumor necrosis factor [TNF]-alpha, Oncostatin M, CD40L, and CD33) and apoptosis (e.g., TNF-related apoptosis-inducing ligand). IL-15 also induced expression of four suppressors of cytokine signaling (SOCS) family genes (SOCS1-3, cytokine-inducible SH2-containing protein), which are classical negative regulators of cytokine signaling. IL-15 strongly suppressed the expression of inhibitory natural killer cell receptor genes, including three C-type lectins (KLRB1, KLRC1, and KLRD1), as well as IL-7Ra and Granzyme H. Finally, IL-15 induced differential expression of TNF receptor superfamily members (CD27 and CD30).

CONCLUSION

These findings suggest that exogenous IL-15 may have a potential role in adoptive immunotherapy by both enhancing proliferation and modulating functionality during ex vivo T-cell expansion.

New cytokine targets in inflammatory rheumatic diseases

With the advent of biological therapies, considerable advances have been achieved in the treatment of inflammatory arthritis. These have arisen primarily from studies elucidating mechanisms of pathophysiology and are best exemplified in the wide use of tumour necrosis factor (TNF) blockade in several rheumatic diseases. The identification of additional pro-inflammatory factors in rheumatic diseases and an understanding of their effector function, now offers major possibilities for the generation of novel therapeutics. To address unmet clinical need, such interventions will ideally fulfil several of the following criteria: (1) control of inflammation, (2) modulation of underlying immune dysfunction - promoting the re-establishment of immune tolerance, (3) protection of targeted tissues such as bone and cartilage - this should encompass promoting healing of previously damaged tissues, (4) preservation of host immune capability - to avoid profound immune suppression and (5) amelioration of co-morbidity associated with underlying inflammatory arthritis. This short review will consider those novel cytokine activities that represent optimal utility as therapeutic targets. Since we wish to reflect the current predominant research effort, we will focus primarily on rheumatoid arthritis (RA) based studies.

Molecular analysis of the methylprednisolone-mediated inhibition of NK-cell function: evidence for different susceptibility of IL-2– versus IL-15–activated NK cells

Steroids have been shown to inhibit the function of fresh or IL-2–activated natural killer (NK) cells. Since IL-15 plays a key role in NK-cell development and function, we comparatively analyzed the effects of methylprednisolone on IL-2– or IL-15–cultured NK cells. Methylprednisolone inhibited the surface expression of the major activating receptors NKp30 and NKp44 in both conditions, whereas NK-cell proliferation and survival were sharply impaired only in IL-2–cultured NK cells. Accordingly, methylprednisolone inhibited Tyr phosphorylation of STAT1, STAT3, and STAT5 in IL-2–cultured NK cells but only marginally in IL-15–cultured NK cells, whereas JAK3 was inhibited under both conditions. Also, the NK cytotoxicity was similarly impaired in IL-2– or IL-15–cultured NK cells. This effect strictly correlated with the inhibition of ERK1/2 Tyr phosphorylation, perforin release, and cytotoxicity in a redirected killing assay against the FcRγ+ P815 target cells upon cross-linking of NKp46, NKG2D, or 2B4 receptors. In contrast, in the case of CD16, inhibition of ERK1/2 Tyr phosphorylation, perforin release, and cytotoxicity were not impaired. Our study suggests a different ability of IL-15–cultured NK cells to survive to steroid treatment, thus offering interesting clues for a correct NK-cell cytokine conditioning in adoptive immunotherapy.

Familial NK cell deficiency associated with impaired IL-2- and IL-15-dependent survival of lymphocytes

We previously reported the clinical phenotype of two siblings with a novel inherited developmental and immunodeficiency syndrome consisting of severe intrauterine growth retardation and the impaired development of specific lymphoid lineages, including transient CD8 alphabeta T lymphopenia and a persistent lack of blood NK cells. We describe here the elucidation of a plausible underlying pathogenic mechanism, with a cellular phenotype of impaired survival of both fresh and herpesvirus saimiri-transformed T cells, in the surviving child. Clearly, NK cells could not be studied. However, peripheral blood T lymphocytes displayed excessive apoptosis ex vivo. Moreover, the survival rates of CD4 and CD8 alphabeta T cell blasts generated in vitro, and herpesvirus saimiri-transformed T cells cultured in vitro, were low, but not nil, following treatment with IL-2 and IL-15. In contrast, Fas-mediated activation-induced cell death was not enhanced, indicating a selective excess of cytokine deprivation-mediated apoptosis. In keeping with the known roles of IL-2 and IL-15 in the development of NK and CD8 T cells in the mouse model, these data suggest that an impaired, but not abolished, survival response to IL-2 and IL-15 accounts for the persistent lack of NK cells and the transient CD8 alphabeta T lymphopenia documented in vivo. Impaired cytokine-mediated lymphocyte survival is likely to be the pathogenic mechanism underlying this novel form of inherited and selective NK deficiency in humans.

Potential therapeutic role of natural killer cells in cancer

Cancer immunotherapy is a growing field that aims at restoring and enhancing immune function to combat oncogenic conditions. One target of this field is natural killer (NK) cells. Part of innate immunity, NK cells are able to kill tumor cells without previous priming. Results from stem cell transplants containing alloreactive donor NK cells and in vitro work have evidenced a great antitumor potential. In addition, NK cells are likely to interact with dendritic cells, potent antigen-presenting cells, thus forming a bridge between innate and adaptive immunity. This review aims to provide an overview of NK cells with particular emphasis on properties that can and are being targeted in order to potentiate the antitumor activity of these cells.

Docking of human interleukin-15 to its specific receptor alpha chain: correlation between molecular modeling and mutagenesis experimental data

A structural model of the sushi domain of IL-15Ralpha was first obtained by homology modeling to study its interactions with IL-15 by means of molecular modeling, peptide scanning, and site-directed mutagenesis. From these experimental data, a putative interacting surface of IL-15Ralpha with a previously published IL-15 model was inferred: Leu25, Leu44, and Glu46 of IL-15 and Arg35 of IL-15Ralpha were found to be key interfacial residues and were subsequently used as filters for the construction of docking solutions. Human IL-15/IL-15Ralpha complexes were constructed in two stages, with a preliminary docking procedure, treating the two partners as rigid bodies and using these filters. In this first stage, two classes of docking solutions were characterized. From a topological point of view, each solution could be derived from the other by reverse orientation of one partner in relation to the other. In a second stage, several further energy refinements clearly favored one solution. Moreover, this unique docking solution was confirmed by molecular modeling of IL-15 mutants previously built and tested in our laboratory. Finally, this complex model, which is a useful tool to study the IL-15/IL-15Ralpha interface, was topologically compared to IL-2/IL-2Ralpha complexes (previous model in the literature and recent crystal structure).

The lytic NK cell immunological synapse and sequential steps in its formation

Natural killer (NK) cells are lymphocytes of the innate immune system that are critical in host defense. They are best known for their ability to mediate cytotoxicity, which involves a coordinated series of events resulting in the directed secretion of lytic granules onto a target cell. This process requires the formation of an immunological synapse in NK cells. The NK cell immunological synapse involves the reorganization of the actin cytoskeleton and clustering of certain cell surface receptors in the NK cell at the interface with the target cell. The lytic NK cell immunological synapse, specialized for mediating cytotoxicity, is further distinguished by the polarization of lytic granules, which are then secreted through this region onto the target cell. These events unfold in a definitive sequence and lead to critical checkpoints that provide regulatory control at specific stages in the formation of the NK cell lytic synapse.

Decreased peritoneal concentrations of interleukin-15 in women with advanced stage endometriosis

OBJECTIVE

To assess the concentrations of interleukin-15 (IL-15) in peritoneal fluid from women with endometriosis and fertile disease-free controls.

STUDY DESIGN

Peritoneal fluid samples were obtained from 50 women with endometriosis and 29 fertile women having tubal ligation. Concentrations of IL-15 were measured.

RESULTS

The mean (S.D.s) concentration of IL-15 in peritoneal fluid was 11.17 pg/mL (3.89) for women with endometriosis, and 12.59 pg/mL (4.11) for fertile disease-free controls. The difference of peritoneal IL-15 concentrations between endometriosis and control women was not statistically significant. However, peritoneal IL-15 concentrations were significantly lower in women with moderate/severe endometriosis when compared with those in women with minimal/mild endometriosis, and in controls (P<0.05). In addition, peritoneal IL-15 concentrations did not correlate with the phase of menstrual cycle in endometriosis or control women.

CONCLUSIONS

Our results suggest that the decreased peritoneal IL-15 concentrations in women with moderate/severe endometriosis imply a role of IL-15 in the pathogenesis of advanced endometriosis as compared to those with minimal/mild endometriosis and fertile disease-free controls.

Expression and significances of interleukin-8 and interleukin-15 in colonic mucosa of colon cancer patients

AIM: To investigate the expression of interleukin-8 (IL-8) and IL-15 in colonic mucosa from colon cancer patients and study their relationships with colon cancer.

METHODS: Immunohistochemical technique was used to detect the expression of IL-8 and IL-15 in 66 patients with colon cancer.

RESULTS: The positive rates of IL-8 and IL-15 were 66.7% (44/66) and 60.6% (40/66), respectively. Significant correlations existed between expression of IL-8, IL-15 and the following factors: clinical stages (IL-8: r = 0.437, P = 0.006; IL-15: r = 0.317, P = 0.014), invasive depth (IL-8: r = 0.332, P = 0.003; IL-15: r = 0.312, P = 0.015), regional lymph node metastasis (IL-8: r = 0.316, P = 0.042; IL-15: r = 0.236, P = 0.017), histologic grades (IL-8: r = 0.826, P = 0.0001; IL-15: r = 0.368, P = 0.001).

CONCLUSION: Detection of IL-8 and IL-15 expression is helpful in assessing the malignant degrees of colon cancer.

Cytokines in breast cancer

In recent decades many advances have occurred in the understanding of the role of cytokines in breast cancer. New signalling pathways of interleukin (IL)-1 family, IL-6, IL-11, IL-18, interferons (IFNs) and interferon regulatory factors 1 (IRF-1) and 2 (IRF-2) have been found within tumour microenvironments and in metastatic sites. Some cytokines (IL-1, IL-6, IL-11, TGFbeta) stimulate while others (IL-12, IL-18, IFNs) inhibit breast cancer proliferation and/or invasion. Similarly, high circulating levels of some cytokines seem to be favourable (soluble IL-2R) while others are unfavourable (IL-1beta, IL-6, IL-8, IL-10, IL-18, gp130) prognostic indicators. So far IL-2, IFNalpha, IFNbeta and occasionally IFNgamma, IL-6, IL-12 have been the cytokines used for anti tumour treatment of advanced breast cancer either to induce or increase hormone sensitivity and/or to stimulate cellular immunity. Disappointing results occurred in most trials; however, two long-term pilot studies suggest that IL-2 and IFNbeta, when used appropriately can have a positive effect on clinical benefit and overall survival of patients with minimal residual disease after chemotherapy or with disseminated disease controlled by conventional endocrine therapy.

The biology of interleukin-2 and interleukin-15: implications for cancer therapy and vaccine design

Interleukin-2 and interleukin-15 have pivotal roles in the control of the life and death of lymphocytes. Although their heterotrimeric receptors have two receptor subunits in common, these two cytokines have contrasting roles in adaptive immune responses. The unique role of interleukin-2 is in the elimination of self-reactive T cells to prevent autoimmunity. By contrast, interleukin-15 is dedicated to the prolonged maintenance of memory T-cell responses to invading pathogens. As discussed in this Review, the biology of these cytokines will affect the development of novel therapies for malignancy and autoimmune diseases, as well as the design of vaccines against infectious diseases.

The regression of a canine Langerhans cell tumour is associated with increased expression of IL-2, TNF-alpha, IFN-gamma and iNOS mRNA

Canine cutaneous histiocytoma is a benign epidermal neoplasm of Langerhans cell origin, which usually displays spontaneous regression. Based on the degree of lymphocytic infiltration, 30 histiocytomas were classified into four groups representing different stages of tumour regression. To elucidate further the mechanisms of the antitumour immune response CD3+, CD21+, CD4+, CD8+ and myeloid/histiocyte antigen+ inflammatory cells were differentiated by immunohistochemistry and quantified. In addition, the number of apoptotic cells was detected using the TdT-mediated biotin-dUTP nick-end labelling (TUNEL) method. Furthermore, the expression of interleukin- (IL-2), IL-12(p40), tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), IL-10 and transforming growth factor-beta (TGF-beta) as well as inducible nitric oxid synthase (iNOS) mRNA was determined by reverse transcription-polymerase chain reaction (RT-PCR). Phenotyping of inflammatory cells revealed a significantly increased infiltration of all lymphocyte subsets and myeloid/histiocytic cells with the onset of tumour regression. The latter was significantly correlated to up-regulation of IL-2, TNF-alpha, IFN-gamma and iNOS mRNA expression. Expression of remaining cytokines and percentage of apoptotic cells showed no group-specific changes. The results indicate an initial infiltration of CD4+ T cells followed by increased expression of Th1 cytokines and recruitment of antitumour effector cells as the principal mechanism for tumour regression. Canine cutaneous histiocytoma is a unique example for an effective immune response in a naturally occurring neoplasm derived from epidermal Langerhans cells and might represent a valuable animal model to investigate tumour immunity.

ITK and IL-15 support two distinct subsets of CD8+ T cells

CD8(+) T cells are commonly divided into naïve CD44(lo)CD122(lo) and "memory phenotype" CD44(hi)CD122(hi) cells. Here we show data suggesting that these two cell populations represent independent CD8(+) T cell subsets. Whereas IL-15(-/-) mice lack CD44(hi)CD122(hi) CD8(+) T cells, mice deficient in the kinase ITK lack CD44(lo)CD122(lo) cells among CD8(+) T cells. The same defects were observed during thymus development. CD44(hi)CD122(hi) cells were found among double-positive thymocytes and increased in frequency during CD8 development in wild-type mice. At the mature stage, IL-15(-/-) mice harbored virtually no CD44(hi)CD122(hi) CD8(+) thymocytes. In contrast, ITK(-/-) mice lacked CD44(lo)CD122(lo) CD8(+) cells at this stage. We generated mice with genetic deletions in both IL-15 and ITK and observed a severe reduction of all CD8(+) T cells. The two CD44(lo)CD122(lo) and CD44(hi)CD122(hi) CD8(+) T cell subsets differed in the periphery in that natural killer (NK) receptor expression was found only on CD44(hi)CD122(hi) CD8(+) T cells. This expression was paralleled by their ability to respond to both T cell receptor and NK receptor engagements. In contrast, CD44(lo)CD122(lo) CD8(+) T cells mounted stronger responses to T cell receptor stimulation but failed to recognize NK receptor ligands. Thus, whereas ITK-dependent CD44(lo)CD122(lo) CD8(+) T cells appear to represent conventional CD8(+) T cells, IL-15-dependent CD44(hi)CD122(hi) CD8(+) T cells may have functions in both adaptive and innate immunity.

Human natural killer cell development and biology

Natural killer cells are important innate immune effector cells with potentially broad applications in the treatment of human malignancy due to their ability to lyse neoplastic cells without the need for tumor-specific antigen recognition. Human NK cells can be divided into two functional subsets based on their surface expression of CD56; CD56(bright) immunoregulatory cells and CD56(dim) cytotoxic cells. In addition to functional differences, these NK cell subsets can be modulated differently by interleukin (IL)-2, which has permitted the development of lower dose, better tolerated IL-2 regimens for the in vivo expansion and activation of NK cells. The importance of early hematopoietic growth factors, such as c-kit ligand and flt-3 ligand, and their synergy with IL-15 in the development of human NK cells in the bone marrow has permitted the investigation of novel cytokine combinations for optimizing in vivo expansion of NK cell in the clinic. The importance of lymph nodes as a site for NK cell development has recently been elucidated. Furthermore, progress in the field of how NK cell recognize target cells via activating and inhibitory receptors, and how the balance of signals from these receptors can modulate NK cell activity has revolutionized our understanding of the selective killing of tumor cells by NK cells while sparing normal cells. In this review, we summarize current understanding of NK cell biology, and highlight how such knowledge may be translated to optimize the efficacy of using autologous or allogeneic NK cell for the immunotherapy of cancer.

The role of supramolecular protein complexes and membrane potential in transmembrane signaling processes of lymphocytes

The formation of protein patterns in lymphocyte plasma membranes is analyzed in the light of past and, also, very recent experiments. The analysis surveys the lateral organization of major histocompatibility complex glycoproteins, intercellular adhesion molecule-1, interleukin-2 and -15 receptors, Kv1.3 K+ ion channels and the T-cell receptor as well as their behavior under different conditions. These molecules form small- and large-scale clusters in the membrane of human lymphocytes. Many of the association motifs occur in other investigated cell types. The conclusions point toward a possible role for ion channel activities, membrane potential changes and alterations of the lateral organization of proteins in transmembrane signaling and cytotoxic interactions. In our outlook new factors that potentially affect membrane protein cluster formation and interactions are discussed. A role for MHC glycoproteins in concentrating membrane proteins and organizing protein patterns is suggested, and the possibility that the membrane potential may modulate protein conformation and, thereby, affect protein-protein interactions is pointed out. A well-defined role for the presence of ion channels in the immune synapse is offered, which could explain the significance of ion channel accumulation in the immune synapse together with the T-cell receptor.

Interferon-alpha/beta upregulate IL-15 expression in vitro and in vivo: analysis in human hepatocellular carcinoma cell lines and in chronic hepatitis C patients during interferon-alpha/beta treatment

Type I interferon (IFN) possesses antiviral and antitumor activities and also having an immune regulatory effect, activating cellular immune response and upregulating several cytokines. Recent study has shown that type I IFN upregurates the dendritic cell production of IL-15 capable of activating natural killer cells and CD8+ memory T lymphocytes. However, it is still unknown if type I IFN induces IL-15 production in non-immune cells and if type I IFN affects IL-15 production in vivo. The present study investigated the effect of type I IFNs on IL-15 expression in hepatocellular carcinoma (HCC) cell lines in vitro and in patients with chronic hepatitis C in vivo. When three HCC cell lines, Huh7, HepG2, and JHH4 were cultured in vitro, IFN upregulation of IL-15 expression was observed at both the mRNA and protein levels. In experiments using Huh7 cells, upregulation of IL-15 expression occurred within 24 h of the start of IFN stimulation, and both IFN-alpha and -beta dose-dependently increased IL-15 production in the range from 100 U/ml to 10,000 U/ml of concentration. IFN-beta showed stronger activity in IL-15 production induction in vitro than IFN-alpha. For in vivo examination, sera were obtained from 21 chronic hepatitis C patients treated with IFN and 29 healthy individuals, and the serum IL-15 level was quantified by ELISA. The serum IL-15 level of chronic hepatitis C patients before IFN treatment was similar to that of the healthy controls and significantly increased only during the IFN administration period. These results confirm that IFN-alpha/beta induce IL-15 production and also suggest that IL-15 may be associated with type I IFN-induced immune response.

Primary human T lymphocytes engineered with a codon-optimized IL-15 gene resist cytokine withdrawal-induced apoptosis and persist long-term in the absence of exogenous cytokine

IL-15 is a common gamma-chain cytokine that has been shown to be more active than IL-2 in several murine cancer immunotherapy models. Although T lymphocytes do not produce IL-15, murine lymphocytes carrying an IL-15 transgene demonstrated superior antitumor activity in the immunotherapy of B16 melanoma. Thus, we sought to investigate the biological impact of constitutive IL-15 expression by human lymphocytes. In this report we describe the generation of a retroviral vector encoding a codon-optimized IL-15 gene. Alternate codon usage significantly enhanced the translational efficiency of this tightly regulated gene in retroviral vector-transduced cells. Activated human CD4+ and CD8+ human lymphocytes expressed IL-15Ralpha and produced high levels of cytokine upon retroviral transduction with the IL-15 vector. IL-15-transduced lymphocytes remained viable for up to 180 days in the absence of exogenous cytokine. IL-15 vector-transduced T cells showed continued proliferation after cytokine withdrawal and resistance to apoptosis while retaining specific Ag recognition. In the setting of adoptive cell transfer, IL-15-transduced lymphocytes may prolong lymphocyte survival in vivo and could potentially enhance antitumor activity.

Natural killer cells in human health and disease

Natural killer (NK) cells are lymphocytes of the innate immune system that are critical in host defense and immune regulation. They are activated or inhibited through the ligation of germline-encoded receptors and are involved in mediating cytotoxicity, in producing cytokines and in providing co-stimulation to cells of the adaptive immune system. NK cells play important roles in viral infections, autoimmunity, pregnancy, cancer and bone marrow transplantation. This review highlights recent developments in the understanding of the role of human NK cells in health and disease.

Activated natural killer cells from patients with acute myeloid leukemia are cytotoxic against autologous leukemic blasts in NOD/SCID mice

Natural killer (NK) cells are implicated in the surveillance of hematological malignancies. They participate in the immune response against residual acute myeloid leukemia (AML) after hematopoietic stem cell transplantation with partial HLA class I disparity. However, the role of NK cells in autologous leukemia-specific immunity remains poorly understood. We studied the function of NK cells in AML patients at diagnosis. Following isolation, CD56+CD3- cells exhibited a high proliferative potential in vitro in response to interleukin (IL)-2. The polyclonal population of activated AML-NK cells expressed normal levels of the activating receptor NKG2D and the major natural cytotoxicity receptor NKp46. AML-NK cells were highly effective with respect to interferon-gamma production, cytotoxicity against HLA class I-deficient K562 erythroleukemia cells in vitro and retardation of tumor growth in vivo in K562-bearing NOD/SCID mice. Importantly, when AML blasts were injected into NOD/SCID mice, a single dose of adoptively transferred autologous AML-NK cells significantly reduced the AML load by 8-77%. Recognition of AML blasts may be related to the observed upregulation of ligands for NKG2D and natural cytotoxicity receptors in vivo. We conclude that AML patient-derived NK cells are fully functional, in support of exploring the benefit of AML immunotherapy with IL-2-stimulated autologous NK cells.

Differential effect of IL-15 and IL-2 on survival of phytohemagglutinin-activated umbilical cord blood T cells

Cytokine immunotherapy using interleukin (IL)-2 and IL-15 may be beneficial for patients receiving umbilical cord blood (CB) transplantation by ameliorating post-transplant T-cell apoptosis. The present study compares the differential effect of IL-15 and IL-2 on survival of phytohemagglutinin (PHA)-activated CB and adult peripheral blood (APB) T lymphocytes. In comparison with IL-2, IL-15 preferentially enhanced the survival of CB PHA-activated T cells by decreasing the caspase-3+ population and by increasing the Bcl-2+ population. Activated CB T cells were more susceptible to TNF-alpha-induced apoptosis compared to their adult counterparts. However, the susceptibility could be abrogated by IL-15 but not by IL-2. IL-15 but not IL-2 down-regulated CD28 expression on both activated CB and APB CD8+ T cells, with a much greater effect seen with CB. Western-blot analysis shows that IL-15 Ralpha is deficient in CB compared to APB immediately after PHA stimulation, while culturing with IL-15 significantly enhanced CB IL-15 Ralpha expression to levels comparable to that of adults. Thus, IL-15 may provide a better therapeutic choice for immune reconstitution than IL-2 post-CB transplantation due to its preferential survival enhancing effect on CB T cells.

Herpesviruses and the innate immune response

Herpesvirus infection leads to the rapid induction of an innate immune response. A central aspect of this host response is the production and secretion of type I interferon. The current model of virus-mediated interferon production includes three stages: sensitization, induction, and amplification. A key mediator of all three stages is the cellular transcription factor interferon regulatory factor 3 (IRF3). Although the precise details of IRF3 activation and interferon production in response to herpesvirus infection are still being elucidated, viral proteins that block components of the interferon pathway, particularly IRF3, have been identified and characterized. In vivo studies have shown that in addition to type I interferon, interleukin-15 (IL-15) and natural killer (NK) cells also play an important role in mediating resistance to herpesvirus infection. Recent investigations have demonstrated a strong association between IRF3, interferon, IL-15, and NK cells. This review will focus on herpesvirus-mediated induction of innate immunity, the central role of the type I interferon response and mechanisms used by herpesviruses to block host antiviral immunity.

A potential role for hydrocortisone in the positive regulation of IL-15–activated NK-cell proliferation and survival

Although glucocorticoids (GCs) have been described as acting mainly as anti-inflammatory and immunosuppressive drugs, they may also positively influence the immune system. In the present study, we demonstrate for the first time that hydrocortisone (HC), in synergy with interleukin-15 (IL-15), induces a dramatic increase in the expansion of peripheral blood–derived CD56+ cells, favoring the preferential outgrowth of classical natural killer (CD56+CD3– NK) over CD56+CD3+ natural killer T (NKT) cells. HC plus IL-15–driven CD56+ cells exhibited an increased potential for cytokine production with no impairment in their NK- and lymphokine-activated killer (LAK) activities. Elevated levels of GC-induced leucine zipper protein (GILZ) messenger RNA (mRNA) were detected in both NK and NKT cells cultured with HC and IL-15, in comparison to IL-15 alone. Phosphorylation status of signal transducer and activator of transcription 5 (STAT5) was not affected by the presence of HC in either of the populations. On the contrary, HC differentially affected the IL-2/IL-15R β- and γ-chain surface expression and the phosphorylation levels of extracellular signal-regulated kinases 1/2 (ERK1/2) in IL-15–activated NK and NKT cells. Our data ascribe a novel role to GCs on mature NK-cell expansion and function and open new perspectives for their use in cellular adoptive cancer immunotherapy.

New strategies for immunosuppression: interfering with cytokines by targeting the Jak/Stat pathway

PURPOSE OF REVIEW

Numerous immunosuppressants are available, but their adverse effects related to actions on nonlymphoid cells is problematic. Cytokines are key regulators of immune and inflammatory responses, and blocking their actions has become an important modality in treating autoimmune disorders. This review will discuss strategies to develop novel immunosuppressants that arise from advances in the understanding of cytokine signaling.

RECENT FINDINGS

It is now recognized that large number of cytokines exert their effect by binding to receptors that activate the Janus kinase/signal transducer and activator of transcription pathway, so targeting intracellular signaling pathways is a logical strategy. A selective inhibitor of Janus kinase 3 has now been generated and is effective for transplant rejection in nonhuman primates and other models. Advances have also been made in understanding the functions of Stat family transcription factors, and approaches to interfering with the action of these DNA binding proteins are being devised. In addition, the identification of negative regulators of cytokine signaling offers additional therapeutic opportunities.

SUMMARY

A selective inhibitor of Janus kinase 3 has now been generated and likely represents a new class of effective immunosuppressants. Strategies for targeting signal transducers and activators of transcription pathway are being intensively studied at present and hold potential promise. Multiple endogenous mechanisms exist for negatively regulating cytokine signaling; whether novel therapies can be devised that exploit these mechanisms remains to be determined.

Cytokines in cancer immunity and immunotherapy

The concept that the immune system recognizes and controls cancer was first postulated over a century ago, and cancer immunity has continued to be vigorously debated and experimentally tested. Mounting evidence in humans and mice supports the involvement of cytokines in tumor initiation, growth, and metastasis. The idea that the immune system detects stressed, transformed, and frankly malignant cells underpins much of the excitement currently surrounding new cytokine therapies in cancer treatment. In this review, we define the contrasting roles that cytokines play in promoting tumor immunity, inflammation, and carcinogenesis. We also discuss the more promising aspects of clinical cytokine use in cancer patients.

Synergy of IL-21 and IL-15 in regulating CD8+ T cell expansion and function

Interleukin (IL)-21 is the most recently recognized of the cytokines that share the common cytokine receptor γ chain (γ_c), which is mutated in humans with X-linked severe combined immunodeficiency. We now report that IL-21 synergistically acts with IL-15 to potently promote the proliferation of both memory (CD44^high) and naive (CD44^low) phenotype CD8⁺ T cells and augment interferon-γ production in vitro. IL-21 also cooperated, albeit more weakly, with IL-7, but not with IL-2. Correspondingly, the expansion and cytotoxicity of CD8⁺ T cells were impaired in IL-21R^−/− mice. Moreover, in vivo administration of IL-21 in combination with IL-15 boosted antigen-specific CD8⁺ T cell numbers and resulted in a cooperative effect on tumor regression, with apparent cures of large, established B16 melanomas. Thus, our studies reveal that IL-21 potently regulates CD8⁺ T cell expansion and effector function, primarily in a synergistic context with IL-15.

Beneficial effect of short-term exposure of human NK cells to IL15/IL12 and IL15/IL18 on cell apoptosis and function

Monokines IL12, IL15, and IL18 have been shown to activate NK cell function, however with high apoptosis induced by their combination within 48 h. Here, we demonstrate for the first time that CD56+ cells incubated for only 18 h with the combination of IL15/IL12 or IL15/IL18, then washed, and further cultured in plain medium, exhibit low levels of apoptosis. These shortly activated CD56+ cells show high killer activity against NK- and LAK-sensitive tumor targets that persists over a culture period of 18 days after two additional 6 h cycles of exposure to the monokines applied every 8 days and also retain their ability for high cytokine production during each exposure. Moreover, these repetitive short-term exposures of CD56+ cells to the monokine combinations result in long-lived CD56+ cells with slower rates of FcgammaRIII receptor (CD16) decline, therefore exhibiting higher antibody depended cytotoxicity, as opposed to the continuous incubation with the monokine combinations. In conclusion, short-term exposure of CD56+ cells to IL15/IL12 or IL15/IL18 at 8-day intervals may hold a promise for improved clinical results in cellular adoptive cancer immunotherapy and for the in vivo injections of the monokines.

Jak3, severe combined immunodeficiency, and a new class of immunosuppressive drugs

The recent elucidation of the multiple molecular mechanisms underlying severe combined immunodeficiency (SCID) is an impressive example of the power of molecular medicine. Analysis of patients and the concomitant generation of animal models mimicking these disorders have quickly provided great insights into the pathophysiology of these potentially devastating illnesses. In this review, we summarize the discoveries that led to the understanding of the role of cytokine receptors and a specific tyrosine kinase, Janus kinase 3 (Jak3), in the pathogenesis of SCID. We discuss how the identification of mutations of Jak3 in autosomal recessive SCID has facilitated the diagnosis of these disorders, offered new insights into the biology of this kinase, permitted new avenues for therapy, and provided the rationale for a generation of a new class of immunosuppressants.

Effective photoimmunotherapy of murine colon carcinoma induced by the combination of photodynamic therapy and dendritic cells

PURPOSE

The unique mechanism of tumor destruction by photodynamic therapy (PDT), resulting from apoptotic and necrotic killing of tumor cells accompanied by local inflammatory reaction and induction of heat shock proteins (HSPs), prompted us to investigate the antitumor effectiveness of the combination of PDT with administration of immature dendritic cells (DCs).

EXPERIMENTAL DESIGN

Confocal microscopy and Western blotting were used to investigate the influence of PDT on the induction of apoptosis and expression of HSP expression in C-26 cells. Confocal microscopy and flow cytometry studies were used to examine phagocytosis of PDT-treated C-26 cells by DCs. Secretion of interleukin (IL)-12 was measured with ELISA. Cytotoxic activity of lymph node cells was evaluated in a standard (51)Cr-release assay. The antitumor effectiveness of PDT in combination with administration of DCs was investigated in in vivo model.

RESULTS

PDT treatment resulted in the induction of apoptotic and necrotic cell death and expression of HSP27, HSP60, HSP72/73, HSP90, HO-1, and GRP78 in C-26 cells. Immature DCs cocultured with PDT-treated C-26 cells efficiently engulfed killed tumor cells, acquired functional features of maturation, and produced substantial amounts of IL-12. Inoculation of immature DCs into the PDT-treated tumors resulted in effective homing to regional and peripheral lymph nodes and stimulation of cytotoxic activity of T and natural killer cells. The combination treatment with PDT and administration of DCs produced effective antitumor response.

CONCLUSIONS

The feasibility and antitumor effectiveness demonstrated in these studies suggest that treatment protocols involving the administration of immature DCs in combination with PDT may have clinical potential.

Efficient infection of human natural killer cells with an EBV/retroviral hybrid vector

Molecular characterization of human natural killer (NK) cells will require targeted gene delivery to inhibit and activate specific signaling pathways, yet to our knowledge, an effective means to deliver such products for long-term gene expression without disrupting normal cellular processes has not been described. In this study, we have developed a retroviral strategy to effectively express gene products in the NK cell, whereby its effector functions of cytotoxicity and cytokine production remain intact. Using an EBV/retroviral hybrid vector, we demonstrate infection of human peripheral blood NK cells with simultaneous expression of a marker for infection--the enhanced green fluorescent protein (EGFP)--along with various genes of interest. This technique results in successful infection of the CD56dim NK population that predominates among human peripheral blood NK and is the effector of antibody-dependent cellular cytotoxicity and natural killing. In addition, we demonstrate infection of the CD56bright NK subset as well as the NK-92 cell line. In summary, we have devised an efficient and reproducible methodology for the targeted delivery of gene products to human NK cells that should now provide opportunities to dissect the molecular processes critical to normal NK cell physiology.

Mechanisms of Superior Anti-Tumor Cytotoxic Response of Interleukin 15-Induced Lymphokine-Activated Killer Cells

Interleukin (IL) 15 is one of the main cytokines controlling cytotoxic lymphocyte survival and growth. Despite its receptor and functional similarity to IL-2, IL-15 affects a wider target cell population and utilizes different mechanisms in cell activation. The role of IL-15 in lymphokine-activated killer (LAK) cell generation in vitro and potential mechanisms of cytotoxicity compared with equivalent low concentration of IL-2 with or without mitogens (phytohemoglutinin (PHA) and anti-CD3 antibody) have been investigated in this study. IL-15 treatment resulted in moderate cell proliferation over 7 days, whereas IL-2 treatment was associated with decreased cell numbers. Unlike IL-2 in combination with mitogens, IL-15 caused increases in both cytotoxic T lymphocytes (CTL) and CD56 LAK cells, particularly cytokine-induced killer and cytolytic natural killer T-cell (CNK-T) subpopulations, which are known to be highly effective in cytotoxicity. IL-15 also increased overall perforin and tumor necrosis factor-alpha expression and more prominently in CTLs. Consequently, IL-15 resulted in superior cytotoxicity against two different NK-sensitive (human K-562 and murine YAC-1) and LAK-sensitive (human Daudi and Raji) cell lines compared with other cytokine combinations. There was also no contribution of mitogens to IL-2-induced cytotoxicity. In conclusion, IL-15 at the concentration of 10 ng/mL used in this study causes moderate proliferation and superior cytotoxicity of LAK cells in vitro that was associated with induction of a specific LAK cell subpopulation profile and related cellular killing mechanisms. These results are encouraging for potential use of IL-15 as part of immunotherapy.

Cytokines in Mycoplasma pneumoniae infections

Mycoplasma pneumoniae (M. pneumoniae) is one of the smallest free-living bacteria known. Along with other unique characteristics of this genus, it lacks the typical peptidoglycan cell wall of most eubacteria. Best known for causing tracheobronchitis and atypical pneumonia in humans, this pathogen also causes a number of extrapulmonary syndromes such as meningitis/encephalitis and arthritis. Recent studies also suggest that infection may be associated with chronic conditions such as asthma. Although the mechanisms of M. pneumoniae pathogenesis remain to be elucidated, one important component of M. pneumoniae infections is the induction of proinflammatory and other cytokines in both acute and chronic conditions. In this review, we survey the induction of cytokines by M. pneumoniae in different model systems, and we discuss the possible role of induced cytokines in M. pneumoniae pathogenesis.

IL-27 Mediates Complete Regression of Orthotopic Primary and Metastatic Murine Neuroblastoma Tumors: Role for CD8+T Cells

We have shown previously that IFN-gamma-inducing cytokines such as IL-12 can mediate potent antitumor effects against murine solid tumors. IL-27 is a newly described IL-12-related cytokine that potentiates various aspects of T and/or NK cell function. We hypothesized that IL-27 might also mediate potent antitumor activity in vivo. TBJ neuroblastoma cells engineered to overexpress IL-27 demonstrated markedly delayed growth compared with control mice, and complete durable tumor regression was observed in >90% of mice bearing either s.c. or orthotopic intra-adrenal tumors, and 40% of mice bearing induced metastatic disease. The majority of mice cured of their original TBJ-IL-27 tumors were resistant to tumor rechallenge. Furthermore, TBJ-IL-27 tumors were heavily infiltrated by CD8(+) T cells, and draining lymph node-derived lymphocytes from mice bearing s.c. TBJ-IL-27 tumors are primed to proliferate more readily when cultured ex vivo with anti-CD3/anti-CD28 compared with lymphocytes from mice bearing control tumors, and to secrete higher levels of IFN-gamma. In addition, marked enhancement of local IFN-gamma gene expression and potent up-regulation of cell surface MHC class I expression are noted within TBJ-IL-27 tumors compared with control tumors. Functionally, these alterations occur in conjunction with the generation of tumor-specific CTL reactivity in mice bearing TBJ-IL-27 tumors, and the induction of tumor regression via mechanisms that are critically dependent on CD8(+), but not CD4(+) T cells or NK cells. Collectively, these studies suggest that IL-27 could be used therapeutically to potentiate the host antitumor immune response in patients with malignancy.

Failed adoptive immunotherapy with tumor-specific T cells: reversal with low-dose interleukin 15 but not low-dose interleukin 2

Adoptive immunotherapy with tumor-specific T cells has emerged as a valid approach for prevention or treatment of diseases, such as melanoma and EBV-associated lymphoma. As interleukin (IL) 15 promotes survival of CD8(+) memory CTLs, we hypothesized that it could be used to enhance antitumor immunity in vivo through the maintenance of adoptively transferred memory CTL. To test this, we treated mice bearing P1A(+) tumors with adoptively transferred T cells possessing a transgenic Valpha8(+) T-cell receptor specific for the P1A tumor antigen (called P1CTL). Mice were then randomized to receive daily low-dose IL-15 (0.5 microg/day) or PBS. Mice receiving the transgenic P1CTL and IL-15 experienced a significantly delayed tumor relapse or complete tumor regression (P < 0.002 compared with PBS), with a striking persistence of the CD8(+) Valpha8(+) P1CTL compared with mice receiving the CD8(+) Valpha8(+) P1CTL and PBS vehicle (26.3 versus 5.1% P < 10(-5)). Animals exhibiting complete tumor regression had a significant population of CD8(+) Valpha8(+) P1CTL (46%) that persisted with IL-15 treatment until 140 days after adoptive transfer and successfully defended them against tumor rechallenge without IL-15. Low-dose IL-2 afforded no protection over vehicle and resulted in lower percentages of T cells with an activated memory phenotype, lower Bcl-2 expression, and lower ex vivo antitumor cytotoxicity compared with mice treated with IL-15. Collectively, the data support the notion that exogenous low-dose IL-15 therapy can enhance and even reverse the limited efficacy of adoptively transferred tumor-specific T-cell therapy and may do so in a fashion that is superior and distinct from exogenous IL-2 therapy.

Hepatic interleuklin 15 (IL-15) expression: implications for local NK/NKT cell homeostasis and development

Interleukin 15 (IL-15) is critical for the development of human and murine natural killer (NK) cells and hepatic-derived NK T cells (NKT) in mice, and for the homeostatic maintenance of NK/NKT and CD8(+) memory T cells. The lymphocyte repertoire of an adult human liver includes significant populations of NK and NKT-like cells, which may arise locally from hepatic haematopoietic stem cells (HSCs). We investigated hepatic IL-15 levels and the expression of IL-2/IL-15-receptor beta-chain (IL-2/IL-15Rbeta; CD122) on mature hepatic lymphocytes and HSCs. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect secreted/intracellular IL-15 transcripts. IL-15 protein was localized using immunohistochemistry; levels were measured by enzyme-linked immunosorbent assay IL-2/IL-15Rbeta expression by flow-cytometry. Normal hepatic IL-15 protein was detected at 0.43 ng/100 mg total protein (n = 11, range 0.10 ng-0.9 ng). There was a significant increase in HCV-infected tissue (1.78 ng, P < 0.005, n = 11, range 0.18-2.43 ng). The staining pattern suggests that infiltrating monocytes and tissue resident Kupffer cells are the main producers. IL-15 protein was detected in supernatants from cultured liver biopsy specimens in the absence of stimulation (mean 175.8 pg/100 mg wet tissue, n = 3), which increased significantly upon stimulation (P < 0.05, mean 231.21 pg). On average, 61% of hepatic HSCs expressed IL-2/IL-15Rbeta suggesting a local lymphopoietic role. Eighty per cent of NK and 45.8% of CD56(+) T cells expressed IL-2/IL-15Rbeta, suggesting involvement in local CD56(+) cell activation and expansion. Constitutive expression of IL-15 protein and IL-2/IL-15Rbeta on hepatic lymphocytes suggests a key role in the generation and maintenance of the unique hepatic lymphoid repertoire. The significant increase observed in HCV-infected liver suggests a role for IL-15 in host antiviral responses in the liver.

Interleukin (IL)-15 and IL-2 Reciprocally Regulate Expression of the Chemokine Receptor CX3CR1 through Selective NFAT1- and NFAT2-dependent Mechanisms

We have recently reported that interleukin (IL)-15 and IL-2, which signal through IL-2Rbetagamma, oppositely regulate expression of the proinflammatory chemokine receptor CX3CR1. Here we delineate molecular mechanisms responsible for this paradox. By using a luciferase reporter plasmid, we identified a 433-bp region spanning the major transcriptional start point of human CX3CR1 that, when expressed in human peripheral blood mononuclear cells (PBMCs), possessed strong constitutive promoter activity. IL-2 and IL-15 treatment increased and abolished this activity, respectively, mimicking their effects on endogenous CX3CR1. IL-2 and IL-15 have been reported to also have opposite effects on the immunoregulatory transcription factor NFAT (nuclear factor of activated T cells), and the 433-bp region contains a kappaB-like NFAT site. The effects of IL-15 and IL-2 on both CX3CR1 reporter activity and endogenous CX3CR1 transcription in PBMCs were abolished by the NFAT inhibitors cyclosporin A and VIVIT. Moreover, mutation of the kappaB-like NFAT sequence markedly attenuated IL-2 and IL-15 modulation of CX3CR1 promoter-reporter activity in PBMCs. Furthermore, chromatin immunoprecipitation revealed that IL-15 promoted specific recruitment of NFAT1 but not NFAT2 to the CX3CR1 promoter, whereas IL-2 had the converse effect. This appears to be relevant in vivo because mouse CX3CR1 mRNA was expressed in both PBMCs and splenocytes from NFAT1-/- mice injected with recombinant IL-15 but was undetectable in cells from IL-15-injected NFAT1+/+ BALB/c mice; as predicted, IL-2 up-regulated cx3cr1 in both mouse strains to a similar extent. Thus, by pharmacologic, genetic, and biochemical criteria in vitro and in vivo, our results suggest that IL-15 and IL-2 oppositely regulate CX3CR1 gene expression by differentially recruiting NFAT1 and NFAT2 to a kappaB-like NFAT site within the CX3CR1 promoter. We propose that expression of CX3CR1 and possibly other immunoregulatory genes may be determined in part by the balance of NFAT1 and NFAT2 activity in leukocytes.

In vivoanti-tumour activity of recombinant MVM parvoviral vectors carrying the human interleukin-2 cDNA

BACKGROUND

The natural oncotropism and oncotoxicity of vectors derived from the autonomous parvovirus, minute virus of mice (prototype strain) [MVM(p)], combined with the immunotherapeutic properties of cytokine transgenes, make them interesting candidates for cancer gene therapy.

METHODS

The in vivo anti-tumour activity of a recombinant parvoviral vector, MVM-IL2, was evaluated in a syngeneic mouse melanoma model that is relatively resistant in vitro to the intrinsic cytotoxicity of wild-type MVM(p).

RESULTS

In vitro infection of the K1735 melanoma cells prior to their injection resulted in loss of tumorigenicity in 70% of mice (7/10). Tumour-free mice were protected against a challenge with non-infected parental cells. In addition, MVM-IL2-infected tumour cells induced an anti-tumour activity on parental cells injected at a distant location. These non-infected tumour cells were injected either at the same time or 7 days before the injection of MVM-IL2-infected cells. In the latter setting, which mimics a therapeutic model for small tumours, 4/10 mice were still tumour-free after 4 months.

CONCLUSIONS

Our results show that (i) the MVM-IL2 parvoviral vector efficiently transduces tumour cells; and (ii) the low multiplicity of infection (MOI = 1) used in our experiments was sufficient to elicit an anti-tumour effect on distant cells, which supports further studies on this vector as a new tool for cancer gene therapy.

Role of trans-cellular IL-15 presentation in the activation of NK cell-mediated killing, which leads to enhanced tumor immunosurveillance

Interleukin 15 (IL-15) is a critical factor for the proliferation and activation of natural killer (NK) and CD8 T cells. Recently, we demonstrated that IL-15Ralpha expressed on monocytes/dendritic cells captures and presents IL-15 to neighboring cells in trans (trans-presentation of IL-15) through cell-cell contact. In the current study, we provide evidence that the IL-15 presented in trans, but not soluble IL-15 at physiologic concentrations, augments the killing activity mediated by NK cells in vitro. In addition, transfection of IL-15Ralpha into a colon carcinoma cell line (MC38) enabled these cells to present IL-15 in trans to NK cells and augmented their killing activity, resulting in the efficient lysis of MC38 cells by NK cells in vitro. Furthermore, these transfected MC38 cells no longer form fatal pulmonary metastases in mice. It was also shown that NK cells play an important role in the rejection of MC38 cells under these circumstances. These results collectively suggest that the IL-15 trans-presentation mechanism operates in vivo to augment the tumor immune surveillance mechanism. Furthermore, our observation provides the scientific basis for a novel strategy to prevent cancer development/metastasis.

Enhancement of the host immune responses in cutaneous T-cell lymphoma by CpG oligodeoxynucleotides and IL-15

Patients with advanced cutaneous T-cell lymphoma (CTCL) exhibit profound defects in cell-mediated immunity. Host immune functions appear to play an integral role in mediating disease-controlling responses in CTCL, therefore we investigated the effects of synthetic oligode-oxynucleotides with CpG motifs (CpG ODN), which have been recognized as immune stimulatory by virtue of activation of dendritic cells (DCs) following binding to Toll-like receptor (TLR) 9. Peripheral blood mononuclear cells (PBMCs) from patients with advanced CTCL (erythroderma with circulating malignant T cells) and healthy volunteers were cultured with either CpG-A or CpG-B ODN. Patients' PBMCs exhibited marked induction of interferon-alpha (IFN-alpha) release following culture with CpG-A. Similarly significant activation of NK cells and CD8 T cells occurred as assessed by up-modulation of CD69 expression and by natural killer lytic activity. Nevertheless, the PBMCs of patients exhibited blunted responses to CpG-A compared to healthy volunteers. In such cases, IL-15 was capable of producing levels of NK activation that were superior to CpG-A, while the combined effects of CpG-A plus IL-15 induced maximal activation of NK cells and further enhanced activation of CD8 T cells. These findings have important implications for the potential enhancement of antitumor immunity among patients with advanced CTCL.

Proliferation and Differentiation of CD8+ T Cells in the Absence of IL-2/15 Receptor β-Chain Expression or STAT5 Activation

Major gains in the efficacy of T cell-based therapies for cancer and infectious diseases could be realized through improved understanding of the signals that control expansion and differentiation of CD8(+) cytolytic T cells. IL-2, IL-15, and the downstream transcription factor STAT5 have all been implicated as important regulators of these processes, yet there are conflicting data regarding their contribution to in vivo T cell responses. We used a murine adoptive T cell transfer model to examine the contribution of IL-2 and IL-15 signaling to the proliferation and differentiation of naive, CD8(+) T cells bearing an OVA-specific TCR transgene (OT-I). OT-I T cells failed to express the high affinity IL-2R (CD25) while proliferating in vivo, irrespective of the mode of Ag delivery. Moreover, OT-I T cells rendered genetically deficient in the shared IL-2/IL-15Rbeta subunit (IL-2Rbeta) demonstrated normal Ag-induced proliferation and cytolytic activity in vivo. Accordingly, activation of STAT5 was not detected in proliferating IL-2Rbeta-deficient OT-I T cells, thus implicating a STAT5-independent cytokine or costimulatory pathway in this process. Even though IL-2 and IL-15 were dispensable for CD8(+) T cell proliferation, systemic infusion of IL-2 nevertheless promoted the expansion of OT-I T cells in vivo. Thus, IL-2 and IL-15 signals are not essential for CD8(+) T cell proliferation or differentiation, but IL-2 can promote supraphysiological expansion when supplied exogenously. These findings challenge current models that place CD8(+) T cell proliferation under the control of STAT5-dependent cytokines and suggest new approaches to the therapeutic manipulation of T cell numbers in vivo.

Identification of an Interleukin-15α Receptor-binding Site on Human Interleukin-15

To identify the epitopes in human interleukin-15 (IL-15) that are responsible for binding to the interleukin-15 receptor alpha chain, antibody and receptor mapping by peptide scanning and site-directed mutagenesis was used. By using peptide scanning, we identified four regions in IL-15. The first region ((85)CKECEELEEKN(95)) is located in the C-D loop and is recognized by a set of non-inhibitory antibodies. The second region ((102)SFVHIVQMFIN(112)) is located in helix D and is recognized by two antibodies that are inhibitory of IL-15 bio-activity but not of IL-15 binding to IL-15Ralpha. The two remaining regions react with a recombinant soluble form of the IL-15Ralpha; the first ((44)LLELQVISL(52), peptide 1) corresponds to a sequence located in the B-helix and the second ((64)ENLII(68), peptide 2) to a sequence located in helix C. The latter is also contained in the epitope recognized by an antibody (monoclonal antibody B-E29) that prevents IL-15 binding to IL-15Ralpha. By site-directed mutagenesis, we confirmed that residues present in peptide 1 (Leu-45, Glu-46, Val-49, Ser-51, and Leu-52) and peptide 2 (Leu-66 and Ile-67) are involved in the binding of IL-15 to IL-15Ralpha. Furthermore, the results presented indicate that residues in the second peptide (Glu-64, Asn-65, and Ile-68) participate in IL-2Rbeta recruitment. This finding could have implications for the dynamics of receptor assembly. These results also indicate that the modes of interaction of IL-15 and IL-2 with their respective alpha chains are not completely analogous. Finally, some of the IL-15 mutants generated in this study displayed agonist or antagonist properties and may be useful as therapeutic agents.

Marrow Stromal Cells for Interleukin-2 Delivery in Cancer Immunotherapy

Marrow stromal cells (MSCs) can be easily gene-modified and clonally expanded making them ideal candidates for transgenic cell therapy. However, recent reports suggest that MSCs possess immunosuppressive effects, which may limit their clinical applications. We investigated whether interleukin (IL)-2 gene-modified MSCs can be used to mount an effective immune response against the poorly immunogenic B16 melanoma model. We first show that primary MSCs mixed with B16 cells and injected subcutaneously in syngeneic recipients do not affect tumor growth. On the other hand, IL-2-producing MSCs mixed with B16 cells significantly delayed tumor growth in an IL-2 dose-dependent manner. Furthermore, we observed that matrix-embedded IL-2-producing MSCs injected in the vicinity of preestablished B16 tumors led to absence of tumor growth in 90% of treated mice (p < 0.001). We demonstrated that tumor-bearing mice treated with IL-2-producing MSCs developed CD8-mediated tumor-specific immunity and significantly delayed tumor growth of a B16 cell challenge (p < 0.05). In addition, treatment of cd8-/-, cd4-/- and beige mice revealed that CD8+ and natural killer (NK) cells, but not CD4+ cells, were required to achieve antitumor effect. In conclusion, MSCs can be exploited to deliver IL-2 and generate effective immune responses against melanoma in mice with normal immune systems.

Cytokines and their role in lymphoid development, differentiation and homeostasis

PURPOSE OF REVIEW

The development of lymphoid tissues as well as the ultimate differentiation of naïve and memory T cells are dependent on cytokines. In this review, we will focus on recent advances in the understanding of molecular mechanisms that regulate lymphoid development, homeostasis and tolerance.

RECENT FINDINGS

Cytokines play a critical role in the development and differentiation of lymphoid cells. In addition, newer data indicate important roles of interleukin-7 and interleukin-15 in lymphoid homeostasis and memory. Furthermore, a new family of heterodimeric cytokines comprising interleukin-12, interleukin-23 and -27 is important for differentiation of helper T cells and cell-mediated immunity. Finally the importance of tumor necrosis factor superfamily members in the development of lymphoid organs has recently been elucidated and will be discussed in detail.

SUMMARY

New cytokines and receptors continue to be identified. The discovery and characterization of cytokines, their receptors and signaling molecules will provide a more complete understanding of normal lymphoid development, differentiation and function. In addition, this knowledge should improve our understanding of the pathogenesis of immunological diseases and hopefully will provide new treatment strategies.

Interleukin-15 enhances human neutrophil phagocytosis by a Syk-dependent mechanism: importance of the IL-15Rα chain

Interleukin-15 (IL-15) is a cytokine that possesses interesting, potential therapeutic properties. However, based on several parameters including activation of neutrophils, it is also recognized as a proinflammatory cytokine. The mechanisms by which IL-15 activates human neutrophil functions are not fully understood. Although these cells express a functional IL-15 receptor (IL-15R) composed of IL-15Ralpha, IL-2/15Rbeta (CD122), and gamma(c) (CD132) subunits, the role of each receptor component has not been investigated in IL-15-induced human neutrophil responses. In the present study, fluorescein-activated cell sorter analysis revealed that the ability of IL-15 to enhance neutrophil phagocytosis is not a result of increased expression of IL-15Ralpha, CD122, or CD132 on the neutrophil cell surface. Pretreatment of neutrophils with specific antibodies to IL-15Ralpha, CD122, or CD132 was found to inhibit phagocytosis of opsonized-sheep red blood cells by nearly 40%, 21%, and 27%, respectively. As expected, pretreatment of neutrophils with anti-IL-2Ralpha (CD25) had no effect. Pretreatment of cells with the Syk inhibitor piceatannol was found to significantly inhibit the ability of IL-15 to enhance phagocytosis. In addition, IL-15 was found to induce tyrosine phosphorylation of Syk that was largely inhibited by pretreating cells with piceatannol. Moreover, we found that Syk kinase is physically associated with IL-15Ralpha. We conclude that IL-15R enhances neutrophil phagocytosis by a Syk-dependent mechanism and that the IL-15Ralpha chain plays a key role in mediating this response, at least by interacting with Syk kinase.

Safety and efficacy of subcutaneous and continuous intravenous infusion rIL-2 in patients with metastatic renal cell carcinoma

A retrospective analysis was conducted on data from four open-label, nonrandomised, phase II trials of recombinant interleukin-2 (rIL-2) in patients with metastatic renal cell carcinoma to compare the safety and efficacy of administration by subcutaneous (s.c.) and continuous intravenous (c.i.v.) infusion (n=103 s.c. and n=225 c.i.v.). No statistically significant differences were found between the cohorts in terms of overall response rate (s.c.: 13.6% vs c.i.v.: 12.4%, P=0.77), response duration (s.c.: 9.8 months vs c.i.v.: 10.1 months, P=0.99), and overall survival (P=0.08). Compared with c.i.v. administration, more patients in the s.c. cohort experienced stable disease (50.5 vs 29.8%) and fewer underwent disease progression (35.0 vs 43.6%). Subcutaneous administration was associated with a significantly lower incidence of grade 3 or 4 adverse events (46 vs 76%; P<0.001), and fewer s.c. patients required dose reductions because of toxicity (20 vs 82%). At the doses and within the schedules tested, this comparative analysis did not detect any difference in efficacy between s.c. and c.i.v. administration of rIL-2 in terms of overall survival, duration of response and response rate in patients with metastatic renal cell carcinoma. However, s.c. delivery of rIL-2 was associated with improved tolerability.