Randomized phase-III study of low-dose cytarabine and etoposide + /- all-trans retinoic acid in older unfit patients with NPM1-mutated acute myeloid leukemia

The aim of this randomized clinical trial was to evaluate the impact of all-trans retinoic acid (ATRA) in combination with non-intensive chemotherapy in older unfit patients (> 60 years) with newly diagnosed NPM1-mutated acute myeloid leukemia. Patients were randomized (1:1) to low-dose chemotherapy with or without open-label ATRA 45 mg/m2, days 8-28; the dose of ATRA was reduced to 45 mg/m2, days 8-10 and 15 mg/m2, days 11-28 after 75 patients due to toxicity. Up to 6 cycles of cytarabine 20 mg/day s.c., bid, days 1-7 and etoposide 100 mg/day, p.o. or i.v., days 1-3 with (ATRA) or without ATRA (CONTROL) were intended. The primary endpoint was overall survival (OS). Between May 2011 and September 2016, 144 patients (median age, 77 years; range, 64-92 years) were randomized (72, CONTROL; 72, ATRA). Baseline characteristics were balanced between the two study arms. The median number of treatment cycles was 2 in ATRA and 2.5 in CONTROL. OS was significantly shorter in the ATRA compared to the CONTROL arm (p = 0.023; median OS: 5 months versus 9.2 months, 2-years OS rate: 7% versus 10%, respectively). Rates of CR/CRi were not different between treatment arms; infections were more common in ATRA beyond treatment cycle one. The addition of ATRA to low-dose cytarabine plus etoposide in an older, unfit patient population was not beneficial, but rather led to an inferior outcome.The clinical trial is registered at clinicaltrialsregister.eu (EudraCT Number: 2010-023409-37, first posted 14/12/2010).

The wolf in sheep's clothing: Platelet-derived "pseudo self" impairs cancer cell "missing self" recognition by NK cells

Metastasis is strongly inhibited in thrombocytopenic mice. This phenotype is reversed by NK cell depletion which indicates that platelets may facilitate tumor progression and metastasis by interfering with NK cell immunosurveillance. Understanding the underlying mechanisms may help us to reinforce anti-tumor immunity and NK-based immunotherapy in cancer patients.

Monocyte-derived dendritic cells display a highly activated phenotype and altered function in patients with familial Mediterranean fever

Dendritic cells (DCs) are sentinels of the immune system that bridge innate and adaptive immunity. By capturing antigens in peripheral tissue, processing and presenting them with concurrent expression of co‐stimulatory molecules and cytokine secretion they control and modulate immune reactions. Through pattern recognition receptors, DCs sense molecules that are associated with infection or tissue damage, frequently resulting in the formation of inflammasomes upon intracellular stimulation. The inherited autoinflammatory familial Mediterranean fever (FMF) is associated with deregulated activity of the pyrin inflammasome leading to acute inflammatory episodes. However, differentiation and function of DCs in this disease are as yet unclear. Therefore, we first determined DC subpopulation frequency in peripheral blood of a cohort of FMF patients. Joint evaluation without classification according to specific patient characteristics, such as mutational status, did not disclose significant differences compared to healthy controls. For the further examination of phenotype and function, we used immature and mature monocyte‐derived DCs (imMo‐DCs, mMo‐DCs) that were generated in vitro from FMF patients. Immunophenotypical analysis of imMo‐DCs revealed a significantly elevated expression of CD83, CD86 and human leukocyte antigen D‐related (HLA‐DR) as well as a significant down‐regulation of CD206, CD209 and glycoprotein NMB (GPNMB) in our FMF patient group. Furthermore, FMF imMo‐DCs presented a significantly higher capacity to migrate and to stimulate the proliferation of unmatched allogeneic T cells. Finally, the transition towards a more mature, and therefore activated, phenotype was additionally reinforced by the fact that peripheral blood DC populations in FMF patients exhibited significantly increased expression of the co‐stimulatory molecule CD86.

Randomized phase-II trial evaluating induction therapy with idarubicin and etoposide plus sequential or concurrent azacitidine and maintenance therapy with azacitidine

The aim of this randomized phase-II study was to evaluate the effect of substituting cytarabine by azacitidine in intensive induction therapy of patients with acute myeloid leukemia (AML). Patients were randomized to four induction schedules for two cycles: STANDARD (idarubicin, cytarabine, etoposide); and azacitidine given prior (PRIOR), concurrently (CONCURRENT), or after (AFTER) therapy with idarubicin and etoposide. Consolidation therapy consisted of allogeneic hematopoietic-cell transplantation or three courses of high-dose cytarabine followed by 2-year maintenance therapy with azacitidine in the azacitidine-arms. AML with CBFB-MYH11, RUNX1-RUNX1T1, mutated NPM1, and FLT3-ITD were excluded and accrued to genotype-specific trials. The primary end point was response to induction therapy. The statistical design was based on an optimal two-stage design applied for each arm separately. During the first stage, 104 patients (median age 62.6, range 18-82 years) were randomized; the study arms PRIOR and CONCURRENT were terminated early due to inefficacy. After randomization of 268 patients, all azacitidine-containing arms showed inferior response rates compared to STANDARD. Event-free and overall survival were significantly inferior in the azacitidine-containing arms compared to the standard arm (p < 0.001 and p = 0.03, respectively). The data from this trial do not support the substitution of cytarabine by azacitidine in intensive induction therapy.

The Deubiquitinase Inhibitor b-AP15 and Its Effect on Phenotype and Function of Monocyte-Derived Dendritic Cells

The ubiquitin-proteasome system is elementary for cellular protein degradation and gained rising attention as a new target for cancer therapy due to promising clinical trials with bortezomib, the first-in class proteasome inhibitor meanwhile approved for multiple myeloma and mantle cell lymphoma. Both bortezomib and next-generation proteasome inhibitors mediate their effects by targeting the 20S core particle of the 26S proteasome. The novel small molecule inhibitor b-AP15 affects upstream elements of the ubiquitin-proteasome cascade by suppressing the deubiquitinase activity of both proteasomal regulatory 19S subunits and showed promising anticancer activity in preclinical models. Nonetheless, effects of inhibitors on the ubiquitin-proteasome system are not exclusively restricted to malignant cells: alteration of natural killer cell-mediated immune responses had already been described for drugs targeting either 19S or 20S proteasomal subunits. Moreover, it has been shown that bortezomib impairs dendritic cell (DC) phenotype and function at different levels. In the present study, we comparatively analyzed effects of bortezomib and b-AP15 on monocyte-derived DCs. In line with previous results, bortezomib exposure impaired maturation, antigen uptake, migration, cytokine secretion and immunostimulation, whereas treatment with b-AP15 had no compromising effects on these DC features. Our findings warrant the further investigation of b-AP15 as an alternative to clinically approved proteasome inhibitors in the therapy of malignancies, especially in the context of combinatorial treatment with DC-based immunotherapies.

Expression of the Immune Checkpoint Modulator OX40 in Acute Lymphoblastic Leukemia Is Associated with BCR-ABL Positivity

OX40 and its ligand are members of the TNF/TNF receptor superfamily, which includes various molecules influencing cellular signaling and function of both tumor and immune cells. The ability of OX40 to promote proliferation and differentiation of activated T cells fueled present attempts to modulate this immune checkpoint to reinforce antitumor immunity. While we recently found evidence for the involvement of OX40 in pathophysiology of acute myeloid leukemia including natural killer (NK) cell immunosurveillance, less is known on its role in acute lymphoblastic leukemia (ALL). In the present study, OX40 expression on ALL cells was significantly associated with positivity for the adverse risk factor BCR-ABL. In line, signaling via OX40 increased metabolic activity of primary ALL cells and resulted in release of cytokines involved in disease pathophysiology. Furthermore, interaction of ALL-expressed OX40 with its cognate ligand on NK cells stimulated ALL cell lysis. The data presented thus not only identify the yet unknown involvement of OX40/OX40L in ALL pathophysiology and NK cell immunosurveillance but also point to the necessity to thoroughly consider the consequences of modulating the OX40/OX40L molecule system beyond its effects on T cells when developing OX40-targeting approaches for cancer immunotherapy.

Tyrosine kinase inhibition increases the cell surface localization of FLT3-ITD and enhances FLT3-directed immunotherapy of acute myeloid leukemia

The fms-related tyrosine kinase 3 (FLT3) receptor has been extensively studied over the past two decades with regard to oncogenic alterations that do not only serve as prognostic markers but also as therapeutic targets in acute myeloid leukemia (AML). Internal tandem duplications (ITDs) became of special interest in this setting as they are associated with unfavorable prognosis. Because of sequence-dependent protein conformational changes FLT3-ITD tends to autophosphorylate and displays a constitutive intracellular localization. Here, we analyzed the effect of tyrosine kinase inhibitors (TKIs) on the localization of the FLT3 receptor and its mutants. TKI treatment increased the surface expression through upregulation of FLT3 and glycosylation of FLT3-ITD and FLT3-D835Y mutants. In T cell-mediated cytotoxicity (TCMC) assays, using a bispecific FLT3 × CD3 antibody construct, the combination with TKI treatment increased TCMC in the FLT3-ITD-positive AML cell lines MOLM-13 and MV4-11, patient-derived xenograft cells and primary patient samples. Our findings provide the basis for rational combination of TKI and FLT3-directed immunotherapy with potential benefit for FLT3-ITD-positive AML patients.

The Immune Checkpoint Modulator OX40 and Its Ligand OX40L in NK-Cell Immunosurveillance and Acute Myeloid Leukemia

The TNF receptor family member OX40 promotes activation and proliferation of T cells, which fuels efforts to modulate this immune checkpoint to reinforce antitumor immunity. Besides T cells, NK cells are a second cytotoxic lymphocyte subset that contributes to antitumor immunity, particularly in leukemia. Accordingly, these cells are being clinically evaluated for cancer treatment through multiple approaches, such as adoptive transfer of ex vivo expanded polyclonal NK cells (pNKC). Here, we analyzed whether and how OX40 and its ligand (OX40L) influence NK-cell function and antileukemia reactivity. We report that OX40 is expressed on leukemic blasts in a substantial percentage of patients with acute myeloid leukemia (AML) and that OX40 can, after stimulation with agonistic OX40 antibodies, mediate proliferation and release of cytokines that act as growth and survival factors for the leukemic cells. We also demonstrate that pNKC differentially express OX40L, depending on the protocol used for their generation. OX40L signaling promoted NK-cell activation, cytokine production, and cytotoxicity, and disruption of OX40-OX40L interaction impaired pNKC reactivity against primary AML cells. Together, our data implicate OX40/OX40L in disease pathophysiology of AML and in NK-cell immunosurveillance. Our findings indicate that effects of the OX40-OX40L receptor-ligand system in other immune cell subsets and also malignant cells should be taken into account when developing OX40-targeted approaches for cancer immunotherapy. Cancer Immunol Res; 6(2); 209-21. ©2018 AACR.

Epidemiological, genetic, and clinical characterization by age of newly diagnosed acute myeloid leukemia based on an academic population-based registry study (AMLSG BiO)

We describe genetic and clinical characteristics of acute myeloid leukemia (AML) patients according to age from an academic population-based registry. Adult patients with newly diagnosed AML at 63 centers in Germany and Austria were followed within the AMLSG BiO registry (NCT01252485). Between January 1, 2012, and December 31, 2014, data of 3525 patients with AML (45% women) were collected. The median age was 65 years (range 18-94). The comparison of age-specific AML incidence rates with epidemiological cancer registries revealed excellent coverage in patients < 70 years old and good coverage up to the age of 80. The distribution according to the European LeukemiaNet (ELN) risk categorization from 2010 was 20% favorable, 31% intermediate-1, 28% intermediate-2, and 21% adverse. With increasing age, the relative but not the absolute prevalence of patients with ELN favorable and intermediate-1 risk (p < 0.001), with activating FLT3 mutations (p < 0.001), with ECOG performance status < 2 (p < 0.001), and with HCT-CI comorbidity index < 3 (p < 0.001) decreased. Regarding treatment, obesity and favorable risk were associated with an intensive treatment, whereas adverse risk, higher age, and comorbidity index > 0 were associated with non-intensive treatment or best supportive care. The AMLSG BiO registry provides reliable population-based distributions of genetic, clinical, and treatment characteristics according to age.

Platelet-mediated shedding of NKG2D ligands impairs NK cell immune-surveillance of tumor cells

Platelets promote metastasis, among others by coating cancer cells traveling through the blood, which results in protection from NK cell immune-surveillance. The underlying mechanisms, however, remain to be fully elucidated. Here we report that platelet-coating reduces surface expression of NKG2D ligands, in particular MICA and MICB, on tumor cells, which was mirrored by enhanced release of their soluble ectodomains. Similar results were obtained upon exposure of tumor cells to platelet-releasate and can be attributed to the sheddases ADAM10 and ADAM17 that are detectable on the platelet surface and in releasate following activation and at higher levels on platelets of patients with metastasized lung cancer compared with healthy controls. Platelet-mediated NKG2DL-shedding in turn resulted in impaired "induced self" recognition by NK cells as revealed by diminished NKG2D-dependent lysis of tumor cells. Our results indicate that platelet-mediated NKG2DL-shedding may be involved in immune-evasion of (metastasizing) tumor cells from NK cell reactivity.

HLA class I-restricted MYD88 L265P-derived peptides as specific targets for lymphoma immunotherapy

Genome sequencing has uncovered an array of recurring somatic mutations in different non-Hodgkin lymphoma (NHL) subtypes. If affecting protein-coding regions, such mutations may yield mutation-derived peptides that may be presented by HLA class I proteins and recognized by cytotoxic T cells. A recurring somatic and oncogenic driver mutation of the Toll-like receptor adaptor protein MYD88, Leu265Pro (L265P) was identified in up to 90% of different NHL subtype patients. We therefore screened the potential of MYD88L265P-derived peptides to elicit cytotoxic T cell responses as tumor-specific neoantigens. Based on in silico predictions, we identified potential MYD88L265P-containing HLA ligands for several HLA class I restrictions. A set of HLA class I MYD88L265P-derived ligands elicited specific cytotoxic T cell responses for HLA-B*07 and -B*15. These data highlight the potential of MYD88L265P mutation-specific peptide-based immunotherapy as a novel personalized treatment approach for patients with MYD88L265P+ NHLs that may complement pharmacological approaches targeting oncogenic MyD88 L265P signaling.

Carfilzomib alters the HLA-presented peptidome of myeloma cells and impairs presentation of peptides with aromatic C-termini

Recent studies suggest that multiple myeloma is an immunogenic disease, which might be effectively targeted by antigen-specific T-cell immunotherapy. As standard of care in myeloma includes proteasome inhibitor therapy, it is of great importance to characterize the effects of this treatment on HLA-restricted antigen presentation and implement only robustly presented targets for immunotherapeutic intervention. Here, we present a study that longitudinally and semi-quantitatively maps the effects of the proteasome inhibitor carfilzomib on HLA-restricted antigen presentation. The relative presentation levels of 4780 different HLA ligands were quantified in an in vitro model employing carfilzomib treatment of MM.1S and U266 myeloma cells, which revealed significant modulation of a substantial fraction of the HLA-presented peptidome. Strikingly, we detected selective down-modulation of HLA ligands with aromatic C-terminal anchor amino acids. This particularly manifested as a marked reduction in the presentation of HLA ligands through the HLA allotypes A*23:01 and A*24:02 on MM.1S cells. These findings implicate that carfilzomib mediates a direct, peptide motif-specific inhibitory effect on HLA ligand processing and presentation. As a substantial proportion of HLA allotypes present peptides with aromatic C-termini, our results may have broad implications for the implementation of antigen-specific treatment approaches in patients undergoing carfilzomib treatment.

Dronabinol has preferential antileukemic activity in acute lymphoblastic and myeloid leukemia with lymphoid differentiation patterns

Background

It has been previously demonstrated in several cancer models, that Dronabinol (THC) may have anti-tumor activity – however, controversial data exists for acute leukemia. We have anecdotal evidence that THC may have contributed to disease control in a patient with acute undifferentiated leukemia.

Methods

To test this hypothesis, we evaluated the antileukemic efficacy of THC in several leukemia cell lines and native leukemia blasts cultured ex vivo. Expression analysis for the CB1/2 receptors was performed by Western immunoblotting and flow cytometry. CB-receptor antagonists as well as a CRISPR double nickase knockdown approach were used to evaluate for receptor specificity of the observed proapoptotic effects.

Results

Meaningful antiproliferative as well as proapoptotic effects were demonstrated in a subset of cases – with a preference of leukemia cells from the lymphatic lineage or acute myeloid leukemia cells expressing lymphatic markers. Induction of apoptosis was mediated via CB1 as well as CB2, and expression of CB receptors was a prerequisite for therapy response in our models. Importantly, we demonstrate that antileukemic concentrations are achievable in vivo.

Conclusion

Our study provides rigorous data to support clinical evaluation of THC as a low-toxic therapy option in a well defined subset of acute leukemia patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-2029-8) contains supplementary material, which is available to authorized users.

Pathogenic fungi regulate immunity by inducing neutrophilic myeloid-derived suppressor cells

Despite continuous contact with fungi, immunocompetent individuals rarely develop pro-inflammatory antifungal immune responses. The underlying tolerogenic mechanisms are incompletely understood. Using both mouse models and human patients, we show that infection with the human pathogenic fungi Aspergillus fumigatus and Candida albicans induces a distinct subset of neutrophilic myeloid-derived suppressor cells (MDSCs), which functionally suppress T and NK cell responses. Mechanistically, pathogenic fungi induce neutrophilic MDSCs through the pattern recognition receptor Dectin-1 and its downstream adaptor protein CARD9. Fungal MDSC induction is further dependent on pathways downstream of Dectin-1 signaling, notably reactive oxygen species (ROS) generation as well as caspase-8 activity and interleukin-1 (IL-1) production. Additionally, exogenous IL-1β induces MDSCs to comparable levels observed during C. albicans infection. Adoptive transfer and survival experiments show that MDSCs are protective during invasive C. albicans infection, but not A. fumigatus infection. These studies define an innate immune mechanism by which pathogenic fungi regulate host defense.

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Pathogenic fungi induce myeloid-derived suppressor cells (MDSCs)

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MDSC induction involves Dectin-1/CARD9, ROS, caspase-8, and IL-1

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MDSCs dampen T and NK cell immune responses

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Adoptive transfer of MDSCs improves survival in Candida infection in vivo

Neutralization of (NK-cell-derived) B-cell activating factor by Belimumab restores sensitivity of chronic lymphoid leukemia cells to direct and Rituximab-induced NK lysis

Natural killer (NK) cells are cytotoxic lymphocytes that substantially contribute to the therapeutic benefit of antitumor antibodies like Rituximab, a crucial component in the treatment of B-cell malignancies. In chronic lymphocytic leukemia (CLL), the ability of NK cells to lyse the malignant cells and to mediate antibody-dependent cellular cytotoxicity upon Fc receptor stimulation is compromised, but the underlying mechanisms are largely unclear. We report here that NK-cells activation-dependently produce the tumor necrosis factor family member 'B-cell activating factor' (BAFF) in soluble form with no detectable surface expression, also in response to Fc receptor triggering by therapeutic CD20-antibodies. BAFF in turn enhanced the metabolic activity of primary CLL cells and impaired direct and Rituximab-induced lysis of CLL cells without affecting NK reactivity per se. The neutralizing BAFF antibody Belimumab, which is approved for treatment of systemic lupus erythematosus, prevented the effects of BAFF on the metabolism of CLL cells and restored their susceptibility to direct and Rituximab-induced NK-cell killing in allogeneic and autologous experimental systems. Our findings unravel the involvement of BAFF in the resistance of CLL cells to NK-cell antitumor immunity and Rituximab treatment and point to a benefit of combinatory approaches employing BAFF-neutralizing drugs in B-cell malignancies.

A "vicious cycle" of NK-cell immune evasion in acute myeloid leukemia mediated by RANKL?

Receptor activator of NFκB ligand (RANKL) is mainly known for its role in bone metabolism, constituting a target for therapeutic interventions. Increasing evidence suggests that RANKL is also involved in oncogenesis and tumor progression, including a prominent role in host-tumor interaction. Our data suggest that targeting RANKL may reinforce natural killer (NK) cell-mediated antitumor responses in patients affected by hematological malignancies.

Mapping the HLA ligandome landscape of acute myeloid leukemia: a targeted approach toward peptide-based immunotherapy

Identification of physiologically relevant peptide vaccine targets calls for the direct analysis of the entirety of naturally presented human leukocyte antigen (HLA) ligands, termed the HLA ligandome. In this study, we implemented this direct approach using immunoprecipitation and mass spectrometry to define acute myeloid leukemia (AML)-associated peptide vaccine targets. Mapping the HLA class I ligandomes of 15 AML patients and 35 healthy controls, more than 25 000 different naturally presented HLA ligands were identified. Target prioritization based on AML exclusivity and high presentation frequency in the AML cohort identified a panel of 132 LiTAAs (ligandome-derived tumor-associated antigens), and 341 corresponding HLA ligands (LiTAPs (ligandome-derived tumor-associated peptides)) represented subset independently in >20% of AML patients. Functional characterization of LiTAPs by interferon-γ ELISPOT (Enzyme-Linked ImmunoSpot) and intracellular cytokine staining confirmed AML-specific CD8(+) T-cell recognition. Of note, our platform identified HLA ligands representing several established AML-associated antigens (e.g. NPM1, MAGED1, PRTN3, MPO, WT1), but found 80% of them to be also represented in healthy control samples. Mapping of HLA class II ligandomes provided additional CD4(+) T-cell epitopes and potentially synergistic embedded HLA ligands, allowing for complementation of a multipeptide vaccine for the immunotherapy of AML.

An Fc-optimized NKG2D-Ig fusion protein for induction of NK cell reactivity against breast cancer

3054

Background: The anti-tumor activity and clinical success of the monoclonal antibody trastuzumab, approved for treatment of HER2/neu-overexpressing breast cancer, is at least partially mediated by induction of antibody dependent cellular cytotoxicity (ADCC). However, only about 20% of patients show HER2/neu overexpression, and trastuzumab treatment is associated with side effects. The ligands of the activating immunoreceptor NKG2D (NKG2DL) are widely expressed on malignant cells, but generally absent on healthy tissue. We aimed to take advantage of this tumor-restricted expression by using NKG2DL as target-antigens on breast cancer cells. To this end we generated NKG2D-Ig fusion proteins with modified Fc moieties and studied their ability to induce NK cell anti-tumor reactivity. Methods: The Fc parts within the constructs were modified by amino acid exchange as previously described (Lazar 2006; Armour 1999). Direct effects on tumor cell viability as well as induction of NK cell activation, degranulation, cytotoxicity and IFN-γ release in cultures with breast cancer cell lines expressing different HER2/neu levels were determined. Results: Compared to NKG2D-Fc containing a wildtype Fc part (NKG2D-Fc-WT) or trastuzumab, our mutants (S239D/I332E and E233P/L234V/L235A/ΔG236/A327G/A330S) displayed highly enhanced (NKG2D-Fc-ADCC) and abrogated (NKG2D-Fc-KO) affinity to the NK cell Fc receptor, respectively. In contrast to trastuzumab, no direct effect of the constructs on tumor cell viability was observed. In cultures of NK cells and breast cancer cells, NKG2D-Fc-KO significantly reduced NK reactivity due to blocking immunostimulatory NKG2D-NKG2DL interaction. NKG2D-Fc-WT substantially enhanced NK reactivity by induction of ADCC, while the effects of NKG2D-Fc-ADCC by far exceeded that of NKG2D-Fc-WT and, in case of HER2/neu-low targets also that of Herceptin. Conclusions: Fc-engineered NKG2D-Ig fusion protein effectively target breast cancer cells for NK anti-tumor reactivity. Due to the tumor-restricted expression of NKG2DL, NKG2D-Fc-ADCC may constitute an attractive means for immunotherapy especially of HER2/neu-low or -negative breast cancer.

Generation and preclinical characterization of a Fc-optimized GITR-Ig fusion protein for induction of NK cell reactivity against leukemia

Natural killer (NK) cells are cytotoxic lymphocytes that largely contribute to the efficacy of therapeutic strategies like allogenic stem cell transplantation in acute myeloid leukemia (AML) and application of Rituximab in chronic lymphocytic leukemia (CLL). The tumor necrosis factor (TNF) family member GITR ligand (GITRL) is frequently expressed on leukemia cells in AML and CLL and impairs the reactivity of NK cells which express GITR and upregulate its expression following activation. We developed a strategy to reinforce NK anti-leukemia reactivity by combining disruption of GITR-GITRL interaction with targeting leukemia cells for NK antibody-dependent cellular cytotoxicity (ADCC) using GITR-Ig fusion proteins with modified Fc moieties. Neutralization of leukemia-expressed GITRL by the GITR domain enhanced cytotoxicity and cytokine production of NK cells depending on activation state with NK reactivity being further largely dependent on the engineered affinity of the fusion proteins to the Fc receptor. Compared with wild-type GITR-Ig, treatment of primary AML and CLL cells with mutants containing a S239D/I332E modification potently increased cytotoxicity, degranulation, and cytokine production of NK cells in a target-antigen-dependent manner with additive effects being observed with CLL cells upon parallel exposure to Rituximab. Fc-optimized GITR-Ig may thus constitute an attractive means for immunotherapy of leukemia that warrants clinical evaluation.

Alterations of the RANKL pathway in blood and bone marrow samples of prostate cancer patients without bone metastases

OBJECTIVES

The receptor activator of the NF-kB ligand (RANKL) pathway is a key mediator of prostate cancer (PC)-induced bone disease. However, little is known about this pathway in patients with non-metastatic PC. We aimed to investigate whether changes of RANKL, its inhibitor osteoprotegerin (OPG) and bone marrow-mesenchymal stromal cells (BM-MSCs) occur in PC patients without manifest bone metastases.

PATIENTS AND METHODS

We determined OPG and soluble RANKL (sRANKL) in serum and corresponding bone marrow (BM) samples of 140 patients before radical prostatectomy by enzyme-linked immunosorbent assay (ELISA). As control serum samples of 50 patients with benign prostate hyperplasia were analyzed. BM mononuclear cells (BMNCs) of 16 PC patients were analyzed for expression of RANKL and CD271 (as marker for MSCs) by flow cytometry.

RESULTS

PC patients had significantly lower serum levels of OPG compared to BPH patients (P = 0.007), whereas no differences were observed for serum sRANKL (P = 0.74). Both OPG and sRANKL concentrations of serum and corresponding BM samples correlated significantly (P < 0.0001 each). Interestingly, in PC patients, lower serum and BM OPG levels were associated with a higher proportion of BM-MSCs (P = 0.04 and 0.0016, respectively). No correlations were observed for sRANKL, OPG, BM-MSCs, and established risk parameters of PC.

DISCUSSION

The results of the study indicate that localized PC is associated with early specific changes of the RANKL pathway in serum and bone marrow (BM). These changes might be part of the pre-metastatic niche of PC and implicate a potential benefit of RANKL inhibition in patients with localized PC.

Receptor activator for NF-κB ligand in acute myeloid leukemia: expression, function, and modulation of NK cell immunosurveillance

The TNF family member receptor activator for NF-κB ligand (RANKL) and its receptors RANK and osteoprotegerin are key regulators of bone remodeling but also influence cellular functions of tumor and immune effector cells. In this work, we studied the involvement of RANK-RANKL interaction in NK cell-mediated immunosurveillance of acute myeloid leukemia (AML). Substantial levels of RANKL were found to be expressed on leukemia cells in 53 of 78 (68%) investigated patients. Signaling via RANKL into the leukemia cells stimulated their metabolic activity and induced the release of cytokines involved in AML pathophysiology. In addition, the immunomodulatory factors released by AML cells upon RANKL signaling impaired the anti-leukemia reactivity of NK cells and induced RANK expression, and NK cells of AML patients displayed significantly upregulated RANK expression compared with healthy controls. Treatment of AML cells with the clinically available RANKL Ab Denosumab resulted in enhanced NK cell anti-leukemia reactivity. This was due to both blockade of the release of NK-inhibitory factors by AML cells and prevention of RANK signaling into NK cells. The latter was found to directly impair NK anti-leukemia reactivity with a more pronounced effect on IFN-γ production compared with cytotoxicity. Together, our data unravel a previously unknown function of the RANK-RANKL molecule system in AML pathophysiology as well as NK cell function and suggest that neutralization of RANKL with therapeutic Abs may serve to reinforce NK cell reactivity in leukemia patients.

RANKL expression, function, and therapeutic targeting in multiple myeloma and chronic lymphocytic leukemia

Bone destruction is a prominent feature of multiple myeloma, but conflicting data exist on the expression and pathophysiologic involvement of the bone remodeling ligand RANKL in this disease and the potential therapeutic benefits of its targeted inhibition. Here, we show that RANKL is expressed by primary multiple myeloma and chronic lymphocytic leukemia (CLL) cells, whereas release of soluble RANKL was observed exclusively with multiple myeloma cells and was strongly influenced by posttranscriptional/posttranslational regulation. Signaling via RANKL into multiple myeloma and CLL cells induced release of cytokines involved in disease pathophysiology. Both the effects of RANKL on osteoclastogenesis and cytokine production by malignant cells could be blocked by disruption of RANK-RANKL interaction with denosumab. As we aimed to combine neutralization of RANKL with induction of antibody-dependent cellular cytotoxicity of natural killer (NK) cells against RANKL-expressing malignant cells and as denosumab does not stimulate NK reactivity, we generated RANK-Fc fusion proteins with modified Fc moieties. The latter displayed similar capacity compared with denosumab to neutralize the effects of RANKL on osteoclastogenesis in vitro, but also potently stimulated NK cell reactivity against primary RANKL-expressing malignant B cells, which was dependent on their engineered affinity to CD16. Our findings introduce Fc-optimized RANK-Ig fusion proteins as attractive tools to neutralize the detrimental function of RANKL while at the same time potently stimulating NK cell antitumor immunity.

Comprehensive analysis of NKG2D ligand expression and release in leukemia: implications for NKG2D-mediated NK cell responses

Ligands of the prototypical activating NK receptor NKG2D render cancer cells susceptible to NK cell-mediated cytolysis if expressed at sufficiently high levels. However, malignant cells employ mechanisms to evade NKG2D-mediated immunosurveillance, such as NKG2D ligand (NKG2DL) shedding resulting in reduced surface expression levels. In addition, systemic downregulation of NKG2D on NK cells of cancer patients has been observed in many studies and was attributed to soluble NKG2DL (sNKG2DL), although there also are conflicting data. Likewise, relevant expression of NKG2DL in leukemia has been reported by some, but not all studies. Hence, we comprehensively studied expression, release, and function of the NKG2D ligands MHC class I chain-related molecules A and B and UL16-binding proteins 1-3 in 205 leukemia patients. Leukemia cells of most patients (75%) expressed at least one NKG2DL at the surface, and all investigated patient sera contained elevated sNKG2DL levels. Besides correlating NKG2DL levels with clinical data and outcome, we demonstrate that sNKG2DL in patient sera reduce NKG2D expression on NK cells, resulting in impaired antileukemia reactivity, which also critically depends on number and levels of surface-expressed NKG2DL. Together, we provide comprehensive data on the relevance of NKG2D/NKG2DL expression, release, and function for NK reactivity in leukemia, which exemplifies the mechanisms underlying NKG2D-mediated tumor immunosurveillance and escape.

High activity of sorafenib in FLT3-ITD-positive acute myeloid leukemia synergizes with allo-immune effects to induce sustained responses

Preliminary evidence suggests that the multikinase inhibitor sorafenib has clinical activity in FLT3-ITD-positive (FLT3-ITD) acute myeloid leukemia (AML). However, the quality and sustainability of achievable remissions and clinical variables that influence the outcome of sorafenib monotherapy are largely undefined. To address these questions, we evaluated sorafenib monotherapy in 65 FLT3-ITD AML patients treated at 23 centers. All but two patients had relapsed or were chemotherapy-refractory after a median of three prior chemotherapy cycles. Twenty-nine patients (45%) had undergone prior allogeneic stem cell transplantation (allo-SCT). The documented best responses were: hematological remission in 24 patients (37%), bone marrow remission in 5 patients (8%), complete remission (with and without normalization of peripheral blood counts) in 15 patients (23%) and molecular remission with undetectable FLT3-ITD mRNA in 10 patients (15%), respectively. Seventeen of the patients without prior allo-SCT (47%) developed sorafenib resistance after a median treatment duration of 136 days (range, 56-270 days). In contrast, allo-SCT patients developed sorafenib resistance less frequently (38%) and significantly later (197 days, range 38-225 days; P=0.03). Sustained remissions were seen exclusively in the allo-SCT cohort. Thus, sorafenib monotherapy has significant activity in FLT3-ITD AML and may synergize with allogeneic immune effects to induce durable remissions.

Generation, selection and preclinical characterization of an Fc-optimized FLT3 antibody for the treatment of myeloid leukemia

The therapeutic efficacy of humanized or chimeric second-generation antitumor antibodies is clearly established, but often limited. In recent years, defined modifications of the glycosylation pattern or the amino-acid sequence of the human immunoglobulin G1 Fc part have resulted in the development of third-generation antibodies with improved capability to recruit Fc receptor-bearing effector cells. The first antibodies of this kind, currently evaluated in early clinical trials, are directed against lymphoma-associated antigens. Fc-engineered antibodies targeting myeloid leukemia are not yet available. We here report on the generation and preclinical characterization of an Fc-optimized antibody directed to the FMS-related tyrosine kinase 3 (FLT3), an antigen expressed on the leukemic blasts of all investigated patients with acute myeloid leukemia (AML). This antibody, termed 4G8SDIEM, mediated markedly enhanced cellular cytotoxicity against FLT3-expressing cell lines as well as blasts of AML patients. FLT3 expression levels on AML cells varied between 300 and 4600 molecules/cell and, in most cases, were substantially higher than those detected on normal hematopoietic precursor cells and dendritic cells (approximately 300 molecules/cell). Antibody-mediated cytotoxicity against these normal cells was not detectable. 4G8SDIEM has been produced in pharmaceutical quality in a university-owned production unit and is currently used for the treatment of leukemia patients.

Platelet-derived MHC class I confers a pseudonormal phenotype to cancer cells that subverts the antitumor reactivity of natural killer immune cells

Natural killer (NK) cells are cytotoxic lymphocytes that play an important role in tumor immunosurveillance, preferentially eliminating targets with low or absent expression of MHC class I and stress-induced expression of ligands for activating NK receptors. Platelets promote metastasis by protecting disseminating tumor cells from NK cell immunosurveillance, but the underlying mechanisms are not well understood. In this study, we show that tumor cells rapidly get coated in the presence of platelets in vitro, and circulating tumor cells of cancer patients display coexpression of platelet markers. Flow cytometry, immunofluorescent staining, confocal microscopy, and analyses on an ultrastructural level using immunoelectron microscopy revealed that such coating may cause transfer of MHC class I onto the tumor cell surface resulting in high-level expression of platelet-derived normal MHC class I. The resulting "phenotype of false pretenses" disrupts recognition of tumor cell missing self, thereby impairing cytotoxicity and IFN-γ production by NK cells. Thus, our data indicate that platelets, by conferring an unsuspicious "pseudonormal" phenotype, may enable a molecular mimicry that allows metastasizing tumor cells to downregulate MHC class I, to escape T-cell-mediated immunity without inducing susceptibility to NK cell reactivity.

Glucocorticoid-induced TNFR-related protein (GITR) ligand modulates cytokine release and NK cell reactivity in chronic lymphocytic leukemia (CLL)

Natural killer (NK) cells play an important role in the immunosurveillance of hematopoietic malignancies. Their reactivity is influenced by activating and inhibitory signals mediated by tumor-expressed ligands for NK receptors. Many members of the tumor necrosis factor (TNF) family modulate differentiation, proliferation, activation and death of both tumor and immune effector cells. The TNF receptor family member glucocorticoid-induced TNFR-related protein (GITR) stimulates anti-tumor immunity in mice, but available data indicate that GITR may mediate different effects in mice and men and impairs the reactivity of human NK cells. Here, we comprehensively studied the expression and function of GITR ligand (GITRL) in leukemia. Among the different leukemia entities, pronounced expression of GITRL on leukemic cells was observed in chronic lymphocytic leukemia (CLL), and the GITR receptor was expressed at significantly higher levels on NK cells of CLL patients compared with healthy controls. Upon GITR-GITRL interaction, signaling via GITRL into the leukemia cells induced the release of interleukin (IL)-6, IL-8 and TNF, which act as growth and survival factors for CLL cells. In addition, GITRL impaired both direct and Rituximab-induced degranulation, cytotoxicity and interferon-γ production of NK cells, which could be restored by GITR blocking antibodies. Thus, GITRL may contribute to disease pathophysiology and resistance to direct and Rituximab-induced NK reactivity in CLL.

Modulation of natural killer cell anti-tumor reactivity by platelets

Natural killer (NK) cells may prevent tumor progression and metastasis. Apart from the direct interaction with their targets, NK cell activity is influenced by the reciprocal interplay with other hematopoietic cells. While the interaction of NK cells e.g. with dendritic cells or monocytes/macrophages is well characterized, knowledge regarding their crosstalk with platelets, another central component of the blood, is still fragmentary. However, studies in mice and men clearly document a strong dependence of tumor progression and metastasis on quantitatively and functionally normal platelets. In mice, metastasis is inhibited by thrombocytopenia, and this effect is reversed by additional NK cell depletion, indicating that platelets may 'indirectly' contribute to tumor dissemination by impairing NK cell anti-tumor reactivity. In humans, circumstantial evidence indicates that metastasizing malignant cells do not travel through the blood alone, but efficiently attract and get coated by platelets, thereby causing release of platelet granule content. Beyond this secretion of various growth factors and cytokines/chemokines, platelets may also influence NK cell function by immunoregulatory molecules expressed on the platelet surface. Here, we review the available data regarding tumor-platelet-NK cell interaction focusing on metastatic tumor spread and discuss the molecular mechanisms underlying this trilateral crosstalk.

The BCR/ABL-inhibitors imatinib, nilotinib and dasatinib differentially affect NK cell reactivity

In chronic myeloid leukemia (CML), BCR/ABL-mediated oncogenic signaling can be targeted with the BCR/ABL-inhibitors Imatinib, Nilotinib and Dasatinib. However, these agents may also affect anti-tumor immunity. Here, we analyzed the effects of the 3 BCR/ABL-inhibitors on natural killer (NK) cell reactivity. Exposure of CML cells (K562, Meg-01) to pharmacological concentrations of Imatinib, Nilotinib and Dasatinib diminished expression of ligands for the activating immunoreceptor NKG2D to a similar extent. This resulted in comparably reduced NK cell cytotoxicity and IFN-gamma production. When direct effects on NK cell responses to K562 and primary CML cells as well as activating cytokines were studied, Dasatinib was found to abrogate NK cytotoxicity and cytokine production. Nilotinib did not alter cytotoxicity but, at high levels, impaired NK cytokine production, while Imatinib had no direct influence on NK cell reactivity. Of note, Nilotinib, but not the other BCR/ABL-inhibitors increased cell death within the preferentially cytokine-secreting CD56(bright)CD16(-) NK cell subset, which may, at least in part, serve to explain the effect of Nilotinib on NK cytokine production. Analysis of NK cell signaling revealed that Dasatinib inhibited proximal signaling events leading to decreased phosphorylation of PI3K and ERK that are crucial for NK cell reactivity. Imatinib and Nilotinib, in contrast, showed no relevant effect on NK cell PI3K or ERK activity. In light of the potential role of NK cells in the immunesurveillance of residual leukemia and for future combinatory immunotherapeutic approaches, our data indicate that choice and dosing of the most suitable BCR/ABL-inhibitor for a given patient require careful consideration.

Platelet-derived transforming growth factor-beta down-regulates NKG2D thereby inhibiting natural killer cell antitumor reactivity

Natural killer (NK) cells play an important role in cancer immunosurveillance and may prevent tumor progression and metastasis due to their ability to mediate direct cellular cytotoxicity and by releasing immunoregulatory cytokines, which shape adaptive immune responses. Their reactivity is governed by various activating and inhibitory molecules expressed on target cells and reciprocal interactions with other hematopoietic cells such as dendritic cells. In mice, thrombocytopenia inhibits metastasis, and this is reversed by NK cell depletion, suggesting that platelets are an important additional player in NK cell-tumor interaction. Moreover, it has been shown that metastasizing tumor cells do not travel through the blood alone but are rapidly coated by platelets. However, the knowledge about the molecular mechanisms by which platelets influence NK cells is fragmentary at best. Here we show that platelet-derived soluble factors, secreted on coating of tumor cells or after stimulation with classic platelet agonists, impair NK cell antitumor reactivity resulting in diminished granule mobilization, cytotoxicity, and IFN-gamma production. The impaired NK cell reactivity was not due to induction of apoptosis but mediated by down-regulation of the activating immunoreceptor natural killer group 2, member D (NKG2D) on NK cells by platelet-derived transforming growth factor beta (TGF-beta). Neutralization of TGF-beta in platelet releasate not only prevented NKG2D down-regulation but also restored NK cell antitumor reactivity. Thus, our data elucidate the molecular basis of the previously described influence of platelets on NK cell antitumor reactivity and suggest that therapeutic intervention in tumor cell-platelet interaction and the resulting TGF-beta release by platelets may serve to enhance antitumor immunity.

The role of soluble and cell-surface expressed 4-1BB ligand in patients with malignant hemopoietic disorders

The TNFR family member 4-1BB and its ligand 4-1BBL are involved in the costimulation of T-cells and tumor-derived soluble (s)4-1BBL may influence the interaction of malignant cells with the immune system. Here, we report that cell-surface-expressed (c)4-1BBL can be expressed on mononuclear blood cells from patients with acute myeloid leukemia (AML) (n = 35), myelodysplasia (n = 5) or non-Hodgkin lymphoma (n = 11) and can be coexpressed on varying proportions of lymphoid or myeloid malignant cells and on dendritic cells differentiated from AML-blasts. Direct correlations between c- and s4-1BBL were not found in the investigated cases. Up to now expression of 4-1BBL has not been described on primary myeloid malignant cells, but only on malignant cells of lymphoid or solid tumor origin or on tumor cell lines. With our work we further contribute to the understanding of the potential role of c/s4-1BBL in immune reactions and its influence on the interaction of tumor and immunoreactive cells.

Glucocorticoid-induced tumor necrosis factor receptor-related protein ligand subverts immunosurveillance of acute myeloid leukemia in humans

The reciprocal interaction of tumor cells with the immune system is influenced by various members of the tumor necrosis factor (TNF)/TNF receptor (TNFR) family, and recently, glucocorticoid-induced TNFR-related protein (GITR) was shown to stimulate antitumor immunity in mice. However, GITR may mediate different effects in mice and men and impairs the reactivity of human natural killer (NK) cells. Here, we studied the role of GITR and its ligand (GITRL) in human acute myeloid leukemia (AML). Surface expression of GITRL was observed on AML cells in six of seven investigated cell lines, and 34 of 60 investigated AML patients whereas healthy CD34(+) cells did not express GITRL. Furthermore, soluble GITRL (sGITRL) was detectable in AML patient sera in 18 of 55 investigated cases. While the presence of GITRL was not restricted to a specific AML subtype, surface expression was significantly associated with monocytic differentiation. Signaling via GITRL into patient AML cells induced the release of TNF and interleukin-10 (IL-10), and this was blocked by the inhibition of mitogen-activated protein kinases extracellular signal-regulated kinase 1/2. Furthermore, triggering GITR by surface-expressed and sGITRL impaired NK cell cytotoxicity and IFN-gamma production in cocultures with leukemia cells, and NK cell reactivity could be restored by blocking GITR and neutralization of sGITRL and IL-10. Thus, whereas a stimulatory role of the GITR-GITRL system in mouse antitumor immunity has been reported, our data show that in humans GITRL expression subverts NK cell immunosurveillance of AML. Our results provide useful information for therapeutic approaches in AML, which, like haploidentical stem cell transplantation, rely on a sufficient NK cell response.

Soluble NKG2D ligands: prevalence, release, and functional impact

Natural Killer (NK) cells are capable to recognize and eliminate malignant cells. Anti-tumor responses of NK cells are promoted by the tumor-associated expression of cell stress-inducible ligands of the activating NK receptor NKG2D. Current evidence suggests that established tumors subvert NKG2D-mediated tumor immunosurveillance by releasing NKG2D ligands (NKG2DL). Release of NKG2DL has been observed in a broad variety of human tumor entities and is thought to interfere with NKG2D-mediated tumor immunity in several ways. Further, levels of soluble NKG2DL (sNKG2DL) were also found to be elevated under various non-malignant conditions, although the functional implications remain largely unclear. Here we review and discuss the available data on the prevalence, release, functional impact, and potential clinical value of sNKG2DL.

Soluble NKG2D ligands in hepatic autoimmune diseases and in benign diseases involved in marker metabolism

BACKGROUND

Proteolytic shedding of the immunostimulatory NKG2D ligands MICA and MICB from cancer cells constitutes a novel immune escape strategy that diminishes antitumor reactivity by NKG2D-bearing cytotoxic lymphocytes. In consequence, serum levels of soluble MICA and MICB are frequently found to be elevated in cancer disease.

PATIENTS AND METHODS

As the diagnostic potential depends strongly on the organ-specific benign diseases and is affected by diseases involved in marker metabolism, both markers were analyzed by ELISA in sera of 141 patients with hepatic autoimmune diseases (34 autoimmune hepatitis, 35 primary sclerosing cholangitis, 72 primary biliary cirrhosis), 18 patients with acute bacterial infections, 21 patients with renal insufficiency, 13 patients with cholestasis and 62 healthy individuals.

RESULTS

Similarly to healthy controls (median sMICA < 30 pg/mL; sMICB < 30 pg/mL), low levels of both markers were generally found in sera of patients with hepatic autoimmune diseases. In contrast, significantly elevated concentrations of sMICA and sMICB were observed in sera of patients with acute infections (median sMICA 890 pg/mL; sMICB 111 pg/mL), in those with renal insufficiency (sMICA 195 pg/mL; sMICB 50 pg/mL), and in those with cholestasis (sMICA 1058 pg/mL; sMICB 146 pg/mL).

CONCLUSION

While hepatic autoimmune diseases have no general impact on the amount of circulating sMICA and sMICB, acute bacterial infections, renal insufficiency and cholestasis can lead to notably elevated serum levels of the NKG2D ligands.

Soluble MICB in malignant diseases: analysis of diagnostic significance and correlation with soluble MICA

Expression of ligands of the immunoreceptor NKG2D such as MICA and MICB has been proposed to play an important role in the immunosurveillance of tumors. Proteolytic shedding of NKG2D ligands from cancer cells therefore constitutes an immune escape mechanism impairing anti-tumor reactivity by NKG2D-bearing cytotoxic lymphocytes. Serum levels of sMICA have been shown to be of diagnostic significance in malignant diseases of various origins. Here, we investigated the potential of soluble MICB, the sister molecule of MICA, as a marker in cancer and its correlation with soluble MICA. Analysis of MICB in sera of 512 individuals revealed slightly higher MICB levels in patients with various malignancies (N = 296; 95th percentile 216 pg/ml; P = 0.069) than in healthy individuals (N = 62; 95th percentile 51 pg/ml). Patients with benign diseases (N = 154; 95th percentile 198 pg/ml) exhibited intermediate MICB levels. In cancer patients, elevated MICB levels correlated significantly with cancer stage and metastasis (P = 0.007 and 0.007, respectively). Between MICB and MICA levels, only a weak correlation was found (r = 0.24). Combination of both markers resulted only in a slightly higher diagnostic power in the high specificity range. The reduction of MICA and MICB surface expression on cells by shedding and the effects of sMICA and sMICB in serum on host lymphocyte NKG2D expression might play a role in late stages of tumor progression by overcoming the confining effect of NK cells and CD8 T cells. While MICB levels are not suited for the diagnosis of cancer in early stages, they may provide additional information for the staging of cancer disease.

The role of leukemia-derived B7-H1 (PD-L1) in tumor–T-cell interactions in humans

OBJECTIVE

Expression of the B7 homolog B7-H1 (PD1-Ligand) has been proposed to enable tumor cells to evade immune surveillance. Recently, B7-H1 on murine leukemia cells was reported to mediate resistance to cytolytic T-cell destruction. We here investigate the expression and function of the B7 homolog B7-H1 in human leukemia.

PATIENTS AND METHODS

Leukemia cells from 30 patients and 9 human leukemia cell lines were investigated for B7-H1 expression by flow cytometry. Functional relevance of B7-H1 for tumor-immune interactions was assessed by coculture experiments using purified, alloreactive CD4 and CD8 T cells in the presence of a neutralizing anti-B7-H1 antibody.

RESULTS

Significant B7-H1 expression levels on leukemia cells were detected in 17 of 30 patients and in eight of nine cell lines. In contrast to various other tumor entities and the data reported from a murine leukemia system, no significant inhibitory effect of leukemia-derived B7-H1 on CD4 and CD8 cytokine production (IFN-gamma, IL-2), proliferation or expression of T-cell activation markers (ICOS, CD69) was observed. Furthermore, in the presence of neutralizing B7-H1 antibody (mAb 5H1) occurred no significant changes in T cell IFN-gamma or IL-2 production or proliferation.

CONCLUSIONS

Our data demonstrate that leukemia-derived B7-H1 seems to have no direct influence on T-cell activation, proliferation, and cytokine production in humans. Further experiments are warranted to delineate factors and characterize yet-unidentified B7-H1 receptor(s) that determine inhibitory and stimulatory functions of B7-H1 in human leukemia.

Serum levels of sCD137 (4-1BB) ligand are prognostic factors for progression in acute myeloid leukemia but not in non-Hodgkin's lymphoma

CD178 (Fas/APO-1 ligand) and CD137 ligand (CD137L) have previously been described in sera of patients with various malignancies and play an important role in the pathogenesis of various diseases. Recently, we demonstrated that low levels of soluble (s) CD137L and high levels of sCD178 correlate significantly with a long progression free survival in patients with myelodysplastic syndrome (MDS). In this study, we correlated sCD137L and sCD178 levels in sera of 42 samples of patients with acute myeloid leukemia (AML) and 46 samples of patients with non-Hodgkin's lymphoma (NHL) with stages, subtypes, and the clinical course of the diseases and determined cut-off values with maximum probability for significant differentiation between cases with higher/lower probability for progress free survival. In contrast to patients with MDS, surprisingly no correlation between sCD178 levels and different subtypes and stages or with prognosis in AML or NHL were observed. Regarding sCD137L, NHL-patients displayed lower levels compared with AML. Statistically significant higher median levels of sCD137L are present in patients with undifferentiated AML (M1/M2, 1,470 pg/mL), poor cytogenetic risk (288 pg/mL) and higher levels of BM-blasts (186 pg/mL) compared with patients with monocytoid AML (M4/M5, 89 pg/mL), intermediate cytogenetic risk (59 pg/mL) and lower levels of BM-blasts (14 pg/mL) respectively. Furthermore, in AML patients sCD137L levels correlate significantly with the probabilities to achieve complete remission (CR), stay in CR or with progress of the disease. Taken together, our data demonstrate that sCD137L can be used as a prognostic factor not only in MDS but also in AML.

Release of MICB molecules by tumor cells: mechanism and soluble MICB in sera of cancer patients

MICA, a ligand of the activating immunoreceptor NKG2D, is released by tumor cells in a soluble form and can be detected in sera of tumor patients at significant levels. Soluble MICA has been proposed to counteract NKG2D-mediated immunosurveillance of tumors. Here, we report that MICB, the second member of the human MIC protein family, is likewise shed by metalloproteases from tumor cells and is present in sera of patients with gastrointestinal tumors. While cell-bound MICB causes downregulation of surface NKG2D, soluble MICB did not alter NKG2D expression on NK cells in vitro. Thus, proteolytic shedding of MICB by tumor cells may impair immunogenicity of tumors primarily by reducing NKG2D-ligand densities on malignant cells.

Soluble MICA in malignant diseases

The immunoreceptor NKG2D activates natural killer cells and costimulates CD8 T cells. The MHC class I-related MICA molecules are ligands of NKG2D and are expressed on malignant, but not on normal, cells. As NKG2D plays an important role in the immunosurveillance of tumors, studies suggest that release of MICA from cancer cells constitutes an immune escape mechanism that systemically impairs antitumor immunity. Here, we investigated the potential of soluble MICA (sMICA) as a marker in cancer. Analysis of sMICA in sera of 512 individuals revealed significantly (p < 0.0001) higher levels in patients with various malignancies (n = 296, median 161 pg/ml) than in healthy individuals (n = 62, median <30 pg/ml). Patients with benign diseases (n = 154, median 84 pg/ml) exhibited intermediate sMICA levels. In cancer patients, elevated sMICA levels correlated significantly with cancer stage and metastasis (p = 0.015 and p = 0.007, respectively). While release of MICA is thought to impair tumor immunity, determination of sMICA levels may provide useful additional information in the diagnosis and staging of cancer.

[Neuro-endocrine tumors of the gastrointestinal tract: epidemiology, classification, prognosis, diagnosis and therapeutic modalities]

The neuro-endocrine tumors of the gastrointestinal tract comprise a heterogeneous group of slow-growing malignancies with great differences regarding their localization, tissue of origin and their entopic and ectopic production of hormones. They can be subdivided in carcinoid tumors and endocrine tumors of the pancreas. According to their secreted products they manifest as endocrinological syndromes or as local space-occupying tumors. This review focuses, besides summarizing the available epidemiological data and describing tumor localization and classification, on the differing symptom complexes and the prognosis of the various tumor entities. Furthermore, the value of available diagnostic techniques and the role of different therapeutic modalities like surgery, radiation, biotherapy and cytostatic chemotherapy are discussed.

Functional expression and release of ligands for the activating immunoreceptor NKG2D in leukemia

NKG2D ligands (NKG2DLs) mark malignant cells for recognition by natural killer (NK) cells and cytotoxic T lymphocytes via the activating immunoreceptor NKG2D. This led to the hypothesis that NKG2DLs play a critical role in tumor immune surveillance. The human NKG2DLs MICA and MICB are expressed on tumors of epithelial origin in vivo. For the other recently described set of human NKG2DLs, the UL16-binding proteins (ULBPs), expression in vivo is as yet undefined. In this study we investigated expression and function of NKG2DLs in leukemia using a panel of newly generated NKG2DL-specific monoclonal antibodies. We report that leukemia cells from patients variously express MIC and ULBP molecules on the cell surface with MICA most frequently detected. Patient leukemia cells expressing MICA were lysed by NK cells in an NKG2D-dependent fashion. Sera of patients, but not of healthy donors, contained elevated levels of soluble MICA (sMICA). We also detected increased sMICB levels in patient sera using a newly established MICB-specific enzyme-linked immunosorbent assay. Reduction of leukemia MIC surface expression by shedding may impair NKG2D-mediated immune surveillance of leukemias. In addition, determination of sMICA and sMICB levels may be implemented as a prognostic parameter in patients with hematopoietic malignancies.

4-1 BB ligand--just another costimulating molecule?

Initially, scientific interest in the 4-1BB/4-1BB Ligand system focused on the role of the 4-1BB (CD137) receptor in the costimulation of T cells. More recently, evidence is accumulating that 4-1BBL is more than "just" the ligand for a costimulatory molecule. In this review we discuss the functional properties of 4-1BB Ligand such as its preference for CD8 positive T cells and the differences to costimulation via the B7/CD28 system. Furthermore, the available data regarding its ability to transduce signals bidirectionally, i.e. also back into the ligand bearing cell, its release as a soluble form following shedding from the cell surface, and its role in the interaction of tumor cells with the immune system are reviewed.

Retinoic acid and vitamin E modulate expression and release of CD178 in carcinoma cells: consequences for induction of apoptosis in CD95-sensitive cells

CD178 (CD95-ligand) is expressed on several tumor cells and likely influences the interaction of the tumor with the host immune system. However, little is known about the mechanisms that regulate its expression on the cell surface. We have evaluated the ability of various compounds and cytokines to regulate cell surface expression and release of soluble CD178 in various carcinoma cell lines. Vitamin E succinate (VES) and retinoic acid (RA) were found to reduce CD178 surface expression, whereas interferon-gamma stimulated a slight upregulation. At 48 h, the regulation of surface CD178 by VES and RA arose from a small decrease in CD178 mRNA and to a greater extent due to an increase in the release of soluble CD178; the latter was blocked by addition of a metalloproteinase inhibitor. Accordingly, VES and RA treatment diminished the ability of tumor cells to kill CD95-sensitive cells and this effect was markedly reduced by the presence of a metalloproteinase inhibitor. Our results indicate that, in vitro, CD178 expression on the cell surface of tumor cells can be regulated by agents that alter both expression and release of the ligand. In vivo, such treatments may play an important role in the outcome of tumor sensitivity or resistance to host immune mechanisms.

Soluble CD137 (4-1BB) ligand is released following leukocyte activation and is found in sera of patients with hematological malignancies

Expression of CD137 ligand (4-1BBL), a member of the TNF family of proteins, has been reported on several types of APCs, various carcinoma cells, and can be induced on activated T cells. In this study, we report that the soluble ligand was released constitutively at low levels from leukocytes and at higher levels following cellular activation. Release from cells was blocked by addition of a metalloproteinase inhibitor which concomitantly caused the accumulation of 4-1BBL on the cell surface. In addition, we show that a soluble form of 4-1BBL was present at high levels in the sera of some patients with various hematological diseases, but only at low levels in healthy donors. Soluble 4-1BBL was active in that it competed with recombinant 4-1BBL for binding to the 4-1BB receptor and was able to costimulate IL-2 and IFN-gamma release from peripheral T cells. These results indicate that the release of soluble 4-1BBL from the cell surface is mediated by one or more sheddases and likely regulates 4-1BB-4-1BBL interactions between cells in vivo. Cleavage of 4-1BBL to an active soluble form would alter both proximal and distal cellular responses, including cell survival and costimulatory or inflammatory responses, that are mediated through the 4-1BB pathway. This, in turn, would likely alter disease progression or outcome.

Commentary: Immune escape versus tumor tolerance: how do tumors evade immune surveillance?

Despite an increasing understanding of immunological mechanisms it is still not clear how tumors evade immune-surveillance of the host and how tumors interact with the immune-system. In particular, the question whether tumors arise because of an insufficient immune response or whether tumor cells employ active strategies to escape the control of the immune system is still open. Data from a great number of in vitro studies and animal models offer arguments for both the theory of an immune escape as well as that of tumor tolerance. In this article the available results regarding the mechanisms of host-tumor-interaction are discussed with focus on these two contrary hypotheses.