ALBERT

Description: NK cells play an important role in the reciprocal interaction of tumor cells with the immune system and participate in the surveillance of hematological malignancies including acute myeloid leukemia (AML). Among the molecules influencing host-tumor interaction are many members of the TNF superfamily, which mediate multiple cellular functions including cellular proliferation, differentiation and cell death. The TNF family member Glucocorticoid-induced TNF Receptor (GITR) costimulates effector T cells, modulates apoptosis and nuclear factor kappa B and abrogates suppression of murine but not human regulatory T cells. Its cognate ligand GITRL has been found in various healthy tissues. Recently we reported that NK cells express GITR, while solid tumors express GITR ligand (GITRL), and GITR/GITRL interaction downregulates NK cell cytotoxicity and IFN-γ production. Here we analyzed the role of GITR and its ligand in AML. We report for the first time that GITRL is expressed on primary AML cells in 18 of 30 patients as determined by FACS and RT-PCR analysis. Reverse signaling through GITRL using a recombinant GITR-Ig fusion protein induces the release of the immunoregulatory cytokines IL-10 and TNF as determined by ELISA. GITRL-mediated cytokine production of AML cells is abrogated by inhibition of mitogen activated protein kinase (MAPK) pathways as demonstrated by addition of the specific p38 MAPK inhibitor SB202190, the specific JNK inhibitor SP600125 and the specific ERK Inhibitor II. Furthermore, binding of AML-expressed GITRL to GITR on NK cells downregulates cellular cytotoxicity and IFN-γ production in AML-NK cell cocultures, which can be overcome by addition of GITR-blocking antibodies as determined by cytotoxicity assays and ELISA. Thus, our data indicate that GITRL expression in AML substantially influences tumor immunoediting and enables the escape of leukemia cells from NK cell-mediated immunosurveillance.

Description: Macrophages are involved in inflammatory and anti-tumor responses by antigen presentation, release of immunoregulatory cytokines and cellular cytotoxicity. Among the molecules influencing macrophage functions are many members of the TNF superfamily. The TNF receptor family member Glucocorticoid-induced TNF Receptor (GITR) costimulates effector T cells, modulates apoptosis and nuclear factor kappa B and abrogates suppression of murine but not human regulatory T cells. Expression of its cognate ligand GITRL has, in humans, been detected in dendritic cells and various healthy nonlymphoid tissues. Up to now, nothing is known regarding the function of human GITRL, while in mice, reverse signaling through GITRL has been shown to influence the activation and survival of macrophages. Here we report for the first time that GITRL is expressed in human macrophages as determined by FACS and RT-PCR analysis. Reverse signaling through GITRL using a recombinant GITR-Ig fusion protein differentially affects expression of costimulatory molecules like CD80, CD86 and B7-H1, death ligands like TNF, CD178 and TRAIL as well as MHC class I and II on the macrophage surface. Furthermore, stimulation of GITRL enhances phagocytosis and respiratory burst of macrophages as determined by analysis of ingestion of PE-labeled polystyrene microspheres and oxidation of dichlor-fluorescein diacetate, respectively by FACS. Interaction of GITRL with its receptor also leads to significantly increased production of proinflammatory cytokines like TNF, IL-6 and IL-8 as determined by ELISA. In addition, stimulation of GITRL significantly increases the killing of various human tumor cell lines by macrophages as determined by cytotoxicity assays. Taken together, our data demonstrate that GITRL plays an important role in the stimulation of macrophage-mediated inflammatory responses and immune responses against tumors.

Description: NK cell anti-tumor reactivity is governed by a balance of activating and inhibitory receptors including various TNF receptor (TNFR) family members. Here we report that human tumor cells release a soluble form of the TNF family member Glucocorticoid-Induced TNFR-Related Protein (GITR) ligand (sGITRL), which can be detected in cell culture supernatants. Tumor-derived sGITRL concentration-dependently reduced NK cell cytotoxicity and IFN-γ production, which could be overcome by neutralization of sGITRL using a GITR-Ig fusion protein. Although sGITRL did not induce apoptosis in NK cells, it diminished nuclear localized RelB, indicating that sGITRL negatively modulates NK cell NF-κB activity. Furthermore, we detected substantial levels of sGITRL in sera of patients with various malignancies, but not in healthy controls. Presence of sGITRL-containing patient serum in cocultures with tumor cells significantly reduced NK cell cytotoxicity and IFN-γ production, which could again be restored by neutralization of sGITRL. The strong correlation of tumor incidence and elevated sGITRL levels indicates that sGITRL is released from cancers in vivo, leading to impaired NK cell immunosurveillance of human tumors. Our data suggest that determination of sGITRL levels might be implemented as a tumor marker in patients, and GITRL neutralization may be used to improve immunotherapeutic strategies relying on NK cell reactivity.

Description: Reciprocal interactions of NK cells with Dendritic Cells (DC) have been shown to influence activation of NK cells as well as maturation or lysis of DC and subsequent adaptive immune responses. However, little is known about the interaction of peripheral blood Monocytes with NK cells. Here we report that stimulation of Toll-like receptors (TLR) on Monocytes using LPS, Pam3Cys, R848 and PolyI:C induced mRNA and surface expression of MICA but no relevant changes of the further ligands of the activating immunoreceptor NKG2D, MICB or ULBP1-3. MICA upregulation upon stimulation with TLR ligands correlated with CD80 and HLA-DR upregulation and increased secretion of the pro-inflammatory cytokines IL-6, IL-8 and TNF by Monocytes. Interestingly, high MICA surface expression on activated Monocytes was not accompanied by a release of MICA in soluble form. The LPS-induced MICA upregulation by Monocytes was highly sensitive since it was observed with as little as 4 ng/ml LPS after 15 hours and was associated with IL-6 secretion and inhibition of apoptosis indicating that Monocytes were activated and functional. To determine whether upregulated MICA expression on Monocytes was detected by NK cells we took advantage of the fact that NKG2D is down-regulated after interacting with its ligands. While NKG2D levels on NK cells were not substantially changed in cultures with unstimulated Monocytes, a marked reduction of NKG2D was observed in the presence of activated MICA-expressing Monocytes. The modulation of NKG2D did not occur when NK cells and monocytes were separated by a transwell filter, which demonstrates that the numerous cytokines produced by TLR-activated Monocytes are not responsible for the NKG2D modulation and confirmes the role of MICA in Monocyte-NK cell interaction. Importantly, TLR-induced MICA expression on Monocytes stimulated IFN-γ production of NK cells, which could be reduced by addition of blocking anti-MICA/B F(ab’)2 fragments while isotype control had no effect. This demonstrates that the observed stimulation of NK cells was in fact specifically due to NKG2D-NKG2DL interaction. Our data indicate that NKG2D-MICA interaction provides a mechanism by which NK cells and Monocytes may communicate directly during innate immune responses to infections in humans.

Description: NK cells play an important role in the reciprocal interaction of tumor cells with the immune system and participate in the surveillance and eradication of hematological malignancies. The activity of NK cells is governed by a balance of activating and inhibitory surface receptors. Glucocorticoid-induced TNF-related protein (GITR) and its ligand (GITRL) are members of the TNF/TNF receptor (TNFR) superfamily, which mediates multiple cellular functions including proliferation, differentiation, and cell death. Recently we reported that NK cells express GITR while cancer cells express GITRL and GITR-GITRL interaction down regulates NK cell-mediated anti-tumor immunity (Baltz et al., FASEB J 2007). Here we demonstrate that GITRL is expressed on 6 of 7 investigated acute myeloid leukemia (AML) cell lines and on primary AML cells in 30 of 52 (59%) patients, while no GITRL expression was detected on CD34+ cells of healthy donors (n=5). GITRL expression was not restricted to a specific French-American-British (FAB) subtype, but was significantly (p

Description: Glucocorticoid-induced TNF-related protein (GITR) and its ligand (GITRL) are members of the TNF/TNF receptor (TNFR) superfamily, which mediates multiple cellular functions including proliferation, differentiation, and cell death. Recently we reported that NK cells express GITR while tumor cells express GITRL, and GITR-GITRL interaction downregulates NK cell-mediated anti-tumor immunity (Baltz et al., FASEB J 2007). Many TNF family members are released as soluble forms, which affects cell-cell interactions by reduction of ligand density and distally modulates effector cells bearing the respective receptor. Here we report that human tumor cells spontaneously release a soluble form of GITRL (sGITRL), which can be detected in tumor cell culture supernatants by ELISA (detection limit 0.01ng/ml). We demonstrated that NK cell cytotoxicity and IFN-γ production in cocultures with the tumor cell lines SK-Mel (Melanoma), PC-3 (prostate), HCT116 (colon), and LX-1 (lung) were significantly (both p

Description: NK cells play an important role in the reciprocal interaction of tumor cells with the immune system and participate in the surveillance and eradication of hematological malignancies including acute myeloid leukemia (AML). NK cell reactivity is governed by a balance of activating and inhibitory receptors including various members of the TNF receptor (TNFR) superfamily. The TNFR superfamily member CD137/4-1BB has been shown to stimulate proliferation and IFN-γ production, but not cytotoxicity of NK cells in mice. Surprisingly, yet nothing is known regarding the consequences of CD137-CD137 ligand (CD137L) interaction for NK cell reactivity in humans. In this study we demonstrate that CD56dimCD16+ but not CD56brightCD16− NK cells express CD137 upon stimulation with the activating cytokines IL-2 and IL-15 with peak expression between 48 and 60h. Furthermore, we found that 5 of 7 investigated AML cell lines and 16 of 51 (33%) primary AML cells of patients expressed substantial CD137L levels, while no CD137L expression was detected on CD34+ cells of healthy donors (n=5). CD137L expression was not restricted to a specific French-American-British (FAB) subtype, but was significantly (p

Description: Background & Aims: Hepatocellular carcinoma (HCC) displays a particular resistance to conventional cytostatic agents. Therefore, alternative treatment strategies focus on novel substances exhibiting anti-neoplastic and/or immunomodulatory activity enhancing for example Natural Killer (NK) cell anti-tumor reactivity. However, the tumor-associated ligands engaging activating NK cell receptors are largely unknown. Exceptions are the NKG2D ligands (NKG2DL) of the MIC and ULBP protein families, which potently stimulate NK cell responses. We studied the consequences of proteasome inhibition with regard to direct and NK cell-mediated effects against HCC. Methods: Primary human hepatocytes (PHH) from different donors, hepatoma cell lines and NK cells were exposed to Bortezomib. Growth and viability of hepatoma cells and PHH as well as immunomodulatory effects including alterations of NKG2DL expression on hepatoma cells, specific induction of NK cell cytotoxicity and IFN-γ production were investigated. Results: Bortezomib treatment inhibited hepatoma cell growth with IC50 values between 2.4 and 7.7 nanomol/liter. These low doses increased MICA/B mRNA levels and total and cell surface protein expression in hepatoma cells, which stimulated cytotoxicity and IFN-γ production of cocultured NK cells. Importantly, while IFN-γ production of NK cells was concentration-dependently reduced, low-dose Bortezomib neither induced NKG2DL expression or cell death in PHH nor altered NK cell cytotoxicity. Conclusions: Low-dose Bortezomib mediates a specific dual anti-tumor effect in HCC by inhibiting tumor cell proliferation and by priming hepatoma cells for NK cell anti-tumor reactivity. Our data suggest the clinical evaluation of Bortezomib treatment in HCC, especially in combination with immunotherapeutic approaches like adoptive NK cell transfer.

Description: Members of the tumor necrosis factor (TNF) superfamily mediate multiple cellular functions including cellular proliferation, differentiation, and cell death. Human Glucocorticoid-induced TNF Receptor (GITR) has been shown to be expressed on T cells, is upregulated following activation and mediates costimulatory signals. The human GITR ligand (GITRL) has been reported to be expressed on antigen presenting cells and various healthy nonlymphoid tissues including small intestine, ovary, testis, kidney and endothelial cells. We analyzed multiple tumor cell lines of hematopoietic and epithelial origin as well as of germ cell lineage and various gliomas by RT-PCR and FACS analysis. Both GITRL m-RNA and protein are expressed in various carcinomas, gliomas and tumor cells of germ cell lineage, but not in hematopoietic tumor cells. Furthermore, we demonstrate that human NK cells constitutively express low levels of GITR, and this expression is upregulated following activation by, e.g., IL-2 or IL-15 as detected by quantitative PCR and FACS analysis. To address the functional interaction of GITRL with its receptor on NK cells, we generated a GITRL-IgG fusion protein (GITRL-Ig). Stimulation of activated NK cells with GITRL-Ig lead to significantly reduced IFN-g production of NK cells as measured by ELISA. Similarly, a significant reduction of IFN-g release was observed following coculture of GITR expressing NK cells with C1R cells transfected with GITRL but not with the respective mock transfectants. Furthermore, ligation of GITR on NK cells lead to significantly decreased killing of target cells as demonstrated by cellular cytotoxicity assays. Taken together, our data demonstrate that GITR not only plays an important role in adaptive immunity but is also involved in the regulation of NK cell effector functions. Since tumor cells express significant levels of GITRL, and ligation of GITR on NK cells markedly reduces cytokine production and cellular cytotoxicity, our data indicate that GITR-GITRL interactions play an important role in the escape of tumor cells from innate immune surveillance.

Description: Members of the TNF superfamily mediate multiple cellular functions, including cellular proliferation, differentiation and cell death. Many members of this protein family are shed from the cell surface as soluble forms, which affects cell-cell interactions by reduction of ligand densities and distally modulates effector cells bearing the respective receptor. The TNF family member Glucocorticoid-induced TNF Receptor (GITR) costimulates effector T cells, modulates apoptosis and NFkappaB and abrogates suppression of murine but not human regulatory T cells. Its cognate ligand GITRL has been found in various healthy tissues. Recently we reported that NK cells express GITR, while tumor cells express GITR ligand (GITRL), and GITR/GITRL interaction downregulates NK cell-mediated anti-tumor effector mechanisms like cytotoxicity and IFN-gamma production. Here we report that human tumor cells spontaneously release a soluble form of GITRL (sGITRL) detectable in culture supernatants by ELISA. Furthermore, we found elevated levels of sGITRL in sera of patients with various malignancies compared to healthy controls. We demonstrate that the release of GITRL from tumor cells can be blocked by inhibition of metalloproteinases, concomitantly causing accumulation of GITRL on the tumor cell surface as determined by FACS analysis. Upregulated GITRL surface expression further increased inhibition of NK cell anti-tumor effector mechanisms, while, in contrast, presence of sGITRL in cocultures of GITRL-expressing tumor cells and GITR-positive NK cells enhanced NK cell cytotoxicity and IFN-gamma production. Thus, in line with the results obtained with other TNF family members, conversion of membrane bound GITRL to its soluble form is associated with downregulation of its function, potentially due to blocking its cognate receptor. Thus, release of sGITRL substantially influences the interaction of tumor cells with NK cells. In addition, determination of sGITRL levels may be implemented as a diagnostic marker in patients with malignancies. Further prospective studies are currently being conducted addressing the value of GITRL as a tumor marker in different tumor entities.