Anita Bringmann

Cancer immunoediting by GITR (glucocorticoid-induced TNF-related protein) ligand in humans: NK cell/tumor cell interactions

Glucocorticoid‐induced TNF‐related protein (GITR) has been shown to stimulate T cell‐mediated antitumor immunity in mice. However, the functional relevance of GITR and its ligand (GITRL) for non‐T cells has yet to be fully explored. In addition, recent evidence suggests that GITR plays different roles in mice and humans. We studied the role of GITR‐GITRL interaction in human tumor immunology and report for the first time that primary gastrointestinal cancers and tumor cell lines of different histological origin express substantial levels of GITRL. Signaling through GITRL down‐regulated the expression of the immunostimulatory molecules CD40 and CD54 and the adhesion molecule EpCAM, and induced production of the immunosuppressive cytokine TGF‐β by tumor cells. On NK cells, GITR is constitutively expressed and up‐regulated following activation. Blocking GITR‐GITRL interaction in cocultures of tumor cells and NK cells substantially increased cytotoxicity and IFN‐γ production of NK cells demonstrating that constitutive expression of GITRL by tumor cells diminishes NK cell antitumor immunity. GITRL‐Ig fusion protein or cell surface‐expressed GITRL did not induce apoptosis in NK cells, but diminished nuclear localized c‐Rel and RelB, indicating that GITR might negatively modulate NK cell NF‐κB activity. Taken together, our data indicate that tumor‐expressed GITRL mediates immunosubversion in humans.—Baltz, K. M., Krusch, M., Bringmann, A., Brossart, P., Mayer, F., Kloss, M., Baessler, T., Kumbier, I., Peterfi, A., Kupka, S., Kroeber, S., Menzel, D., Radsak, M. P., Rammensee, H.‐G., Salih, H. R. Cancer immu‐noediting by GITR (glucocorticoid‐induced TNF‐related protein) ligand in humans: NK cell/tumor cell interactions. FASEB J. 21, 2442–2454 (2007)

BCR-ABL Activity Is Critical for the Immunogenicity of Chronic Myelogenous Leukemia Cells

Chronic myelogenous leukemia (CML) is a myeloproliferative disorder caused by excessive granulopoiesis due to the formation of the constitutively active tyrosine kinase BCR-ABL. An effective drug against CML is imatinib mesylate, a tyrosine kinase inhibitor acting on Abl kinases, c-KIT, and platelet-derived growth factor receptor. Recently, a study revealed that patients treated with imatinib showed impaired CTL responses compared with patients treated with IFN-alpha, which might be due to a treatment-induced reduction in immunogenicity of CML cells or immunosuppressive effects. In our study, we found that inhibition of BCR-ABL leads to a down-regulation of immunogenic antigens on the CML cells in response to imatinib treatment, which results in the inhibition of CML-directed immune responses. By treating CML cells with imatinib, we could show that the resulting inhibition of BCR-ABL leads to a decreased expression of tumor antigens, including survivin, adipophilin, hTERT, WT-1, Bcl-x(L), and Bcl-2 in correlation to a decreased development of CML-specific CTLs. In contrast, this reduction in immunogenicity was not observed when a CML cell line resistant to the inhibitory effects of imatinib was used, but could be confirmed by transfection with specific small interfering RNA against BCR-ABL or imatinib treatment of primary CML cells.

Neutralization of tumor-derived soluble glucocorticoid-induced TNFR-related protein ligand increases NK cell anti-tumor reactivity.

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-gamma 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-kappaB 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-gamma 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.

RNA Vaccines in Cancer Treatment

The Cancer Report from the World Health Organization states that in the year 2000 12% of all death cases worldwide were caused by cancer. In the western world, the cancer death rates are often devastating, being at about 25%. This fact stresses the urgency to find effective cures against malignant diseases. New approaches in the treatment of cancer focus on the development of immunotherapies to fight the disease. Besides other methods, the usage of tumor-specific RNA as part of vaccines is investigated lately. RNA, administered alone or used for transfection of dendritic cells, shows several advantages as a vaccine including feasibility, applicability, safeness, and effectiveness when it comes to the generation of immune responses. This review concentrates on results from in vitro experiments and recent trials using RNA vaccines to present an overview about this specific strategy.

Regulation of dectin-1–mediated dendritic cell activation by peroxisome proliferator–activated receptor-gamma ligand troglitazone

Dectin-1 is the major receptor for fungal β-glucans. The activation of Dectin-1 leads to the up-regulation of surface molecules on dendritic cells (DCs) and cytokine secretion. Furthermore, Dectin-1 is important for the recruitment of leukocytes and the production of inflammatory mediators. Peroxisome proliferator-activated receptor-γ (PPAR-γ) and its ligands, cyclopentenone prostaglandins or thiazolidinediones, have modulatory effects on B-cell, T-cell, and DC function. In the present study, we analyzed the effects of troglitazone (TGZ), a high-affinity synthetic PPAR-γ ligand, on the Dectin-1-mediated activation of monocyte-derived human DCs. Dectin-1-mediated activation of DCs was inhibited by TGZ, as shown by down-regulation of costimulatory molecules and reduced secretion of cytokines and chemokines involved in T-lymphocyte activation. Furthermore, TGZ inhibited the T-cell-stimulatory capacity of DCs. These effects were not due to a diminished expression of Dectin-1 or to a reduced phosphorylation of spleen tyrosine kinase; they were mediated by the inhibition of downstream signaling molecules such as mitogen-activated protein kinases and nuclear factor-κB. Furthermore, curdlan-mediated accumulation of caspase recruitment domain 9 (CARD9) in the cytosol was inhibited by TGZ. Our data demonstrate that the PPAR-γ ligand TGZ inhibits Dectin-1-mediated activation by interfering with CARD9, mitogen-activated protein kinase, and nuclear factor-κB signaling pathways. This confirms their important role as negative-feedback regulators of potentially harmful inflammatory responses.