Heike Voigt

Macrophage Migration Inhibitory Factor Contributes to the Immune Escape of Ovarian Cancer by Down-Regulating NKG2D

The proinflammatory cytokine macrophage migration inhibitory factor (MIF) stimulates tumor cell proliferation, migration, and metastasis; promotes tumor angiogenesis; suppresses p53-mediated apoptosis; and inhibits antitumor immunity by largely unknown mechanisms. We here describe an overexpression of MIF in ovarian cancer that correlates with malignancy and the presence of ascites. Functionally, we find that MIF may contribute to the immune escape of ovarian carcinoma by transcriptionally down-regulating NKG2D in vitro and in vivo which impairs NK cell cytotoxicity toward tumor cells. Together with the additional tumorigenic properties of MIF, this finding provides a rationale for novel small-molecule inhibitors of MIF to be used for the treatment of MIF-secreting cancers.

Mouse models for melanoma: a personal perspective

Please cite this paper as: Mouse models for melanoma: a personal perspective. Experimental Dermatology 2010; 19: 157–164.

Microphthalmia-Associated Transcription Factor Gene Amplification in Metastatic Melanoma Is a Prognostic Marker for Patient Survival, But Not a Predictive Marker for Chemosensitivity and Chemotherapy Response

Purpose: The microphthalmia-associated transcription factor (MITF) is regarded as a key oncogene of the melanocytic lineage since it was detected by a genome-wide analysis to be strongly amplified in 15% to 20% of metastatic melanomas. MITF gene amplification was shown to be associated with a reduced survival in metastatic melanoma patients, and reduction of MITF activity was shown to sensitize melanoma cell lines to chemotherapeutics, suggesting the intratumoral MITF gene copy number as a predictive biomarker of response and survival after chemotherapy. Patients and Methods: To validate this hypothesis, we investigated MITF gene amplification in tumor tissues obtained from 116 metastatic melanoma patients before an individualized sensitivity-directed chemotherapy using quantitative real-time PCR. MITF amplification rates were correlated with tumor chemosensitivity quantified by an ATP-based luminescence assay and with chemotherapy outcome in terms of response and survival. Results: Of 116 tumor tissues, 104 were evaluable for MITF gene amplification. Strong amplification (≥4 copies per cell) was detected in 24 of 104 tissues (23%), whereas 62 of 104 tissues (60%) harbored >3 copies per cell. Strong MITF gene amplification was associated with a reduced disease-specific survival (P = 0.031). However, no correlation was found between MITF copy number and in vitro chemosensitivity or in vivo chemotherapy response. Conclusion: Our findings suggest that strong amplifications of the melanoma oncogene MITF affects patient survival but does not influence tumor chemosensitivity and chemotherapy response. Thus, the MITF gene copy number seems a useful prognostic marker in metastatic melanoma but could not be confirmed as a predictive marker of chemosensitivity and chemotherapy response.

CD147 Impacts Angiogenesis and Metastasis Formation

CD147 is highly expressed on many tumor cells; its role for tumor invasiveness and metastasis has been deduced from its capacity to induce MMPs, i.e., MMP-1, -2, -3, and -9. However, in the murine B16 melanoma model, MMP-2/-9 expression occurs independent of CD147. To scrutinize the impact of CD147 on metastasis formation and angiogenesis in this model, CD147 was stably knocked down in B16 cells. This silencing of CD147 expression resulted in a reduced capability of the tumor cells to metastasize to the draining lymph nodes. Notably, the CD147 knock down caused a decreased VEGF expression in vivo accompanied by reduced blood vessel formation. Thus, in the B16 melanoma model, CD147 promotes metastasis formation by induction of angiogenesis in an MMP independent manner.

Immunological tumor destruction in a murine melanoma model by targeted LTα independent of secondary lymphoid tissue

BackgroundWe previously demonstrated that targeting lymphotoxin α (LTα) to the tumor evokes its immunological destruction in a syngeneic B16 melanoma model. Since treatment was associated with the induction of peritumoral tertiary lymphoid tissue, we speculated that the induced immune response was initiated at the tumor site.Methods and resultsIn order to directly test this notion, we analyzed the efficacy of tumor targeted LTα in LTα knock-out (LTα−/−) mice which lack peripheral lymph nodes. To this end, we demonstrate that tumor-targeted LTα mediates the induction of specific T-cell responses even in the absence of secondary lymphoid organs. In addition, this effect is accompanied by the initiation of tertiary lymphoid tissue at the tumor site in which B and T lymphocytes are compartmentalized in defined areas and which harbor expanded numbers of tumor specific T cells as demonstrated by in situ TRP-2/Kb tetramer staining. Mechanistically, targeted LTα therapy seems to induce changes at the tumor site which allows a coordinated interaction of immune competent cells triggering the induction of tertiary lymphoid tissue. ConclusionThus, our data demonstrate that targeted LTα promotes an accelerated immune response by enabling the priming of T cells at the tumor site.

MAPK-independent impairment of T-cell responses by the multikinase inhibitor sorafenib.

Sorafenib, originally developed as CRAF inhibitor but soon recognized as a multikinase inhibitor, is currently widely tested for the treatment of different cancers either alone or in combination therapy. However, the clinical success, particularly in immunogenic tumors such as melanoma, was less than anticipated. Because T-cell activation is tightly regulated by a multitude of kinases, we scrutinized effects of sorafenib on immune responses. To this end, comprehensive in vitro studies revealed that the presence of sorafenib concentrations comparable with observed plasma levels in patients strongly impairs the activation of T cells. Notably, even established tumor-specific immune responses are influenced by sorafenib. Indeed, ELISPOT data of peripheral blood lymphocytes obtained from melanoma patients vaccinated against survivin show markedly diminished survivin-specific immune responses in the presence of sorafenib. Surprisingly, inhibition of T-cell activation was not associated with reduced extracellular signal-regulated kinase phosphorylation. In fact, on T-cell receptor stimulation phospho-extracellular signal-regulated kinase and phospho-mitogen-activated protein kinase kinase levels were found to be elevated in the presence of sorafenib, showing the complexity of signal transduction events following T-cell receptor stimulation. In conclusion, our data show that T-cell function is sensitive toward the multikinase inhibitor sorafenib in a mitogen-activated protein kinase-independent fashion. This observation has important implications for the use of sorafenib as therapy for immunogenic cancers. [Mol Cancer Ther 2009;8(2):433–40]

Bcl-2 expression in rituximab refractory cutaneous B-cell lymphoma.

Rituximab has been established as an effective and safe therapy for cutaneous B-cell lymphoma (CBCL). Different survival pathways, that is the Raf/MEK/Erk- or the p38MAPK cascade, have been suggested as downstream mediators of rituximab and may be involved in treatment failure. Biopsies from four patients, suffering from different subtypes of CBCL, which were obtained at various time points of relapse during or after therapy with 375 mg rituximab per m2 of body surface area, were analysed for the expression of CD20, CD3, Ki-67, Raf-kinase inhibitory protein (RKIP) and bcl-2 by immunohistochemistry. No CD20-loss variants, that is the suggested main tumour escape mechanism to rituximab therapy, were observed in any specimen of relapsing CBCL. Notably, the expression of proapoptotic RKIP remained increased in these tumour samples. This was concomitated by a constant to slightly reduced proliferation status as demonstrated by Ki-67 staining. However, relapsing CBCL exhibited a strong upregulation of the antiapoptotic molecule bcl-2 in comparison to pretherapeutic levels. The immunohistochemical analyses of this case series of rituximab refractory CBCL suggest that upregulation of bcl-2 may play a major role in therapy resistance.

Identification and characterization of survivin‐derived H‐2Kb‐restricted CTL epitopes

Survivin is overexpressed in several malignancies and in tumor‐associated endothelium making it an attractive target for therapeutic cytotoxic T‐cell responses. Thus, it would be important to test this notion in preclinical models. Consequently, we screened the murine survivin sequence for potential binding Kb‐restricted octamer peptide epitopes. Two epitopes, which bind strongly to Kb, were selected to test their immunogenicity in vivo. Spleen cells from mice vaccinated by intradermal injection of mature DC pulsed with these peptides displayed reactivity to the respective epitopes. The natural processing and presentation of these epitopes by tumor cells was evident by the killing of murine melanoma cells by vaccination‐induced T cells. Subcutaneous challenge with syngeneic melanoma demonstrated the protective immunity of this vaccination. Notably, analysis of the vessel density in subcutaneous tumors revealed that survivin‐specific vaccination significantly reduced the number of intratumoral vessels. In summary, we demonstrated the immunogenicity of two Kb‐restricted peptide epitopes derived from the murine survivin protein; moreover, survivin‐specific vaccination not only resulted in a reduction of tumor cells but also the tumor supplying blood vessels. The presented preclinical model for survivin‐directed vaccination may serve as a valuable tool to improve already running clinical trials in a syngeneic tumor model.

CD28‐mediated costimulation impacts on the differentiation of DC vaccination‐induced T cell responses

Costimulatory signals such as the ones elicited by CD28/B7 receptor ligation are essential for efficient T cell activation but their role in anti‐tumour immune responses remains controversial. In the present study we compared the efficacy of DC vaccination‐induced melanoma specific T cell responses to control the development of subcutaneous tumours and pulmonary metastases in CD28‐deficient mice. Lack of CD28‐mediated costimulatory signals accelerated tumour development in both model systems and also the load of pulmonary metastases was strongly increased by the end of the observation period. To scrutinize whether lack of CD28 signalling influences priming, homing or effector function of Trp‐2180−188/Kb‐reactive T cells we investigated the characteristics of circulating and tumour infiltrating T cells. No difference in the frequency of Trp‐2180−188/Kb‐reactive CD8+ T cells could be demonstrated among the cellular infiltrate of subcutaneous tumours after DC vaccination between both genotypes. However, the number of IFN‐γ‐producing Trp‐2‐reactive cells was substantially lower in CD28‐deficient mice and also their cytotoxicity was reduced. This suggests that CD28‐mediated costimulatory signals are essential for differentiation of functional tumour‐specific CD8+ T‐effector cells despite having no impact on the homing of primed CD8+ T cells.

Characterization of mouse MAGE-derived H-2Kb-restricted CTL epitopes

Immunogenic peptide epitopes from tumor‐associated antigens serve as targets for cellular immune responses in numerous clinical trials for therapeutic vaccinations. From these it became evident that prevailing questions can only be addressed in animal models. Hence, problems arise from the fact that while for human melanoma many different immunogenic peptide epitopes are known, for mouse melanoma the available selection is very restricted. To overcome this limitation, we applied reverse immunology to identify Kb‐restricted epitopes derived of mouse MAGE. Two epitopes which bind strongly to Kb were selected to test for their immunogenicity in vivo. Spleen cells from mice vaccinated by intradermal injection of mature dendritic cells pulsed with these peptides displayed reactivity to the respective epitopes as measured by enzyme‐linked immunospot assays and tetramer staining. The processing and presentation of these epitopes was evident by the killing of melanoma cells by the vaccination‐induced T cells. Moreover, intravenous challenge with syngeneic melanoma cells demonstrated the protective immunity induced by this vaccination. In summary, we demonstrate the immunogenicity of two Kb‐restricted peptide epitopes derived from mouse MAGE proteins which may serve as valuable tool for preclinical evaluation of vaccination strategies.