Triple-negative breast cancer (TNBC) is a high medical need disease with limited treatment options. CD8+ T cell-mediated immunotherapy may represent an attractive approach to address TNBC. The objectives of this study were to assess the expression of CXorf61 in TNBCs and healthy tissues and to evaluate its capability to induce T cell responses.We show by transcriptional profiling of a broad comprehensive set of normal human tissue that CXorf61 expression is strictly restricted to testis. 53% of TNBC patients express this antigen in at least 30% of their tumor cells. In CXorf61-negative breast cancer cell lines CXorf61 expression is activated by treatment with the hypomethylating agent 5-aza-2′-deoxycytidine.By vaccination of HLA-A*02-transgenic mice with CXorf61 encoding RNA we obtained high frequencies of CXorf61-specific T cells. Cloning and characterization of T cell receptors (TCRs) from responding T cells resulted in the identification of the two HLA-A*0201-restricted T cell epitopes CXorf6166–74 and CXorf6179–87. Furthermore, by in vitro priming of human CD8+ T cells derived from a healthy donor recognizing CXorf6166–74 we were able to induce a strong antigen-specific immune response and clone a human TCR recognizing this epitope.In summary, our data confirms this antigen as promising target for T cell based therapies.

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The process of how a benign tumour turns invasive and capable to survive in distant organs remains poorly understood, despite the evidence that metastasis formation is the primary cause of cancer patient mortality. This ignorance is partly due to the lack of appropriate animal models from which to investigate this complex process. The retinoblastoma (Rb) tumour suppressor pathway (pRb/E2F) is mutated in almost all human tumours, and a number of laboratories have now established pRb- or E2F-deficient mouse models. Consistent with the role of mutation in retinoblastoma in cancer biology, Rb heterozygous mice are prone to develop tumours. Among the ensuing tumours, the medullary thyroid carcinomas (MTCs) have a lessened tendency to form secondary cancers and metastases. Intriguingly, if an E2f3 mutation is introduced in this genetic background, more aggressive MTCs develop, which metastasize more frequently. Gene chip microarrays, however, provide an unbiased approach for examining the genome-wide expression levels and enable identification of a large set of metastasis-enriched gene sets. The identified genes may simply represent putative markers of the disease stage. Alternatively, genes may be identified that causally determine a link to the onset of metastasis. We describe the use of gene chip microarrays for identification of putative markers enriched in metastatic mouse MTCs. The chapter details how the most promising candidates are verified using additional methods, such as quantitative real-time PCR. In this case, co-transfection of the E2F-transcription factor using a heterologous reporter gene system is suggestive of E2Fs directly regulating putative metastasis markers.

The retinoblastoma tumor suppressor protein (pRb) was the first tumor suppressor to be identified. The E2F family of transcription factors is considered the best-studied class of interaction partners of pRB. Specifically, E2F1-3 are all capable to control re-entry and progression through the S-phase of the cell cycle. The simplified view is that hypo-phosphorylated pRb is bound by E2F and recruits chromatin remodeling complexes to represses the transcription of E2F target genes. Upon cell cycle progression pRb is phosphorylated leading to a release of E2Fs and the subsequent progression through the G1/S-transition. In order to understand the consequences of deregulation of the pRb/E2F-pathway, a number of groups have established mouse knock-out models of various members of this pathway. Using a combined knockout mouse model it was demonstrated that E2F3 contributes to both the inappropriate proliferation and p53-dependent apoptosis that arises in pRb-deficient embryos. Furthermore, it was shown that absence of E2F3 results on one hand in the attenuation of the growth of pituitary adenomas, on the other hand it promotes the development of medullary thyroid carcinomas (MTCs) yielding metastases at an increased frequency. Since this is one of the few existing mouse models to study metastasis, we wished to use this model to identify novel markers and mechanisms that regulate this process. We established the whole genomic transcriptional profile of mouse MTCs harvested from Rb/E2f3 mutant mice. The comparison of metastatic MTCs with non-metastatic tumors defined a data set of 123 putative metastatic markers. Among this data set, we identified a cluster of 22 genes that are directly involved in the formation of the kinetochore, establishment of the centromere or play a distinct role in the spindle assembly checkpoint. We validated the expression of these novel metastatic markers using mouse RNA, as well as material from human metastatic MTC biopsies. Importantly, we were able to establish that the same genes were only upregulated in metastatic tumors utilizing immunhistochemistry on sections of human metastatic MTCs but not in non-metastatic counterparts. Moreover, chromatin immunoprecipitation assays support that these genes are direct targets of the pRB/E2F-pathway. In summary we identified novel markers of metastasis. Moreover, these markers are also putative E2F target genes, the fact of which emphasizes the important contribution of E2Fs to tumor progression. Citation Information: Cancer Res 2009;69(23 Suppl):C36.