The host immune response has

The host immune response has been identified as a critical regulator of tumor development and progression (Dunn et al., 2004; Fridman et al., 2013; Hadrup et al., 2013). Several types of immune tetramisole participate in immunosurveillance by direct killing or production of cytokines. Our expression profiling experiments revealed that the majority of genes related to immunity and defense were significantly downregulated in Evi-GOF teratomas. Accordingly, less CD45+ leukocytes had infiltrated Evi-GOF teratomas. Most notably, we observed a 50% reduction of CD3+ T cells in Evi-GOF teratomas. Low densities of both CD8+ cytotoxic T cells and CD45RO+ memory T cells are associated with poor clinical outcome (Fridman et al., 2013; Becht et al., 2014; Hadrup et al., 2013). The results of our teratoma experiments support a model whereby high Wnt activity facilitated the escape from the anti-tumor immune control by T cell exclusion. Recent results on Wnt/β-catenin signaling in melanoma have revealed a correlation of canonical Wnt signaling with lack of T-cell infiltration in mouse models as well as in human patient biopsies suggesting a similar role of Wnt signaling in different types of tumors (Spranger et al., 2015). Our analysis revealed no overt changes in T cell activation or effector differentiation, indicating that excessive Wnt signaling impairs T cell recruitment and/or tumor infiltration, rather than intratumoral T cell activation. Alternatively, the moderate Evi overexpression in ESCs via the Rosa26 promoter was insufficient to challenge the balance of these T cell subsets. Regardless of the exact mechanism, elevated Wnt levels promote increased tumor growth and this effect is mediated through attenuated immune surveillance. The role of Wnt signaling in mature T cell differentiation is still controversially discussed. Recent publications using pharmacological or genetic approaches support a role for β-catenin as well as the β-catenin downstream transcription factor TCF-1 (transcription factor 7) in memory T cell development (Gattinoni et al., 2009; Zhao et al., 2010). Whereas other reports showed that expression of stabilized or deleted β-catenin was dispensable in functional memory T cell differentiation (Prlic and Bevan, 2011; Driessens et al., 2010). It is of note that TCF-1 can be activated independently of β-catenin cooperation and therefore does not reflect in all cases exclusive Wnt response (Grumolato et al., 2013; Sprowl and Waterman, 2013). Similarly, studies addressing Wnt/β-catenin signaling in Treg and Th17 function showed on the one hand that stable β-catenin expression in Tregs supports Treg survival and immune response (Ding et al., 2008), whereas TCF-1 deficient mutants revealed stronger suppressive ability of (van Loosdregt et al., 2013). Our teratoma analysis showed an increase in CD4+CD25+FoxP3+ Tregs population in Evi-GOF tumors indicating that enhanced Wnt secretion supports Treg availability. Further experimental analyses will be necessary to clarify whether this phenotype correlates with β-catenin or β-catenin-independent Wnt signaling in T cell populations. Tregs suppress inflammatory mechanisms and thereby attenuate inflammation-associated tumor progression. Otherwise regulatory T cells also inhibit anti-tumor T cell responses, thereby supporting cancer escape from immune surveillance. These different functions are probably driven by different Treg subsets, which might depend on the cancer type and mutation status. (Blatner et al., 2012; Keerthivasan et al., 2014). Recent reports showed that active Wnt/β-catenin signaling in Tregs correlates with promotion of colon cancer (Keerthivasan et al., 2014). Further studies are necessary to address this issue in other Wnt-related cancer settings. Moreover, several reports exist, which delineate a role of Wnt signaling in Th17 differentiation during T cell development and mature T cell differentiation (Ma et al., 2011; Dai et al., 2016; Muranski et al., 2011). Our results showed an increase in IL17 producing CD4+ T cells in Evi-GOF teratomas indicating that enhanced Wnt secretion is involved in elevated Th17 response. The supportive or inhibitory role of Th17 in malignancy is still a matter of debate suggesting that Th17 cells play a dynamic role in cancer immunity depending on the type of inflammatory response and cancer (Martin et al. 2012; Wang et al., 2009; Iida et al., 2011). Recent reports showed that constitutive activation of β-catenin promotes chromatin accessibility and target gene expression for Th17 commitment, which sustained pathogenic inflammation and predispose to cancer (Keerthivasan et al., 2014). Our phenotypical analyses tend towards the same direction. Nevertheless additional studies are necessary to enroll a more detailed leukocyte population analysis including expression pattern of target genes and cytokines as well as Wnt signal activity.