Tumor suppressive function of E2F-1 on PTEN-induced serrated colorectal carcinogenesis.

Many human cancers present Phosphatase and tensin homolog (PTEN) deficiency and between 20 and 30% of colorectal tumors show PTEN loss. The transcription factor, E2 promoter binding factor 1 (E2F-1), exhibits tumor promoter or suppressive functions depending on cellular type and tissue context, but its role in the progression and development of colorectal carcinogenesis was largely unknown. Here, using a tamoxifen-inducible PTEN knockout mouse model, we have demonstrated that loss of PTEN leads to the development of colorectal tumorigenesis through the serrated pathway. Next, we studied PTEN loss-driven colorectal lesions in the context of E2F-1 deficiency in vivo. Our results revealed that monoallelic and biallelic absence of E2F-1 led to an increased incidence and progression of serrated tumorigenesis induced by PTEN loss. Finally, we investigated the mechanisms by which double PTEN/E2F-1 deficiency leads to enhanced tumorigenesis. We found that colorectal tumors from PTEN/E2F-1 double knockout mice and the human colorectal carcinoma cell line HT29 with shRNA-mediated downregulation of PTEN and E2F-1 exhibit hyperactivation of the RAS-MAPK pathway, accumulation of DNA damage and resistance to apoptosis. To date, this is the first preclinical study evaluating the effect of genetic deletion of E2F-1 in colorectal malignancies driven by PTEN deficiency. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Deletion of Pten in CD45-expressing cells leads to development of T-cell lymphoblastic lymphoma but not myeloid malignancies.

Since its discovery in the late 1990s, Pten has turned out to be one of the most important tumor suppressor genes. Pten loss results in increased activation of the phosphatidylinositol 3-kinase/Akt signaling pathway, which is associated with increased proliferation, survival, and neoplastic growth. Here, we have addressed the effects of conditional deletion of Pten in hematopoietic cells by crossing Pten conditional knockout mice with a knock-in mouse expressing the Cre recombinase in the CD45 locus. CD45 is also known as leukocyte common antigen, and it is expressed in virtually all white cells and in hematopoietic stem cells. Using a reporter mouse, we demonstrate that CD45:Cre mouse displays recombinase activity in both myeloid and lymphoid cells. However, deletion of Pten in CD45-expressing cells induces development of T-cell acute lymphoblastic leukemia and lymphoma, but not other hematologic malignancies.

Palbociclib has antitumour effects on Pten-deficient endometrial neoplasias.

PTEN is one of the most frequently mutated genes in human cancers. The frequency of PTEN alterations is particularly high in endometrial carcinomas. Loss of PTEN leads to dysregulation of cell division, and promotes the accumulation of cell cycle complexes such as cyclin D1-CDK4/6, which is an important feature of the tumour phenotype. Cell cycle proteins have been presented as key targets in the treatment of the pathogenesis of cancer, and several CDK inhibitors have been developed as a strategy to generate new anticancer drugs. Palbociclib (PD-332991) specifically inhibits CDK4/6, and it has been approved for use in metastatic breast cancer in combination with letrazole. Here, we used a tamoxifen-inducible Pten knockout mouse model to assess the antitumour effects of cyclin D1 knockout and CDK4/6 inhibition by palbociclib on endometrial tumours. Interestingly, both cyclin D1 deficiency and palbociclib treatment triggered shrinkage of endometrial neoplasias. In addition, palbociclib treatment significantly increased the survival of Pten-deficient mice, and, as expected, had a general effect in reducing tumour cell proliferation. To further analyse the effects of palbociclib on endometrial carcinoma, we established subcutaneous tumours with human endometrial cancer cell lines and primary endometrial cancer xenografts, which allowed us to provide more translational and predictive data. To date, this is the first preclinical study evaluating the response to CDK4/6 inhibition in endometrial malignancies driven by PTEN deficiency, and it reveals an important role of cyclin D-CDK4/6 activity in their development. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Annexin-A2 as predictor biomarker of recurrent disease in endometrial cancer.

Endometrial carcinomas, the most common malignant tumour of the female genital tract, are usually diagnosed at an early stage with uterine-confined disease and an overall favourable prognosis. However, up to 20% of endometrial carcinomas will end up in recurrent disease, associated with a drop in survival and representing the major clinical challenge. Management of this group of risk patients relies on robust biomarkers that may predict which endometrial carcinomas will relapse. For this, we performed a proteomic analysis comparing primary lesions with recurrences and identified ANXA2 as a potential biomarker associated with recurrent disease that we further validated in an independent series of samples by immunohistochemistry. We demonstrated in vitro a role for ANXA2 in the promotion of metastasis rather than interfering with sensitivity to radio/chemotherapy. In addition, ANXA2 silencing resulted in a reduced metastatic pattern in a mice model of endometrial cancer dissemination, with a limited presence of circulating tumor cells. Finally, a retrospective study in a cohort of 93 patients showed that ANXA2 effectively predicted those endometrioid endometrial carcinomas that finally recurred. Importantly, ANXA2 demonstrated a predictive value also among low risk Stage I endometrioid endometrial carcinomas, highlighting the clinical utility of ANXA2 biomarker as predictor of recurrent disease in endometrial cancer. Retrospective and prospective studies are ongoing to validate ANXA2 as a potential tool for optimal stratification of patients susceptible to receive radical surgery and radio/chemotherapy.

Pro-inflammatory cytokines: emerging players regulating HSC function in normal and diseased hematopoiesis.

Hematopoiesis is the hierarchical process in which all lineages of blood cells are produced by self-renewing hematopoietic stem cells (HSCs) in the bone marrow (BM). While the regulatory factors that maintain proper HSC function and lineage output under normal conditions are well understood, significantly less is known about how HSC fate is regulated in response to inflammation or disease. As many blood disorders are associated with overproduction of pro-inflammatory cytokines, significant interest has emerged in understanding the impact of these factors on HSC function. In this review we highlight key advances demonstrating the impact of pro-inflammatory cytokines on the biology of HSCs and the BM niche, and address ongoing questions regarding their role in normal and pathogenic hematopoiesis.

ERα-mediated repression of pro-inflammatory cytokine expression by glucocorticoids reveals a crucial role for TNFα and IL1α in lumen formation and maintenance.

Most glandular tissues comprise polarized epithelial cells organized around a single central lumen. Although there is active research investigating the molecular networks involved in the regulation of lumenogenesis, little is known about the extracellular factors that influence lumen formation and maintenance. Using a three-dimensional culture system of epithelial endometrial cells, we have revealed a new role for pro-inflammatory cytokines such as TNFα and IL1α in the formation and, more importantly, maintenance of a single central lumen. We also studied the mechanism by which glucocorticoids repress TNFα and IL1α expression. Interestingly, regulation of pro-inflammatory cytokine expression and subsequent lumen formation is mediated by estrogen receptor α (ERα) but not by the glucocorticoid receptor. Finally, we investigated the signaling pathways involved in the regulation of lumen formation by pro-inflammatory cytokines. Our results demonstrate that activation of the ERK/MAPK signaling pathway, but not the PI3K/Akt signaling pathway, is important for the formation and maintenance of a single central lumen. In summary, our results suggest a novel role for ERα-regulated pro-inflammatory cytokine expression in lumen formation and maintenance.

Long-term estradiol exposure is a direct mitogen for insulin/EGF-primed endometrial cells and drives PTEN loss-induced hyperplasic growth.

Loss of tumor-suppressor PTEN is the most common alteration in endometrial carcinoma. However, the relationship between loss of PTEN, growth factors [eg, insulin/insulin-like growth factor (IGF)-1], epidermal growth factor (EGF), and hyperestrogenism in the development of endometrial carcinoma is still controversial. By using three-dimensional (3D) cultures of PTEN(+/+) and PTEN(+/-) endometrial epithelial cells, we investigated the effects of EGF, insulin/IGF, and estradiol in endometrial cell proliferation. We have previously demonstrated that 3D cultures of endometrial cells require EGF and insulin/IGF to proliferate. Herein, we demonstrate that, in the presence of EGF and insulin/IGF, long-term estradiol treatment directly induces proliferation of 3D cultures. Moreover, we show that the mitogenic effects of estradiol require the presence of insulin/IGF and EGF, because withdrawal of such factors completely abolishes estradiol-induced proliferation. In the presence of EGF and insulin/IGF, PTEN(+/-) and PTEN(+/+) spheroids display a similar rate of proliferation. However, the addition of estradiol causes an exaggerated proliferation of PTEN(+/-) cultures, leading to formation of complex structures, such as those observed in endometrial hyperplasia or carcinoma. In summary, we demonstrate that EGF and insulin/IGF prime endometrial epithelial cells to direct the mitogenic effects of estradiol. Furthermore, PTEN deficiency results in enhanced responsiveness to this combination, leading to the development of hyperplasia of endometrial cells in culture.

KSR1 is overexpressed in endometrial carcinoma and regulates proliferation and TRAIL-induced apoptosis by modulating FLIP levels.

The Raf/MEK/extracellular signal-regulated kinase (ERK) pathway participates in many processes altered in development and progression of cancer in human beings such as proliferation, transformation, differentiation, and apoptosis. Kinase suppressor of Ras 1 (KSR1) can interact with various kinases of the Raf/MEK/extracellular signal-regulated kinase pathway to enhance its activation. The role of KSR1 in endometrial carcinogenesis was investigated. cDNA and tissue microarrays demonstrated that expression of KSR1 was up-regulated in endometrial carcinoma. Furthermore, inhibition of KSR1 expression by specific small hairpin RNA resulted in reduction of both proliferation and anchorage-independent cell growth properties of endometrial cancer cells. Because inhibition of apoptosis has a pivotal role in endometrial carcinogenesis, the effects of KSR1 in regulation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis were investigated. KSR1 knock-down sensitized resistant endometrial cell lines to both TRAIL- and Fas-induced apoptosis. Sensitization to TRAIL and agonistic anti-Fas antibody was caused by down-regulation of FLIP (FLICE-inhibitory protein). Also investigated was the molecular mechanism by which KSR1 regulates FLIP protein levels. It was demonstrated that KSR1 small hairpin RNA did not affect FLIP transcription or degradation. Rather, FLIP down-regulation was caused by Fas-associated death domain protein-dependent inhibition of FLIP translation triggered after TRAIL stimulation in KSR1-silenced cells. Re-expression of heterologous KSR1 in cells with down-regulated endogenous KSR1 restored FLIP protein levels and TRAIL resistance. In conclusion, KSR1 regulates endometrial sensitivity to TRAIL by regulating FLIP levels.

Stem cells in human endometrium and endometrial carcinoma.

This study reviews the current knowledge about endometrial somatic stem cells and endometrial cancer stem cells. It describes the main features of somatic stem cells, such as high proliferative potential, self renewal, differentiation into 1 or more lineages, retention of a DNA synthesis label (BrdU), and some methods to identify them (Hoechst dye exclusion test, immunophenotyping). The most likely markers for endometrial somatic stem cells (Oct-4, Musashi-1, CD31, CD34, and CD144) are also mentioned. The study also reviews the literature regarding endometrial cancer stem cells. Results obtained by evaluations of the side population in endometrial cancer cell lines and studies on putative cancer stem cell markers are also discussed. The possible roles of endometrial cancer stem cells in metastasis and resistance to anticancer treatment are also mentioned.

A Smad3-PTEN regulatory loop controls proliferation and apoptotic responses to TGF-ß in mouse endometrium.

The TGF-ß/Smad and the PI3K/AKT signaling pathways are important regulators of proliferation and apoptosis, and their alterations lead to cancer development. TGF-ß acts as a tumor suppressor in premalignant cells, but it is a tumor promoter for cancerous cells. Such dichotomous actions are dictated by different cellular contexts. Here, we have unveiled a PTEN-Smad3 regulatory loop that provides a new insight in the complex cross talk between TGF-ß/Smad and PI3K/AKT signaling pathways. We demonstrate that TGF-ß triggers apoptosis of wild-type polarized endometrial epithelial cells by a Smad3-dependent activation of PTEN transcription, which results in the inhibition of PI3K/AKT signaling pathway. We show that specific Smad3 knockdown or knockout reduces basal and TGF-ß-induced PTEN expression in endometrial cells, resulting in a blockade of TGF-ß-induced apoptosis and an enhancement of cell proliferation. Likewise Smad3 deletion, PTEN knockout prevents TGF-ß-induced apoptosis and increases cell proliferation by increasing PI3K/AKT/mTOR signaling. In summary, our results demonstrate that Smad3-PTEN signaling axis determine cellular responses to TGF-ß.

Cytoplasmic cyclin D1 regulates cell invasion and metastasis through the phosphorylation of paxillin.

Cyclin D1 (Ccnd1) together with its binding partner Cdk4 act as a transcriptional regulator to control cell proliferation and migration, and abnormal Ccnd1·Cdk4 expression promotes tumour growth and metastasis. While different nuclear Ccnd1·Cdk4 targets participating in cell proliferation and tissue development have been identified, little is known about how Ccnd1·Cdk4 controls cell adherence and invasion. Here, we show that the focal adhesion component paxillin is a cytoplasmic substrate of Ccnd1·Cdk4. This complex phosphorylates a fraction of paxillin specifically associated to the cell membrane, and promotes Rac1 activation, thereby triggering membrane ruffling and cell invasion in both normal fibroblasts and tumour cells. Our results demonstrate that localization of Ccnd1·Cdk4 to the cytoplasm does not simply act to restrain cell proliferation, but constitutes a functionally relevant mechanism operating under normal and pathological conditions to control cell adhesion, migration and metastasis through activation of a Ccnd1·Cdk4-paxillin-Rac1 axis.

Effects of the multikinase inhibitors Sorafenib and Regorafenib in PTEN deficient neoplasias.

The phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) axis is frequently dysregulated in cancer due to mutations in different nodes of the pathway or constitutive activation of receptor tyrosine kinases. Multikinase inhibitors as sorafenib and regorafenib represent a therapeutic approach for the treatment of these types of tumours. In the present study, we have evaluated the anti-tumoural effects of Sorafenib and Regorafenib on endometrial, prostate and thyroid neoplasias. Both inhibitors reduced cell viability in vitro and lead to a disruption of the PI3K/AKT/mTOR pathway. In vivo, we have demonstrated that Sorafenib and Regorafenib reduce thyroid hyperplasias induced by the loss of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), although none of the treatments eliminated the disease. Altogether, we present the first study that correlates the response to multikinase inhibitors with a specific mutation. Moreover, this is the first report characterising the response to Regorafenib in thyroid, prostate and endometrial neoplasias.

Combinatorial therapy using dovitinib and ICI182.780 (fulvestrant) blocks tumoral activity of endometrial cancer cells.

Mutations in fibroblast growth factor receptor 2 (FGFR2) have been recently described as a molecular-specific feature in endometrial carcinomas and the presence of activated FGFR2 mutations is associated with poor prognosis. For that reason, inhibition of FGFR2 could be a therapeutic target in the treatment of endometriod carcinomas. In this work, we investigated the antitumoral activity of dovitinib (a multiple kinase inhibitor) in human endometrial cancer cell (ECC) lines. We found that dovitinib caused cell growth arrest, loss of clonogenic growth, and cell-cycle arrest in FGFR2-mutated ECCs in in vitro and in vivo experiments. Next, we investigated the mechanistic basis of dovitinib effects. We could determine that dovitinib modified expression levels of well-known key cell-cycle regulatory proteins that induce cellular senescence. To further investigate the role of dovitinib, we analyzed its effect on estrogen receptor α (ER-α) expression. Surprisingly, we discovered that dovitinib enhances ER-α expression in FGFR2-mutant ECCs. Because blocking one signaling pathway is often not sufficient to cause total tumor regression and the effectiveness of individual inhibitors is often short-lived, we examined the impact of targeting FGFR2 with dovitinib in combination with a selective ER antagonist, fulvestrant (ICI182.780). Combination of dovitinib plus ICI182.780 resulted in a significantly higher inhibition of cell growth than dovitinib treatment alone. These findings suggest that combinatory therapies using dovitinib plus ICI182.780 treatment can be truly effective in patients with endometrial carcinomas carrying FGFR2 mutations.

Optimal protocol for PTEN immunostaining; role of analytical and preanalytical variables in PTEN staining in normal and neoplastic endometrial, breast, and prostatic tissues.

In some tumors, phosphatase and tensin homolog (PTEN) inactivation may have prognostic importance and predictive value for targeted therapies. Immunohistochemistry (IHC) may be an effective method to demonstrate PTEN loss. It was claimed that PTEN IHC showed poor reproducibility, lack of standardization, and variable effects of preanalytical factors. In this study, we developed an optimal protocol for PTEN IHC, with clone 6H2.1, by checking the relevance of analytical variables in normal tissue and tumors of endometrium, breast, and prostate. Pattern and intensity of cellular staining and background nonspecific staining were quantified and subjected to statistical analysis by linear mixed models. The proposed protocol showed a statistically best performance (P < .05) and included a high target retrieval solution, 1:100 primary antibody dilution (2.925 mg/L), FLEX diluent, and EnVisionFLEX+ detection method, with a sensitivity and specificity of 72.33% and 78.57%, respectively. Staining specificity was confirmed in cell lines and animal models. Endometrial carcinomas with PTEN genetic abnormalities showed statistically lower staining than tumors without alterations (mean histoscores, 34.66 and 119.28, respectively; P = .01). Controlled preanalytical factors (delayed fixation and overfixation) did not show any statistically significant effect on staining with optimal protocol (P > .001). However, there was a trend of significance for decreased staining and fixation under high temperature. Moreover, staining was better in endometrial aspirates than in matched hysterectomy specimens, subjected to less controlled preanalytical variables (mean histoscores, 80 and 40, respectively; P = .002). A scoring system combining intensity of staining and percentage of positive cells was statistically associated with PTEN alterations (P = .01).

Combination of Vorinostat and caspase-8 inhibition exhibits high anti-tumoral activity on endometrial cancer cells.

Histone deacetylase inhibitors such as Vorinostat display anti-neoplastic activity against a variety of solid tumors. Here, we have investigated the anti-tumoral activity of Vorinostat on endometrial cancer cells. We have found that Vorinostat caused cell growth arrest, loss of clonogenic growth and apoptosis of endometrial cancer cells. Vorinostat-induced the activation of caspase-8 and -9, the initiators caspases of the extrinsic and the intrinsic apoptotic pathways, respectively. Next, we investigated the role of the extrinsic pathway in apoptosis triggered by Vorinostat. We found that Vorinostat caused a dramatic decrease of FLIP mRNA and protein levels. However, overexpression of the long from of FLIP did not block Vorinostat-induced apoptosis. To further investigate the role of extrinsic apoptotic pathway in Vorinostat-induced apoptosis, we performed an shRNA-mediated knock-down of caspase-8. Surprisingly, downregulation of caspase-8 alone caused a marked decrease in clonogenic ability and reduced the growth of endometrial cancer xenografts in vivo, revealing that targeting caspase-8 may be an attractive target for anticancer therapy on endometrial tumors. Furthermore, combination of caspase-8 inhibition and Vorinostat treatment caused an enhancement of apoptotic cell death and a further decrease of clonogenic growth of endometrial cancer cells. More importantly, combination of Vorinostat and caspase-8 inhibition caused a nearly complete inhibition of tumor xenograft growth. Finally, we demonstrate that cell death triggered by Vorinostat alone or in combination with caspase-8 shRNAs was inhibited by the anti-apoptotic protein Bcl-XL. Our results suggest that combinatory therapies using Vorinostat treatment and caspase-8 inhibition can be an effective treatment for endometrial carcinomas.

Epithelial-to-mesenchymal transition and stem cells in endometrial cancer.

This review article describes the main features of epithelial-to-mesenchymal transition (EMT) and its possible role in understanding myometrial invasion in endometrial carcinoma (EC), as well as the development of malignant mixed Müllerian tumor (MMMT). Moreover, the article discusses the possible role of somatic (SSC) and cancer stem cells (CSC) in EC. Different transcriptional repressors of E-cadherin have been identified in EMT, including Snail and Slug, ZEB1 and ZEB2, and E47 and Twist. The expression of some of these genes is increased at the myoinvasive front and correlates inversely with E-cadherin inmunoreactivity. Whereas the transient occurrence of the EMT phenomenon is important for myometrial invasion in conventional EC, MMMT shows permanent expression of EMT leading to repression of E-cadherin and increased expression of mesenchymal markers including proteins involved in skeletal muscle development. An SSC population, identified as a side population, assessed by the Hoechst dye exclusion test has been identified in human endometrium. CSCs have been defined in analogy to SSC as cancer cells that have the capacity to self-renew, which means undergoing divisions that allow the generation of more identical CSCs and give rise to the variety of more differentiated cells found in the malignancy. Although published data show that CD133(+) cells retain the characteristics of CSC, there is no conclusive evidence showing that CD133 is the universal marker for EC stem cells. Finally, a possible role for endometrial stem cells in the development of ovarian endometriosis and ovarian endometrioid carcinoma is commented.

An inducible knockout mouse to model the cell-autonomous role of PTEN in initiating endometrial, prostate and thyroid neoplasias.

PTEN is one of the most frequently mutated tumor suppressor genes in human cancers. The role of PTEN in carcinogenesis has been validated by knockout mouse models. PTEN heterozygous mice develop neoplasms in multiple organs. Unfortunately, the embryonic lethality of biallelic excision of PTEN has inhibited the study of complete PTEN deletion in the development and progression of cancer. By crossing PTEN conditional knockout mice with transgenic mice expressing a tamoxifen-inducible Cre-ER(T) under the control of a chicken actin promoter, we have generated a tamoxifen-inducible mouse model that allows temporal control of PTEN deletion. Interestingly, administration of a single dose of tamoxifen resulted in PTEN deletion mainly in epithelial cells, but not in stromal, mesenchymal or hematopoietic cells. Using the mT/mG double-fluorescent Cre reporter mice, we demonstrate that epithelial-specific PTEN excision was caused by differential Cre activity among tissues and cells types. Tamoxifen-induced deletion of PTEN resulted in extremely rapid and consistent formation of endometrial in situ adenocarcinoma, prostate intraepithelial neoplasia and thyroid hyperplasia. We also analyzed the role of PTEN ablation in other epithelial cells, such as the tubular cells of the kidney, hepatocytes, colonic epithelial cells or bronchiolar epithelium, but those tissues did not exhibit neoplastic growth. Finally, to validate this model as a tool to assay the efficacy of anti-tumor drugs in PTEN deficiency, we administered the mTOR inhibitor everolimus to mice with induced PTEN deletion. Everolimus dramatically reduced the progression of endometrial proliferations and significantly reduced thyroid hyperplasia. This model could be a valuable tool to study the cell-autonomous mechanisms involved in PTEN-loss-induced carcinogenesis and provides a good platform to study the effect of anti-neoplastic drugs on PTEN-negative tumors.

Defects in innate immunity render breast cancer initiating cells permissive to oncolytic adenovirus.

BACKGROUND: Cancer stem cells/initiating cells (CSC/CIC), are thought to exist as a small population in malignant tissues. They are resistant to conventional cancer treatments and possibly underlie post-treatment relapse. The CIC population can be targeted with capsid modified oncolytic adenoviruses. METHODOLOGY/PRINCIPAL FINDINGS: We studied the mechanisms of innate immunity to oncolytic adenovirus Ad5/3-Delta24 in conventional treatment resistant non-CIC breast cancer cells, breast cancer CD44(+)/CD24(-/low) CIC population and normal breast tissue CD44(+)/CD24(-/low) stem cells. We compared virus recognition by pattern recognition receptors for adenovirus, Toll-like receptors (TLR) 2 and 9 and virus induced type I interferon (IFN) response regulation in these cell types. We show TLR mediated virus recognition in these non-immune cell types. Normal tissue stem cells have intact type I IFN signaling. Furthermore, TLR9 and TLR2 reside constantly in recognition sites, implying constant activation. In contrast, breast cancer CD44(+)/CD24(-/low) CIC have dysregulated innate immune responses featuring dysfunctional virus recognition caused by impaired trafficking of TLR9 and cofactor MyD88 and the absence of TLR2, having a deleterious impact on TLR pattern recognition receptor signaling. Furthermore, the CIC have increased inhibitory signaling via the suppressor of cytokine signaling/Tyro3/Axl/Mer receptor tyrosine kinase (SOCS/TAM) pathway. These defects in contribute to dysfunctional induction of type I IFN response in CIC and therefore permissivity to oncolytic adenovirus. CONCLUSIONS/SIGNIFICANCE: CICs may underlie the incurable nature of relapsed or metastatic cancers and are therefore an important target regarding diagnostic and prognostic aspects as well as treatment of the disease. This study addresses the mechanisms of innate infection immunity in stem cells deepening the understanding of stem cell biology and may benefit not only virotherapy but also immunotherapy in general.