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BackgroundRhabdomyosarcomas (RMSs) are the most frequent soft tissue sarcoma in children and adolescents, defined by skeletal muscle differentiation and the status of FOXO1 fusions. In pediatric malignancies, in particular RMS, scant and controversial observations are reported about PD-L1 expression as a putative biomarker and few immune checkpoint clinical trials are conducted.MethodsPD-L1 assessment was evaluated by immunohistochemistry (IHC) utilizing two anti-PDL1 antibodies, in a pilot cohort of 25 RMS. Results were confirmed in primary and commercial RMS cell lines by cytofluorimetric analysis and IHC.ResultsPD-L1 expression was detectable, by both anti-PD-L1 antibodies, in the immune contexture of immune cells infiltrating and/or surrounding the tumor, in 15/25 (60%) RMS, while absent expression was observed in neoplastic cells. Flow cytometry analysis and PD-L1 IHC of commercial and primary RMS cell lines confirmed a very small percentage of PD-L1 positive-tumor cells, under the detection limits of conventional IHC. Interestingly, increased PD-L1 expression was observed in the immune contexture of 4 RMS cases post chemotherapy compared to their matched pre-treatment samples.ConclusionHere we identify a peculiar pattern of PD-L1 expression in our RMS series with scanty positive-tumor cells detected by flow cytometry, and recurrent expression in the immune cells surrounding or infiltrating the tumor burden.Electronic supplementary materialThe online version of this article (10.1186/s12885-018-4554-8) contains supplementary material, which is available to authorized users.

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In lung cancer CD133+ cells have properties of cancer initiating cells (CICs) as stemness features, high tumorigenic potential and chemoresistance. Within the CD133+ CICs, we have recently identified a specific subset, defined as CD133+CXCR4+EpCAM-, endowed with high dissemination and metastatic potential (metastasis initiating cells, MICs). In normal tissues stem cells reside in specialized niches composed of both stromal cells and extracellular matrix proteins (ECM) while factors responsible for CICs maintenance and modulation are relatively unknown. Collagen, the most abundant protein of ECM, plays a pivotal role in mediating regulation of adhesion, survival and proliferation of tumor cells. The relevance of collagen glycosylation, a fundamental post-translational modification controlling several biological processes, remains however largely unexplored. To investigate the effects of interactions between tumor cells and differentially glycosylated ECM epitopes, we cultured primary (LT73) and established lung cancer cell lines (A549, H460) on type I collagen films neo-glycosylated with glucose, galactose or sialic acid residues. Our results showed a general increase of CICs subsets, evaluated by flow cytometry, in tumor cells cultured on glycosylated collagen compared to pristine collagen or tissue culture plates with a concomitant increased expression of stemness-related genes. Particularly, we observed that collagen functionalized with glucose had the highest efficiency in enriching for MICs (3-fold change). Analysis of proliferation and viability of tumor cells cultured on collagen films showed that glucose residues were particularly proficient in causing G1 phase growth arrest and cell death compared to pristine collagen resulting in an overall decrease in the bulk population and CICs enrichment. In PKH label-retention assays, glucose-glycosylated collagen also selected and increased the fraction of PHK-labeled quiescent tumor cells, enriched for MICs component, confirming the preferential selection/survival of MICs subset. Using LT73 cell line depleted for CD133+ cells, we then proved that CICs increase was also due to a de novo generation of CD133+ cells and in particular of CD133+CXCR4+EpCAM- metastatic subset through non-CICs to CICs conversion. The immunophenotypic increase of CD133+ cells was functionally validated in vivo by a limiting dilution tumorigenic assay that estimated a 4.6 higher frequency of CICs in LT73 cells cultured on glucose-glycosylated collagen compared to control group. Moreover tumors derived from cells exposed to glucose residues retained a higher contents of MICs associated with an increased dissemination potential compared to controls. Our results suggest that differential collagen glycosylation could play an essential role in the creation of a niche favorable for the generation and selection/survival of lung metastasis initiating cells. Citation Format: Giulia Bertolini, Cecilia Gardelli, Francesca Andriani, Massimo Moro, Laura Russo, Laura Cipolla, Gabriella Sozzi, Luca Roz. Differential glycosylation of extracellular matrix specifically modulates lung cancer initiating cells subsets. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3351.