Polycomb Repressor Complexes (PRCs) are important regulators of embryogenesis. In embryonic stem (ES) cells many genes that regulate subsequent stages in development are enriched at their promoters for PRC1, PRC2 and Ser 5-phosphorylated RNA Polymerase II (RNAP), and contain domains of 'bivalent' chromatin (enriched for H3K4me3; histone H3 di- or trimethylated at Lys 4 and H3K27me3; histone H3 trimethylated at Lys 27). Loss of individual PRC components in ES cells can lead to gene de-repression and to unscheduled differentiation. Here we show that Jarid2 is a novel subunit of PRC2 that is required for the co-recruitment of PRC1 and RNAP to genes that regulate development in ES cells. Jarid2-deficient ES cells showed reduced H3K4me2/me3 and H3K27me3 marking and PRC1/PRC2 recruitment, and did not efficiently establish Ser 5-phosporylated RNAP at target genes. ES cells lacking Jarid2, in contrast to previously characterized PRC1 and PRC2 mutants, did not inappropriately express PRC2 target genes. Instead, they show a severely compromised capacity for successful differentiation towards neural or mesodermal fates and failed to correctly initiate lineage-specific gene expression in vitro. Collectively, these data indicate that transcriptional priming of bivalent genes in pluripotent ES cells is Jarid2-dependent, and suggests that priming is critical for subsequent multi-lineage differentiation.

Tumor mutational burden (TMB), the total number of somatic coding mutations in a tumor, is emerging as a promising biomarker for immunotherapy response in cancer patients. TMB can be quantitated by a number of NGS-based sequencing technologies. Whole Exome Sequencing (WES) allows comprehensive measurement of TMB and is considered the gold standard. However, to date WES remains confined to research settings, due to high cost of the large genomic space sequenced. In the clinical setting, instead, targeted enrichment panels (gene panels) of various genomic sizes are emerging as the routine technology for TMB assessment. This stimulated the development of various methods for panel-based TMB quantification, and prompted the multiplication of studies assessing whether TMB can be confidently estimated from the smaller genomic space sampled by gene panels. In this review, we inventory the collection of available gene panels tested for this purpose, illustrating their technical specifications and describing their accuracy and clinical value in TMB assessment. Moreover, we highlight how various experimental, platform-related or methodological variables, as well as bioinformatic pipelines, influence panel-based TMB quantification. The lack of harmonization in panel-based TMB quantification, of adequate methods to convert TMB estimates across different panels and of robust predictive cutoffs, currently represents one of the main limitations to adopt TMB as a biomarker in clinical practice. This overview on the heterogeneous landscape of panel-based TMB quantification aims at providing a context to discuss common standards and illustrates the strong need of further validation and consolidation studies for the clinical interpretation of panel-based TMB values. Electronic supplementary material The online version of this article (10.1186/s40425-019-0647-4) contains supplementary material, which is available to authorized users.

Highlights d Metformin plus fasting-induced hypoglycemia synergistically reduces tumor growth d PP2A-GSK3b-MCL-1 axis mediates the synergistic cytotoxicity of the combination d Simultaneous CIP2A inhibition and B56d upregulation dictate combination specificity

Group 2 innate lymphoid cells (ILC2s) are involved in human diseases, such as allergy, atopic dermatitis and nasal polyposis, but their function in human cancer remains unclear. Here we show that, in acute promyelocytic leukaemia (APL), ILC2s are increased and hyper-activated through the interaction of CRTH2 and NKp30 with elevated tumour-derived PGD2 and B7H6, respectively. ILC2s, in turn, activate monocytic myeloid-derived suppressor cells (M-MDSCs) via IL-13 secretion. Upon treating APL with all-trans retinoic acid and achieving complete remission, the levels of PGD2, NKp30, ILC2s, IL-13 and M-MDSCs are restored. Similarly, disruption of this tumour immunosuppressive axis by specifically blocking PGD2, IL-13 and NKp30 partially restores ILC2 and M-MDSC levels and results in increased survival. Thus, using APL as a model, we uncover a tolerogenic pathway that may represent a relevant immunosuppressive, therapeutic targetable, mechanism operating in various human tumour types, as supported by our observations in prostate cancer.