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Resistance to immune checkpoint therapy (ICT) presents a growing clinical challenge. The tumor microenvironment (TME) and its components, namely tumor-associated macrophages (TAMs) and cancer-associated fibroblasts (CAFs), play a pivotal role in ICT resistance; however, the underlying mechanisms remain under investigation. In this study, we identify expression of TNF-Stimulated Factor 6 (TSG-6) in ICT-resistant pancreatic tumors, compared to ICT-sensitive melanoma tumors, both in mouse and human. TSG-6 is expressed by CAFs within the TME, where suppressive macrophages expressing Arg1 , Mafb , and Mrc1 , along with TSG-6 ligand Cd44 , predominate. Furthermore, TSG-6 expressing CAFs co-localize with the CD44 expressing macrophages in the TME. TSG-6 inhibition in combination with ICT improves therapy response and survival in pancreatic tumor-bearing mice by reducing macrophages expressing immunosuppressive phenotypes and increasing CD8 T cells. Overall, our findings propose TSG-6 as a therapeutic target to enhance ICT response in non-responsive tumors. Pancreatic ductal carcinoma (PDAC) is characterized by an immunosuppressive tumor microenvironment (TME) enriched in stromal cells. Here the authors show that TSG-6-positive cancer associated fibroblasts modulate myeloid cell responses and that TSG-6 targeting improves response to immune checkpoint inhibitors in preclinical PDAC models.

The activation and functional differentiation of CD8 + T cells are linked to metabolic pathways that result in the production of lactate. Lactylation is a lactate-derived histone post-translational modification; however, the relevance of histone lactylation in the context of CD8 + T cell activation and function is not known. Here, we show the enrichment of H3K18 lactylation (H3K18la) and H3K9 lactylation (H3K9la) in human and mouse CD8 + T cells, which act as transcription initiators of key genes regulating CD8 + T cell function. Further, we note distinct patterns of H3K18la and H3K9la in CD8 + T cell subsets linked to their specific metabolic profiles. Additionally, we find that modulation of H3K18la and H3K9la by targeting metabolic and epigenetic pathways influence CD8 + T cell effector function, including antitumor immunity, in preclinical models. Overall, our study uncovers the potential roles of H3K18la and H3K9la in CD8 + T cells. Goswami and colleagues describe how lactylation of histone lysine residues regulates the transcriptome, metabolism and function of CD8 + T cells.

Glioblastoma (GBM) tumors are enriched in immune-suppressive myeloid cells and are refractory to immune checkpoint therapy (ICT). Targeting epigenetic pathways to reprogram the functional phenotype of immune-suppressive myeloid cells to overcome resistance to ICT remains unexplored. Single-cell and spatial transcriptomic analyses of human GBM tumors demonstrated high expression of an epigenetic enzyme-histone 3 lysine 27 demethylase (KDM6B)-in intratumoral immune-suppressive myeloid cell subsets. Importantly, myeloid cell-specific Kdm6b deletion enhanced proinflammatory pathways and improved survival in GBM tumor-bearing mice. Mechanistic studies showed that the absence of Kdm6b enhances antigen presentation, interferon response and phagocytosis in myeloid cells by inhibition of mediators of immune suppression including Mafb, Socs3 and Sirpa. Further, pharmacological inhibition of KDM6B mirrored the functional phenotype of Kdm6b-deleted myeloid cells and enhanced anti-PD1 efficacy. This study thus identified KDM6B as an epigenetic regulator of the functional phenotype of myeloid cell subsets and a potential therapeutic target for enhanced response to ICT.

Glioblastoma (GBM) tumors are enriched in immune-suppressive myeloid cells and are refractory to immune checkpoint therapy (ICT). Targeting epigenetic pathways to reprogram the functional phenotype of immune-suppressive myeloid cells to overcome resistance to ICT remains unexplored. Single-cell and spatial transcriptomic analyses of human GBM tumors demonstrated high expression of an epigenetic enzyme - histone 3 lysine 27 demethylase (KDM6B) in intra-tumoral immune-suppressive myeloid cell subsets. Importantly, myeloid-cell specific Kdm6b deletion enhanced pro-inflammatory pathways and improved survival in GBM tumor-bearing mice. Mechanistic studies elucidated that the absence of Kdm6b enhances antigen-presentation, interferon response and phagocytosis in myeloid cells by inhibiting mediators of immune suppression including Mafb, Socs3 and Sirpa. Further, pharmacological inhibition of KDM6B mirrored the functional phenotype of Kdm6b deleted myeloid cells and enhanced anti-PD1 efficacy. Thus, this study identified KDM6B as an epigenetic regulator of the functional phenotype of myeloid cell subsets and a potential therapeutic target to improve response to ICT.Competing Interest StatementP.S. reports consulting, advisory roles, and/or stocks/ownership for Achelois, Apricity Health, BioAlta, Codiak BioSciences, Constellation, Dragonfly Therapeutics, Forty-Seven Inc., Hummingbird, ImaginAb, Jounce Therapeutics, Lava Therapeutics, Lytix Biopharma, Marker Therapeutics, BioNTx, Oncolytics, Glympse, Infinity Pharma, and Polaris and owns a patent licensed to Jounce Therapeutics.