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Background: The heterogeneity limits the effective application of immune checkpoint inhibitors for patients with stomach adenocarcinoma (STAD). Precise immunotyping can help select people who may benefit from immunotherapy and guide postoperative management by describing the characteristics of tumor microenvironment. Methods: Gene expression profiles and clinical information of patients were collected from ACRG and TCGA-STAD datasets. The immune subtypes (ISs) were identified by consensus clustering analysis. The tumor immune microenvironments (TIME) of each IS were characterized using a series of immunogenomics methods and further confirmed by multiplex immunohistochemistry (mIHC) staining in clinical samples. Two online datasets and one in-house dataset were utilized to construct and validate a prognostic immune-related gene (IRG) signature. Results: STAD patients were stratified into five reproducible ISs. IS1 (immune deserve subtype) had low immune infiltration and the highest degree of HER2 gene mutation. With abundant CD8+ T cells infiltration and activated cytotoxicity reaction, patients in the IS2 (immune-activated subtype) had the best overall survival (OS). IS3 and IS4 subtypes were both in the reactive stroma state and indicated the worst prognosis. However, IS3 (immune-inhibited subtype) was characterized by enrichment of FAP+ fibroblasts and upregulated TGF-β signaling pathway, while IS4 (activated stroma subtype) was characterized by enrichment of ACTA2+ fibroblasts. In addition, mIHC staining confirmed that TGF-β upregulated FAP+ fibroblasts were independent risk factor of OS. IS5 (chronic inflammation subtype) displayed moderate immune cells infiltration and had a relatively good survival. Lastly, we developed a nine-IRG signature model with a robust performance on overall survival prognostication. Conclusions: The immunotyping is indicative for characterize the TIME heterogeneity and the prediction of tumor prognosis for STADs, which may provide valuable stratification for the design of future immunotherapy. [ABSTRACT FROM AUTHOR]

The cell-free DNA (cfDNA) methylation profile in liquid biopsy has been utilized to diagnose early-stage disease and estimate therapy response. However, typical clinical procedures are capable of purifying only very small amounts of cfDNA. Whole-genome bisulfite sequencing (WGBS) is the gold standard for measuring DNA methylation; however, WGBS using small amounts of fragmented DNA introduces a critical challenge for data analysis, namely a low-mapping ratio. The resulting low sequencing depth and low coverage of CpG sites genome-wide is a bottleneck for the clinical application of cfDNA-based WGBS assays. We developed LiBis (Low-input Bisulfite Sequencing), a novel method for low-input WGBS data alignment. By dynamically clipping initially unmapped reads and remapping clipped fragments, we judiciously rescued those reads and uniquely aligned them to the genome. By substantially increasing the mapping ratio by up to 88%, LiBis dramatically improved the number of informative CpGs and the precision in quantifying the methylation status of individual CpG sites. LiBis significantly improved the cost efficiency of low-input WGBS experiments by dynamically removing contamination introduced by random priming. The high sensitivity and cost effectiveness afforded by LiBis for low-input samples will allow the discovery of genetic and epigenetic features suitable for downstream analysis and biomarker identification using liquid biopsy. [ABSTRACT FROM AUTHOR]

Despite the immense success of immune checkpoint blockade (ICB) in cancer treatment, many tumors, including melanoma, exhibit innate or adaptive resistance. Tumor-intrinsic T-cell deficiency and T-cell dysfunction have been identified as essential factors in the emergence of ICB resistance. Here, we found that protein arginine methyltransferase 1 (PRMT1) expression was inversely correlated with the number and activity of CD8+ T cells within melanoma specimen. PRMT1 deficiency or inhibition with DCPT1061 significantly restrained refractory melanoma growth and increased intratumoral CD8+ T cells in vivo. Moreover, PRMT1 deletion in melanoma cells facilitated formation of double-stranded RNA derived from endogenous retroviral elements (ERV) and stimulated an intracellular interferon response. Mechanistically, PRMT1 deficiency repressed the expression of DNA methyltransferase 1 (DNMT1) by attenuating modification of H4R3me2a and H3K27ac at enhancer regions of Dnmt1, and DNMT1 downregulation consequently activated ERV transcription and the interferon signaling. Importantly, PRMT1 inhibition with DCPT1061 synergized with PD-1 blockade to suppress tumor progression and increase the proportion of CD8+ T cells as well as IFNγ+CD8+ T cells in vivo. Together, these results reveal an unrecognized role and mechanism of PRMT1 in regulating antitumor T-cell immunity, suggesting PRMT1 inhibition as a potent strategy to increase the efficacy of ICB., Significance: Targeting PRMT1 stimulates interferon signaling by increasing expression of endogenous retroviral elements and double-stranded RNA through repression of DNMT1, which induces antitumor immunity and synergizes with immunotherapy to suppress tumor progression., (©2023 American Association for Cancer Research.)