Effect of H3K18 lactylation in cancer-associated fibroblasts on malignant pleural effusion progression via recruiting of TNFR2 ⁺ Tregs.

e20028 Background: TNFR2 + Tregs, which are recognized as the maximally suppressive subset of Tregs, play a pivotal role in maintaining the immunosuppressive environment within tumors via dampening the anti-tumor response of CD8 + T cells. Our previous research indicated a significant increase in TNFR2 + Tregs in malignant pleural effusion (MPE), leading to a poor prognosis for MPE patients. However, the mechanisms underlying this accumulation have remained unclear. Methods: RNA-sequencing analysis was performed to portray the chemotactic profiles of TNFR2 + Tregs. The chemotaxis axis of TNFR2 + Tregs were identified through transwell assays and MPE models. Single-cell RNA sequencing (scRNA-seq) analysis from public database and CUT&Tag assays were used to investigate the mechanisms that regulating the chemotactic axis. Results: In current study, we have uncovered that the CXCL16/CXCR6 axis is of importance in recruiting TNFR2 + Tregs to MPE. Additionally, cancer-associated fibroblasts (CAFs) have been identified as the primary driver of this chemotactic pathway. Mechanistically, within the hypoxic milieu characteristic of the pleural cavity, CAFs in MPE engage in glycolysis, which in turn leads to an increase in the production of endogenous lactate. The elevated lactate induces H3K18 lactylation in the promoter regions of both the CXCL16 gene and its transcription factor FOXO3, thereby upregulating CXCL16 expression. Subsequently, TNFR2 + Tregs, which highly express CXCR6, the only receptor for CXCL16, are efficiently recruited to MPE. The influx of TNFR2 + Tregs intensifies the immunosuppression within MPE, thereby facilitating disease progression. Conclusions: CAFs-derived lactate induces CXCL16 expression via H3K18 lactylation, facilitating TNFR2 + Treg recruitment and accelerating MPE progression. This study reveals a novel regulatory mechanism governing immunosuppression in MPE, providing new insights for developing therapeutic strategies aimed at disrupting this immunosuppressive process.