MNDA promotes immunosuppression in microsatellite instability-high colorectal cancer by facilitating PMN-MDSC infiltration via H3K18 lactylation

BACKGROUND: Immune checkpoint inhibitors (ICIs) targeting programmed death-1 (PD-1) have demonstrated significant clinical benefit in colorectal cancer (CRC) with microsatellite instability-high (MSI-H) status, yet a substantial subset of patients remains resistant to therapy. Understanding the mechanisms of resistance and identifying new therapeutic targets are urgently needed. METHODS: We established a murine MC38-based MSI-H CRC model to investigate the variability in PD-1 treatment response and performed single-cell RNA sequencing (scRNA-seq) on tumors from patients with PD-1-sensitive and PD-1-resistant CRC. Immune cell subsets and signaling pathways were analyzed using CellChat and AUCell, and gene expression enrichment was performed. Functional assays, including RNA-seq, ChIP-seq, qRT-PCR, and Co-IP, were employed to characterize the role of MNDA and its downstream targets. RESULTS: scRNA-seq analysis revealed a significant enrichment of polymorphonuclear neutrophil myeloid-derived suppressor cells (PMN-MDSCs) in PD-1-resistant MSI-H CRC, accompanied by increased lactylation activity and high MNDA expression. Further investigations revealed that MNDA recruits the histone acetyltransferase EP300 to the CXCR2 promoter, mediating H3K18 lactylation and enhancing CXCR2 transcription. This promotes PMN-MDSC infiltration and the establishment of an immunosuppressive microenvironment, thereby impairing PD-1 efficacy. Inhibition of the MNDA/EP300-CXCR2 axis reversed H3K18la modification, reduced PMN-MDSC infiltration, remodeled the immune microenvironment, and restored sensitivity to PD-1 therapy. CONCLUSIONS: Our study reveals a novel mechanism by which MNDA-driven H3K18 lactylation of the CXCR2 promoter facilitates immune evasion and PD-1 resistance in MSI-H CRC. Targeting the MNDA/EP300-CXCR2 regulatory axis represents a promising strategy for overcoming ICI resistance and enhancing the therapeutic benefit in CRC.