DNMT1 is associated with anti-PD-1 resistance and regulates the STAT3/PD-L1-CD8⁺ T-cell axis in melanoma

Transcriptomic analysis of melanoma (MM) patients receiving anti-programmed cell death protein 1 (anti-PD-1) blockade identified differentially expressed genes and co-expression modules associated with therapeutic response. Integrated transcriptomic and proteomic analyses, together with least absolute shrinkage and selection operator (LASSO) regression, identified deoxyribonucleic acid (DNA) methyltransferase 1 (DNMT1) as a key resistance-associated factor. Functional enrichment suggested that DNMT1 was involved in DNA methylation, immune activation, and extracellular matrix remodeling. Further immune infiltration and single-cell analyses showed that high DNMT1 expression was associated with reduced cluster of differentiation 8-positive (CD8⁺) T-cell infiltration and an immunosuppressive tumor microenvironment. Mechanistically, DNMT1 was linked to signal transducer and activator of transcription 3 (STAT3) activation and programmed death-ligand 1 (PD-L1) upregulation. In MM cell models, DNMT1 knockdown reduced STAT3/PD-L1 signaling and enhanced CD8⁺ T-cell cytotoxic activity, as reflected by increased interferon gamma (IFN-γ) and Granzyme B production. Both genetic DNMT1 knockdown and pharmacological DNMT1 inhibition enhanced CD8⁺ T-cell-mediated antitumor activity in MM-CD8⁺ T-cell co-culture systems, and nivolumab further strengthened these effects under in vitro conditions. These findings identify DNMT1 as a resistance-associated epigenetic regulator and suggest that DNMT1 may participate in anti-PD-1 resistance through the STAT3/PD-L1-CD8⁺ T-cell axis. Further in vivo studies are required to validate whether DNMT1 inhibition can enhance the therapeutic efficacy of anti-PD-1 therapy in MM.