Ectopic HLA-II Expression in ESCC: Exploration of Its Relationship with Neoantigen Burden and Patient Survival

Ectopic expression of human leukocyte antigen class II (HLA-II) on tumor cells correlates with anti-tumor immunity and prognosis in various cancers, but its role in esophageal squamous cell carcinoma (ESCC) remains unclear. HLA-II expression was evaluated in 34 ESCC tissue sections and a 102-sample tissue microarray (TMA) using immunohistochemistry (IHC) and in 10 ESCC cell lines via flow cytometry. Transcriptome sequencing of KYSE270, KYSE180, KYSE450, and KYSE510 was performed to investigate HLA-II regulatory mechanisms, while tumor samples from 104 ESCC patients were analyzed for neoantigen load. The prognostic significance of neoantigen burden was assessed using Cox regression. HLA-II was ectopically expressed in ESCC, with positivity rates of 20.59% (34 tissues) and 25.49% (TMA). Among 10 ESCC cell lines, only KYSE270 exhibited spontaneous HLA-II expression. Transcriptome analysis revealed 1278 KYSE270-specific genes enriched in immune-related pathways (e.g., "Cytokine-cytokine receptor interaction"), suggesting immune-mediated HLA-II regulation. IFN-γ stimulation induced HLA-II expression in KYSE180, KYSE450, and KYSE510, indicating broader inducible HLA-II potential. In 104 patients, MHC-II-restricted neoantigen burden varied widely (0-75) and lacked direct correlation with HLA-II expression. Additionally, MHC-II-restricted neoantigen load was not significantly associated with overall survival (p > 0.05). Ectopic HLA-II expression in ESCC may influence the tumor immune microenvironment, while the prognostic value of MHC-II-restricted neoantigen burden in ESCC remains unclear, providing potential implications for immunotherapy strategies.