LncRNA MIR31HG facilitates immune escape in head and neck squamous cell carcinoma by promoting heterotypic cell-in-cell formation.

The aggressive nature of head and neck squamous cell carcinoma (HNSCC) is profoundly shaped by a complex interplay between malignant cells and the host immune system. A key feature of this interplay is the formation of cell-in-cell (CIC) structures, which facilitate immune evasion and contribute to shaping the tumor microenvironment. Long non-coding RNAs (lncRNAs), including MIR31HG, have emerged as crucial modulators of tumor immunity and metastasis. In this study, we investigated the role of MIR31HG in orchestrating heterotypic CIC formation and assessed its impact on tumor growth, immune surveillance, and chemoresistance in HNSCC. Analysis of TCGA and GTEx datasets confirmed the differential expression of CIC-related genes between HNSCC and normal tissues. Functional assays demonstrated that CIC structure formation substantially augmented the malignant properties of Cal27 cells, including increased resistance to both cisplatin and gemcitabine. Critically, genetic depletion of MIR31HG in CIC-positive cells (CIC⁺ sh-MIR31HG) potently suppressed tumor progression, as evidenced by reduced cell proliferation and increased apoptosis. Furthermore, silencing MIR31HG also remodeled the immunosuppressive landscape; it downregulated the expression of immune checkpoint protein PD-L1 and decreased the secretion of immunosuppressive cytokines TGF-β and IL-10. This intervention also reversed therapeutic resistance, rendering CIC⁺ sh-MIR31HG cells more susceptible to cisplatin- and gemcitabine-induced apoptosis. These findings were validated in a murine xenograft model, where histological analyses confirmed that tumors originating from CIC⁺ sh-MIR31HG cells displayed reduced volume and elevated apoptotic activity. Collectively, MIR31HG is a pivotal regulator of heterotypic CIC formation in HNSCC. This mechanism promotes HNSCC cell survival, fosters an immunosuppressive microenvironment, and drives chemoresistance. Therefore, targeting MIR31HG represents a viable therapeutic avenue to disrupt immune resistance and enhance chemosensitivity in HNSCC.