CD81 drives immune evasion in radioresistant glioblastoma by blocking selective autophagic degradation of CD274/PD-L1

Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor, for which radiotherapy constitutes the key component of standard comprehensive treatment; however, tumor relapse could inevitably arise from intrinsically radioresistant GBM subclones. Radiotherapy exerts biphasic regulatory effects on the tumor immune microenvironment (TIME), with transient activation followed by sustained immunosuppression. Nevertheless, it remains elusive how radioresistant GBM cells remodel such an immunosuppressive TIME to evade immune surveillance. Herein, integrative analyses encompassing clinical specimens, public single-cell RNA-seq datasets, orthotopic glioma models, primary CD8⁺ T cell co-culture systems, and tandem mass tag (TMT) proteomics indicated that CD81 was highly expressed in radioresistant GBM and governed GBM immune evasion. CD81-high tumor cells were surrounded by functionally exhausted CD8⁺ T cells, alongside immunosuppressive signature within neighboring myeloid and NK cells. CD81 depletion promoted selective macroautophagic/autophagic degradation of CD274/PD-L1, increased CD8⁺ T cell infiltration and cytotoxic activity, reduced M2-like tumor-associated macrophages, and suppressed intracranial tumor growth. Moreover, CD81-knockdown augmented the antitumor efficacy of anti-PDCD1/PD-1, yielding a pronounced survival benefit when combined with radiotherapy. Mechanistically, CD81 interacted with CD274 via its large extracellular loop (LEL) and recruited the deubiquitinase USP14 through its cytoplasmic C-terminal tail (CCT). This resultant ternary complex erased K63-linked ubiquitination at the K280 residue of CD274, thereby abolishing SQSTM1/p62-dependent recognition and subsequent autophagy-lysosomal degradation of CD274 to maintain its protein stability. Collectively, our work establishes CD81 as a pivotal bridge connecting radioresistance to immune escape via sustaining CD274 abundance in GBM, highlighting CD81 as a promising therapeutic target to optimize radioimmunotherapy.Abbreviations: BBB: blood-brain barrier; CTLs: cytotoxic T lymphocytes; CCK-8: cell counting kit-8; ELISA: enzyme-linked immunosorbent assay; GBM: glioblastoma; IHC: Immunohistochemistry; GZMB: granzyme B; MDSCs: myeloid-derived suppressor cells; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; OS: overall survival; PFA: paraformaldehyde; PLA: proximity ligation assay; PRF1: Perforin1; STR: short tandem repeat; SQSTM1: sequestosome 1; TMT: tandem mass tag; TMZ: temozolomide; TME: tumor microenvironment; TDEs: tumor-derived exosomes; T_regs: regulatory T cells; WT: wild type.