Clonal LIMD1 loss drives PD-L1 immune evasion via ARIH1-dependent ubiquitination in lung cancer.

LIMD1, a tumour suppressor located at chromosome 3p21.3, is frequently lost in non-small-cell lung cancer, yet its role in tumour-immune interactions remains unclear. Here, we show LIMD1 loss increases PD-L1 protein abundance across multiple lung cancer models and primary airway epithelial cells. Mechanistically, LIMD1 restrains PD-L1 through post-transcriptional and post-translational mechanisms. LIMD1 loss can relieve microRNA-mediated repression of the CD274 3'UTR, and LIMD1 loss can also disrupt ARIH1-PD-L1 association, reduce PD-L1 polyubiquitination, and stabilise PD-L1 protein without a commensurate increase in CD274 transcript levels in isogenic models. Functionally, LIMD1-deficient tumour cells suppress CD8+ T-cell activation in vitro and show enhanced sensitivity to PD-1/PD-L1 blockade in tumour-PBMC co-culture assays. Analysis of TRACERx non-small-cell lung cancer samples revealed clonal LIMD1 loss of heterozygosity in ∼40% of lung adenocarcinomas, where it is associated with increased tumour PD-L1 expression. Across independent patient cohorts receiving immune checkpoint blockade, low LIMD1 expression was enriched among responders. We identify LIMD1 as a tumour-intrinsic regulator of PD-L1 turnover and suggest that tumour suppressor loss can shape immune checkpoint biology and influence immunotherapy response.