EIF5B drives integrated stress response-dependent translation of PD-L1 in lung cancer

Cancer cells express high levels of PD-L1, a ligand of the PD-1 receptor on T cells, allowing tumors to suppress T cell activity 1-3. Clinical trials utilizing monoclonal antibodies that disrupt the PD-1/PD-L1 immune checkpoint have yielded remarkable results, with PD-1 immunotherapy approved as a first-line therapy for human lung cancer patients 4-6. Despite significant progress in targeting this pathway, the mechanisms through which PD-L1 is upregulated in non-small cell lung cancer (NSCLC) and other tumor types remain incompletely understood. Here we used CRISPR-based screening to identify regulators of PDL1 in human lung cancer cells, revealing potent induction of PD-L1 levels upon disruption of the heme biosynthesis pathway. Impairment of heme production activates the integrated stress response (ISR), allowing bypass of inhibitory upstream open reading frames in the PD-L1 5¢ UTR, resulting in enhanced PD-L1 translation and suppression of anti-tumor immunity. We further demonstrated that ISR-dependent translation of PD-L1 requires the translation initiation factor EIF5B. EIF5B overexpression, which is frequent in human lung cancers and is associated with poor prognosis, is sufficient to induce PD-L1. These findings uncover a new mechanism of immune checkpoint activation and suggest novel targets for therapeutic intervention. H358 cells were transuced with lentiCRISPR V2 library virus, selected and sorted by PD-L1-APC. Genomic DNA was isolated and deep sequencing was performed to identify sgRNA enriched in sorted vs unsorted cells