Abstract

The programmed cell death protein 1 (PD-1) / programmed death-ligand 1 (PD-L1) axis represents a cornerstone of cancer immunotherapy, yet the dynamic shuttling of PD-L1 between endosomal recycling and lysosomal degradation routes limits durable responses. Using a CRISPR screen targeting glycosphingolipid metabolism, we identify transmembrane 9 superfamily member 2 (TM9SF2) as a key regulator of PD-L1 levels. TM9SF2 orchestrates a dual mechanism: it recruits phosphoglycerate kinase 1 (PGK1) to promote PD-L1 recycling to the plasma membrane while dismantling the huntingtin-interacting protein 1-related protein (HIP1R)-mediated lysosomal degradation pathway. Genetic or pharmacological disruption of the TM9SF2-PGK1 complex depletes PD-L1 levels and boosts antitumor immunity. Further, the endogenous ceramide species Cer(d18:1/26:0) destabilizes this complex, triggering PD-L1 lysosomal destruction and potentiating antitumor immunity. These findings delineate a ceramide-gated sorting mechanism within the endosomal network, revealing a druggable metabolic switch to disrupt immune evasion and amplify checkpoint blockade efficacy. The PD-1/PD-L1 pathway is central to immunotherapy, but PD-L1 recycling limits durable responses. This study identifies TM9SF2 as a key regulator of PD-L1 trafficking and shows that disrupting its PGK1-dependent complex depletes PD-L1 and enhances antitumor immunity.