Abstract
Background
Metabolic reprogramming within the tumor microenvironment is a pivotal barrier to effective immune checkpoint blockade (ICB). While programmed death ligand 1 (PD-L1) is well characterized as a ligand inhibiting T-cell function, its intrinsic ‘reverse signaling’ role in regulating tumor metabolism and shaping the immune landscape remains poorly understood. Here, we investigated the metabolic determinants of resistance to anti-programmed cell death protein 1 (anti-PD-1) therapy and the underlying molecular mechanisms.
Methods
Integrated metabolomics and transcriptomics were performed on tumor samples from patients with non-small cell lung cancer and cell lines. Mechanisms were delineated using RNA sequencing, cleavage under targets and tagmentation assays, metabolic flux analysis, and coculture systems. The therapeutic efficacy of targeting metabolic effectors was evaluated in syngeneic mouse models and correlated with immune profiling.
Results
We identified a distinct metabolic signature characterized by aberrant pyruvate accumulation in patients resistant to anti-PD-1 therapy. Mechanistically, we demonstrate that antibody-mediated ligation of PD-L1 triggers an intrinsic endoplasmic reticulum (ER) stress response via the PERK–ATF4–CHOP axis. ATF4 acts as a transcriptional activator that directly upregulates pyruvate dehydrogenase kinase 4 (PDK4) (blocking pyruvate oxidation) and glutaminase (GLS) (promoting glutaminolysis), creating a ‘dual-hit’ metabolic rewiring that drives intracellular pyruvate build-up. Subsequently, tumor-secreted pyruvate is taken up by tumor-associated macrophages (TAMs) via MCT1, inducing mitochondrial reactive oxygen species accumulation and driving them into a state of cellular senescence. These senescent TAMs upregulate PD-L1 via STAT3 signaling, thereby reinforcing an immunosuppressive feedback loop. Pharmacological inhibition of PDK4 and GLS effectively abolished pyruvate accumulation, prevented macrophage senescence, and restored CD8+ T-cell cytotoxicity.
Conclusions
Our study identifies a novel ‘PD-L1–ER stress–pyruvate–macrophage senescence’ axis as a key mechanism underlying primary resistance to ICB. These findings highlight the non-canonical reverse-signaling function of PD-L1 in metabolic remodeling and propose that targeting the PDK4/GLS-dependent pyruvate surge offers a promising therapeutic strategy to sensitize tumors to anti-PD-1 immunotherapy.