Programmed cell death ligand 1 (PD-L1) and major histocompatibility complex class I (MHC-I) serve as crucial mediators in tumor immune escape mechanisms and in conferring resistance to PD-1/PD-L1 checkpoint inhibition. In this study, we found that elevated expression of every miRNA within the miR-23a/27a/24−2 cluster was linked to worse patient outcomes, enhanced immune evasion, and reduced response to PD-1/PD-L1 therapy in non-small cell lung cancer (NSCLC) cases. Increased levels of these cluster miRNAs promoted PD-L1 upregulation via direct suppression of Cbl proto-oncogene B (CBLB) and led to MHC-I downregulation by boosting eukaryotic translation initiation factor 3B (eIF3B) through inhibition of microphthalmia-associated transcription factor (MITF). We further showed that sustained expression of the miR-23a/27a/24−2 cluster in NSCLC relies on augmented Wnt/β-catenin pathway activity, which enhances binding of transcription factor 4 (TCF4) to the cluster's promoter region. Importantly, therapeutic inhibition of the eIF3B axis markedly improved responsiveness to PD-1/PD-L1 blockade in NSCLC tumors with strong miR-23a/27a/24−2 cluster activity. This improvement stemmed from restored MHC-I levels without diminishing the cluster-driven high PD-L1 status. Collectively, our findings delineate how these cluster miRNAs perpetuate their own transcription and elucidate the pathways through which they facilitate tumor immune avoidance and therapy resistance to PD-1/PD-L1 inhibitors. Moreover, we introduce an innovative treatment modality for NSCLC characterized by robust miR-23a/27a/24−2 cluster expression.
