CD274 and non-small cell lung carcinoma: Of note, knock-down of circ-CPA4 decreased the expression levels of exosomal PD-L1 in the supernatants, which were restored by downregulating let-7 miRNA (Fig. 4j, k), suggesting that circ-CPA4 regulated intracellular and extracellular exosomal PD-L1 in NSCLC cells by sponging let-7 miRNA.