Integrative analysis of PD-L1 DNA status, mRNA status and protein status, and their clinicopathological correlation, in diffuse large B-cell lymphoma

Aims: The protein expression of programmed death-ligand 1 (PD-L1) has been recognised as being a biomarker for poor prognosis in diffuse large B-cell lymphoma (DLBCL). The aims of this study were to determine PD-L1 DNA status and mRNA status, and to explore whether they contribute to protein expression and their clinicopathological correlation in DLBCL.

Methods and results: In this study, we used fluorescence in-situ hybridisation, RNA in-situ hybridisation and immunohistochemistry to determine PD-L1 status at three different levels in 287 DLBCL samples with follow-up. Their correlation and clinical pathological relevance were also analysed. Our results showed that 1.7% (3/175) of patients had PD-L1 DNA amplification, 19.9% (57/287) had high PD-L1 mRNA expression, and 11.8% (34/287) had high PD-L1 protein expression. Both mRNA and protein expression of PD-L1 were significantly higher in non-germinal centre B-cell-like (GCB) DLBCL than in GCB DLBCL (P < 0.05). In addition, the patients with high PD-L1 mRNA or high PD-L1 protein expression but no PD-L1 DNA amplification had significantly poorer overall survival (OS) than those with low PD-L1 expression (P < 0.05). Furthermore, we found that PD-L1 mRNA and PD-L1 protein expression were highly correlated (P = 0.012), which was observed in all three samples with DNA amplification.

Conclusions: PD-L1 DNA amplification is a rare event, PD-L1 mRNA is the main contributor to the high PD-L1 protein expression, and the latter two will serve as important biomarkers for predicting the prognosis of DLBCL patients and selecting them for immunotherapy.