PD L1 is upregulated by EBV driven LMP1 through NF kB pathway and correlates with poor prognosis in natural killer/T cell lymphoma
BackgroundNatural killer/T cell lymphoma (NKTCL) is an Epstein Barr virus (EBV) associated, highly aggressive lymphoma. Treatment outcome remains sub optimal, especially for advanced stage or relapsed diseases. Programmed cell death receptor 1 (PD 1) and PD ligand 1 (PD L1) have become promising therapeutic targets for various malignancies, but their role in the pathogenesis and their interactions with EBV in NKTCL remains to be investigated.MethodsExpression of PD L1 was measured in NK 92 (EBV negative) and SNK 6 (EBV positive) cells by western blot, quantitative real time PCR and enzyme linked immunosorbent assay, and flow cytometry, respectively. Latent membrane protein 1 (LMP1) harboring lentiviral vectors were transfected into NK 92 cells to examine the correlation between LMP1 and PD L1 expression. Proteins in the downstream pathways of LMP1 signaling were measured in NK 92 cells transfected with LMP1 harboring or negative control vectors as well as in SNK 6 cells. PD L1 expression on tumor specimens and serum concentration of soluble PD L1 were collected in a retrospective cohort of patients with Ann Arbor stage I~II NKTCL, and their prognostic significance were analyzed.ResultsExpression of PD L1 was significantly higher in SNK 6 cells than in NK 92 cells, at both protein and mRNA levels. Expression of PD L1 was remarkably upregulated in NK 92 cells transfected with LMP1 harboring lentiviral vectors compared with those transfected with negative control vectors. Proteins in the MAPK/NF kB pathway were upregulated in LMP1 expressing NK 92 cells compared with the negative control. Selective inhibitors of those proteins induced significant downregulation of PD L1 expression in LMP1 expressing NK 92 cells as well as in SNK 6 cells. Patients with a high concentration of serum soluble PD L1 =3.4 ng/ml) or with a high percentage of PD L1 expression in tumor specimens =38 exhibited significantly lower response rate to treatment and remarkably worse survival, compared with their counterparts. A high concentration of serum soluble PD L1 and a high percentage of PD L1 expression in tumor specimens were independent adverse prognostic factors among patients with stage I~II NKTCL.ConclusionsPD L1 expression positively correlated LMP1 expression in NKTCL, which was probably mediated by the MAPK/NF kB pathway. PD L1 expression in serum and tumor tissues has significant prognostic value for early stage NKTCL.
Journal of Hematology Oncology