Abstract
MicroRNA (miRNA)s are dysregulated in Diffuse large B-cell lymphoma (DLBCL), where they reflect the malignant B-cells and the immune infiltrate within the tumor microenvironment. There remains a paucity of data in DLBCL regarding cell-free (c-f) miRNA as disease response biomarkers. Immunosuppressive monocyte/macrophages, which are enriched in DLBCL, are disease response markers in DLBCL, with miRNA key regulators of their immunosuppressive function. Our aim was to determine whether plasma miRNA that reflect the activity of the malignant B-cell and/or immunosuppressive monocytes/macrophages, have value as minimally-invasive disease response biomarkers in DLBCL. Quantification of 99 DLBCL tissues, to select miRNA implicated in immunosuppressive monocytes/macrophage biology, found miR-494 differentially elevated. In a discovery cohort (22 patients), pre-therapy c-f miR-494 and miR-21 but not miR-155 were raised relative to healthy plasma. Both miR-494 and miR-21 levels 3-6 months reduced post immuno-chemotherapy. The validation cohort (56 patients) was from a prospective clinical trial. Interestingly, in sequential samples both miRNAs decreased in patients becoming Positron Emission Tomography/Computerized Tomography (PET/CT)-ve, but not in those remaining interim-PET/CT+. Patient monocytes were phenotypically and functionally immunosuppressive with ex-vivo monocyte depletion enhancing T-cell proliferation in patient but not healthy samples. Pre-therapy monocytes showed an immunosuppressive transcriptome and raised levels of miR-494. MiR-494 was present in all c-f nanoparticle fractions but was most readily detectable in unfractionated plasma. Circulating c-f miR-494 and miR-21 are disease response biomarkers with differential response stratified by interim-PET/CT in patients with DLBCL. Further studies are required to explore their manipulation as potential therapeutic targets.