GPI-Anchored Fibromodulin as a Novel Target in Chronic Lymphocytic Leukemia: Diagnostic and Therapeutic Implications

Abstract

<strong>Background:</strong> We have previously reported the aberrant expression of Fibromodulin (FMOD) in patients with chronic lymphocytic leukemia (CLL). Although FMOD has been considered as a cytoplasmic or secretory protein, we discovered the cell surface expression of FMOD in leukemic B cells via anchoring with glycosylphosphatidylinositol (GPI). <strong>Objective:</strong> To evaluate FMOD as a new biomarker in CLL patients in comparison with healthy individuals. <strong>Methods:</strong> A monoclonal antibody was generated against human FMOD. The cell surface expression of FMOD in 52 CLL patients and 45 healthy individuals were compared by flow cytometry. A bacterial phosphatidylinositol-specific phospholipase C (PI-PLC) was used to determine the cell surface localization of FMOD using ELISA and flow cytometry techniques. Annexin V-FITC and propidium iodide (PI) was used to detect apoptosis induction in CLL PBMCs following <em>in vitro </em>incubation with anti-FMOD mAb. <strong>Results:</strong> The results demonstrated the widespread cell surface expression of GPI-anchored FMOD in CLL patients (median: 79.9 %), although healthy individuals had low FMOD expression (median: 6.2 %) (p≤0.0001). The cut-off value of FMOD expression was estimated with high sensitivity and specificity at 17.9%. Furthermore, <em>in vitro</em> apoptosis induction of leukemic cells following incubation with anti-FMOD mAb showed a direct apoptosis of CLL cells (27.9%) with very low effect on healthy PBMCs (6%). <strong>Conclusion:</strong> The membrane-anchoring of FMOD by means of a GPI moiety in leukemic cells supports FMOD as a highly potential diagnostic and therapeutic target in CLL patients.