Dottorato in INNOVATION IN IMMUNO-MEDIATED AND HEMATOLOGICAL DISORDERS

Titolo della tesi: "Impact of extracellular-vesicles associated NKG2D ligands on NK cell-mediated cancer immunesurveillance”

Multiple Myeloma (MM) is a malignancy of terminally differentiated plasma cells (PCs) located in the bone marrow and is still an incurable disease characterized by immune dysfunction. Natural Killer (NK) cells are innate cytotoxic lymphoid cells that play a crucial role in the immune surveillance against MM and their activity is regulated by a balance of signals derived from the engagement of inhibitory and activating receptors. In this context, NKG2D represents an activating receptor that binds to stress-induced ligands belonging to MIC and ULBP families and expressed on the cell surface as transmembrane or GPI-anchored proteins. The secretion of NKG2D ligands (NKG2DLs) through protease-mediated cleavage or by extracellular vesicle (EV) is a mode to control their cell surface levels and a mechanism used by cancer cells to evade NKG2D-mediated immunosurveillance. By using as model a human NKG2DL-transfected Multiple Myeloma (MM) cell line we investigated how the NKG2DLs associated to EVs could affect NK cell-mediated functions. Our findings show that: i) NKG2DLs belonging to MIC and ULBP families are all expressed on the surface of EVs; ii) persistent stimulation mediated by NKG2DL+EVs causes NKG2D downmodulation “in vitro” and “in vivo” leading to impaired NKG2D-mediated functions; iii) NKG2DLs can be transferred by vesicles to NK cells causing fratricide. iv) focusing on MM as relevant model of tumor-NK cell interactions, we found enrichment of EVs expressing NKG2DLs and in the bone marrow of a cohort of multiple myeloma patients. The accumulation of NKG2DLs associated to EVs in the tumor microenvironment could favor the suppression of NK cell activity either by NKG2D down-modulation or by fratricide of NK cell dressed with EV-derived NKG2DLs.