Rituximab Binding Endows CD20+ Extracellular Vesicles With NK Cell-Activating Properties in B Cell Lymphoma.

Non-Hodgkin lymphoma (NHL), predominantly B cell lymphomas (B-NHL), is currently treated with chemotherapy combined with rituximab (RTX), an anti-CD20 monoclonal antibody. Despite substantial therapeutic advances, treatment resistance and disease relapse continue to affect a significant fraction of patients. The mechanisms by which the tumour microenvironment and other factors influence RTX efficacy are not fully elucidated. Herein, we hypothesized that CD20+ extracellular vesicles (EVs) shed by B cell lymphomas are recognized by RTX forming immune complexes that modulate natural killer (NK) cell activity via Fcγ receptor (FcγR) interactions. EVs isolated from lymph node explants and plasma samples of B-NHL patients contained abundant CD20+ vesicles, which were particularly enriched in advanced disease. RTX specifically bound CD20 on these EVs, generating EV-RTX immune complexes. Functional studies employing EVs from a B-NHL cell line and from patient-derived samples demonstrated that, whereas EVs suppressed NK cell activation and cytotoxicity, EV-RTX immune complexes reversed this inhibitory effect and enhanced NK cell effector functions. Indeed, EV-RTX immune complexes specifically triggered FcγRIIIa-dependent NK cell activation, evidenced by increased Syk phosphorylation, CD69 expression, and enhanced lytic activity against target cells. Our findings uncover a previously unrecognized mechanism by which RTX, through the formation of immune complexes with CD20+ EVs, promotes NK cell activation and may enhance therapeutic efficacy. More broadly, these results demonstrate that antibody binding can endow EVs with novel immunomodulatory properties, revealing a potential mechanism by which therapeutic antibodies reshape EV function and influence anti-tumour immunity.