Immune effector Cell-Associated Neurotoxicity Syndrome (ICANS) is a common and serious neurological complication associated with the use of CAR-T cells. The mechanisms involved are still poorly understood but studies suggest that inflammation during treatment leads to an increase in the permeability of the barrier between the brain and the blood vessels and the emission of extracellular vesicles (EVs) circulating between the brain and the blood vessels. EVs are biological particles that play an important role in cellular communication and the modulation of several physiological processes. The VESICANS study aims to characterize the EVs released before and during CAR-T cells treatment and upon the occurrence of ICANS, using flow cytometry, electron microscopy, Nanoparticle Tracking Analysis associated with MRI assessment of the barrier between the brain and blood. This study will ultimately contribute to facilitating the prevention and treatment of this toxicity which affects the prognosis of patients.