Cytomorphology of Chimeric Antigen Receptor T-Cells (CAR-T)

Our direct observation of lymphoid subsets with peculiar morphological characteristics in the infusion bag provides a description of morphological features of CAR-T cells and a proof of concept that these are not acquired in vivo secondary to the encounter with the antigen but already present at the time of infusion secondary to viral transduction and in-vitro stimulation. Further studies will be critical to verify if different activation protocols and co-stimulatory molecules in CAR construct, period of resting before sample freezing, and other preparation factors have a role in determining the heterogeneous morphology of these cells. From a practical standpoint, we underline that the observation of apparently abnormal or immature cells in peripheral blood smears obtained after CAR-T cell infusions should not be immediately be ascribed to the possible occurrence or relapse of a malignant disorder.