CAR T cells are genetically modified cells engineered to recognize CD19 on tumor cells. The immune synapse formed between a CAR T cell and a target antigen-presenting cell (APC) has unique characteristics, one of which is the accumulation of Kv1.3. By generating CAR T cells with retroviral transduction, and the activation of B cells with the engineered T cells, Kv1.3 accumulation at the synapse was captured with confocal microscopy and further analyzed with flow cytometry.