The robust cellular immunity in B-CLL patients against EBV [2] therefore prompted us to investigate the potential of tailored exosomes to redirect this immunity to malignant B cells. We present a novel approach for the targeted transfer of functional cellular proteins to B cells via tailored gp350+ exosomes. In this approach, gp350 has a dual function: (i) it confers B-cell tropism to exosomes so that they specifically co-transfer proteins of interest and (ii) it is a viral neo-antigen for these cells so that they efficiently reactive gp350-specific T cells. As a proof of concept, we show that tailored gp350+ exosomes can co-transfer functional CD154 as immune accessory molecule to B-CLL cells, which are subsequently stimulated to express surface molecules like CD54, CD80, CD86 and CD95 and stimulate autologous tumor-and EBVspecific T cells.