These exosomes do not contain gp350 and, therefore, the T cells must have recognized cellular antigens. To test whether T cells specific for B-CLL-associated antigens had been reactivated, we incubated them with irradiated EBV-negative B-blasts [22] from an HLA-A2-matched donor as a negative control or B-blasts loaded with HLA-A2 restricted peptides derived from B-CLLassociated antigens, namely MDM [23] , ETV5 [24] and PU.1 [25] . As shown in Figure 4D , peptide-loaded B-blasts were efficiently lysed by the T cells stimulated with CD154+/gp350+ exosomes whereas B blasts not loaded with peptides were completely ignored. Lysis of target cells was efficiently reduced upon addition of an MHC class I-specific antibody, W6/32, demonstrating the antigen specificity of the effector T cells.