Abstract: The invention is directed to a method for activating CAR cells having at least one chimeric antigen binding receptor in a sample by incubating the sample with at least one substrate provided on its surface with at least one anti-CAR idiotype antibody and/or at least one antigen selected from the group consisting of CD19, CD20, CD22, BCMA, CD33, MSLN, CD123, HER2, GD2, EGFR, PSMA, MUC1, CD318, TSPAN8, CD66c, CEA, CLA, CD276, FolR1, CLEC12A, CLL-1 and CD371, and with at least one costimulatory molecule selected from the group consisting of CD28, CD2, CD6, CD26, CD53 and LFA-1 characterized in that the sample is incubated with the at least substrate in suspension thereby activating the CAR T cells to express markers selected from the group consisting of mRNA, effector molecules or cell surface activation markers.