ROR1 and B-cell chronic lymphocytic leukemia: To test our hypothesis that enhanced costimulation on LN-derived CLL cells directly mediates CAR T-cell effector function, we performed repeat stimulation assays using aCLL cells and found that both CAR-ROR1 and CAR19 T cells had enhanced proliferation with an aCLL stimulus compared to unactivated CLL cells (Fig. 6C).