Furthermore, we chose to use a 4-1BB–signaling CAR due to the clinical success of Kymriah, a CD19-directed, 4-1BB–signaling CAR, and the observation that a CD28-signaling CD19-directed CAR also demonstrated similarly reduced proliferation in response to CLL cells (Supplementary Fig. S1C). Here, CD19 is linked to B-cell chronic lymphocytic leukemia.