A. Seven blood samples from patients with ALL were collected and CD19 and BAFF-R expression were analyzed with flow cytometry. N=3 for CD19+BAFF-R+; N=1 for CD19+BAFF-R-; N=2 CD19-BAFF-R+; N=1 for CD19+BAFF-R+. B-C. T cell-depleted patient samples were co-cultured with BAFF-R and CD19 monospecific or CD19-BAFF-R(l) dual CAR T cells at 1:2 ratio for 6 hours. CD107a expression was analyzed with flow cytometry. Representative data of CD107a expression under EGFR (CAR) gated population and accumulative data are presented. Experiments were conducted in triplicate for each patient specimen. D. Specific lysis of CAR T cells against primary ALL cells. Effector CAR T cells were CD19-BAFF-R(l) dual or BAFF-R and CD19 monospecific CAR T cells at 10:1 E:T. Mock T cells were used as negative control. Experiments were conducted in triplicate and analyzed by a Student’s t-test. ****P<0.0001, ****P<0.0001, ***P<0.001, **P<0.01, *P<0.05, NS: not statistically significant.