(A) Experimental layout of depletion experiments based on the transfer of m19BBE-transduced cells targeting CD19⁺ ALL tumor cells. Mice were inoculated with 1 × 10⁶ ALL tumor cells i.v.; 6 days later they were sublethally irradiated (5 Gy), and 24 hours later they received 3 × 10⁶ CD8⁺ m19BBE CAR T cells. Cohorts of mice were left untreated or treated with 2 doses of 1 mg cetuximab on day 21 and day 28 and bled weekly to monitor T cell, normal B cell, and tumor cell frequency. (B–D) Summary of flow cytometry analysis of CD45.2⁺CD8⁺EGFR⁺ m19BBE mouse T cell frequency (B), CD45.1⁺CD19⁺ endogenous normal B cell frequency (C), and CD45.2⁺CD19⁺ tumor cell frequency (D) in the peripheral blood of mice with ALL tumors left untreated (black), mice irradiated with 5 Gy (gray), mice irradiated and treated with m19BBE CAR T cells (red), or mice irradiated and treated with m19BBE CAR T cells followed by cetuximab depletion (blue). Non–tumor-bearing WT mice are shown for comparison (dotted black line). Means ± SEM are plotted. n = 6 per group. (E) Kaplan-Meier survival analysis of mice inoculated with ALL tumor cells and left untreated (black), irradiated with 5 Gy (gray), treated with m19BBE T cells (red), or treated with m19BBE T cells and cetuximab (blue). Statistical significance was determined using log-rank Mantel-Cox test; *P ≤ 0.05, ****P ≤ 0.0001. n = 6 per group. (F) Representative flow cytometry data from peripheral blood of ALL tumor-bearing mice (left) 2 weeks after tumor inoculation and spleens and bone marrow of m19BBE/cetuximab-treated mice (middle) or WT non–tumor-bearing mice (right) 10 weeks after T cell transfer. Plots are gated on live CD19⁺ cells.