NKTR-255–treated mice are protected against tumor rechallenge. NSG mice were injected IV with 5 × 10⁵ Raji cells. Seven days later, tumor-bearing mice received 0.8 × 10⁶ CD19 CAR T cells (1:1 CD8⁺:CD4⁺) IV. Cohorts of mice (n = 6 per group) received either buffer or NKTR-255 at 0.3 mg/kg IV weekly starting on day 7. One control group did not receive CAR T cells. Mice that cleared the tumor were rechallenged with 5 × 10⁵ Raji cells on day 36. A separate cohort of mice with no previous treatment was also injected with Raji cells on the same day as a control group (n = 3). (A) Schematic of experimental setup. (B) Bioluminescence imaging of Raji tumor burden at indicated time points.