Treatment-free interval duration during T-cell engager conditioning shapes simulated T-cell exhaustion and post-transfer tumor control

Abstract

Background: Blinatumomab, a CD3/CD19 bispecific T-cell engager (TCE), is effective in relapsed/refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL), but responses may be limited by T cell exhaustion. A recent preclinical study found that incorporating a 7-day treatment-free interval (TFI) into TCE exposure reduced T cell exhaustion and improved subsequent antitumor activity compared with continuous exposure. Methods: Based on this preclinical study, we developed an agent-based model (ABM) to evaluate alternative TFIs by simulating T cell-tumor cell interactions, in which TCE availability influences T cell activation, tumor-cell killing, and T cell exhaustion. To reproduce the experimental design, simulations included a 14-day in vitro conditioning phase with varying TCE schedules, followed by an adoptive cell transfer (ACT) phase in which post-transfer tumor control was evaluated. Results: Our ABM reproduced the experimentally observed reduction in CD8+ T cell exhaustion following a 7-day TFI versus continuous TCE exposure (CONT). Among tested TFIs, the 7-day TFI produced the lowest exhaustion (p_adj = 3.52e-17 vs. CONT) and lowest tumor burden (p_adj = 1.93e-16 vs. CONT). The 5-day TFI was the only other tested schedule to significantly reduce tumor burden relative to CONT. Shifting the 7-day TFI from the second to the first week of conditioning altered T cell phenotype at harvest but not tumor control during the ACT phase (p_adj = 0.87). Limiting TCE exposure during the in vitro phase to one day further reduced tumor burden (all p_adj < 5e-17), with exposure on the first day outperforming exposure immediately before T cell harvest (p_adj = 3.6e-10). Conclusions: The benefit of TFIs depends on interval duration and schedule organization. Our findings also highlight a potential limitation of current preclinical TFI testing. Because tumor cells are replenished rather than allowed to grow during in vitro conditioning, prolonged TFIs carry no penalty from tumor growth. Models that apply TFIs directly to growing tumors are needed to determine whether reduced T cell exhaustion outweighs tumor progression during treatment withdrawal.