CAR T-Cell Durability and Response Monitoring

The discussion focuses on predicting CAR T-cell therapy durability and identifying patients who may achieve cure without subsequent interventions. Dr. Park reviews available data across different products, noting stronger evidence in pediatric ALL populations compared to adult datasets.

For tisagenlecleucel in pediatric patients and obecabtagene autoleucel (obe-cel) in adults using 4-1BB co-stimulatory domains, early MRD negativity by next-generation sequencing (10^-6 sensitivity) at one month, sustained through three months with concomitant B-cell aplasia, correlates with favorable outcomes. However, clinical decision-making regarding transplant typically occurs between one and three months, creating practical challenges in applying this retrospective data prospectively.

Dr. Park explains that brexucabtagene autoleucel (brexucel), utilizing CD28 co-stimulatory domains, demonstrates different persistence patterns with expected B-cell recovery, making B-cell aplasia less reliable as a durability indicator. For obe-cel, data from the FELIX study demonstrates correlation between T-cell persistence at three and six months with improved progression-free survival and event-free survival, though earlier markers would provide greater clinical utility.

Both physicians emphasize the complexity of persistence data interpretation, as absence of detectable CAR T-cells does not guarantee relapse, whereas multiple factors including disease burden, prior transplant status, and patient-specific variables influence outcomes. Dr. Park describes institutional monitoring of both CAR T-cell persistence through digital PCR and B-cell populations at regular intervals, though prospective validation for clinical decision-making remains incomplete.

Dr. Muffly shares counterintuitive observations from patients receiving CARs in MRD-negative remission, noting robust expansion despite minimal disease burden, challenging traditional assumptions about CAR T-cell functionality and suggesting disease burden does not completely predict expansion patterns.