Circulating <scp>CAR</scp> T‐Cells After Treatment With Axicabtagene Ciloleucel in Patients With Relapsed/Refractory Aggressive B‐Cell Lymphomas and Its Association to Treatment Outcome

ABSTRACT Objectives This study investigates the expansion of CAR T‐cells and its association to treatment outcome. Methods Patients with aggressive B‐cell lymphomas treated with anti‐CD19 CAR T‐cell therapy axicabtagene ciloleucel (axi‐cel) at Skåne and Sahlgrenska University Hospitals from 2019 to October 2024 were included. CAR T‐cells in peripheral blood were measured by flow cytometry. Association between maximum levels of CAR T‐cells and response, progression‐free survival, overall survival, cytokine release syndrome (CRS) and immune effector cell‐associated neurotoxicity syndrome (ICANS) were investigated. Results Peak CAR T‐cell levels were higher among patients with complete response (CR) at Day 30 ( p = 0.013) and at 12 months ( p = 0.036). CD8 + CAR T‐cells were higher in patients with CR (median 135.7, IQR 52.8–433.9) compared to patients not obtaining CR (median 23.2, IQR 11.1–103.3) ( p = 0.003). The ratio of CD4 + :CD8 + CAR T‐cells was lower in patients obtaining CR ( p = 0.046). Patients with CAR T‐cells above 52.4 CAR T‐cells/μL showed superior progression‐free survival ( p &lt; 0.001). Conclusion Our study indicates that CAR T‐cell levels after axi‐cel correlate to durable response, progression‐free survival, and that expansion of CD8 + CAR T‐cells might be of specific importance for efficacy. Potentially, CAR T‐cell levels may be used to enable early detection of patients with high risk of CAR T‐cell treatment failure.