Harmonization on defining B‐cell recovery post CD19‐CAR T‐cell therapy in B‐cell acute lymphoblastic leukemia: An international consensus statement

Abstract Relapse following CD19‐targeting chimeric antigen receptor T‐cell therapy (CD19‐CAR) remains a major barrier to long‐term cure in relapsed/refractory B‐cell acute lymphoblastic leukemia, with nearly 50% of patients relapsing within 6 months. Early B‐cell recovery (BCR), as detected by the re‐emergence of CD19‐positive cells, has been strongly associated with relapse risk and serves as a surrogate marker for loss of CAR T‐cell persistence. However, clinical use of BCR is hindered by variability in monitoring practices, including inconsistent definitions, timing, and measurement across institutions. To address this gap, we convened an international working group of pediatric cellular therapy experts to establish a consensus definition for BCR. Our collaborative effort outlines standardized criteria for BCR assessment aimed at improving comparability across studies and guiding post‐CAR T‐cell surveillance strategies.