Longitudinal single-cell immunoprofiling links durable CAR T response to sustained activation and clonotypic expansion of the native cytotoxic T cell repertoire

CD19-directed chimeric antigen receptor (CAR) T-cell therapy has transformed outcomes for patients with relapsed/refractory large B-cell lymphoma (LBCL), yet the mechanisms underlying durable remission remain incompletely understood. While CAR T-cell persistence is associated with response, long-term remission can occur despite rapid CAR T clearance, suggesting the involvement of additional immune mechanisms. To investigate the role of the native T-cell repertoire in shaping response durability, we performed single-cell RNA and TCR sequencing (scRNA-seq/scTCR-seq) on longitudinal peripheral blood samples from LBCL patients treated with axicabtagene ciloleucel (axi-cel) in the ZUMA-1 trial. We compared immune landscapes and clonotypic dynamics among patients achieving durable remission (>1 year), those experiencing early relapse (<6 months), and those with refractory disease. Patients with long-term remission exhibited increased cytotoxic, proinflammatory, and proliferative native T-cell subsets, while early relapse was associated with immunoregulatory populations that may suppress T-cell activation. TCR profiling revealed robust clonotypic expansion of native cytotoxic T cells post-infusion in durable responders, with expansion patterns strongly predicting clinical outcomes. Notably, TCR screens did not identify known viral targets, suggesting tumor-specific immunity may mediate ongoing remission. These findings propose native T-cell clonotypic expansion as a key determinant of durable response to CAR T therapy and highlight its predictive potential for long-term clinical outcomes.