The goal of this clinical trial is to evaluate the efficacy and safety of early secondary infusion of CD19 CAR T-cell therapy in adults with relapsed/refractory diffuse large B-cell lymphoma (DLBCL), guided by ctDNA monitoring. The main questions it aims to answer are:
1. Efficacy: Does early secondary CAR-T infusion improve the 3-month complete remission (CR) rate and long-term survival outcomes (e.g., 1-year PFS, OS)?
2. Safety: What are the adverse events associated with secondary CAR-T infusion, such as cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity (ICANS), and infections?
This is a single-arm, single-center, prospective study. All participants will receive:
* Leukapheresis to collect T cells for CAR-T manufacturing.
* Preconditioning chemotherapy (fludarabine and cyclophosphamide) to prepare the body for CAR-T infusion.
* Two CD19 CAR-T infusions: The first infusion (2×10⁶ cells/kg) followed by a second infusion (same dose) if ctDNA remains positive when PET/CT shows CR or PET/CT shows PR within 60 days post-first infusion.
Participants will undergo:
* Frequent hospital monitoring for ≥14 days post-infusion to manage potential toxicities.
* Regular follow-ups (e.g., blood tests, ctDNA analysis, PET/CT scans) at scheduled intervals up to 12 months.
* Continuous safety assessments, including CRS grading, neurological evaluations, and infection monitoring.