title: CXCR4
design: In this study, we found that lentiviral transduction caused significant CXCR4 downregulation on T-cells, leading to impaired migration to CXCL12. The CXCR4 receptor-overexpressed (CXCR4hi) CD19 CAR-T and BCMA CAR-T cells showed superior tumor tracking and clearance capacities in localized and systemically disseminated models of B-cell lymphoma and MM, respectively. Notably, CXCR4-modification facilitated homing of CAR-T cells and accumulation in bone marrow, which further promoted memory T-cell differentiation, persistence and prolonged anti-tumor activity. Building on these findings, an investigator-initiated clinical trial (IIT) evaluating CXCR4hi CD19 CAR-T cells in patients with relapsed/refractory B-cell malignancies (NCT04684472) achieved encouraging efficacy: the low-dose cohort yielded 3 complete responses (CR) and 1 partial response (PR) within one-month post-infusion. These findings support CXCR4 modification as a strategy to improve CAR-T cell efficacy in hematologic B-cell malignancies, warranting further clinical investigation.