PURPOSE: We designed a CD19-targeted chimeric antigen receptor (CAR) comprising a calibrated signaling module, termed 1XX, that differs from that of conventional CD28/CD3ζ and 4-1BB/CD3ζ CARs. Preclinical data demonstrated that 1XX CARs generated potent effector function without undermining T-cell persistence. We hypothesized that 1XX CAR T cells may be effective at low doses and elicit minimal toxicities. METHODS: In this first-in-human, phase I, dose escalation and expansion clinical trial, patients with relapsed or refractory large B-cell lymphoma received 19(T2)28z-1XX CAR T cells at four dose levels (DLs), ranging from 25 to 200 × 10. RESULTS: Twenty-eight patients underwent apheresis and received CAR T cells. Sixteen and 12 patients were treated in the dose escalation and expansion cohorts, respectively. The overall response rate (ORR) was 82% and complete response (CR) rate was 71% in the entire cohort. The lowest dose of 25 × 10 was selected for dose expansion. In 16 patients treated at this DL, 88% achieved ORR and 75% CR. With the median follow-up of 24 months, the 1-year event-free survival was 61% (95% CI, 45 to 82) and 14 patients remain in continuous CR beyond 12 months. In all cohorts, grade ≥3 cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome rates were low at 4% and 7%, respectively. 1XX CAR T-cell products contain a higher proportion of CD8 T cells with memory features, and CAR T-cell persistence has been detected beyond 1-2 years in patients with ongoing remission. CONCLUSION: The calibrated potency of the 1XX CAR affords excellent efficacy at low cell doses with favorable toxicity profiles and may benefit the treatment of other hematologic malignancies, solid tumors, and autoimmunity.