Summary: Background: Current approved chimeric antigen receptor (CAR) T-cell products are autologous cell therapies that are costly and poorly accessible to patients. We aimed to evaluate the safety and antitumor activity of a novel off-the-shelf anti-CD19 CAR-engineered allogeneic double-negative T cells (RJMty19) in patients with relapsed/refractory large B-cell lymphoma. We report the results from a first-in-human, open-label, single-dose, phase 1 study of allogeneic CD19-specific CAR double-negative T (CAR-DNT) cells. Methods: Eligibility criteria included the presence of measurable lesions, at least 2 lines of prior immunochemotherapy, and an ECOG score of 0–1. We evaluated four dose levels (DL) of RJMty19 in a 3 + 3 dose-escalation scheme: 1 × 106, 3 × 106, 9 × 106 and 2 × 107 CAR-DNT cells per kilogram of body weight. All patients received lymphodepleting chemotherapy with fludarabine and cyclophosphamide. The primary endpoints were dose-limiting toxicities (DLTs), incidence of adverse events (AEs), and clinically significant laboratory abnormalities. Secondary endpoints included evaluation of standard cellular pharmacokinetic parameters, immunogenicity, objective response rates (ORR), and disease control rate (DCR) per Lugano 2014 criteria. Findings: A total of 12 patients were enrolled between 22 July 2022 and 27 July 2023. Among these patients, 66% were classified as stage IV, 75% had an IPI score of 3 or higher, representing an intermediate risk or worse. The maximum tolerated dose was not reached because no DLT was observed. Four patient experienced grade 1 or 2 cytokine release syndrome and dizziness. The most common AEs were hematologic toxicities, including neutropenia (N = 12, 100%), leukopenia (N = 12, 100%), lymphopenia (N = 10, 83%), thrombocytopenia (N = 6, 50%), febrile neutropenia (N = 3, 25%), and anemia (N = 3, 25%). Seven subjects died till the cut-off date, five of them died of disease progression and two of them died of COVID 19. In all patients (N = 12), the ORR was 25% and CRR was 8.3%. DL1 and DL2 patients benefited less from the therapy (ORR: 17%, N = 1; DCR: 33%, N = 2). However, all DL3 patients achieved disease control (N = 3, 100%), and all DL4 patients achieved objective response (N = 3, 100%). Interpretation: Our results demonstrate that CD19-CAR-DNT cells appear to be well tolerated with promising antitumor activity in LBCL patients. Further study of this product with a larger sample size is warranted. This phase 1 study is registered on clinicaltrials.gov (NCT05453669). Funding: Wyze Biotech. Co., Ltd.