A phase I study of allogeneic anti-CD19 CAR-T therapy for patients with CD19+ relapsed/refractory acute B-lymphoblastic leukemia.

6525 Background: Acute B-lymphoblastic leukemia (B-ALL), characterized by CD19 expression, responds well to CD19-targeted CAR-T therapy. However, autologous CAR-T is limited by cost and accessibility. We've developed RD06-03, an allogeneic CAR-T product engineered with TCR/Gene-X knockout and NK inhibitory molecule overexpression, exhibiting resistance to allogeneic rejection and enhanced anti-tumor effects without inducing graft-versus-host disease (GvHD). Our phase 1 trial (NCT06307600) aims to assess the safety and efficacy of RD06-03 in R/R B-ALL patients, offering a novel "off-the-shelf" solution. Methods: Patients aged 3-70 years with CD19+ R/R B-ALL were eligible and enrolled in a dose escalation study with dosing groups (CAR+ T cells/kg) of DL1: 1×10^5, DL2: 3×10^5, DL3: 5×10^5 and EDL (exploratory dose level): 6.5×10^5. All patients received lymphodepletion with fludarabine (30mg/m^2/day) and cyclophosphamide (500mg/m^2/day) for 3 days before CAR-T infusion. Dose-limiting toxicity (DLT) and the maximum tolerated dose (MTD) were evaluated using accelerated titration and "3+3" escalation, followed by case expansion at the appropriate dose. Results: As of December 15, 2024, six R/R B-ALL patients were enrolled (DL1: 1, DL2: 3, DL3: 1 and EDL: 1) with a median age of 37.5 years (range, 18-63) and a median of 3 prior therapies (range, 2-8+). One patient relapsed after unrelated umbilical cord blood transplantation. Baseline median bone marrow blasts were 41.9% (range, 10%-88.5%). RD06-03 was well tolerated with no DLT, neurotoxicity or GvHD observed. CRS occurred in 4 of 6 patients (66.7%, all Grade 1) with a median duration of 2.5 days (range, 1-4). For doses above DL2, all 5 patients achieved CR/CRi (100%) with undetectable MRD, indicating a deep remission. The majority of responders remain in remission, with the longest remission duration reaching 147 days and a median follow-up of 128 days (range, 60-175). Robust expansion was observed in all patients receiving doses above DL2, with rapid expansion occurring at a median of 4 days post-infusion. The median peak expansion exceeded 1 million copies/μg DNA, with a median persistence of 28 days and the longest persistence surpassing 3 months. Conclusions: The phase I trial of RD06-03 confirms its safety and efficacy in patients with R/R B-ALL. Notably, RD06-03's engineered TCR/Gene-X and NK inhibitory molecules enhance its resistance to rejection and antileukemic activity without GvHD. RD06-03 demonstrates robust persistence, achieving a 100% CR/CRi rate in medium- to high-dose groups, which is even lower than that of autologous CAR-T, while maintaining a manageable safety profile under standard lymphodepletion. This aligns with its genetic modifications designed for optimal immune rejection resistance. Further studies are essential to solidify these findings and explore RD06-03's therapeutic potential. Clinical trial information: NCT06307600 .