Final Results of Phase I/II Study of Donor-Derived CAR T Cells Engineered with Sleeping Beauty in Pediatric and Adult Patients with B-Cell Acute Lymphoblastic Leukemia Relapsed Post-HSCT

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Introduction Non-viral engineering of allogeneic T cells is a promising alternative option to produce a fit CAR T cell product. We recently proposed the use of Sleeping Beauty (SB) transposon to engineer donor-derived cytokine-induced killer (CIK) cells (CARCIK-CD19) for the treatment of B-cell acute lymphoblastic leukemia (B-ALL) patients relapsed after allogeneic hematopoietic stem cell transplantation (HSCT) (Magnani C et al.: JCI 2020). Here we report the final results of a phase I/II study evaluating the safety and efficacy of CARCIK-CD19 cells (FT01CARCIK, Clinical trial.gov, NCT03389035). Methods We conducted a multi-center, phase I/II dose-escalation (n=12) and dose expansion (n=9) trial in patients relapsed after HSCT. After approval by the Agenzia Italiana del Farmaco (AIFA), 6 additional patients were treated on a compassionate base use and were considered in the final analysis. CARCIK-CD19 cells were manufactured as described (Magnani C et al.: JCI 2020). CARCIK-CD19 were obtained by HLA-identical sibling (n=7, 26%), matched unrelated (n= 10, 37%), and haploidentical donors (n=10, 37%). After lymphodepletion with Fludarabine (30 mg/m2/day x 4 days) and Cyclophosphamide (500 mg/m2/day x 2 days), patients received a single CARCIK-CD19 infusion. Bridging therapy was allowed before CAR-T cell infusion. The Bayesian Optimal Interval (BOIN) design was used for the dose escalation part of the trial. The primary objectives were to define the Maximum Tolerated Dose (MTD) and the recommended Phase II dose as well as the safety. Secondary objectives included the rate of complete hematologic response (CR), duration of response (DOR), event-free (EFS), and overall survival (OS). DOR and EFS were censored when patient underwent a new anticancer therapy. Results A total of 27 patients (4 children and 23 adults) were infused between February 2018 and August 2021. A successful production of CARCIK-CD19 cells was achieved for all patients. The first 9 patients were treated with increasing numbers of CARCIK cells, in groups of three patients per dose level (1x106 /kg, 3x106/kg and 7.5x106/kg), whereas the remaining 18 patients (67%) received the highest planned dose level of 15x106 cells/Kg, as no dose limiting toxicity (DLT) was observed. The median number of prior therapies was 4 (range, 2-8) with a median time interval from HSCT to relapse of 8 months. We enrolled 25 patients (93%) with >5% bone marrow (BM) blasts with a median of 50% (range, 5-100%) at enrollment and 4% (range, 0-96%) after lymphodepletion. Two patients in the compassionate use group, presented extramedullary diseases without BM involvement. CRS occurred in 9 patients (4 patients with grade I and 5 with grade II) and immune effector cell-associated neurotoxicity-ICAN (grade 3) in 2 patients at the two highest doses. Although 10 out of 27 had experienced GvHD after the previous HSCT, GvHD never occurred after treatment with CARCIK-CD19. Nine patients had infections, of which 6 of grade 3 or higher. CR was achieved by 18 out of 27 patients (66.7%, 95%CI=46.0-83.5%) and by 16 out of 21 patients treated with the two highest doses (76.2%, 95%CI=52.8-91.8%). Fourteen (77.8%) of the overall responders and 13 of the responders at the highest doses (81.3%) were MRD-negative. With a median follow up of 2.8 years (range, 0.05-4.4 years, last update as of July 2022), a significantly better EFS was observed in patients treated with the highest doses (p=0.0265). For the 21 patients treated at the two highest dose levels, the median EFS and OS were 4 and 12 months, respectively (Figure 1). At 6 months, the EFS and OS were 41.5% (SE=11.6) and 71.4% (SE=9.9), respectively. The median DOR of the 16 patients in CR was 9.5 months, with a 6-months DOR of 54.4% (SE=13.8). By univariate analysis, EFS was significantly associated with the % of blasts after lymphodepletion (≥ 5% vs <5%) (p=0.0245). Conclusions In this phase I/II dose-finding study, SB-engineered CAR T cells demonstrated an excellent safety profile with anti-leukemia activity in heavily pretreated patients with B-ALL relapsed after HSCT. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

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