Safety and Efficacy of Low Dose CD19 Targeted Chimeric Antigen Receptor T (CAR-T) Cell Immunotherapy in 47 Cases with Relapsed Refractory B-Cell Acute Lymphoblastic Leukemia (B-ALL)

Abstract

AbstractIntroduction: Patients (pts) with relapsed refractory B-ALL are mostly incurable by chemotherapy. The disease free survival (DFS) is low even treatment with allogeneic hematopoietic stem cell transplantation (allo-HSCT). We explored treatment of 47 cases of relapsed refractory B-ALL with low dose CD19 CAR-T cells and assessed the clinical safety and efficacy.Patients and Methods: (6-8)X107 pts’ peripheral blood mononuclear cells(PBMCs) were activated with CD3 and CD28 antibodies for 24h, then transduced with the lentivirus encoding anti-CD19-CD3zeta-4-1BB CAR (Image1/Picture1) and cultured for 5-6 days in serum-free media containing IL2,IL7,IL15,IL21. All pts except one who had persistent cytopenia received cyclophosphamide 250 mg/m2/d X 3d, and fludarabine 30 mg/m2/d X 3d, then CAR-T cell infusion. Between Jul.31 2015 and Jul. 15 2016, a total of 47 cases were treated with CAR-T cells (Chart1). 37/47 cases had frank hematologically relapsed refractory B-ALL, who could not achieve complete remission (CR) after more than 1 cycles of chemotherapy. The median prior chemotherapy duration was 18 months. The median pre-treatment bone marrow blast percentage was 67% (6.5-98.5%). The most recently treated 15 cases had their PB blasts <30% and had no brain mass. 10/47 cases had persistent positive minimal residual disease (MRD) per flow cytometry (FCM) after more than 3 cycle of chemotherapy, except one who had severe pneumonia after 1 cycle of chemotherapy. The MRD pre-treatment were ranging from 0.01%-1.53%.Chart 1: Characteristics of Patients Pre-CAR-TImage 1/Picture 1:Results: The pts received a median of 10 (0.5-140) X104cells/kg CAR-T cells, and the most recently treated 15 cases all received 10 X 104cells/kg. The median observation period was 201 days (20-368 days). On day 16-20 after CAR-T infusion, 31/35 (88.6%) relapsed hematological refractory cases achieved CR or incomplete CR(Cri), and 29/35 cases (82.9%) achieved negative MRD by FCM(CMR: complete molecular remission). No extramedullary leukemia was detected in any cases with residual disease. The most recently treated 15 consecutive cases all achieved CR with only mild (<grade 2) cytokine release syndrome (CRS). 2 cases could not be evaluated for efficacy because 1 died from severe pancytopenia and 1 died from intracranial hemorrhage during the first month of the study. 4 cases did not achieve CR but all those pts only received less than 5x104/kg CAR-T cells. 15/17 CR cases were bridged into allo-HSCT and have remained in CMR with a median follow-up of 197 days (100-303 days). 25 CR cases have been followed up for more than 60 days, 5/25 pts had hematological relapse and 4/25 pts became MRD+ again. The median time to relapse was 64 days (52-193 days), with 5 pts CD19-, 2 CD19dim and 2 CD19+ by FCM. The major side effect was CRS. The median time to development of CRS was 7 days (1-12) with median CRS grade 2 (1-5). 9/10 (90%) refractory MRD+ cases became MRD- after CAR-T treatment. The median time to development of CRS of this group of patients was at day 6 (day 6-7) with median CRS grade 1 (0-1).Conclusion: Our anti-CD19 CAR-T cell therapy can result in a high CR/CRi /CMR rate in pts with refractory B-ALL and could overcome pre-existing risk factors for poor outcomes, including complex chromosome abnormalities, poor gene mutations, inherited predisposing gene mutation, extramedullary leukemia etc. Pts could be safely bridged into allo-HSCT for potential cure. The dose of infused CAR-T cells in our patients was far lower than previously reported in the literature and the culture period was only 6-7 days, which could dramatically reduce the cost of the CAR-T therapy. 10X104cells/kg of CAR-T cells was a safe and effective number for treating B-ALL. The major complication was CRS and the severity of CRS was directly correlated with the number of malignant B cells in the PB. The efficacy of CAR-T therapy was correlated to the infused number of CAR-T cells. The most recently treated 15 consecutive cases all achieved CR without severe CRS suggesting that the optimal number of CAR-T cells and patient selection are important for the efficacy and safety. [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.