Donor origin CAR19 T cell infusion for B‐ALL relapsed after allogeneic hematopoietic stem cell transplantation

Patients with relapsing B-cell acute lymphoblastic leukemia (B-ALL) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) have a dismal prognosis, with a median survival of less than 6 months. The treatment of relapsed B-ALL following allo-HSCT is challenging, and there is no standard approach available. Chimeric antigen receptor (CAR)-modified T cells with anti-CD19 specificity are a highly effective novel immune therapy for relapse/refractory B-cell malignancies. Autologous CAR19 T cell therapy has shown promising results for the treatment of leukemia, especially B-ALL. Allogeneic CAR19 T cell therapy for patients with B-cell malignancies that progress after alloHSCT have also been investigated, and the preliminary results have verified the efficacy and safety of this approach. Here, focusing on homogeneous cases of relapsed B-ALL after allo-HSCT, we report the analysis of clinical factors that are associated with initial and durable response to donor origin CAR19 T cell therapy, cytokine release syndrome (CRS), and other toxic effects from original transplant donors and the recipients. Between March 2016 and October 2017, 15 BALL patients with morphological relapse after allo-HSCT were enrolled in this study at the First Affiliated Hospital of Soochow University. This study was approved by the ethical committee of institute of the First Affiliated Hospital of Soochow University (identifier: 2015070, approved in September 2015), and all patients gave written informed consent. CAR-expressing T cells used in our study were produced from five patients' original transplant donors and the other 10 recipients themselves, respectively. Ten recipients underwent apheresis for peripheral blood mononuclear cell (PBMC) collection before salvage chemotherapy or 1 month after chemotherapy when their donor chimerisms (DC) of peripheral blood were all above 80%. Cell culture and lentiviral transductions were performed as described in the supplementary data. All patients received lymphodepleting chemotherapy as conditioning treatment with fludarabine 30 mg/m/d × 3d and cyclophosphamide 300 mg/m/d × 3d (FC) except patient 1 and 9 due to severe hypocellularity. Two days after conditioning chemotherapy, CAR19 T cells provided by the Unicar-Therapy Bio-Medicine Technology Co. (Shanghai, China) at a total dose of 0.1-1 × 10 cells per kilogram (kg) were infused by dose escalation within 3 days. More than 5% bone marrow blasts at the time of CAR19 T cells infusion was defined as high disease burden, while less than 5% blasts was viewed as low disease burden. Minimal residual disease (MRD)-negative complete remission (CR) was defined as less than 0.01% bone marrow blasts. The basic clinical characteristics of patients are summarized in Table 1. The final number of infused T-cells and the corresponding immunophenotypic data for each patient are summarized in Table supplement. The CD8:CD4 ratio of infused total T cells or CAR19+ T cells showed no difference between two T-cell sources (Figure supplement). CAR19+ T cells were monitored dynamically in blood of all patients at multiple time points in 2 to 4 weeks after infusion. Compared with CAR+ T cells derived from donors, those from recipients did not show difference in peak blood levels (Figure supplement). No statistically significant difference was found in peak blood levels according to Philadelphia chromosome status, type of transplant, and time to relapse after transplant, either (Figure supplement). Eleven and eight of 15 patients achieved a CR and a MRD-negative CR at 1 month post CAR19 T cell infusion, respectively. Two patients died of severe CRS within 1 month post CART treatment. Patient 7 obtained partial remission (PR), and patient 15 was not evaluated because of neurotoxic effects which led to death at 2 months after CAR19 T cell infusion. Further analysis demonstrated that CR rate was significantly higher in patients who relapsed late (more than 6 months) after transplant than that in patients who relapsed early (less than 6 months) (P = .02) (Table supplement). At a median follow-up of 17 months (range, 1 to 22 months), the median overall survival among the 15 patients was 10 months (95% CI, 1.4 to 18.5), and the median disease-free survival was 8 months (95% CI, 0 to 20.8) (Figure 1A, B). Overall survival was significantly longer in patients who relapsed late after transplant than those who relapsed early (P = .04) (Figure 1C). Survival analysis revealed that there was no correlation to Philadelphia chromosome status, type of transplant, or CAR T-cell source (Figure 1D,E,F). Among the 11 patients who had complete remissions, we found no significant difference in disease free survival based on the clinical factors mentioned above including time to relapse after transplant (data not shown). In our study, severe CRS and CAR-T-cell-related encephalopathy syndrome (CRES) (≧grade 3) occurred in 4/15 patients, manifesting fever, hypotension, hypoxemia, or encephalopathy. Patient 6 and 14 died of severe CRS, and patient 15 died of CRES. There was a tendency that severe CRS and CRES occurrence rates in patients who relapsed early post-transplant were higher than in patients who relapsed late. But no statistical significance was achieved (P = .28) (Table supplement). No graft versus host disease (GVHD) caused by CAR19 T cell infusion was observed. In our study, 10 patients were treated by CAR-T cells derived from themselves with DCs of more than 80% when their T cells were collected. Therefore, these CAR-T cells were viewed as derived Received: 19 June 2019 Revised: 13 September 2019 Accepted: 16 September 2019 DOI: 10.1002/hon.2682