Decitabine in Combination with Fludarabine and Cyclophosphamide As Lymphodepletion Regimen Followed By CD19/CD22 Bispecific Targeted CAR-T Therapy Significantly Improves Survival in Relapsed/Refractory B-ALL Patients: A Pilot Study

Background: CD19/CD22 bispecific targeted chimeric antigen receptor T cell (CAR-T) therapy has achieved impressive progress in patients with relapsed/refractory B cell acute lymphoblastic leukemia (R/R B-ALL), with high rates of complete remission (CR). However, T cell exhaustion caused by de novo DNA methylation restricts the capacity of CAR-T. Decitabine (DAC), a DNA methyltransferase inhibitor, has been demonstrated to reverse exhaustion-associated DNA-methylation programs, promote the rejuvenation of CAR-T cells and enhance anti-leukemic effect of CAR-T cells in vitro. To date, there are limited reports about the use of DAC as a part of lymphodepletion therapy before CAR-T cell therapy. Here, we report efficacy and safety of DAC in combination with fludarabine and cyclophosphamide (FC) regimen followed by CD19/CD22 CAR-T cell therapy for patients with R/R B-ALL.

Method:We conducted a phase 1/2 clinical trial to investigate the efficacy and safety of CD19/CD22 CAR-T in the treatment of R/R B-ALL (NCT03614858). Fourteen patients were treated with DAC (total dose 100mg/m ² in 3 days) followed by FC regimen (fludarabine 30mg/m ² × 3d and cyclophosphamide 300mg/m ² × 3d) (DAC group), while twelve patients received FC regimen prior to CAR-T cell infusion (CON group). A total of 1 or 2 × 10 ⁷ CAR-T cells/kg were infused at dose escalation.

Results: Baseline characteristics of patients in both groups had no significant differences except previous hematopoietic stem cell transplantation (HSCT). There were more patients with relapse after HSCT in DAC group (42.9% versus 0%, P=0.017). All patients did not achieve remission before lymphodepletion. The day 28 CR rates were 100% in DAC group and 91.7% in CON group. Furthermore, minimal residual disease (MRD) negative CR rates were 71.4% and 58.3%, respectively (P = 0.683). There was no significant difference in the proportion of nontransplant patients after CAR-T treatment between two groups. Among the nontransplant patients after CAR-T infusion in DAC group, 16.7% (1/6) of patients relapsed at 4 months. However, among 4 nontransplant patients in CON group, 1 patient achieved NR after CAR-T therapy and 3 patients relapsed at 1.5, 5, and 10 months. There were significant differences in overall survival (OS) and leukemia-free survival (LFS) between two groups: 3-year OS, 88.9% (DAC) versus 33.3% (CON), P = 0.01 and 3-year LFS, 92.3% (DAC) versus 21.8% (CON), P = 0.002. Multivariable analysis showed that addition of DAC to the lymphodepletion regimen was associated with better OS (hazard ratio [HR] 0.107, [95% CI, 0.013-0.875], P = 0.037) and LFS (HR 0.081, [95% CI, 0.01-0.65], P = 0.018). Cytokine release syndrome was observed in all patients.

Conclusion: In summary, DAC in combination with FC regimen followed by CD19CD22 CAR-T cells was feasible and well tolerated. Our study demonstrated DAC combined with FC was an independent prognostic factor correlated with better survival in relapsed/refractory B-ALL patients.