Chimeric Antigen Receptor T Cell Therapy followed by Unrelated Cord Blood Transplantation for the Treatment of Relapsed/Refractory B Cell Acute Lymphoblastic Leukemia in Children and Young Adults: Superior Survival but Relatively High Post-Transplantation Relapse.

Several studies have indicated that chimeric antigen receptor (CAR) T cell therapy followed by allogeneic hematopoietic stem cell transplantation is beneficial for treating patients with relapsed or refractory (R/R) B cell acute lymphoblastic leukemia (B-ALL). Whether consolidative unrelated cord blood transplantation (UCBT) is suitable in R/R B-ALL after CAR-T therapy remain uncertain. We aimed to assess the efficacy and safety of CAR-T therapy before UCBT in children and young adults with R/R B-ALL. We retrospectively analyzed 43 patients aged <18 years with R/R B-ALL who underwent single-unit UCBT at the First Affiliated Hospital of the University of Science and Technology of China between February 2012 and November 2020. Among them, 21 patients achieved complete remission (CR) following CAR-T therapy before UCBT (the CAR-T group), and the remaining 22 patients remained in nonremission (NR) without prior CAR-T therapy before UCBT (the NR group). The clinical outcomes in the 2 groups were analyzed. The median time from CAR-T therapy to UCBT was 62 days (range, 42 to 185 days). There were no significant between-group differences in the incidences of grade II-IV acute graft-versus-host disease (GVHD), grade III-IV acute GVHD, and 2-year extensive chronic GVHD. Compared with the NR group, the CAR-T group had a lower 2-year cumulative incidence of transplantation-related mortality and higher probabilities of 2-year overall survival, leukemia-free survival, and GVHD-free relapse-free survival (P = .037, .005, .028, and .017, respectively). However, the 2-year cumulative incidence of relapse (CIR) was comparably high in the 2 groups (26.7% in the CAR-T group and 38.3% in the NR group; P = .41). In the CAR-T group, patients who were minimal residual disease (MRD)-positive before UCBT had a higher CIR compared with those who were MRD-negative before UCBT (66.7% versus 19.2%; P = .006). CAR-T therapy followed by UCBT produces superior survival in R/R B-ALL, but treated patients still have a high post-transplantation relapse rate.