Analysis of the therapeutic effect of allogeneic hematopoietic stem cell transplantation in the treatment of pediatric acute lymphoblastic leukemia with E2A::HLF fusion gene: a case series.

Background: The fusion gene E2A::HLF (TCF3::HLF) is present in <1% of B-cell acute lymphoblastic leukemia (ALL) patients, mainly in older children and adolescents. Patients with E2A::HLF fusion B-ALL consistently have dismal outcomes, even after hematopoietic stem cell transplantation (HSCT). Chimeric antigen receptor T-cell (CAR-T) therapy and donor lymphocyte infusion (DLI) applied in this kind of disease have rarely been reported. In this case series, we will focus on the safety and effectiveness of CAR-T and DLI treatments. This may refine therapeutic strategies and improve survival for this high-risk subgroup. Case Description: In this case series, we review the clinical course of 4 pediatric patients with E2A::HLF fusion B-ALL. All four patients treated with Chinese Children Leukemia Group (CCLG)-2018-ALL protocol based on high-risk stratification. Two patients (case 1 and case 4) maintained non-remission after intensive therapy and then accepted CD19-CAR-T therapy. All four patients achieved complete remission before HSCT and were negative for minimal residual disease and E2A::HLF fusion in the bone marrow. One patient (case 3) succumbed to complication of HSCT. Two patients (case 1 and case 4) who accepted DLI treatment after HSCT were still alive. One patient (case 2) relapsed after HSCT. Although accepting CAR-T and DLI treatments after HSCT, she died due to primary disease recurrent relapse. Conclusions: The combination of CAR-T-cell therapy before HSCT and pro-DLI treatment after HSCT may represent an effective strategy to improve outcomes in these pediatric patients.