Positive impact of high-throughput drug sensitivity assay and salvage autologous CD19 CAR-T therapy on second marrow relapse of acute lymphoblastic leukemia with NT5C2 mutation

Abstract Background: Recently, the five-year survival rate of pediatric acute lymphoblastic leukemia (ALL) has reached 90%. However, recurrence remains common following treatment. Recently, chimeric antigen receptor (CAR)-T cell immunotherapy has been shown to be effective in control of relapsed/refractory B-cell malignancies. Although lymphocyte-depleting conditioning chemotherapy, including fludarabine and cyclophosphamide, has increased the efficacy of CAR T-cell therapy, reduction in the tumor load before CAR-T cell infusion is still a challenge. Case presentation: A 12-year-old girl diagnosed with intermediate risk B-ALL in 2017 received chemotherapy according to CCLG-2008 ALL protocol and achieved a complete remission (CR) after induction. However, four years later, she had a first bone marrow relapse and received treatment with HKPHOSG Relapsed ALL 2007 protocol. During maintenance chemotherapy, approximately one year after the first relapse, she developed a second bone marrow relapse with NT5C2 gene mutation detected. Flow cytometry analysis showed that the blasts were CD19 positive. Tumor burden was not well controlled after DEAV (dexamethasone, cytarabine, etoposide) chemotherapy, with the blasts in bone marrow increasing from 49.3% to 96%. The analysis of high-throughput drug sensitivity of tumor resistant genes was consistent with the poor response to chemotherapy. As the leukemia cells progressed rapidly with extremely high burden, CD19 CAR-T cell immunotherapy bridged to hematopoietic stem cell transplantation (HSCT) was introduced at this stage. Following peripheral lymphocyte apheresis, the patient received lymphodepleting conditioning with fludarabine and cyclophosphamide three days before CAR-T cell infusion. Dexamethasone and carfilzomib were then given according to the outcome of high-throughput drug sensitivity test. Around 68.6% blasts were detected by flow cytometry at the day of CAR-T cell infusion. After infusion of CAR-T cells，the patient experienced grade 1 cytokine release syndrome without immune effector cell-associated neurotoxicity syndrome. CR of morphology and molecule biology was achieved on day 28 after CAR-T cell infusion. Finally, the child received haploid-HSCT and remained in remission. Conclusions：Overall, this report reveals that the combination of drug sensitivity test with lymphodepleting conditioning could significantly reduce the tumor burden before infusion of CAR-T cells, and as a result, patients may achieve deeper remission and obtain opportunity for transplantation.Trial registration: clinicaltrials.gov, NCT04016129. Registered 11 July 2019, https://www.clinicaltrials.gov/ct2/show/NCT04016129