Safety and Efficacy of CD22/ CD19 CAR-T and Auto-HSCT “Sandwich”Strategy As Consolidation Therapy for Ph Negative B Cell Acute Lymphoblastic Leukemia

Introduction: Chimeric antigen receptor T-cell (CAR-T) therapy has shown an impressive remission rate in relapsed and refractory B-ALL, however relapse after CAR-T cell therapy is currently the challenging issue. Multiantigen CAR-T cells and the combination of CAR-T cells with other regimens may reduce the relapse rate and prolong leukemia-free survival (LFS) and overall survival (OS). The main purpose of this study is to observe the safety and efficacy of CD22/CD19 CAR-T and Auto-HSCT “Sandwich” strategy in Ph negative (Ph^-) B-ALL patients.

Methods: A total of 33 newly diagnosed Ph^- B-ALL patients were enrolled in this study (NCT05470777). These patients received induction and consolidation chemotherapy according to standard protocols. Autologous lymphocytes were collected at week 4 after induction chemotherapy. Afterwards, autologous CAR T-cells targeting CD22 and CD19 (CAR-T 1, co-stimulatory molecule was 4-1BB and infusion dose was 5×10⁶/kg, respectively) were sequential infused after lymphodepletion chemotherapy with fludarabine and cytophosphamide. Autologous stem cells mobilization and collection were performed at 6-8 weeks after CAR T-cells infusion. After conditioned with modified BuCy regimen, autologous stem cells transplantation (auto-HSCT) was conducted. Sequential infusion of CD22 and CD19 CAR-T cells was performed on the second day after transplantation (CAR-T 2, co-stimulatory molecules and dose as CAR-T 1). No maintenance therapy was performed after auto-HSCT. Measurable detectable disease (MRD) was monitored by flow cytometry and IGHV leader-based next generation sequencing. Persistence of CAR T-cells were detected using real time quantitative RT-PCR (qPCR).

Results: Three of the enrolled patients were Ph-like B-ALL. Twenty (60.6%) patients had poor-risk factors according to NCCN guidelines. Grade 1-2 cytokine release syndrome (CRS) occurred in 7(22.6%) and 8(25.8%) patients after CAR-T 1 and CAR-T 2, respectively. No severe CRS (Grade 3-4) or immune effector cell associated neurotoxicity syndrome (ICANS) occurred. After CAR-T 1 therapy, all patients achieved MRD negative complete remission (MRD^-CR). Until the last follow-up on July 1^st, 2024, the median follow-up was 21 months (range, 6-44 months). Thirty two (96.7%) patients are alive and 26 (78.8%) patients remain MRD^-CR. Duration of continuous MRD^-CR was observed in 9 patients for more than 2 years and in 19 patients for more than 1 year. The median OS and leukemia-free survival LFS are not reached. Two (5.4%) patients experienced relapse after CAR-T 1 and 5 (13.5%) patients after CAR-T 2, all of them experienced CD19 positive relapse. The median recurrence time of patients who completed “Sandwich” strategy was 5 months (range, 3-10 months). Four of 7 relapsed patients received allo-HSCT, 2 relapsed patients who declined allo-HSCT received Blinatumomab, and 1 patient was undergoing the chemotherapy as re-induction treatment. Five of them were still in MRD-CR with a median remission duration of 11 months (range, 3-15 months). One patient who relapsed after CAR-T 1 died of disease progression at 3 months after allo-HSCT，

Conclusions: Our preliminary study demonstrated that CD22/CD19 CAR-T and Auto-HSCT “Sandwich” strategy as a consolidation strategy showed favorable safety and efficacy in Ph^- B-ALL. CD22/CD19 CAR-T resulted in deeper remission before transplantation. The new strategy may benefit patients from LFS and OS.