LAUSR

TO THE EDITOR: Acute lymphoblastic leukemia (ALL) is a clinically and genetically heterogeneous hematopoietic malignancy, and 75% of ALL cases in adults are of B-cell lineage [1]. The Ikaros protein plays a vital role in lymphocyte differentiation and hematopoiesis. This transcription factor is mainly encoded and regulated by the IKZF1 gene [2], located in 7p12.2 and comprises of seven exons generating more than 10 isoforms through alternative splicing. Of the isoforms, IK1-3 is active and functional, while the IK4-10 isoform exerts a dominantnegative effect that impairs Ikaros’ normal function [3]. Further, IKZF1 deletion is associated with chemotherapy resistance and cancer relapse [4]. Numerous studies have depicted unfavorable clinical outcomes of IKZF1 deletion in children and adults with ALL and the management of treatment in ALL patients with IKZF1 deletion remain challenging and complicated. In recent years, CD19-targeted Chimeric antigen receptor T (CAR-T) cell therapy has achieved significant milestones in R/R B-ALL. Despite high efficacy, post-CAR-T recurrence remains the main obstacle [5] and successive consolidation therapy following CD19 CAR-T cell treatment might be the optimal strategy to reduce recurrence rates and maintain CR status. Haploidentical hematopoietic stem-cell transplantation (haplo-HSCT) is widely established as a potentially curative treatment for B-ALL patients. Interestingly, our previous research showed significant LFS and OS improvement in R/R ALL patients with pre-transplant minimal residual disease (MRD) negativity by employing haplo-HSCT after CAR-T treatment [6]. Here, we reported 11 patients with IKZF1deleted R/R B-ALL, who were previously not responsive to chemotherapy or experienced rapid post-therapy disease relapse, who received CD19 CAR-T treatment at the Bone Marrow Transplantation Center, First Affiliated Hospital of Zhejiang University School of Medicine, from November 2016 to April 2021. Patient characteristics are summarized in Supplementary Table S1. Eleven B-ALL patients with IKZF1 deletion (five females and six males; age range: 17–66 years) were enrolled in this study. Four of the 11 patients (patients 1–3 and patient 11) were non-responsive to standard chemotherapy, while the remaining (patients 4–10) relapsed rapidly after chemotherapy. Moreover, patient 4 underwent reduced-intensity conditioning peripheral stem-cell transplantations from unrelated matched donors in a Taiwanese local hospital. Unfortunately, recurrence was observed 7 months after transplantation. Based on the previously reported standard manufacturing procedures, the CD19 CAR-T cells were generated via lentiviral vectors, engineered with 4-1BB costimulatory domains [5]. All 11 patients received CD19 CAR-T cell infusion at doses of 0.3 × 106/kg to 12.5 × 106/kg, with a median dose of 3.5 × 106/kg. The treatment protocols and clinical outcomes are depicted in Supplementary Materials and Supplementary Table S2. Cytokine release syndrome (CRS) was observed in all patients, from which two patients had grade 1 CRS, five patients had grade 2 CRS, and four had grade 3 CRS. No patients were graded as grade 4 or 5 CRS. The CRS was fully controlled and well-managed in all patients. Seven patients received only supportive care, two accepted supportive care and tocilizumab treatment (IL-6 receptor-blocking monoclonal antibody), one received supportive care accompanied with corticosteroid treatment, and one accepted supportive therapy with tocilizumab and corticosteroids. The body temperature of the patients, the percentages of peripheral blood (PB) CD19 CAR-T/CD3 T cells, and C-reactive protein (CRP) all increased during CRS after CAR-T cell infusion, while the serum levels of IL-6, IL-10, and IFN-γ were prominently increased during CRS occurrence (Fig. 1A–F). The tendencies of other cytokines including IL-2, IL-4, TNF-α, and IL-17A are shown in Supplementary Fig. S1. Neurotoxicity symptoms were not observed in any patients. Bone marrow aspirations were performed in all patients. The disease and treatment responses were assessed and evaluated from the collected samples. As a result, all patients achieved CR morphologically or CR with incomplete count recovery (CRi) within 1 month of CD19 CAR-T cell treatment. The flow cytometry results also revealed that 30 days after the CD19 CAR-T cell infusion, all 11 patients remained MRD-negative (Supplementary Table S2). Patients 1–4 and 7 successfully received haplo-HSCT treatments. Unfortunately, four patients (patients 5, 6, 8, and 9) experienced relapse at 1.2 months, 3 months, 2 months, and 9.1 months after receiving CAR-T cell therapy, respectively. However, three of the four patients who had recurrence after CAR-T treatment had a CD19-negative relapse, while another had a CD19-positive relapse. Furthermore, patient 8 remained in remission after ponatinib and venetoclax treatment, following which haplo-HSCT treatment was carried out. Patients 5, 6, and 9 died due to disease progressions (Fig. 1G and Supplementary Table S2). Five out of 11 (45.45%) patients received successfully bridged CAR-T cell therapy with haplo-HSCT. Patients achieved CR and negative MRD after consolidating with haplo-HSCT. The median OS was 17.11 months (95% confidence interval (CI) 6.15–28.07 months), which was longer than those who had not opted for HSCT (6.21 months, 95% CI 0.13–12.29 months; p= 0.046) (Fig. 1H,