Sequential Infusion of Anti-CD22 and Anti-CD19 Chimeric Antigen Receptor T Cells for Adult Patients with Refractory/Relapsed B-Cell Acute Lymphoblastic Leukemia

Clinical trials of second generation chimeric antigen receptor engineered T cells (CAR-T cells) have yielded unprecedented efficacy in refractory/relapsed B-cell acute lymphoblastic leukemia (B-ALL), especially in children and young adult. However, antigen loss relapse has been observed in approximately 14% of patients in anti-CD19 CAR-T cell therapy across institutions, which emerges as a challenge for the long-term disease control of this promising immunotherapy. Recently, CD19/CD20 and CD19/CD22 dual antigen targeting have been proposed to overcome antigen loss relapse after the administration of anti-CD19 CAR-T cells. This strategy may result in enhanced anti-tumor activity, while safety concern regarding the risk of cytokine release syndrome (CRS) due to significant CAR-T cell activation and cytokine release needs to be addressed.

Here, we conducted an open-label, single-center and single-arm pilot study of sequential infusion of anti-CD22 and anti-CD19 CAR-T cells. We aimed to evaluate its safety and efficacy in adult patients with refractory or relapsed B-ALL. This trial is registered with ChiCTR, number ChiCTR-OPN-16008526.

Between March 2016 and March 2017, 27 patients with refractory or relapsed B-ALL were enrolled in this clinical trial, with a median age of 30±12 years (range, 18-62 years). Thirteen patients (48.1%) had a history of at least two prior relapsed or primary refractory disease. Twenty-six patients received fludarabine and cyclophosphamide before the infusion of CAR-T cells. The median cell dosages of anti-CD22 and anti-CD19 CAR-T cells were 2.44 ± 1.02 × 10⁶ /kg and 1.98 ± 1.05 × 10⁶ /kg, respectively. 24/29 (88.9%) patients achieved CR or Cri, including 7 patients who received prior hematopoietic stem cell transplantation, and 13/27 (48.1%) patients achieved minimal residual disease negative (MRD^-) CR accessed by flow cytometry. Sustained remission was achieved with a 6-month overall survival rate of 79% (95% CI, 66-97) and an event-free survival rate of 72% (95% CI, 55-95). 24/29 (88.9%) patients experienced CRS and 6/27 (22.2%) patients had reversible sever CRS (grade 3-4). And 3/27 (11.1%) patients developed neurotoxicity. Multi-color flow cytometry was used to screen and quantitate MRD in blood, bone marrow and cerebrospinal fluid. Antigen escape of CD19 and CD22 was not detected in any relapsed patient post-CAR-T cell therapy.

Our results indicated that sequential infusion of third generation Anti-CD22 and Anti-CD19 CAR-T cell therapy is feasible and safe for patients with refractory/relapsed B-ALL. Dual antigen targeting should be a promising approach for overcoming antigen escape relapse, while needs to be further determined in our clinical trial.