Manufacturing Characteristics and Early Outcomes of a Tandem aCD22-aCD19 CAR-T Therapy for Childhood and Adult Relapsed/Refractory Acute Precursor B Lymphoblastic Leukemia

Abstract

Introduction

Real-world data shows that 50% of B-ALL patients with CD19-41BBz-CAR-T and 80% with CD19-28z-CAR-T eventually relapse due to antigen escape or loss of CAR-T persistence. This often necessitates consolidation with haematopoietic stem cell transplant (HSCT) while in post-CAR-T remission, which has significant long-term effects.

Objectives

To address the limitations of aCD19 CAR-T therapy, we conducted a Phase I/II trial investigating tandem aCD22-aCD19 CAR-T therapy (MB-CART2219.1) for relapsed/refractory (r/r) B-ALL. (NCT 05429905). We hypothesised that simultaneous targeting of CD19 and CD22 would improve leukaemia-free survival (LFS) after CAR-T without needing HSCT consolidation.

Methods

Patients aged 2 to 75 who had multiply relapsed B-ALL or who had refractory MRD after consolidation chemotherapy were eligible, including those with relapsed extramedullary disease, prior CAR-T or immunotherapy after a washout period. Patients received fludarabine and cyclophosphamide lymphodepletion followed by a single fresh infusion of MB-CART2219.1 manufactured in a 12-day vein-to-vein protocol. We assessed bone marrow disease response by flow-MRD and ddPCR-MRD. We generated knowledge on cellular kinetics and immune signatures of MB-CART2219.1 using multiparameter flow immunophenotyping and single-cell RNA sequencing.

Results

Eleven patients (7 paediatric, 4 adults) received MB-CART2219.1 for r/r B-ALL. CAR-T cells were predominantly central and effector memory and minimally exhausted. Mean %CAR+ T cells in the final product was 77.7% (aCD19 CAR) and 82.1% (aCD22 CAR). The primary aims of our phase I study were met in the paediatric cohort, with an RP2D of 2.5 × 10^6/kg CAR+ T cells. Besides CRS, notable severe adverse events included IEC-HLH and delayed cytopenias. No neurotoxicity was reported. Our interim efficacy analysis for Phase I showed a 91% MRD-negative complete remission rate, a 12-month LFS probability of 63.6% ± 14.5% and 12-month overall survival of 77.9% ± 14.1% without transplant consolidation, surpassing historical benchmarks. Multi-omic data provided insights into the MB-CART2219.1 CAR-T product and post-infusion signatures in our responders. A durable clinical response associated favourably with CAR-T product effector signatures (CD62L-, CD27-, CD56+, low Treg), cytotoxic transcriptome (GZMB, IFNG, TNFSF10) and a balanced CD4/8 ratio. Post-infusion, clinical response was associated with CD8+ CART activation signatures at peak expansion and the acquisition of CD127 at day 28.

Conclusion

MB-CART2219.1 is a promising definitive treatment for multiply relapsed or primary refractory (high MRD) B-ALL. An ongoing Phase II study will confirm the early efficacy and safety results. Multiomic analysis in a representative subset of patients suggests that cytotoxic effector potential of CAR-T is important for long-term response.