Tandem CD19/CD22 Dual Targets CAR-T Cells Therapy Acquires Superior CR Rate Than CD19 CAR-T Cells: A Case Controlled Study

Background: CD19 chimeric antigen receptor (CAR) T-cells therapy has shown unprecedented success in relapsed/refractory (r/r) ALL. Now it is recommended for the treatment of patients up to 25 years with r/r precursor B-ALL. Despite its high response rate, approximately 50% of r/r ALL patients relapsed after CD19 CAR T-cell therapy, which was mainly due to CD19 antigen loss or short persistence of CAR T-cells in vivo. CD19 and CD22 dual target CAR T-cells have demonstrated to reduce relapse post CD19 CAR T-cell therapy in limited cases. This study was designed to investigate the efficacy and safety of CD19/CD22 dual targets CAR-T cells and the correlation between that and CD19 CAR-T cells.

Methods: A novel tandem CD19/CD22 CAR-T construct with CD28 and OX40 co-stimulatory domains were administered. All patients received FC (fludarabine, 30 mg/m², days 1-3 and cyclophosphamide, 300 mg/m², days 1-3) based regimen chemotherapy pre-infusion. Median infusion dose of CAR-T cells was 1(0.5-2.5) *10⁷ cells/kg. All the patients accepted the bone marrow examination 28 days post CAR-T infusion.

We conducted a retrospective, case controlled study analysis at the First Hospital of Soochow University. Every patient with active disease treated with CD19/CD22 CAR-T cells therapy was paired with one control subject who received CD19 CAR-T cells from January 2017 to September 2019. We matched the control group to prevent bias according to: (1) bone marrow blast before CAR-T infusion; (2) extramedullary involvement; (3) cytogenetic risk groups according to NCCN guideline; (4) transplantation status pre-infusion.

Results: From 2017 Oct to 2020 Jul, 36 patients were enrolled into the clinical trial (NCT: 03614858). Patients who accepted more than 4 previous treatments account for 58.3% and 8 patients received stem cell transplantation pre-infusion. Bone marrow blasts 40.75 (0~94.5)%. After tandem CD19/CD22 CAR-T infusion, all patients achieved completely remission (CR) and minimal residual disease negative (MRD-) CR rate is 77.8%. The 6-month OS rate is 88.36% and 12-month OS rate is 70.6%. The 6-month LFS rate is 88.072% and the 12-month LFS rate is 69.216%. CAR-T bridging HSCT (25/36) obviously improves the 1-year LFS rate compared with non-transplantation group (11/36) (82.309% vs 31.169%, p=0.0135). All the side effects were mild and can be relieved through support treatments. 8 out of 36 patients developed with grade 3~4 CRS. 2 patients had HLH but soon relieved through low dose steroids.

28 out of 36 patients who accepted dual targets CAR-T cells didn't get complete remission before infusion. Therefore, 28 patients were enrolled in the CD19 CAR-T group. There are no significant differences between two groups at baseline. The CR rate was higher in CD19/CD22 group than that in CD19 group(100% vs 53.57%, p=0.000), so was MRD-CR rate(71.43% vs 42.86%,p=0.000). In survival analysis, 6 month overall survival rate of CD19/CD22 group was 69.276% while CD19 group was 53.571%. Of 28 patients who received dual target treatment, 7 patents relapsed while 4 relapsed out of 15 CR patients in CD19 group.

Conclusions:The tandem CD19/22 dual CAR-T cell therapy is a safe and high efficacy treatment for R/R ALL patients. Our study demonstrated that dual targets CAR-T cells acquires higher CR rate than CD19 CAR-T cells. It is possible that multi-targeted CAR-T cell therapy may overcome this resistance mechanism and improve clinical outcomes.