Tandem CD19/CD22 Dual Targets CAR T-Cells Bridging Hematopoietic Stem Cells Transplantation Acquires Robust Remission for Relapsed and Refractory B Acute Lymphoblastic Leukemia Patients

Background: CD19 chimeric antigen receptor T (CAR-T) cells have demonstrated impressive early response rates in relapse and refractory B acute lymphoblastic leukemia (r/r B-ALL). However, a high rate of patients suffered a relapse, which occurred in a large subset of other trials and confers dismal outcomes. Dual targets approaches are proved to optimize the response rate and prevent CD19 ^- relapse. Alternatively, limited patients accepted the tandem CD19/CD22 CAR-T therapy, but the clinical trials in a large scale to investigate the tandem CAR-T were rare.

Methods: We conducted an open label, single center clinical trial at the First Affiliated Hospital of Soochow University to investigate the efficacy and safety of tandem CD19/CD22 dual targets CAR T-cells for r/r B-ALL. All patients received FC (fludarabine, 30 mg/m2, days 1-3 and cyclophosphamide, 300 mg/m2, days 1-3) based chemotherapy as the lymphodepleting regimen. Median infusion dose of CAR-T cells was 1(0.5-2.5) *10 ⁷ cells/kg.

Results: From October 2017 to June 2021, a total of 47 patients were treated with CD19/CD22 CAR T-cells and included in our analysis.

Among the 47 patients, primary refractory B-ALL patients account for 44.68%. 27 patients (57.4%) had a high disease burden, with 20% or more blasts in BM. Consequently, at day 28 assessment, 47 patients (100%) got hematological CR and the 40 out of 47 patients (85.1%) achieved minimal residual disease complete remission (MRD ^-CR).

The toxicities of CD19/CD22 CAR T-cells therapy were reversible and clinically manageable. Cytokine reverse syndrome of any grades occurred in 41 of 47 patients (87.23%) and was severe (grade>2) in 8 (17.02%). Immune effector cell-associated neurotoxicity happened in one patient. The most common severe hematological abnormalities were grade 3/4 leukopenia (74.47%). Serious thrombocytopenia and anemia occurred in 48.93% and 57.44% patients. The non-hematological toxicity were reversible with tight monitoring and support care.

Within a median follow-up of 21.83 months (range, 2.57 to 42.53), the median overall survival (OS) and leukemia free survival (LFS) for the entire cohort have not reached. The OS rate of all the patients was 93.569% (95%CI, 80.97% to 97.832%) at 6 months, 78.721% (95%CI, 60.719% to 87.625%) at 1 year and 74.578% (95%CI, 55.263% to 84.969%) at 2 years in all patients. The LFS rate was 87.031% (95%CI, 73.375% to 93.958%) and 68.297% (95%CI, 51.419% to 80.365%) at 6 month and 1 year, respectively. The 6-months cumulative incidence of relapse (CIR) was 8.96%, while 1-year CIR was 23.254%.

Thirty-four of 47 patients (72.34%) proceeded to a bridging allogeneic hematopoietic stem cell transplantation (allo-HSCT). The OS of HSCT group was 94.118% at 6 months and 80.420% at 1 year. The 6-months OS of no-HSCT group was 83.916%, while 1-year OS was 74.592%. The HSCT group had significantly better LFS and lower CIR than the no-HSCT group (LFS, p=0.0459; CIR, p=0.0267). We initially performed multivariable Cox regression analyses, which shows that better long-term survival in patients with MRD ^-CR status, as well as bridging allo-HSCT.

Conclusions: Tandem CD19/CD22 CAR-T cells are safety and highly effective in inducing CR for r/r B-ALL patients. The consolidative allo-HSCT can provide long-term durable disease control in these patients.