Sequential CD19 and CD22 CAR-T Therapy in Relapsed/Refractory Acute Lymphoblastic Leukemia

Background: Chimeric antigen receptor (CAR)-T cell therapy has shown promise in treating relapsed/refractory (R/R) acute lymphoblastic leukemia (ALL). However, high relapse rates remain a significant challenge, and antigen-loss relapse is a common cause of treatment failure. Sequential targeting of CD19 and CD22 with CAR-T cells has emerged as a potential strategy to address this issue, although research in adult patients is relatively limited.

Methods: Our retrospective study evaluated the efficacy and safety of sequential CD19 and CD22 CAR-T cell therapy in adult patients with R/R B-ALL who were ineligible for allogeneic hematopoietic stem cell transplantation (allo-HSCT). Patients underwent CD19 CAR-T cell infusion followed by CD22 CAR-T cell infusion after at least one month. Key endpoints included minimal residual disease-negative complete remission (MRD^-CR), overall survival (OS), leukemia-free survival (LFS), and safety outcomes.

Results: 23 participants were enrolled, with a median age of 58.1 years (range, 25.9 to 76.0). High-risk cytogenetic and genomic aberrations were detected in 13 (56.5%) patients, and 5 patients had extramedullary disease (EMD) involvement at baseline. Median interval between two CAR-T infusions was 3.8 months (range, 1.8 to 8.8). Hematological adverse events of grade 3 or worse occurred at similar rates after both CAR-T infusions. There were no treatment-related deaths. CRS occurred in 78.3% of patients following CD19 CAR-T therapy and 39.1% following CD22 CAR-T therapy. Two (8.7%) patients experienced grade 2 ICANS during CD19 CAR-T, and no ICANS was reported during CD22 CAR-T therapy. Infection rates were 30.4% during the first infusion and 26.1% during the second infusion, with all cases successfully resolved. Median peak CAR T-cell levels were significantly higher in the first cycle compared to the second cycle (353.2/μL vs 34.5/μL, P=0.002), suggesting a more robust initial expansion. Peak CD22 CAR-T cell levels were significantly lower in patients who relapsed (P=0.034), while peak CD19 CAR-T cell levels showed no significant difference between 2 groups (P=0.29).

With a median follow-up of 17.7 months, 65.2% of patients were alive, and 60.9% remained in MRD-CR. The median OS and LFS for the cohort were 25.4 months and 20.8 months, respectively. OS and LFS rates were 91.1% and 65.1% at 1 year, and 56.8% and 44.7% at 2 years. A total of 8 patients suffered leukemia relapse, with a median time from CD19 CAR-T of 8.5 months (range, 5.1 to 20.8). Relapse types included CD19⁺CD22⁺ (n=6, 75%), CD19^-CD22⁺ (n=1, 12.5%), and CD19^-CD22^- (n=1,12.5%). The cumulative incidences of relapse were 30.5% at 1 year and 44.5% at 2 years. Multivariate analyses for OS and LFS confirmed that higher baseline leukemia burden (≥64%) and the presence of EMD were significant risk factors of inferior outcomes. Among patients with durable responses, 21.4% (3/14) maintained BCA longer than 6 months following CD22 CAR-T infusion. Of the 8 relapsed patients, loss of BCA preceding relapse was observed in 3 cases (37.5%), concurrent loss of BCA and relapse in 4 cases (50%), ongoing BCA in 1 case (12.5%).

Conclusion: Sequential CD19 and CD22 CAR-T cell therapy demonstrates durable efficacy and a manageable safety profile in relapsed/refractory B-ALL, providing a promising option to address antigen-loss relapse and improve long-term outcomes in patients ineligible for allo-HSCT.