Allogeneic, donor-derived, second-generation, CD19-directed CAR-T cells for the treatment of pediatric relapsed/refractory BCP-ALL

• Allogeneic, donor-derived CD19 CAR-T cells can be readily generated for the treatment of pediatric patients with relapsed/refractory BCP-ALL.

• Allogeneic CD19 CAR-T cells are effective, and compared with autologous CAR, they neither increase toxicity, nor induce high GVHD incidence.

Autologous CD19-directed chimeric antigen receptor (CAR)-T cells have shown unprecedented efficacy in children with relapsed/refractory B-cell precursor acute lymphoblastic leukemia (BCP-ALL). However, patients either relapsing after allogeneic hematopoietic stem cell transplantation (allo-HSCT) or displaying profound lymphopenia and/or rapidly progressing disease often cannot access autologous products. These hurdles may be overcome by allogeneic, donor-derived CAR-T cells. We tested donor-derived T cells transduced with a second-generation (4.1BB) CD19-directed CAR for treatment of patients with BCP-ALL in a hospital-exemption setting. Two constructs were tested: a retroviral construct incorporating the suicide gene inducible caspase-9 (CD19-CAR–Retro_ALLO) first and then a lentiviral construct and an automated, Prodigy-based manufacturing process (CD19-CAR–Lenti_ALLO). Thirteen children/young adults received ALLO–CAR-T cells between March 2021 and October 2022. Doses ranged between 1.0 × 10⁶ and 3.0 × 10⁶ CAR-T cells per kg. The toxicity profile was comparable with that of autologous CAR-T cells, characterized mainly by cytopenia, cytokine release syndrome (maximum grade 1), and grade 2 immune-effector cell–associated neurotoxicity syndrome. One case of acute graft-versus-host disease (GVHD) occurred and was rapidly controlled with steroids and ruxolitinib. None of the other patients, including 3 given ALLO–CAR-T cells from an HLA-haploidentical donor, experienced GVHD. Two patients received ALLO–CAR-T cells before HSCT and showed a significant expansion of CAR-T cells without any sign of GVHD. All patients obtained complete remission (CR) with absence of minimal residual disease in the bone marrow. With a median follow-up of 12 months (range, 5-21), 8 of 13 patients maintained CR. Allogeneic anti-CD19 CAR-T cells can effectively treat highly refractory BCP-ALL relapsing after allo-HSCT without showing increased toxicity as compared with autologous CAR-T cells.