Abstract

One-year relapse rates of leukemia patients treated with CD19-targeted CAR-T cells (CAR19T) are >60% partly due to CAR19T intrinsic mechanisms and their interaction with leukemic cells and their microenvironment. Here, we have comprehensively characterized the expression of inhibitory immune checkpoint receptors (ICRs) in T-cells, and their ligands in both leukemic cells and mesenchymal stromal cells (MSC) from bone marrow (BM) of pediatric and adult primary B-cell acute lymphoblastic leukemia (ALL) patients at diagnosis and relapse. Among all the ICRs-ligands analyzed, our results reveal a significant upregulation of the ICR TIM3 and its ligand Galectin-9 in T-cells and B-ALL/MSCs, respectively, during disease progression. The expression of TIM3 and Galectin-9 was significantly upregulated by CAR19Ts and CAR19T-resistant B-ALL cells, respectively, after in vitro cytotoxicity assays. Further in vivo assays using a TIM3 molecular decoy engineered to be secreted by T cells underpinned an inhibitory role for TIM3:Galectin-9 axis in CAR19T cell function and expansion. Targeting TIM3:Galectin-9 axis may represent a promising co-adjuvant therapy in B-ALL patients treated with CAR19Ts.