A TIM-3-Fc decoy secreted by engineered T cells improves CD19 CAR-T cell therapy in B-cell acute lymphoblastic leukemia

• Galectin-9-TIM-3 axis is upregulated in B-ALL, negatively correlates with clinical outcome and galectin-9 impairs CAR19-T cell function.

• Blocking galectin-9-TIM-3 axis with a TIM-3-Fc decoy secreted by engineered T cells enhances the efficacy and persistence of CAR19-T cells.

Relapsed or refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL) remains a challenging disease with a dismal prognosis. Despite the revolutionary impact of CD19-directed chimeric antigen receptor (CAR19)-T cell therapy, >50% of patients relapse within a year. Both leukemia cell-intrinsic factors favoring immune escape and poor CAR-T cell persistence contribute significantly to clinical failure. Moreover, the expression of immune checkpoint receptors (ICRs) and their ligands within the complex bone marrow (BM) microenvironment may contribute to leukemia progression and therapy resistance. Here, we comprehensively characterized the expression of ICRs and their ligands in leukemic blasts, T cells, and mesenchymal stromal cells (MSCs) from B-ALL BM samples at diagnosis (n=47) and relapse (n=38), comparing them with age-matched healthy BM controls. Our findings reveal a significant upregulated expression of TIM-3 in T cells, and its ligand galectin-9 in both blasts and MSCs throughout disease progression. The expression levels of galectin-9 in B-ALL blasts and TIM-3 in CAR19-T cells negatively correlate with clinical outcome. Furthermore, we demonstrate that galectin-9 impairs CAR19-T cell homeostasis and cytotoxicity. Notably, an engineered TIM-3-Fc decoy receptor, delivered either by primary T cells co-administered with CAR19-T cells or via a bicistronic all-in-one CAR19-TIM-3-Fc construct, improved the anti-leukemia efficacy and persistence of CAR19-T cells in B-ALL patient-derived xenograft models. Mechanistically, CAR19-TIM-3-Fc-T cell treatment promotes the in vivo expansion of both transduced and bystander effector and memory T cells, as determined by spectral flow cytometry. Collectively, these potent and persistent TIM-3-Fc decoy-armored CAR19-T cells offer a promising therapeutic strategy for R/R B-ALL patients.