Infusion of ex-vivo expanded human TCR-αβ+ double-negative regulatory T cells delays onset of xenogeneic graft-versus-host disease

Despite the demonstration of potent immunosuppressive function of T cell receptor (TCR)-αβ⁺ double-negative regulatory T cells (DN T_regs ), scarce numbers and lack of effective expansion method limit their clinical applications. Here we describe an approach that allows for ∼3500-fold ex-vivo expansion of human DN T_regs within 3 weeks with > 97% purity. Ex-vivo-expanded DN T_regs suppress proliferation of polyclonally stimulated autologous T and B cells in vitro through direct cell-to-cell contact. In vivo, we demonstrate for the first time that infusion of human DN T_regs delayed an onset of xenogeneic graft-versus-host disease (GVHD) significantly in a humanized mouse model. Furthermore, preincubation of ex-vivo-expanded DN T_regs with a mechanistic target of rapamycin (mTOR) inhibitor rapamycin enhanced their immune regulatory function further. Taken together, this study demonstrates that human DN T_regs can be expanded ex vivo to therapeutic numbers. The expanded DN T_regs can suppress proliferation of T and B cells and attenuate GVHD, highlighting the potential clinical use of DN T_regs to mitigate GVHD.