Engineered suppressor T cells overexpressing IFN-α and PD-L1 inhibit GVHD but retain GVL effects in mice

Living cell therapy for immune regulation could potentially achieve long-lasting effects on inhibiting graft-versus-host disease (GVHD), a life-threatening complication after allogeneic hematopoietic cell transplantation (allo-HCT). However, novel immune regulatory cells with better persistence and sustained immune modulatory function are needed. Here, we demonstrate that engineering human T cells to co-express IFN-α2 and PD-L1 (named αp-T cells) rendered them a potent capacity to inhibit xenogeneic GVHD without impairing anti-leukemia in immunodeficient mice. These αp-T cells maintained stable expression of PD-L1 and IFN-α and potent immunosuppressive effects in peripheral tissues during GVHD control. CD4⁺ αp-T cells activated transcriptional programs that promoted effector differentiation, exhaustion, and proliferation inhibition in both themselves and their treated conventional T (conv-T) cells, ultimately reducing GVHD. These CD4⁺ αp-T cells created a synergistic regulatory loop that modulated conv-T cell responses, in which IFN-α suppressed expansion and survival of activated conv-T cells, promoted their differentiation into PD-1⁺TIM3⁺ exhaustion-like T cells, and sensitized them to PD-L1-mediated suppression. We further verified these regulatory effects of murine CD4⁺ αp-T cells on reducing GVHD in immunocompetent mice of allo-HCT. Thus, αp-T cells may represent a novel translational strategy to improve the safety and efficacy of allo-HCT and inhibit other inflammatory disorders in a broad context.