Abstract
To enhance Treg-targeted IL-2-dependent therapy for autoimmunity, we developed a fusion protein of mouse (m) IL-2 linked to CD25. mIL-2/CD25 has a long half-life, acts as a selective agonist for the high-affinity IL-2R, at a low dose (LD) preferentially targets Tregs and is more effective than IL-2 at limiting autoimmunity in models of type 1 diabetes (T1D) and lupus. To explore the mechanism for T1D suppression, we assessed the effect of LD-mIL-2/CD25 on the global islet immune landscape in female NOD mice with scRNA-seq and flow cytometry. In the pancreas, LD mIL-2/CD25 reduced CD4+Foxp3- and CD8+ T cells, especially effector-phenotypic and highly proliferating CD8+ T cells, but increased Tregs, particularly ST2+ eTregs, and ILC2s. In addition, a CD8+ T cell subset expressing an exhaustion-related gene signature was identified. TCR repertoire analysis revealed multiple dominant clonotypes associated with effector-phenotypic CD4+Foxp3- and CD8+ T cells in untreated diseased NOD mice, which were reduced by LD mIL-2/CD25. Consistent with this finding, peptide-MHC tetramer staining showed that LD mIL-2/CD25 reduced autoantigen-reactive CD4+ and CD8+ T cells in islets. Our findings suggest that Tregs regulate autoimmunity in NOD mice in part by limiting the expansion of autoreactive T cells. Moreover, mIL-2/CD25 may also function through Tregs to promote exhaustion of CD8+ T cells, and this may reflect an active mechanism by which Tregs regulate some autoreactive T cells.