Selectively Agonizing Treg in Type 1 Diabetes with IL-2 Muteins

Regulatory T cells (Treg) play a pivotal role in maintaining self-tolerance. For their development and function, Treg rely on interleukin-2 (IL-2) and efficiently compete with other immune cells for IL-2 by expressing the highest levels of the IL-2 receptor alpha-chain (IL-2Ra or CD25). Treg deficiencies and alterations of the IL-2 pathway have been reported in several autoimmune diseases including type 1 diabetes (T1D) where the loss of self-tolerance leads to the destruction of insulin-producing beta cells in the pancreas. Low-dose IL-2 therapy has been shown to be successful in several autoimmune and inflammatory conditions; however, the potential for IL-2 to activate pro-inflammatory immune cells raises concerns regarding its widespread utility, particularly in type 1 diabetes (T1D) where pathogenic autoreactive T cells are activated by IL-2. Hence, there is a need to develop novel IL-2 based therapeutics with enhanced Treg-specificity. We have generated a series of Fc-fused murine IL-2 muteins (Fc.IL-2 mutein) to optimize Treg-selectivity, tissue distribution and PK. Twenty-eight Fc.IL-2 muteins were screened for their signaling potency and surface retention on Treg. Eight of the mutein candidates, showing a reduced signaling in Treg but prolonged association with CD25, were further characterized in vitro. Two of the weakest muteins were tested in vivo and showed a greater enrichment and Ki-67 induction in Treg compared to wild type (WT) IL-2, and less effect on CD4+ T effector cells, CD8+ cells and NK cells. Finally, in the non-obese diabetic mouse model of T1D, we observed a significantly improved protection in mice treated infrequently with Fc.IL-2 mutein compared to WT IL-2, and, unexpectedly, differences in efficacy between WT and mutein were more pronounced at a very high dose level. Altogether, our data suggest that Fc.IL-2 mutein treatment represent a safer and more efficient alternative for the WT IL-2 therapy, allowing a selective Treg enrichment and a targeted control of the autoimmune response.