OP0023 GENERATION OF PT101, A HIGHLY SELECTIVE IL-2 MUTEIN FOR TREATMENT OF AUTOIMMUNE DISEASES
Authors: J. Visweswaraiah, E. Sampson, P. Petaipimol, A. Monsef, K. Kis-Toth, K. L. Otipoby, J. Sundy, N. Higginson-Scott, J. Viney
Journal: Annals of the Rheumatic Diseases (2021)

Background: Regulatory T cells (Tregs) play a critical role in immune homeostasis and are dysfunctional in many autoimmune diseases. Interleukin 2 (IL-2) drives the proliferation and function of Tregs. via the heterotrimeric IL-2 receptor (CD25/CD122/CD132). As a result, CD25 loss-of-function in mice is associated with Treg deficiency and widespread autoimmunity. Low dose IL-2 is being evaluated for treatment of autoimmune diseases and has been shown to expand Tregs, however it has a narrow selectivity window before activating conventional T cells and natural killer cells. To enhance IL-2 selectivity and improve its therapeutic utility for activating and expanding Tregs, mutations can be introduced that reduce CD122/CD132 affinity thus creating a dependency on CD25 binding for signaling through CD122/CD132 upon IL-2 facilitated CD25/CD122/CD132 trimer formation. Objectives: To generate a highly selective IL-2 mutein that activates and expands Tregs selectively that can be used for treatment of autoimmune diseases Methods: Using a structure guided approach, we introduced mutations in IL-2 that significantly decreased CD122 binding affinity in addition to other mutations that increased CD25 binding affinity. Finally, we explored additional mutations, format, orientation, and linker lengths to generate the most potent, selective molecule with drug-like manufacturability. These structure activity relationship efforts culminated in the generation of PT101, a mutant IL-2 Fc fusion that is selective in activating and expanding Tregs in vitro and in vivo. Results: PT101 selectively induced STAT5 phosphorylation in human and cynomolgus monkey Tregs in vitro. In humanized NOD-scid IL-2Rg-null (NSG) mice and cynomolgus monkeys, administration of PT101 dose-dependently and selectively expanded Tregs without significant effects on other immune cell types, and without eliciting proinflammatory cytokine production. The Tregs from PT101-dosed humanized mice have increased expression of FOXP3 and CD25, suggesting enhanced function and stability. In a Phase 1a single ascending dose clinical trial, PT101 was well-tolerated and selectively expanded total Tregs, with a mean maximal increase of up to 3.6-fold over baseline in healthy volunteers. There was no evidence of expansion of natural killer cells nor pro-inflammatory conventional T cells at any of the doses studied. Conclusion: PT101 selectively activated and expanded Tregs without significant effects on other immune cell types, and without eliciting proinflammatory cytokine production. These Tregs have enhanced function and stability as seen by increase in expression of FOXP3 and CD25 in these cells. PT101 maintained selectivity in Phase 1 a clinical trial with no evidence of expansion of natural killer cells nor pro-inflammatory conventional T at any dose studied. A Phase 1b/2a clinical trial in patients with ulcerative colitis and a Phase 2 clinical trial in patients with systemic lupus erythematosus are planned to further evaluate PT101. Disclosure of Interests: None declared