Background/Purpose: Low-dose IL-2 with enhanced sensitivity to Treg cells has been proved to be safe and efficacious in multiple autoimmune disorders (AIDs) including SLE, RA, Psoriasis, Ulcerative Colitis etc. However, poor PK profile, insufficient regulating window of Treg/Teff as well as mild NK activation remain to be the issues limiting the clinical applications of IL2. Herein, we used rational design strategies to generate SIM802 with both increased thermal stability and selective property which led to potent and preferential stimulation of Treg cells in different animal species, including cynomolgus monkeys.

Methods: A computation-driven design workflow integrating machine-learning-based predictions and physics-based free energy calculations, were used to design stability improved point mutations. Single-point mutagenesis was also introduced to the residues critical for IL-2/IL-2Rβ binding interface. In vitro activities were determined by IL-2 receptor binding, STAT5 phosphorylation and NK proliferation assays. Pharmacokinetics (PK), pharmacodynamics (PD) and safety were assessed in both mice and cynomolgus monkeys. The efficacy to suppress inflammation in vivo was assessed in the models of delayed-type hypersensitivity (DTH) and graft versus host disease (GvHD).

Results: SIM802 remains the binding activity to CHO-K1 IL-2Rαβγ with attenuated binding activity to CHO-K1 IL-2Rβγ in comparison with wild-type IL-2. It preferentially activates STAT5 phosphorylation of Treg cells over CD4+CD25-Foxp3- and CD8+T cells. The Tm value of SIM802 has markedly increased with more than 12℃ compared with wild-type IL-2. In Balb/c mice and human PBMC engrafted mice, administration of stability-enhanced SIM802 significantly increases both splenic Treg/Tcon and Treg/CD8+T ratios. The ability of SIM802 to suppress antigen-induced inflammation in vivo was measured using a KLH-induced DTH model. The results show that SIM802 strongly inhibits ear inflammation in a dose-dependent manner, with 69% ear thickness reduction at 0.2 mpk or 80% at 1mpk. In another PBMC engrafted GvHD model, SIM802 effectively suppresses the weight loss and death rate of mice. Administration of 0.05 mpk SIM802 results in maximal 66-fold increase of total Treg cells in monkeys, with mild changes in the numbers of CD4+Foxp3- cells and almost no changes in the numbers of CD8+ Teff and NK cells. The ratio of Treg/CD4+T and Treg/Teff cells increases to 36% and 92%, respectively, from the baseline of 2.9% and 2.4%, respectively. Moreover, a nearly 10-fold increase of Treg cells at 14 days after the treatment suggests its long lasting effects on Treg regulation.

Conclusion: SIM802 demonstrates the best-in-class potential among Treg-selective IL-2 mutein molecules. It elicits dose-dependent anti-inflammatory efficacy in mice, and preferential and sustained activation of Treg cells in monkeys. Strong and sustained Treg expansion with limited pro-inflammatory activity of SIM802 may result in a larger therapeutic window and less frequency dosing in the clinical use. SIM802 is currently in IND enabling stage and Phase 1 clinical study in healthy volunteers will be investigated early 2023.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/mutants-improving-stability-enhance-the-potency-of-treg-selective-il-2-mutein-for-the-treatment-of-autoimmune-disorders/