Receptor occupancy and blocking of STAT5 signaling by an anti-IL-7 receptor antibody in cynomolgus monkeys

BackgroundInterleukin-7 receptor (IL-7R) is associated with autoimmune disease. Blocking its activation by interleukin-7 (IL-7) with a therapeutic monoclonal antibody may reduce pathogenic T cells and effectively control the autoimmune response in these disorders. MethodsTwo flow cytometry-based assays were developed and implemented to evaluate the interaction between cell surface IL-7R and an anti-IL-7R monoclonal antibody (Ab1). The receptor occupancy assay utilized competing and noncompeting commercial detection antibodies for free and total IL-7R, respectively. STAT5 phosphorylation (pSTAT5) was measured as a proximal biomarker of IL-7R inhibition by Ab1. ResultsMonkeys administered Ab1 had no free IL-7R detectable on the CD3+ T cell surface at 0.25 hours postdose through day 4, in all treatment groups. Ab1 treatment resulted in a significant reduction in total IL-7R, dropping to 53%, 44%, and 55% on day 4 at 0.3, 3, and 30mg/kg, respectively, compared to predose levels. There were treatment-related decreases in the ability of IL-7 to induce STAT5 phosphorylation in both CD4+ and CD8+ T cells in monkey blood samples from all treated animals from 0.25 hours through Day 4 postdose. ConclusionsThe nonclinical receptor occupancy assay was developed and applied to detect free and total IL-7R on the surface of CD3+ T cells in cynomolgus monkeys treated with Ab1. The results showed good correlation with the phosphorylation of STAT5 and serum concentration of Ab1. The approach for IL-7R occupancy and pSTAT5 measurements established in monkeys can be utilized in clinical trials for pharmacokinetic/pharmacodynamic evaluation of Ab1 effect in humans. (c) 2015 International Clinical Cytometry Society