Interleukin‐7 receptor α (IL‐7Rα) 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.

Two flow cytometry‐based assays were developed and implemented to evaluate the interaction between cell surface IL‐7Rα and an anti‐IL‐7Rα monoclonal antibody (Ab1). The receptor occupancy assay utilized competing and noncompeting commercial detection antibodies for “free” and “total” IL‐7Rα, respectively. STAT5 phosphorylation (pSTAT5) was measured as a proximal biomarker of IL‐7Rα inhibition by Ab1.

Monkeys administered Ab1 had no free IL‐7Rα 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‐7Rα, dropping to 53%, 44%, and 55% on day 4 at 0.3, 3, and 30 mg/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.

The nonclinical receptor occupancy assay was developed and applied to detect free and total IL‐7Rα 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‐7Rα occupancy and pSTAT5 measurements established in monkeys can be utilized in clinical trials for pharmacokinetic/pharmacodynamic evaluation of Ab1 effect in humans. © 2015 International Clinical Cytometry Society