Figure 3

ATR-107 competes with IL-21 for receptor binding on naïve B-cells (CD19⁺CD27^-). A: Increasing concentrations of IL-21 decreased binding of ATR-107-A647 to the naïve B-cells as measured by the A647 fluorescence using flow cytometry. Maximum binding was determined by incubating human blood with ATR-107-A647 (3.6 ug/mL) in the absence of IL-21. Non-specific binding (NSB) was subtracted from each data point and the resulting value expressed as a percentage of maximum binding. B: Representative flow cytometry histograms showing the overlay of the receptor occupancy performed without (blue line), or with either excessive concentration of IL-21 (707 nM, red line) or ATR-107 (363 ug/ml, black line). At least 2000 CD19⁺CD27^-events were acquired for analysis.