Figure 1.

Equivalent targeting of human FcRn by the DX-2507 IgG and Fab constructs. A, a representative SPR sensorgram of human sFcRn injected at multiple concentrations over surface-immobilized DX-2507 IgG. Color lines show the measured RU value during the association and dissociation phases, whereas the solid black line is the best fit to a 1:1 Langmuir model. Average fits are presented in Table 1. B, SPR sensorgram as in A, but the biosensor surface was coated with DX-2507 Fab. C, flow cytometry experiments show that increasing concentrations of DX-2507 IgG (blue circles) and Fab (red circles) can compete with fluorescent IgG-AF488 binding to HEK293T cells expressing human FcRn (expressed as a shift in the mean FITC peak), in contrast to a control IgG (DX-2300; green triangles) that only targets FcRn through the canonical Fc interaction. In the absence of expressed FcRn, there is a low IgG-AF488 signal that is not competed by DX-2507. Error bars, S.D. of replicates (n ≥ 2); solid lines, fit to an IC₅₀ equation.