Fig. 1: Antibodies with improved mFcRn affinity at neutral pH enhance brain penetration and target engagement in wild-type mice.

A–F A single dose (50 mg/kg) of control (anti-gD), anti-BACE1, or anti-BACE1-YTE hIgG1 antibodies was delivered by IV injection to wild-type (C57BL/6 J) (A–C) or hFcRn transgenic (Tg32) mice (D–F). Plasma antibody concentrations (A, D), brain antibody concentrations (B, E) and brain Aβ concentrations (C, F) were monitored for 7 days following dosing. In wild-type mice, anti-BACE1 YTE shows faster clearance (A), improved brain uptake (B) and improved pharmacodynamic activity (C) as compared to WT anti-BACE1. In hFcRn mice, improved serum exposure was noted for anti-BACE YTE over WT (D), while no differences in brain uptake or activity are seen (E, F). n = 4 biologically independent animals per group per time point. (G, H) A single IV injection (20 mg/kg) of anti-Aβ hIgG4 or anti-Aβ hIgG4-YTE was administered to PS2APP transgenic mice. 5 days later, animals were euthanized and brains harvested and assessed for target engagement (G, H). Antibody binding to Aβ in the mossy fiber hippocampal tract (G) and to peri-plaque associated halos in the prefrontal cortex (H) was visualized by immunostaining with anti-hIgG-Alexa594 antibody (red). Plaques are labeled with methoxy-X04 (blue). Scale bar: 500 µm (G), 200 µm (H). n = 4 biologically independent animals per group. I–K Non-binding antibodies bearing Fc mutations were administered to wild-type (SCID) mice by single dose IV injection (40 mg/kg). I Affinities (K_D) of mIgG2a variants to mFcRn at pH 6.0 and pH 7.4 as measured by SPR. Serum antibody concentration (J) and brain antibody concentration (K) were monitored for 42 days following dosing. n = 3 biologically independent animals per group per time point. mFcRn variants M252Y and M252Y.Q309T show faster clearance, while all variants show enhanced brain uptake through 10 days post-dose. (Statistical significance between Fc variant treated groups and respective WT treated group was evaluated over time by 2-way ANOVA or mixed effect analysis with Tukey or Dunnett’s multiple comparisons test using Graphpad Prism 9.5.1; *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001).