Fc engineering can modulate the Fc–FcγR interaction and thus enhance the potency of Abs that target membrane-bound Ags, but it has not been applied to Abs that target soluble Ags. In this study, we revealed a previously unknown function of inhibitory FcγRII in vivo and, using an Ab that binds to Ag pH dependently, demonstrated that the function can be exploited to target soluble Ag. Because pH-dependent Ab dissociates Ag in acidic endosome, its Ag clearance from circulation reflects the cellular uptake rate of Ag/Ab complexes. In vivo studies showed that FcγR but not neonatal FcR contributes to Ag clearance by the pH-dependent Ab, and when Fc binding to mouse FcγRII and III was increased, Ag clearance was markedly accelerated in wild-type mice and FcR γ-chain knockout mice, but the effect was diminished in FcγRII knockout mice. This demonstrates that mouse FcγRII efficiently promotes Ab uptake into the cell and its subsequent recycling back to the cell surface. Furthermore, when a human IgG1 Fc variant with selectively increased binding to human FcγRIIb was tested in human FcγRIIb transgenic mice, Ag clearance was accelerated without compromising the Ab half-life. Taken together, inhibitory FcγRIIb was found to play a prominent role in the cellular uptake of monomeric Ag/Ab immune complexes in vivo, and when the Fc of a pH-dependent Ab was engineered to selectively enhance human FcγRIIb binding, the Ab could accelerate soluble Ag clearance from circulation. We assume such a function would enhance the therapeutic potency of Abs that target soluble Ags.
Myostatin, a member of the transforming growth factor-β superfamily, is an attractive target for muscle disease therapy because of its role as a negative regulator of muscle growth and strength. Here, we describe a novel antibody therapeutic approach that maximizes the potential of myostatin-targeted therapy. We generated an antibody, GYM329, that specifically binds the latent form of myostatin and inhibits its activation. Additionally, via “sweeping antibody technology”, GYM329 reduces or “sweeps” myostatin in the muscle and plasma. Compared with conventional anti-myostatin agents, GYM329 and its surrogate antibody exhibit superior muscle strength-improvement effects in three different mouse disease models. We also demonstrate that the superior efficacy of GYM329 is due to its myostatin specificity and sweeping capability. Furthermore, we show that a GYM329 surrogate increases muscle mass in normal cynomolgus monkeys without any obvious toxicity. Our findings indicate the potential of GYM329 to improve muscle strength in patients with muscular disorders.
A conventional antibody targeting a soluble antigen in circulation typically requires a huge dosage and frequent intravenous administration to neutralize the antigen. This is because antigen degradation is reduced by the formation of antigen–antibody immune complexes, which escape from lysosomal degradation using neonatal Fc receptor (FcRn)-mediated recycling. To address this, we developed an antigen-sweeping antibody that combines pH-dependent antigen binding and Fc engineering to enhance Fc receptor binding. The sweeping antibody actively eliminates the plasma antigens by increasing the cellular uptake of the immune complex and dissociating the antigens in the acidic endosome for degradation. Strong antigen sweeping can reduce the dosage, potentially achieve higher efficacy, and expand the scope of antigen space available for targeting by antibodies. In this study, to further improve the sweeping efficacy, we developed a novel antibody Fc variant by enhancing Fcγ receptor IIb (FcγRIIb) binding and modulating charge characteristics for increased cellular uptake of the immune complex, together with enhancing FcRn binding for efficient salvage of the antigen-free antibodies. Our Fc variant achieved strong antigen sweeping in cynomolgus monkeys with antibody pharmacokinetics comparable to a wild-type human IgG 1 antibody. The positive-charge substitutions enhanced uptake of the immune complex by FcγRIIb-expressing cells in vitro, which was completely inhibited by an anti-FcγRIIb antibody. This suggests that the strong in vivo sweeping efficacy improved by the charge engineering is more likely achieved by FcγRIIb-dependent uptake of the immune complex rather than nonspecific uptake. We expect this novel Fc engineering can maximize the antigen sweeping efficacy even in humans and create novel therapeutic antibodies that meet unmet medical needs for patients.
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